Study On The Effect Of Emulsion Coagulant And Ultrasonic Treatment On The Quality Of Tofu

Tofu is a traditional deep-processed soybean product in China that is high in protein,unsaturated fatty acids,and a variety of physiological active substances,making it very popular with consumers.With the diversification of the consumer market,consumers have varying expectations for the quality of tofu.As a result,in order to meet the demands of various consumption scenarios,it has become the focus of research to uncover the inherent law of the effect of processing conditions on tofu quality.Tofu’s edible quality is determined by bittern gelation.The gelation rate of protein has a significant impact on the gel network structure,and the solidification rate is closely related to the aggregation behavior of protein molecules,tofu texture properties,yield,and water state in this process.Furthermore,high-intensity ultrasound can alter the structure and gel properties of soybean protein,influencing the formation of tofu network gel.In this paper,W/O emulsion coagulant was prepared,and the effect of W/O emulsion coagulant on tofu quality was investigated,revealing the internal law of coagulation rate influencing tofu gel behavior.The formation mechanism of tofu gel network structure was further investigated on this basis,in conjunction with ultrasonic treatment.The following are the main findings of the research:1.Firstly,the preparation conditions of W/O emulation coagulant were defined with the encapsulation efficiency and storage stability as evaluation indicators,and its slowly release characteristics were studied.The optimum preparation conditions of lotion are as follows:the addition amount of emulsifier is 0.8%,the mass ratio of water phase（2.6 mol/L magnesium chloride solution）to oil phase（polyglycerol ricinolate and sunflower oil）is 4︰6,the high-speed shear rate is 11000 r/min,the ultrasonic strength is 7W/cm²,and the ultrasonic time is5min.Under this preparation condition,the encapsulation efficiency of emulation to magnesium chloride solution is up to 98%,the particle size distribution is uniform,and the average particle size is 192.48 nm.The shear strength has a significant effect on the emulation release rate,and the emulation exhibits a slow release performance,effectively delaying the gel formation rate and extending the setting time from 3 s to approximately 30 s.2.Secondly,the effects of different solidification rates on the yield,moisture content,color,texture and other quality characteristics of tofu were systematically studied,and the internal law of the influence of solidification rates on the gel behavior of tofu was revealed using low field nuclear magnetic resonance,endogenous fluorescence spectrum,fourier transform infrared spectroscopy,scanning electron microscope and other methods.When the shear rate≤7000 r/min,the solidification rate of W/O tofu decreases,the gel network structure formed is more uniform,the water content and yield of W/O tofu increase significantly,and the macroscopic performance is that the brightness of tofu increases,the surface is smoother,the roughness decreases,and there is no obvious graininess.However,when the intermolecular forces inside W/O tofu are reduced due to the slow solidification rate,the position of intermolecular hydrogen bonds changes,the amount ofβ-sheet increases,and the hardness of W/O tofu is greatly reduced.3.Based on the fact that boiling provides the material basis for protein coagulation during the pulping process,and in order to improve the texture characteristics of W/O tofu,high field intensity ultrasound is used to assist in pulping,the effect of ultrasound on the particle size,free sulfhydryl group,surface hydrophobicity,and other properties of soybean milk was studied,as well as the effect of ultrasound on the texture of tofu and the formation of gel.Ultrasonic assisted pulping reduced the particle size of soybean milk,expanded the protein structure in soybean milk,exposed more basic amino acids,free sulfhydryl groups,and hydrophobic groups,and altered protein sensitivity to magnesium ions.Emulation coagulant combined with ultrasonic treatment increased intermolecular forces in W/O-H tofu,such as disulfide bond and hydrophobic interaction,forming a uniform and dense network and improving the texture characteristics of W/O-H tofu.4.Finally,the quality differences of 13 commercially available salted tofu（bittern tofu and gypsum tofu）,W/O tofu,and W/O-H tofu were objectively evaluated using principal component analysis.Principal component analysis was used to extract the first three principal components,with a cumulative contribution rate of 82.52%.Principal component 1 primarily reflects hardness,gumminess,chewiness,T₂₁,and T₂₂ variation information,principal component 2 primarily synthesizes cohesiveness and resilience information,and principal component 3 primarily represents springiness.The quality of W/O tofu in terms of hardness and water state,as well as the fluidity of water molecules in the tofu network,is primarily changed by regulating the release rate of coagulants on the main component 1.The emulation coagulant combined with ultrasonic treatment primarily changed the hardness of tofu in the aspect of principal component 1.