| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 89 === Eight strains of lactic acid bacteria, including Bifidobacterium longum 15708 and B6, Lactobacillus acidophilus LA-1 and N1, Lactobacillus bulgaricus 448 and 449, Streptococcus thermophilus 573 and MC were investigated for their antimutagenicity against N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) by bacterial system (Ames test) and mammalian cell system (Comet assay and MTT cell viability assay). In Ames test, the higher antimutagenicity was shown in milk cultured with B. longum B6 and L. acidophilus LA-1 (95.3﹪and 93.8﹪). After the preincubation of the cultured milk for 30 min, the antimutagenicity of all strains expect B. longum B6 and L. acidophilus LA-1 were increased. To study the antimutagenicity of whole cell, casein (one of the milk compounds) and selected metabolites (cystein), MNNG-binding capacity of the whole cell was found and they could reduce the amount of His+ revertants in Ames test. The antimutagenicity of cystein increased with the increase of the amount but casein was weak. The antimutagenicity of lactic acid bacteria was due to a desmutagenic action but not a bio-antimutagenic action. Both in Comet assay and MTT assay, the milk cultured with B. longum B6、L. acidophilus LA-1、 L. bulgaricus 449 and S. thermophilus MC exhibited higher protection against MNNG-induced DNA damage and cyctoxicity in Intestine 407 cell. The eight strains of lactic acid bacteria did not reduce the nitrate to nitrite. The milk cultured with lactic acid bacteria and MRS cell-free supernatant could inhibit the growth of five strains of nitrate-reduction bacteria. MNNG cannot induce formation of reactive oxygen species and lipid peroxidation to increase oxidative stress.
In this study, MNNG, a direct-acting mutagenic/carcinogenic compound, was used as a representative compound for N-nitroso compounds and the milk cultured with lactic acid bacteria shown strongly inhibited the mutagenicity of MNNG. The results showed that the antimutagenicity of cultured milk may due to the MNNG-binding capacity of whole cell and some metabolites produced during fermentation (such as thiol-containing breakdown products of protein). We postulate that the lactic acid bacteria may reduce the damage cause by nitrite in vivo, if them could not reduce nitrate to nitrite and decrease the production of nitrite.
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