Influence of microbial fermentation on the antioxidant activity of phenolic substances in Saccharomyces cerevisiae.

AIM: Using in vitro assay and eukaryotic cell model of Saccharomyces cerevisiae, we investigated the impact of microbial fermentation on the antioxidant activity of phenolic substances. METHODS AND RESULTS: Caffeic acid phenethyl ester (CAPE) and mangiferin were fermented by lactic acid bacteria (LAB), and the antioxidant activity of the fermented products was compared to that of the pure substances. This comparison was assessed using high-performance liquid chromatography (HPLC), in vitro by 2,2-Diphenyl-1-picrylhydrazyl (DPPH), and in vivo in yeast cells. The wild-type strain (BY4741) and its isogenic mutants in glutathione (Δgsh1), catalase (Δctt1), and superoxide dismutase (Δsod1) were treated with CAPE and mangiferin, fermented or not, and exposed to hydrogen peroxide (H2O2)-induced stress. The antioxidant activity was evaluated by cellular viability, intracellular oxidation, and lipid peroxidation. We expected that fermentation would change the antioxidant activity of phenolic substances. While HPLC analysis revealed changes in the composition of fermented products, significant alterations in antioxidant activity were only observed when using mutant strains. The fermentation of mangiferin increased dependency on GSH compared to the respective pure phenolic substance to resolve H2O2-induced stress. Additionally, CAPE appeared to act as a preconditioning agent, enhancing antioxidant responses, and promoting increased tolerance to H2O2 stress, and this mechanism was maintained after fermentation. CONCLUSIONS: This study highlights that fermentation impacts the enzymatic mechanism of oxidative stress resolution, even though differences could not be observed in in vitro assays or in the wild-type strain.

Role of milk and honey in the tolerance of lactobacilli to oxidative stress.

In the development of functional probiotic food, the carrier matrices should be carefully selected and optimized to ensure the highest levels of probiotic survival in the symbiotic food along storage. Because milk and honey food matrices are rich in antioxidant substances, the aim of the research was to evaluate their effect in protecting lactobacilli from reactive oxygen species (ROS) generated by the addition of hydrogen peroxide. Viability assays were performed with and without the addition of H2O2, in three different matrices: 0.9% peptone saline, 5% honey, or 12% reconstituted skim milk. The milk matrix provided protection for the Lacticaseibacillus paracasei DTA83 and Lacticaseibacillus rhamnosus DTA76. However, this protective effect was not observed in the survival of Lactobacillus acidophilus La 5. Honey solution did not maintain the viability of probiotic microorganisms exposed to hydrogen peroxide and, on the contrary, caused a significant reduction in the population of L. rhamnosus DTA76 (p < 0.001). Lower membrane lipid peroxidation due to H2O2 exposure was observed in L. acidophilus La 5 and L. rhamnosus DTA76, but this marker showed no relation with viability. It was concluded: (i) lactobacilli from the Lacticaseibacillus genus were the ones that benefited most from the lactic environment; (ii) the absence of the protective effect of honey was possibly due to the presence of Fe2+ which reacts with H2O2 to produce hydroxyl radicals; and (iii) cell viability did not correlate with membrane lipid peroxidation, and it is not a good marker to evaluate this type of damage in cells of different microorganisms.