Study On Preparation Of Soy Protein Isolate-Oligosaccharides Maillard Reaction Products And Their Application On Microencapsulation Of Probiotics

Probiotics are live microorganisms that have health benefits on human body.However,they are sensitive to the external environments.Unfavorable factors such as acid,alkali,heat,oxygen,mechanical force and digestive enzymes can easily inactivate probiotics,resulting in a decrease in their value,which limits the application of probiotics in food industry.In view of the above-mentioned problems,microencapsulation technology is a reliable means for protecting probiotics and has broad application prospects.Maillard reaction products(MRPs)are common products of protein glycosylation in food processing.They have good film-forming,emulsifying and antioxidant properties,which are considered to be good microencapsulation wall materials.However,the studies at home and abroad are mainly focused on the MRPs of proteins and monosaccharides or polysaccharides.There are few reports on the MRPs of proteins and oligosaccharides.In addition,MRPs are more used for microencapsulation of natural products such as fish oil and vitamins.The researches on the encapsulation of probiotics are less and unsystematic.In this study,soy protein isolate(SPI)and isomaltooligosaccharide(IMO)or xylooligosaccharide(XOS)or galactooligosaccharide(GOS)were chosen as raw materials to prepare a series of MRPs by the wet-heating Maillard reaction.In addition,the related characterization and functional properties of MRPs were studied.After that,SPI-IMO_MRPs60(80?,60 min),SPI-XOS_MRPs30(80?,30 min)and SPI-GOS_MRPs60(80?,60 min)were selected as the wall materials for the microencapsulation of Lactobacillus casei(L.casei).The processing stability of microcapsules and their related properties after simulated gastrointestinal digestion were investigated.The main results are as follows:(1)SPI could be conjugated with oligosaccharides via the wet-heating Maillard reaction.During the Maillard reaction at 80?,the p H values,intermediate indexes and browning indexes of MRPs increased with the extension of reaction time(0?180 min).Among which,SPI and XOS showed the fastest reaction speed.The maximum grafting degrees of SPI-IMO_MRPs,SPI-XOS_MRPs and SPI-GOS_MRPs were 24.52%±1.41%,26.33%±0.46%and25.10%±0.97%at reaction for 150 min,respectively.Characterization results such as Fourier transform infrared spectrometer,polyacrylamide gel electrophoresis and circular dichroism also confirmed the formation of MRPs.(2)Maillard reaction enhanced the reducing power,·OH radical-scavenging activity and DPPH radical-scavenging activity of MRPs.Moreover,it helped improve the viabilities of oxidative damaged Hep G2 cells and reduce the intracellular reactive oxygen species(ROS)levels.However,the increase of antioxidant activity was related to the substrates and degree of Maillard reaction.At the same reaction time,SPI-XOS_MRPs showed stronger antioxidant activity than SPI-IMO_MRPs and SPI-GOS_MRPs.Considering the functional characteristics of MRPs and the possible health risks caused by the increase of Maillard reaction degree,SPI-IMO_MRPs60,SPI-XOS_MRPs30 and SPI-GOS_MRPs60 were selected for the following studies.(3)Simulated gastrointestinal digestion could weaken reducing power of MRPs.SPI-XOS_MRPS30 had the highest reducing power after simulated digestion.There was no significant difference on the viabilities of oxidative damaged Hep G2 cells between the digested MRPs and their corresponding raw mixtures(p>0.05).However,the digested MRPs showed stronger intracellular ROS-scavenging ability(p<0.05).The digested MRPs displayed excellent pathogenic resistance to Escherichia coli and Staphylococcus aureus.Moreover,they could be used as carbon sources and nitrogen sources to promote the growth of L.casei.These results suggested that SPI-oligosaccharides MRPs may be great wall materials for probiotics microencapsulation.(4)The encapsulation yields of the L.casei microcapsules prepared by SPI-IMO_MRPs60,SPI-XOS_MRPs30 and SPI-GOS_MRPs60 were more than 60%,and their particle sizes were about 7?m.Microcapsules displayed cohesive blocks with continuous surface and smooth protuberances,which showed outstanding thermal stability,mechanical stability and storage stability.During simulated gastrointestinal digestion,the microcapsules prepared by MRPs provided excellent protection to L.casei,whose viable counts decreased by only 0.29?1.14log CFU·m L^-1.Except for SPI-XOS_MRPs30/L.casei microcapsules,the reducing power of the other microcapsules decreased significantly after simulated digestion(p<0.05).Comprehensive evaluation showed that SPI-XOS_MRPs30 had greater application potential in the microencapsulation of L.casei.This study provides detailed data for the developments of SPI-oligosaccharides MRPs as new wall materials for probiotics microencapsulation.At the same time,it offers a feasible scheme for the effective protection of probiotics in food industry,which is of great significance.