Peroxidases are found in almost all vegetables. The activity of these enzymes can be an indicator of the vegetable quality as it normally increases during ripening. Also, the peroxidase activity is decreased during blanching, a standard processing of vegetables prior to freezing.1
The following application note describes the determination of the peroxidase activity in vegetables using the MQuant® Peroxidase test strips.
Under the catalytic effect of peroxidase, an organic redox indicator is converted into a blue compound. The visual comparison of the reaction zone of the test strip with the fields of a color scale shows whether there is any peroxidase activity present (+, ++) or not (-).
As a rule, every blue discoloration of the reaction zone is caused by peroxidase activity.
Various vegetables (e.g. carrots, potatoes, string beans, red cabbage)
MQuant® Peroxidase Test (Product No. 117828)
Potassium dihydrogen phosphate for analysis (Product No. 104873)
di-Sodium hydrogen phosphate dihydrate for analysis (Product No. 106580)
Water for analysis or distilled water (Product No. 116754)
Sodium hydroxide solution 1 mol/l (Product No. 109137)
Hydrochloric acid 1 mol/l (Product No. 109057)
Blender (e.g. ULTRA-TURRAX®)
Place 1.95 g of potassium dihydrogen phosphate for analysis and 1.01 g of di-sodium hydrogen phosphate dehydrate for analysis, accurately weighed, into a 1000-ml glass beaker and dissolve in about 900 ml of water for analysis. Check the pH of the solution and adjust, if necessary, with hydrochloric acid or sodium hydroxide solution. Subsequently transfer this solution to a 1000-ml volumetric flask and make up to the mark with water for analysis.
Chop the vegetables in a blender. Place 20 g of chopped vegetables into a 250-ml glass beaker, add about 70 ml of extraction solution and homogenize. Care must be taken that the temperature does not exceed 40 °C. Subsequently filter off through a folded filter. Use the filtrate for the analysis.
Determine with the above-mentioned test kit.
The color fields serve merely as a rough orientation. As a rule, every blue discoloration of the reaction zone is caused by peroxidase activity.
Note: The different values between fresh and frozen vegetables result of the food technology process to blanch vegetables before freezing. Therefore, peroxidase in frozen vegetables is deactivated. Because of that it is possible to differ fresh vegetables from blanched ones or to verify the blanch process.
The peroxidase activity of the following vegetables was determined using the MQuant® test strips:
The MQuant® Peroxidase test strip is a quick and easy way to analyze the peroxidase values in vegetables and therefore allow to determine the quality and differ between fresh and frozen vegetables.