Development of soy protein isolate-carrageenan conjugates through Maillard reaction for the microencapsulation of Bifidobacterium longum

Abstract

Maillard reaction between soy protein isolate (SPI) and Ι-carrageenan (IC) was conducted through a combined approach of spray drying and dry heating, and the performance of Maillard reaction products (MRPs) in protecting Bifidobacterium longum was investigated. The degree of graft of MRPs was increased rapidly during the spray drying process, but changed slowly in the subsequent dry heating. FTIR measurement indicated high level of glycosylation in MRPs after spray drying, suggesting that the Maillard reaction was rapidly initiated. Microrheology analysis revealed that the MRP solution reached the highest macroscopic viscosity when the sample was heated for 6 h after spray drying. The MRPs were used to encapsulate Bifidobacterium longum by spray drying or freeze drying. Among all the MRPs, the one prepared with a SPI: IC ratio of 1:3 and dry heated for 6 h after spray drying was the most effective one in protecting the bacteria during storage. In vitro digestion test showed that the viability of the bacteria was reduced by 2.38 log units when exposed to simulated gastric juice after 120 min, and by 0.74 log units when exposed to simulated intestinal fluid after 120 min. MRPs can also protect the bacteria during pasturization (85 °C), and the number of the bacteria was reduced by 1.56 log units after 5 min and by 2.05 log units after 30 min.