Encapsulation of Lactobacillus rhamnosus GG in chymosin treated milk protein-alginate microgel

Abstract

Encapsulation of probiotic bacteria helps to protect its viability in food and enhances bioavailability in the human body. Alginate, a widely used gellant, singly cannot offer adequate protection to the encapsulated probiotics because the porosity of its micro-particles limits its stability in acidic conditions. Milk protein concentrate (MPC) is known to enhance gel strength. This study attempts to use chymosin treated MPC (1.0% solids w/w) as a co-gelling agent with sodium alginate (1.0%, 1.5% and 2.0% solids w/w) to enhance encapsulation of Lactobacillus rhamnosus GG (LGG) by adopting a continuous impinging aerosol technique using CaCl2. The moisture content of microgel paste of test formulations ranged from 88.1% to 90.4% (w/w) (P>0.05). Amongst the alginate MPC composite formulations, microparticles comprising of 1.0% alginate and 1.0% MPC solids exhibited highest (P<0.05) probiotic count (7.27 log CFU/g solids) and lowest viability reduction (P<0.05). Confocal image of its microparticle illustrate the presence of live bacteria, which appear as green, rod-shaped entities, entrapped within dark gel matrix. Under simulated gastric condition of pH 2 at 37oC, its microgel particle exhibited detectable viability upto 15 minutes. In case of 1.0% alginate control microgel, comparatively higher viability was noted in the 5th minute, which was undetectable by the 10th minute. With a progressive increase in alginate concentration among test formulations, cell count decreased, suggesting milk protein positively impacted viability. Microgel of 1.0% MPC control exhibited lowest loss of viable cells (0.93 log CFU/g solids). Optical image of its microparticles appeared as large flocculate rather than spherical microgel, as observed with alginate control microparticles, suggesting MPC alone is unable to produce microgels. While this study infers better viability of microparticles comprising of 1.0 % alginate and 1.0 % MPC, it opens avenues for further research for strengthening co-gelation for probiotic survival in low pH.