Optimization of maltooligosyl fructofuranosidesproduction by recombinant β-cyclodextrin glycosyltransferase / 生物工程学报

Coupling sugar is a kind of new sweetener which can substitute sucrose. It has a good application prospect in food, medicine and other fields because of its good coloration, water retention and anti caries. The purpose of this study was to find cheap and easily available donor and acceptor, and to optimize the preparation process of coupling sugar by using β-cyclodextrin glycosyltransferase from Bacilluscirculans 251. Using sucrose as acceptor, the factors of preparing coupling sugar was optimized, including enzyme dosage, starch types, temperature, pH, ratio of starch/sucrose, and cooperation of isoamylase and β-CGTase. When 105 g/L potato starch and 95 g/L sucrose was used as substrates, the yield of coupling sugar reached 88.4%, which was catalyzed by 13.5 U/g immobilized β-CGTase and 45.0 U/g isoamylase under the conditions of pH 5.5 and 40 °C for 21 h. In this study, isoamylase and β-CGTase were used to prepare coupling sugar innovatively. This method had obvious advantages in yield and cost, which laid both theoretical and experimental foundation for the industrial enzymatic preparation of coupling sugars.

Extra-cellular isoamylase production by Rhizopus oryzae in solid-state fermentation of agro wastes

Extra-cellular isoamylase was produced by Rhizopus oryzae PR7 in solid-state fermentations of various agro wastes, among which millet, oat, tapioca, and arum (Colocasia esculenta) showed promising results. The highest amount of enzyme production was obtained after 72 h of growth at 28°C. The optimum pH for enzyme production was - 8.0. Among the various additives tested, enzyme production increased with ions such as Ca2+, Mg2+ and also with cysteine, GSH, and DTT. The enzyme synthesis was reduced in the presence of thiol inhibitors like Cu2+ and pCMB. The surfactants like Tween-40, Tween-80 and Triton X-100 helped in enhancing the enzyme activity. The production could be further increased by using the combinations of substrates. The ability to produce high amount of isoamylase within a relatively very short period and the capability of degrading wastes could make the strain suitable for commercial production of the enzyme.