Mathematical modelling of the diffusion of ascorbic acid during water blanching of surface frozen potato strips

Abstract

Summary Partial freezing is a promising technique in producing good quality french fries, especially for potatoes stored for an extended period and containing large amounts of reducing sugars. The cell damage of the potato strip caused by surface freezing facilitates surface leaching of reducing sugars and other soluble solids like ascorbic acid, preventing undesirable dark colour in the finish-fried products. A theoretical study to describe the diffusion of ascorbic acid during the water blanching at 50°C of surface frozen potato strips (10 x 10 x 80 mm) is developed. Ascorbic acid profiles as a function of blanching time, position in the potato strip and thickness of the frozen layer are shown as well as average retention as a function of blanching time, frozen layer thickness, apparent diffusion coefficient and mass transfer coefficient of ascorbic acid. Significant changes in the ascorbic acid concentration during blanching are produced in the frozen layer. Ascorbic acid average retention is mainly influenced by frozen layer thickness and temperature, and the mass transfer coefficient is less important.