不同处理方法对芽苗菜表面微生物的控制和消除

Different Methods to Control and Eliminate the Microorganisms on the Surface of Sprouts

为了深入研究即食蔬菜在不同处理下微生物的消长变化及种群结构变化规律,本实验从芽苗菜入手,采用水洗,辐照、冷热激,含氯消毒剂、有标识杀菌成分的清洗剂等5种方法对芽苗菜进行处理,建立微生物总数动态生长模型,利用微生物宏基因组学的方法调查处理前后的微生物种群丰度变化,选择性培养后采用基质解析电离飞行时间质谱法(MALDI-TOF MS)对优势种群进行鉴定。实验结果表明即食芽苗菜微生物总数稳定在一个数量级(5~6 lg CFU/g),处理会将微生物种群结构平衡打破,但经过一段时间微生物总量会恢复之前稳定水平。其中辐照方法影响最为明显;水活性方法(水洗,冷热激,有标识杀菌成分的清洗剂清洗)影响相对较小且恢复较快,但内含不同成分,微生物控制效果稍有差异。实验结论为处理原理的差异是影响微生物种群结构的主要原因。此外辐照方法会将芽苗菜优势种群假单胞菌属和乳酸菌属改变为芽孢菌属,并在其中检出蜡样芽孢杆菌,增加了食用安全风险,就是说即食蔬菜微生物的控制最有效的方法并不一定是最安全的方法。在即食果蔬微生物控制中不仅要考虑微生物总量的降低也需要综合微生物微观生态学的其他因素。

This research started with five different treatments of sprouts i.e. water washing, irradiation, cold and heat shocks, application of chlorine-containing disinfectant or cleaning agent with a labelled bactericidal component, to investigate in depth the changing trends of the microbial growth and decline and the population structure of microorganisms in the ready-to-eat vegetables under different treatments. The dynamic growth models for the total amount of microorganisms were then established. The changes in the abundance of microbial populations before and after the individual treatment were investigated by metagenomics, and matrix-assisted laser desorption ionization time of flight mass spectrometry（MALDI-TOF-MS） was used to identify the dominant population after selective culture. The experimental results showed that the total number of microorganisms in the ready-to-eat sprouts remained constant at an order of magnitude（5-6 lg CFU/g）. The treatments broke the balance of the microbial population structure, however, the total number of microorganisms would return to the previous stable level after a certain period of time. Among the different treatments, irradiation exhibited the most obvious influence. The methods capably of altering water activity（i.e. water washing, cold and heat shocks and cleaning agent with a labelled bactericidal component） seemed less effective causing quicker recovery of microbial amounts, with the effect on microorganisms slightly varying with the different labelled bactericidal component. It was concluded that the differences in the working mechanisms underlying the treatments accounted mainly for the changes in microbial population structure. In addition, the irradiation method could change the dominant population in the sprouts, Pseudomonas Sp. and Lactobacillus Sp, into Bacillus Sp.（with Bacillus cereus detected）, which increased food poisoning risk with its consumption. That is, the most effective method of suppressing the microorganisms in the ready-to-eat vegetables is not necessarily the safest method. In the control of microorganisms in ready-to-eat fruits and vegetables, not only the reduction of the total microbial amount but also other factors related to the microecology of microorganisms must be considered.