Acetic Acid Catalysis Processing Technology Of Soybean Meal

The variou s anti-nutritional factors(ANFs)contained in natural soybean meal(SBM)can seriously interfere with the digestion,absorption,physiological health and production performance of animals,which must be properly processed before it can be used a s animal feed.In view of the problem of traditional fermentation methods,su ch as long time-consuming,labor intensity and difficult to control,an effective method with mild and recyclable acetic acid wa s established to reduce the ANFs in SBM in this paper,which focused on two k ey ANFs indicators of allergenic proteins and trypsin inhibitor(TI).Considering the negative influence of temperature on the soluble protein components in SBM,the auxiliary catalyst-acetic acid processing technology was further developed to reduce the processing temperature and improve the nutritional value of SBM.Overall,this study provides an efficient,simple and quick approa ch for redu cing ANFs in SBM while maintaining its nutritional value.On this ba sis,the mechanism of the degra dation of ANFs and the changes of protein conformation during the processing of acetic acid and auxiliary a dditives was investigated.The main findings are as follows:The acetic a cid-catalyzed processing can significa ntly reduce the hydrothermal temperature required for the redu ction of ANFs in SBM,and ca n basically maintain the amino acid composition of the raw material,but reduced the protein solubility(PS)of SBM.After the treatment of SBM with a 10% acetic acid solution(solid-liquid ratio of 1:5)at 70 °C for 20 min,the allergenic proteins were completely degra ded,and the TI wa s reduced from 5.15 mg/g to 1.03 mg/g.However,significant a mount of soluble proteins was lost,the PS value of SBM a fter the treatment was reduced from 91.81% to 78.85%,but still me t the international standard for feed SBM(GB/T 19541-2004).Compared to conventional heating methods,the acetic acid-catalyzed processing can lower the treatment temperature while increa sing the soluble protein content.The three main process parameters of acetic acid-catalyzed processing were analyzed.The impact of variables on the degradation of ANFs wa s found to be in the order of acetic acid concentration>reaction temperature>rea ction time,and the impact of the variables on the PS values followed the order: reaction tempera ture>acetic acid concentration>reaction time.In order to reduce the loss of nutritional value of soy protein caused by acetic acid-catalyzed processing,a n auxiliary catalyst-acetic acid processing technology was further developed to reduce the temperature and better maintain the original nutritional value of SBM on the basis of degrade ANFs.It wa s found that Fe(II)-assisted acetic acid processing can significa ntly reduce the ANFs of SBM under low temperature conditions,and further preserve the original nutritional value of SBM.Compared with the ra w SBM,Fe(II)-assisted acid treatment redu ced TI content significantly from 5.20 to 0.86 mg/g a nd allergenic proteins were completely degraded,using 10% acetic acid and 0.15% Fe(II)at 55 °C for 30 min(solid-liquid ratio 1:5).The PS value of SBM after Fe(II)-assisted acid treatment was 84.21%,which wa s 6.80% higher than that of the single acetic a cid method at 70 °C.Moreover,the degradation effects of different acids against ANFs u nder the sa me pH conditions were investigated.It wa s found that the degradation effect of a cetic acid was better than that of sulfuric a cid and acetic a cid,which probably caused by the partial dissociation characteristics of acetic acid.Acetic acid can provide more proton hydrogen,which is more condu cive to the degra dation of ANFs.Meanwhile,the effect of Fe(II)on the ANFs degradation wa s higher than that of the protonic a cid provided by the addition of a cid,indicating that the Fe(II)-assisted a cid treatment was more beneficial to the degradation of ANFs in SBM.Changes in protein structure and microenvironment play an important role in the degradation of ANFs in SBM.In this study,the Fe(II)-a ssisted degra dation was explained with respect to the cha nges in structures,conformation and surface hydrophobicity of soybean prot ein isolate(SPI).We found that the degradation of ANFs in SBM was a ssociated with the changes in the conformation of SPI.Red-shift of maximu m emission wavelength indicated that Fe(II)-a ssisted acid induced molecular unfolding of SPI and increa sed surfa ce hydrophobicity.It wa s found that Fe(II)improved the acid-mediated dissociation of SPI by promoting the exposure of hydrophobic groups.Meanwhile,negative correlation of ANS hydrophobicity to PS indicated that the decrea se in protein solubility in pretr eated soy meal may be related to the exposure of hydrophobic groups.Investigation of protein secondary structure revealed that Fe(II)-assisted a cid treatment decreased the ?-sheet structure by 4.65% and increa sed the ?-helical content by 7.37%.This demonstrated that Fe(II)and acetic acid synergistically degra de ANFs by altering protein conformations in SBM.In conclusion,Fe(II)-assisted a cid treatment is an effective method for improving the nutritional quality of SBM via changes in SPI conformation.