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1. Blanching

2. Introduction
• Most vegetables and some fruits are blanched
prior to further processing operations
• Blanching is a mild heat treatment, but is not a
method of preservation.
• It is a pretreatment usually performed between
preparation and subsequent processing.
• Blanching consists of heating the food rapidly to a
predetermined temperature, holding for a
specified time, then either cooling rapidly or
passing immediately to the next processing stage.

3. Purpose
• The major purpose : inactivate enzymes,
reduce number of m.o
• Effect : reduce quality

4. Blanching causes
• cell death and physical and metabolic chaos within the
cells.
• leads to enzyme destruction as well as damage to the
cytoplasmic and other membranes, which become
permeable to water and solutes
• loss of turgor pressure
• Water and solutes may pass into and out of the cells, a
major consequence being nutrient loss from the tissue.
• cell constituents, which had previously been
compartmentalised in subcellular organelles, become
free to move and interact within the cell.

5. Effect of blanching
on cell tissues
S, starch gelatinised; CM, cytoplasmic membranes
altered; CW, cell walls little altered; P, pectins modified; N, nucleus and
cytoplasmic proteins denatured; C, chloroplasts and chromoplasts
distorted

6. Role of Blanching
• Storage product
• Packaging
• Further benefit

7. A. Storage product
• loss of colour or texture, production of off odours and
flavours or breakdown of nutrients --- enzymes
activities peroxidases, catalases and lipoxygenases.
• Peroxidase and catalase : indicator of blanching
effectiveness
• peroxidase is chosen due to easy to measure and it is
the most heat resistant of the enzymes
• complete inactivation of peroxidase may not be
necessary and retention of a small percentage of the
enzyme following blanching of some vegetables may
be acceptable

8. B. Packaging
• Blanching causes the removal of gases from plant tissues :---- helps
achieve vaccuum in the cans, preventing expansion of air during
processing and hence reducing strain on the containers and the risk
of misshapen cans and/or faulty seams., removing oxygen is useful
in avoiding oxidation of the product and corrosion of the can,
removal of surface dust affects in brightening the colour of some
products, especially green vegetables.
• Shrinking and softening of the tissue :--- benefit in terms of
achieving filled weight into containers, possible to reduce the
tinplate requirement in canning, facilitate the filling of containers.
• controling the time/temperature : ----- avoid overprocessing,
leading to excessive loss of texture
• Calcium chloride addition to blanching water helps to maintain the
texture of plant tissue through the formation of calcium pectate
complexes.

9. C. Further benefit
• final cleaning and decontamination process.
• Removing pesticide residues from the surface
of vegetables
• Reductions in microorganism content : ---very
useful in frozen or dried foods where surviving
organisms can multiply on thawing or
rehydration and in before heat sterilisation if
large numbers of microorganisms are present
before processing.

10. Controlling factors
• Factors :
– fruit or vegetable properties, especially thermal conductivity, which
will be determined by type, cultivar, degree of maturity etc.;
– overall blanching effect required for the processed product, which
could be expressed in many ways including: achieving a specified
central temperature, achieving a specified level of peroxidase
inactivation, retaining a specified proportion of vitamin C;
– size and shape of food pieces;
– method of heating and temperature of blanching medium.
• Time/temperature combinations vary very widely for different
foods and different processes and must be determined specifically
for any situation. Holding times of 1–15 min at 70–100 C are
normal.

11. Efek pada pangan
• Nutrisi
• Warna dan flavour
• Tekstur

12. Nutrisi
• Some minerals, water-soluble vitamins and other water-
soluble components are lost during blanching. Losses of
vitamins are mostly due to leaching, thermal destruction
and, to a lesser extent, oxidation. The extent of vitamin loss
depends on a number of factors including:
– the maturity of the food and variety
– methods used in preparation of the food, particularly the extent
of cutting, slicing or dicing
– the surface-area-to-volume ratio of the pieces of food
– method of blanching
– time and temperature of blanching (lower vitamin losses at
higher temperatures for shorter times)
– the method of cooling
– the ratio of water to food (in both water blanching and cooling).

14. Warna dan flavour
• Blanching brightens the colour of some foods by removing air and
dust on the surface and thus altering the wavelength of reflected
light. The time and temperature of blanching also influence the
change in food pigments according to their D value
• Sodium carbonate (0.125% w/w) or calcium oxide are often added
to blancher water to protect chlorophyll and to retain the colour of
green vegetables, although the increase in pH may increase losses
of ascorbic acid.
• Enzymic browning of cut apples and potatoes is prevented by
holding the food in dilute (2% w/w) brine prior to blanching. When
correctly blanched, most foods have no significant changes to
flavour or aroma, but under-blanching can lead to the development
of off-flavours during storage of dried or frozen foods.

15. Tekstur
• One of the purposes of blanching is to soften the
texture of vegetables to facilitate filling into containers
prior to canning. However, when used for freezing or
drying, the time–temperature conditions needed to
achieve enzyme inactivation cause an excessive loss of
texture in some types of food (for example certain
varieties of potato) and in large pieces of food.
• Calcium chloride (1–2%) is therefore added to blancher
water to form insoluble calcium pectate complexes and
thus to maintain firmness in the tissues.

16. Blanching Equipment
blancher–cooler

17. IQB steam blanching

18. counter-current blancher

19. Advantages and limitations of conventional
steam and hot-water blanchers

20. Prediksi waktu blanching

21. PINDAH PANAS PADA BLANCHING:
UNSTEADY STATE
• pindah panas yang suhunya berubah karena
bahan dipanaskan atau didinginkan.
• Proses sangat rumit, melibatkan penyelesaian
menggunakan persamaan Fourier yang ditulis
dalam bentuk diferensial parsial dalam tiga
dimensi.

22. persamaan
• faktor suhu, biot number, fourier number