RATE LIMITING MECHANISMS IN CAUSTIC POTATO PEELING

Abstract

The caustic peeling rates of potatoes is considered from an analytical and experimental point of view. The analysis considers the process to be governed by the competing rates of mass transport within the potato (diffusion) and chemical reaction. The chemical reaction between caustic and chlorogenic acid is singled out for analysis since the product of this reaction is a yellow salt which is easily measured by calorimetry. Simplified equations for the concentration of the yellow salt as a function of time is obtained for the two limiting extremes of diffusion controlled rates and reaction controlled rates. Experiments on Idaho Russetts indicate that, over the first 2–3 min of immersion in caustic, the process is diffusion controlled. It is also shown that it is the outer skin which presents the large diffusion resistance. For reasonable times after this initial period the process is reaction controlled and very sensitive to temperature. The implications of these results with respect to processing techniques (e.g., the dry peel process) and sequences is considered and discussed.