Study on the effects of thermal treatments on polyphenol retention, enzyme activity and browning of apple puree

Apple(Malus domestica) puree is widely used as a substitute for sucrose to improve the health properties of foods due to its natural sweetness and nutritional advantages. Thermal treatment has become a critical part of quality control in the processing of apple puree in order to extend the shelf life and improve quality. Polyphenol degradation and enzymatic browning during thermal treatments of apple puree are key factors leading to nutrient loss and color deterioration. This study investigated the effects of a temperature–time combination on the quality of cooked apple puree in this systematic study.

Golden Delicious apples were used as raw material and were peeled, ground and processed at different temperatures (87-102°C) and times (6-17 min). Total polyphenols, peroxidase, polyphenol oxidase and total antioxidant capacity were evaluated for fresh apples and purees based on chemical analysis. Moreover, puree viscosity was measured with a rheometer, while syneresis was evaluated by quantifying the liquid release.

The results showed that browning of apple puree increased when the temperature was higher than 100 °C and the heating time was less than 12 min. The lowest polyphenol concentrations were found in uncooked purees (control), as polyphenols may have been released with warming. Moreover, the highest temperature significantly increased the puree consistency by increasing viscosity and limiting syneresis. No enzymatic activity was found in cooked puree, indicating that the lowest temperature was suitable for color and polyphenol preservation. This study provides a basis for process optimization for balancing nutrient retention and browning control in apple puree processing.