Analysis of factors related to browning of red sour soup during fermentation.

As a traditional fermentation food, red sour soup (RSS) is very popular in China. However, browning is always occurred during the process of fermentation, which influences the sensory quality of RSS and limits its further application. Thus, it is meaningful to elucidate the main factors related to browning during the process of fermentation. Herein, the changes in various factors related to browning from group spontaneous (RSS-SF) and inoculant fermentation (RSS-IF) were determined and analyzed. Firstly, the activity changes of enzymes related to browning indicated that browning of group RSS-SF and RSS-IF during fermentation was not related to enzymatic browning. Secondly, path analysis revealed that the main factors related to non-enzymatic browning of group RSS-SF and RSS-IF were oxidation of polyphenol and degradation of ascorbic acid (Vc). The results of this study not only identifies the main factors associate with browning of RSS, but also provides foundation on how to control the browning of RSS in further study.

Controllable preparation of chitosan oligosaccharides via a recombinant chitosanase from marine Streptomyces lydicus S1 and its potential application on preservation of pre-packaged tofu.

Chitosan oligosaccharides (COSs) are widely applied in many areas due to its various biological activities. Controllable preparation of COSs with desired degree of polymerization (DP) via suitable chitosanase is of great value. Herein, a novel glycoside hydrolase (GH) family 46 chitosanase (SlCsn46) from marine Streptomyces lydicus S1 was prepared, characterized and used to controllably produce COSs with different DP. The specific activity of purified recombinant SlCsn46 was 1,008.5 U/mg. The optimal temperature and pH of purified SlCsn46 were 50°C and 6.0, respectively. Metal ions Mn2+ could improve the stability of SlCsn46. Additionally, SlCsn46 can efficiently hydrolyze 2% and 4% colloidal chitosan to prepare COSs with DP 2-4, 2-5, and 2-6 by adjusting the amount of SlCsn46 added. Moreover, COSs with DP 2-4, 2-5, and 2-6 exhibited potential application value for prolonging the shelf-life of pre-packaged Tofu. The water-holding capacity (WHC), sensorial properties, total viable count (TVC), pH and total volatile base nitrogen (TVB-N) of pre-packed tofu incorporated with 4 mg/mL COSs with DP 2-4, 2-5, and 2-6 were better than those of the control during 15 days of storage at 10°C. Thus, the controllable hydrolysis strategy provides an effective method to prepare COSs with desired DP and its potential application on preservation of pre-packed tofu.