Enzymatic Synthesis of Sucrose-6-acetate by a Novel Immobilized Fructosyltransferase From Aspergillus sp. GX-0010.

BACKGROUND: Sucralose is an ideal food sweetener and sucrose-6-acetate (s-6-a) is a key intermediate for synthesis of sucralose. Synthesis of s-6-a was studied by free fructosyltransferase (FTase) from Aspergillus oryzae. Because of the limitations of free enzyme in stability and reusability, a FTase obtained from the new isolated Aspergillus sp. GX-0010 was immobilized and investigated for the potential of s-6-a synthesis. OBJECTIVES: The synthesis of s-6-a with sucrose and glucose-6-acetate (g-6-a) by immobilized fructosyltransferase (IFTase) from a novel Aspergillus sp. GX-0010 was studied, and its synthesis conditions were also optimized. MATERIALS AND METHODS: Aspergillus sp. GX-0010 was isolated. The effects of reaction time, ratio of g-6-a to sucrose, pH, substrate (sucrose and g-6-a) concentrations, IFTase concentration and temperature on the synthesis of s-6-a were investigated. RESULTS: IFTase was able to catalyze sucrose and g-6-a to synthesize the s-6-a. Thermal and pH stability of IFTase were promoted once compared to the FTase. The optimal condition for IFTase catalysis was obtained at 50 °C, 60 min reaction time, pH 6.5, 1:2 ratio of g-6-a to sucrose and 35.0 g.L-1 concentration of enzyme. Under this optimal condition, a g-6-a conversion rate of 24.96% was reached. CONCLUSIONS: This study showed IFTase has a great potential in the biosynthesis of s-6-a, a key intermediate of sucralose synthesis.

An innovative method for preparation of acid-free-water-soluble low-molecular-weight chitosan (AFWSLMWC).

The ozone generated from compressed oxygen by a laboratory-scale corona discharge generator was used for the preparation of acid-free-water-soluble low-molecular-weight chitosan (AFWSLMWC). Factors affecting the percent yield of AFWSLMWC were studied in batch experiments. AFWSLMWC with a molecular weight of 4.3-13.1kDa was obtained. IR spectra demonstrated that the chemical structures of AFWSLMWC were not modified during the depolymerisation process. There was no significant change of the total degree of deacetylation (DD) of AFWSLMWC, compared with the initial chitosan. The method is promisingly suitable for scale-up manufacture of acid-free-water-soluble low-molecular-weight chitosan.

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards.

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards is investigated. The UV absorbance of a pure chitosan solution is contributed additively by the N-acetylglucosamine and glucosamine residues; the absorbance divided by the total molar concentration of the residues (A/c(t)) is linearly related to the degree of acetylation (DA). Using acetyl glucosamine and glucosamine hydrochloride as standards in 0.1M hydrochloric acid solution, the equation obtained by linear regression is A/c(t)=3.3615 DA+0.0218, R(2)=0.9958. The DA of the analytical sample (m milligram of chitosan in V liters solution) can be calculated by.