Kinetics of extraction of reducing sugar during blanching of potato slices

Abstract

Kinetics of extraction of reducing sugars from potato slices was studied during blanching. Two models based on Fick’s law were used to describe loss of reducing sugars during blanching at 60, 75 and 90 °C. The first one is the classic model with a constant effective reducing sugar diffusion coefficient. The second model considers that the diffusion coefficient varies during the blanching process. The variable diffusivity model fitted the experimental data better than the constant diffusivity model (RMS average values of 8% vs. 15%, respectively). The constant effective reducing sugar diffusivity increased with blanching temperature, and the calculated activation energy for this process was 3.4 kJ/mol. The effective reducing sugar diffusion coefficient in the variable diffusivity model decreased with blanching time and temperature and behaved similarly at 75 and 90 °C, while for slices blanched at 60 °C this coefficient was considerable higher after the initial 30 s of blanching. This observation is attributed to the gelatinization of starch at temperatures above 60 °C which results in changes of original microstructure of potato, thereby making the diffusion of reducing sugars more difficult. Low temperature–long time blanching (BLTSt) gave better quality potato chips (lighter and less oily) than those blanched at high temperature–short time combination (BHTSt). No significant effect ( p > 0.05) of blanching treatment conditions were observed on porosity and texture on the resultant potato chips.