The document discusses heat processing methods used in food technology, focusing on blanching. It defines blanching as a heat treatment used to inactivate enzymes in fruits and vegetables prior to further processing. The document describes different blanching methods including steam blanching and hot water blanching. It also discusses newer techniques such as individual quick blanching that aim to minimize nutrient losses and improve process efficiency.

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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