Abstract: Effects of adding different nutriments in MRS medium on the growth of S.thermophilus ST-2 were examined.The optimum enrichment medium of S.thermophilus ST-2 was screened by orthogonality test.The results showed that adding maize hydrolyzates,tomato juice,beer,lactose in MRS medium obviously promoted the growth of S.thermophilus ST-2(P<0.01),but adding pepton,yeast extracts,CaCl2 in MRS medium exerted insignificantly effects on the growth of S.thermophilus ST-2(P>0.01).The optimum enrichment mediums obtained by orthogonality test consisted of adding maize hydrolyzates0.3%,tomato juice7.5%,beer5.0%,lactose1.0% in MRS medium.The living number of S.thermophilus ST-2 cultivated in the optimum enrichment medium for 24 hours at 37℃ was 4.69×109cfu/ml.Compared to controlling MRS medium,40.78 times of increase in the viable counts of bacteria was observed.

Key words: S.Thermophilus , Promoting-growth substances , Enrichment medium