dehydration of mediterranean fruit and vegetables: scientific and technical aspect of emerging...

Dehydration of mediterranean fruit and vegetables: scientific and technical aspect of emerging technologies

with particular reference on semi-moist products

Marco Dalla RosaFull Professor

Food Technology

University of Bologna (Italy)

Presentation content

1. Typology of fruit mostly addressed to drying in the mediterranean area

2. Possible use of drying fruit and vegetables in food industry and

consumption by consumers.

3. Conventional and non conventional drying technologies. Overview on

Principles / applications / problems

4. Tentative data on production / import /export of dried fruit and vegetables

5. Quality changes during drying

6. Use of drying technique to obtain moist and semi-moist products for

direct consumption and industrial utilisation

7. Combination of drying / stabilisation processing technologies

8. Direct formulation / osmotic dehydration and problems related to

industrial application

9. Concluding remarks and future trends

Product typology

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DRIED /DEHYDRATED FRUIT & VEGETABLES for Direct Consumption

Food for:just preservation /reserve food to overcome

seasons •-->in the past

• for emergencies •-->in particular situations and extreme

sports

• functional and easy / ready to eat healthy food

• --->nowadays

Product typology (2)


DRIED /DEHYDRATED FRUIT & VEGETABLES for Industrial Use

Food for:Candying (fruit), dried spices, gastronomic

use, colourants, •-->in the past and after Food technological

revolution (from 50’s)

• to replace fresh ingredients •-->for new products

• functional and easy / ready to eat healthy complex food with fruit & vegetables benefit attraction (semi-moist, moist & frozen foods)

• --->nowadays

Raw material typologyFRUITS•Apples (Malus sylvestris Mill.) are peeled, cored, sliced, and dried artificially, and frequently treated with sulfur dioxide.

* Apricots (Prunus armeniaca L.) are picked when ripe and either sun-dried or artificially dried. They may be blanched with burning sulfur or a bisulfite solution.

* Dates (Phoenix dactylifera L.) are grown in hot, dry regions and usually do not require artificial drying.

* Figs (Ficus carica L.) can be allowed to ripen and partly dry on the trees. Processing may include fumigation, washing, and bleaching with sulfur dioxide, followed by additional drying. Smyrna-type figs require pollination by the fig wasp [Blastophaga psenes (L.)]. Other kinds will ripen without pollination.

* Peaches and nectarines [Prunus persica (L.) Batsch] are halved, pitted, usually exposed to sulfur fumes, and then either sun-dried or artificially dried. Nectarines are merely smooth-skinned varieties of peaches.

* Pears (Pyrus communis L.) may be halved, peeled, and sliced, or peeled, halved, and cored before sulfuring and dehydration either by the sun or by artificial means.

•Prunes are the dried fruit of certain varieties of the European plum (Prunus domestica L.). Current industry practice involves heat-drying the prunes in dehydrators.

• Strawberry (Fragaria ananassa) cutted in half, sun dried or freeze-dried

• Grapes, (raisins / sultanas) different varieties of seedless grapes are suitable for drying, both sun drying and air-drying. Dipping in oil or lipid emulsion is used to aggregate pruin and improve drying kinetic

• Orange peels, traditional food from drying/candying; organic growth is preferred to avoid chemical residue

• Chestnut, both whole chestnuts and flour are obtained from traditional drying in hot airQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Vegetables• Tomato (Lycopersicon esculentum Mill)

• Spinach

• Asparagus

• Mushroom & truffles

• Potato i.e. flakes.

• Leaf vegetables

• Formulated (designed dry food) --- ready meal (vegetables as ingredients)

• Spices (including onions and garlic)

• others (plant extracts)

Requirements for drying suitability

• dry weight (soluble + unsoluble solid

content),

• acceptable ripening level (flavour, taste,

colour) and sufficient mechanical resistance

when processed

• Sugar / acids ratio

• volume, uniform shape,

• uniform and resistant colour (pigmentation)

• low tendency to EB/NEB browning

• stone weight,

• flesh/stone ratio,

• water activity lowering kinetic

• hours required for drying

Statistical data

Seedless grapes (sultanas)importSeedless grapes export



Dried fruit

Dried vegetables exportDried vegetables import

Dried apple&pears export

Dried apple&pears import

Dried prunes export

Dried prunes import

Dried apricot export

Dried apricot import

Dried mushrooms export World

Mushroom & truffles UE

Dried figs export

Dried fruits and vegetables

• Dry / extra dry (whole,pieces, flakes, powders)

• Moist / semi-moist (I.M.F.)

