Evaluating probiotic survival during in vitro gastrointestinal digestion of elderly targeted fermented milk formulations

The aging process is associated with physiological changes that can compromise the overall health and the gastrointestinal tract. High-protein fermented milks stand out as dietary alternatives, as they may support health and help preserve muscle mass, contributing to prevent conditions such as sarcopenia, which is common in this age group. Furthermore, this matrix may serve as a vehicle for probiotics, which can help balance the gut microbiota and promote healthy aging. However, to confer these benefits, probiotics must remain viable until they reach the intestine, highlighting the importance of evaluating the effect of the protein matrix on their resistance to digestion. Thus, aiming to develop probiotic high protein fermented milk formulations for the elderly population, this study evaluated the viability of Lacticaseibacillus rhamnosus during in vitro gastrointestinal digestion. Two formulations of fermented milk were prepared by standardizing milk to 14% total solids and 6% protein using either whey protein isolate (WPI) or calcium caseinate (CC). These formulations were inoculated with 3% of activated L. rhamnosus and incubated at 37°C for 15h. The fermented milks were then subjected to in vitro simulated digestion according to INFOGEST protocol, under older adult conditions. The probiotic viability was tracked during digestion. All experiments were performed in triplicate. The effects of the digestive process, the dairy matrix, and the interaction of these factors on probiotic viability were evaluated using factorial ANOVA. The dairy matrix did not affect the viability of the probiotic microorganism. However, significant differences were observed throughout the phases of the digestive process. The fermented milks had an average probiotic count of 9.07 log UFC/mL, and no significant reduction was observed during the gastric phase, resulting in an average count of 8.65 log UFC/mL. On the intestinal phase of digestion, significant reduction in the probiotic viability was observed, resulting in an average count of 7.27 log UFC/mL. Thus, our results showed that both dairy matrices evaluated (WPI or CC supplementation) are suitable vehicles for the probiotic delivery. However, the digestive process significantly impacted the survival of the microorganism, with a marked reduction during the intestinal phase. Nonetheless, the probiotic exhibited high survival until the final phase of digestion, suggesting its potential viability for colonization of the intestinal microbiota.