Effects Of Different Factors On Properties Of Whey Protein Concentrate/Pullulan Gel And The Interaction Mechanism

Gels are used widely in the food industry.Proteins and polysaccharides are the two types of biological macromolecules used commonly in edible gels.The previous research in our team used whey protein concentrate(WPC)and pullulan(PUL)to prepare a heat-induced gel which was used to coat lactic acid bacteria and improve the survival rate in the simulated gastrointestinal environment.However,studies related to interaction mechanisms of the WPC/PUL gel have not been reported.In this study,the WPC/PUL gel was used as the research object.The microstructure,rheological properties,water-holding capacity,and the interaction between proteins and polysaccharides of the WPC/PUL gel under different PUL concentration,p H,heating temperature,and Na Cl addition conditions were determined to study the gelation mechanism of the WPC/PUL gel.This will provide a theoretical basis for the wider application of the WPC/PUL gel in the food industry.The main experimental results are as follows:The effect of different factors on the microstructure and rheological properties of the WPC/PUL gels was measured by scanning electron microscope and rotational rheometer.The results showed that the addition of PUL can improve the dense and regular porous structure of WPC gel and the gel had a higher storage modulus(G’).The WPC/PUL gel had a better structure,more regular pores and higher G’value under neutral conditions.As the heating temperature increased,the WPC/PUL gel changed from a lamellar structure to a regular porous structure and the G’value also increased.The addition of Na Cl has a negative effect on the formation of the WPC/PUL gel.The dense porous structure provided a guarantee for the water-holding capacity of the WPC/PUL gel and the high G’value presented the strong interaction force inside the WPC/PUL gel.The water-holding capacity is an important indicator for hydrogels.In this study,the effect of different factors on the water-holding capacity of the WPC/PUL gel was measured by drying kinetic experiments.The mathematical models were used to determine the optimal model during drying process,and the activation energy(E_a)was used to characterize the water-holding capacity of the WPC/PUL gel.The results showed that the Page model fitted best and was the most suitable for characterizing the moisture change of the WPC/PUL gel during drying process.The addition of PUL was beneficial to enhancing the water-holding capacity of the gel.With PUL concentration increased,the WPC/PUL gel had larger E_a and better water-holding capacity.The gels prepared at p H 7.0 and 7.5 had better water-holding capacity;during gel formation,the higher the heating temperature,the better the water-holding capacity of the WPC/PUL gel.The WPC/PUL gels with the addition of Na Cl had poor water-holding capacity.Electrostatic interaction,disulfide bonds,hydrophobic interaction,and hydrogen bonds are some of the common interactions in mixed systems of proteins and polysaccharides.Zeta-potential method,Ellman’s regent method,ANS probe,and infrared spectroscopy were used to characterize changes in interactions of the WPC/PUL gel system.The results showed that the addition of PUL made up for the shortcomings of WPC gels and promoted the electrostatic interaction,hydrophobic interaction,and hydrogen bonding formation in the WPC/PUL gel directly or indirectly.The increase in p H destroyed the spatial structure of macromolecules against hydrophobic interaction and hydrogen bonding.Heating promoted the thermal aggregation of whey protein,the higher the heating temperature,the stronger the interaction between proteins and polysaccharides.The addition of Na Cl caused some inhibitory effects on electrostatic interaction,hydrophobic interaction,and hydrogen bonds because of electrostatic shielding.Based on all the results of this study,it can be inferred that the formation of the WPC/PUL gel may be the result of a combination of electrostatic interaction,disulfide bonds,hydrophobic interaction,and hydrogen bonds.In conclusion,the WPC/PUL gel formed with 8.0%PUL,neutral p H and higher temperature had better gel properties,and the combination of the electrostatic interaction,disulfide bond,hydrophobic interaction and hydrogen bonding is the main mechanism of the WPC/PUL gel formation.