Complex Carbohydrates in Australian Rice Products—Influence of Microwave Cooking and Food Processing

Abstract

Raw and parboiled white and brown rice from three Australian cultivars (Calrose, Doongara and Waxy) were analysed for total and enzymically resistant starch (RS), and for water-soluble and water-insoluble non-starch polysaccharides (NSP). Raw white and brown rice from these cultivars were also analysed for starch and RS after cooking in a microwave oven or rice cooker and cooling or freezing of the cooked rice. Generally, starch was higher in white rice samples than in the corresponding brown rice and was higher in parboiled white and brown Calrose but not Doongara or Waxy. The starch content of white and brown rice was maintained or increased by cooking in a microwave oven or rice cooker except with Waxy. In extruded and drum-dried rice flour, rice-pop and rice cakes, starch content was the same as in the corresponding raw material. RS was higher in rice products and in brown and parboiled rice than in white rice and was often increased by cooling or freezing cooked rice but it never exceeded 1.5% of total starch. Total NSP were lower in white (1.8-2.3%) than brown rice (3.1-3.5%) and were increased slightly by parboiling. The ratio soluble/insoluble NSP was higher in white rice than in brown rice. NSP sugar composition varied between the three cultivars and, in products made from Calrose, was also affected by procesing.