towards more natural emulsifiers

Towards more natural

emulsifiers

Eric Dickinson

Processed foodstuffs typically exist in the form of complex, multiphase, multicomponent colloidal systems. The key mol. ecules that facilitate the formation and stabilization of these structures during processing are called 'emulsifiers'. The role of emulsifiers is essential for the successful formulation of many food emulsion products such as ice cream, mayon- naise, margarine and lowfat spreads. This article reviews the various chemical types of emulsifiers and considers the balance between 'natural' and 'synthetic' emulsifiers available to the food technologist today. The difficulties of moving towards a greater use of natural emulsifiers in food or non- food emulsion formulations are briefly indicated.

An emulsifier (see Glossary) is a surface-active substance. It has a strong tendency to adsorb at oil-water interfaces, thereby promoting the tbrmation and rapid stabilization of emulsion droplets by interfacial action. In molecular terms it is an amphiphilic compound containing a hydrophilic (water-loving) part and a lipophilic fiat-loving) part. A small-molecule emulsifier, or surfactant, typically contains a polar or charged head group that is linked to one or more fatty acid chains. Food proteins and some food polysaccharides can act as polymeric emulsifying agents. Such macromolecules can also act as stabilizers by conferring long-term stability on an emulsion.

As used in the lbod industry, the term 'emulsifier' traditionally refers to small-molecule surfactants. An emulsifier does not necessarily confer long-term stability - it simply has the capacity to adsorb rapidly at the fresh interface created during emulsification, thereby protecting newly tbrmed oil or water droplets against immediate recoalescence ~,-~. Long-term stability is usually provided by proteins or polysaccharides. The role of a good emulsion stabilizer is to keep the droplets apart once they have been formed. This protects the emulsion against processes such as creaming, flocculation and coalescence during long-term storage ~,-'.

Natural emulsifying ingredients in milk or eggs are used to make emulsion-based foods in the kitchen ~. Many food emulsions produced on an industrial scale

Eric Dickinson is at the Procter Department of Food Science, Universily of Leeds, Leeds, UK LS2 tilT.

Review , j i I1'11]11 '1 I ¸ I ' 1 ' l i t I]rl ]1

arc also stabilizcd by thcsc same natural proteinaceous emulsifiers. In addition, a wide range of synthetic emulsifiers is also used in commercial formulations, sometimes to improve emulsification, although more fre- quently to impart other desirable qualities to the product during processing, distribution and storage. In fact, many so-called food emulsifiers (Box 1) are added to products to perform functions not directly related to emulsification, for example to control fat polymorphism, to inhibit staling, or to promote fat globule clumping during whipping or freezing. However, despite the technological importance of emulsifiers, there is now growing consumer pressure to cut their use in foods. The challenge to replace these additives by effective natural alternatives is quite a formidable one.

Hydrophile-lipophile balance Oil-in-water emulsions are stabilized by water-soluble

(predominantly hydrophilic) emulsifiers, whereas water- in-oil emulsions are stabilized by oil-soluble (predominantly lipophilic) emulsifiers. Because they are predominantly hydrophilic, biopolymers are useful only for stabilizing oil-in-water systems; the opposite is the case for most naturally occurring surface-active lipids.

The most widely quoted system for classifying (small-molecule) emulsifiers is the hydrophile.-lipophile balance (HLB) concept of Griffin 4. A low HLB number means that the emulsifier is lipophilic, and a high value

Glossary

Emulsifier: Single chemical substance, or mixture of substances, that lowers the tension at the oil-water interface, and has the capacity for promoting emulsion formation and short-term stabilization.

Stabilizer: Chemical compound (usually polymeric) conferring long-term emulsion stability by forming a protective barrier around the surface of droplets or in the liquid between the droplets.

Stable emulsion: Emulsion that shows no detectable change in droplet size distribution or self-association of droplets over a certain period of time.

Creaming: Gravity separation of oil droplets into a concentrated and often distinct layer at the top of an oil-in-water emulsion.

