Milk Quality Improvement Program, Department of Food Science, Cornell University, Ithaca, NY 14853.
Milk Quality Improvement Program, Department of Food Science, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 2019 Nov;102(11):9689-9701. doi: 10.3168/jds.2019-16304. Epub 2019 Aug 22.
Sporeforming bacteria are responsible for the spoilage of several dairy products including fluid milk, cheese, and products manufactured using dried dairy powders as ingredients. Sporeforming bacteria represent a considerable challenge for the dairy industry because they primarily enter the dairy product continuum at the farm, survive processing hurdles, and subsequently grow in finished products. As such, strategies to reduce spoilage due to this group of bacterial contaminants have focused on understanding the effect of farm level factors on the presence of spores in bulk tank raw milk with the goal of reducing spore levels in raw milk, as well as understanding processing contributions to spore levels and outgrowth in finished products. The goal of the current study was to investigate sources of spores in the farm environment and survey farm management practices to identify variables using multimodel inference, a model averaging approach that eliminates the uncertainty of traditional model selection approaches, that affect the presence and levels of spores in bulk tank raw milk. To this end, environmental samples including feed, bedding, manure, soil, water, and so on, and bulk tank raw milk were collected twice from 17 upstate New York dairy farms over a 19-mo period and the presence and levels of various spore types (e.g., psychrotolerant, mesophilic, thermophilic, highly heat resistant thermophilic, specially thermoresistant thermophilic, and anaerobic butyric acid bacteria) were assessed. Manure had the highest level of spores for 4 out of 5 aerobic spore types with mean counts of 5.87, 5.22, 4.35, and 3.68 log cfu/g of mesophilic, thermophilic, highly heat resistant thermophilic, and specially thermoresistant thermophilic spores, respectively. In contrast, bulk tank raw milk had mean spore levels below 1 log cfu/mL across spore types. Multimodel inference was used to determine variables (i.e., management factors, environmental spore levels, and meteorological data from each sampling) that were important for presence or levels of each spore type in bulk tank raw milk. Analyses indicated that variables of importance for more than one spore type included the residual level of spores in milk from individual cows after thorough teat cleaning and forestripping, udder hygiene, clipping or flaming of udders, spore level in feed commodities, spore level in parlor air, how often bedding was topped up or changed, the use of recycled manure bedding, and the use of sawdust bedding. These results improve our understanding of how spores transfer from environmental sources into bulk tank raw milk and provide information that can be used to design intervention trials aimed at reducing spore levels in raw milk.
产孢细菌是导致包括液态奶、奶酪和使用干燥乳制品粉末作为原料制成的产品在内的几种乳制品变质的原因。产孢细菌对乳制品行业构成了相当大的挑战，因为它们主要在农场进入乳制品连续体，在加工过程中幸存下来，然后在成品中生长。因此，减少由于这组细菌污染物引起的变质的策略侧重于了解农场水平因素对散装奶中孢子存在的影响，目的是降低原料奶中的孢子水平，以及了解加工对孢子水平和成品中生长的影响。本研究的目的是调查农场环境中的孢子来源，并调查农场管理实践，以使用多模型推理来识别变量，多模型推理是一种模型平均方法，可消除传统模型选择方法的不确定性，从而影响散装奶中孢子的存在和水平。为此，在 19 个月的时间里，从纽约州北部的 17 个奶牛场收集了环境样本（包括饲料、垫料、粪便、土壤、水等）和散装奶，并评估了各种孢子类型（如嗜冷、中温、高温、高度耐热高温、特殊耐热高温和厌氧丁酸细菌）的存在和水平。粪便对 5 种需氧孢子类型中的 4 种具有最高的孢子水平，中温、高温、高度耐热高温和特殊耐热高温孢子的平均计数分别为 5.87、5.22、4.35 和 3.68 log cfu/g。相比之下，散装奶中各种孢子类型的孢子水平均低于 1 log cfu/mL。多模型推理用于确定对散装奶中每种孢子类型的存在或水平重要的变量（即管理因素、环境孢子水平和每次采样的气象数据）。分析表明，对一种以上孢子类型重要的变量包括彻底擦洗和挤奶后个体奶牛奶中残留的孢子水平、乳房卫生、剪毛或烧毛、饲料商品中的孢子水平、牛舍空气中的孢子水平、垫料补充或更换的频率、使用再生粪便垫料和使用木屑垫料。这些结果提高了我们对孢子如何从环境来源转移到散装奶中的理解，并提供了可用于设计旨在降低原料奶中孢子水平的干预试验的信息。
