Journal of Food Science vol:75 issue:4 pages:C336-C340
The thermal stability of vitamin C ( including L-ascorbic acid [L-AA] and dehydroascorbic acid [DHAA]) in crushed broccoli was evaluated in the temperature range of 30 to 90 degrees C whereas that of ascorbic acid oxidase (AAO) was evaluated in the temperature range of 20 to 95 degrees C. Thermal treatments ( for 15 min) of crushed broccoli at 30 to 60 degrees C resulted in conversion of L-AA to DHAA whereas treatments at 70 to 90 degrees C retained vitamin C as L-AA. These observations indicated that enzymes ( for example, AAO) could play a major role in the initial phase ( that is, oxidation of L-AA to DHAA) of vitamin C degradation in broccoli. Consequently, a study to evaluate the temperature-time conditions that could result in AAO inactivation in broccoli was carried out. In this study, higher AAO activity was observed in broccoli florets than stalks. During thermal treatments for 10 min, AAO in broccoli florets and stalks was stable until around 50 degrees C. A 10-min thermal treatment at 80 degrees C almost completely inactivated AAO in broccoli. AAO inactivation followed 1st order kinetics in the temperature range of 55 to 65 degrees C. Based on this study, a thermal treatment above 70 degrees C is recommended for crushed vegetable products to prevent oxidation of L-AA to DHAA, the onset of vitamin C degradation.