work to extend the shelf life of leafy vegetable progresses

8/3/2019 Work to Extend the Shelf Life of Leafy Vegetable Progresses

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A Publication of the Australian Centre for International Agricultural Research Postharvest Technology Program

NUMBER 55 DECEMBER 2000

Postharvest Newsletter

Collaborative research visitsand presentations of research

results at several regional andinternational conferences wereimportant components of what hasbeen a busy year for PHT/1994/016, reports Dr Tim OHare, leaderof project activities in Australia.

Tim is a member of the Queens-land Horticultural Institute (QHI), partof the Queensland Department ofPrimary Industries (QDPI), and isbased at the Gatton Research Station.The project is a collaboration be-

tween researchers in Australia andChina. In Australia the project in-volves researchers at the Universityof Adelaide (UA) and AgricultureVictoria (AV) as well as the QDPIteam, while the research teams inChina are in the Hangzhou Universityof Commerce (HUC) and the BeijingVegetable Research Centre (BVRC).

Research highlights

In order to elucidate any effects ofmodified atmosphere (MA) packaging

on shelf life in broccoli, the QDPI teamconducted experiments in whichcommodity was stored at 10C in a 2%oxygen: 5% carbon dioxide atmos-phere. It found that the shelf life ofbroccoli florets held under theseconditions was increased by about200% compared with an increase inshelf life of only 26% when fumigatedwith the ethylene inhibitor 1-MCP.

In Adelaide, research continued on,among other things, the impact ofpreharvest water stress and harvesttime on storage characteristics of

Chinese cabbage, through a series ofexperiments begun in 1999. Resultsfrom energy substrate analysis andchlorophyll fluorescence measure-ments support results obtained forother parameters, e.g. relative watercontent and weight loss, in indicatingthat the time of day of harvest andwater stress applied during growthhave no significant effect on thepostharvest life of Chinese cabbage.

BVRC researchers continued theirdetailed studies to elucidate bio-chemical differences between Chinese

cabbage leaves of differing physi-ological ages. On the more appliedfront, they continued studies of thestorage benefits of heat shock treat-ments of broccoli. They confirmedtheir earlier finding that heat-treatedbroccoli will store for significantlylonger than untreated broccoli. Both

ethylene and carbon dioxide produc-tion were lower in the treated com-modity than in the controls.

NEWS FROM PROJECT PHT/1994/016

Work to extend the shelf life ofleafy vegetables progresses

IN THIS ISSUEIN THIS ISSUEIN THIS ISSUEIN THIS ISSUEIN THIS ISSUEWork to extend the shelf life of leafy

vegetables progresses ... page 1

Keeping phosphine in the pest controlarmoury ... page 3

ACIAR meeting helps spread the news

on rice cracking ... page 4Free agricultural engineering textbook

offer ... page 4

Food and water: essential forlife...and peace ... page 5

Proficiency testing for mycotoxinanalysis ... page 6

Managing maize stocks in developingcountries ... page 7

Action against mycotoxins in WestAfrica ... page 12

Training courses at NRI ... page 12

Forthcoming meeting: IHC2002 ...page 12

ELISA technology transfer workshopsin Vietnam

Aflatoxin in chilli products a hot topicin Australia ... page 14

Moroccos horticultural exportchallenge ... page 15

Current Awareness ... page 16

Contributors to this issue:

Greg Banova, Bruce Champ,Ed Highley, Greg Johnson,

Tim OHare, Mary Webb,Kate Wilkinson

Continued on page 2.

Amikha Prasad (QDPI), Wang Xiangyang

(HUC), Tim OHare (QDPI), and ZhengShufang (BVRC) assessing a mizuna MAPtrial at the Gatton (Queensland)Postharvest laboratories.

Tim OHare, Lung Wong (QDPI), and Hang

Guangrong (HIAE) translating Chineseresearch results into English at the Gattonlaboratories.


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A study by researchers at HUCfound that the shelf life of pak choycould, by the use of modified atmos-phere film packaging, be extended to1418 days at 10C, as comparedwith 10 days in control samples.

Like the Adelaide team, one of thetopics of research at AV was thepossible effects of water stress duringgrowth on storage characterististics.The AV team studied the effect ofintermittent water stress on shelf lifeand physiology of pak choy. Theresearchers found no linkage betweenstress and shelf life, but made someinteresting observations with abearing on product quality. Forexample, it was found that stressedplants were much greener than

controls in the first few days afterstress was relieved. In contrast, plantssubjected to superoptimal waterconditions in an earlier experimentgrew very large but their leaves werepale and very easily damaged. Theresearchers speculate that, if stressedplants were harvested after they hadrecovered from the stress but beforethe enhanced colour had disap-peared, shelf life might be enhancedbecause of the higher chlorophyllcontent. A general conclusion drawnis that too much water can be as bad

as too little and that field watermonitoring may be one way in whichplant quality could be optimised.

Inter-laboratory activities

Mr Li Wu (BVRC)and Prof. ShenLianqing (HUC) advanced projectactivities with researchers in Ad-elaide, Melbourne, and Brisbane inOctober 1999. This followed theirparticipation in the AustralasianPostharvest Conference in NewZealand. It was a good opportunityfor them to discuss project issues

with Trish Grant (AV) and KerryPorter (UA) whom they had notpreviously had the opportunity tomeet.

John Bagshaw, Lung Wong, andAmanda Able (QDPI) visitedHangzhou staff (Prof. Shen and WangGuanglin) and students (HuangGuangrong, Yu Ping, and Sun Liang)following the 19th ASEAN/1st APECSeminar on Postharvest Technology,held in Ho Chi Minh City, Vietnam inNovember 1999. They discussed dataon handling systems for leafy vegeta-bles and made plans for futurehandling trials. Then, in companywith Zheng Shufang (BVRC), a field

study was made to collect data onChinese cabbage handling systems inthe Beijing area.

Tim OHare (QDPI), Andreas

Kljeber (UA), and Michelle Robbins(QDPI ACIAR officer) visitedBVRC in April 2000 to discussresearch that had occurred since themeetings in Australia (October1999) and that planned for the sixmonths to follow. This was the firsttime Michelle had travelled to Chinaand the visit provided her with arange of insights.

Zheng Shufang (BVRC), WangXiangyang (HUC), and HuangGuangrong (HIAE) made an extendedvisit to the Gatton laboratory during

2000. From April to August, theChinese scientists worked on analy-ses of handling systems with QDPIs

John Bagshaw and Lung Wong,experimental design with AmandaAble, modified atmosphere packagingof mizuna with Tim OHare, andsugar analysis and heat-shock trialsusing pak choy with Lung Wong,Amikha Prasad, Amanda Able.

During their time in Australia, ourChinese colleagues stayed at Univer-sity of Queensland accommodation in

Gatton. This gave them a taste ofliving in the country, but they alsohad opportunities to visit Brisbaneand the surrounding area and thusalso experience something of life inurban Australia.

Planning for a workshop in China

A workshop on Vegetablepostharvest/supply chain manage-ment is being planned for early May2001 in Beijing. This workshop willbe held in conjunction with otherprojects with an interest in thepostharvest management of perish-able commodities and with theproponents of potential new activitiescurrently making their way throughthe ACIAR project developmentcycle.

The workshop will probably followthe end-of-project review (Chineseactivities) for PHT/1994/016 which istentatively scheduled to take place atBVRC on 30 April 2001, possiblyextending to 1 May, depending on theavailability of the reviewers. The

review of Australian activities willlikely be made during the secondweek of May 2001 at Gatton, againdependent on the reviewers sched-ules.

Paper presentations

Project members from both Australiaand China presented their results atseveral major conferences during theyear. Twelve papers in all were pre-sented at four conferences in fourcountries. Four papers were presentedat the Australasian Postharvest Confer-ence, in New Zealand in October 1999,six at the 19th ASEAN/1st APECSeminar on Postharvest Technology, inVietnam in November 1999 (see page16 of this issue), and one each at theInternational Society for HorticulturalScience (ISHS) Postharvest 2000Symposium, in Israel in March 2000,and the 3rd International BrassicaSymposium in the UK in September2000. A list of the presentations can befound at .

Extending the shelf life

of leafy vegetables...from

page 1

Project PHT/1994/016synopsis

Extending the shelf life of leafy

vegetables is an ACIAR-funded

project which commenced in July

1998. The objective of the project is

to adapt or remove rate-limiting

procedures contributing to

postharvest wastage, optimiseagronomic and postharvest

handling procedures to increase

shelf life, and to identify the

inherent physiological factors

limiting shelf life that should be

targeted for future biotechno-

logical control and breeding

strategies. The commodities being

studied are pak choy, Chinese

cabbage, broccoli and Oriental

bunching onions. The project

involves 17 research scientists from

QDPI, UA, AV, BVRC (China) and

HUC (China) working on handling

systems assessment, agronomy,

plant biochemistry, and

postharvest physiology.s

Concluded at foot of page 3.

Zheng Shufang (BVRC), Li Wu (BVRC), andJohn Bagshaw (QDPI) gatheringpostharvest loss data with a local farmerin the Beijing area.


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Fumigation remains the majormethod for disinfesting grain ofinsect pests right around the world.Until about 10 years ago the twomain weapons in the grain fumiga-tors armoury were methyl bromideand phosphine. Now use of methylbromide is being phased out byinternational agreement because itwas found to be contributing todepletion of the Earths ozone layer.

