Study On The Change Of Chemical Composition And Lactic Acid Bacteria In Sauerkraut During Natural Fermentation

Sauerkraut, as a kind of popular lactic acid fermented vegetable products, originated in Northeast China and North China and had a long history. It was deeply loved by the masses because of its nutrient-rich, acid fresh and crisp, solution greasy appetizers and so on. In recent years, sauerkraut with its unique nutritional value and rich resources of lactic acid bacteria, caused the close attention of nutritionists, microbiologists and micro ecologists. In the study, the dynamic changes of chemical composition and microbial indicators were monitored in the process of sauerkraut fermentation. There had a comprehensive systematic research for the diversity of lactic acid bacteria in fermented sauerkraut, using the polymerase chain reaction (PCR) combined with denaturing gradient gel electrophoresis (DGGE) molecular biology techniques, through the study of the sequence analysis of 16S rDNA V3 area. The issue had a positive significance to improve the value-added products of vegetables and to enhance the quality of sauerkraut, to promote sauerkraut industry industrialization and standardization development, for the research and development of beneficial lactic acid bacteria. Research content and conclusions of this paper was listed as follows:The content of chemical composition were monitored during sauerkraut natural fermentation. The results showed that:during fermentation, the total acid content increased, pH value gradually decreased, and finally were stabilized; Soluble protein content declining with time to steady, while reducing sugar and amino acid nitrogen content showed a decreasing trend after a slight increase, eventually reached a steady state on the fermentation 35th days. With the extension of sauerkraut fermentation time, nitrite content increased firstly and then decreased and it fluctuated in a certain range. In the 9th days occurs "nitrite peak", its content of up to 69.76mg/kg, much higher than the national standard. As environmental acidity increasing, nitrite is decomposed destroyed and the content decreased gradually.After fermentation for about the 20th days, nitrite levels were lower than 20mg/kg, in line with national standard.Microbial indicators during natural fermentation sauerkraut were analyzed, the results show that:the initial stage of fermentation, the fermentation liquid was rich in nutrients, enough oxygen, aerobic microorganisms (such as Escherichia coli, yeast, etc.) to growth and reproduction, the total number of colonies showed a rising trend, number reached nearly 108 on the fermentation 15th days. Along with the fermentation process, lactic acid bacteria become the dominant bacteria, to multiply and produce acid, inhibited the growth of other bacteria, resulting in the total number of bacteria and yeast number decreased, while Escherichia coli was not detected in the fermentation 20d, in line with food hygiene standards. In the Post-fermentation, microbial metabolism of nutrients deficiencies, fermentation rate gradually slow down or even stop, the number of lactic acid bacteria decreased, the final amount remains within the range of 104 to 105 orders of magnitude, then the presence of lactic acid bacteria at this time promoted the formation of sauerkraut "sour sweet" flavor sauerkraut and extended its shelf life.In the study, by directly extracted the total DNA of sauerkraut sample, its 16S rDNA V3 region was PCR amplified and the used DGGE molecular biology techniques systematically studied the diversity of lactic acid bacteria in sauerkraut fermentation process. DGGE profiles showed diversity of lactic acid bacteria at different fermentation periods.There is a certain degree of difference in the number of electrophoretic bands, strength and migration rates at sauerkraut different fermentation times. When sauerkraut fermented 40th days, bacterial diversity index and richness index reached its maximum,3.457 and 6.077 respectively, indicating the highest bacterial population diversity in sauerkraut; through cloning and sequencing, the similarity between the measured sequences and the lactic acid bacteria 16S rDNA V3 sequences in the known database was as high as 99%-100%. Lactobacillus was the dominant bacteria during sauerkraut fermentation, Lactococcus lactis, Lactobacillus lactis and Lactobacillus pentosus were the predominant microflora in early periods and Lactobacillus plantarum was the predominant microflora in the middle and later periods. In The study, Lactobacillus salivarius and Lactobacillus iwatensis were founded, which using traditional methods and molecular ecology methods were not isolated form the natural fermented sauerkraut. These results showed intuitively the diversity of lactic acid bacteria in the natural fermented sauerkraut, which provided a theoretical support for exploring good lactic acid bacteria fermentation agent and the fermented vegetable industry to achieve scale and standardization.