Study On The Respiration Of Lactococcus Lactis

Lactococcus lactis is a gram- positive and facultative anaerobe. when the heme is present, it can change the metabolism,L. lactis can form a respiratory chain and carry on aerobic respiration in the presence of heme. As a result of respiration, L. lactis has a greater growth rate and a higher survival rate, so it can raise the function as assistant starter culture. Recently, there has been a penetrating study of aerobic respiration on abroad, but haven't find related report in china.In this study, the L. lactis which could undergo aerobic respiration was selected to study its metabolism mechanism of aerobic respiration and the influence factors , in order to raise the growth rate and the survival rate of L. lactis which is used for fermentation. So this study provide proof for the research of L. lactis's respiration. We made a optimization of freeze-dry technology for the strain in order to study it further. So study on the L. lactis'aerobic respiration contribute to decreasing harm which oxygen of fermentive material doing to L. lactis'cell, providing a safe way to extending the shelf life of food.The heme was added into medium to cultivate the available strains and provided aerobic environment at the same time in the L. lactis'screening test. By detecting,, we can get the strains with a increased biomass, a higher pH and the cytochrome oxidase which showed positive ,then we could make a further test. Contrasting with the screening strains which cultivated under the condition of aerobic and anaerobic, we could carry on a test about the change of the screening strains'aerobic respiration metabolite from the changed content of lactic acid and biacetyl in the fermentation liquid; Contrasting with the changed content of ATP enzyme activity, we could carry on a test about the change of the screening strains'aerobic respiration energy metabolism from the thallus which cultivated under the condition of aerobic and anaerobic in the fermentation liquid; As the target that the screening strains'cell survival rate under the condition of aerobic and anaerobic, then determined whether we could lengthen the cell's survival time; As the target that the screening strains'centrifugate survival rate and loss percentage under different centrifugate conditions, then we could determine the best condition of the centrifugate;We could get the best freeze-dry condition when we had made a study on the strains'freeze-dry experiment.Through above experiment, we have selected a strain KLDS 4.0316 who can use heme to aerobic respiration and whose biomass increased 50% compared to the original strain cultivating without adding with heme. After 30 days storage at 4℃, the viable count of strains cultivated under condition of No Ox/No H didn't detect, while that of cultivated under condition of Ox/H was remain 108 CFU/ml. In addition, during the process of growth, the metabolite of Lactococcus lactis KLDS 4.0316 undergoing respiration when heme is present through cultivating changed, the production of lactic acid decreased 48% ,and the production of diacetyl increased 3.78 times. The H+-ATPase activity increased 3.01 times. The L. lactis's survival and loss rate of centrifuge is cut down when centrifgual force step up and the centrifuge time extend, in the final we chose 6000g×10min as it has the best effect. freeze-dry conditions with Maximum survival is the temperature -30℃,the thickness of fluid is 10mm, and the protectant is 1%cane-sugar and 4%mannitol. The survival of freeze-dry is 79%, viable count can achieve 3.2×10¹⁰ cfu/g.Base on the aerobic respiration study of strains in Lab, we selected a strain who can undergo aerobic respiration, we detected cytochrome oxidase in colony, checked it has the ability to respiration; the content of lactic acid decreased, the content of biacetyl raised, certificated the metabolism changed; H+-ATPase activity increased, revealed the metabolic energy increased, which can provided more energy, accelerated the growth rate; meanwhile, when conserved the strains in different conditions, its survival increased significantly, Validated the patent of abroad about which can extend cell survival. Though the study of centrifuge and freeze drying, we can provide reference for its used as starter culture.