Effect of different formalin concentrations on some species of lactic acid bacteria in raw milk

Abstract

The influence of formalin at 0.008,0.012,0.016 and 0.020% concentrations on the some species of lactic acid bacteria such as Lactobacillus acidophilus ,Streptococcus thermophilus (Streptococcus salivarius subsp. thermophilus), Leuconostoc dextranicum, Lactobacillus bulgaricus( Lactobacillus delbrueckii subsp. bulgaricus) and Bifidobacterium animalis subsp. lactis in raw milk.The results were revealed that the addition of formalin to milk had obvious effect on all kinds of bacteria used and the effect was either bacteriostatic or bactericidal and this mainly depend on formalin concentration , kind of bacteria and period of exposure, in addition, the influence on acid development by lactic acid bacteria , The results indicated that 0.008% concentration was inhibitory for all bacteria used and the effect depend on the exposure time and the kind of bacteria.Formalin at 0.012% had bacteriostatic effect on Leuconostoc dextranicum, Lact. bulgaricus ,Strept. thermophilus and Lact. acidophilus , while the bacteria Bifidobacterium resisted this concentration for 2 days and 0.016% formalin was bactericidal after 3 days of exposure. The effect of concentration 0.02% was bactericidal for more than two days for type of bacteria.