Flocculation: Association of discrete emulsion droplets under the influence of attractive interparticle forces.

Coalescence: Joining together of two or more creamed or flocculated droplets to form a larger spherical droplet.

Thermodynamic incompatibility: Tendency of a mixed solution of protein and polysaccharide to separate into distinct protein-rich and polysaccharide-rich phases under the influence of net repulsive protein-polysaccharide interactions.

Surface potential: Electrical potential at the surface of a charged droplet or particle in an electrostatically stabilized emulsion or colloidal dispersion [a value of absolute magnitude below -20 mV is usually too small by itself to confer stability with respect to flocculation or coalesccncel.

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means that it is hydrophilic. Formulae are available for calculating HLB numbers by adding together the weighted contributions of hydrophilicity and lipophil- icity from all the different types of chemical groups in emulsifier molecules, and tabulations of HLB numbers are available in the literature "~. This group summation method may also be applied to mixtures of emulsifiers. Such a procedure is useful to the emulsion technologist since it has long been recognized that an appropriate blend of emulsifiers usually produces a more stable emulsion than one prepared with a single emulsifier of the same HLB number.

Though it is useful for classifying emulsifiers, the HLB concept is of little value in the formulation of food products 6. This is because most food emulsions are stabilized by proteins for which the simple HLB concept is quite inapplicable. Another defect of the HLB approach is that it takes no account of interactions of emulsifiers with other food ingredients (see Box 2).

Small-molecule emulsifiers Lecithin is the only really natural small-molecule

emulsifier available for normal use. It consists of a mixture of various phospholipids, and is a natural constituent of both animal and vegetable products. Purified egg lecithin is used as the sole emulsion stabilizer of parenteral emulsions made hy the pharmaceutical industry for drug delivery and intravenous nutrition 7-9. These parenteral oil-in-water emulsions are usually based on vegetable oils (e.g. 10-20%, v/v, soybean oil emulsified with 1-2%, w/w, lecithin). Average droplet sizes are typically well below I I am and the long-term stability is generally very good (e.g. >2 years at 4°C). It is reported ~" that oil droplets emulsified with lecithin have a surface potential in the range - 4 0 mV to -50 mV when freshly prepared. This value varies with the composition of the lecithin, and can increase on storage due to the oxidation of fat to form free fatty acids~L Since parenteral emulsions are predominantly stabilized by an electrostatic mechanism in accordance with classical colloid stability theory ~, any variation in droplet surface charge due to the source of the lecithin or the break- down of lipids during storage is of considerable practical importance.

The main commercial source of lecithin is plant seed, especially soybean. The major constituents of egg and soybean lecithins are phosphatidylcholine, phosphatidyl- ethanolamine and lysophosphatidylcholine. Phosphatidyl- choline is the main constituent of both egg and soybean lecithins; soybean lecithin is also rich in phosphatidyl- ethanolamine. Both of these phospholipids are zwitter- ionic and do not contribute significantly to the net charge on the emulsion droplets at physiological pH. It seems, therefore, that it is the minor anionic components of the lecithins (phosphatidylserine, phosphatidic acid, etc.) that provide the negative charge at the oil-water interlace, and hence are predominantly responsible for the electrostatic stabilization of parenteral emulsions.

Lecithin is universally accepted for medicinal and food use because its constituent phospholipids can be

Box 1. Some common food emulsifiers and their official identification numbers (E numbers) within the European Community

E322 Lecithin E410 Locust bean gum E412 Guar gum E413 Gum tragacanth E414 Gum arabic E461 Methylcellulose E471 Glycerol monostearate E472 Esters of monoglycerides E473 Sucrose esters of fatty acids E475 Polyglyceml esters of fatty acids E477 Propylene glycol esters of fatty acids E481 Sodium steamyl-2-1actylate E482 Calcium stearoyl-2-1a~.tylate

metabolized in vivo. it is one of a very small group of emulsifiers that is 'generally recognized as safe' (GRAS) by the US Food and Drug Administration. Other food emulsifiers coming under this category are monoglycerides, phospfiorylated monoglycerides, and diacetyl-tartaric acid esters of monoglycerides (DATEM) ~2. Monoglycerides certainly occur naturally - they are present as impurities in all food-grade tri- glycetide oils - but the ones used as food emulsifiers are produced artificially. The same is true for DATEM, which are used as dough strengtheners in baked goods.

