Location: Grain Quality and Structure ResearchTitle: Digestibility of rice (Oryza sativa L.) flours and starches differing in amylose content Author
Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2011
Publication Date: 8/10/2011
Citation: Zhu, L., Liu, Q., Wilson, J.D., Gu, M. and Shi, Y. 2011. Digestibility of rice (Oryza sativa L.) flours and starches differing in amylose content. Carbohydrate Polymers. 86:1751-1759. Interpretive Summary: Rice is second only to maize in world production and a primary staple in Asia. The objectives of this study were to determine the digestibility of rice starches with a wide range of amylose content, including a newly developed rice variety with greater than 50% amylose content. Amylose content was positively correlated with resistant starch and total dietary fiber content in rice flours containing from 1.7 to 55% amylose. Compared to low-amylose rice and waxy rice starches, the intermediate-amylose rice starch had a higher proportion of amylose as well as longer amylopectin chains. These chains have the ability to form more stable double helices and stronger crystallites reducing enzyme access. The newly developed high-amylose rice (55%) showed a predominantly B-type x-ray pattern, greater proportion of long amylopectin branch chains, a higher gelatinization temperature and semi-compound starch granules which may be attributed to it increased resistance to starch digestion. Determining factors affecting starch digestibility is critical with regard to creating unique functional and nutritional foods.
Technical Abstract: Digestibility of starches in four rice samples with amylose content (AC) from 1.7 to 55.4%, including a newly developed high-amylose rice, was investigated. An in vitro enzymatic starch digestion method an an AOAC method were applied to correlate rapidly digestible starch (RDS), slowly digestible starch (SDS), resistant starch (RS) and total dietary fiber (TDF) content with the AC in the samples. SDS content decreased and RS and TDF content increased with the increase in AC. The low-amylose rice (AC=16.1%) had weak granules and was lower in RS and TDF content even though it had a higher AC compared to waxy rice. The digestibility of the starches was not correlated with granule size. The newly developed high-amylose rice starch exhibited a predominant B-type x-ray diffraction pattern, a great proportion of long chains in amylopectin, high gelatination temperature and semi-compound starch granules which are attributed to its increased resistance to enzyme digestion.