Immobilization Of Lactobacillus By Calcium Alginate And Its Fermentation Degradation Of Soybean Protein Isolate

In this paper,the changes of p H,total acid?based on lactic acid?and the number of viable bacteria in the fermentation process were taken as indicators to study the fermentation performance of six lactic acid bacteria experimental strains in the soybean protein isolate?SPI?-glucose system,and screened out the lactic acid bacteria experimental strains suitable for good growth in this system.The immobilized lactic acid bacteria were prepared by extrusion method,and the best immobilization conditions were determined by single factor test and orthogonal test.Finally,the differences of fermentation performance and SPI degradation between free and immobilized lactic acid bacteria were compared,which provided theoretical basis for the application of lactic acid bacteria and immobilized lactic acid bacteria to modified SPI in the future.The main results are as follows:?1?According to the changes of p H,total acid?calculated by lactic acid?and the number of viable bacteria,it was found that the fermentation performance of L.rhamnosus?LR-D?in SPI glucose system was better than that of other lab strains.After 12 hours of fermentation,LR-D can reduce the p H of the fermentation system to below 4.0,and the total acid of the LR-D fermentation system?calculated by lactic acid?is higher than that of other lactic acid bacteria fermentation systems?calculated by lactic acid?,indicating that LR-D has strong acid producing ability.During the fermentation process,the number of viable bacteria of LR-D was always higher than other experimental strains of lactic acid bacteria,indicating that LR-D can grow well in the SPI-glucose system.?2?Prepare immobilized LR-D by extrusion method.The results of single factor test and orthogonal test show that the best immobilization conditions are:2.5 g/100 m L sodium alginate solution as the carrier solution,2.0 g/100 m L Ca Cl₂solution as the solidification solution,and the immobilization time is 2 h.The immobilized LR-D prepared under this condition has the largest cell embedding rate of 83.35%,has good mechanical strength,and has good storage stability at 4?and 25?.Studies have found that the fermentation capacity of free LR-D in the SPI-glucose system is greater than that of immobilized LR-D in this fermentation system.?3?Comparing the difference between free LR-D and immobilized LR-D to degrade SPI,the results show that LR-D fermentation will degrade SPI.In contrast,immobilized LR-D degrades SPI less than free LR-D Degradation of SPI;The particle size distribution results show that the particle size of the fermented SPI presents a unimodal distribution.With the extension of the fermentation time,the average particle size of free LR-D and immobilized LR-D fermented SPI increased significantly;The absolute value of the?-potential of the fermented SPI sample decreased.In comparison,the absolute value of the?-potential of the system after the immobilized LR-D fermented SPI was lower than that after the free LR-D fermented SPI.?4?Structural characterization of free LR-D and immobilized LR-D fermentation SPI samples.The UV absorption spectrum results showed that the maximum UV absorption peak intensity of the SPI samples of immobilized LR-D fermentation was smaller than that of free LR-D.The infrared spectroscopy results showed that the intensity of the amide I band absorption peak of the immobilized LR-D fermentation SPI sample was gradually decreasing.The results of circular dichroism showed that the?-helical content and the random curl content of the fermented SPI under the two conditions showed an overall downward trend,while the?-sheet and?-turn content increased.Fluorescence spectrum results show that the maximum absorption wavelength of fermented SPI has a red shift.The increase trend of the free sulfhydryl content of SPI samples fermented with immobilized LR-D is far less than that of SPI fermented samples with free LR-D.SEM results showed that the spherical structure of SPI gradually opened to form an irregular sheet-like structure,and the surface of the sample gradually appeared holes and clusters appeared.?5?Study the influence of LR-D fermentation on the solubility and emulsification of SPI.The results show that LR-D fermentation can significantly improve the solubility of SPI under acidic conditions.The EAI values of free LR-D and immobilized LR-D showed a trend of first increasing and then decreasing,but they were generally higher than the EAI value of the original SPI,and the emulsification activity of the immobilized LR-D fermentation SPI samples decreased to a lower degree;The emulsion stability of fermented SPI is not as good as SPI.Compared with free LR-D fermented SPI,immobilized LR-D has a lower degradation effect on SPI,and the degree of emulsification stability changes is smaller.