An alkaline protease from Kocuria kristinae F7: properties and characterization of its hydrolysates from soy protein

Enzyme Bioprospection of Marine-Derived Actinobacteria from the Chilean Coast and New Insight in the Mechanism of Keratin Degradation in Streptomyces sp. G11C

Marine actinobacteria are viewed as a promising source of enzymes with potential technological applications. They contribute to the turnover of complex biopolymers, such as pectin, lignocellulose, chitin, and keratin, being able to secrete a wide variety of extracellular enzymes. Among these, keratinases are a valuable alternative for recycling keratin-rich waste, which is generated in large quantities by the poultry industry. In this work, we explored the biocatalytic potential of 75 marine-derived actinobacterial strains, focusing mainly on the search for keratinases. A major part of the strains secreted industrially important enzymes, such as proteases, lipases, cellulases, amylases, and keratinases. Among these, we identified two streptomycete strains that presented great potential for recycling keratin wastes-Streptomyces sp. CHA1 and Streptomyces sp. G11C. Substrate concentration, incubation temperature, and, to a lesser extent, inoculum size were found to be important parameters that influenced the production of keratinolytic enzymes in both strains. In addition, proteomic analysis of culture broths from Streptomyces sp. G11C on turkey feathers showed a high abundance and diversity of peptidases, belonging mainly to the serine and metallo-superfamilies. Two proteases from families S08 and M06 were highly expressed. These results contributed to elucidate the mechanism of keratin degradation mediated by streptomycetes.

Effect of microwave sterilization on maturation time and quality of low-salt sufu

The objective of this study was to reduce the microorganism number and salt content in pehtze by microwave sterilization. The maturation time and quality of low-salt sufu were evaluated. The microorganism inactivation rate, moisture content and water activity of the pehtze, which was used for the growth of the starter culture, showed that 4,250 W for 30 s was suitable for the preparation of low-salt sufu. With regard to the physicochemical properties of sufu, 120-day sufu samples obtained by traditional high-salt (14%) fermentation and 75-day sufu samples obtained by low-salt (4%) fermentation met the standard requirements. With regard to the sensory characteristics of sufu, the taste and after taste scores of 75-day low-salt sufu samples were significantly higher than those of 120-day high-salt sufu samples (p < .05).The overall acceptance score of low-salt sufu samples also was higher than that of high-salt sufu samples. The contents of free amino acids and the profiles of typical flavor compounds partly explained the sensory quality and shorter ripening time of sufu manufactured. The total biogenic amine contents were reduced by 46%.

Main parameters and the dynamics of volatile compounds during the fermentation of Chinese Mao-tofu from Huangshan region

The physico-chemical parameters and kinetics of the volatile compounds during the fermentation of Chinese Mao-tofu was investigated. The levels of water soluble proteins, amino nitrogen and acidity increased gradually throughout the fermentation process, while that of reducing sugars peaked after 2 days before gradually declining. The protease activity increased significantly and reached the maximum levels at day 3, then it slightly decreased. The hardness and firmness decreased during the first 3 days, but both increased subsequently. The viscosity and adhesiveness was inversely related to the hardness and firmness. Forty-four volatile compounds were identified and quantified. Correlation analysis revealed significant correlation of the content of water soluble proteins and amino nitrogen with most volatile compounds. Acidity levels were positively correlated with that of ethyl caproate and hexyl alcohol, and negatively with 2-methyl butyric acid, palmitic acid, ethyl laurate, 1-octen-3-ol and 1-nonanol. Reducing sugar content was also positively correlated with ethyl caproate.

Evaluation of autochthonous micrococcus strains as starter cultures for the production of Kedong sufu

AIMS

The technological properties of 22 micrococcus strains from traditional fermented Kedong sufu were evaluated in order to develop autochthonous starter cultures.

METHODS AND RESULTS

The proteolytic, autolytic and lipolytic activity, salt tolerance, production and degradation of the biogenic amines of six Micrococcus luteus, nine Kocuria kristinae and seven Kocuria rosea were evaluated. The results indicated that these micrococcus strains exhibited a certain technological diversity, and the results also indicated the best properties to be used in mixed starter cultures. Based on the above findings, two sets of autochthonous starters were formulated. Considering the physicochemical properties and sensory characteristics of sufu, the maturation period of sufu was shortened by 30 days. The profiles of free amino acids and peptides partly revealed the mechanism of sensory quality and shorter ripening time of sufu manufactured using autochthonous mixed starters. Compared to back-slopping fermentation, sufu manufactured with selected autochthonous starter cultures exhibited lower levels of total biogenic amines.

CONCLUSIONS

The selected strains could be used as starter to avoid the accumulation of high concentrations of biogenic amines while also maintaining typical sensory characteristics and preserving the autochthonous strains of the traditional Kedong sufu. The maturation times of Kedong sufu were shortened by 30 days with application of the autochthonous starter.

SIGNIFICANCE AND IMPACT OF THE STUDY

Autochthonous mixed starters can reduce the generation of biogenic amines, speed up the sufu maturation process and preserve typical sensory quality. Furthermore, the rotation of two sets of mixed starter cultures can effectively resist phage attack during the production of sufu.