Studies On ACE Inhibitory Activity And γ-aminobutyric Acid In Fermented Skim Milk By Lactobacillus

In this paper, eighty-one strains of Lactobacillus were isolated from the koumiss in Xinjiang, China.The strains were cultivated in skim milk medium and TYG broth with 1% (w/v) of L-monosodium glutamate (L-MSG) via screening. The results revealed that ACE inhibitory activity of three strains was higher than other strains and one strain changed L-MSG intoγ-aminobutyric acid(GABA) only, one strain not only produced ACE inhibitory peptides but also changed L-MSG into GABA. Identification above the five strains was done using 16S ribosomal DNA (rDNA) analysis. The results revealed that the sequence of 16S rDNA of three strains showed 99% homology to L. helveticus, one strain showed 100% homology to L. kefiranofaciens subsp. kefirgranum and one strain showed 100% homology to L. fermentum.The ACE inhibitory activity, free amino nitrogen, pH value, titratable acidity and optical density(OD) of L. helveticus ND01,E2303,D5401 and L. kefiranofaciens subsp. kefirgranum C5301-2 fermented skim milk were determined and GABA of L. helveticus ND01 and L. helveticus E2303 were determined. L. helveticus ND01 not only produced ACE inhibitory peptides but also produced GABA in fermented skim milk. The L. helveticus ND01 fermented skim milk at 37°C for 24 and 30 hours, The maximum of ACE inhibitory activity and GABA were 67.18% and 165.11mg/L, respectively. The culture medium of L. helveticus ND01 fermented skim milk would be optimized.The single factor experiments showed that the ACE inhibitory activity of 11% skim milk with 0.4% soybean or 1.5% whey powder fermented by L. helveticus ND01 improved(P<0.05) compared with the control. In orthogonal experiments, the variance analysis results were as follows: 11% skim milk with 0.4% soybean, 0.5% whey powder, 1.5% glucose and 0.003% MnSO4·5H2O, the ACE inhibitory activity reached 96.80%(P<0.001) compared with the control.