Microbial characterization and diversity of artisanal Ranchero cheese with emphasis in Lactococcus strains

Abstract The aim of this work is to characterize the natural microflora of artisanal Ranchero cheese and to identify Lactococcus isolates. Ten artisanal Ranchero cheese samples made with raw milk were obtained from local producers located in different geographical areas. Aerobic mesophilic, Staphylococci, Psychrophilic , total coliforms, molds, yeast and, lactic acid bacteria (LAB) (Lactococcus , Streptococcus mesophilic and thermophilic, Lactobacillus , Enterococcus, Leuconostoc) were numbered through agar plating. LAB isolates were classified by genus. Then, nineteen randomly selected presumptive Lactococcus isolates were assigned to specie by PCR amplification and DNA sequence. A high number of aerobic mesophilic Staphylococci, Psychrophilic, total coliforms, molds, and yeast were found. Lactococci, mesophilic and thermophilic Streptococci and Lactobacilli were the dominant LAB. Enterococci and Leuconostoc were also present. The isolates were identified as L. lactis subsp. lactis and L. garvieae . And both were found to be the dominant Lactococcus species that could be selected and used in a starter culture. Sanitation deficiencies in the production of artisanal Ranchero cheese were evident, which may translate into being a potential consumers health risk factor.

摘要：本研究旨在表征兰切罗手工奶酪（artisanal Ranchero cheese）的天然微菌群，并分离鉴定乳球菌属（Lactococcus）分离株。研究从不同地理区域的本地生产商处采集了10份以生乳（raw milk）制作的兰切罗手工奶酪样品。通过琼脂平板计数法，对需氧嗜温菌、葡萄球菌属（Staphylococci）、嗜冷菌（Psychrophilic）、总大肠菌群、霉菌、酵母菌及乳酸菌（lactic acid bacteria, LAB）——涵盖乳球菌属、嗜温/嗜热链球菌属、乳杆菌属（Lactobacillus）、肠球菌属（Enterococcus）、明串珠菌属（Leuconostoc）——进行计数。随后按属水平对乳酸菌分离株进行分类，随机选取19株疑似乳球菌属分离株，采用聚合酶链式反应（Polymerase Chain Reaction, PCR）扩增结合DNA测序完成菌种鉴定。结果显示，样品中需氧嗜温菌、葡萄球菌、嗜冷菌、总大肠菌群、霉菌及酵母菌含量较高；乳球菌、嗜温与嗜热链球菌及乳杆菌为优势乳酸菌类群，肠球菌与明串珠菌亦有检出。经鉴定，分离株为乳酸乳球菌乳酸亚种（L. lactis subsp. lactis）与加维乳球菌（L. garvieae），二者均为可入选发酵剂菌种（starter culture）的优势乳球菌菌株。本研究发现，兰切罗手工奶酪的生产过程存在明显的卫生缺陷，这可能构成消费者健康的潜在风险因素。