Food Processing Technology. (Degree & Diploma)

1. Y.Bavaneethan.
Lecturer
Department of Food Technology
SLGTI.
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2. Heat Processing Overview
 Heat processing using steam or water
– Blanching | Pasteurisation | Heat sterilisation
 Heat processing using hot air
– Dehydration | Baking and roasting
 Heat processing using hot oils
– Frying
 Heat processing by direct and radiated energy
– Dielectric | Ohmic | Infrared
 Processing by The Removal of Heat
– Chilling | Controlled- or modified-atmosphere
storage and packaging | Freezing | Freeze drying
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3. Blanching
Blanching is used to
– lower enzymatic activity in vegetables and fruits
Not final method of preservation but as a pre-
treatment,
– between the preparation of the raw material and
further processing steps
Combined with peeling and/or cleaning
Some vegetables are not blanched
– specific location of the enzymes
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4.  Foods are blanched to inactivate enzymes, prior to
other preservative
– freezing, drying, canning
 Effectiveness of blanching. (marker enzymes )
– Absence of peroxidase enzyme after blanching
– Peroxidase is the most widely distributed heat
resistant enzyme
 Enzymes which causes undesirable changes in fruits &
vegetables
– Lipoxygenase
– Polyphenol oxidase
– Polygalactouranase
– Chlorophyllase
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5. Main objectives of blanching:
– Inactivation of enzymes
– Reduction of the microbial contamination
– Reduction of the volume
– Air removal
– Preheating
– Cleaning
 Blanching –
– Softens vegetable tissues
• facilitate filling into containers
– Removes air from intercellular spaces
• increases the density of food
– Help to formation of a head-space vacuum in cans12/4/2017 Y.BAVANEETHAN 5

6. thermal
conductivity
of food
size & shape
of food
convective
heat
transfer
coefficient
heating
medium
temperature
controlling
rate of
heating at
centre
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7. Methods of blanching
1. Steam blanching- steam for 30-90 sec
2. Hot water blanching - dipping in hot water for 1-5
minutes
 Reduce the energy consumption and reduce the loss of
soluble components of foods,
– reduces the volume and polluting potential of
effluents
 Steam blanching results higher nutrient retention than
hot water.
 After blanching, cooling is by cold-air or cold-water
sprays.
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8. 1. Cooling with running water (fluming)
– increases leaching losses,
– gain weight by absorbing water
2. Air cooling
– weight loss due to evaporation
– nutrient retention
 Nutrition retention - method of preparation
– slicing and peeling increase nutrition losses and
reduce the yield
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9. Steam blanchers
Specific for foods with a large area of cut surfaces
 leaching losses < hot-water blanchers.
Mesh conveyor carries food,
 through a steam atmosphere in a tunnel
 typically 15m x 1–1.5m
Water sprays at the inlet and outlet to condense
escaping steam.
Food enter & leave blancher through rotary valves or
hydrostatic seals
 reduce steam losses
 increase energy efficiency
 steam may be re-used.
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10. Steam blanching
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11. Blancher–cooler
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12. Batch fluidised-bed blanchers
• Batch fluidised-bed blanchers
– mixture of air & steam
– fluidises & heats product simultaneously.
• Advantages:
– faster, more uniform heating
– good mixing of product
– reduction of effluent volume
– shorter processing times
– smaller losses of vitamins & other soluble heat
sensitive components.
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13. Hot-water blanchers
Holds food in hot water (70-100ºC) for a
specified time
Then move to a dewatering-cooling section.
reel blancher
Food enters a slowly rotating cylindrical mesh drum
partly submerged in hot water.
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15. Pipe blanchers
• A continuous insulated metal pipe fitted with
feed & discharge ports.
• Hot water is re-circulated through pipe & food
• Large capacity while occupying a small
floor space.
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17.  Both method of blanching………
 The time-temperature require to ensure enzyme
inactivation
• centre of the product
 Overheating of food - loss of texture and other
sensorial characteristics
 To over come this problem, ---- IQB-system
(individual quick blanching)
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18. IQB-system (individual quick blanching)
 In the first stage – Heating stage
– food is heated( sufficiently high temperature) in a
single layer to inactivate enzymes
 In the second stage (adiabatic holding)
– a deep bed of food is held for sufficient time
• allow the temperature at the centre of each piece
 Cooling stage - fog spray to saturate the cold air with
moisture.
 Nutrient losses during steam blanching are reduced by,
– exposing the food to warm air (65ºC)
– preliminary drying operation (‘pre-conditioning’)12/4/2017 Y.BAVANEETHAN 18

