| Sufu is a Chinese traditional fermented soy product, with a high nutritional value. However, in industrialized production process, sufu primarily have mass instability, long fermentation period and so on. Pure bacterium fermented sufu and enzyme fermented sufu, which is an effective ways to solve the above problems. KeDong sufu is a typical bacterial fermented sufu. On the basis of previous work, using microbial technology studied the strain characteristics of Kocuria rosea KDF3; using enzyme technology studied the enzymatic properties of Kocuria rosea KDF3; on the basis of these researchs, using the Kocuria rosea KDF3as a leavening agent to fermente KeDong sufu, and utilizing Kocuria rosea KDF3protease enzyme prepared KeDong sufu; meanwhile, tracked and monitored sufu physical and chemical characteristics during the fermentation process; in the end, using fermentation technology optimized the fermentation medium and process parameters of the Kocuria rosea KDF3.Strains characteristic of Kocuria rosea KDF3showed that the strain was gram-positive, non-spore, strong proteolytic capacity. What’s more, the optimum growth temperature of Kocuria rosea KDF3was30℃, and the optimum pH was8.0. In10%NaCl and15%ethanol, Kocuria rosea KDF3showed strong resistance acceptability.Characterization of Kocuria rosea KDF3protease KRP3showed that the KRP3protease exhibited maximal activity at50℃and pH8.0. It was stable at pH6.0-8.0and the temperature between20℃～40℃. It was inactivate under60℃for30min, and showed high stability in the presence of10%ethanol and11%NaCl. The activity of KRP3was enhanced by the presence of Ca2+and Mn2+ions.The results of Kocuria rosea KDF3fermented the KeDong sufu showed following results. For the maturity analysis the moisture content, amino nitrogen and total acidity were reached maturity index when the sufu was fermented for90d. In terms of texture, with the extension of fermeted time the hardness of sufu became smaller. There was negative correlation between adhesiveness and hardness, from30to120d, the hardness decreased from1100g to300g, and the adhesiveness increased from4.6gsec to52gsec. For the changes of peptide, the total peak area was increased from13811.5mAUxs of30d to62941.8mAUxs of120d. The different peaks reflected the process of the protein transformed into different kinds of polypeptide gradually. For the free amino acid, from the30d to120d, the total amino acid increased from968.8mg/100g sufu to2070mg/100g sufu, and total essential amino acids increased from337.25mg/100g sufu to988.7mg/100g sufu. The concentration of glutamic acid which is umami amino acid is higher than the threshold value, and lysine that is bitter amino acid follewed. The unique flavor of sufu was formed in the cooperation of all these flavor amino acids together.The results of Kocuria rosea KDF3protease fermented sufu showed the following results. In terms of maturity and structure analysis, although extracellular protease hydrolysis the internal large protein colloidal particle making its protein colloidal particles decreased significantly and presenting some holes in the surface of the sufu, there were still some great gaps between the sufu made by protease fermenting. For the maturity and structure, the total peak area increased from10428.4mAUxs of60d to13100mAUxs of120d, and there was no significant difference. The different peaks reflected the process of the protein transformed into different kinds of polypeptide gradually. The total free amino acid increased from161.64mg/100g sufu to315.75mg/100g sufu, and the total essential amino acids increased from148.89mg/100g sufu to123.07mg/100g sufu during the60～120d. Among them, the glutamic acid largely exceed the threshold and followed by the valine.Using response surface methodology, this research optimized the Kocuria rosea KDF3culture medium and its fermentation conditions. The optimized formula of culture medium was:maltose,14.19g/L; peptone:yeast extract=1:1, and the concentration was71.42g/L; dipotassium hydrogen phosphate,5.16g/L. On this condition, the total number of bacteria colonies reached4.60x109CFU/mL. Cultivation of Kocuria rosea KDF3showed that the optimum temperature of Kocuria rosea KDF3is30℃, the optimum pH was8.0, the oscillation frequency is150r/min, in this condition the total number of bacteria colonies reached6.24x109CFU/mL.Based on the above results, Kocuria rosea KDF3can be used as a potential starter culture strain during the production of sufu. However, the protease KRP3is not fit to apply in sufu fermentation in the form of single enzyme. |
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