The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the bette...The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the better known products for its contribution to the buttery aroma of dairy products. A lot of documents deal with ways to improve diacetyl concentration in food matrices. Apart from these organoleptic advantages, in a microbial ecosystem, the citrate metabolism gives selective advantages to citrate positive microorganisms. Citrate metabolism allows the LAB to use another carbon source for their growth, withstand acidic conditions and generate a “proton motive force” (PMF). Moreover, the citrate/glucid co-metabolism leads to the fast release of organic compounds known for having bacteriostatic effects. Under specific conditions, the C4?pathway liberates diacetyl which is bacteriostatic. In this review we first describe the citrate metabolism and the enzymes involved in the two homo- and heterofermentative LABLc diacetylactisandLeuconostocspp. Moreover, the way to shift the metabolic pathway toward the production of aromatic compounds is discussed for both of these fermentative types of bacteria. Finally, the selective advantages of citrate metabolism for LAB in complex microbial ecosystems are delineated.展开更多
为探讨水稻秸秆饲料化的可行性,以中粳水稻秸秆为青贮原料,研究了添加乳酸菌和米糠对水稻秸秆青贮料品质的影响。将新鲜稻草切碎后加入添加物,设乳酸菌组、米糠组、乳酸菌+米糠组,乳酸菌添加量为1 kg鲜稻草中加入0.02 g 1.6×105CF...为探讨水稻秸秆饲料化的可行性,以中粳水稻秸秆为青贮原料,研究了添加乳酸菌和米糠对水稻秸秆青贮料品质的影响。将新鲜稻草切碎后加入添加物,设乳酸菌组、米糠组、乳酸菌+米糠组,乳酸菌添加量为1 kg鲜稻草中加入0.02 g 1.6×105CFU/g乳酸菌制剂,米糠添加量为1 kg鲜稻草中加入100 g米糠,同时设对照组(无添加物)。原料装入聚乙烯袋青贮,45 d后开袋检测。结果表明,与对照相比,乳酸菌组稻草青贮料的可溶性碳水化合物含量、干物质回收率、乳酸含量和乳酸/乙酸值分别提高了60.63%、3.82%、134.78%和332.64%,挥发性脂肪酸含量、氨态氮/总氮值分别降低了53.74%、36.68%,且差异均达显著水平(P<0.05);米糠组稻草青贮料的可溶性碳水化合物含量、干物质回收率、乳酸含量和乳酸/乙酸值较对照组分别提高了31.06%、17.08%、157.10%和349.31%,挥发性脂肪酸含量、氨态氮/总氮值分别降低了44.90%、46.68%,且与对照差异均达显著水平(P<0.05)。乳酸菌+米糠组的青贮料发酵品质最佳,除酸性洗涤纤维含量与对照差异不显著(P>0.05)外,其他指标均显著优于对照(P<0.05)。pH与挥发性脂肪酸含量呈较强的正相关性,而与乳酸含量和氨态氮/总氮值呈较强的负相关性。综合各测定指标结果表明,同时添加乳酸菌和米糠能更好地改善稻草青贮料品质。展开更多
文摘The citrate metabolism has been extensively studied in lactic acid bacteria (LAB) for its aroma compound production. Among the 4-carbon (C4) by-products obtained from citrate fermentation, diacetyl is one of the better known products for its contribution to the buttery aroma of dairy products. A lot of documents deal with ways to improve diacetyl concentration in food matrices. Apart from these organoleptic advantages, in a microbial ecosystem, the citrate metabolism gives selective advantages to citrate positive microorganisms. Citrate metabolism allows the LAB to use another carbon source for their growth, withstand acidic conditions and generate a “proton motive force” (PMF). Moreover, the citrate/glucid co-metabolism leads to the fast release of organic compounds known for having bacteriostatic effects. Under specific conditions, the C4?pathway liberates diacetyl which is bacteriostatic. In this review we first describe the citrate metabolism and the enzymes involved in the two homo- and heterofermentative LABLc diacetylactisandLeuconostocspp. Moreover, the way to shift the metabolic pathway toward the production of aromatic compounds is discussed for both of these fermentative types of bacteria. Finally, the selective advantages of citrate metabolism for LAB in complex microbial ecosystems are delineated.
