远红外对黄曲霉孢子的杀灭效果及其机理研究

Effect of far-infrared on the inactivation of the Aspergillus flavus sporesand its mechanisms

利用远红外辐照技术(far infrared irradiation,FIR)处理接种黄曲霉孢子的大米,研究其对黄曲霉(Aspergillus flavus)孢子的杀灭效果和黄曲霉菌产黄曲霉毒素B 1(aflatoxin B 1,AFB 1)能力的影响,同时考察处理前后黄曲霉孢子的细胞结构变化。结果表明,大米含水率为20%和30%(质量分数)时,辐照115℃处理5 min,表面黄曲霉孢子对数降低值分别为2.04±0.17和2.96±0.28,AFB1总量分别下降56.61%和63.34%,单位菌体产毒量分别下降27.64%和38.94%。远红外辐照后,噻唑蓝(methylthiazolyldipheny-tetrazolium bromide,MTT)比色法显示孢子活力降低,通过荧光显微镜观察到被碘化丙啶染色的细胞数增多,扫描电子显微镜结果显示孢子细胞结构被破坏,孢子坍塌凹陷,胞内物泄露;圆二色谱结果表明当结合保温处理时,胞内蛋白变性失活加速,无规则卷曲相对含量明显增加,黄曲霉孢子失活。远红外辐照对孢子的作用影响了其生长代谢过程,并对其细胞结构产生了破坏,从而降低了黄曲霉和黄曲霉毒素污染粮食的风险。

Compared with the traditional food thermal processing,far infrared irradiation(FIR)was more efficient and energy savings without chemical residues,which had a broad application prospect in food sterilization.The objectives of this study were to evaluate the effect of FIR on the inactivation of Aspergillus flavus spores inoculated in rice and the reduction of aflatoxin B 1 production.In addition,changes of the cell morphological of A.flavus spores were studied after FIR treatment.When the moisture content of rice was 20%and 30%,FIR heating at 115℃for 5 min resulted in(2.04±0.17)and(2.96±0.28)-log reductions of A.flavus spores,respectively.The total amount of AFB 1 decreased by 56.61%and 63.34%,respectively.And the amount of AFB 1 produced by unit dry weight of the mycelium decreased by 27.64%and 38.94%,respectively.After FIR treatment,MTT measurement showed a decrease in the viability of spores.A significant increase in number of cells stained by propidium iodide was observed using fluorescence microscopes.Cell membrane damage and the leakage of intracellular substances of A.flavus spores were observed by SEM.Results of circular dichroism spectroscopy(CD)suggested protein denaturation accelerated and the relative content of random curl increased when FIR combined with tempering treatment,which induced the inactivation of A.flavus spores.The FIR treatment affected the growth and metabolism process of A.flavus spores with the destruction of cell structure.As a result,the risk of A.flavus spores and AFB1 infection in grain was reduced after FIR treatment.