Effect of processing on in vitro glycemic indices and carbohydrate catabolizing enzyme inhibitory properties of some tropical grain legumes

Abstract

Background: Glycemic index (GI) is often used as a measure of how a particular food can elicit rise in blood glucose and low GI foods have often been advocated as  therapeutically important in managing  hyperglycemia. Legumes are important staple foods especially in developing countries due to being cheap but rich sources of proteins. This study sought to investigate the effect of processing (roasting and boiling) on the glycemic indices, soluble sugar and starch contents as well as the α-amylase and α-glucosidase inhibitory properties of some tropical grain legumes; soybean (Glycine max (L.) Merrill), African yam bean (Spenostylis stenocarpa Harms) and bambara groundnut (Vigna subterranea (L.) Verdc).
Methods: Each sample was divided into three portions; one portion was roasted, another boiled, while the last portion was not processed. Thereafter, the samples  were analyzed for their in vitro glycemic indices, soluble sugar and starch contents as well as, in vitro α-amylase and α-glucosidase inhibitory properties.
Results: The result revealed that roasting caused a decrease in the glycemic indices, starch and sugar contents of the samples. In addition, roasting also caused an increase in the α-amylase and α-glucosidase inhibitory property of all samples.
Conclusion: Hence, roasting of the legume grains appeared to be a better processing method in that it led to low soluble sugar and starch content, with a concomitant decrease in their glycemic indices as well as increased α-amylase and α- glucosidase inhibitory properties which are good qualities for potential  antidiabetic food and food components; nevertheless, roasted bambara groundnut appeared to be the most promising.

Key words: Legume grains, Thermal processing, Glycemic response, Hyperglycemia