Chlorella vulgaris protein isolate effectively protects Lacticaseibacillus rhamnosus GG viability during processing, storage, and in vitro digestion

This study examined the protective effect of Chlorella vulgaris protein isolate (CPI) on the biological activity of Lacticaseibacillus rhamnosus GG (LGG) during lyophilisation, storage, and in vitro digestion. Prior to lyophilisation, the probiotic suspensions were either fermented to pH 4.5 (CF) or left untreated (CNT). The microstructure, physicochemical, and thermal properties of the resulting probiotic powders were analysed, along with the LGG cell adhesion to an in vitro intestinal epithelium co-culture (Caco-2/HT29-MTX) model. The powders exhibited a compact, flaky, microporous structure with sharp edges. No significant effect of fermentation on the thermal properties of the powders was detected. A hybrid type II−III water vapour sorption isotherm was observed for all samples. The protein secondary structure of the samples consisted mainly of α-helix (68–75 %), followed by β-sheet (20–27 %) and aggregated strands (3–5 %). Embedment of LGG cells in CPI-based matrices provided effective lyoprotection, with CNT offering greater stability than CF. Elevated storage temperature and relative humidity (RH) conditions accelerated LGG inactivation, particularly in CF. While a sufficient proportion of LGG cells survived the harsh conditions of in vitro digestion, pre-fermentation had a negligible impact. Additionally, the adhesion capacity of the LGG cells to the intestinal mucus layer was satisfactory (>4 log CFU g−1). Overall, CPI exhibits strong stabilising properties for LGG viability and represents a promising single-cell-based alternative to conventional (dairy or plant) proteins for probiotic food formulations.