Methyl bromide was a particularlyuseful fumigant because of its effec-tiveness and rapid action, the lattercharacteristic giving it major roles in,for example, quarantine treatmentsand the disinfestation of export grainimmediately before transport. Physi-cal treatments such as high-tempera-ture disinfestation are being re-searched as possible replacements formethyl bromide in these applications.

Retention of phosphine essential

For the present, however, we are leftwith phosphine as virtually the onlygrain fumigant available for routineoperational use. Phosphine is a vastlydifferent material to methyl bromide.

Though, when properly applied, it isjust as effective as methyl bromide, theexposure times required are muchlonger and, to ensure complete kill ofall life stages of all insects present, theexposure time and the dosage must becarefully controlled. In short, theprocedures for its efficacious use aremore complex and the potential forfailed fumigations is much greater.Failed fumigations not only leave thetreated commodity at risk, but alsocreate conditions conducive to the

development of resistance to phosphinein the insect populations being treated.Since phosphine, as we have alreadynoted, is the sole, remaining opera-tional fumigant, the development andspread of high level resistance to itwould be disastrous for the worldsgrain industries.

New project in China, Vietnam,and Australia

A new ACIAR project (PHT/1998/137: Integrating effective phosphinefumigation practices into grainstorage systems in China, Vietnamand Australia), scheduled to start in

the new year, will research phosphinetreatment protocols that will ensurethe long-term availability of thisinvaluable fumigant. The commis-sioned organisation in Australia is theQueensland Department of PrimaryIndustries (QDPI). In China, projectresearch in three institutes theZhengzhou Institute of Technology,the Chengdu Grain Storage ResearchInstitute, and the Guangzhou Institutefor Cereal Science Research willbe coordinated by the State Adminis-tration of Grain, while the Plant

Protection Department and the Post-harvest Technology Institute, both inHanoi, will lead the effort in Vietnam.

Australia, China and Vietnamproduce, respectively, about 2530,495, and 30 million tonnes of rice,wheat, maize, and other grains peryear. In each country, about 80% ofproduction is fumigated with phos-phine. Because of the combinedadvantages of low cost, relative easeof use, acceptance as a residue-freetreatment, and for the other reasons

mentioned above, this fumigant willremain the central component ofinsect pest management for theforeseeable future in Australia andthroughout Asia.

Preventing phosphine resistance

In an earlier ACIAR project (PHT/1994/015), QDPI entomologists,working with colleagues in China andIndia, found that resistance in targetpests is indeed a severe threat to thecontinued efficacy of phosphine as agrain treatment. But resistance wasnot the only factor involved in thecontrol failures with phosphine thatwere being recorded. In particular, itwas found that authorities in allpartner countries need to improvefumigation practices and formulatenational fumigation standards. It wasclear too that research was neededinto technical innovations to enhancethe efficacy of phosphine, that

management strategies to controlpsocid pests must be developed, andthat phosphine resistance levels instored grain insects must be moni-tored while national standards arebeing developed and implemented.

These research and operationalneeds will be addressed in the newproject, the overall objective of whichis to protect and enhance the utilityof phosphine as a fumigant for grainand to more fully integrate it into pestmanagement in grain storage sys-tems. Specific aims are to:

improve fumigation practice inChina, Vietnam, and Australia byundertaking training programs;

formulate national fumigationstandards for China, Vietnam, andAustralia;

investigate potential innovations toenhance the efficacy of phosphinefumigation; and

determine the key factors prevent-ing effective control of psocidswith phosphine. s

NEWS FROM PROJECT PHT/1998/137

Keeping phosphine in thegrain pest control armoury

Dr OHare says that the ISHSsymposium was especially informa-tive, providing an excellent chance tocatch up on global developments inpostharvest research, and particularlyto gauge where the projects workstood in relation to research onsenescence around the world. Hereports that the projectss work onpak choy senescence appears to beyielding results that are at the fore-front of understanding what makes aleaf reach the end of its shelf life.

An interesting and informativearticle on the symposium, written byE.W. Hewitt, Chair of the ISHSPostharvest Commission, appears inChronica Horticulturae, the ISHSmagazine, volume 40, number 2. Ofparticular interest perhaps, given thecurrent focus on quality and relatedissues, is Dr Hewitts report of anaddress by Dr Adel Kader:

A timely reminder that quality in theeyes of the consumer constitutes manyattributes and that flavour and aroma,

as well as crispness and juiciness, willincreasingly become key decisionmaking features with buyers of freshfruit and vegetables, was provided by

Dr Adel Kader, University of Califor-nia, USA. He reminded the audiencethat introduction of quality assurancesystems to all crops was essential forthe successful development andretention of markets, and that benefitswere to be gained by developingsystems that were consistent and tookinto account a wider spread ofattributes than those commonly usedtoday. The ability to segregateproduct lines as a result of non-destructive techniques for measuringquality in line, has become possiblethrough the development of a range

of technologies, some of which arenow being introduced into commercialpackhouses. s

Extending leafy vegetable

shelf life...from page 2


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Professor Otto Kunze of TexasA&M University, USA wasrecently named by the American

Society of Agricultural Engineers(ASAE) for his association withone of the Outstanding Agricul-tural Engineering Achievements ofthe 20th Century.

Swimming against the tide ofmainstream scientific opinion at thetime, Professor Kunze for many yearsworked to confirm by experiment andto tenaciously promote his views onthe causes of rice fissuring, a phe-nomenon with the potential to se-verely reduce grain quality. In the

end, his views prevailed. The citationfrom the ASAE journal reads asfollows:

Rice Fissuring Mechanism

Rice, the staple food for over half theworlds population, is produced inabundance worldwide. For many years,however, several million tons of ricewere wasted annually due to the lackof understanding the problem of ricefissuring or sun-cracking. In 1924, E.B.Copeland of The University of the

Philippines introduced an explanationfor sun cracking of rice grains thatreceived wide acceptance for three

decades. Copeland wrote, Suncracking, as the word indicates, is afine cross-wise cracking of the grain,typically due to exposure to the sunand rapid drying. The effect is that anexcessive proportion of the grainsbreak in milling, etc.

In the early 1960s, ASAE member OttoR. Kunze, a professor at Texas A&MUniversity, found that rice drying in thesun evaporated moisture from the grainsurface, causing the grain center to bein compression. The internal crackingof the grain was then caused bytension which developed when thegrain reabsorbed moisture at night in

the field. Since Kunzes finding wascontrary to the accepted dogma, hiswork had to be documented convinc-ingly with data, words and photographsbefore it was accepted for publication.Kunzes results corroborated thoseobtained in 1930 by earlier research-ers, such as Kondo and Okamura ofJapan, which though published hadbeen ignored and rejected by thescientific community. Successivepublications continued to affirm thevalidity of the mechanism, which

PROGRAM NEWS

ACIAR meeting helps spreadthe news on rice cracking

gradually gained recognition andacceptance. Rice growing countriestook notice and the research findingswere soon applied, opening the door tonew and improved rice harvesting andprocessing capabilities.

Professor Kunze was an invitedspeaker at the ACIAR-cosponsoredinternational conference on Graindrying in Asia, held in Bangkok inOctober 1995. He presented a paperentitled Effect of drying on grainquality, which includes a detailedcoverage of the mechanisms of ricefissuring and their implications (seeACIAR Proceedings No. 71). Follow-ing the ASAE announcement, Profes-sor Kunze wrote to Bruce Champ,manager of the Postharvest Technol-ogy Program at the time of theBangkok conference, to thank him forthe role the conference played inspreading the word on the truecauses of rice cracking. Part of hismessage was: I am indebted to

many people for this [ASAE] citation.The exposure which our work re-ceived at the Grain Drying in AsiaConference was helpful to bring ourresearch to the attention of manyrice scientists throughout the world.

A nice endorsement of the benefitsof international meetings on highpriority commodities and issues ofthe type supported by ACIAR. s

As a result of marketingchanges, Associate ProfessorCliff Studman (Massey University,New Zealand), the author of thetextbook Agricultural and Horti-cultural Engineering, has ac-quired a number of copies of thistextbook which he is prepared to

make available free of charge asclass text sets to teachers inuniversities in developing coun-tries, though they must cover thecost of freight(see later).

Sets of books are available incartons containing 25 copies. Univer-sity teachers in developing countrieswho wish to take advantage of thisopportunity should contact A/Prof.Studman at email address

giving details of their university course

and the numbers of students involved.The textbook contains 500 pages

of engineering material for first and

second year degree students inagricultural and horticultural engineer-ing. Included in the contents arechapters on: surveying; the engineer-ing approach; basic physics andmodelling systems; workshop meth-ods and welding techniques; hydrau-lics and farm water supply principles;electricity and electronics; power

systems; thermal systems; buildingstructures and design, including soils,foundations, concrete, timber andsteel, greenhouses and fruit supportstructures; stock fencing design;electric fencing; milking machinetechnology; the design of milkingsheds; postharvest systems; and anintroduction to environmental pollu-tion issues. The coverage is aimed atstudents who have a limited under-standing of engineering, and who wishto undertake courses in agriculture orhorticultural science. First publishedin 1990 by Butterworths, it has beenadopted as a student text by severaluniversities.

The offer to less developed countryuniversities is made on the under-standing that the books will not beoffered for resale, and that theywould be retained by the universitylecturer concerned and the universitylibrary as a set of textbooks forstudent use over several years. Thereceiving university will be required topay the cost of shipment of the textbook sets from New Zealand. Theoffer is made subject to stocks beingavailable and is on a first-come, first-served basis.

