2.6. a-Glucosidase inhibitory assay
This assay was carried out to investigate the in vitro inhibitory activity of EESS on sucrase and maltase (aglucosidases). Although a-glucosidase isolated from yeast is extensively used as a screening material for a-glucosidase inhibitors, the results did not always agree with those obtained in mammals. Therefore, we used a small intestine homogenate of a mouse as a-glucosidase solution because we speculated that it would better reflect the in vivo state.The inhibitory effect was measured by slightly modifying the method used by “Dahlqvist” [24]. After 20 hours of fasting, part of the animals’ small intestine immediately below the duodenum and immediately above the cecum was cut, rinsed with ice-cold saline, and homogenized with 12 mL of maleate buffer (100 mM, pH 6). The homogenate was used as a-glucosidase solution. The assay mixture consisted of 100 mM maleate buffer (pH 6), 2% (w/v) of each sugar substrate solution (100 ml), and the sample
extract (20e640 mg/mL). The mixture was preincubated for 5 minutes at 37_C, and the reaction was initiated by adding crude a-glucosidase solution (50 ml), followed by incubating the mixture again for 10 minutes at 37_C. The amount of glucose released in this reaction was determined by a commercially available glucose estimation kit (Span Diagnostic Ltd., Mumbai, India). The rate of carbohydrate decomposition was calculated as a percentage ratio to the amount of glucose obtained when the carbohydrate was completely digested. The rate of prevention was calculated by the following formula: Inhibition rate (%)Z[{(amount of glucose produced by the
positive control) e (amount of glucose produced by the addition of EESS) e (glucose production value in blank)/ (amount of glucose produced by the positive control)}]_100.