All other commonly used food emulsifiers ~3 can be regarded as synthetic. Their incorporation into foods is restricted to specific applications and levels of usage, and legislation restricting their exploitation differs from country to country. For instance, high-HLB poly- oxyethylene sorbitan esters (also called 'polysorbates' or 'Tweens') are permitted in the USA but not in Japan, whereas sucrose esters have been restricted in the USA but are widely acceptable in Japan ~. Like most food emulsifiers, polysorbates and sucrose esters are non- ionic surfactants. Amongst the few synthetic anionic surfactants used in lbods are the stearoyl lactylates, the succinylated monoglyceddes, and DATEM. Cationic surfactants are toxic and are therefore not allowed for food use.

Proteins as emulsifiers Proteins are natural polymeric emulsifiers. The ther-

modynamic driving force for protein adsorption is removal of nonpolar amino acid residues from the hydrogen-bonding environment of the bulk aqueous solution and the simultaneous displacement of vicinal water molecules from the hydrophobic environment of the oil-water interface ~4. Following adsorption during emulsification, the protein forms a macromolecular bar- tier, which protects the droplets against flocculation and coalescence. All soluble proteins can bc used as emulsifiers, though some are clearly more effective than others. A favourable feature of a good proteinaceous emulsifier is ease of unfolding at the interface u. Adsorbed proteins may take up a wide range of macromolecular configurations, ranging from the fully ex- tended disordered protein (e.g. [I-casein), which may lie fiat at the interface, to the compact globular protein (e.g.

Trends in Food Science & Technology October 1993 IVol. 41 331

The emulsifying behaviour of proteins and the stabilizing properties of adsorbed protein layers in food emulsions are affected by interactions of proteins with other food components.

I~mteln-surfadant interactions may lead to43'44:

• reduction in surface activity due to specific binding of lipophilic tail to hydrophobic ~ite on protei n ;

structure of protein, thereby enhancing molecular flexih l i~ and hence the rate of rearrangement at the interface;

. change in net charge on stabilizing macromolecular layer following binding of ionic surfactants;

• change in viscoelasticity of adsorbed layer due to interfacial protein- surfaclant complexation or protein-surfactant competitive adsorption;

• incorporation of proteins into surfactant micelles, vesicles and bilayers,

Pmtein.-Imlysaccharide interactions may lead t045,46:

• reduction in surface activity due to electrostatic complexation;

• enhancement in overall stabilizing layer thickness and efficiency due to electrostatic complexation;

• increased flocculation due to protein-polysaccharide thermodynamic incompatibility;

• increased stabilily with respect to coalescence due to covalent complex formation.

These interactions may be used to enhance the emulsifying properties of existing protein emulsifiers by complexing them with lipids or polysaccharides during physical processing operations (heating, drying, extrusion, i high pressure), Examples of such natural composite emulsifying agents are protein-lecithin complexes produced by sonication 47 and protein- ~olysaccharide covalent complexes produced by slow dry-heating 45,46,48.

[~-Iactoglobulin), which may remain in the native folded state. The extent of unfolding depends on the available surface area, the amount of time spent in contact with the interface, and the macromolecular structure prior to adsorption ",~t~.

