Microencapsulation of Lactobacillus acidophilus La-05 and incorporation in vegan milks: Physicochemical characteristics and survival during storage, exposure to stress conditions, and simulated gastrointestinal digestion

Abstract

The effect of microencapsulation of L. acidophilus La-05 (8 log CFU/mL) by external ionic gelation technique in alginate (30 g/L; AM) and alginate coated with a low molecular weight chitosan solution (5 g/L; AC5M) on the survival of the freeze-dried probiotic culture during storage (7 °C; 0, 7, 15, 30, 60, 90 and 120 days), and exposure to temperature (72, 85 and 90 °C), pH (2, 4, and 6), and NaCl (10, 15 and 20 g/L) were studied. Furthermore, vegan milks (soybean and rice milks) added with microencapsulated probiotic cultures were evaluated for the physicochemical characteristics and survival of the probiotic culture during refrigerated storage (7 °C; 7 days) and in vitro digestion. Free cells were used as control. AM and AC5M showed similar microencapsulation yield (>90%) with uniform and spherical microparticles dispersed without agglomeration. Scanning electron microscopy showed that chitosan was able to cover the porous structure of the alginate particles, resulting in a more stabilized microparticle. The microencapsulation provided higher probiotic protection to storage, thermal treatment, NaCl and pH (decreases of ~1 log CFU/mL) compared to the free cells (decreases of ~3, 4, 2 and 3 log CFU/mL, respectively), and increased probiotic survival during refrigerated storage and in vitro digestion of vegan milks compared to free cells (decreases of ~1 and 4 log CFU/mL, respectively). Only microencapsulated probiotic cultures (AM and AC5M) maintained suitable probiotic counts (>6 log CFU/mL) during storage, exposure to stress conditions and simulated gastrointestinal digestion. Chitosan coating increased the probiotic survival in the vegan milks during refrigerated storage. Microencapsulation by external ionic gelation in alginate proved to be a suitable microencapsulation technique to improve the probiotic survival to storage, stress conditions (temperature, pH and NaCl) and simulated gastrointestinal conditions. This was the first study that evaluated the addition of probiotic cultures to rice and soybean milks, proving that the vegan milks could be considered suitable carriers for microencapsulated probiotic cultures.

Keywords: Biopolymers; Encapsulation; Freeze-drying; In vitro digestion; Probiotic; Rice milk; Soybean milk.