Pre-exposure of Lactobacillus acidophilus to stress conditions impacts the metabolites and bioaccessibility of calcium and carotenoids in fermented dairy products.

This study evaluated the impact of fermentation with Lactobacillus acidophilus pre-subjected to acid, osmotic, and oxidative stress conditions on the production of metabolites and the bioaccessibility of nutrients and bioactive compounds in fermented milks and yogurts. The products were added with orange bagasse (additional calcium - Ca source) and buriti pulp (carotenoids source). Gas chromatography coupled with mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) were used to analyze the volatile and non-volatile compounds metabolites from fermentation, respectively. In vitro digestion assays (dialysis and micellization) evaluated the bioaccessibility of Ca and carotenoids. Results showed that fermentation with L. acidophilus, previously exposed to acid, osmotic, and oxidative stress conditions, increased the production of volatiles such as higher alcohols and compounds derived from amino acid catabolism (1-butanol, 1-decanol, 1-nonanol, nonanoic acid, 2-ethyl 1-hexanol, 1-methoxy-2-propanol). Also, when this microorganism was subjected to osmotic and oxidative stress, an increase in the bioaccessibility of Ca in natural fermented milks from 4.1 % to 13.3-15.5 % and in the same products fortified with orange bagasse from 5.3 % to 9.3-10.8 % (when compared to the non-stressed condition) were observed. Conversely, the use of L. acidophilus - non-stressed or subjected to oxidative stress - reduced the bioaccessibility of carotenoids in products containing buriti pulp from 9.6 % to 7.8 % and 4.1  % (in yogurts); and, from 4.1 % to 2.0 % (in fermented milks), when compared to control. Thus, the pre-exposure of probiotics to stress conditions may impact not only the sensory and biochemical characteristics of fermented products, but also the bioaccessibility of nutrients and bioactive compounds.