Effect of dissolved oxygen on redox potential and milk acidification by lactic acid bacteria isolated from a DL-starter culture

Abstract

Milk acidification by DL-starter cultures [cultures containing Lactococcus lactis diacetylactis (D) and Leuconostoc (L) species] depends on the oxidation-reduction (redox) potential in milk; however, the mechanisms behind this effect are not completely clear. The objective of this study was to investigate the effect of dissolved oxygen on acidification kinetics and redox potential during milk fermentation by lactic acid bacteria (LAB). Fermentations were conducted by single strains isolated from mixed DL-starter culture, including Lactococcus lactis ssp. lactis, Lactococcus lactis ssp. cremoris, and Leuconostoc mesenteroides ssp. cremoris, by the DL-starter culture, and by the type strains. High and low levels of oxygen were produced by flushing milk with oxygen or nitrogen, respectively. The kinetics of milk acidification was characterized by the maximum rate and time of acidification (Vamax and Tamax), the maximum rate and time of reduction (Vrmax and Trmax), the minimum redox potential (Eh7 final), and time of reaching Eh7 final (Trfinal). Variations in kinetic parameters were observed at both the species and strain levels. Two of the Lc. lactis ssp. lactis strains were not able to lower redox potential to negative values. Kinetic parameters of the DL-starter culture were comparable with the best acidifying and reducing strains, indicating their additive effects. Acidification curves were mostly diauxic at all oxygen levels, displaying 2 maxima of acidification rate: before (aerobic maximum) and after (anaerobic maximum) oxygen depletion. The redox potential decreased concurrently with oxygen consumption and continued to decrease at slower rate until reaching the final values, indicating involvement of both oxygen and microbiological activity in the redox state of milk. Oxygen flushing had a negative effect on reduction and acidification capacity of tested LAB. Reduction was significantly delayed at high initial oxygen, exhibiting longer Trmax, Trfinal, or both. Concurrently, anaerobic acidification rate maximum Vamax was decreased and Tamax was extended. Fermentation kinetics in nitrogen-flushed milk was not statistically different from that in untreated milk except for Lc. lactis ssp. lactis CHCC D2, which showed faster reduction time after nitrogen flushing. This study clarifies the relationship between the redox state in milk and acidification kinetics of the predominant subspecies in DL-starter cultures. This knowledge is important for dairies to ensure optimized, fast, and controlled milk fermentations, leading to greater standardization of dairy products.

Transcriptome analysis of Lactococcus lactis subsp. lactis during milk acidification as affected by dissolved oxygen and the redox potential

“…lactis DSM20481 T was grown exponentially during the first 8 h fermentation and reached the stationary phase after 10 h fermentation at a cell density of 8.5 Log 10 cfu/mL. Growth kinetics of L. lactis DSM20481 T in milk was not significantly affected by treatments (data not shown), in accordance with reported effects of initial oxygen on L. lactis fermentations (Cretenet et al, 2014;Larsen et al, 2015).…”

“…We showed recently that initial levels of dissolved oxygen had an effect on acidification kinetics and the ability of L. lactis strains to decrease the redox potential in milk (Larsen et al, 2015). In this study, global gene expression of L. lactis subsp.…”

Fortification of milk with plant extracts modifies the acidification and reducing capacities of yoghurt bacteria

“…The drop in E h value of milk was explained in literature by the consumption of dissolved oxygen and the biological reducing activity of L. lactis (Jeanson et al ), and L. lactis and L. mesonteroides (Larsen et al ). To prove this hypothesis, Jeanson et al () used a mutant that could not consume dissolved oxygen and found that this mutant reduced the culture medium, which confirmed the presence of reducing activity system in L. lactis .…”

“…The decrease in E h7 value of the samples would be related to the consumption of dissolved oxygen in the first phase of fermentation followed by the production of metabolites with reducing property by the bacteria (Cachon et al ; Jeanson et al ; Larsen et al ). Living organisms are generally capable of producing antioxidants such as NADH, NADPH, glutathione and uric acid to reduce the damage of oxidative stress (Lin and Yen ).…”

Estabilidade Do Leite Ao Álcool Ainda Pode Ser Um Indicador Confiável?

“…A relação entre pH, ácido lático e número de micro-organismos foi completamente elucidada durante a década de 1920 e até hoje é explorada pela tecnologia de alimentos (1) . Essa relação ainda serve de base legal para provas que mensuram a acidez do leite brasileiro, como a acidez na escala Dornic, um parâmetro indireto para pH e contagem de micro-organismos (2) .…”