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Wang R.,Jiangnan University | Wang R.,Foshan Haitian Flavouring and Food Co. | Zhang M.,Jiangnan University | Mujumdar A.S.,National University of Singapore | Jiang H.,Jiangnan University
Journal of Food Engineering | Year: 2011

Potato puree was used to prepare re-structured potato slices. The effect of salt and sucrose content on microwave freeze drying (MFD) and the variation of the dielectric properties of the potato slices were studied. Results showed that the dielectric constant (′) and loss factor (″) of the potato purees decreased significantly after freezing. Both salt and sucrose addition increased ′ and ″ of the samples at low temperatures (-25 to -5 °C). The salt content had greater influence relative to sucrose content on dielectric properties of the samples. Sucrose addition shows insignificant influence on dielectric properties of the thawing samples; while for the salted samples, ′ decreased gradually with increasing salt content and ″ increased significantly with increasing salt content and temperature. MFD drying rate was significant higher after adding salt and sugar. © 2011 Elsevier Ltd. All rights reserved.

Liu Y.H.,Sun Yat Sen University | Ye M.,Foshan Haitian Flavouring and Food Co. | Lu Y.,Sun Yat Sen University | Zhang X.,Sun Yat Sen University | Li G.,Sun Yat Sen University
Applied Microbiology and Biotechnology | Year: 2011

To obtain better performing laccases for textile dyes decolorization, random mutagenesis of Lac591, a metagenome-derived alkaline laccase, was carried out. After three rounds of error-prone PCR and high-throughput screening by assaying enzymatic activity toward the phenolic substrate 2,6-dimethoxyphenol (2,6-DMP), a mutant (Lac3T93) with remarkably improved enzymatic activity was obtained. Sequence analysis revealed that four amino acid substitutions (N40S, V55A, F62L, and E316V) were accumulated in the Lac3T93. Compared to the wild-type enzyme, the specific activity of Lac3T93 toward 2,6-DMP was increased to 4.8-fold (61.22 U/mg), and its optimal temperature and pH were changed to 60°C and 8.0 from 55°C and 7.5 of the wild-type enzyme, respectively. Furthermore, the degradation ability of Lac3T93 for textile dyes was investigated, and the new variant represented improved decolorization percentage for four industrial dyes with complex phenyl structure (Basic Blue 3, Methylene Blue, Bromophenol Blue, and Crystal Violet) and higher decolorization efficiency for Indigo Carmine than that of the parent enzyme. Furthermore, the decolorization percentage of Lac3T93 for five dyes in the absence of hydroxybenzotrizole (HBT) is clearly higher than those of the wild-type enzyme with 1 mM HBT, and HBT can further improve its decolorization ability. © 2011 Springer-Verlag.

Ye M.,South China University of Technology | Ye M.,Foshan Haitian Flavouring and Food Co. | Liu X.,Foshan Haitian Flavouring and Food Co. | Zhao L.,Foshan Haitian Flavouring and Food Co.
Biotechnology | Year: 2013

L-glutaminase could hydrolyze L-glutamine to L-glutamic acid which is an important 'Umami' substance. To obtain a salt-tolerant L-glutaminase for application in Chinese soy sauce fermentation, B. amyloliquefaciens Y-9 producing salt-tolerant L-glutaminase was isolated from mangrove sediment. The production of L-glutaminase in Solid State Fermentation (SSF) using agro-industrial residues was optimized using a central composite design of the Response Surface Methodology and the enzyme was purified which was used for further characterization including the optimum and stability of pH and temperature, effect of metal ions, substrate specificity and application to soy sauce fermentation. Under optimized conditions the experimental maximum yield of L-glutaminase reached 19.64±0.63 U gds-1 which is the highest yield obtained in SSF so far. The L-glutaminase was purified to homogeneity with final specific activity of 196.2 U mg-1 protein. The enzyme showed high activity (68% of the original activity) in the presence of 20% NaCl. The enzyme was most stable at pH 5.0 and was highly stable over an acidic pH range (3.0-7.0). These results indicate that this enzyme has a higher salt tolerance and an acidic stability. Furthermore, in Chinese soy sauce fermentation model reaction, the addition of glutaminase from B. amyloliquefaciens Y-9 was highly effective for the production of glutamic acid. This study indicates a possibility to establish economical large-scale production of L-glutaminase and this enzyme is suitable for application in soy sauce liquid fermentation with high-salt process. © 2013 Asian Network for Scientific Information.

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