dehydration of mediterranean fruit and vegetables: scientific and technical aspect of emerging...
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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)
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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
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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
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Product typology (2)
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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
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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.
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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)
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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
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Statistical data
Seedless grapes (sultanas)importSeedless grapes export
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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
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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
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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
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Permitted additives
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Stability: thermodynamic approach
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Stability: thermodynamic approach
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Stability: thermodynamic approach
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Stability: thermodynamic approach
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Stability: thermodynamic approach
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Stability: thermodynamic approach
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In a complex food where the dehydrated ingredient is included
i.e.:Ice creamCakesDairy foodsYoghurt………
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Stability: thermodynamic approach
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In such a systemPartially dehydratedFruit or vegetablesCan be usefulTo reduce the Moisture transfer
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Stability: kinetic approach
Physical stabilityof dried /extra driedProducts is relatedto Tg NOT to water activity
Above Tg:CakingLoss of free flowingStickiness
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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)
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Sun / solar drying
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Sun / solar drying
Slow drying
Low control of processing conditions
Microbial risks (mycotoxins)
High level of enzymic browning
NEB during storage
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Air drying
TraditionalConvective static(discontinuous) dryingOn trays
Prunes,Sultanas,Apricots……
Slow drying kineticHigh browning levelHigh shrinkage
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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
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Air drying: technological evolution
Continuos net drier
Fluidised-bed drier
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Drum drying
operation
sizing
flaking
Turbo - drying
Turbo technology
Turbo-drier capacity
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Spray drying
ICF Cibec Industry
Spray driers
Granulator
Instatizer
Niro pilot plant
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Freeze - drying
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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
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RF / Microwave drying
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Mw drying
Njihus et al., 1998
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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)
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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
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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
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Osmotic soluteWater &soluble solids
cell wall
cell membrane
intercellularspace
OSMOTIC SOLUTION
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•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
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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)
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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
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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
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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
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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
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Direct Osmosis / Impregnation
(CIRAD©, 1998)
TECHNOLOGY of the PROCESS
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Osmotic treatment technology
Semi-Continuous plant (vacuum impregnation)
Continuos plant
Products (tropical fruits)
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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).
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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
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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
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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
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70’s
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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
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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
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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
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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
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