The Isolation Of Pediococcus Acidilactici And Studies On Its Solid-state Fermentation Conditions And Application

The problems of antibiotic residues in livestock products and resistance to antibiotics have become more serious due to the uncontrolled use of antibiotics in animal feed additives. Thus finding a substitute of antibiotics that is harmless to both humans and animals is the key to the sustainable development of the livestock industry. Some probiotics, having the ability to keep the natural balance of intestinal microflora of animals and improve their immunity and feed efficiency, have been received extensive attention in many countries over the years.One strain of probiotic, P1, isolated from a healthy pig’s intestinal tract, was identified as Pediococcus acidilactici according to the results of morphological, physiological and biochemical characteristics, and the 16s rDNA sequence analysis and phylogenetic tree construction.The effects of the carbon sources, nitrogen sources, inorganic salts, fermentation temperature, initial pH, ratio of substrate to water,seed age, inoculum size, fermentation time have on the viable count of Pediococcus acidilactici of solid-unsterile fermentation were studied by using the single-factor experiments. On the basis of previous results, the most significant factor was identified and the fermentation method was optimized by response surface method. The quadratic regression equation model of fermentation temperature, ratio of substrate to water, inoculum size and fermentation time were established. The results proved to be highly reliable, which the model could explain 94.61% of the variation in the response value and Adj R-Squared is 0.9461, Adeq precision is 19.626, C.V is 1.65%. The results showed that the optimal fermentation medium were as follows: wheat bran 50%, corn flour 50%, fish meal 0.15%, CH3COONa 2.5%, K2HPO4 0.2%, CaCO3 0.6%, NaCl 3%; and the optimal fermentation conditions were:fermentation temperature 37.5 ℃, initial pH value 7.0, ratio of substrate to water 1.0:0.75, seed age 4d, inoculum size 17%, fermentation time 4.2d.Under these conditions, the viable count of Pediococcus acidilactici reached 2.89×1010 CFU/g, compared with the theoretical expectation of 2.93x1010CFU/g, the relative error is only 1.44%.This model, is proved to be capable of predicting the actual solid-state fermentation conditions of Pediococcus acidilactici, has great significance in industry.The studies of application of Pediococcus acidilactici in pig farming showed that feeding the 0.3% Pediococcus acidilactici in weaned piglets, the average daily gain increased 6.41%, the feed conversion ratio decreased 23.44%, the rate of diarrhea decreased 67.37%, the cost decreased 24.57%, comparing to the control group (feeding basal diet); feeding the 0.2% Pediococcus acidilactici in finishing pigs. The average daily gain increased 16.95%, the feed conversion ratio decreased 20.62%, the rate of diarrhea decreased 78.43%, the cost decreased 0.63%.