Screening Of LAB Strains Isolated From Minority Natural Fermented Dairy Products With High-acetaldehyde Producing And Optimizing Their Fermentation Conditions

The main purpose of this paper is to select the high-acetaldehyde production Lactic acid bacteria (LAB) from 103 strains isolated from the natural fermented milk which were sampled from the minority region of Qinghai,Mongolia,Xinjiang,Inner mongolia an so on. By first screening, further screening and single factor fermentation and L9(34)orthogonal design experiments, the strains of of higher-acetaldehyde production and the optimal fermentation conditions were determined . The main results were as follows:The first step:First screening and Further screening9 strains which have higher-acetaldehyde producting isolated from 103 lactic acid bacteria. Among of 9 strains,2 were S. thermophilus (S5,S11), 1 was Lb. dellbrueckii subsp. bulgaricus(L6), 1 was Lactococcus lactis subsp. cremoris (A29), 1 was L. casei. subsp. Pseudoplantaurm(QH3-6-1),2 were L. acidophilus(QH3-6-2,QH3-1-1), 1 was L. helveticus(QH3-1-2), 1 was L. gasserri (QH5-1)In the fermentation process in different LAB,from the variance of acetaldehyde,we can see that lactobacillus strains results of acetaldehyde is significantly higher than lactococcus strains. The average value of acetaldehyde reached 47.30μg/ml in L.acidophilus.But the acetaldehyde of lactococcus strains is about 10μg/ml.From the variance of free amino nitrogen(FAN),we can see that Lactobacillus protein degradation capacity will be greater than lactis.The average value of FAN in Lb. dellbrueckii subsp. bulgaricus to achieve 6.68mmol/ml. But the FAN in lactococcus strains is lower or nearly exist.In fermented indexes correlation coefficient analysis:Significant negative correlation existed only between TA and pH value in lactococcus strains (p<0.001); The rest is poor correlation(P>0.05). But from the fermented indexes correlation analysis in Lactobacillus. The result showed that the correlation between inoculation viable count and TA is negative ( P<0.05); the negative correlation existed between pH value and TA (p<0.05); pH value and FAN hassignificant negative correlation(p<0.001);.the significant positive correlation existed between TA and acetaldehyde ( P<0.001).The second step: single-factor test processIn the single-factor test process, the results were as follows: The effects factors of acetaldehyde in 9 strains Lactic acid bacteria are different. Adding the threonine has significant impact on the results of acetaldehyde in all of LAB.Meanwhile Mn ions, vitamin C, sucrose have notableable enhancement effect.Inoculation viable count cannot ascertain for acetaldehyde production.The concentration of O2,adjust acidity inhabit the production of acetaldehyde.The third step:orthogonal test processIn Orthogonal test process,the variance analysis results were as follows: Only a few factors has correlation(P<0.05), there factors each other may even be inhibiting role.