Studies on rice starch : the accumulation and properties of starches in the stem, pollen and grain of some rice varieties grown in southern New South Wales

Abstract

A group of rice varieties known to differ in grain cooking quality were grown together in southern New South Wales. The accumulation and properties of starch were followed from seedling emergence to harvest. Stem starch increased steadily in all Horintiws until flowering and then decreased as Sie atau: filled and ripened. Starches isolated from rice stems 8 and 16 weeks after seedling emergence had similar properties for all varieties. The two varieties that have grain with waxy endosperm starch had non-waxy stem starch. The high levels of starch present in rice stems may make a significant contributiotno grain yield and requires further study. | Pollen was collected and analysed for starch, protein, lipid, ash and sugar content. Rice pollen was found to contain about 22% starch. Within a variety starch isolated from pollen had a similar amylose content to mature endosperm starch. Rice varieties with waxy endosperm starch had waxy pollen starch. The analysis of rice pollen for starch and amylose content may be of use in rice breeding programmes. New crossbred lines could be sorted into amylose classes before harvest. The accumulation and properties of starch in developing grain was investigated. All varieties were found to increase in amylose content and decrease in gelatinisation temperature as wit. ripening progressed. The molecular size of the amylose also increased during ripening. Mature grain was harvested and the Brabender paste viscosity, cooked grain texture and starch properties studied. All varieties had properties within the previously reported range. Chalky cored endosperm is observed as an opaque centre in otherwise translucent grain. It detracts from the visual appeal of a rice sample and consequently reduces its market value. Light and scanning electron microscopic investigations of chalky cored endosperm revealed that it is due to small air spaces present in the endosperm tissue. Chalky tissue is less densely packed than translucent tissue. The properties of starch isolated from chalky and translucent parts of grain were similar. Two methods of eke ateet originally developed for clinical chemistry were adopted and standardised for general use.