Formation of soy protein isolate-carrageenan complex coacervates for improved viability of Bifidobacterium longum during pasteurization and in vitro digestion

•B. longum was encapsulated in soy protein isolate-carrageenan complex coacervates.•Complex coacervates produced at pH 3 had higher yields and entrapment efficiency.•Best viability was achieved for 10:1 soy protein isolate-carrageenan ratio. Soy protein isolate (SPI) and carrageenan (IC) complex coacervates were formed through electrostatic attractions for encapsulating Bifidobacterium longum. The effects of pH (2.0–5.0) and SPI:IC mass ratios (10:1, 15:1, 20:1) on coacervate yield, entrapment efficiency and viability of the probiotic bacteria were investigated. The coacervates produced at pH 3 had higher yields and entrapment efficiency, and a SPI:IC mass ratio of 10:1 produced a complex coacervate with more compact microstructure. Compared to the native ones, the bacteria encapsulated in the coacervates had significantly improved viability during storage (4 °C), pasteurization (85 °C for 5, 10 and 30 min) and in vitro dynamic gastric and intestinal digestion. The findings also suggested that the coacervate with a SPI:IC ratio of 10:1 was more capable to protect the bacteria from loss against different stresses. This study provides a novel approach for designing efficient microcapsules containing probiotic bacteria with enhanced functional properties.