Low Aqueous Medium Research Articles

A modified colorimetric method for determining the activity of wheat germ lipase in low-aqueous media

Copper soap colorimetry is a common way to determine the free fatty acids of grain. However, when determining the lipase activity of grain by copper soap colorimetry its accuracy is frequently affected by the degree of mixedness between lipase and substrate. Grain lipase extraction and purification steps are quite cumbersome as well. To overcome these shortcomings, a modified colorimetric method was established for the determining of wheat germ lipase activity in a low-aqueous media. First, we partially defatted wheat germ, then adjusted it to a certain water activity, added some olive oil, extracted the free fatty acids after incubating for a period of time, then determined the absorbance of reaction system by copper soap colorimetry. Finally we obtained the activity of wheat germ lipase by calculation. The optimum conditions were: coordinated the water activity of wheat germ to 0.84, the addition of 0.75 ml olive oil per gram wheat germ and incubation for 4 h at 55 °C. It was calculated that the lipase ...

Immobilization of Lipase on Macroporous Resin and Its Application in Synthesis of Biodiesel in Low Aqueous Media

Lipase from Candida sp. 99-125 was immobilized by physical adsorption onto macroporous resins. The results showed that the nonpolar resin NKA was the best carrier used in low aqueous media. 98.98 % of degree of immobilization could be achieved when the adsorption procedure was performed in the presence of heptane. The lipolytic activity and the apparent activity recovery of lipase adsorbed on resin in heptane were 4.07 and 3.43 times higher than that of lipase adsorbed in sodium phosphate buffer, respectively. The catalytic properties of immobilized lipase for production of biodiesel in low aqueous media were studied. Immobilized lipase displayed the highest activity when the crude enzyme/resin weight ratio was 1.92:1 and the water content (water/ oil weight ratio) was 15 % at 40 °C under pH 7.4. As lipase was adsorbed on NKA in heptane to produce biodiesel, the batch conversion rate reached 97.3 % when a three-step methanolysis protocol was used. After 19 consecutive batches, the conversion rate remained 70.2 %.

A kinetic study of almond-β-glucosidase catalysed synthesis of hexyl-glycosides in low aqueous media: Influence of glycosyl donor and water activity

A variety of alkyl and aryl glycosides were investigated as substrates for almond β-glucosidase catalysed synthesis of hexyl-β- d-glycosides in low aqueous hexanol media. The rate-limiting step in the organic media was determined to be the glycosylation of the enzyme. The kinetic constants V max, K m (glycosyl donor) and V max/ K m were all influenced by the water activity and they all increased in value with increasing water activity. The increase in V max/ K m was mainly determined by the increase in V max and a plot of log( V max/ K m) versus water activity resulted in a straight line with similar slopes for all glycosides but with different absolute values and thus the most reactive substrate p-nitrophenyl glucoside was the best one in the entire water activity range studied (0.53–0.96). The preference for the two competing acceptors, hexanol and water, was not affected by the aglycon part of the glucoside. Surprisingly, the ratio between trans glycosylation and hydrolysis increased with increasing water activity. A decrease in water activity caused an increase in equilibrium yield of hexyl glycoside, as expected, but was not beneficial for the kinetically controlled yield.