Department of Nutrition, Dietetics and Food Sciences, Utah State University, Logan, Utah 84322-8700, USA.
J Dairy Sci. 2011 Sep;94(9):4329-35. doi: 10.3168/jds.2011-4219.
Traditional aged Cheddar cheese does not support Listeria monocytogenes growth and, in fact, gradual inactivation of the organism occurs during storage due to intrinsic characteristics of Cheddar cheese, such as presence of starter cultures, salt content, and acidity. However, consuming high-salt (sodium) levels is a health concern and the dairy industry is responding by creating reduced-salt cheeses. The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of L. monocytogenes in low-salt compared with regular-salt Cheddar cheese at 2 pH levels stored at 4, 10, and 21°C. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high pH and aged for 10 wk, resulting in 4 treatments: 0.7% NaCl and pH 5.1 (low salt and low pH); 0.7% NaCl and pH 5.5 (low salt and high pH); 1.8% NaCl and pH 5.8 (standard salt and high pH); and 1.8% NaCl and pH 5.3 (standard salt and low pH). Each treatment was comminuted and inoculated with a 5-strain cocktail of L. monocytogenes at a target level of 3.5 log cfu/g, then divided and incubated at 4, 10, and 21°C. Survival or growth of L. monocytogenes was monitored for up to 90, 90, and 30 d, respectively. Listeria monocytogenes decreased by 0.14 to 1.48 log cfu/g in all treatments. At the end of incubation at a given temperature, no significant difference existed in L. monocytogenes survival between the low and standard salt treatments at either low or high pH. Listeria monocytogenes counts decreased gradually regardless of a continuous increase in pH (end pH of 5.3 to 6.9) of low-salt treatments at all study temperatures. This study demonstrated that post-aging inoculation of L. monocytogenes into low-salt (0.7%, wt/wt) Cheddar cheeses at an initial pH of 5.1 to 5.5 does not support growth at 4, 10, and 21°C up to 90, 90, and 30 d, respectively. As none of the treatments demonstrated more than a 1.5 log reduction in L. monocytogenes counts, the need for good sanitation practices to prevent post-manufacturing cross contamination remains.
传统 aged Cheddar 奶酪不支持李斯特菌的生长，事实上，由于切达干酪的固有特性，如发酵剂的存在、盐含量和酸度，在储存过程中，该生物体的活力逐渐下降。然而，摄入高盐（钠）水平是一个健康问题，乳制品行业正在通过生产低盐奶酪来应对。低盐奶酪的微生物稳定性尚未得到很好的记录。本研究比较了在 4°C、10°C 和 21°C 下储存的低盐和常规盐切达干酪中李斯特菌在低 pH 值（pH5.1 和 pH5.5）和高 pH 值（pH5.8 和 pH5.3）下的存活情况。切达干酪配方为 0.7%和 1.8%NaCl（wt/wt），pH 值分别为 5.1 和 5.5（低盐和低 pH 值）以及 pH 值为 5.8 和 5.3（标准盐和低 pH 值），并进行了为期 10 周的老化，共得到 4 种处理：0.7%NaCl 和 pH5.1（低盐和低 pH 值）；0.7%NaCl 和 pH5.5（低盐和高 pH 值）；1.8%NaCl 和 pH5.8（标准盐和高 pH 值）；以及 1.8%NaCl 和 pH5.3（标准盐和低 pH 值）。每个处理均被粉碎并接种 5 株李斯特菌的混合菌液，目标浓度为 3.5 log cfu/g，然后分为两部分，在 4°C、10°C 和 21°C 下孵育。分别监测李斯特菌的存活或生长，最长可达 90、90 和 30 天。所有处理中李斯特菌的数量减少了 0.14 到 1.48 log cfu/g。在给定温度下孵育结束时，低 pH 值（5.1 和 5.5）和高 pH 值（5.8 和 5.3）下的低盐和标准盐处理之间的李斯特菌存活没有显著差异。无论低盐处理的 pH 值是否持续升高（终 pH 值为 5.3 至 6.9），李斯特菌的数量都在逐渐减少，这在所有研究温度下均如此。本研究表明，在初始 pH 值为 5.1 至 5.5 的低盐（0.7%，wt/wt）切达干酪中进行低 pH 值（5.1 至 5.5）和高 pH 值（5.8 至 5.3）下的老化后接种李斯特菌，在 4°C、10°C 和 21°C 下分别不支持长达 90、90 和 30 天的生长。由于所有处理中李斯特菌数量的减少都不超过 1.5 log，因此仍然需要良好的卫生实践来防止生产后交叉污染。