Examples of recent freight costsfor shipping 25 books are:

South Pacific region US$51

East Asia US$69

Europe US$80

Rest of World US$101

For other universities, copies maybe obtained by contacting the author atthe above email address. The cost isUS$30 plus the cost of postage fromNew Zealand (around US$16). s

Free agricultural engineeringtextbook offer


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No fear can stand up to hunger, nopatience can wear it out, disgust

simply does not exist where hunger is;and as to superstition, beliefs, andwhat you may call principles, they areless than chaff in a breeze. Dont youknow the devilry of lingering starvation,its exasperating torment, its blackthoughts, its sombre and broodingferocity? It takes a man all his inbornstrength to fight hunger properly. Itsreally easier to face bereavement,dishonour, and perdition of ones soulthan this kind of prolonged hunger.

Joseph Conrad, Heart of Darkness

That there is enough food to

feed all the worlds peopleseems to be generally agreed. Thatso many people nevertheless endevery day hungry is seen as adistribution problem. Thats thepicture now, but what about 20years hence, when we will need tohave increased grain productionby 40% if we are to feed a pre-dicted world population of 7.5billion?

Many scientists are optimistic thatfood production can be increased

sufficiently to keep pace with popula-tion growth, even on a shrinking areaof arable land available for cropping.Some have a great deal of faith ingenetic engineering being able toproduce a gene revolution inagriculture even bigger than thegreen revolution of the 1970s. Butcan we engineer a way through thedistribution problem? Many econo-mists see free trade as delivering thatparticular miracle.

There is no doubt that, even now,the distribution problem is a cause ofserious conflict in many parts of theworld. Shortages of food, and water,foster insecurity, anxiety, and eventu-ally desperation among the peoplethey affect.

In the developed world, securitymight mostly be thought of in termsof military security a negligible orlow risk of being attacked and, in theunlikely event of an attack occurring,the capacity to repel it. In many partsof the developing world, on the otherhand, security is more likely to be

thought of in terms of ready day-to-day access to food and water, allow-ing freedom from the spectres ofhunger and disease.

That these two ways of thinkingabout security are in fact not so verydifferent was highlighted by many ofthe speakers at an internationalconference held in Canberra duringAugust. Food, water and war:security in a world of conflict, aconference organised by the CrawfordFund, drew speakers from verydiverse backgrounds, but most wereagreed that hungry people, becomediscontented people, become disaf-fected people, become people whoare more readily swayed by what DrIndra de Soysa of the University ofBonn, Germany, frighteningly calledconflict entrepreneurs. Thus, thecollapse of food security can quicklylead to the collapse of local, national,or regional security in the widersense.

Dr de Soysa noted that high foodprices and land distribution issueswere primary causes of fractiousness,the former often leading to urbanfood riots. From his research, he hasfound that such conflicts are usuallyinitiated by elite groups in the com-munity, who do no fighting them-selves. The fighters are the poor, whoare generally also the losers. War-lords and other conflict instigatorsdisplay economically rationalbehaviour; by inciting conflict theystand, through their position andactivities, to make greater returnsfrom conflict than from peace.Tragically in such circumstances, thedisaffected poor may feel they arefighting for justice or freedom, butthey are often only cannon fodder

in the money-making enterprises ofthe elites.

Whatever the causes of conflict,civil unrest can have a multiplierimpact on developing economies inwhich agriculture is the primaryengine for development. This pointwas elaborated by two other speakersat the conference Mr AlexanderDowner, the Minister for Foreign

Affairs in the Australian Government,and Admiral Chris Barrie, Chief of theAustralian Defence Forces. Cropstake time to grow and livestock mustbe tended; if the cycle is broken bycivil unrest caused by food insecurity,food shortages may become evenmore entrenched and serious. Admi-ral Barrie made the deceptivelysimple point that people will fight forfood if they have to ... for whicheverarmy offers the best prospects ofdelivering. Food is a stronger driverthan allegiances and politics.

Dr Alan Dupont of the AustralianNational University added a few extraterms to an already complex secu-rity equation. In terms of what hecalled human security there is oftennow a divergence between theinterests of the people and those ofthe state, explaining why most of theconflicts around the world are local orintra-state rather than betweencountries. Dr Dupont seemed to be alittle less sanguine than some otherspeakers about our capacity to meetthe populationfood challenge. The

availability of adequate supplies ofwater suitable for a range of purposesis emerging as a problem in bothdeveloped and developing countries.The gene revolution might bereliant to some degree or other onirrigated cropping. Environmentaldegradation, HIV AIDS, and globalwarming are a few other factorsbearing on human security over thenext few decades.

Three other speakers in the Food,water and war focused on issuesrelating to water: the topic of Profes-

sor Adel El-Beltagy, Director Generalof the International Center for Agri-cultural Research in the Dry Areas,was Strategic options for alleviatingconflicts over water in dry areas; DrMeryl Williams, Director General ofthe International Center for LivingAquatic Resources Management,spoke on Fish wars: science isshaping a new peace agenda; andfor Mr Don Blackmore, Chief Execu-tive Officer of Australias MurrayDarling Basin Commission, the topicwas Dams: the dilemma.

CONFERENCE REPORT

Food and water: essential forlife...and peaceEd Highley

Concluded at foot of page 13.


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Proficiency testing provides anindependent and unbiasedassessment of the performance ofall aspects of the laboratory being

tested.Proficiency testing is not to beconfused with collaborative trials inwhich the method, rather than thelaboratory, is being tested. In profi-ciency tests the laboratory is encour-aged to use its usual analyticalmethod, simulating the testing of aroutine laboratory sample as closely aspossible. While the outcome of theanalysis may be dependent on thechoice of method, it could also beaffected by the performance of labora-tory equipment or the analyst. Those

laboratories performing well can ensurehigh standards are maintained andthose performing unsatisfactorily canimplement corrective action rapidly.Thus, proficiency testing provides themeans by which external customerscan compare competence in carryingout specific tests. The requirements forestablishing and running proficiencytesting schemes are stipulated in anISO/IUPAC/AOAC International Harmo-nised Protocol (Thompson and Wood1993).

This external check of quality is a

powerful addition to a laboratorysown internal quality systems, particu-larly for analysts involved in thequantification of mycotoxins, and whomay be undertaking such work withina legislative framework, for exampleas set out by the European Union(EC 1998).

The variety of raw materials thatmay contain mycotoxins makes itdifficult to ensure proficiency testscover the range of matrices thatanalysts routinely encounter. Hence, inpractice proficiency testing tends to

concentrate on those commodities ofmajor interest and occasionally includematrices known to present analyticaldifficulty. It is important to use, whereavailable, food samples naturallycontaminated with the mycotoxin inquestion. Spiked samples may notbehave in the same way as regardsmycotoxin extraction and recovery.

The distribution of mycotoxinswithin a contaminated food is notori-ously non-uniform. Homogeneity

testing therefore is a vital part of testmaterial preparation in order toensure each participant receives anidentical test material. The Harmo-nised Protocol (Thompson and Wood

1993) stipulates a strict homogeneitytesting procedure and only when theresulting data pass the appropriatestatistical tests should the test mate-rial be used for a proficiency test.

Most proficiency testing schemesreport the performance of partici-pants in terms of a z-score:

where

x = the participants reported result,= the assigned value, and

= the target value for standarddeviation.

The assigned value should be thebest estimate of the true concentra-tion of the analyte. It can be obtainedfrom the mean of results submittedby participants by using robuststatistics to ensure that the influenceof any outliers is minimised.

The target value for standarddeviation defines the scale of accept-able variation among laboratories ineach particular test. It may be ob-

tained from collaborative trial data,relevant legislation or from theappropriate form of the Horwitzequation (Thompson 2000).

The Food Analysis PerformanceAssessment Scheme (FAPAS) wasestablished by the UK Ministry ofAgriculture, Fisheries and Food at theCentral Science Laboratory (CSL) in1990. Ten years later it has become

the premier international scheme ofits type. An outline of the FAPAS

mycotoxin program for 20012002 isshown in the table below.

For further details contact:

FAPAS,CSL, Sand Hutton, York, YO41 1LZ,UKFax: +44 1904 462111Email:[email protected]: www.csl.gov.uk

References

EC (European Commission) 1998.European Commission Regulation No.1525/98.

Thompson, M. 2000. Recent trends ininter-laboratory precision at ppb andsub-ppb concentrations in relation tofitness for purpose criteria in profi-ciency testing, Analyst, 125, 385386.

Thompson, M. and Wood, R.. 1993. Theinternational harmonised protocol forthe proficiency testing of (chemical)analytical laboratories. Journal of theAssociation of Official AnalyticalChemists International, 76, 929940. s

Proficiency testing formycotoxin analysis*

* This article was contributed by FAPAS

,the Food Analysis Performance Assess-ment Scheme of the UK Ministry ofAgriculture, Fisheries and Food.

X

FAPAS mycotoxin proficiency tests available in 20012002

Mycotoxin Matrix

Aflatoxins B/G &/or total Maize, peanut powder, spice, peanut butter, sunflowerseeds, dried fruit/figs

Aflatoxin M1

Milk, yoghurt

Patulin Apple juice & apple puree

Ochratoxin A Cereal, coffee, dried fruit

Deoxynivalenol Wheat flour

Fumonisins Maize

Zearalenone Maize

z

x X

=

( )

All aboutsoybeans

The Proceedings of the ThirdInternational Soybean Process-ing and Utilization Conference,recently published, contains morethan 270 papers from 22 countriesaround the world.

