α-amylase was immobilized on acid-activated montmorillonite K-10 via adsorption and covalent linkage. The immobilized enzymes were characterized by X-ray diffraction (XRD), surface area measurements, 27Al nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Surface area measurements indicate pore blockage due to linking of the enzyme in the vicinity of the pore mouth. The XRD demonstrates intercalation of enzyme upon immobilization. The NMR studies indicate that, during adsorption, tetrahedral Al sites are involved, while covalent binding occurs exclusively on the octahedral Al sites. The SEM images depict the changed morphology of the clay surface due to immobilization. The efficiency of immobilized enzymes for starch hydrolysis was tested in a batch and a fixed-bed reactor and the performances were compared. The immobilized α-amylase showed a broad pH profile and improved stability characteristics in both reactor types when compared to the free enzyme. The effectiveness factor increased in the fixed-bed reactor, implying that diffusional restrictions to mass transfer operate in the heterogeneous reaction and the use of a fixed-bed reactor leads to a reduction in these diffusional resistances. In the continuous run, 100% initial activity was maintained for 72 h, and after 96 h, >80% activity was retained.

The activity of a crude enzyme preparation extracted from hepatopancreas in the digestive tract of the giant cricket Brachytrupes membranaceus (Drury) was assayed for amylase and α-glucosidase. Amylase- and α-glucosidase-specific activities were estimated to be 3.31 and 13.02 UI/mg, respectively. The zymogram analysis of the crude enzymatic extract showed the existence of two isoforms of amylase. For α-glucosidase, the zymogram analysis showed one form only. Both the amylolytic activities exhibited optimum pH at 6.6 and 7.0, respectively, for amylase and α-glucosidase. As for optimum temperature, values were estimated at 55 and 40 °C for amylase and α-glucosidase activities, respectively. Amylase activity was found to be stable at pH 6.6–7.6 and temperatures up to 55 °C. The corresponding values for α-glucosidase were pH 6–7 and up to 40 °C. Amylolytic enzymes of B.membranaceus were activated by Ca2+ and Ba2+ and inhibited by chemical agents such as ethylenediaminetetraacetic acid, 4-chloromercuribenzoic acid and dithionitrobenzoic acid. The analysis of hydrolytic products after soluble starch hydrolysis by the enzyme preparation from the digestive tract of B. membranaceus by thin layer chromatography revealed that glucose and maltose were the major products. The present study showed that these amylolytic enzymes play a fundamental role in energy production for this insect.

Physico-chemical properties of dietary fibres might be involved in metabolic control, particularly of the postprandial blood glucose response. The aim of the present study was to look at the effects of the content of soluble fibres and of the particle size of solid fibres on in vitro and in vivo starch hydrolysis and on the subsequent glucose absorption as well as the triacylglycerolaemia. Two sources of dietary fibres, one, with soluble fibres (beet pulp), the other with mostly insoluble fibres (wheat bran), were added at the rate of 60 g/kg to a meal simulating human food. The fibre sources were ground in order to obtain two different particle sizes (250 and 500 μm). Beet pulp decreased significantly (P < 0·05) initial in vitro hydrolysis whereas wheat bran increased starch hydrolysis in the first 10 min. Wheat bran and beet pulp, whatever its particle size, lowered the post-prandial triacylglycerol response. No significant effect was found with dietary fibre-supplemented diets on postprandial glycaemic and insulinaemic values. High correlation was found between initial in vitro starch hydrolysis and mean areas under the insulinaemic curves. This in vitro model can be used to predict initial in vivo digestion of carbohydrates from complex foods.