Effect Of Ultrasound Pretreatment On Soybean Oil-body Emulsion And MTG-catalyzed Tofu Gel

This paper mainly studied the changes of soybean oil-body and the properties of its emulsion after ultrasound pretreatment.Then the soybean oil-body emulsion after ultrasound pretreatment was mixed with the non-oil body components of soymilk to form the reconstituent soymilk.The effects of soybean oil-body emulsion after ultrasound pretreatment on the reconstituent soymilk and MTG-catalyzed reconstituent tofu gel were studied.And whole soymilk was treated by ultrasound to explore the effect on MTG-catalyzed tofu gel.By comparing the changes in the properties of soybean oil-body and the whole soymilk after ultrasound pretreatment and the effect on the properties of MTG-catalyzed tofu gel,the internal relationship was analyzed.The main conclusions were as follows:(1)The effect of ultrasound pretreatment on soybean oil-body emulsion was studied.After ultrasound pretreatment,the particle size and polydispersity index(PDI)of soybean oil-body emulsion significantly diminished,generating more uniform distribution of oil droplets.Moreover,the surface protein structure of soybean oil-body was destroyed,exposing more hydrophobic groups and improving the surface hydrophobicity of soybean oil-body emulsion.Treatment of soybean oil-body emulsion with ultrasound led to an enhancement in the absolute value of Zeta potential and the viscosity,revealing the escalation of emulsion stability.Furthermore,the particle size of oil droplets reduction after ultrasound pretreatment made the evenly distributed microstructure,which enhanced the stability of soybean oil-body emulsion.(2)The effect of ultrasound pretreatment of soybean oil-body emulsion on MTG-catalyzed reconstituent tofu gel was studied.After ultrasound pretreatment,the particle size of the reconstituent soymilk significantly decreased,attaining the minimum of 630.8 nm.And the particle size demonstrated a bimodal distribution,in which the left peak was consistent with the distribution of the soybean oil-body emulsion by ultrasound pretreatment.The absolute value of Zeta potential of the recombinant soymilk obviously increased with ultrasound pretreatment,whereby optimum values were obtained after treated for 15 or 20 min,as evidenced by Zeta potential analysis.The strength and water-holding capacity(WHC)of MTG-catalyzed reconstituent tofu gel increased with the extension of ultrasound treatment time of soybean oil-body emulsion,which was consistent with the change of soybean oil-body emulsion stability.Fourier transform infrared spectroscopy(FTIR)showed that ultrasound pretreatment of soybean oil-body emulsion had no significant effect on the formation of tofu gel induced by MTG.However,the microstructure showed that the enhancement of soybean oil-body emulsion stability after ultrasound pretreatment was favorable for the formation of compact and uniform gel network.(3)The effect of ultrasound pretreatment on the properties of soymilk and tofu gel derived thereof were investigated.Treatment of soymilk with ultrasound led to a reduction in the particle size and the minimum value was 1.256 ?m.However,the expansion of protein structure enhanced the surface hydrophobicity of soymilk,which achieving a maximum value when treated for 15 min.Subsequently,MTG was added to ultrasound-treated soymilk to promote the soy protein crosslinking.The gel strength,WHC,and non-freezable water content of MTG-catalyzed tofu gel obtained from treated soymilk increased with the extension of the ultrasound treatment time by116.07%?43.07%? 55.48%,whereas the free sulfhydryl content decreased because of the formation of disulfide bonds.FTIR demonstrated variations in the secondary structure of MTG-catalyzed tofu gel.Furthermore,soymilk's exposure to high-intensity ultrasound pretreatment led to a tofu gel with a dense,homogeneous,and stable network structure,as explored by scanning electron microscopy(SEM).