The Research Of Membrane Separation Technology For The Enriching Concentration Of Lactic Acid Bacteria Culture

With the rapidly development of fermented dairy product industry, It's very important to research and develop high activity concentrated yoghourt starter culture for promoting the industrial process of lactic acid bacteria starter and development of fermented dairy industry. cells enriching concentration is one of the critical technology of high-activity concentrated freeze-drying yoghourt starter. At present centrifugal separation is commonly used in the industrial production, but this method has large damage to the cells and low recovery rate, and pyruvate and carbonylacyl group like diacetyl which are precipitated with cells can react with amino group in cells, resulting in the acceleration of cell death. In this paper, new membrane separation technology instead of traditionally centrifugal separation is utilized to concentrate cells, so as to determine whether this method could improve the shortage of centrifugal separation.The topics of the research include: I. six strains of Lactabacillus delbrueckii ssp. Bulgaricus and Streptococcus thermopHilus, three for each, are identified by pHysiological biochemistry test such as carbohydrate fermentation, gelatin liquefaction, hydrogen sulfide reduction, azotate reduction, amylohydrolysis, salt-tolerated, and acid-tolerated test. II. The pH of optimizing whey powder mediums before sterilization are determined through observing the state of the optimizing mediums after sterilizing and adjusting their's pH. III. KLDS1.8501 and KLDS3.8501 were used in this study. Through confirming of the optimum reaction conditions, equation of linear regression was constructed between light absorption value and viable count, with the feasibility of applying MTT method to bacteria-counting to be discussed. IV. By comparing the flux intensity and attenuation of membranes which have different apertures, the type of ceramic membrane is determined. V. The best manipulation parameters of microfiltration membrane are studied by measuring the flux intensity and the change of death rate. VI. Through one-step and two-step chemical clean respectively, five chemical abluents, HNO₃,NaOH,NaClO,Na-EDTA,and SDS are choosed to determine the best program of membrane cleaning.â…¦. Compare survival, recovery and fermented activities of membrane Separation with the ones of centrifugal separation.The results of the experiments are: I. Strains KLDS1.9201,KLDS1.9205, KLDS1.8501 are identified as Lactabacillus delbrueckii ssp. Bulgaricus; KLDS3.8501,KLDS3.0503,KLDS3.9207 as Streptococcus thermopHilus by pHysiological biochemistry test. II. The PH of the optimizing mediums of Lactabacillus delbrueckii ssp. Bulgaricus and Streptococcus thermopHilus should be respectively adjusted to 6.6 and 6.9 before sterilization. III. As to reflect the viable count exactly by MTT method, the count range of KLDS1.8501 and KLDS3.8501 must be adjusted to 5.5×106².18×10⁷CFU/mL, 6.4×10⁶⁵.12×10⁷CFU/mL, respectively. Equation of linear regressions of them were y=1.222x-0.06, y=5.759x+0.034, respectively, under the optimum reaction conditions. However, the difference between MTT colorimetric analysis antigenic and plate count method was significant in the actual application. IV. The 0.2μm(dimension) inorganic ceramic membrane is choosed to use for separating and concentrating fermentation broth of St. thermopHilus. V. The best working parameters of membrane when St.thermopHilus are separated and concentrated are determined as follows, the pressure is 0.15MPa, temperature 45℃, And in this operational condition the viability of cells could be 90%. VI. The best method of cleaning is to use 1% NaC1O×15min firstly and then by 1.5%SDS×15min. After cleaning, the water filtration ratio is 99%.â…¦. Compared with centrifugal separation, membrane Separation can increase significantly the survival, recovery and fermented activities.MTT colorimetry can express rudely changing trend of lactic acid bacteria, but it can not detect accurately the survival of Lactobacillus bulgaricus and Streptococcus thermopHilus.We concluded that membrane separation technology can be used for cells enriching concentration of LAB, and that comparing with the centrifugal separation, it has the advantages of higher separating viability and stronger fermentation ability of cells.