Solid-state Cultivation Of Mixed Probiotics Using Corn Bran

Corn bran, as the main by-product of corn processing industry, is mostly used as animal feed, but the utilization rate is very low because of the complex structure of corn bran. In corn bran, lignin and hemicellulose are firmly together by covalent bonds so as to form a dense mesh structure to embed cellulose in it. Aspergillus niger is known as aerobic and safety fungus in the nature and used as a kind of important industrial microorganisms. It can not only be used as microbial agents that can be added to the feed for breeding animals, but also can produce more than ten kinds of enzymes, such as cellulase, amylase, glucanase, pectinase, xylanase and phytase etc. Saccharomyces cerevisiae is served as intestinal probiotics. It can effectively maintain the intestinal health and regulate gastrointestinal peristalsis, and is also helpful in the intestinal digestion and absorption. So yeast can maintain the intestinal micro-ecology environment, protect the probiotic bacteria and repair the body of the ecological environment when the intestinal environment is destroyed. In this paper, solid-state culture of A. niger and S. cerevisiae was studied by using corn bran as main material.Firstly, the conditions of the culture medium were optimized for A. niger seed. The initial pH, speed, aeration and carbon source were investigated to optimize the nutritional and environmental conditions for improving the activity of protease, cellulase and the number of living cells. The optimized cultivation conditions for A. niger were as follows: the optimum initial pH was 5. The growth of A. niger can be inhibited when the pH was lower than 5, but,A. niger can grow well in neutral environment. The activity of enzyme was restrained when the rotation speed was more or less than 200 rpm and the aeration rate was more or less than 0.75 vvm. Under the above conditions, the cellulase activity reached 20.43 U/mL, and it was 1.52 times to initial culture condition. Industrial-grade glucose also needs to be added to improve the activity of cellulase and the number of living cells. The optimum adding amount was 15 g/L and the number of living probiotic cells reached 105 cfu/mL, the activity of enzyme was 3.45 times to initial culture condition.Secondly, solid-state culture of A. niger was studied by using corn bran as main material. Inorganic nitrogen and water content were investigated for improving the activity of enzyme and the number of living cells. Urea was selected and the best content was 0.5%. The activity of enzyme and the number of living cells was restrained when water content was more or less than 60%.Thirdly, single-factor and orthogonal experiments for wheat bran addition, cultivation period and inoculation amount were used to optimize the nutritional and environmental conditions for improving the activity of protease, cellulase and the number of living cells. The optimized cultivation conditions for A. niger were as follows:wheat bran 15% (P<0.05), inoculation amount 20%, cultivation period 7 days.Finally, the co-culture time and ratio were investigated when co-culture of A. niger and S. cerevisiae were conducted. The best co-culture condition as follows:the ratio of A. niger to S. cerevisiae was 3:1, and co-culture time was 1 day. Under the above conditions, the cellulase activity reached 622.11U/g, the protease activity achieved 605.55U/g, and the total number of living probiotic cells reached more than ten billion per gram.