The milk protein casein is the most widely used proteinaceous emulsifier. The main source of this protein is in nonfat milk powders or soluble caseinates (sodium or potassium salts) ~. As used in many food formulations, casein is a heterogeneous aggregated protein; one of the most important monomeric casein components involved in emulsification is 13-casein. Having many proline residues and no cysteines, [3-casein is a flexible protein with little ordered secondary structure and no intramolecular crosslinks -'~. To a first approximation the molecular structure of [3-casein can be likened to a mod- erately non-random linear copolymer :~ composed of a mixture of hydrophilic and hydrophobic monomers dis- tributed along the polypeptide chain. A more careful analysis of the primary structure indicates 2-' the presence of 40-50 residues at the N-terminus that are predominantly hydrophilic and mainly negatively charged at pH 7. The combined experimental evidence -'3 is consis- tent with the view that much of the adsorbed 13-casein is directly associated with the surface, with the hydrophilic tail at the N-terminus extending significantly into the aqueous medium. The relatively large overall layer

thickness for adsorbed ~-casein contrasts with the dense thin monolayer formed by globular proteins adsorbed at the oil-water interface (e.g. 13-1actoglobulin). Such a monoh,yer may he regarded as a close-packed film of interacting deformable particles 24.

Limited enzymic hydrolysis of food proteins generally improves their solubility and emulsifying capacity, but long-term emulsion stability may be impaired 25--'s. Though the literature on the subject is diverse and sometimes apparently contradictory, it does seem that for any particular protease and food protein there is an optimum degree of hydrolysis beyond which any improved functionality is lost. For instance, the emulsifying properties of the soy protein glycinin (1 1S globu- lin) are improved by tryptic hydrolysis, but the lowest molecular weight fragments exhibit the poorest emulsifying properties -'~. High molecular weight hydrophilic gelatin, which is a relatively poor protein emulsifier, can be transformed into low molecular weight biosurfactants by the cnzyme-catalysed attachment of hydrophobic side chains 3~''~1.

Hydrocolloids as emulsifiers High molecular weight water-soluble biopolymers -

so-called hydrocolloids - make an important contri- bution to the control of stability and texture in many food products ~-'. Most hydrocolloids are polysaccharides with relatively low surface activity at oil-water interfaces. This means that they are not expected to form primary adsorbed layers in systems also containing small- molecule surfactants or proteins. The conventionally perceived role of hydrocolloids is that they stabilize emulsions by modification of the theological properties of the aqueous continuous phase ~-', though low con- centrations of hydroeolloids may lead to greater in- stability by inducing depletion flocculation ~3-~.

Despite the above, it is clear that several natural hydrocolloids can be used successfully as emulsifiers. The most notable of these is gum arabic, the natural exudate from Acacia senegal, which is widely used for emulsifying ltavour oils to make cloudy beverage emulsions. Physicochemical studies of gum arabic suggesr ~* that it consists of a mixture of high molecular weight branched ionic polysaccharides in combination with a small amount of protein (-2%, w/w). Its special film- forming and emulsifying properties may arise from the presence of this small protein fraction "-3'~. Serine and hydroxyproline residues are believed to be involved in covalently linking the carbohydrate to the protein to form an arabinogalactan-protein complex.

Gum arabic is a genuine emulsifier in its own right, although its surface activity is low compared with most food proteins. To compensate for this, a high concen- tration of the emulsifier must be used in practice: a gum:oil weight ratio of roughly 1:1, as compared with a protein:oil ratio of about 1:10 for the equivalent milk-protein-stabilized emulsion. It has been demon- strated ~° that the surface shear viscosity of a gum arabic film adsorbed at the oil-water interface is little affected by subsequent dilution of the aqueous sub-phase. This

332 Trends in Food Science & Technology October 1993 IVol. 41

means that, once a stabilizing layer has lormcd at thc oil-water interface by adsorption from a gum arabic solution, its viscoelastic properties are maintained even when the major part of the hydrocolloid sample is removed from the aqueous phase in contact with the adsorbed layer.

Hydrocolloids that are completely free from contaminating protein may also have emulsifying properties if the polysaccharide contains sufficient hydrophobic groups (methyl, acetyl, etc.). Chemically modified derivatives such as highly substituted methyl cellulose give surface activities similar to those of the best food emulsifiers 6. Natural protein-free polysaccharides that have some ability to form coarse emulsions are the galactomannans: guar gum and locust bean gum 4L4-'. Under certain conditions these gums adsorb to form ordered and oriented thick films with strong birefrin- gency, but unlike gum arabic films the galactomannan films are not stable to dilution 42.