19. IQB-system
Surface moisture evaporates & surfaces then
absorb condensing steam during IQB.
Pre-conditioning + IQB
– reduce nutrient losses by 81% for green beans
– 75% for Brussels sprouts
– 61% for peas & 53% for lima beans
 no reduction in the yield of blanched food
Complete inactivation of peroxidase & minimum
loss in quality
– retention of 76–85% of ascorbic acid.
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20. Individual quick blanching
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21. Effect on foods
1. Nutrients
 Some minerals, water-soluble vitamins and other
water-soluble components are lost during blanching.
 Losses of vitamins mostly by
– leaching, thermal destruction and oxidation.
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22. Nutrition loss depends on:
– maturity and variety
– methods of preparation (cutting, slicing or
dicing)
– surface-area-to-volume ratio of the pieces
– method of blanching
– time and temperature of blanching (lower
vitamin losses at HTST)
– method of cooling
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24. Colour and flavour
 Brightens the colour of foods
– removing air and dust on the surface
 Sodium carbonate (0.125% w/w) or calcium oxide
added to blancher water
– protect chlorophyll and retain the colour of green
vegetables
 Increase in pH may increase losses of ascorbic acid
 Enzymatic browning of cut apples and potatoes is
prevented
– holding the food in dilute (2% w/w) brine prior to
blanching.
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25. Texture
 One of the purposes of blanching is to soften the
texture of vegetables
– facilitate filling into containers
 Calcium chloride (1–2%) added to blancher water
– form insoluble calcium pectate complexes
– this is help to maintain firmness of the tissues.
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27. References
• BOMBEN, J. C., DIETRICH, W. C., FARKAS, D. F., HUDSON, J. S. and
DE MARCHENA, E. S. (1973) Pilot plant evaluation of individual quick
blanching for vegetables. J. Food Sci. 38, 590–594.
• BOMBEN, J. C., DIETRICH, W. C., HUDSON, J. S., HAMILTON, H. K.
and FARKAS, D.F. (1975) Yields and solids loss in steam blanching,
cooling and freezing vegetables. J. Food Sci. 40, 660–664.
• CUMMING, D. B., STARK, R. and SANFORD, K. A. (1981) The effect
of an individual quick blanching method on ascorbic acid retention in
selected vegetables. J. Food Process Preserv. 5, 31–37.
• CUMMING, D. B., STARK, R., TIMBERS, G. E. and COWMEADOW,
R. (1984) A new blanching system for the food industry, II, Commercial
design and testing. J. Food Process Preserv. 8, 137–150.
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28. References….
• GILBERT, H., BAXERRES, J. L. and KIM, H. (1980) In: P. Linko, Y.
Malkki, J. Olkku and J. Larinkan (eds) Food Process Engineering, Vol. 1.
Applied Science, London, pp. 75–85.
• HALLSTROM, B., SKJOLDERBRAND, C. and TRAGARDH, C. (1988)
Heat Transfer and Food Products. Elsevier Applied Science, London, pp.
158–242.
• LAZAR, M. E., LUND, D. B. and DIETRICH, W. C. (1971) IQB – a new
concept in blanching. Food Technol. 25, 684– 686.
• PHILIPPON, J. (1984) Methods de blanchiment-refroidissement des
legumes destines a la congelation. Sci. Aliments 4, 523–550.
• SCOTT, E. P., CARROAD, P. A., RUMSEY, T. R., HORN, J.,
BUHLERT, J. and ROSE, W. W. (1981) Energy consumption in steam
blanchers. J. Food Process Engng 5, 77–88.
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