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University of Bologna (Italy)

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1 University of Bologna (Italy)
Dehydration of mediterranean fruit and vegetables: scientific and technical aspect of emerging technologies with particular reference on semi-moist products Marco Dalla Rosa Full Professor Food Technology University of Bologna (Italy)

2 Presentation content Typology of fruit mostly addressed to drying in the mediterranean area Possible use of drying fruit and vegetables in food industry and consumption by consumers. Conventional and non conventional drying technologies. Overview on Principles / applications / problems Tentative data on production / import /export of dried fruit and vegetables Quality changes during drying Use of drying technique to obtain moist and semi-moist products for direct consumption and industrial utilisation Combination of drying / stabilisation processing technologies Direct formulation / osmotic dehydration and problems related to industrial application Concluding remarks and future trends

3 Product typology 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

4 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

5 Raw material typology FRUITS
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 air

6 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)

7 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

8 Statistical data Dried fruit Dried vegetables export
Dried vegetables import Seedless grapes (sultanas)import Seedless grapes export Dried apple&pears export Dried apple&pears import Dried prunes export Dried figs export Dried prunes import Dried mushrooms export World Dried apricot export Mushroom & truffles UE Dried apricot import

9 Dried fruits and vegetables
Dry / extra dry (whole,pieces, flakes, powders) Classification vs.-physical state Moist / semi-moist (I.M.F.) Candied / semi-candied Direct consumption Industrial use in complex foods Classification vs. Final users: ready to eat, inclusions in moist complex food, ingredients in dry foods

10 Quality properties of dried foods
Chemical 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 damages EB / NEB Use of additives (common) Long process time Incomplete reconstitution

11 Permitted additives

12 Stability: thermodynamic approach

13 Stability: thermodynamic approach

14 Stability: thermodynamic approach

15 Stability: thermodynamic approach

16 Stability: thermodynamic approach

17 Stability: thermodynamic approach
In a complex food where the dehydrated ingredient is included i.e.: Ice cream Cakes Dairy foods Yoghurt ………

18 Stability: thermodynamic approach
In such a system Partially dehydrated Fruit or vegetables Can be useful To reduce the Moisture transfer

19 Stability: kinetic approach
Physical stability of dried /extra dried Products is related to Tg NOT to water activity Above Tg: Caking Loss of free flowing Stickiness

20 Drying Technologies Air (convective) drying Drum (contact) drying
Sun / solar drying (slow drying) Air (convective) drying Drum (contact) drying Spray drying (fluid extracts / beverages) Microwaves (volumic heating) Direct Osmosis (dewatering impregnation)

21 Sun / solar drying

22 Sun / solar drying Slow drying Low control of processing conditions
Microbial risks (mycotoxins) High level of enzymic browning NEB during storage

23 Air drying Traditional Convective static (discontinuous) drying
On trays Prunes, Sultanas, Apricots …… Slow drying kinetic High browning level High shrinkage

24 Air drying: technological evolution
Convective belt drying To prevent Enzymic browning Continuos sulphiting tank Faster drying kinetic Less browning (exp.NEB) Higher retention of thermolabile nutrients Leaf vegetables drying

25 Air drying: technological evolution
Continuos net drier Fluidised-bed drier

26 Drum drying Turbo - drying operation sizing flaking Turbo technology
Turbo-drier capacity

27 Spray drying ICF Cibec Industry Niro pilot plant Spray driers
Granulator Instatizer

28 Freeze - drying

29 Freeze - drying: high quality?
Flavour and texture Are maintaining if the process is carried out Below Tg Air drying Feeze drying Then best retention of flavour (i.e.:truffles) and tissue structure

30 RF / Microwave drying

31 Mw drying Njihus et al., 1998

32 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)

33 Chairperson 3rd SubGroup
(Concerted Action FAIR CT 96/1118) Chairperson 3rd SubGroup

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


36 MAIN OBJECTIVE 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

37 APPLICATION FIELDS Vegetal origin products (fruit, vegetables) Animal origin products (meat and fish derivatives) 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

38 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

39 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

40 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

41 FAIR CT96-1118 C.A.: working groups

Direct Osmosis / Impregnation TECHNOLOGY of the PROCESS (CIRAD©, 1998)

43 Osmotic treatment technology
Semi-Continuous plant (vacuum impregnation) Products (tropical fruits) Continuos plant

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

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

46 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

47 Kiwifruit OT-MPF during chilled storage
Modification of colour Microbial growth

48 70’s


50 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

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

52 Reconstitution /Rehydration
Modulation of water uptake Control of : aw and f.p. Amount of frozen water Texture at sub-freezing temperature Rehydration of air dried strawberry Rehydration of freeze dried strawberry

53 Conclusions Drying / 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

54 References Cohen J.S. and Yang T.C.S., Trends in Fd. Science & Technol., 6, 1995, pp 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 , 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 (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 (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), , 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 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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