EFFECT OF DIFFERENT TYPES OF HEAT TREATMENT ON INVERTASE ACTIVITY IN HONEY

Honey is important food stuff, which is often consumed fresh or used in other meals. Liquid honey is more demanded in market, so solid honey often is heated in order to melt it. One of the most traditional ways to melt the honey is by heating using thermal treatment usually in higher temperature than 50 degrees C. Using microwave ovens are very popular approach to heat food and its popularity is growing, so it is important to understand, how food and its substances are being influenced by microwave heating. One of the most heat-sensitive enzymes is invertase. The aim of the research is to study and to compare, how invertase activity in honey is affected by heating it in the microwave oven and in the thermostat, while changing microwave oven power, heating duration and heating temperature in thermostat. p-Nitrophenyl-alpha-D-glucopyranoside (pNPG) is used as a substrate for the determination of the invertase number in honey. pNPG is split into glucose and p-nitrophenol by alpha-glucosidase (invertase, sucrase). By adjusting the pH-value to 9.5 the enzymatic reaction is stopped and at the same time nitrophenol is transformed into the nitrophenolate anion, which corresponds to the amount of converted substrate and is determined photometrically at 400 nm. Analyzing different honey samples, the following results were obtained. When honey samples were heated in 450 W microwave oven, invertase activity significantly decreased after 20 seconds. After 25 seconds invertase activity decreased 5.8 times, after 30 seconds - 12.5 times. After heating honey samples in thermostat in 60 degrees C for 120 minutes, invertase activity decreased only twice. Summarizing research results, we concluded, that invertase activity changes are significantly higher in honey samples, heated in the microwave oven, than honey samples, heated in the thermostat.