Nutritional Quality of Microwave and Pressure Cooked Rice (Oryza sativa) Varieties

Abstract

The objective of the study was to determine the nutrient content, soluble and insoluble dietary fibre and in vitro protein and starch digestibility in four different microwave and pressure cooked rice ( Oryza sativa) varieties. The rice varieties selected were Bangara Tegalu (BT, nonaromatic), Gowri sanna(nonaromatic), Jeera (mildly flavoured) and Basmati (aromatic). These were washed and cooked by microwave and pressure cooking methods and analysed for moisture, protein, thiamin, fat, total ash, iron, phosphorus, calcium, starch, dietary fibre and in vitro protein and starch digestibilities along with their raw unwashed controls by using standard techniques. The protein content of raw and cooked rice varieties ranged from 7.5 to 11.6g/100g and 7.4–11.2g/100g, respectively. There was a significant difference ( p 0.05) in the protein content of two varieties of pressure and microwave cooked rice. The fat content of raw samples was 0.5–0.6g/100g. Cooking by both methods brought about a significant ( p 0.01) decrease (20–60%) in the fat content of samples. Between cooking methods there was no significant difference ( p 0.05). The thiamin content of raw rice varieties were between 0.16mg and 0.21mg/100g showing a significant decrease on cooking by 29–63% (pressure cooking) and 38–69% (microwave cooking). The iron content in raw samples ranged from 1.5 to 1.9mg/100g and decreased by 33–50% on cooking. The calcium (9–16mg/100g) and phosphorus (82–165mg/100g) content also showed significant decrease by cooking. The total dietary fibre in all samples was between 2.24 to 3.03g/100g, a large proportion of which was insoluble (1.97–3.00g/100g). The in vitro protein digestibility of the pressure cooked samples (82.1–91.0%) was slightly higher than the microwave cooked samples (80.0–90.8%). The starch digestibility between cooked samples were similar (92.6–93.8%) but significantly higher than raw samples. It can be concluded that cooking as such influenced the nutritional quality of rice but between the two cooking methods there were no significant differences.