Nutritional and In vitro Glycemic Properties of Selected Indigenous Tubers

Abstract

Tacca involucrata, Dioscorea angawa and Dioscorea bulbifera are tubers which are usually boiled or roasted and consumed without sauce by the rural population in the Northern part of Nigeria. This study was conducted to evaluate the nutritional and in vitro glycemic properties of three indigenous tubers (Tacca involucrata, Dioscorea angawa and Dioscorea bulbifera). These tubers were subjected to processing. A batch was processed into raw flours, another batch was boiled for 30 min and another batch boiled for 1 h after which the samples were dried at 60°C for 48 h to obtain boiled treated flour samples. The flour samples were then analysed for proximate composition, minerals, amylose/amylopectin content, alpha amylase and alpha glucosidase using -standard methods. The results of the study indicated that boiling significantly (P<0.05) increased the carbohydrate content of the raw flour samples from 79 to 81%, 79 to 84% and 85 to 88%  for Dioscorea angawa, Tacca involucrata Dioscorea bulbifera resspectively. Amylopectin content increased from (69.38±0.02%, 70.80±0.02%, 71.95±0.01%) in the raw samples to (76.56±0.05%, 74.50±0.01%, 73.32±0.01%) after 1 h boiling for Dioscorea angawa, Dioscorea bulibifera, Tacca involucrata, respectively. In vitro Alpha amylase increased its activity from (38.27±0.01 mg/g, 49.16±0.06 mg/g, 53.51±0.01 mg/g) in the raw samples to (70.29±0.5 mg/g, 65.93±0.01 mg/g, 118.76±0.03 mg/g) after 1 h boiling for Dioscorea angawa, Dioscorea bulbifera and Tacca involucrata, respectively and in vitro alpha glucosidase activities of the tubers increased from (566.11±0.01 mg/g, 603.25±0.01 mg/g, 644.43±0.04 mg/g) in the raw samples to (822.03±0.07 mg/g, 992.14±0.01 mg/g 1014.12±0.01 mg/g) in samples boiled for 1 h. Boiling these tubers for 1 h increased the rate of activity of the in vitro enzymes involved in the breaking down of starch to simple sugars.