A Research On The Degradation Of Aflatoxin B₁ In Corn With Water-assisted Microwave Irradiation And Analysis Of The Products

Corn is one of the primary crops in the world and is used as a raw material of food,feed,and industrial products.Due to high levels of aflatoxin B₁（AFB₁）contamination in maize,aflatoxin contamination in food and feed causes significant economic losses and health risks worldwide every year.According to the latest report,aflatoxin contamination in food and feed results in a huge worldwide economic loss each year.Aflatoxin B₁（AFB₁）is one type of aflatoxin,which is an extremely potent liver carcinogen.Therefore,it has become a highly concerning problem to find suitable methods to reduce AFB₁ in corn.In this study,water-assisted microwave irradiation（WMI）was used to degrade AFB₁.First,the important role of water molecules in the process of microwave irradiation degradation of AFB₁ was studied,the effect and law of degradation of AFB₁ were discussed,and the chemical reaction kinetics of AFB₁ degradation and the non-thermal effects in the degradation process were analyzed.Second,the products of WMI degradation of AFB₁ and the influence of various factors on the types of degradation products were studied by high-resolution mass spectrometry technology,and the degradation path of AFB₁ was determined.Finally,the effect of WMI on the degradation of AFB₁ in corn and the influence of various factors on the degradation effect were analyzed.Meanwhile,the influence of WMI on the main quality of corn in the process of degradation of AFB₁ was analyzed.These results indicated that:（1）In the process of WMI degradation of AFB₁,water molecules could be used as a heat transfer medium to increase the heating rate of AFB₁.At the same time,the temperature required for microwave degradation of AFB₁ in water was lower than other heat transfer media.Under high-pressure airtight conditions,the greater the microwave power,the higher the temperature of the system,which was conducive to the degradation of AFB₁.However,when the microwave heating temperature was constant,the degradation rate of AFB₁ could also be increased by increasing the microwave power.In addition,the effect of WMI degradation of AFB₁ was affected by the initial concentration of AFB₁.Within a certain concentration range（0.05 mg/L～5 mg/L）,the degradation rate of AFB₁ increased first and then decreased with the increase of the initial concentration of AFB₁.The non-thermal effect in the process of WMI degradation of AFB₁ accelerated the degradation rate of AFB₁ and promoted the degradation of AFB₁.Besides,the study on the kinetics of WMI degradation of AFB₁ showed that the degradation process was pseudo-first-order reaction kinetics.（2）After AFB₁ was degraded by WMI,six major degradation products were found through UHPLC-Q-Orbitrap detection and difference analysis with SIEVE software.The change of microwave heating temperature affected the types of AFB₁ degradation products,while the microwave heating time,microwave heating power,and the initial concentration of AFB₁ mainly affected the number of AFB₁ degradation products.Then,the chemical structures of the six degradation products were inferred based on the molecular formulas and the MS-MS information of the six degradation products,and the chemical structure of AFB₁.Finally,the correct chemical structure of the six degradation products was verified and determined by the chemical structure verification software Mass Frontier 7.0.At the same time,the pathway of AFB₁degradation by WMI was speculated based on the chemical structure of the degradation products.It was the most important degradation method for AFB₁ to hydrolyze the lactone ring of AFB₁.If the WMI heating temperature was higher（≥130℃）,the hydrolysis of the furan ring structure could occur simultaneously.And after AFB₁ was degraded,its two most important toxic groups（C（8）-C（9）double bond and lactone ring）were destroyed,indicating that the toxicity of the six degradation products was significantly reduced.（3）Corn grain size,microwave heating temperature,solid-liquid ratio,microwave power and initial concentration of AFB₁ were all important factors affecting the effect of water-assisted microwave degradation of AFB₁.Under the same treatment conditions,the degradation effect of AFB₁ in corn flour was better than that in corn kernels.In addition,a larger heating rate was not conducive to accurate control of the termination temperature.It was determined that a microwave power of 2 W/g（400 W/200 g）was appropriate for heating.With the increase of microwave heating temperature（100°C～160°C）,the degradation rate of AFB₁increased from 6.6%to 90.6%.With the decrease of the material-to-liquid ratio（1:1～1:9）,the degradation rate of AFB₁ increased from 45.6%to 62.5%.With the increase of microwave power（200 W～800 W）under normal pressure,the degradation rate of AFB₁increased from 49.1%to 83.3%.As the initial content of AFB₁ in corn increased（120μg/kg～400μg/kg）,the degradation rate of AFB₁ increased from 62.0%to 74.0%.In addition,studies on the degradation kinetic model of AFB₁ in corn under different conditions show that the process of WMI degradation of AFB₁ in corn also conforms to the pseudo-first-order kinetic model.（4）The degradation of AFB₁ in corn by WMI had a significant impact on corn quality,such as the color,mold number,peroxide value,in vitro digestibility and gelatinization characteristics of corn.Among them,WMI treatment could effectively change the color of corn,kill toxin-producing molds in corn and increase the in vitro digestibility of corn flour（the percentage of fast and slow digestible starch increased）.With the extension of the treatment time,the peroxide value,resistant starch,hot paste stability and cold paste stability of corn flour showed an increasing trend.With the increase of temperature,the peroxide value in corn showed a trend of first increasing and then decreasing,the hot paste stability and cold paste stability of corn flour showed a trend of increasing,but it did not affect the resistant starch content in corn flour.With the decrease of the material-to-liquid ratio,the peroxide value and the content of resistant starch in corn showed a trend of continuous decrease.With the increase of processing microwave power under normal pressure,the peroxide value of corn,the stability of hot paste and the stability of cold paste of corn flour showed an increasing trend,the resistant starch had little effect.The above results showed that WMI could effectively degrade AFB₁,and water molecules as an auxiliary agent could reduce the temperature required for microwave degradation of AFB₁,increase the degradation rate of AFB₁,and cause AFB₁ to be degraded at a lower temperature.It revealed the fact that water molecules were not only the solvent of AFB₁ in the degradation process of AFB₁,but also participated in the degradation reaction of AFB₁.When using WMI to degrade AFB₁ in corn,the degradation rate of AFB₁ could be increased by increasing the microwave heating temperature,microwave power,AFB₁ content in corn,and reducing the material-to-liquid ratio.Especially after reducing the material-to-liquid ratio（increasing the ratio of water）,the degradation rate of AFB₁ could be further increased,the browning of corn color and the increase of peroxide value could be avoided,and the production of resistant starch could also be inhibited.At the same time,the gelatinization characteristics of the corn were closest to that of untreated corn.It demonstrated that WMI had potential advantages and feasibilities in the degradation of AFB₁ in corn.