Enumeration and MALDI-TOF MS identification of contaminating bacteria in foods containing lactic acid bacteria
LING Li1, LYU Jingzhang2,3, CHEN Jing4, JIANG Yue5, WAN Zhigang2,3, LIU Jingwen1, YAN Qiongying4, LU Xingan6*
1(Guangzhou Customs Technology Center, Guangzhou 510623, China) 2(Shenzhen Academy of Inspection and Quarantine, Shenzhen 518045, China) 3(Food Inspection and Quarantine Technology Center of Shenzhen Customs District, Shenzhen 518045, China) 4(Shenzhen Academy of Metrology and Quality Inspection, Shenzhen 518131, China) 5(Guangdong Pharmaceutical University, Zhongshan 528045, China) 6(Chinese Academy of Inspection and Quarantine,Beijing 100176, China)
摘要 为对乳酸菌食品中的污染菌进行计数和鉴定,采用MRS琼脂对6种乳酸菌粉和12种市售乳酸菌食品中的乳酸菌进行计数,同时用平板计数琼脂(plate count agar,PCA)、不含糖的计数琼脂(count agar sugar free, CASF)对上述样品中的菌落总数和非乳酸菌进行计数。对PCA和CASF平板上的菌落,采用基质辅助激光解吸电离飞行时间质谱(matrix-assisted laser desorption/ ionization time of flight mass spectrometry,MALDI-TOF MS)进行鉴定。数据显示,乳酸菌粉的乳酸菌计数结果为3.2×1010～4.7×1010CFU/g,PCA和CASF平板上没有菌落生长。12种市售乳酸菌食品的乳酸菌计数结果均高于106CFU/g。MALDI-TOF MS鉴定发现,PCA上的菌落既有乳酸菌,又有非乳酸菌;乳酸菌不能在CASF平板上形成菌落,在CASF平板上生长的菌落,经鉴定均为非乳酸菌,属于乳酸菌食品中的污染菌。采用不含糖的计数琼脂CASF结合MALDI-TOF MS鉴定技术,可迅速准确对乳酸菌食品中污染菌进行计数和鉴定。
Abstract: To enumerate and identify the contaminating bacteria in foods containing lactic acid bacteria(LAB), MRS agar was used to enumerate the LAB in six starter powders and 12 kinds of commercial LAB-containing foods. Meanwhile, total aerobic microorganisms and non-LAB were enumerated by plate counting agar (PCA) and count agar sugar free (CASF) respectively. The colonies on PCA and CASF plates were identified by matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF MS). In starter powders, the numbers of LAB ranged from 3.2×1010-4.7×1010 CFU/g and no colony was found on PCA and CASF plates. In all commercial foods containing LAB, the numbers of LAB were higher than 106 CFU/g. After identified by MALDI-TOF MS, the colonies on the PCA plates were proved to contain both LAB and non-LAB while the colonies on the CASF plates were identified as non-LAB. The non-LAB belonged to the contaminating bacteria in LAB foods. Based on these results, this study revealed that the contaminating bacteria in commercial foods containing LAB can be enumerated by CASF and identified by MALDI-TOF MS quickly and accurately.
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2022, Vol. 48 
