THE INFLUENCE OF FOOD PREPARATION METHODS ON THE IN-VITRO DIGESTIBILITY OF STARCH IN POTATOES

For nutritional purposes, starch may be divided into rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). These fractions can be determined in vitro by a new analytical technique. Using this classification and technique the digestibility of starch from potatoes processed in various ways has been assessed. Potato starch was highly resistant to hydrolysis bv amylase when raw but was rendered rapidly digestible bv all conventional cooking techniques. After cooling, cooked potato contained a small proportion of RS formed as the result of processing. Isolated potato starch was rapidly digestible when cooked with water but, when made into biscuits cooked under dry conditions, much of the resistance was retained. Further analysis of the RS showed that, in raw potato and in potato biscuits cooked under dry conditions, resistance to digestion was due to the structure of the starch granules whereas, after cooking with water and cooling, the resistance was mainly attributable to retrogradation of starch.