| Summary: | 碩士 === 東海大學 === 畜產學系 === 88 === The study was conducted to select slime-producing lactic acid bacteria for manufacturing ropy yogurt, in order to replace the addition of pectin in the traditional yogurt, and to save the cost of production and improve the quality of yogurt.
Ten strains of commercial lactic acid bacteria, five modified media (MEPS-1, MEPS-2, MEPS-3, MRS plus broth and Elliker broth), four incubation temperatures (27, 32, 37 and 42℃) and three incubation times (8, 16 and 24 hours) were used in the experiments. The results showed that the thread forming property of MEPS-2 medium（9% SNF skimmilk containing 0.35% yeast extract, 0.35% peptone and 5% lactose）under 32℃ at 16 hours was significantly higher than other treatment combinations (P<0.05), so using it as the selective conditions.
Twelve commercial fermented dairy products were collected and then the above selective conditions were used to select the slime-producing lactic acid bacteria. It was found that five products named Ⅰ, Ⅱ, Ⅲ, Ⅳ and Ⅴ, had the thread forming property. After a series of isolation procedures, four slime-producing strains named A1, A2, B2 and E were purified. A1 and A2 were identified as Streptococcus thermophilus, and B2 and E were identified as Lactobacillus bulgaricus.
According to the combination of rod and coccus to match A1, A2, B2 and E. The change of qualities during four-weeks storage of 10% SNF yogurt made with L+S, A1+B2 or A2+E culture incubated at 32℃ and 42℃ was determined. The results showed that, the thread forming property, viscosity , syneresis and lactic acid bacterial counts of A1+B2 and A2+E sets were significantly better than L+S set when incubating at 32℃ or 42℃ (P<0.05), and 32℃ group was better than 42℃ group. The sensory evaluation results of ropy and traditional yogurt showed that, A1+B2 and A2+E sets had lower syneresis, higher viscosity, smoother texture and higher overall aceeptiablity.
Evaluating the qualities of 12% SNF yogurt made with Lactobacillus bulgaricus CCRC 14098 (L) + Streptococcus thermophilus CCRC 12268 (S), L+S+A1, L+S+A2, L+S+B2 and L+S+E culture incubated at 27, 32, 37 and 42℃. The results showed that, the thread forming property, viscosity and syneresis of L+S+A1, L+S+A2, L+S+B2 and L+S+E sets were significantly better than L+S set (P<0.05), and 32℃ group was significantly better than others (P<0.05).
Comparing the qualities of ropy yogurt and traditional yogurt containing pectin. It was found that, the thread forming property and viscosity of traditional yogurt were significantly increased with the amount of SNF and pectin increased (P<0.05), and the syneresis was significantly decreased with the amount of SNF and pectin increased (P<0.05). In addition, the thread forming property, viscosity and syneresis of ropy yogurt were still significantly better than the traditional yogurt containing 0.5% pectin (P<0.05).
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