Future outlook The most important natural emulsifiers currently in

use are food proteins, and there seems no reason to believe that this situation will change in the foreseeable future. There is scope for improving the emulsifying properties of proteins by physical treatment (milling, ultrahigh pressure, heating, etc.) or by enzyme treatment. In contrast, chemical treatment renders the deriva- tive 'synthetic' and its use is therefore counterproduc- tive. Perhaps the best short-term prospect for improving protein emulsifier pertbrmance lies in exploitation of Lhe functionality of protein complexes with phospholipids or polysaccharides (see Box 2), where the two components are brought together by physical or enzymic treatment. In the long term, it should be possible to produce proteins with enhanced emulsification and stabilizing properties using genetic engineering techniques.

The only natural small-molecule emulsifier readily available is lecithin, but this has its own special charac- teristics, and it certainly cannot be used to replace all the other synthetic emulsifiers of low and high HLB number currently added to food product formulations. One way forward is to synthesize small-molecule surfactants using enzymes, for example glucoside esters formed in the presence of iipase4'L Another promising class of 'green' surfactants are linear peptides made from, say, 10-30 amino acid residues. In principle, these could be produced with a specific optimum sequence of hydrophilic and nonpolar groups, thereby combining the favourable features of proteins with those of the most effective small-molecule surfactants. Further research in this area would certainly seem to offer exciting prospects for increasing the range of available emulsifiers.

References 1 Dickinson, E. and Stainsby, G. (1982) Colloids in Food, Elsevier 2 Dickinson, F. fl992) An Introduction to Food Colloids, Oxford

University Press

3 McGee, tl. (I 9°4) On Food and Cooking: The Science and Lore of the Kitchen, Unwin Hyman

4 Griffin, W.C. 11949) I. 5oc. Cosmel. Chem. 1, 311-326 5 Becher, P. (1985) in Encyclopedia of Emulsion Technology

(Vol. 2)(Becher, P.. ed.I, pp. 425-512, Marcel Dekker 6 Darling, D.F. and Birkelt, R.J. I1987) in Food Emulsions and Foams

(Dickinson, E., ed.), pp. 1-29, Royal Society of Chemistry 7 Davis, S.S., Washington, C., West, P., Ilium, L., Liversidge, G.,

Sternson, L. and Kirsh, R. (19871 Ann. NYAcad. 5ci. 507, 75-88 8 Collins-Gold, L.C., Lyons, R.T. and Barlholow, L.C. (1990) Adv. Drug

Defivery Rev. 5, 189-208 9 Prankerd, RJ. and Slella, V.J. 11990) ]. Parent. Sci. Technol. 44,

139-149 10 Washington, C., Chawla, A., Christy, N. and Davis, S.S. (1989) Int. 1.

Pharm. 54, 191-197 t l Washington, C. and Davis, S.S. 11987) Int. I. Pharm. 39, 33-37 12 Hasenhuetll, G.L {1990) A. L Chem. L Syrup. Set. 86, 35-43 13 Dziezak, I.D. (1988) Food TechnoL 42(10), 172-186 14 Dickinson, E. (1992) in Emulsions -A Fundamentaland Practical

Approach (Sj6blom, J., edJ, pp. 25-40, Kluwer 15 Dickinson, E. (1986) Food Hydrocolleids 1, 3-23 16 Mitchell, J.R. I1986) in Developments in Food Proteins - 4

(Hudson, B.J.F., ed.), pp. 291-338, Elsevier 17 Dickinson, E., Murray, B.S. and Stainsby, G. 119881 in Advances in

Food Emulsions and Foams (Dickinson, E. and Stainsby, G., eds), pp. 123-162, Elsevier

18 Tornberg, E., Olsson, A. a~',d Persson, K. (1990) in Food Emulsions 12nd edn) (Larsson, K. and Friberg, S.E., eds), pp. 247-326, Marcel Dekker

