Studies On Bio-transformation Of Waste Fish By Microbial Fermentation

Waste fish is rich in protein. It also contains fat and many substances with biological activity. It is good natural resources for fermentation material. Through microbial fermentation, waste fish could biotransformated into fermented products which were rich in nutrients and contained high effective complex microbial community.First,36 Bacillus strains were isolated from fish waste. Based on the performance testing of protease activity, antimicrobial activity to vibrio and ability to decompose fish waste, Four strains (FS03、FS05、FS06 and FS07) were screened successfully. Through the physiological and biochemical examinations and phylogenetic tree construction based on the 16s rDNA sequences, FS03、FS05、FS07 were the strains of bacillus subtitle. FS06 was a strain of bacillus methylotrophilus. According to the ability of decompose fish waste,2 yeast strains and 2 lactobacillus were isolated and screened from the related market products respectively.The results of nutritional determination of waste fish showed that the component of protein was 17.49%, total sugar was 0.47%, and raw fat was 5.06%. There are 17 kinds of amino acids, relatively rich in glutamic acid, arginine, Tianmen glycine. There were considerable amounts of unsaturated fatty acid in fatty acid composition. So the fish waste is a good source of nutrition.In order to improve the viable cell counts, the condition optimization for decomposing fish waste of bacillus, yeast and lactobacillus were studied by the single-factor experiments and orthogonal design. Various factors, such as waste fish,brown sugar, inorganic nitrogen source, inorganic ions, temperature, pH, inoculum volumes were studied. The results showed the medium components of bacillus were fish waste 250g/L, brown sugar 20g/L, ammonium chloride 15 g/L, magnesium sulfate 15 g/L. The optimum fermentation condition of bacillus were fermentation temperature 37℃, fish waste 250g/L, pH 7.5, inoculum volumes 6%. The medium components of yeast were fish waste 350g/L. brown sugar 40g/L, ammonium sulfate 10g/L, dipotassium phosphate 15g/L. The optimum fermentation condition of yeast were fermentation temperature 30℃, fish waste 250g/L, pH 6.5, inoculum volumes 12%. The medium components of lactobacillus were fish waste 150g/L, brown sugar 40g/L, ammonium sulfate 15g/L, magnesium sulfate 15g/L. The optimum fermentation condition of lactobacillus were fermentation temperature 35℃, fish waste 250g/L, pH 6.0, inoculum volumes 9%.The medium components of mixed culture fermentation were preliminarily screened,the result showed waste fish, brown sugar, ammonium sulfate, magnesium sulfate, dipotassium phosphate. In order to get high viable cell counts the conditions optimization for mixed culture fermentation were studied by the single-factor experiments and orthogonal test. The result showed the optimum conditions were fermentation temperature 33℃, fish waste 250g/L, the inoculum volumes 9%, the ratio of bacillus to yeast to lactobacillus 4:2:2.Fish waste was fermented by two typical yeast and lactobacillus respectively. Through sensory score evaluation, yeast and lactobacillus also could deodorize effectively in different degrees. Compared with control group, the fishy smell of fish waste was decreased significantly, odor smelled well. Yeast fermentation showed better deodorization effect than lactobacillus fermentation and the optimum inoculum volumes was 2%. In the end crude protein content was improved, especial in yeast fermentation.