The Study Of Organic Acid Induced Tofu Formation And Gelation Mechanism

Tofu has historically been popular in Asia as an excellent source of protein and essential amino acids,and has been growing in popularity worldwide.As a kind of soybean products,the research of tofu is very extensive.There are few studies on the gelation of tofu induced by organic acids such as malic acid,citric acid and tartaric acid.Through systematical research of organic acid induced tofu formation,analysis the influences of salt,polysaccharide on the gelation behavior of tofu induced by organic acid,illustrate the gelation mechanism.Meanwhile providing theoretical basis for the development of organic acid tofu and the application of organic acids in the field of protein gel.Firstly,the effects of different organic acid coagulants on the physical and chemical properties of tofu were studied.The results showed that storage modulus,hardness,water-holding capacity,non-freezable water content,and in-gel hydrophobic interactions were optimal when tofu was prepared with 0.14 g/100 m L organic acids,while reduced when more than 0.14 g/100 m L was used.The storage modulus,hardness,water-holding capacity,non-freezable water content,and in-gel hydrophobic interactions of tofu prepared with 0.14 g/100 m L citric acid were maximum,reached 433.78 Pa,200.46 g,79.91%,13.04% and 6.07 g/L,respectively.Slower acidification during gelling in the presence of 0.14 g/100 m L organic acid promoted protein-protein hydrophobic interactions,resulting in a higher elastic modulus.Moreover,the tofu products showed higher water-holding capacity and non-freezable water content,as well as more compact gel microstructures.Notably,tofu prepared with citric or malic acid was of better quality than tofu prepared with tartaric acid.Collectively,the results demonstrate that soft or firm tofu with desirable physicochemical properties can be prepared with organic acids if acidification is adequately controlled during gelation.Salt combined with citric acid have synergistic effects on the gelation behavior of soymilk and mechanical properties of tofu.The results illustrated that citric acid tofu generated with addition of slight KCl or Ca SO4 presented higher elasticity and water holding capacity.The water holding capacity of these tofu were similar to that of gypsum tofu and more firm than it,while the springiness of gypsum tofu was higher,comparatively.The rheological frequency sweeping of tofu indicated that citric tofu induced with addition of 0.15 g/100 m L Ca SO4 resulted the maximum storage modulus with a frequency of 1 Hz,was 3766.87 Pa,besides the maximum hardness,339.33 g;the analysis of chemical forces showed that,at this time,ionic bonds,hydrogen bonds and hydrophobic interactions in tofu were highest,reached 30.39 g-2/L,31.26 g-2/L and 7.95 g/L,respectively.Besides,medium aggregates size and compact gel network correlated with the high values of water holding capacity,as well as the high hardness of citric acid tofu.However,exceed than 0.10 g/100 m L KCl,0.05 g/100 m L Ca Cl2 or 0.15 g/100 m L Ca SO4 resulted in decreasing of hydrophobic interactions,leading to forming large aggregates,coarse network,poor texture,and low water holding capacity.The synergistic effect of Ca SO4 or KCl with citric acid significantly improve water holding capacity,elasticity and hardness of tofu,reducing the usage level of Ca SO4 in the production of gypsum tofu meanwhile.Polysaccharides can significantly improve the physical and chemical properties of citric acid induced tofu.Results illustrated that different types and usage level of polysaccharides influence the phychemical properties of citric acid induced tofu to different degree.Non-ionic polysaccharides influence the properties of citric acid induced tofu mainly through phase separation and the physical filling effect,while that of anionic polysaccharide were mainly through phase separation and electrostatic attraction.Addition of 0.03 g/100 m L locust bean gum,water holding capacity,hardness,storage modulus and hydrophobic interactions of citric acid induced tofu reached the maximum,were 79.54 %,158.30 g,338.83 Pa and 6.76 g/L,respectively,and the microstructure of tofu was dense.Addition of 0.02 g/100 m L guar gum,the water holding capacity,storage modulus and hydrophobic interactions of tofu were highest,reached 79.70%,324.51 Pa and 6.71 g/L,respectively,the highest hardness was 136.36 g when guar gum usage level was 0.03 g/100 m L.Addition of 0.02 g/100 m L κ-carrageenan,the hardness of citric acid induced tofu was highest,was 121.60 g,the water holding capacity,storage modulus and hydrophobic interactions reached the maximum with addition of 0.03 g/100 m L κ-carrageenan,were 79.39%,354.59 Pa and 7.16 g/L,respectively.Gellan gum significantly improved the hardness and water holding capacity of citric acid tofu,the water holding capacity,hydrogen bonds and ionic bonds were highest,were 81.94%,28.44 g-2/L,29.10 g-2/L,respectively,when the usage level was 0.03 g/100 ml.Meanwhile hardness,storage modulus and hydrophobic interactions reached the maximum with addition of 0.04 g/100 ml gellan gum,reached 190.93 g,385.97 Pa and 7.49 g/L,respectively.