Studies On The Mechanism,emulsifying Application Of Physical Pretreatment And Transglutaminase-set Soy Protein Isolate And Wheat Gluten Mixture Gelation

The objective of the research is focus on the exploration of the mechanism and gel properties of microbial transglutaminase(TGase)induced soy protein isolate(SPI)and wheat gluten(WG)mixtures hydrocolloids and emulsion gels.The structural characteristics and function of SPI/WG mixtures gel by different pretreatment methods(microwave/ultrasound/ultrahigh pressure)and TGase cross-linking are evaluated.In addition,we examined the interfacial mechanism of TGase-set SPI/WG mixture-stabilized emulsion gels.Therefore the primary aims of this present research are to provide the theoretical support to achieve the new plant protein gel materials and related biological products.The main conclusions were as follows:(1)The effects of microwave pretreatment on the gelation properties of SPI/WG cross-linked with TGase were studied.Interestingly,the gel strength,water holding capacity(WHC),and storage modulus(G?)values of TGase-induced SPI/WG gels were dramatically improved with the increasing microwave power.Moreover,the TGase crosslinking reaction promoted the formation of disulfide bonds,markedly reducing the free SH group and soluble protein contents of gels.Fourier transform infrared spectroscopy(FTIR)analysis of SPI/WG gels showed that microwave pretreatment decreased the proportion of ?-helices and ?-turns and increased the proportion of ?-sheets.Results from scanning electron microscopy(SEM)indicated that the SPI/WG gels had denser and more homogeneous microstructures after microwave pretreatment.(2)The TGase-induced gelation properties of SPI and WG mixtures with high intensity ultrasonic pretreatment were investigated.Ultrasonic treatment reduced the particle size of SPI/WG molecules,which led to improvements in surface hydrophobicity(Ho)and free sulfhydryl(SH)group content.However,TGase crosslinking facilitated the formation of disulfide bonds,markedly decreasing the content of free SH groups.Ultrasonic treatment improved the gel strength,water holding capacity,and G? and resulted in denser and more homogeneous networks of TGase-induced SPI/WG gels.In addition,ultrasonic treatment changed the secondary structure of the gel samples as determined by FTIR analysis,with a reduction in ?-helices and ?-turns and an increase in ?-sheets and random coils.(3)The TGase-induced gelation properties and thermal gelling ability of SPI/WG mixture following ultrahigh pressure(UHP)pretreatment were elucidated.UHP treatment induced unfolding and aggregation within SPI/WG protein molecules,which led to increases in free SH group content and Ho.However,the TGase crosslinking reaction facilitated the formation of hydrophobic interactions and disulfide bonds and thus resulted in higher gel strength,water holding capacity,and denser and more homogeneous gel networks of TGase cross-linked SPI/WG gels.Rheological measurements revealed that the addition of UHP steps might generate a higher storage modulus(G?)value of TGase-induced SPI/WG gelation during the heating-cooling cycle(25 ?C?95 ?C?25 ?C).Our results indicated that various chemical interactions including covalent interactions(i.e.,?-(?-glutamyl)lysine bonds and disulfide bonds)and non-covalent interactions(i.e.,electrostatic forces and hydrophobic interactions)were involved in SPI/WG gel network structures.Furthermore,UHP treatment reduced the ?-helix and ?-turn content but increased the ?-sheet and random coil structures.(4)The characteristics and interfacial mechanism of TGase-set SPI/WG mixture-stabilized emulsion gels at various oil fraction(?)values(0.1–0.5)were explored.Increasing ? dramatically facilitated the storage modulus G? and water holding capacity.The independence of G?? to frequency was largely associated with the formed perpetual crosslinking chemical network induced by TGase.Moreover,interfacial protein adsorption observations indicated that the increase of ? with an enhanced droplet size distribution and Zeta potential led to increased amounts of gel matrix-entrapped protein and interfacial protein concentration.The solvent turbidity variation was closely related to the interactive forces of gel network formation,highlighting that the network was largely maintained by hydrophobic interactions and disulfide bonds in the inter-droplet bridging.