Q. Effectiveness of blanching by peroxidase inactivity test?

• check the adequacy of the blanching process,

• appreciate the importance of time-temperature relationship in blanching process, and

• select an effective pre-treatment before any processing with maximum retention of the sensory attributes.

Principle

Raw or under blanched vegetables discolour, lose flavour and develop off flavours during processing. The loss of quality is caused by enzymatic action. Peroxidase is the most heat-resistant enzymes present in all vegetables. When these are inactivated by heating, the enzymatic processes, in general would have been inhibited as other heat resistant enzymes would have also been inactivated. Hence, blanched vegetables should have been tested for their inactivation.

Materials Required

Green leafy vegetable

Other vegetable

0.08 % of peroxide solution H2O2: Dilute 2.8 ml of 30% H₂O₂ with water and store in a dark bottle in a refrigerator. Prepare fresh every week

0.5 % Guaiacol in 50% ethyl alcohol

Stop-watch

Thermometers

Beakers

Pestle and Mortar

Test Tubes

Funnel

Cotton Distilled Water

Procedure

Carry out the activity following the procedure enumerated herewith:

1) Wash the given sample of vegetable thoroughly.

2) Dice or cut the vegetable.

3) Blanch small edible portions of vegetables at 85ºC, 100ºC for different time and then carry out the following test for peroxidase activity.

4) After blanching put the vegetable immediately under cold water.

5) Take 10 g of representative sample.

6) Grind in a mortar using sand and 30 ml water added in small portions.

7) Filter through cotton cloth.

8) To 2.0 ml of filtrate, add 20 ml of distilled water in a test tube and mix.

9) Add 1 ml of 0.5 % guaiacol solution and then 0.08% H₂O₂ solution and keep aside.

10) Observe for the development of a brown ring.

11) If no brown ring formation takes place in 3-5 minutes consider the test to be negative (i.e., inactive peroxidase test) and the product to be adequately blanched.