Queso Fresco has a limited shelf life and has been shown to support the rapid growth of Listeria monocytogenes during refrigerated storage. In addition to improving quality and extending shelf life, modified atmosphere packaging (MAP) has been used to control the growth of pathogenic microorganisms in foods. The objectives of this study were to determine the effects of MAP conditions on the survival and growth of spoilage microorganisms and L. monocytogenes during storage of Queso Fresco manufactured without starter cultures. For L. monocytogenes experiments, cheeses were surface inoculated at ∼4 log₁₀ cfu/g before packaging. Inoculated and uninoculated (shelf life experiments) cheeses were placed in 75-µm-high barrier pouches, packaged under 1 of 7 conditions including air, vacuum, or combinations of N₂ and CO₂ [100% N₂ (MAP1), 30% CO₂:70% N₂ (MAP2), 50% CO₂:50% N₂ (MAP3), or 70% CO₂:30% N₂ (MAP4), 100% CO₂ (MAP5)], and stored at 7°C. Samples were removed weekly through 35 d of storage. Listeria monocytogenes counts were determined for inoculated samples. Uninoculated samples were assayed for mesophilic and psychrotolerant counts, lactic acid bacteria, coliforms, and yeast and mold. In general, cheeses packaged under conditions consisting of higher contents of CO₂ had lower pH levels during storage compared with those stored in conditions with lower levels or no CO₂ at all. Similarly, the antimicrobial efficacy of MAP in controlling spoilage microorganisms increased with increasing CO₂ content, whereas conditions consisting of 100% N₂, vacuum, or air were less effective. Mean L. monocytogenes counts remained near inoculation levels for all treatments at d 1 but increased ∼2 log₁₀ cfu/g on cheeses packaged in air, vacuum, and 100% N₂ (MAP1) conditions at d 7 and an additional ∼1.5 log₁₀ cfu/g at d 14 where they remained through 35 d. In contrast, treatments consisting of 70% CO₂ (MAP4) and 100% CO₂ (MAP5) limited increases in mean L. monocytogenes counts to <1 log₁₀ cfu/g through 14 d and ∼1.5 log₁₀ cfu/g by d 21. Mean L. monocytogenes counts increased to levels significantly higher than inoculation (d 0) on cheeses stored in MAP2 on d 21, on d 28 for MAP3 and MAP4, and on d 35 for cheeses stored under MAP5 conditions. Overall, significant treatment × time interactions were observed between air, vacuum, and MAP1 when each was compared with MAP2, MAP3, MAP4, and MAP5. These data demonstrate that packaging fresh cheese under modified atmospheres containing CO₂ may be a promising approach to extend shelf life while limiting L. monocytogenes growth during cold storage.

Queso Fresco的保质期有限，并且已被证明可在冷藏过程中支持单核细胞增生李斯特菌的快速生长。除了提高质量和延长保质期外，气调包装（MAP）已用于控制食品中病原微生物的生长。这项研究的目的是确定MAP条件对未经发酵培养的Queso Fresco储存期间腐败微生物和单核细胞增生李斯特菌的存活和生长的影响。对于单核细胞增生李斯特氏菌实验，将奶酪表面接种约4 log ₁₀包装前cfu / g。将已接种和未接种的奶酪（保存期实验）放在75 µm高的隔离袋中，在7种条件中的1种下包装，包括空气，真空或N ₂和CO _2的组合[100％N ₂（MAP1），30％ CO ₂：70％N ₂（MAP2），50％CO ₂：50％N ₂（MAP3）或70％CO ₂：30％N ₂（MAP4），100％CO ₂（MAP5）]，并储存在7℃。每周取样35天，直至存放35天。李斯特菌确定接种样品的计数。对未接种样品进行了中温和抗精神病药计数，乳酸菌，大肠菌群以及酵母菌和霉菌的检测。通常，与在较低水平或根本没有CO _2的条件下储存的奶酪相比，在包含较高CO ₂含量的条件下包装的奶酪在储存过程中具有较低的pH值。同样，MAP在控制腐败微生物中的抗菌功效随CO ₂含量的增加而增加，而由100％N ₂，真空或空气组成的条件效果较差。所有治疗在d 1时单核细胞增生李斯特氏菌的平均计数仍保持在接种水平附近，但增加〜2 log ₁₀在空气中，真空和100％N ₂（MAP1）条件下包装的奶酪在第7天时为cfu / g，在第14天时额外保持在约1.5 log ₁₀ cfu / g，直到第35天。相比之下，由70％CO ₂（MAP4）和100％CO ₂（MAP5）组成的治疗在14 d内平均单核细胞增生李斯特菌计数增加至<1 log ₁₀ cfu / g，到d约为1.5 log ₁₀ cfu / g。 21.平均单核细胞增生李斯特菌在第21天，在MAP28和MAP4的第28天以及在MAP5条件下存储的奶酪的第35天，计数增加到显着高于MAP2中存储的奶酪接种（d 0）的水平。总体而言，将空气，真空和MAP1与MAP2，MAP3，MAP4和MAP5进行比较时，观察到了显着的治疗×时间相互作用。这些数据表明，在含有CO _2的改良气氛下包装新鲜奶酪可能是延长保质期同时限制冷藏过程中单核细胞增生李斯特氏菌生长的一种有前途的方法。