High Viscosity And Low Postacidification Of Yoghurt Culture And Its Application

The active research and development of the yoghurt starters had great significance in improving the quality of yogurt and the level of starters with the rapid development of dairy industry in China. In this paper, A compose of PZST4-PZLB5 with characteristics of high viscosity and low acidification were picked out by fermenting milk with a single strain or two strains of starter, in order to solve two major problems (low viscosity and serious postacidification) of commercial yogurt in shelf. Specific conclusions were as follows:(1) Six strains of S. thermophilus and Five strains of L. bulgaricus were isolated and purified from commercial starters.A compose of PZST4-PZLB5 was selected by fermenting milk with a single strain or two strains of starter, with G027 as the control. The product showed its special properties: high viscosity and low acidification.(2) The media and culture condition for PZST4 were optimized. The optimum medium was: glucose 13.3g/L, soy peptone 8.9g/L, yeast extract 8.9g/L, beef powder 8.9g/L, Na₂HPO₄ 6.75g/L, NaH₂PO₄ 16.75g/L and MgSO₄·7H₂O 100mg/L. The optimum culture condition were: temperature 37℃, inoculums 5%, initial pH 6.8, cultivation time 16h.(3) The media and culture condition for PZLB5 were optimized. The optimum medium was: glucose 13.3g/L, soy peptone 8.9g/L, yeast extract 8.9g/L, beef powder 8.9g/L, sodium citrate 1.25g/L, sodium acetate 3.125g/L, K₂HPO₄ 1.25g/L, MgSO₄·7H₂O 200mg/L and MnSO₄·5H₂O 50mg/L. The optimum culture condition were: temperature 37℃, inoculums 5%, initial pH 6.5, cultivation time 18h.(4) The proportion of S. thermophilus and L. bulgaricus was optimized. The result showed that: when the ratio of PZST4 and PZLB5 was 50:1, the yogurt showed its good property of high viscosity and low postacidification.