• Candied / semi-candied

Direct consumption

Industrial use in complex foods

Classification vs.-physical state

Classification vs. Final users: ready to eat, inclusions in moist complex food, ingredients in dry foods

Quality properties of dried foodsChemical and physical stability at ambient temperature

mixin ability with other dry ingredients

modulation of final moisture during rehydration

control ability of final texture

Weight and volume reduction

low costs of packaging and transportation

PROBLEMS

Thermal damagesEB / NEB

Use of additives (common)

Long process time

Incomplete reconstitution

Permitted additives

Stability: thermodynamic approach


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In a complex food where the dehydrated ingredient is included

i.e.:Ice creamCakesDairy foodsYoghurt………



In such a systemPartially dehydratedFruit or vegetablesCan be usefulTo reduce the Moisture transfer

Stability: kinetic approach

Physical stabilityof dried /extra driedProducts is relatedto Tg NOT to water activity

Above Tg:CakingLoss of free flowingStickiness

Drying Technologies

• Sun / solar drying (slow drying)

• Air (convective) drying

• Drum (contact) drying

• Spray drying (fluid extracts / beverages)

• Microwaves (volumic heating)

• Direct Osmosis (dewatering impregnation)

Sun / solar drying

Sun / solar drying

Slow drying

Low control of processing conditions

Microbial risks (mycotoxins)

High level of enzymic browning

NEB during storage

Air drying

TraditionalConvective static(discontinuous) dryingOn trays

Prunes,Sultanas,Apricots……

Slow drying kineticHigh browning levelHigh shrinkage

Air drying: technological evolution

Convective belt drying

Continuos sulphiting tank

Leaf vegetables drying

Faster drying kineticLess browning (exp.NEB)Higher retention of

thermolabile nutrients

To prevent Enzymic browning

Air drying: technological evolution

Continuos net drier

Fluidised-bed drier

Drum drying

operation

sizing

flaking

Turbo - drying

Turbo technology

Turbo-drier capacity

Spray drying

ICF Cibec Industry

Spray driers

Granulator

Instatizer

Niro pilot plant

Freeze - drying

Freeze - drying: high quality?

Air drying

Feeze drying

Flavourand textureAre maintaining ifthe process iscarried outBelow Tg

Then best retention of flavour (i.e.:truffles) and tissue structure

RF / Microwave drying

Mw drying

Njihus et al., 1998

Combination of technologies Air drying - Freeze drying

Air/Osmodrying - freezing

Air/spray/drum drying - reconstitution

Direct osmosis - air drying

High temperature osmosis (osmoblanching) - air drying

Osmosis - Blanching - Air drying

Sulphitation - Blanching - Air drying

OBJECTIVES Control of degradative phenomena

Reduction of process time

Increasing productivity and plant flexibility

Different and controlled (modulated) texture moldifications

Increase of storability (shelf-life prolongation; reduction toxins, biological hazards)

Overview on Osmotic treatments and

derivatives

Marco Dalla Rosa

Full professor of Food Technology

University of Bologna – site of Cesena

ITALY

(Concerted ActionFAIR CT 96/1118)

Chairperson 3rd SubGroup

BASICS OF OSMOTIC TREATMENTS

Contact between food and a hypertonic solution (high sugar / salt concentration)

The difference of osmotic pression or chemical potential origins a driving force that leads to a water molecules migration

Cell membrane can be considered “pseudo-semi permeablewalls”

A selective diffusion of solutes occurs from cell to solution and viceversa

Osmotic soluteWater &soluble solids

cell wall

cell membrane

intercellularspace

OSMOTIC SOLUTION

•partial dehydration at ambient temperature

•Water removal without phase or state transition

•possible modification of food composition and

food functional properties

• improvement of some food characteristics like

texture and colour

•limited tissue damage

•Potential energy saving process in respect to

evaporative dehydration

MAIN OBJECTIVE

TECHNOLOGICAL ASPECTS

Unit operation: stand alone or combined with other process of food stabilization as a functionof the final product:

– only partial dehydration–Impregnation / direct formulation– controlled reconstitution of dried product

APPLICATION FIELDS

•Vegetal origin products (fruit, vegetables)•Animal origin products (meat and fish derivatives)

Process parameters

•Temperature•Time of treatment•Concentration of the solution•Type of solute/s used (salt/sugars)•Pression (vacuum, high pression)•Agitation•product/solution Ratio•Technology (continuos / batch)•Structure of food material

Main modification occurring in the food material during osmotic treatment :

•Variation of composition

• lowering of water activity / Freezing point depression

• Possible variation of glass transition temperature

•Modification of nutritional / functional value

•Enrichment of volatile in the head space

•Colour stabilisation

•Texture modification

•Slow down of enzymatic activities

•Reduction of freezable water

•Limited shrinkage

•Cell vitality modification

Technological hurdle: Solution management

• It strongly depends by the type of the foodstuff undergoing to the osmotic treatment

• It is necessary to implement a minimal level of technology to set up a medium or large production allows to manage the used / spent solutions

• To avoid sanitary problem in managing the solution and to maintain at low level the microbial load of treated foods, a control system such as HACCP must be implemented

