Development and characterisation of whey protein micro-beads as potential matrices for probiotic protection

This study evaluated the efficacy of whey protein isolate (WPI) as an encapsulation matrix for the maintenance of Lactobacillus rhamnosus GG viability during simulated gastro-intestinal studies. Micro-bead characteristics were investigated using microscopy, chromatography, laser diffractometry and zeta potential analysis. Heat-treated WPI (11%, w/v) blended with stationary phase cultures demonstrated an instant gelation impetus in acetate buffer (0.5 M), tempered to 35 °C in the presence of Tween-20 (0.04%). Atomic force microscopy (AFM) demonstrated that micro-bead extrusion at pH 4.6 fuelled strong cohesive interactions within protein-probiotic amalgams; an electrostatic alliance further highlighted by zeta potential analysis. Optimization of encapsulation conditions generated self-supporting structures (200 ± 1.2 μm) with high micro-bead strength and individual loading capacity of 2.7 × 104 cfu/micro-bead. Plate enumeration demonstrated that micro-bead extrusion had no detrimental effect on cell viability due to the perpetuation of stationary phase concentrations (109 cfu/mL). This finding was further validated by LIVE/DEAD microscopy staining, which visualized the homogenous distribution of live probiotics throughout micro-bead matrices. Following 3 h in vitro stomach incubation (pH 1.8; 37 °C), micro-beads laden with 1010 cfu demonstrated acid-stability and peptic-resistance, characteristics required for optimum probiotic refuge. However, enzyme-activated intestinal conditions catalysed a synergistic response engaging rapid matrix disintegration and controlled probiotic release. Matrix digestion was monitored by chromatography, which witnessed the sequential release of peptides <2 kDa after 30 min. In conclusion, this study led to the development and design of a protein encapsulation polymer based on congruent matrix interactions for reinforced probiotic protection during challenging situations for their targeted delivery to intestinal absorption sites.