储存玉米中黄曲霉毒素主要产生菌的检测及污染预防研究

通过对储存玉米霉变初期的感官症状观察、分离菌的PCR检测及在不同环境条件下的生长预测模型建立,探讨了识别、预防储存玉米发生黄曲霉毒素及其主要产生菌污染的实用方法。结果表明:籽粒色泽及致密性改变、表面有潮湿感、粮堆内局部发热等症状的出现可表征储存玉米有可能发生真菌污染。以毒素合成相关的全局性调控因子veA基因为靶标,对污染玉米样品分离菌进行PCR检测,扩增出约1.9kb的条带,与预期大小相符,证明污染菌是黄曲霉或寄生曲霉。污染曲霉在不同玉米水分活度和环境温度下的生长数据,经Baranyi函数拟合、估测其最大生长速度,并建立了生长速度随玉米水分活度和环境温度变化的多项式回归模型;模型显示玉米水分活度和环境温度对污染曲霉的生长影响具有协同性;要确保储存玉米安全,储存参数的限值选择应远离适合污染菌生长的区域。本研究为储存玉米安全管理决策、玉米水分活度和环境温度限值的选择及调控提供支持,利于降低储存玉米的黄曲霉毒素及其主要产生曲霉(黄曲霉或寄生曲霉)的污染风险。

Detection and prevention of the main aflatoxigenic Aspergillus contamination in stored corn

Practical methods were developed based on observation of the early signs and symptoms of corn mildew, PCR detection of the Aspergillus strain isolated from the contaminated corn, and establishment of the predictive models for the growth of the isolate under different corn water activities and environmental temperatures. The results indicated that the occurrence of sensory symptoms, such as changes in color and luster, moist feeling over the surface of the corn kernels, and local hot spots in the corn piles, were characterized as the trend of fungal contamination under variable storage conditions. Additionally, PCR assay was carried out using the fungal global regulator veA as the detective target and a PCR product of the expected size (1.9 kb) was generated, indicating that the isolate is A. flavus or A. parasiticus strain. Moreover, the predictive models for the growth of the isolate were constructed via fitting the primary Baranyi model to the growth data of the isolate collected under different corn water activities and environmental temperatures, for estimating the maximum colony growth rates of the isolate. The obtained maximum growth rates were then modeled as a function of corn water activity and environmental temperature by using second-order polynomial equation. The developed models indicated that corn water activity and environmental temperature have interactive effects on the growth of the isolate and for corn safety storage, the set critical limits should be away from the growth region. Totally, this research could support the decision-making for corn safety storage, the set and monitoring of the critical limits for corn water activity and environmental temperature, and thus favor to the control of aflatoxin and aflatoxigenic A. flavus or A. parasiticus contamination in stored corn.