Use of Lacticaseibacillus rhamnosus LRB in high-protein multifunctional fermented milk targeted for older adults.

High-protein fermented milks are promising vehicles for delivering probiotics and bioactive compounds, contributing to health promotion, particularly in the context of healthy aging. This study evaluated the effect of fermenting dairy formulations with different protein profiles using Lacticaseibacillus rhamnosus, with a focus on bioactive potential and peptide bioaccessibility. Milk was supplemented with calcium caseinate (CC) or whey protein isolate (WPI) to obtain distinct protein profiles. Fermented and non-fermented formulations were submitted to in vitro gastrointestinal digestion under older adults' conditions, followed by the assessment of probiotic viability, bacterial growth-promoting effect, angiotensin-converting enzyme (ACE) inhibitory activity, and peptide bioaccessibility. L. rhamnosus remained highly viable after intestinal digestion (7.27 log CFU/mL). Fermentation also exerted a positive effect on L. rhamnosus growth-promoting potential, particularly in the WPI-supplemented formulation. Furthermore, formulations containing WPI exhibited greater ACE inhibition. The peptide profile revealed sequences derived from caseins, especially the β-casein fraction, including peptides previously described as bioactive. Overall, these findings highlight the combined role of fermentation by L. rhamnosus and protein profile in modulating the bioactive potential of high-protein fermented milks. The results also support their potential as multifunctional matrices capable of delivering bioaccessible peptides with biological relevance, contributing to the development of products aimed at promoting health during aging.