Degradation And Diverting Rules Of Wheat Mycotoxins In The Processing

Mycotoxin is one of the most important contaminants hazarding food safety, to minimize thecontamination on grains, and set a foundation for the safety risk assessment of wheat contaminated withmycotoxins, mycotoxins levels in wheat infected by Fusarium head blight (FHB) were investigated, andthe relationship between severity levels of FHB and mycotoxin levels was studied. In the meanwhile,the transformation mechanism and degradation rules of mycotoxins in wheat milling, wheat-basedproducts processing and storage, and the mechanism and ability of microorganism on mycotoxinsclearing were studied, and the main conclusions are as follows:1. The investigation of mycotoxin levels in wheat infected by FHB in four provinces in2012demonstrated that, the occurrence of FHB was generally accompanied by the contamination ofmycotoxins, and the occurrence of FHB and production of mycotoxins were influenced by weathercondition. Deoxynivalenol (DON),15-acetyldeoxynivalenol (15-ADON),3-acetyldeoxynivalenol(3-ADON), Zearalenone (ZEN) and Sterigmatocystin (SMC) were the main mycotoxins detected in thisinvestigation, and the over-limit rates of DON and ZEN were67.11%and28.95%, respectively. Wheatcollected from A province was the most severely mycotoxin-contaminated in relation to the detectionrate, over-limit rate and contamination levels.2. There were distinct linear correlations between the severity levels of wheat infected by FHBand DON, deoxynivalenol-3-glucoside (D3G) contents, and the linear regression models werecalculated as YDON=257.78XDI+2315.61(r=0.96) and YD3G=41.81XDI-43.79(r=0.96). According to themodels, the predictive contents of DON when compared with the measured contents were overestimatedby59%whereas the predictive contents of D3G when compared with the measured contents wereunderestimated by42%, when predicting mycotoxin levels of wheat infected by FHB. This may beexplained that the occurrence of FHB and production of mycotoxin in the filed influenced by wheatvarieties, Fusarium species, and epidemiological conditions, thus it is difficult to accurately forecastmycotoxin contamination levels.3. Concentrations of DON and D3G were1.2to2.2times and2.9to4.4times higher in bran thanthat in wheat grain，and they were slightly lower in shorts compared to bran. Reductions of79to90%for DON and23to39%for D3G in flour were observed, respectively, compared to wheat grain. Withrespect to wheat grain, the distribution of DON was35%in bran,27%in shorts, and9%in flour, andthe distribution of D3G was77%in bran,58%in shorts, and37%in flour. Milling decreased the totalamount of DON but increased the amount of D3G, which may be explained that, wheat grains weresubjected to extrusion and shear forces of the grinder roll during milling, and the temperature becameincreasingly high as milling time continued, thus modification of mycotoxin structure by interactionwith wheat components may occur, and DON bound to starch.4. DON levels approximately doubled when flour was processed into Chinese steamed bread (CSB)and baked bread, whereas D3G levels were significantly lower. This may be explained by the conversion of D3G to DON under the influence of hydrolase released by yeast during CSB and bakedbread processing. DON and D3G concentrations in noodles decreased after cooking due to leaching ofthe mycotoxins into the cooking water. Retention levels of DON and D3G from flour to cooked Asiannoodles were nearly50%and20%, respectively, of the original levels.5. More than85%of ZEN in wheat remained in bran and shorts and less than15%in flour afterwheat was milled. ZEN concentrations doubled in bran and shorts and decreased by46～89%in wheatflour as compared to that in wheat. ZEN levels approximately doubled when flour was processed intoCSB and baked bread, while decreased about50%when flour was processed into noodles and cookeddue to ZEN leaching into the cooking water.6. Storage might exert significant influences on the concentrations of DON and D3G. As theincreasing of storage time, DON contents in wheat stored under different temperatures and in differentpackaging materials deceased, and DON levels decreased averagely by40%during storage30～90days.DON in wheat flour stored under different temperatures and in different packaging materials increasedgradually as time increasing. After storing for180days, D3G contents in most wheat samples storedunder different temperatures and in different packaging materials increased, which increased averagelyby31.76%; D3G contents in wheat flour samples stored under different temperatures and in differentpackaging materials increased as the storage time extension.7. Lactic acid bacteria has the ability of clearing DON, and the mechanism was physical binding,rather than degrading DON to other metabolites. The binding rate of Lactobacillus pentosus23130,Lactobacillus rhamnosus23119, and Pediococcus pentosaceus23190to DON in liquid were all higherthan80%. Heat treatment and acid treatment were able to increase the binding ability of LAB to DON.After heat treatment, the binding ability to DON of Weissella confuse23465increased by more than40%comparing with viable LAB, while alkali treatment had no significant impact.