19 lost, R., Dannenberg, E. and Gumy, D. (1990) in Proceedings of the XlII International Dairy Congress, Montreal (Vol. 2) (Canadian Committee, eds), pp. 1481-1491, Mutual Press, Oltawa, Canada

20 Swaisgood, H.E. (1982) in Developments in Dairy Chemistry IVol. 1 ) (Fox, P.F., ed.), pp. 1-59, Elsevier

21 Balazs, A.C. {19931Acc. Chem. Res. 26, 63-68 22 Dalgleish, D.G. and Louver, I. (1991) in Food Polymers, Gels and

Colloids IDickinson, E., ed.), pp. 113-122, Royal Society of Chemislry 23 Dickinson, E. (1992) J. Chem. 5oc. Faraday Trans. 88, 2973-2983 24 de Feijler, J.A. and Beniamins, J. 11982) J. Colloid Interl;ice Sci. 90, 289-292 25 Zakaria, E. and McFeeters, R, (1978) Lebensm. Wissen. Technol. 11,42-44 26 Adler-Nissen, I. (1986) Enzymic Hydrol},sis of Food Proteins, Elsevier 27 Arai, S. and Watanahe, M. (1988) in Advances in Food Emulsioos and

Foams (Dickinson, E. and Stainsby, G., eds), pp. 189-220, Elsevier 28 Lakkis, I. and Villola, R. I1990) A. L Chem. E. Syrup. Set. 86, 87-101 29 Kamala, Y,, Ochiai, K. and Yamauchi, E. ll 984) Agrk'. Biol. Chem. 48,

1147-1152 30 Shimada, A., Yazawa, E. and Arai, S. (1982) ~,ric. Biol. Chem. 46,173-182 31 Arai, S., Watanabe, M. and Fujii, N. (1984) Agric. Biol. Chem. 48,

1861-1866 32 Dickinson, E. {1988} in Gums and 5tabilisers for the Food Industry

IVol. 41 (Phillips, G.O., Wedlock, D.J. and Williams, P.A., eds), pp. 249-263, IRL Press

33 Gunning, P.A., Hibberd, D.J., Howe, A.M. and Robins, M.M. 11988) Food HydrocoUoids 2, 119-129

34 Cao, Y., Dickinson, E. and Wedlock, D.J. (I 9901 Food Hydrocolloids 4, 185-195

35 Dickinson, E. and Semenova, M.G. (1992) I. Chem. 5oc. Faraday Trans. 88, 849-854

36 Williams, P.A., Phillips, G.O. and Randall, R.C. (1990) in Gums and 5tabilisers tot the Food Industry (Vol. 5) (Phillips, G.O., Wedlock, D.J. and Williams, P.A., edsl, pp. 25-36, IRI_ Press

37 Randall, R.C., Phillips, G.O. and Williams, P.A. 11988l Food Hydrocolloids 2, 131 - 140

38 Dickinson, E., Murray, B.S., Slainsby, G. and Anderson, D.M.W. 11988) Food Hydrocolloids 2, 477-490

39 Dickinson, E., Galazka, V.B. and Anderson, D.M.W. (1991) Carbohydr. Polym. 14, 373-392

Trends in Food Science & Technology October 1993 [Vol. 4J 333

40 Dickinson, E., Elverson, D.I. and Murray, B.S, (1989) Food Hydrocolloids 3, 101-114

41 Reichman, D, and Garti, N. (1991) in Food Polymers, Gels and Colloids (Dickinson. E., ed.), pp. 549-556, Royal Society of Chemistry

42 Garti, N. and Reichman, D. Food Structure (in press) 43 Dickinson, E. and Woskelt, C.M. (1989) in Food Colloids (Bee, R.D,

Richmond, P. and Mingins, I., eds), pp. 74-96, Royal Society of Chemistry 44 Dickinson, E. (1993) in Interactions of Surfactants with Polymers and

Proteins (Goddard, E.D. and Ananthapadmanabhan, K.P., eds), pp. 295-317, CRC Press

