Polyphenoloxidase (PPO) activity and osmotic dehydration in Granny Smith apple

Abstract

AbstractOsmotic dehydration (OD) permits the preservation of foods via a decrease in water content and an increase in solute concentration. Osmotically dehydrated fruits such as apple are suitable for the manufacture of desserts, cakes, salads, yoghurts, etc. Different microstructural and engineering aspects of OD are already known, but its effects on enzymatic activity are still unknown. This study analyses the activity of polyphenoloxidase (PPO) in fresh Granny Smith apples and the effect that OD by immersion in sucrose‐saturated syrup has on this activity. The low PPO activity found in the edible parenchyma of osmotically dehydrated apples is attributed to penetration by the osmotic agent and flooding of the intercellular spaces, which produces a low moisture content and a limited O2 concentration in the immediate environment of the enzyme. These results show that OD prevents enzyme–substrate interaction. Thus the low PPO activity would reduce browning of this type of product. Copyright © 2005 Society of Chemical Industry