FAIR CT96-1118 C.A.: working groups

GROUP 2

COMBINED PROCESSES

GROUP 1

UNIT OPERATION

GROUP 3

SOLUTION MANAGEMENT

OSMOTIC

PROCESS

RAW

MATERIAL

OSMOTIC

SOLUTION

OSMOTICALLY

TREATED

PRODUCT

DILUTED

SOLUTION

OTHER USES

FREEZING CONVECTIVE DRYING

PASTEURISATION MICROWAVE DRYING

HIGH PRESSURE TREATMENT

CONCENTRATION

SOLUTE

INCORPORATION

Osmotic treatment technology

Semi-Continuous plant (vacuum impregnation)

Continuos plant

Products (tropical fruits)

Combination Osmo-dryingtime

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

0,910,930,950,97

Aw

SG -

O

WL

- O

SG -

DO

WL

DO

WL

- D

Strawberry

Water loss

Solid gain

: Mass transfer during air-drying (D), osmotic treatment (O) and dehydro-osmo treatment of strawberry (DO).

Combination Osmo-drying

Sorption isotherm during air-drying (D), osmotic treatment (O) and dehydro-osmo treatment of blueberry (DO).

0

1

2

3

4

5

6

7

0,94 0,95 0,96 0,97 0,98 0,99 1

Aw

O TO TD TDO

Blueberry

OT and Minimally processed fruit

- shelf-life prolongation;

- partial protection from enzymatic activity (colour

modification);- quality standardisation for unripe fruits- initial reduction of texture

- improvement of sugars/acids ratio;-protection from superficial dehydration -reduction of microbial growth- are cell still alive???.

Effect of osmotic treatment

0

1

2

3

4

5

6

7

0 4 8 12 16 20

TEMPO (giorni)

TAL QUALE

OSMOTIZZATO

0

2

4

6

8

10

12

14

16

0 4 8 12 16 20

TEMPO (giorni)

OSMOTIZZATO

NON OSMOTIZZATO

Kiwifruit OT-MPF during chilled storage

Modification of colour Microbial growth

70’s

1985

Use of solutes at different D.E. to modulate WL/SG

Effect of salt addition on kinetics and quality

Influence of solute uptake on water activity

Influence of different shapes (A/L) on O.D. kinetics

Explore implication of tissue structure for mass transport phenomena during OT

Improve knowledge concerning the mechanism of water and solute transfer during OT in relation to cell vitality

In the last ten years more basic researches to Understand transfer mechanisms during OT in

the Plant tissues

Reconstitution /Rehydration

Modulation of water uptake

Control of :aw and f.p.

Amount of frozen water

Texture at sub-freezingtemperature

Rehydration of air dried strawberryRehydration of freeze dried strawberry

ConclusionsDrying / dehydration not only to obtain shelf stable food

Moist and semi moist fruit and vegetables can be used as Functional ingredient in complex food

More research is necessary to assess the chemical, biochemical and textural changes

Alternative preliminary treatments sholud be improved to avoid or reduce the amount of sulphite

References•Cohen J.S. and Yang T.C.S., Trends in Fd. Science & Technol., 6, 1995, pp.20-25.•Dalla Rosa M., Mastrocola D., Pittia P., Barbanti D., Sacchetti G. Combined Techniques to Improve the Quality of Processed Berry Fruits to be used as Ingredient in Complex Foods. International Congress on Engineering and Foods, Puebla, (Messico), pp.1335-1340, 2001•Dalla Rosa M.; Giroux F.Osmotic treatments (OT) and problems related to the solution management Journal of Food Engineering, August 2001, vol. 49, no. 2, pp. 223-236(14).•Gianotti A.; Sacchetti G.; Guerzoni M.E.; Dalla Rosa M Microbial aspects on short-time osmotic treatment of kiwifruit Journal of Food Engineering, August 2001, vol. 49, no. 2, pp. 265-270(6).•Mastrocola D., Barbanti D., Dalla Rosa M. and Pittia P. Physico-chemical characteristics of dehydrated apple cubes reconstituted in sugar solutions, J.of Food Sci., 63, (3), 495-498, 1998.•Mastrocola, D., Lerici C.R., Dalla Rosa M., Impregnation of dehydrated fruit pieces. In: Industrial application of osmotic dehydration/treatments of food, M. Dalla Rosa and W.E.L. Spiess, Forum, Udine, 1999•Nijhuis, H.H., Torringa, H.M., Muresan, S., Yuksel, D., Leguijt, C. and Kloek, W., Trends in Fd. Science & Technol., 9, 1998, pp.13-20.•Zocca A., Magnanini E., Lerici C.R., Dalla Rosa M. e Pinnavaia G.: "Essiccazione della frutta mediante un impianto alimentato ad energia solare." in Atti 1a Conferenza Internazionale "Energia e Agricoltura", Milano (I), aprile 1983

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