The impact of processing on starch digestibility

The rice production process involves growing, harvesting, storage and milling. In particular, nitrogen nutrition and storage conditions influence milling properties (head rice yield), translucense and colour. Given that the positive health properties of rice are of increasing interest to the consumer and the food industry, research into the impact of production processing on GI is warranted. An in vitro starch digestibility method was used to screen two sets of samples. For sample set (1), milled rice varieties were exposed to high application rates of nitrogen (240 kg/HA) and samples were collected over three crop years. The extreme rates of nitrogen-treated samples, which also had the highest protein contents, showed no difference in starch digestibility to samples which were not treated. For sample set (2), milled rice varieties were stored at 3 temperatures (4, 25 and 37 C) for up to 1 year. Samples were collected over 5 time-points over the year. The starch digestibility decreased with increasing storage time and temperature. The outcome of this project provides important information on the limits of endogenous rice proteins on starch digestibility as well as the importance of controlling temperature and moisture during storage.