Study of various concentrations of resistant starch and chitosan on microstructure, rheological properties and viability of encapsulated probiotic bacteria in drinking yoghurt

The aim of this study was to investigate the effect of microencapsulation with sodium alginate/ resistant starch and sodium alginate/chitosan on microstructure, rheological properties and viability of Lactobacillus acidophilus and bifidobactrium animalis subs lactis in drinking yoghurts. Role of different encapsulation parameters, such as resistant starch and chitosan concentration (0, 0.5, 1 and 2 %) and encapsulation time (0, 10, 20 and 30 min) in providing protection to the bacteria were also evaluated. Results showed that the addition of starch and chitosan at 1% concentration to alginate mix and 10 min resulted in increased viable counts of lactobacillus acidophilus and bifidobactrium animalis subs lactis cells after 7 days storage at 4˚C. Drinking yoghurts with alginate/resistant starch microcapsules had shown more viability (3.6×1011 and 6.6×1011 for Lactobacillus acidophilus and bifidobactrium animalis subs lactis, respectively) than encapsulated samples with alginate/chitosan (2.1×1010 and 6.8×1010 for Lactobacillus acidophilus and bifidobactrium animalis subs lactis, respectively). Optical microscopic image of 50 beads at 40× magnification showed that the bead shape was spherical with a mean diameter of about 300–500 µm, and cross-section and internal appearance of coated alginate-resistant starch bead at 100× magnification showed that bacterial cells were located inside of beads. The distribution of beads in drinking yoghurt texture was uniform. Encapsulation increased apparent viscosity and consistency coefficient and decreased flow behaviour index. The best fitted rheological model for the control (without microcapsules) was Power law and for rest of the samples was Herschel-Bulkley.