Study On Enzymatic Degradation Of Zearalenone To Produce Zero Trans Fatty Acid Corn Oil

In China,the acid value and the content of zearalenone（ZEN）of crude corn oil are generally high.Chemical refining can effectively remove both,but the refining consumption is large and the oil yield is low.Physical refining is more suitable for processing high acid value corn crude oil,but the prerequisite is that the pretreatment is complete and ZEN is removed up,otherwise it not only affects the taste and color,but also poses serious food safety risks.Conventional pretreatment methods such as hydration degumming and clay adsorption can only partially remove ZEN.The remaining ZEN must be removed by the subsequent deodorization.And it is necessary to increase the deodorization depth by long-term distillation with a large amount of high-temperature steam,resulting in a large amount of trans fatty acids generated and increasing new safety risks.It has become a difficult problem for corn oil refining to not only improve the oil yield,but also meet the"dual control"requirements of lower trans fatty acids and ZEN.Therefore,according to the requirements of physical refining,this article uses ZEN degrading enzyme（ZHD）to pretreat corn crude oil to specifically remove ZEN and inhibit the formation of trans fatty acids while maximizing the retention of beneficial components in the oil.The main research contents are as follows:1、Using a single factor test,under the constraint of zero trans fatty acid content in finished corn oil,the effects of deodorization process conditions on trans fatty acid production and ZEN content in corn oil were investigated to determine the ZEN limit of the oil to be deodorized.The results show that the structure of ZEN had not changed before and after deodorization.The prerequisite for ensuring the zero trans fatty acid content of the finished corn oil was to control the deodorization temperature below 230℃,the deodorization time within 60 minutes,and the phosphorus content of the oil to be deodorized was not greater than 5 mg/kg,and the iron content was not greater than 0.1 mg/kg.At this condition,the ZEN removal rate was between 55%and69%.When the ZEN content of the oil to be deodorized is controlled lower than 900μg/kg,the content of ZEN in finished corn oil was possible to meet the EU limit requirement（400μg/kg）.2、Liquid mass spectrometry（LC-MS）was used to identify the intermediate and final products of the reaction.The main factors affecting the reaction rate and process of ZHD were investigated based on Michaelis equation and the kinetics and thermodynamics of the reaction process were studied.The results showed that when the stirring speed was lower than 150 r/min,external diffusion was the key control condition for the reaction,and the effect of external diffusion on the reaction speed could be eliminated through high-speed shear mixing.The maximum speed of the ZHD degradation reaction was 0.97μmol/kg·min,Km is 11476μmol/kg,the Michaelis equation was V=0.97[S]/（11476+[S]）.There were two types of intermediate products in the reaction process.Under the action of ZHD,ZEN first forms the intermediate productⅠTrp-Leu-Asp-Gly-ZEN●H₂O,and then generates the intermediate productⅡDehydration W-ZEN.Afterwards,the lactone bond opens to form C₁₈H₂₄O₆,and finally automatically decarboxylates to form a decarboxylated product C₁₇H₂₄O₄.Intermediate products and end products are generated under different p H conditions,and the reaction is easier to proceed in a neutral alkaline environment.The intermediate products first increased and then decreased with time,while the content of end products continued to grow.3、A semi continuous process for enzymatic degradation of ZEN in corn crude oil with different ZEN content was studied using single factor and response surface methodology experiments.The results showed that the optimal process conditions were temperature 39.01℃,p H 8.08,time 3.9 h,enzyme addition 44.7 mg/kg,and the degradation rate of ZEN reached 94.66%.From the perspective of cost control,the process conditions could be optimized to a temperature of 37.29-42.61℃,p H 7.6-8.4,time 3.12-3.96 h,and enzyme addition within the range of 37.3-39.9 mg/kg.Enzymatic hydrolysis of corn oil to be deodorized with different initial ZEN content was carried out under optimized process conditions,and it was found that when the initial ZEN content was 1000,3000,and 5000μg/kg and the enzyme dosages were 10,20,and 30 mg/kg correspondingly,the content of ZEN could reduce to 900μg/kg。4、In the semi continuous process,ZHD can only be used once and has a high cost.The process conditions for immobilization of ZHD macroporous resin were studied using a single factor method,and repeated application tests were also conducted.The results showed that the optimal conditions for enzyme immobilization were as follows:the amount of macroporous resin DA201 added was 1 g,the adsorption temperature was 35℃,the adsorption time was 3 h,the buffer p H was 7.5,and the amount of enzyme added was 3 ml.At these conditions,the immobilization rate reached 83.3%.Kinetic studies had found that the degradation reaction of IZHD is not affected by external diffusion,with a maximum reaction rate of 0.598μmol/kg·min,Michaelis constant 10628μmol/kg,the Michaelis equation is V=0.598[S]/（10628+[S]）.After immobilization,both Km and Vm of the enzyme decreased.The optimal application conditions for immobilized enzyme were as follows:temperature 45℃,p H 8,time 4 h,addition amount of immobilized ZHD 50 g/kg,degradation rate 92.46%.The degradation rate decreased with the increase of the number of uses,and the conversion rate reached 48.42%when the number of uses reached 6.5、A 200 times process magnification was conducted with compared it with traditional refining methods.The results showed that the physical refining of corn oil by enzymatic degradation combining with deodorization had a beneficial concomitant retention rate of over 80%and a ZEN content of less than 400μg/kg,yield greater than 90%,trans acid content controlled within 0.3%.It can be marked as zero,meeting the"dual control"requirements of TFA and ZEN,and has more advantages than traditional methods.In summary,this article has studied the pretreatment process of crude corn oil with ZHD and its semi continuous,immobilized enzyme degradation process.While maximizing the retention of beneficial components in the oil,it specifically removes ZEN and inhibits the formation of trans fatty acids,providing a technical basis for the production of trans fatty acids and ZEN"dual control"corn oil.