The theme of the conference was

2000: Dawn of the Innovative Era forSoybeans. The topics of the eightmain conference sessions were:

Production for processing and utilisa-tion; Quality control; Nutrition andphysiological functionality; Traditionalproducts; Modern processing andutilisation of foods; Edible oil andfeeds; Innovative non-food uses; andStrategies for dissemination. Theconference ended with a publicsymposium, intriguingly entitled Themiracle of Asiamarvellous fer-mented soyfoods.

There is much to interestpostharvest specialists in this volume.

Can any reader enlighten us as to itscost and availability? If so, pleasecontact . s


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Maize (Zea mays) is the worlds

third most important cerealcrop after rice and wheat. It hasbeen predicted that the demand formaize in the coming two decadeswill grow faster than that for anyother cereal crop in the developingworld. Maize recently surpassedcassava as Africas most impor-tant food crop in terms of caloriesconsumed, and its production insub-Saharan Africa has increasedan average of 2.6% annually overthe past 25 years. In Asia, the

demand for maize, which was 138million tonnes in 1993, is pre-dicted to reach 243 million tonnesby 2020. China alone could wit-ness a 94% increase in maizedemand over this period.

Many farmers grow maize simplyto provide enough food for theirfamilies to survive, but in some partsof the developing world, especially inLatin America and Asia, commercialproduction of maize for animal feedand industrial uses is increasing. InThailand, for example, domestic

consumption of the maize cropincreased from around 30% in 1985to 75% in 1990 as a result of thegrowth of the poultry industries.

Maize is produced on more than 80million hectares in developing countriesalone, in a vast array of climates andconditions. In north-eastern China, forinstance, where there are only about140 frost-free days, the growing periodis relatively short and it is possible togrow only a single crop each year.Highland maize in Mexico and theAndean region of South America growsslowly in the relatively low tempera-tures and farmers must wait up to ninemonths to harvest. At the other ex-treme, tropical environments are suitedfor year-round production, and it iscommon for two crops per year to begrown.

With increasing urban encroachmentinto the best farming land and littleadditional land suited to maize produc-tion, where will developing countriesget the extra maize that they want?Imports may offer a partial solution,

but the larger, domestic portion willrely on two facets: improvements inboth productivity and postproductionmanagement. However much we areable to improve production in thefuture, we can maximise the benefits ofthese improvements only if we havethe postharvest capabilities to matchthem.

Improving production

Productivity of maize in developingcountries is less than half that of thedeveloped world. This reflects lowsoil fertility and acidic soils, re-

stricted use of fertilisers, the occur-rence of droughts and floods, theeffects of weeds, diseases, and fieldpests, poor infrastructure, andfarmers low cash reserves. Seedproduction and availability are criticalin subsistence economies wherepoor-yielding varieties are perpetu-ated and the introduction of hybridmaize has precluded farmers fromcollecting seed for future crops.

Given that we want more maize tobe produced on the same (or evenless) land, increasing the productivity

of individual maize plants is essential.Current research is concentrating onincreasing production through high-yielding varieties, hybrids, and inbredlines, resource management, training,and other innovative strategies.

In addition, the International Maizeand Wheat Improvement Center(CIMMYT) is developing qualityprotein maize (QPM), a new productthat could contribute significantly tothe wellbeing of millions of resource-poor farmers and consumers in Asia,Africa and Latin America. Thenutritive value of the protein in QPMis high, approaching that of proteinfrom skim milk. As a bonus, QPMhas superior yields: 10% more thanleading commercial varieties ofnormal maize. CIMMYT is alsoworking to enhance other nutritionalcomponents of QPM maize, includingzinc, iron and vitamin A.

Furthermore, researchers are alsodeveloping maize varieties that canwithstand drought and infertile soils,and have improved resistance to

stored grain pests.Improving production is only part

of the answer. At least equally

important is the postharvest handlingof the maize in order to reduce lossesand maintain the quality of theharvested crop. If more grain could beheld safely without losses untilneeded, Some pressure would betaken off the need to increase produc-tion, and fewer resources would bewasted. It is clearly more efficient topreserve what has already beenproduced than to use fresh resourcesto produce more.

Current postharvest practices

In many countries, postharvestconditions for maize are far from ideal.For example, farmers in Ethiopia lose25% of their grain during storage andare further penalised with a 25% pricereduction for the remaining damagedgrain. One of the few means by whichfarmers will be able to obtain betterprofit margins and alleviate poverty isto improve the ways they handle the

grain at and after harvest. They needhelp to do this.

In developing countries, maize isusually hand picked. The harvestedmaize may accumulate on farms forup to five days waiting for drying,machine shelling and sale. Significantquality deterioration can occur at thistime, particularly of wet maize, whichis most prone to the two main agentsof deterioration insects and fungi.

Sun drying remains the mostcommon means of drying maize in

developing countries. Sun drying maytake place in the field, in farmersdrying yards, at grain depots, underdwellings or any other convenientlocation. It is a labour-intensiveactivity and in many countries therecontinues to be a strong drift oflabour from rural to urban areas. Therecommended maximum moisturecontent (m.c.) for safe storage andtransport of maize is 14.5%; the idealstorage moisture content is 14%.

Maize is then stored in a variety ofways, usually depending on local

custom: it can be stored on the cob,with or without husks, or as shelledgrain. It can be kept in earthen potsor metal containers, in jute gunnysacks, or hung as cobs or in manyother ways. There are advantages anddisadvantages to all these methods.

Sacks made from wovenpolypropylene are replacing jute sacksfor commodity storing in many devel-oping countries. In sub-Saharan Africathis has been accompanied by anincrease in stackburn, a condition inwhich maize becomes discoloured

during storage; losing commercial andpossibly nutritional value. Stackburn is

REVIEW ARTICLE

Managing maize stocks indeveloping countries*Mary Webb and Ed Highley

* This review was compiled using informa-tion from the sources listed at the end ofthe article. Continued on next page.


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8

caused by chemical changes in thegrain induced by high temperaturesduring storage; it may in part be theresult of non-enzymic browning.Studies in Zimbabwe and elsewherehave identified insect metabolic activityas one possible cause of heating.

Storage of maize cobs in cribs ispopular in many countries throughoutthe world. This is a very simple, low

cost technique, in which cobs can besafely stored for 612 months depend-ing on the environmental conditions.One study showed that crib storagedried the grain from 40% to 16% m.c.during storage with no visible mouldgrowth during the storage period.However, there was 28% insect infesta-tion and 50% germination loss after 7months of storage.

The value of mechanical drying isbeing increasingly appreciated, espe-cially in areas where timely andcomplete sun drying is not possible

and cheap sources of energy forheating are available. There are manytypes of mechanical dryers availableand in use, including flat-bed dryers,rotary dryers, fluidised-bed dryers,mixed flow dryers, and so on. It isimportant that the right type andcapacity of dryer is selected so that itmatches the drying task and that thedryer operators are fully trained in itsuse.

In China, an estimated 13001500maize dryers have been installed inrecent years in the three north-eastern

provinces of Liaoning, Jilin andHeilongjiang and in the Inner MongoliaAutonomous Region. Almost all ofthem are indirectly heated, coal-firedcontinuous-flow dryers. There arereports that many of them, owing toimproper design and poor quality ofmanufacture and erection, are notworking well, resulting in quantitativeand qualitative losses of maize. Never-theless, in the absence of knowledgeabout the availability of better alterna-tives, such dryers are still beingproduced and sold.

Thus, despite many technologicaladvances made over several decades,many problems are still prevalent inthe postharvest handling of maize,particularly in developing countries.

Problems encountered

Grain deterioration

The deterioration of grain begins atharvest and the rate of quality lossdepends on handling and storageconditions. The main problems are

linked in that badly handled grain ismore likely to be attacked by insectsand insect-damaged grain is moresusceptible to fungal growth.

The postharvest problems associ-ated with maize vary depending on theenvironmental conditions in which it isgrown. For example, in north-easternChina, the maize is harvested as theweather is cooling in fact, the maizeoften freezes in the field and is main-tained in that state until the followingspring, at which time drying hugeamounts of rapidly thawing, highmoisture grain becomes a formidableproblem. China is not alone; in manyother countries, merchants and storageoperators cannot cope with the largeamounts of grain which arrive atdepots at peak harvest time. In South-east Asia and other tropical areaswhere two crops are grown per year,one of these is necessarily harvestedduring the rainy season, thus makingproper sun drying a major challenge.

The Chinese grain system receivesmaize with a high moisture content of2530%, sometimes as high as 35%.

If the initial moisture content of maizeis very high, it is difficult to reduce itto the recommended 14% in onedrying pass without damaging thegrain. One solution here is two-stagedrying, mentioned again later in thisarticle.

Another important feature of thecurrent situation may be that, as inThailand, there are no incentives forfarmers to dry their grain to less than18% m.c.

Storage problems have increasedas traditional varieties have been

replaced by improved, high-yieldingvarieties which are generally moresusceptible to insect damage thanthose of local origin, thus increasingthe need for insecticides. Studies inMalawi have shown that hybrid maizesuffers from very high losses (morethan 20%) in traditional storage if leftuntreated. The message here is thatthe full benefits of the new varietiescannot be captured without increasedattention to storage management.

