A roselle (Hibiscus sabdariffa Linn.) tea extract was found to have high inhibitory activity against porcine pancreatic alpha-amylase. Hibiscus acid and its 6-methyl ester were respectively isolated as active principles from the 50% methanol and acetone extracts of roselle tea. The activity of each isolate was compared to that of structurally related citric acid, a previously known inhibitor of fungal alpha-amylase.

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Germinated grains have been known as sources of Gamma-aminobutyric acid (GABA) that provide beneficial effects for human health. This study was aimed to investigate GABA production, dietary fiber, antioxidant activity, and the effect of cooking on GABA loss in germinated legumes and sesame. The highest GABA content was found in germinated mung bean, (0.8068 g kg-1 , 24 h incubation) followed by germinated soybean, germinated black bean and soaked sesame. Beside GABA, dietary fiber content also increased in all grains during germination where the insoluble dietary fiber fractions were always found in higher proportions to soluble dietary fiber fractions. Dur results also confirmed that germinated mung bean is a rich source of GABA and dietary fibers. Microwave cooking resulted in the smallest loss of GABA in mung bean and sesame, while steaming led to the least GABA content loss in soybean and black bean. Therefore microwave cooking and steaming are the most recommended cooking processes to preserve GABA in germinated legumes and sesame.

The aim of this research was to investigate the extraction yield and physicochemical properties of sago starch extracted after enzymatic pretreatment. Sago pith was enzymatic-pretreated by varying enzyme (cellulase enzyme complex) concentration, pretreatment time, and sago pith slurry concentration. The extracted sago starch was analyzed for its properties, e.g., extraction yield, pasting and thermal properties, and in vitro starch digestibility. Sago pith contained 82% (db) starch. The extraction yield and reducing sugar released increased with enzyme concentration and pretreatment time. The optimum enzymatic pretreatment conditions were 10% (w/w) sago pith slurry, enzyme concentration of 0.25 mL (618 carboxymethylcellulose unit and 139 p-nitrophenyl-b-D-glucopyranoside unit)/g substrate, and 24 h pretreatment time, providing the highest extraction yield of 71.36% (w/w sago pith, db), while control method, without enzymatic pretreatment, provided 61.01% extraction yield. Results from pasting and thermal properties confirmed that the granular stability, resistance to shear, and crystalline perfection of sago starch were improved due to hydrothermal effect of annealing during enzymatic pretreatment. The enzymatic-pretreated sago starch also had lower retrogradation but higher starch digestibility than the control sago starch. The enzymatic pretreatment enhanced the extraction yield of sago starch and also improved its quality by the effect of annealing.

Hibiscus acid, an alpha-amylase inhibitor isolated from roselle tea, and its derivatives were compared in an inhibition test for starch digestion. An alpha-amylase-added Caco-2 system was established as a useful model to evaluate the effects of alpha-glucosidase inhibitors on starch digestion. Hibiscus acid showed weak inhibition in this model system, and the methyl ester derivatives showed even weaker or no acitivity.