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Postprandial glycemic control is important in the prevention and therapy of type-2 diabetes and related diseases.
Carbohydrate is the main proportion of food consumed daily and the main energy source, but proper management of
type-2 diabetes requires an adequate and proper selection of carbohydrates. Therefore, this study sought to assess the
effect of processing of yam flour [white yam (Dioscorea rotundata Poir); water yam (Dioscorea alata Lam) and
yellow yam (Dioscorea cayenensis Poir)] to paste on the glycemic indices. The yam varieties were prepared into
flour and paste from which; aqueous extracts were subsequently produced. The glycemic index, starch, sugar,
amylose, amylopectin contents and amylose/amylopectin ratio were determined. Inhibitory action of the yam
products on key enzymes linked to type-2 diabetes (α-amylase and α-glucosidase) was determined. The pasting
process caused a significant (P < 0.05) decrease in the starch, sugar and amylose contents, and a significant (P <
0.05) increase in amylopectin and glycemic index of all the yam varieties except in water yam. The sugar contents of
the yams ranged from 4.36% (yellow yam) to 6.44% (white yam) for flour and 3.72% (yellow yam) to 5.07% (white
yam) for paste. Also, the amylose/amylopectin ratio ranged from 0.54 (water yam) to 0.80 (white yam) for flour and
0.33 (water yam) to 0.53 (white and yellow yams) for paste. The yam extracts inhibited α-amylase and α-
glucosidase activities in vitro in a dose-dependent pattern (1- 4mg/mL); however, the pasting process caused
significant (P < 0.05) increase in the α-amylase and α-glucosidase inhibitory activities. Therefore, it thus appears
that processing of yam varieties into paste (browned) would decrease the starch, sugar, amylose contents and
amylose/amylopectin ratio while inhibition of α-amylase and α-glucosidase activities; and glycemic index increase
(except water yam). In conclusion, water yam seems to be a better carbohydrate source for diabetic patients of all the
yams studied.
Keywords: Yam, Dioscorea spp., Glycemic index, Amylose, Amylopectin, inhibitory