Insect infestation

During storage, maize can beinfested with insects and mites, fungi,microorganisms and rodents. Insectscause massive losses to stored cropsthroughout the world and maize is noexception. Typical insect pests ofstored maize include Sitophilus zeamais(maize weevil), Prostephanus truncatus(larger grain borer), Sitotroga cerealella(Angoumois grain moth) and Tribolium(flour beetle) species.

Factors affecting infestationinclude:

grain moisture content grainstored at high moisture levels (3035%) deteriorates rapidly;

storage form (on the cob, orshelled) different pests prefereach form;

temperature and humidity hightemperatures (2630C) andrelative humidities (7080%) areoptimal conditions for the develop-ment of storage pests such asProstephanusand Sitophilus;

level of hygiene in the storage

place; type of store; and

level of infestation before harvest.

Insect control currently relies mainlyon the use of chemical pesticides insecticides and fumigants. For healthand environmental reasons, there isincreasing concern worldwide about theuse of such pesticides. Some marketswill not accept commodity containingeven minute amounts of pesticideresidues. The use of methyl bromide,formerly one of the two most important

grain fumigants, is being phased out,and the effectiveness of the remainingone, phosphine, is being compromisedby improper use (see article in thisissue). Alternatives include fumiga-tion with controlled or modifiedatmosphere storage using gases suchas carbon dioxide and nitrogen. Otherfarmer practices are varied and includespraying the stored maize with ash andpepper, smoking of the storage struc-ture, and a host of other traditionalremedies.

Fungal damage and mycotoxincontamination

Fungi can invade the grain beforeharvest (field fungi) or after harvest(storage fungi). The primary factorsinfluencing fungal growth in storedfood products are temperature andmoisture content. Fungi can causetwo quite distinct, though not unre-lated, problems in stored commodi-ties: spoilage resulting from fungalgrowth (moulding), and mycotoxinformation. Mould growth in grains cancause loss of weight, loss of nutritive

value, poor milling quality or deterio-ration in flavour, colour, or otherorganoleptic qualities. Losses fromspoilage, though much less danger-ous than the presence of fungaltoxins, may be of greater economicsignificance. Spoilage and downgrad-ing may be caused by growth of fungibefore harvest, or may be the resultof inadequate drying or mismanage-ment in storage. Particularly in thetropics, conditions are often perfectfor fungi and it is difficult to controlcommodity moisture. Damaged grain

is more prone to fungal invasion (andtherefore mycotoxin contamination).

Continued on next page.


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9

Grain can be damaged throughpostharvest procedures, such asshelling, or by insect attack. Insectsalso cause damage through increasedmoisture caused by their activities.

Mycotoxins are poisonous chemicalcompounds produced by certain fungalspecies which infect maize (and othercrops). They can be acute poisons, orhave chronic or cumulative effects, and

have great significance in the health ofhumans and livestock. In a highproportion of maize that has receivedless than ideal postharvest treatment,a range of mycotoxins is likely to befound. The majority of these areproduced by two genera of fungi:Fusarium(fumonisins, fusarin andtrichothecenes) and Aspergillus(aflatoxins).

Aflatoxins are potent humancarcinogens and interfere with thefunctioning of the immune system.Epidemiological data continue to

show that chronic exposure toaflatoxins causes liver cancer. An-other aspect of aflatoxin that hasserious human health implications isthe transfer of an aflatoxin B

1

metabolite aflatoxin M1

into the milkof lactating animals. There arereports that up to 70% of all stocks ofmaize in the Philippines are contami-nated with aflatoxins.

A number ofFusariumspeciesaffect maize both before and afterharvest and the high toxicity of themycotoxins they produce is being

increasingly recognised. Fumonisinshave been found as a very commoncontaminant of maize-based food andfeed in Africa, China, France, Indone-sia, Italy, the Philippines, SouthAmerica, Thailand, and the USA.Fusarium moniliforme is the mostcommon fungus on maize in mostparts of the world. Consumption ofF. moniliforme-infected maize isassociated with a high incidence ofhuman oesophageal cancer in south-ern Africa and parts of China. One ofthe most serious toxigenic fungi in

Canada and the north-eastern USA isF. graminearum, which is associatedwith ear rot in maize. The principleinoculum source ofF. graminearum ishost debris, e.g. old maize stalks,ears and stubble, and debris of smallgrain cereals left on the soil surface.Weeds also serve as a source ofmould inoculum. The risk of contami-nation here could be reduced bygreater attention to hygiene and cropmanagement.

Animals are affected to varyingdegrees by different mycotoxins. For

example, aflatoxins are particularlytoxic to chickens, causing a range ofproblems including increased suscep-

tibility to disease. Pigs are particu-larly vulnerable to Fusariummycotoxins, whereas poultry arerelatively resistant. Cattle are thoughtto be generally less susceptible to theeffects of mycotoxins because thetoxins are degraded in the rumen.

As well as directly affecting thehealth and productivity of livestock,mouldy feed may be less attractive to

animals and has the potential to causetwo different types of residues in meatthat might then be consumed byhumans. Firstly, specific residues ofmycotoxins may occur. Secondly, mostfungi produce a range of antibiotics,and these might be detected in bacte-rial inhibitory tests used to screen meatfor residues of therapeutic antibiotics.The secondary effects on humans havenot yet been ascertained.

By far the most important cause ofmycotoxin problems is failure to drygrains adequately before storage.

Difficulties in sun drying and/or theinexperience of farmers and traders inthe use of dryers are importantfactors here.

Possible solutions

Solving any one of the postharvestproblems encountered in maize helpsto solve another. For example, reduc-ing the level of insect damage helpsreduce fungal attack of the grain.Hence, a system of integrated com-modity management that combines the

most appropriate methods of handling,storage and therapeutic treatments isthe most effective approach to main-taining the highest possible quality ofmaize after harvest.

The key aspects of adequate graindrying and good storage conditionsare able to minimise or preventphysical deterioration, insect andother pests, fungal invasion and otherpostharvest problems.

Proper grain drying

Wet grain management is arguably

the most important aspect ofpostharvest maize handling, as itaffects how long the maize can bestored safely, by moderating itssusceptibility to insect and fungalattack. Prevention of fungal invasionof commodities by drying to a safemoisture content for storage is by farthe most effective method of avoidingmycotoxin problems, as fungi cannotgrow (and hence mycotoxins cannotbe produced) in properly dried food.

The best way to prevent andcontrol mycotoxins in maize is to:

dry the grain as soon after harvestand as rapidly as feasible;

avoid grain damage (includingmechanical and insect damage);and

ensure proper storage conditions.

Under suitable environmentalconditions, sun drying is a goodoption, especially where the cobs (orgrain) can be dried under cover, butwith good exposure to sunlight andnatural ventilation, such as under the

edge of a house. Drying maize on thecob, before shelling, is a very goodpractice to reduce grain damage(damaged grain being more prone tofungal invasion).

The benefits of mechanical dryingare increasingly being appreciated,especially in wetter climates wheretimely sun drying is often impossible.Where mechanical drying is possible,drying conditions and equipmentshould be carefully selected, asimproper drying can result in highcosts, low efficiencies, high millinglosses, poor quality of the grain orreduced germination capacity of driedseeds. Research in China has shownthat it is possible to dry high mois-ture content maize in one drying passprovided certain continuous-flowdryer types are used with appropriatetempering. These dryers also give thebest drying throughput, dryinguniformity and energy efficiency. Flat-bed dryers for maize on the cob arepopular in Vietnam. They are locallydesigned and manufactured, areeffective, entail a low initial invest-

ment, and have a low operating cost.Two-stage drying is gaining in

popularity in many parts of the devel-oping world, including the Philippines,Thailand and, most recently, China,where the effectiveness of the tech-nique has been proven in a program ofgrain drying research supported byACIAR since the early 1980s. A currentACIAR project (PHT/1994/037) aimsto improve two-stage drying of wetmaize in north-eastern China. Theproject is based at Harbin inHeilongjiang province.

In two-stage drying, the highmoisture grains (more than 24%m.c.) are dried rapidly to a moremanageable level of about 18%,followed by slow drying to 14%. Thebenefits of two-stage drying includeimproved grain handling capability,premium grain quality, lower operat-ing and drying costs, more affordableinvestment, ease of operation, andflexible drying capacities. The secondstage can be undertaken in-store. In-store drying, sometimes calleddryeration, has an added potentialbenefit of insect control.



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It may reduce the temperaturewithin the grain to a level at whichinsects cannot reproduce and insome instances may kill any insectsalready present.

Storage

Ideally, storage should be in bagsor structures which are impermeableto moisture.

On a small scale, polyethylenebags are effective; on a large scale,safe storage requires well-designedstructures with floors and wallsimpervious to moisture. Appropriatelytimed aeration with ambient air of asuitable temperature and moisturecontent can be helpful. All large-scalestorage areas should be equippedwith instruments for measuring insideand outside temperatures and abso-lute humidities, so that air appropri-ate for aeration can be selected. Inmodern storage systems, the opera-

tion of aeration fans is usually auto-matically controlled using sensorsand a microprocessor.

Sealed storage under modifiedatmospheres for insect control is alsovery effective for controlling fungalgrowth, provided the grain is ad-equately dried before storage, andprovided diurnal temperature fluctua-tions within the storage are minimised.It is also useful in keeping out rodents.Sealed plastic enclosures such as thosedeveloped and tested in ACIARprojects PHT/1983/007 and PHT/1988/

045 and the Israeli Volcani cubesprovide these conditions, and have theadvantage that they can be used tosafely store grain outdoors where nosuitable storage buildings are available.Shade screens and an upper layer ofstraw or husks insulate the stack fromdiurnal temperature fluctuations. Withinthe storage ecosystem sealed structure,an oxygen-depleted and carbondioxide-enriched atmosphere is gener-ated which arrests insect development.Grain is protected by maintaining thenumber of live insects below the

threshold of economic damage withoutthe need for pesticides.

