The Effect Of Ultrasonic-TGase Cross-linking On The Properties Of Whey Protein-based Acid Cryogels And The Slow-release Effect Of The Gels

With the development of dairy processing technology,whey protein has gradually become an additive component of various functional foods and nutritional products due to its high nutritional value and ideal functional properties.Nonetheless,the excellent properties of whey protein have not been fully exploited,especially the gel properties.Whey protein itself has good gel properties,and high-concentration whey protein solution can gel during low-temperature storage after heat treatment,and it can also be induced to gel by acid.Whey protein gel has broad application potential in the field of food and medicine due to its good gel structure,amphiphilicity,nutrition and biological activity.To further modify the gel properties of whey protein,and to explore the properties of whey protein gel in the aspect of entrapment and controlled release,has practical significance for the high-value utilization of albumin.In this study,high-intensity ultrasound（HUS）was used to assist transglutaminase（TGase）to treat whey protein soluble polymer（WPISA）.Gluconolactone（GDL）induced gel formation,analyzed the effect of HUS and TGase cross-linking on WPISA gel properties,and explored the entrapment of riboflavin by whey protein hydrogel and its freeze-thaw stability and release characteristics.The main results are as follows:（1）The effects of HUS on the structure,physicochemical,rheological and gel properties of TGase-crosslinked WPISA were investigated.Whey protein isolate solution（10%,85%,15min）was preheated to prepare whey protein soluble polymer（WPISA）.High-intensity ultrasound（HUS,20 k Hz）was used to treat the WPISA solution for 10-40 minutes.Incubate at 50°C for 4h.The results of sodium dodecyl sulfate polyacrylamide gel electrophoresis（SDS-PAGE）showed that after coincubation with TGase,a polymer appeared between 40-180 k Da,indicating the occurrence of WPISA-TGase covalent cross-linking reaction.After HUS treatment（≥ 10 min）,the content of WPISA-TGase covalent crosslinks increased significantly,indicating that HUS pretreatment of WPISA promoted the occurrence of proteasepromoted crosslinking reactions.It was found by calculating the content of free amino acids that the content of free amino acids decreased significantly（P < 0.05）,indicating that HUS increased the degree of TGase-catalyzed WPISA cross-linking reaction.HUS significantly（p < 0.05）increased the particle size,endogenous fluorescence intensity and surface hydrophobicity of TGase-crosslinked WPISA,but had no significant（P> 0.05）effect on its Zeta potential and total free thiol content.HUS significantly increased the apparent viscosity and consistency index of TGasecrosslinked WPISA（p < 0.05）,indicating that more high molecular weight polymers were produced.HUS significantly increased（p < 0.05）the water-holding capacity and gel strength of TGase-crosslinked WPISA-induced gels via glucono-δ-lactone（GDL）.HUS treatment can enhance the extent to which TGase catalyzes crosslinking of WPISA,thereby improving its rheology and gelation.（2）The effects of HUS pretreatment on the gel properties of WPISA emulsions were investigated.HUS was used to treat WPISA for 5-15 min,and after cross-linking with TGase,the WPISA-TGase cross-linked product was used as the water phase,and corn oil was used as the oil phase.The rheological results showed that HUS-TGase treatment delayed the onset gelation time of the WPISA emulsion,but significantly increased the gel storage modulus（G’）after gel formation（25°C）and during storage（4°C）.The frequency scan results showed that all gels had similar frequency dependence at 4°C and 25°C,and HUS-TGase treatment significantly（p < 0.05）increased the viscoelasticity of WPISA-stabilized emulsion gels.It was found by texture analysis that HUS-TGase treatment enhanced the gel hardness,cohesiveness,elasticity and chewiness of WPISA-stabilized emulsion gels.HUS-TGase treatment significantly improved the water-holding capacity of the gel while reducing the swelling of the gel（p < 0.05）.The gel network forces were analyzed by the solubility of the gel matrix in different solutions,and the ?-（γ-glutamyl）lysine isopeptide bonds formed by non-covalent interactions,disulfide bonds and TGase cross-linking were all Involved in the formation of gel network.In conclusion,HUS combined with TGase treatment can improve the gel properties of WPISA-stabilized emulsions.（3）The WPISA treated with HUS and TGase was used as the gel matrix,and the cryogel was used as the carrier to embed riboflavin,and the freeze-thaw stability of the gel and the slow-release characteristics of riboflavin were studied.After 3freeze-thaw cycles,compared with WPISA hydrogels,HUS-TGase-treated hydrogels showed a more dense and uniform gel network structure,higher riboflavin retention,lower water absorption,Changes in WHC and gel texture significantly improved the freeze-thaw stability of riboflavin-loaded WPISA hydrogels.In addition,HUS combined with TGase treatment significantly reduced the swelling rate and protein erosion of WPISA gel in simulated gastrointestinal fluid,which promoted the sustained release of riboflavin in simulated gastrointestinal fluid.After 3 freeze-thaw cycles,the riboflavin release rate was increased for all gel samples compared to the control.Because the porous structure formed by HUS-TGase-treated hydrogel after freezing and thawing is more dense and uniform,it can alleviate the accelerated release rate of riboflavin caused by repeated freezing and thawing.The RitgerPeppas model was found to have a good fit by release kinetic analysis.