Milk protein-based cryogel monoliths as novel encapsulants of probiotic bacteria. Part II: Lacticaseibacillus rhamnosus GG storage stability and bioactivity under in vitro digestion

Abstract

The aim of the study was to assess the ability of milk protein-based cryogel monoliths to preserve the biological activity of Lacticaseibacillus rhamnosus GG (LGG) under cryogenic processing, temperature – aw controlled storage and under in vitro gastrointestinal conditions. The cryogelation process did not result in any significant cellular injuries (losses < 0.5 logCFU.g−1) due to the achievement of a vitreous state under the cryogenic conditions implemented. Among the tested storage conditions, temperature was the most impactful parameter on LGG inactivation rates (kLGG = 0.002−0.008 to 0.25−0.56 day−1 for 5 and 37 °C, respectively), followed by protein composition (i.e. the presence of sodium caseinate alleviated the lethality of LGG). Glassy cryogels stored at aw ≤ 0.33 enabled good LGG survivability (kLGG 0.033−0.045 day−1) compared to their rubbery analogues (i.e. aw > 0.33). The cryogels exhibited limited disintegration during gastric processing, which aided LGG cells to resist gastric stressors, while complete disintegration occurred during the intestinal step, facilitating the release of LGG cells and promoting the cryogel matrix's digestibility (>64%). LGG counts in the intestinal phases remained high (>8.2 logCFU.g−1), and the peptidomic profiling confirmed the release of bioactive peptides including angiotensin-converting enzyme and dipeptidyl peptidase-4 inhibitory, antimicrobial, and antioxidant peptides.