The basics of pest control

Once the grain has been properlydried, there are, according to theInternational Institute of TropicalAgriculture (IITA), four major types ofcontrol measures applicable to maizestorage:

inspection;

housekeeping/sanitation;

chemical methods; and

physical and mechanical methods.Sorting maize before shelling and/

or storage is an effective way ofphysically removing visibly damagedcobs. The procedure, although time-consuming, has the potential tosignificantly reduce subsequentproblems. Ensuring that the areaused to store the maize is free of dirtand other contaminants is anotherbasic step which reduces the risk ofinsect or fungal infestations arising inthe store itself. In other words,hygiene and other good storage-management practices are of para-mount importance.

Pesticide use

The use of pesticides is still themost common means of achievingtherapeutic pest control.

Fungicides are commonly used tocontrol mycotoxin-producing fungalgrowth, and fumigant and residualinsecticide use is still prevalent. Foreffective disinfestation using fumi-

gants, the two most important factorsare provision of a gastight enclosure,and good distribution of gas through-out the commodity. It is critical thatall insects in all parts of the storagebe exposed to the required concen-tration of fumigant for the requiredtime. Leaky enclosures lead to failedfumigations, loss of commodity andthe risk of selecting for resistance tothe fumigant among the survivinginsects.

Increasingly, traditional insecti-cides based on plant derivatives are

being used in integrated pest man-agement systems. In such systems,fumigations are undertaken spar-ingly, in conjunction with bestpractice management techniques ofclean storage areas, hygiene andalternative control methods.

Adequate protection of storedmaize against P. truncatushas beenrecently achieved by treating onlythe top 20% and bottom 30% ofgrain, after a study of the insectsbehaviour revealed their tendency tomove down a grain bulk.

Insects and fungi are developingresistance to a range of chemicalpesticides, and the number ofpesticides is being reduced, so theneed for alternative approaches isbecoming increasingly urgent.

Alternative pest control methods

Grain chilling. Increasingly,chilled aeration in which the graintemperature is lowered independentof ambient conditions for the controlof insect development, is a popular

means of preserving grain quality.Grain is cooled using a mobilerefrigeration system that controls

both the temperature and therelative humidity of the aeration air.While effective, this method is tooexpensive for most situations inemerging economies, though it hasbeen used in paddy storages by amajor rice marketing authority inMalaysia.

Grain cooling using refrigeration,and other strategies such as the use

of controlled atmospheres or pre-servatives or natural inhibitors arenot usually feasible in developingcountries as they are almost alwaysmore expensive than effectivedrying.

Inert dusts and other materials. Themove away from chemical pesticideshas renewed interest in the use of inertsubstances to keep insects at bay.Worldwide, locally available inertmaterials have been used by communi-ties for many generations to protecttheir stored commodities. The main

drawback of such materials, whichinclude wood ash, lime and fine sand,is the large quantities required toprovide protection. Their mode ofaction is probably a combination oftheir abrasive qualities and the inhibi-tion of normal insect behaviour. Inertdusts bring about death by desiccation,and as a result their performance isaffected by ambient relative humidity.They have been proven effective inboth laboratory and large-scale trialsagainst a range of storage pests. In arecent Indonesian study, zeolite a

hydrated silicate compound close incomposition to the common mineralfeldspar had been successful inkilling 100% ofS. zeamaisduringstorage of three months. Dryacide, anactivated amorphous silica used widelyas a surface treatment of stored wheatin Australia, also provides an effectivemeans of disinfesting storage facilitiesand farm machinery. It can be dryblown or applied as an aqueous slurryas appropriate.

Biological control. One successstory has been the biological control

of P. truncatus, the larger grainborer, which was accidentallyintroduced to Africa from CentralAmerica with devastating effects onmaize. Previously, the main optionfor farmers to reduce losses was toadmix pesticide with their grainwhich was costly and had the usualhealth and environmental implica-tions. Careful research led to identi-fication of a predatory beetleTeretriosoma nigrescenswhich isnow being used successfully tocontrol the borer.



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Although relatively costly inresearch terms, studying insect lifecycles, physiology and behaviour todevelop strategies to outwit them,can lead to solutions which areharmless to all but the target pest,e.g. in Kentucky, USA, S. cerealellahas been successfully controlledthrough timing strategies, such asearly harvesting, which minimise thewindow of exposure to potentialcolonising moths. The change to bulkhandling of grain has also markedlyreduced the importance of this pest.

Bacterial antagonism is beinginvestigated as an alternative meansof fungal/mycotoxin control. Forexample, inoculation of grain withBacillus megateriumcan reduceAspergilluspopulations and aflatoxincontent. Although the mechanism ofaction and the antagonisticmetabolite of the bacterium have yetto be characterised, the technique

illustrates the potential use of biologi-cal control on a wide variety of targetorganisms. In addition, researchersare obtaining promising results byintentionally introducing into fieldcrops fungal strains that do notproduce mycotoxins but whichsuccessfully out-compete strains thatdo, with the result of reducing overallmycotoxin contamination.

Other methods. In a recent study,insect growth regulators were shownto be effective in protecting unshelledmaize against S. zeamaisand shelled

maize against S. cerealella. Very fewinsect growth regulators are regis-tered for food storage use, but this islikely to change as pressure toreduce reliance on conventionalinsecticides mounts.

Physical treatments with heat orirradiation are also being tested.These have the advantage of beingresidue free.

Decontamination

Approaches to mycotoxin decon-tamination have included physical,

biological and chemical treatment ofgrain, as well as dietary manipulationsto minimise the effects of contaminat-ing mycotoxins on the animal, e.g.ammoniation has been shown to be aneffective method of detoxifying animalfeedstuffs. In cases of light to moderateFusariuminfestation and mycotoxincontamination, physical or chemicalmethods for cleaning the kernelsurface, and hence removing the moreheavily contaminated particulatematter, have proven effective inreducing mycotoxin concentrations.

These include dehulling, washing androasting. Many other methods havebeen tried with varying levels of

success: density segregation of con-taminated from non-contaminatedkernels, food processing practices, andtreatment with chemicals such assodium bisulfite, ozone, ammonia,ammonium carbonate, sodium carbon-ate, and calcium hydroxide. Otherstrategies have included dilution ofcontaminated grain with uncontami-nated grain, the use of binding agents,anion exchange and so forth.

Funding, education and socialfactors

There is a trend toward reducingpublicly funded research and dissemi-nation efforts for maize. This isparticularly worrying given the factthat small-scale farmers in manyregions are not served by privatecompanies.

Teaching farmers, traders andcooperatives correct procedures for

drying, fumigating, and other storageand handling practices is the key tosuccess in the postharvest handling ofmaize. Just as important, however, isto explain the reasoning behind thesetechniques if the people growing,handling, storing and marketing thegrain understand how and why graindeteriorates, it places them in a betterposition to improve their practices, andthey are more likely to do so. Forexample, many farmers are unawarethat maize kept moist and in unsuitablestorage is prone to aflatoxin contami-nation. Providing (financial) incentivesto farmers and processors to achievelower moisture contents in their storedgrain would probably also see a higherlevel of compliance. The importance oftraining farmers is highlighted in arecent survey which found a significantrelationship between training and thelevel of technology utilisation in thePhilippines. Also, farmers themselves,with their extensive local knowledge,can contribute to better methods ofhandling and storage. The best way tocapture the benefits of this localknowledge and increase levels ofadoption of technologies that areshown to be effective may be throughfarmer participatory research projects.

In addition, social factors such asgender issues need to be consideredwhen undertaking research and exten-sion which is aimed at helping develop-ing countries, as these may play acrucial role in whether the outputs aretaken up by their intended beneficiar-ies. For example, at the village level inmany countries it is women who do thebulk of the postharvest work. Theyshould therefore be among the primarytargets for research and training inbetter postharvest management of thecrop.

Acknowledgments

The authors thank Dr BruceChamp for his expert comments onthis review, but acknowledge that anyerrors of interpretation are theirs.

Sources

Banks, H.J., Wright, E.J. and Damcevski,K.A., ed. 1998. Stored grain in Aus-

tralia. Proceedings of the AustralianPostharvest Technical Conference,Canberra, 2629 May 1998. Canberra,Stored Grain Research Laboratory,CSIRO Entomology.

Champ, B.R., Highley, E. and Johnson,G.I., ed. 1996. Grain drying in Asia.Proceedings of an international confer-ence held at the FAO Regional Officefor Asia and the Pacific, Bangkok,Thailand, 1720 October 1995. ACIARProceedings No. 71.

Champ, B.R., Highley, E., Hocking, A.D.and Pitt, J.I., ed. 1991. Fungi andmycotoxins in stored products. Pro-

ceedings of an international conferenceheld at Bangkok, Thailand, 2326 April1991. ACIAR Proceedings No. 36.

GASGA (Group for Assistance on SystemsRelating to Grain After-harvest) 1997.Mycotoxins in grain. Technical LeafletNo. 3. Wageningen, The Netherlands,CTA (Technical Centre for Agriculturaland Rural Co-operation).

