Effects of Nicotinic Acid on Lactic Acid Fermentation of Streptococcus bovis by an in Vitro Method

The effects of nicotinic acid on lactic acid fermentation of Streptococcus bovis were investigated by an in vitro method in this experiment. One-factor completely randomized design w as used. The experiment consisted of four groups,in w hich four levels of nicotinic acid [0( control),0.05,0.25 and 0.50 mg /mL,respectively]w ere supplemented in the culture medium,each group had four replicates. After culturing for 0,2,4,6,12 and 24 h under 39 ℃,the bacteria density and pH of culture medium w ere determined; after culturing for 12 h,the lactic acid fermentation parameters and nicotinamide adenine dinucleotide( NAD) concentrations of cultured medium w ere determined. The results show ed as follow s: w ith the increase of nicotinic acid supplemental level,the bacteria density show ed a decreasing tendency,and the average value of that from 0 to24 h in 0.50 mg /mL nicotinic acid group w as the low est,w hich w as significantly low er than that in the other groups( P0.01). The supplementation of nicotinic acid significantly increased culture medium pH from 2 to24 h( P0.05 or P0.01). The supplementation of nicotinic acid had no significant effects on the glucose degradation rate per density unit of bacteria( P0.05),but the lactic acid production per density unit of bacteria and lactic acid production efficiency w ere significantly decreased( P0.05 or P0.01); the activity of lactate dehydrogenase in experimental groups w as significantly higher than that in control group( P0.01 or P0.05).Oxidation state NAD( NAD+) concentration was not affected by nicotinic acid( P0.05),while reduction state NAD( NADH) concentration w as increased w ith the increase of nicotinic acid supplemental level,and the differences among groups w ere significant( P0.01). Under this experimental condition,nicotinic acid can inhibit the proliferation of Streptococcus bovis,keep glycolysis occurring by ensuring steady supplementation of NAD+resulting in lactic acid production reducing,and ultimately increase culture medium pH. The supplemental level of 0.50 mg /mL has the best performance.