KINETICS OF BROWNING OF SULTANA GRAPES
No Thumbnail Available
Date
1987
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Heat inactivation of polyphenoloxidase (PPO) in sultana grapes between 83.degree. and 98.degree. C followed zero order kinetics with an activation energy of 13.7-16.7 kcal/mol. A high correlation (r = 0.973) was found between the residual PPO activity and darkness of the raisins (Hunterlab L value) after drying at 50.degree. C. Reaction rate for enzymatic browning increased with higher water activities while non-enzymatic browning showed the typical bell-shaped curve with a maximum around 0.8. Light-colored raisins were obtained without the use of SO2 by pretreating the grapes with a 2 min dip in 93.degree. C water that inactivated PPO and improved mass transfer through the skin. This latter effect was compared to that of other treatments such as ethyl oleate and caustic soda by drying studies and scanning electron microscopy.