Highley, E., Wright, E.J., Banks, H.J. andChamp, B.R., ed. 1994. Stored productprotection. Proceedings of the 6th

International Working Conference onStored-product Protection, 1723 April1994, Canberra, Australia, Volumes 1

and 2. Wallingford, CAB International.Jin Zuxun, Liang Quan, Liang Yongsheng,

Tan Xianchang and Guan Lianghua, ed.1999. Stored product protection.Proceedings of the 7th InternationalWorking Conference on Stored-productProtection, 1419 October 1998,Beijing, P.R. China, Volumes 1 and 2.Chengdu, Sichuan Province, SichuanPublishing House of Science andTechnology.

Johnson, G.I., Le Van To, Nguyen DuyDuc and Webb, M.C., ed. 2000. Qualityassurance in agricultural produce.Proceedings of the 19th ASEAN/1st

APEC Seminar on Postharvest Technol-ogy, Ho Chi Minh City, Vietnam, 912November 1999. ACIAR ProceedingsNo. 100.

Internet websites (November 2000):

CIMMYT (International Maize and WheatImprovement Center):.

IFPRI (International Food Policy ResearchInstitute): .

IITA (International Institute of TropicalAgriculture): .

INPhO (Information Network on Post-

harvest Operations): .


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Ghana, Togo, and Benin arejoining forces to fight thetoxin-producing fungus, Aspergil-lus flavus, which is contaminating

maize and other widely consumedcrops in West Africa. The funguscan produce aflatoxins whichpenetrate the body only throughthe consumption of either grain-based food or poultry and cattlefed with such food.

Aflatoxin contamination of maize,peanuts and other food crops isconsidered to be a major cause ofhepatocellular carcinoma (livercancer) in humans. The voluntaryorganisation, Rotary International,has now launched a program to

eradicate aflatoxin in the three WestAfrican countries. This follows asurvey it conducted, the results ofwhich showed a strong correlationbetween the presence of aflatoxin inthe blood and the incidence of livercancer.

Aflatoxins can also contaminatehuman milk and thereby be absorbedby feeding infants. As a result, theirimmune system is affected. Thiscontributes to high infant mortalityrates and to impaired health through-

out the childs life, said Dr KittyCardwell, a member of Rotary Inter-national and an expert on aflatoxins

Action against mycotoxins inWest Africa

US FDA recommendationsThe US Food and Drug

Administration initiates regulatory

action when aflatoxin exceeds 0.5

ppb in milk for human consumption.

Drying maize kernels to 15.5%

moisture or lower within 2448 hours

of harvest will minimise the risk of

fungal growth and consequent

aflatoxin production. This assumes

that maize and other grain seeds

are not already infected with

A. flavusin the standing crop.

Research by United StatesDepartment of Agriculture scientists

has demonstrated that two maize

lines which are resistant to infection

by A. flavusare also resistant to

infection by Fusarium moniliforme,

another maize ear-rotting fungus

that produces fumonisins, another

class of mycotoxin. These maize lines

may be useful in developing lines

which not only resist infection by the

two fungi but also to production of

the mycotoxins. s

who is based at the InternationalInstitute for Tropical Agriculture inIbadan, Nigeria. Infant mortality ratesstand at 76 per 1000 in Ghana, 97per 1000 in Benin, and 77 per 1000in Togo, compared with about 2 per1000 in Australia, for example.

According to the World HealthOrganization (WHO), the permittedlevel in food products of aflatoxins is

zero parts per billion (0 ppb) forchildren, 20 ppb for adults and 55ppb for animals. These norms arenot respected in West Africa. Somestudies show populations consuming100 ppb per day since they wereborn, Dr Cardwell lamented. Thestudies reveal that consumers are notaware they are eating contaminatedfood. The problem with aflatoxin isthat farmers cannot see the fungusthat produces it on the maize. Moreo-ver, it is colourless and it does notdisappear after cooking or fermenta-

tion.According to the authors of the

Rotary survey, The corn seeds areseverely damaged in West Africabecause they remain too long in thefields where they are attacked bymany insects. As a result, theygenerally have higher levels ofaflatoxin. Damage by infestations ofinsects generally makes the grainmuch more susceptible to fungalinvasion. s

The Natural Resources Instituteoffers programs leading to aPost-graduate Diploma/Master ofScience in Grain Storage Manage-ment and Post-Harvest Horticul-

ture. Both programs are offered inboth in attendance and compu-ter-mediated distance learning(CMDL) modes of delivery.

In attendance programmes:

PGDip. 12 March to 29 June2001

MSc 2July onwards

CMDL programs:

Dates on request.

TRAINING NEWS

Courses at NRI, Universityof Greenwich, UK

Food Safety PGDip/MSc (subjectto validation)

This is a new course, scheduled tostart in September 2001. A 45-weekfull-time program will address the

needs of professionals working infood and agriculture who seek awider view of food safety issues.

NRI also offers professional shortcourses, which can be tailored to suitclients needs.

For further details on training atNRI, please contact:

The Training Support UnitThe Natural Resources InstituteChatham MaritimeKent, ME4 4TB.Fax: +44 1634 883577Email:

Web page: . s

FORTHCOMING MEETING

IHC2002

The 26th International Horticul-

tural Congress and Exhibition,sponsored by the InternationalSociety for Horticultural Scienceand implemented by the CanadianSociety of Horticultural Science,will be held in Toronto, Canada on

1117 August 2002. The confer-ence theme will be HorticultureArt & Science for Life.

Various items in a list of colloquiagiven in a recently released circularwill be of potential interest to thepostharvest community, in particularthe proposed colloquium on Foodsafety issues and concerns:transgenic foods, balancing microbialand pesticide risks, ensuring thesafety of fresh produce. For furtherinformation on this and other aspectsof the program visit the conferences

web site at . s


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As part of ACIAR Project PHT/1996/004, Monitoringmycotoxins and pesticides in grain

and food production systems forrisk management in Vietnam andAustralia, two project workshopswere held at the Post-HarvestTechnology Institute (PHTl) in HoChi Minh City in September 2000.

The workshops focused on develop-ing ELISA (enzyme-linkedimmunosorbent assay) technology forpreparing specific antibodies tomycotoxins and pesticides. It is in-tended that these antibodies will beused to provide simple, inexpensive

ELISA testing kits to be used fordetecting these contaminants in theagricultural produce of Vietnam. Apartfrom their important role in protectinghuman and animal health, these testswill be used to provide quality assur-ance for Vietnamese produce such asmaize meal, soybeans, groundnuts, riceand coffee destined for domesticconsumption and for export.

Both workshops were opened byDr Le Van To, Director of the PHTl,and leader of the Vietnamese team,who remarked that this was an

occasion to train the trainers. Thetechnology will be transferred later tousers in the field, once the ACIARproject has successfully developed

the test kits in formats more suitablefor use in widespread monitoring.

The first of the workshops was

held from 1214 September andprovided specialised training in thesynthesis of the chemicals (haptens)needed to raise specific antibodies tomycotoxins and pesticides. Workshopleaders were Dr Robin Allan, Dr AliceLee, and project leader Professor IvanKennedy, all from the University ofSydney. The PHTI has now set up alaboratory to carry out this synthesis.It is run by Mr Vo Thanh Hau whorecently returned from the Universityof Sydney where he received trainingin the operational techniques re-

quired. Access to a nuclear magneticresonance spectrometer (NMR) toprepare these chemicals and confirmtheir structure is also required andproject leaders are very pleased thataccess to NMR technology can bearranged in Ho Chi Minh City with thecooperation of Professor Cho PhamNgoc Son of the Centre for AnalyticalSystems and Experimentation(CASE). Professor Sons Centre iscurrently the only institution inVietnam with a suitable 200 MHzNMR instrument. Other participants in

the workshop, apart from PHTIpersonnel, were from the Universityof Ho ChiMinh City (HCMCU) andthe University of Agriculture andForestry, HCMC (UAF).

On the final day of the first work-shop, participants tested somechemical products prepared asanalogues of DDT insecticide. These

products can now be linked toproteins for injection into rabbits toproduce specific antibodies that willbe characterised and incorporatedinto test kits by Mr Bui Van Thin ofthe PHTI. Mr Thin will spend time atthe University of Sydney in early2001 to obtain further training inoptimising the ELISA assays.

The second workshop, which ran

from 1821 September, aimed toprovide training in the analysis by highperformance liquid chromatography(HPLC) of mycotoxins such asaflatoxins and ochratoxin. The work-shop was conducted by Ms KarenJackson of the Australian Wheat BoardLtd based in Werribee, Victoria withassistance from the University ofSydney team. With its new HPLC nowinstalled and running (purchased withfunding from ACIAR and supplied byShimadzu at a very favourable price)the PHTI will be able to validate the

results obtained with the ELISA kitsand those by other cooperating labora-tories or field workers who use the kitsas prototypes for commercial productsthat may be made in the future.

The ACIAR research project, justinto the second year of its three-yearterm, now moves into its next phaseof preparing prototype test kits forboth aflatoxins and organochlorinepesticides. It is expected that thesewill be launched at future workshopswhere PHTI staff will train the futureusers of the technology based at

various institutes and agencies inVietnam. Dr Tran Van An, a seniormember of the PHTI team, is hopefulthat this will be possible for anaflatoxin kit, one of the highestpriority toxins being studied in theproject, in the first half of 2001. s

PROJECT PHT/1996/004 NEWS

ELISA technology transferworkshops in Vietnam*

* This article by Greg Banova, ACIARCountry Manager in Vietnam, firstappeared in the ACIAR Vietnam Newslet-ter, JulySeptember 2000.

