Maillard Modified Soy Protein Isolate And Its Application In Microencapsulation Of Lactobacillus Reuteri

In this paper,the soy protein isolate(SPI)was modified by Maillard reaction.And taking the solubility of modified soy protein isolate lactose Maillard reaction products(SPI-MRPs)as an index,the Maillard reaction conditions were optimized by single factor experiment and response surface methodology.The functional properties and structural characterization of SPI-MRPs obtained from the optimized conditions were measured,and the functional properties and structural changes before and after modification were compared.The optimized SPI-MRPs was used as microcapsule wall material and glutamine transaminase(TGase)as a crosslinker to prepare microcapsules of Lactobacillus.The microencapsulation rate of Lactobacillus Reuteri NCUF 203.1was taken as an index to optimize the conditions for preparation of microcapsules by single factor experiment and response surface test.The physical properties,simulated digestion experiments and storage stability of Lactobacillus microcapsule were determined.The main results are as follows:(1)Used mallard reaction modified SPI to improve its solubility.In the SPI-lactose reaction system,the effect of reaction temperature,reaction time and SPI concentration on the solubility of SPI-MRPs was investigated.After the response surface optimization,the reaction temperature,reaction time and protein concentration had a significant effect on the solubility of SPI-MRPs.The optimal reaction conditions were reaction time 160 min,reaction temperature 89℃ and protein concentration 6%.The test results showed that the solubility of SPI-MRPs was 64.74±2.72%,and the gap between the model predicted value was small.(2)Compared with the functional properties and structural characteristics of SPI and SPI-MRPs,compared to SPI,SPI-MRPs emulsification,emulsification stability,foaming,foam stability and gel strength are better.Under the condition of 1Omg/mL concentration,the emulsifying property of SPI-MRPs increased by 259%compared with SPI.Under the condition of 1Omg/mL concentration,the emulsifying stability of SPI-MRPs increased by 55.71%compared with that of SPI.At the same concentration,the foaming capacity of SPI-MRPs increased by 100%compared with SPI.Under the condition of 10 mg/mL concentration,the foaming capacity of SPI-MRPs increased by 58.53%compared with SPI.The strength of Maillard modified xingSPI-MRPs gel is 32.77 times higher than that of SPI(3)Structural characterization through a variety of methods.SDS-PAGE electrophoresis showed that some bands disappeared or weakened,indicating that Maillard reaction occurred between SPI and lactose.Fluorescence spectra showed that the maximum absorption wavelength of modified SPI-MRPs had blue shift and hydrophobicity increased.Compared with SPI FTIR,the absorption peak of R1R2C=CH2 group and R1CH=CHR2(CIS)group appeared in the FTIR of Mallad products,and the absorption strength of C-OH group changed.CD chromatography showed that the content of protein helix and beta fold decreased,the content of beta rotation and random curl increased,and the structure of protein two tended to be loose SEM was used to observe the protein particles and surface morphology before and after the modification.It was found that the SPI of spherical particles was modified by Millard to form a fragmented rigid structure,and the surface structure was also more rough.(4)Taking SPI-MRPs as the wall material and using TGase as the crosslinker,the microcapsules of Lactobacillus were prepared by internal source emulsification gel.In the process of preparing Lactobacillus microcapsules,the reaction time,the amount of TGase,the concentration of SPI-MRPs,the reaction pH and the reaction temperature on the microencapsulation rate of Lactobacillus microcapsules were investigated Influence.The response surface optimization experiments showed that the amount of TGase,the concentration of SPI-MRPs and the reaction time had significant influence on the embedding rate of Lactobacillus microcapsules,and the reaction temperature had a extremely significant influence on the embedding rate of Lactobacillus microcapsules.The optimal reaction conditions after the actual adjustment:the reaction temperature was 72 min and 20.6 U/g of TGase.The concentration of SPI-MRPs was 11.50%and the reaction temperature was 38.The test results showed that the encapsulation rate of Lactobacillus microcapsule was 76.93±7.34%,and the difference was smaller than that of the model(5)The water content and particle size of Soy protein isolate-microcapsule(SPI-M)and Soy protein isolate-Maillard reaction products-microcapsule(SPI-MRPs-M)were compared and analyzed,and the appearance of two kind of microcapsules were observed.The water content of SPI-M and SPI-MRPs-M was 8.6%and 8.63%respectively,and there was no significant difference;the size of the grain was 91 μm and 68 μm respectively.There are obvious differences in the appearance of the two kinds of microcapsules,and the appearance of SPI-MRPs-M is more round and uniform(6)In vitro digestion experiments showed that SPI-MRPs-M had better protection against Lactobacillus.After digestion of simulated gastric juice,the number of living bacteria in SPI-M and SPI-MRPs-M decreased by 2.41 Log cfu/mL and 1.88 Log cfu/mL respectively.After digestion,the number of live bacteria released by SPI-M and SPI-MRPs-M were 8.90 Log cfu/mL and 8.72 Log cfu/mL respectively.The number of viable bacteria in SPI-M and SPI-MRPs-M decreased by 4.58 Log cfu/mL and 3.99 Log cfu/mL respectively.The number of viable bacteria of SPI-M and SPI-MRPs-M was 6.04 Log cfu/g and 6.64 Log cfu/g after storing 30 d at 25℃.The number of viable bacteria of SPI-M and SPI-MRPs-M was 5.88 Log cfu/g and 6.50 Log cfu/g after storing 30 d at 37℃.