PHYSICAL AND CHEMICAL METHODS OF EVALUATION FOODS

Peroxidase Qualitative Determination in Plant Tissue to Top

Principle: Peroxidases have been found in most plant cells investigated and seems to be a normal component of such cells. Partial purification of the enzyme has now been achieved from several sources, notably from figs, and isolated in pure state only from horseradish (HRP).

The chemical reactions underlying the function of peroxidase are not known in detail. The reactions are in the principle the following:
ROOH + AH2-- H2O + ROH + A

Properties of HRP: Since peroxidase has been isolated from horseradish only, some properties of HRP are listed:

1 Substrate specifity is high; only H2)2, methyl hydrogen peroxide and ethyl hydrogen peroxide combine with HRP to give active E-S complexes.
2 Isoelectric point; pH 7.2
3 Solubility; 5 g are soluble oin 100 mL of water if traces of salts are present
4 pH stability; if warm, the enzyme is stable up to 63C. At room temperature, HRP is stable for weeks. partial recovery of activity after cooling of heated solution is reported.

Experiment

Cook a potato in boiling water for 15 minutes.

Heat a potato in microwave oven for

0 minutes
2 minutes
4 minutes
6 minutes

Cut the potatoes in half and do the guaiacol solution test and the benzidine test (each on 1/2 potato).

REFERENCES to Top

Qualitative Test: From Collins, J.L. and I.E. McCarty. 1969. Comparison of microwave energy with boiling water for blanching whole potatoes. Food Technology 23: 63(337).

´ ´ Updated: Wednesday, October 31, 2007. ´ Oregon State University.
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