45 Dickimon, F. and Galazka, V.B. (1991) Food Hydrocolloids 5. 281-296 46 Dickinson, E. (1993)in Food Colloids andPolymers:Stabifityaod

Mechanical Properties (Dickinson, E. and Walslra, P., eds), pp. 77-93, Royal Society of Chemistry

47 Nakamura, R., Mizutani, R., Yano, M. and Hayakawa, S. 119881 I. Agric. Food Chem. 36, 729-732

48 Kalo, A., Mifuru, R., Matsudomi, N. and Kobayashi, K. (1992) Biosci. Biotech. Biochem. 56, 567-571

49 Bj6rkling, F., Godlfredsen, S.E. and Kirk, O. (1991) Trends Biotechnol. 9, 360-363

Perspectives on aflatoxin

control for human food

and animal feed

Douglas L. Park and Bailin Liang

Aflatoxins are potent carcinogenic, mutagenic and terato-

genic metabolites produced by molds that grow on food and

feed. Their toxicity has caused severe health and economic problems worldwide. Human exposure to aflatoxins can arise from the direct consumption of contaminated commodities such as corn (maize), peanuts or figs, or from the consumption of foods from animals previously exposed to aflatoxin in feeds (milk and egg products). Food safety monitoring programs for aflatoxins have been established for raw and fin- ished products; these include establishment of regulatory limits or guidelines, monitoring programs for aflatoxin levels

in susceptible products, and decontamination procedures and/or the diversion of contaminated producls to lower-risk uses.

Aflatoxins, potent carcinogenic, mutagenic and terato- genie metabolites produced by the fungal species AspergiUus flavus and AspergiUus parasiticus, can con- taminate human foods and animal feeds. Such contamination is the result of (currently unavoidable) invasion by the molds betbre and during harvest, or because of

Douglas t. Park and Bailin tiang are at the Department ot Nutritional Sciences, Universily of Arizona, Tucson, AZ 85721, USA.

Review i 1, i i LL i~

improper storage of agricultural commodities t. The major agricultural commodities affected with aflatoxins are corn (maize), peanuts, figs, tree nuts, rice, dried fruit, pumpkin seeds and cottonseeds. Aflatoxin residues can also occur in the milk of lactating dairy animals following the ingestion of aflatoxin-contaminated feed 2. Human exposure to aflatoxins can result from the direct consumption of contaminated commodities, or from the consumption of foods from animals previously exposed to aflatoxin in feeds (milk and egg products). The sig- nificance of the risk due to aflatoxin contamination is dependent on the toxicological properties of the particular compound (acute, subacute, reproductive or long- term toxicity; mutagenicity; teratogenicity) as well as on the extent of the exposure (occurrence, incidence, level of contamination).

Unquestionably, prevention is the best method for controlling mycotoxin contamination. However, pre- harvest invasion of the mold and its subsequent pro- duction of aflatoxin are currently unavoidable.

Hazards associated with the toxins must be removed if the products are to be used for food or feed purposes. Mycotoxin control programs include the establishment of regulatory limits or guidelines, monitoring programs for mycotoxin levels in susceptible products, and decontamination procedures and/or strategies for the diversion of contaminated products to lower-risk uses. Research into the development of decontamination procedures has been underway for over 20 yea~. The decontamination procedures currently used are based on physical, chemical or biological removal, or on physical or chemical inactivation. The ammoniation of corn, peanuts, cotton- seed and meals to alter the toxic and carcinogenic effects of contaminating aflatoxins appears to have practical applications and has been the subject of intense research efforts by scientists in various government agencies and universities worldwide.

This review describes the acute and chronic toxicity/carcinogenic potential of aflatoxins, the ration- ale for the control of human exposure, and monitoring and decontamination programs that have been put into u s e .

334 ~'~ ~. El,~,,,,.r st,,.,,~, P~hl,,h~,r~ U,i. ~Ut<t .~.'4 -.~.'44/'~ VS~,~,... Trends in Food Science & Technology October 1993 IVol. 41

towards more natural emulsifiers

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