Lactobacillus plantarum immobilized onto soymilk residue (Okara) for the enhancement of soymilk fermentation and cell survival under simulated gastrointestinal conditions

Cell immobilization is an alternative to microencapsulation for the maintenance of cells in a liquid medium. However, artificial immobilization carriers are expensive and pose a high safety risk. This study aimed to evaluate the potential of okara, a food-grade byproduct from soymilk production, as a natural immobilizer for L. plantarum 70810 cells. The study also aimed to evaluate the effects of okara-immobilized L. plantarum 70810 cells on soymilk fermentation, glucosidic isoflavone bioconversion, and cell resistance to gastrointestinal (GI) stress. Scanning electron microscopy revealed that the lactobacilli cells attached and bound to okara’s surface. Compared with the free cells (FL), immobilized Lactobacillus plantarum (IL) cells exhibited a significantly higher specific growth rate and shorter lag phase of growth, a faster decrease in pH and increase in titrable acidity, and a higher soymilk viscosity. Similarly, IL in soymilk showed higher productions of daizein and genistein compared with the control. Compared with FL, IL showed reinforced resistance to simulatedGI stress in vitro that included low pH, low pH plus pepsin, pancreatin, and bile salt. Our results indicate that okara is a new potential immobilization carrier to enhance the growth and glucosidic isoflavone bioconversion activities of L. plantarum in soymilk and improve cell survivability following GI transit.