Copies of the proceedings of theconference, which contains all thepapers presented, are available freeof charge from The Crawford Fund,Hilda Stevenson House, 1 LeonardStreet, Parkville, Victoria 3052,Australia; fax: +61 3 9347 3224;email: .

So what messages emerged fromthis thought-provoking conference?The main one was certainly thatglobal security can never be fullyachieved while large numbers ofpeople around the world remaindesperately short of food and water,

and thousands die every day fromstarvation or from diseases linked toscarcity of clean water. Where thereis hunger, there will usually be anger;and where there is anger there can beno peace.

The problem remains soluble, butbecomes more difficult as timepasses. To solve it, developed anddeveloping country governmentsmust commit themselves to increasedsupport for agricultural research national and international toprovide the means for producing thefood that will be needed by a rapidlygrowing world population; and toredoubling their efforts to dismantle

the walls to free flow of food that are,along with poverty, the main causesof the distribution problem. Povertycan be overcome only through

economic growth, and here againagriculture and agricultural researchhave large roles to play, becauseagriculture is the engine that canpower economic growth in manydeveloping countries. s

Food and water: essential

for life...and peace...from

page 5


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An interesting, but worrying,spin-off of a recent AdelaideUniversity research project onchilli cultivation was the finding

that many imported chilli prepara-tions contained much higher thanacceptable concentrations ofaflatoxin, a cancer-causing agentproduced by fungi that invade a

range of susceptible foodstuffs.

The project, funded by the RuralIndustries Research and DevelopmentCorporation (RIRDC) and led byDr Andreas Klieber, who is also amember of the ACIAR projectPHT/1994/016 team (see report in thisissue), sought to determine the bestconditions for growing and harvestingchillies in South Australia, preparethem for spice manufacture, andprevent the resultant spice fromspoiling.

Virtually all the chilli spice currentlyused in Australia is imported. A surveyof 90 products made by the research-ers showed extensive contaminationwith aflatoxins (see accompanyingtable). Overall only 9% of samplescomplied with Australian standards,with another 12% marginal, Dr Klieberreported. This survey, he said,

shows that considerable improvementsneed to be made to produce a safefood for consumers. Importers need toinsist on better quality assurance andtesting by producers, but a significantopportunity exists for local producersto develop a safe product that willreplace imported products of unknownsafety.

When the findings of Dr Kliebersresearch on chillies were published inthe Adelaide University newspaper inearly August, the news about afla-toxin in chilli preparations generated,

not surprisingly, a great deal ofinterest and concern. Australia is acountry notable for its ethnic, andtherefore culinary, diversity and thelevel of consumption of spices such

as chillies is significant and growing.Given the incidence and levels ofcontamination, was it safe to continueconsuming imported products?

Dr Klieber put the following view: Iwould say that people should not stopeating chillies. The aim of our reportwas really to get the industry to startmonitoring for contamination and tocorrect problems, as they are legallybound to. This reduces the overall loadof aflatoxins that we may be exposedto, and that can only be healthy,especially since we as a nation areeating more chillies and other spices.

The Australia New Zealand FoodAuthority (ANZFA), which is respon-sible for food safety matters, an-nounced that it would conduct asurvey into the risks posed to thosewho eat imported chilli products.ANZFA calculated that the likelyexposure to aflatoxins in those peoplewho eat a lot of chillies is about 80%of that expected from people con-suming peanuts containing themaximum permissible level of 15micrograms per kilogram (g/kg)aflatoxin. They concluded that dietaryexposure to aflatoxins from chillies,while significant, is not as high asthat from peanuts.

Dr Klieber agreed, but noted that80% is pretty close to 100% and thattherefore as peanuts are beingmonitored so also should spices.

ANZFA subsequently released astatement clarifying the nature andsource of aflatoxin in food, and ex-plaining that the Food Standards Codelimits its level in nuts to 15 g/kg and

Aflatoxin in chilli productsa hot topic in Australia

Aflatoxin levels (g/kg) found in a survey of chilli products imported into Australia

Product type No. of samples Mean Standard Minimum Maximum Samples Samples

tested deviation passed a marginalb

(%) (%)

Chilli powder 26 25 16 7 71 0 8

Paprika powder 21 24 20 7 89 0 5

Chilli crushed 12 13 8 2 28 17 17

Chilli whole 11 13 13 0 49 18 9

Chilli minced 5 9 9 1 24 40 20

Chilli sauce 15 14 10 2 39 13 27

All 90 19 15 0 89 9 12

a 5 g/kg; b 5+ to 10 g/kg

Note: The highest level found was 89 g/kg.

in other foods to 5 g/kg. ANZFAconcluded that, on the basis of theknown toxicity of these substances andthe level of consumption of chillies inAustralia, the levels are not consideredto pose a significant health risk.

This concurs broadly withDr Kliebers original findings, whichstated that significant consumption ofchilli and paprika spice could be in

the order of 25 grams per day. Inthe worst measured case of contami-nated product in Dr Kliebers study,this would translate to 0.5 g ofaflatoxin consumed per day.

Nevertheless, all parties involvedin the issue have recognised the needfor vigilance. ANZFA has asked theAustralian Quarantine and InspectionService (AQIS) to increase themonitoring and testing of importedchilli-based foods, including otherspice products which may be suscep-tible to aflatoxin contamination. The

Authority has also briefed all Austral-ian State and Territory jurisdictionson the matter. s

CURRENT AWARENESS ... frompage 16

Romolo will be based at PHTI forsix months, to work on extending theresults of ACIAR project PHT/1997/131: Computer aided learning forgrain pest management. He will helpto set up a grain insect resistance

laboratory to test for resistance topesticides and phosphine in grainpests and instruct technicians in theproper use of phosphine for fumigat-ing ships and warehouses.

Romolo said, before departing forHo Chi Minh City, Im really lookingforward to training with the Vietnam-ese scientists and technicians. It willbe interesting with my understandingof the Vietnamese language but I willbe relying on an Australian developedCD-ROM that demonstrates correcttreatment of stored grains. s


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The north-west African nation ofMorocco, with coastlines onthe Mediterranean Sea and theAtlantic Ocean, has long enjoyed a

thriving export market for itshorticultural produce.The countrys diverse climates

allow for the production of a widerange of temperate, subtropical andtropical fruits and vegetables. Annu-ally, Morocco produces about 67million tonnes of fruits and vegeta-bles. Overall, more than 90% ofexported horticultural produce hasEuropean Union (EU) markets as itsfinal destination.

Citrus and tomato fruits

Two of Moroccos most importantexport fruit crops are citrus andtomato. A paper by A. Ait-Oubahouand M. El-Otmani in the recentlypublished ACIAR Proceedings 100(see item on page 16), upon whichthis article is based, reports that 1.5million tonnes of citrus fruits and450,000750,000 tonnes of toma-toes are produced annually, withaverage export quantities of about55,000600,000 tonnes for citrusand 230,000250,000 tonnes fortomatoes. The EU markets are thedominant recipients: 75% of ex-ported citrus fruit (30% to Franceand 15% to Germany), and 80% oftomatoes.

Citrus fruit is by far the mostimportant horticultural export crop,with the harvest season starting inlate September and finishing in June.The main exported varieties areClementine mandarins and Washing-ton navel and Valencia late or-anges. The tomato export industry isbased on winter production. Importa-

tion into Europe is allowed fromOctober to the end of April, withquotas for each month and an annualtotal of 150,000 tonnes.

Import barriers

Since the entry of Spain andPortugal as full members of theEuropean Economic Community in

1986, Europe has restricted Moroc-can imports to protect its members.Preferential access is granted forsome products that are not producedin Europe, while other crops aresubjected to different restrictions, e.g.Moroccan tomatoes are acceptedonly in the off-season, when theEuropean weather means that toma-toes cannot be grown and thereforethe imports represent no competitionto European producers. As well asthe annual and monthly quotas notedabove, prices are regulated. Other

restrictions include pesticide residuelevels in the products, sanitarycertification, declaration of importa-tion, banning of certain chemicals,and stipulations on packaging types.

Overcoming these barriers

Morocco is addressing this exportchallenge in three ways: attention toquality assurance; diversifying exportmarkets; and introducing new fruitvarieties.

Quality assurance

In order to maintain its Europeanmarkets, Morocco has been obligedto address the strict EU requirements.This has necessitated a cooperativeapproach between growers, exporters,and specialists from private andgovernment organisations.

Quality control and standardisationare under the responsibility of apublic sector enterprise known asEtablissement Autonome du Contrleet de la Coordination desExportations (EACCE). Other activi-

ties of EACCE include quality inspec-tion, certification for export products,and coordination of exported quanti-ties through consultation with export-ing groups and associations. EACCEhas two laboratories, in Casablancaand Agadir, for quality analysis ofdifferent crops, and offices in severalEuropean countries to follow thequality, quantities and prices of theproducts. An advisory institutionfinanced by associations of growersof citrus and vegetables SocitAgricole des Services au Maroc(SASMA) is also participatingthrough technical support and tech-nology transfer. SASMA has laborato-ries for quality and pesticide residue

analysis, and growers can seekinformation and support free ofcharge. Both EACCE and SASMA,together with a variety of otherinstitutions, are heavily involved withgrowers and exporters in order toproduce and ensure good qualityproduce for export.

The collaborative approach has ledto implementation of improved

irrigation and fertilisation technology,a field sanit

work to extend the shelf life of leafy vegetable progresses

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