| Summary: | 碩士 === 國立中興大學 === 畜產學系 === 92 === Study on fermentation conditions and protectants for preservation of Lactobacillus reuteri Pg 4
Feed were supplemented with probiotics is a tendency in the recent years, in order to distribute probiotics and preservation cell counts in the feed, therefore, freeze drying was used to make powder. However, dehydration and storage can damage to cell. Therefore, addition of protectants can decrease the damage of cells during dehydration and storage. The purpose of this study was to investigate the optimum fermentation medium and the conditions of Lactobacillus reuteri Pg 4. In addition, effect of different protectants on the stability during storage of freeze dried Lactobacillus reuteri Pg 4 was studied. In the fermentation medium study, medium contain various nitrogen（yeast extract and peptone）and carbon（glucose and sucrose）sources were used for cultivation of Lactobacillus reuteri Pg 4. The results showed that the highest concentration was obtained with medium which contains yeast extract and sucrose（modify medium）. The modify medium can also reach to 9.1 log cfu/mL. The modify medium were used and performed at 37℃, 250 rpm, and pH were controlled at 5.0, 6.0, and 7.0 in the fermenter. The results showed that reached to the highest cell counts（9.3 log cfu/mL）at 12 hours of fermentation at pH 5.0. Different concentrations（5％, 10％, and 20％）of protectants including skim milk, sodium glutamate, sucrose, and maltodextrin or mix protectants were tested for their protective effect of Lactobacillus reuteri Pg 4 during freeze drying. The results showed that 10％ and 20％ skim milk were the best protectants tested along. The highest cell counts were obtained with combinations of 20％skim milk +20％sucrose（SM20S20）, 20％skim milk+ 5％maltodextrin（SM20M5）, and 20％ skim milk（SM20）. Dried powder obtained from SM20, SM20S20, and SM20M5 were stored at -20℃, 4℃, and 25℃ and storage stability were examined. The results showed cell counts of the protected powder were maintain 8 log cfu/g after 60 days of storage at -20℃ and 4℃, whereas decrease to 7 log cfu/g was obtained at 25℃ after 45 days of storage. The best protectant was obtained with SM20S20 for three different storage temperatures. In Pg 4 strain characterization assay, indicate the strain of protected with protectants still have abilities of pH, bile tolerance, and adherence to the crop epithelial cell after 60 days of storage at 4℃. From the results described above, modify medium can be used for cultivation of Lactobacillus reuteri Pg 4 and fermentation was performed at 37℃, 250 rpm, and pH 5.0 have the best growth. The better stability of freeze dried Lactobacillus reuteri Pg 4 was obtained when Lactobacillus reuteri Pg 4 cells were protected with SM20S20 during freeze drying and storaged at 4℃ resulted in cell counts of 9.8 log cfu/g.
Key words: Lactobacillus reuteri Pg 4, Fermentation conditions, Freeze-drying, Protectants.
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