SOP: Test for Peroxidase Activity in Vegetables

GIFSQ — Global Institute for Food Safety & Quality

Principle

Peroxidase is among the most heat-resistant enzymes in vegetables. Its residual activity, shown by the guaiacol–hydrogen peroxide colour reaction, has been found to correlate with the keeping quality of frozen vegetables in frozen storage; the test is applicable to frozen peas, snap beans, asparagus and cut corn, and may hold good for other frozen vegetables.

Apparatus required

• Mortar and pestle
• Cotton gauze
• Test tubes

Reagents

a. Hydrogen peroxide, 0.08% solution (H₂O₂): dilute 2.8 ml of 30% H₂O₂ with water; store in a dark bottle in a refrigerator; prepare fresh every week.

b. Guaiacol, 0.5% solution in 50% ethyl alcohol.

c. Water, 30 ml, added in small portions during grinding.

Sample preparation

Cut the tissue into small pieces. Take 10 g of a representative sample and grind it in a mortar using sand, adding 30 ml of water in small portions. Filter through a cotton gauze.

Procedure

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

↓

Add 1 ml of 0.5% guaiacol solution and then 1 ml of 0.08% H₂O₂ solution, mix thoroughly, and store

↓

Watch for colour development for 3.5 min

↓

Prepare a blank without the addition of guaiacol and H₂O₂

Interpretation

• If no colour develops in 3.5 min, the test is negative and the product is adequately blanched.
• If the test is positive, the colour developed within 3.5 min is easily recognisable.
• If the colour develops after 3.5 min, the test is still considered negative.

Precautions

• Add the guaiacol before the hydrogen peroxide, and mix thoroughly after each addition.
• Read the result strictly at 3.5 min; colour appearing later does not count as positive.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.