Improvement Of Gelation Of Soy Protein And Its Application In Plant-based Egg Analogs

With the rise of plant-based foods,plant-based egg analogs are valued for being free of allergens and cholesterol,unaffected by avian influenza,and more environmentally friendly and sustainable.Soy protein,the main source of protein for plant-based products,still has a gap in its gelation properties compared with animal proteins.Many studies on soy protein gelation enhancement have focused on molecular mechanisms and individual links or factors affecting the thermal gelation process,and despite significant results,they still do not meet the level of gel strength compared to egg white proteins.Therefore,further enhancement of the gelation properties of soy protein is an urgent need for the application of soy protein in plant-based egg analogs as well as other food processing products.This topic breaks through the above limitations of controlling a single factor or a single link,and explores the pathways that can simultaneously control the aggregate size or surface charge of soy protein to enhance the thermal gelation properties of Soy protein isolate(SPI).On this basis,commercial polysaccharides that can interact with soy protein are screened to improve the gel strength of the composite gel and reach the application in steamed egg products.The main contents are as follows:Firstly,the effects of preheating treatment,p H regulation,potential regulation and linkage treatment on the gel properties of soy protein were investigated.The influencing factors of linkage treatment to enhance the gel strength were explored by detailing the particle size distribution,ζ potential,surface hydrophobicity,non-reduction electrophoresis and reduction electrophoresis of the material,rheological properties,microstructure and interaction forces of the gel molecules.The results showed that the p H and Na Cl linkage treatment was a good way to enhance the gel strength,and the addition of 100 m M Na Cl at p H 6.0 could increase the thermal gel strength of soy protein up to 5.3 times than untreated gel.The particle size distribution around 100 nm and the ζ potential value around-30 favored the formation of gels with coarse network skeleton and relatively uniform pore size,resulting in high gel strength and high water holding capacity.The particle size distribution around 10 nm and the ζ potential value around-35 nm are conducive to the formation of gels with a fine network skeleton and small pore size,with high transparency and high water holding capacity,but limited strength.Outside the 1000 nm particle size distribution range and ζ potential values below-20,the gel network skeleton is rough,the pore size is unevenly distributed,and the gels have low transparency,poor water holding capacity,and weak strength.These results suggest that by controlling the p H and ionic strength of the SPI protein system,the forces driving the formation of protein gels can be effectively controlled and the balance between the aggregation of protein molecules by their own interactions and the interaction with the solvent can be effectively balanced to enhance the gel strength and water holding capacity.Then,the effects of different protein-glutaminase(PG)concentrations on thermal and calcium-induced gels of soy protein heat-treated under different conditions were investigated,and the mechanisms of calcium-induced gels to improve the water holding capacity of gels were explored by detailed discussion of the particle size distribution,surface hydrophobicity,nonreducing and reducing electrophoresis of the materials,rheological properties,microstructure,and interaction forces of the gel molecules.The mechanism of calcium-induced gels to improve the water holding capacity of gel was discussed.The results showed that the mild denaturation and structural unfolding of SPI facilitated the deamidation of PG,and the results of particle size,surface hydrophobicity,and electrophoresis showed that heat treatment led to molecular aggregation and enhanced hydrophobicity,while deamidation also led to an increase in the particle size of SPI.The gel strength results showed that the enhancement of SPI thermal gels by PG was relatively limited,and the PG deamidation treatment reduced the gel strength of SPI calcium-induced gels but significantly improved their water holding capacity.The best water holding capacity(98.5%)was obtained for calcium-induced gels at 95°C and 5 U/g PG treatment,and the water holding capacity was enhanced by 46.4% compared to the samples without PG treatment.The increase in heat treatment intensity led to the enhancement of hydrogen bonding,hydrophobic interactions and disulfide bonding in the gelation process,and the gel strength was improved.With the increase in PG concentration,the percentage of soluble protein increased,the water holding capacity increased significantly,and the gel exhibited a smooth and delicate appearance with a more homogeneous and ordered structure in scanning electron microscopy images.The above results indicate that soy protein using heat treatment combined with PG treatment can simultaneously improve the hydrophobicity of SPI as well as release more sites of calcium bridges through deamidation,thus substantially improving the water holding capacity,which provides a new idea for the industrial production of wellstructured calcium-induced gels.To further enhance the thermal gelation of SPI,11 different commercially available polysaccharides were selected to be compounded with soy protein at different ratios of concentration based on the gelation properties of the polysaccharides and whether they were charged or not.The high ester pectin that could enhance the highest gel strength of SPI was screened based on gel strength.The effects of compounding ratio,p H and ionic strength on the mixed system of pectin and soy protein were then further investigated.The results showed that in the range of 0.5-10% pectin addition concentration,2% was the optimum pectin addition,and the gel strength increased to 3.9 times than untreated gel.p H and Na Cl linkage treatment significantly affected the composite gels,and the highest gel strength and good gel water retention were achieved at p H 6.5 without Na Cl addition,and the gel strength could be increased to 5.3 times.The particle size and ζ potential of the composite system strongly influenced the gel temperature and final elastic modulus.The decrease of p H and the addition of Na Cl caused a wider particle size distribution of the SPI-pectin system with a higher percentage of large particle size components,which resulted in a significant tendency of phase separation and a decrease of water holding capacity.The gel strength decreased significantly when the particle size distribution was above 2000 nm.Hydrogen bonding and hydrophobic interactions are the main forces in composite gels,where the differences in hydrophobic interactions between gels of different systems are more obvious than hydrogen bonding.Finally,three preferred plant-based egg analogs white mock formulations with good gelation properties,100 m M Na Cl+p H 6.0,100 m M Na Cl+0.4%Vc and 2% pectin+p H 6.5,were combined with 25% oil content of vegetable fat powder to form mock plant-based egg whites analogs and whole egg analogs,and the appearance,texture and sensory evaluation of each sample were compared with egg whites and egg yolks after steaming.The results showed that in the plant-based egg white analog system,the appearance and sensory evaluation of the100 m M Na Cl+0.4% Vc sample was the most similar compared with the real egg white gel,but the gel strength was slightly deficient,and the gel strength of the 2% pectin+p H 6.5 sample was the closest but yellowish in appearance.In the plant-based egg yolk analog system,the gel strength of the 2% pectin+p H 6.5 sample was higher than that of the whole egg gel and had a smooth appearance without noticeable pores,which was most similar to the real whole egg gel.The steaming time affected the plant-based egg analogs,and the gel strength increased with increasing steaming time.In summary,the linkage of different pretreatments is an effective way to enhance the gel properties of SPI,the linkage of p H and Na Cl can significantly improve the gel strength of SPI,and the addition of PG to SPI with different degrees of thermal denaturation can significantly improve the water holding capacity of calcium-induced gels.The addition of pectin to SPI can effectively improve its gel strength while reducing the gel temperature,which provides new ideas for the application of plant-based egg analogs and the application of SPI in plant-based egg analog was expanded.