Relating starch structure in rice to its digestibility

Abstract

Rice is a globally important crop and a major staple for over two-thirds of the world's population. Australian grown rice is renowned for its high and consistent quality and is the preferred choice in the domestic and many international rice markets. A long-established focus on quality in the Australian rice breeding program has led to a range of new varieties for different cuisines, for example sushi, long grain, medium grain and fragrant rice types. Development of new varieties takes up to 10 years from parental cross to a pure seed line that boasts sound agronomic, pest and disease resistance and the desired combination of quality traits. Selection techniques vary for each generation, and for each trait. This is a huge undertaking with upwards of 6500 breeding lines assessed for physical quality each year, and more than 3000 samples assessed for cooking qualities. As new consumer trends emerge, new market opportunities for rice are uncovered such as the recent shift toward more health-conscious consumer decisions. Development of more varieties with lower glycaemic index is one avenue to explore further. For this, additional, more well-understood tools are required to measure, predict and/or actively select for this trait at different stages of the breeding and quality program. Apparent amylose content is currently the only published link available with which researchers can predict the digestibility characteristics of a given rice sample. While the correlation between these attributes is good (r2 = 0.73), it is also indicative that there are other drivers at play. This is highlighted in instances where glycaemic index can vary by up to 20 points at a given apparent amylose content. There is a gap in the understanding of which levels of starch structure, if any, can account for the differences observed in digestibility where apparent amylose content is similar. To explore this, multiple levels of starch structure were assessed in different rice varieties using a combination of novel and well-established characterisation methods. The determination of factors of starch structure relevant to digestibility in this study was intended to better understand the drivers of digestibility in rice grains. And through this, attempt to provide new tools with which to assess samples likely to exhibit a higher or lower digestibility, thus allowing for better selectivity in breeding where certain digestibility characteristics are a grain quality goal. This was achieved through the characterisation of multiple features of starch structure which were found to provide valuable input to refining the understanding of rice digestibility.

Date of Award	2020
Original language	English