Studies On Diacetyl Produced By Lactic Acid Bacteria In Traditional Fermented Diary Product

Citrate-utilizing lactic acid bacteria play an important role in many food processes.They are responsible for the production of the flavoring compound diacetyl.102 lactic acid bacteria ,which isolated from traditional dairy product were subjected to producing diacetyl.According to diacetyl yield detected by O-phenylenediamine spectrophotometric method,we got 10 high diacetyl-producing strains.Namely L. acidophillus QH3-6-2 and QH3-1-1,L. casei QH3-6-1,L. helveticus QH3-1-2,L. bulgaricus L6,L. gasserri QH5-1,Lactococcus lactis A29,Leuconostoc M11,S. thermophilus S5 and S11.The diacetyl yield of L. acidophillus QH3-6-2 is maximum in the all,reach to 109.76μg/mL.The fermenting conditions were optimized using single factor experiments,that is to say to confirm the factors influencing diacetyl yield. The addition of Mn²⁺ ion,sucrose,glycine and Vc were significant influence to L. acidophillus QH3-6-2 and QH3-1-1,L. casei QH3-6-1,L. S. thermophilus S5. The addition of Mn²⁺ ion,sucrose, glycine and citric acid were significant influence to L. helveticus QH3-1-2 and L. gasserri QH5-1. The addition of citric acid,glucose,glycine and Vc were significant influence to S. thermophilus S11. The addition of Cu²⁺ ion,glucose,glycine and Vc were significant influence to Lactococcus lactis A29.While the addition of Mg²⁺ion,sucrose,glycine and Vc were significant influence to bulgaricus L6 and Leuconostoc M11..In orthogonal design experiment,according to optimization medial,the diacetyl yield of strains had greatly improved. The medial's optimum condition of L. acidophillus QH3-6-2 and QH3-1-1,L.casei QH3-6-1 and L. helveticus QH3-1-2 were adding Mn²⁺ to0.15mg/100ml,adding sucrose to 1.00 g/100ml, adding glycine to 0.20%, adding Vc to 0.10%; The medial's optimum condition of L. gasserri QH5-1 were adding Mn²⁺ to0.05mg/100ml,adding sucrose to 2.00 g/100ml, adding glycine to 0.80%, adding Vc to 0.10%;The choose of high-diacetyl producing lactic acid bacteria and the study of factors influencing diacetyl yield,which settele the foundation of diacetyl formation and flavored yoghurt.