Foaming Properties Of Soy Protein And Its Hydrolysates And Its Application In Cakes

Although soy protein is nutritional and cheap,its foaming capacity and foam stability are not good enough to satisfy the application in cakes.In this paper,the soy protein was modified by different enzymatic hydrolysis.Furthermore,the interfacial shear rheological behavior of the protein at different pH and its interaction with different baking ingredients at the interface were studied to improve the foaming property of soy protein and broaden the application of soy protein in foam-based food such as sponge cakes.The structure and foaming properties of soy protein isolate(SPI),?-conglycinin(7S),soy protein selective hydrolysate(SPSH),and soy protein limited hydrolysate(SPLH)were analyzed and compared.Electrophoresis results showed that SPSH selectively hydrolyzed the 11 S subunit and only retained the 7S subunit.The degree of hydrolysis of SPLH was controlled to 1%,leaving only the polypeptide chain with a relative molecular mass of about 10 kDa.The particle size and ?-potential measurement analysis indicated that both hydrolyzes significantly reduced the particle size of the soy protein and the amount of surface charge.The surface tension of SPSH and SPLH was lower.The interfacial shear rheological behavior results indicated that the adsorption speed of SPI and 7S was slow,and SPLH adsorbed to the interface quickly.7S and peptides existed in SPSH,which made SPSH adsorb to the interface quickly and form a viscoelastic interfacial film simultaneously.The whipping experiments results showed that the foam expansion of SPSH and SPLH increased significantly from 450% to 680% and 700%,respectively.In order to broaden the application of soy protein in acid whipping condition,the structure and foaming properties of four soy proteins at pH 4,pH 3 and pH 2 were studied.The particle size and ?-potential results showed that the particle size of the four proteins increased near the isoelectric point.Under the acid condition,the surface tension of 7S,SPSH,and SPLH was less than that under the neutral condition.The interfacial shear rheological behavior results showed that under the acid condition,the interfacial viscoelasticity of the four proteins was enhanced,and they adsorbed to the interface faster.The globulin maintained the linear viscoelastic region,and the polypeptide increased the interfacial elasticity.The whipping experiments results showed that at acidic pH,the foam expansion of 7S,SPSH,and SPLH was higher than that at pH 7 and the foaming stability of the four soy proteins was higher than that at pH 7.In order to explore the reason why soy protein could not be added to the whole egg system in large quantities and could not synergize with whole egg liquid,the interaction of four soy proteins with egg white(EW)and egg yolk(EY)was studied.There was a synergistic effect between EW and SPI,7S,and there was competitive adsorption between EW and SPSH,SPLH.EY mainly adsorbed to the interface in the mixture of EY and SPI,7S and SPLH,and the interface film was fluid-like.There was almost no linear viscoelastic region and it would be destroyed when the frequency increased.SPSH could improve the shear resistance of EY's interfacial film.The mixture of EY and SPSH had a weak protein adsorption layer at the interface,but when whipping speed increased,the interfacial film was dominated by viscosity.In order to enhance the thermal stability and thermosetting of soy protein foam,the interaction of water-soluble temperature-induced gelling polysaccharide hydroxypropyl methylcellulose(HPMC)with four soy proteins was studied.Two kinds of HPMC with different relative molecular masses and degrees of substitution,called F50 and K4 M,were used in the experiment.The particle size results indicated that SPSH combined to F50 and K4 M through non-covalent interactions to produce a new protein-hydroxypropyl methylcellulose complex,while no complex was formed between other proteins and HPMC.The ?-potential results indicated that F50 and K4 M partially shield the surface charge of the protein.The interfacial shear rheological results showed that the interaction pattern of HPMC and soy protein at the air-water interface was influenced by the protein structure and HPMC relative molecular mass.In terms of foam expansion,as long as it does not have too much impact on viscosity,the effect of HPMC on the rapid equilibrium of protein at the air-water interface was much greater than that of the interfacial film.The oscillation temperature sweep experiment results found that HPMC significantly increased the final G' of the soy protein gel and lowered the gel formation temperature.In order to promote the application of high-foaming soy protein in the baking system,and to fit the reality of the widespread use of cake oil in existing baking systems,the effects of eight emulsifier commonly used in cakes with different HLB values on the soy protein at the oilwater interface were tested.Polyglycerol fatty acid ester significantly increased the elastic modulus and adsorption speed of SPI,7S,and SPSH.Polyoxyethylene sorbitan monostearate and diacetyl tartaric acid mono-diglyceride exhibited a fluid-like interfacial film at the oil-water interface of the four soy proteins,as well as sodium stearoyl lactylate at the oil-water interface of SPSH.Finally,SPSH with high foam expansion was used instead of 50% of eggs to make the sponge cake,and the effects of F50 and polyglycerol fatty acid ester on the properties of sponge cake were studied.It was found that F50 can effectively maintain the center height and specific volume of the sponge cake with non-oiling formula,and polyglycerol fatty acid ester can better maintain the volume and specific volume of the sponge cake with oiling formula.In the nonoiling and oiling formula,F50 and polyglycerol fatty acid ester showed good synergistic effect,and the texture and sensory quality of the cake were good,which were close to the whole egg sponge cake.