Preparation Of Soybean Protein Isolate And Its Effect On Lactic Acid Bacteria Protection

To make probiotics tolerate the destroy of the gastric acid and bile salt, thus reaching the intestine in large quantities is the preconditions to exert probiotic effect on host. This study has combined microcapsulation techniques with the intestinal-solubility technology, and used soybean protein isolated (SPI) and chitosan (CS) as the substrates for microcapsulation of probiotics represented by Lactobacillus delbrueckii (LD); then the microcapsulation effects were evaluated.This study developed and optimized the LD-loaded SPI microcapsule and ID-loaded SPI-CS microcapsule via circulatory changes of pH (Simple coacervation). The processes of microcapsulation have been optimized and the structure of microcapsules was characterized. Through simulating gastrointestinal tract test, the sustained and targeted-release effects of the microcapsules were evaluated.The main process and the results are as follows:(1) The optimal technological conditions for preparing SPI microcapsule are as follows:9%(w/v) SPI solution, pH 9.0, the stirring speed at 700 r/min, and SPI solution: bacteria suspension liquid at 1:1 (v/v). At these conditions, the encapsulation rate can reach 67.08%. The best technological conditions for preparing SPI-CS microcapsule is: the concentration of CS solution is 4 mg/mL, and SPI microcapsule:CS solution =1:1(v/v), with embedding rate at 99.02%.(2) The structure of microcapsule was characterized through the scanning electron microscopy (SEM), Fourier infrared spectrum (FTIR), thermal gravitational (TG) analysis, and so on. Through the SEM observation, the surface of blank SPI microcapsule is smooth, but part of the microcapsule collapses because it is hollow. The surface of LD-loaded SPI microcapsule sticks large amount of bacteria, and the structure become more spherical and full. The surface of SPI-CS microsphere was coarse and had cracks, with fewer bacteria on the surface. A lot of bacteria can be seen inside the SPI microcapsule. The FTIR results show that compared with SPI solution, SPI microcapsule showed no new peaks, and the peak shapes are similar. SPI-CS microcapsule and CS solution have the same tendency, which proves that CS just adheres on the surface SPI microcapsule. The results of TG analysis show that the TG50 of two kinds of capsule is between the two kinds of material, and along with the addition of CS, the tempreture is lower, it improves that the addition of CS affect SPI microcapsule’s TG.(3) Simulated gastrointestinal tract test:After passing through simulation gastrointestinal tract, naked bacteria density decreases from over 1010 CFU/mL to 105CFU/mL, descendind nearly 5log units, which means that it cannot reach the request of at least 107 CFU/mL in gastrointestinal tract and will not have probiotic function. While the bacterial density in SPI microcapsule decreased from over 1010 CFU/mL to 108 CFU/mL after simulated gastrointestinal tract test, descending 2log units. It can compensate for the number of lost probiotics in gastrointestinal, maintaining over 107 CFU/mL, thus playing probiotic function.This study developed probiotics-loaded microcapsules by repeatedly changing pH value for the first time. This method has many advantages, such as temperate conditions, high encapsulation rate, and good microcapsulating effects. The results put a way for further development of the compound microcapsule.