Study On Preparation Of Peanut Tofu And Its Gel Formation Process

The present study proposed a novel method of making peanut tofu from low-temperature peanut cakes?LTPC?by combining biological enzyme and high-temperature cooking?HTPC?treatment.The effect of different processing conditions on tofu texture and yield was studied,and quality difference between the obtained peanut tofu and the commercial soybean tofu was compared.Moreover,the functional properties?thermal property,particle size distribution,and rheological property?and the structure?SDS-PAGE,protein secondary structure,and tertiary structure?of peanut proteins and the microstructure of peanut tofu were also analyzed.Pilot processing technology was also established and peanut tofu product was developed.At last,we initially clarified the gel formation process of peanut tofu.The detailed results were shown as follows:The processing technology for peanut tofu was established and optimized,and the tofu quality was analyzed.The result showed that enzyme-treated peanut milk which initially existed as a liquid directly transformed into gel-like substances,and we could make the peanut tofu by simply pressing.The optimum processing parameters were as follows:peanut cake oil content 6.89%,the liquid to solid ratio1:7?m/v?,enzyme amount 0.75‰,enzyme treatment time 2 h,cooking temperature 115??0.17 MPa?,cooking time 20 min.Under these conditions,the hardness,chewiness,springness,and yield of the obtained peanut tofu were 279.6 g,145.35 g,0.97 and 225.2 g/100 g,respectively.The water-holding capacity?WHC?of the peanut tofu was 81.88%,which was better than that of the commercial soybean tofu,and the cooking loss was 0.89%,which was close to that of the soybean tofu.Besides,the peanut tofu had the advantage of color with a significantly lower b value?8.38?than that of soybean bitter tofu?16.56?and gypsum tofu?15.86??p?0.05?.The functional properties of peanut proteins as affected by typical processing conditions during tofu processing were studied.The T_d of the arachin and conarachin fractions of peanut milk proteins was 115.24?and 95.04?,respectively,and?H was 9.56 J/g and 1.10 J/g,respectively.After biological treatment?0.75%?,the T_d of the two fractions increased to 116.57?and 95.85?,respectively,and the?H increased to 8.59 J/g and 1.52 J/g,respectively.Meanwhile,protein molecules were crosslinked to form protein aggregates through covalent bonds,with increased particle size distribution and higher apparent viscosity;HTPC treatment?115?,0.17 MPa?could completely denature the peanut proteins,lead to a more uniform and concentrated particle size distribution,but it did not change the fluid type of peanut proteins,which still belonged to a pseudoplastic non-newtonian fluid.The structure of peanut proteins and the microstructure of peanut tofu as affected by typical processing conditions were studied.SDS-PAGE analysis showed that the subunits of peanut proteins were crosslinked to form protein aggregates with higher molecular weight?⁷5 kDa,130 kDa and beyond?through covalent bonds.Fourier Transform infrared spectroscopy?FTIR?analysis showed that the content of?-helix,?-sheet,?-turn,and random coil of peanut proteins was 45.2%,33.4%,21.4%,and the proteins became loose after combined enzyme treatment?0.75‰?and HTPC treatment.The tertiary structure analysis showed that the surface hydrophobicity?H₀?and the total free sulphydryl content?TFS?of peanut protein were 88.89 and 6.06?mol/g,respectively.After enzyme treatment?0.75‰?,the H0 decreased to 47.48,but the TFS increased to 7.18?mol/g.When HTPC treatment and pressing were applied,the H0 and the TFS of peanut proteins in tofu were 33.09 and 2.08?mol/g,respectively,which were both significantly lower than those in peanut milk?p?0.05?,indicating the formation of hydrophobicity interactions and disulfide bonds.The scanning electron microscope?SEM?results showed that all the peanut tofu gels exhibited a honey-comb structure,and the addition of enzyme?0.75‰?made the gel network become denser with evenly-distributed small pores.Pilot peanut tofu processing technology?supermarket scale?was established and peanut tofu products were developed.For one batch,about 4 kg of peanut cakes were processed into tofu products?¹2 kg?.The pilot-scale tofu had a bigger hardness,springness,and chewiness with the yield,WHC,and cooking loss 284.7 g/100 g,83.43%,and 0.81%,respectively,which were significantly better than the small-scale tofu?p?0.05?.