Correlation of pasting behaviors with total phenolic compounds and starch digestibility of indigenous pigmented rice grown in upper Northern Thailand
Background: Thailand has one of the most important rice genetic resources with white, light brown, brown, red, and purple rice bran colors. The latter believed to have potential for health benefits due to their phenolic content. Recently researchers have indicated that starch digestive enzymes, including salivary and pancreatic α-amylases and α-glucosidases, can be inhibited by phenolic compounds. Although pasting properties of rice flour are key determinants of quality significantly impacting the final product texture, there is no in-depth study on their correlation with phenolic compound and starch digestibility.
Methods: Rice flour from twelve varieties, three from each of five bran colors (white, brown, red, and purple), were evaluated for pasting properties (RVA-3D), total phenolic compounds, amylose content, resistant starch and estimated glycemic index. Simple correlation coefficients were calculated for the relationships between pasting properties (final viscosity, breakdown, setback and pasting temperature) and total phenolic compounds, resistant starch and estimated glycemic index.
Results: Within each rice variety, red and purple pigmented flours had higher total phenolic compounds (TPC) and more resistant starch than that of white flours. The TPC and resistant starch content of the flours ranged between 7.83- 47.3 mg/L and 2.44–10.50% respectively, and producing 60-80 of estimated glycemic index. Viscosity behavior showed that pigmented with low amylose rice had lower viscosity temperature than that of pigmented with high amylose rice flour, but higher in peak viscosity. Correlation coefficients of pasting temperature, final viscosity, break down and setback with TCP was observed to be inversely related to glycemic index. However, it was positively correlated to the resistant starch and amylose content.
Conclusions: Pigmented rice flour is a better source of TPC and resistant starch which in turn provides low glycemic index. This could help reduce the onset of type 2 diabetes and other related chronic diseases. In addition, this study provides impact of pasting behavior – TPC- resistant starch of rice flour relationships, which have important implication for utilization in food industry.Keywords: total phenolic compounds, amylose content, resistant starch, glycemic index
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