EFFECTS OF DRYING METHODS AND TEA PREPARATIONTEMPERATURE ON THE DEGRADATION OF ANTIOXIDANTSIN INDIAN GOOSEBERRY TEA

摘要

Hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD) of Indiangooseberry flake were carried out at various drying temperatures (65 and 75°C) and absolutepressures (7, 10 and 13 kPa) to monitor the drying kinetics and quality changes, in terms ofcolor changes and antioxidant activity, of the product. The dried gooseberry flake was thensoaked in hot water at 70, 80 and 90°C to prepare Indian gooseberry tea. In terms of the dryingkinetics, the drying temperature had an effect on the moisture reduction rate of the samples inall cases. Vacuum drying, however, took shorter time to dry the product to the desired moisturecontent. Regarding the nutritional quality of the dried flake, it was found that the amount ofascorbic acid in the flake dried by vacuum drying was higher than those dried by hot air dryingand LPSSD. However, LPSSD could retain flavonoid compounds better than did other dryingtechniques. On the other hand, total polyphenolic compounds and the total antioxidant activityof the dried flake were not significantly different among all cases. Regarding the release ofantioxidants from the flake during tea preparation, no significant difference was observedbetween using the water temperature of 70, 80 and 90°C. Due to the more porous structure ofLPSSD flake, however, higher compound degradation was noted. Nevertheless, it could stillbe concluded that drying the flake by LPSSD at 75°C and 7 kPa could best retain the activecompounds, i.e., 62% of ascorbic acid, 91% of flavonoid compounds, 81% of totalpolyphenolic compounds and 83% of antioxidant activity; appropriate water temperature andtime for tea preparation was 90°C and 5 minutes, respectively.