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
Forty obligate heterofermentative lactic acid bacilli(HB)isolated from dairy environment as non-starter lactic acid bacteria(NSLAB)were studied regarding their potential as novel starter cultures for fermented foods.P...Forty obligate heterofermentative lactic acid bacilli(HB)isolated from dairy environment as non-starter lactic acid bacteria(NSLAB)were studied regarding their potential as novel starter cultures for fermented foods.Preliminary genotipic and phenotypic tests allowed the selection of 16 strains,identified as Limosilactobacillus fermentum(12 strains),Levilactobacillus brevis(2),Lentilactobacillus buchneri(1)and Weissella confusa(1).They were initially studied at the technological level,focusing on stress factors(low temperature,heat,salt and acidic media),growth in milk,viability after freezing and thawing and growth in cereal-based matrices.Based on this,six strains were chosen for further studies:L.brevis(LB61 and LB66),L.buchneri(LBu39),L.fermentum(LF22 and LF68)and W.confusa(W20).The selected strains grew well in wheat and gluten-free(GF)doughs,produced exopolysaccharides,acetic and lactic acid in a ratio(<1:5)that allowed the inhibition of undesirable organisms without causing off-flavours,and had good salt resistance.Among them,Weissella confusa W20 was used as starter culture for sourdough fermentation to manufacture gluten-free breads,showing noticeable improvements at the organoleptic level in comparison to GF breads fermented only with yeast.This work remarks the importance of studying the potential of wild strains to find alternative matrices beyond those from where they were isolated.With this regard,our investigation allowed the selection of six dairy strains with potential as starter cultures for bread making,which reaffirms that allochthonous strains can be suitable for sourdough preparation.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.
基金supported by the Agencia Nacional de Promoción Científica y Tecnológica(ANPCyT,Project PICT 2018-02935,Argentina)the Agencia Santafesina de Ciencia,Tecnología e Innovación(ASACTeI,Project IO-2017-00096,Argentina).
文摘Forty obligate heterofermentative lactic acid bacilli(HB)isolated from dairy environment as non-starter lactic acid bacteria(NSLAB)were studied regarding their potential as novel starter cultures for fermented foods.Preliminary genotipic and phenotypic tests allowed the selection of 16 strains,identified as Limosilactobacillus fermentum(12 strains),Levilactobacillus brevis(2),Lentilactobacillus buchneri(1)and Weissella confusa(1).They were initially studied at the technological level,focusing on stress factors(low temperature,heat,salt and acidic media),growth in milk,viability after freezing and thawing and growth in cereal-based matrices.Based on this,six strains were chosen for further studies:L.brevis(LB61 and LB66),L.buchneri(LBu39),L.fermentum(LF22 and LF68)and W.confusa(W20).The selected strains grew well in wheat and gluten-free(GF)doughs,produced exopolysaccharides,acetic and lactic acid in a ratio(<1:5)that allowed the inhibition of undesirable organisms without causing off-flavours,and had good salt resistance.Among them,Weissella confusa W20 was used as starter culture for sourdough fermentation to manufacture gluten-free breads,showing noticeable improvements at the organoleptic level in comparison to GF breads fermented only with yeast.This work remarks the importance of studying the potential of wild strains to find alternative matrices beyond those from where they were isolated.With this regard,our investigation allowed the selection of six dairy strains with potential as starter cultures for bread making,which reaffirms that allochthonous strains can be suitable for sourdough preparation.
