Department of Veterinary Medicine, University of Sassari, Via Vienna, 2, 07100 Sassari (SS), Italy; Department of Agronomy, Food, Natural Resources, Animals and Environment, DAFNAE, University of Padova, Viale dell'Università 16, 35020 Legnaro, (PD), Italy.
Department of Agronomy, Food, Natural Resources, Animals and Environment, DAFNAE, University of Padova, Viale dell'Università 16, 35020 Legnaro, (PD), Italy.
Food Res Int. 2023 Oct;172:113101. doi: 10.1016/j.foodres.2023.113101. Epub 2023 Jun 12.
Cheese production is an applied biotechnology whose proper outcome relies strictly on the complex interactive dynamics which unfold within defined microbial groups. These may start being active from the collection of milk and continue up to its final stages of maturation. One of the critical parameters playing a major role is the milk refrigeration temperature before pasteurization as it can affect the proportion of psychrotrophic taxa abundance in the total milk bacterial population. While a standard temperature of 4 °C is the common choice, due to its general growth control effect, it does have a potential drawback. This is due to the fact that some cold-tolerant genera present a proteolytic activity with uncompleted proliferation, which could negatively affect curd clotting and regular cheese maturation. Moreover, accidental thermal variations of milk before cheese-making, in a plus or minus direction, can occur both at farm collection sites and during transfer to dairy plant. This present research, directly commissioned by a major fresh cheese-producing company, includes an in-factory trial. In this trial, a gradient of temperatures from 4 °C to 13 °C, which were subsequently reversed, was purposely adopted to: (a) verify sensory alterations in the resulting product at different maturation stages, and, (b) analyze, in parallel, using DNA extraction and 16S-metabarcoding sequencing from the same samples, the presence, abundance and corresponding taxonomical identity of all the bacteria featured in communities found in milk and cheese samples. Overall, 1,714 different variants were detected and sorted into 394 identified taxa. Significant bacterial community shifts in cheese were observed in response to milk refrigeration temperature and subsequently associated with samples having altered scores in sensory panel tests. In particular, proteolytic psychrotrophes were outcompeted by Enterobacteriales and by other taxa at the peak temperature of 13 °C, but aggressively increased in the descent phases, upon the cooling down of milk to values of 7 °C. Relevant clues have been collected for better anticipation of thermal abuse effects or parameter variations allowing for improved handling of technical processing conditions by the cheese manufacturing industry.
奶酪生产是一种应用生物技术，其恰当的结果严格依赖于在定义的微生物群体中展开的复杂相互作用动态。这些动态可能从收集牛奶开始，并持续到其成熟的最后阶段。发挥主要作用的关键参数之一是巴氏杀菌前的牛奶冷藏温度，因为它会影响牛奶中总细菌种群中嗜冷菌的比例。虽然 4°C 是常见的选择，因为它具有普遍的生长控制作用，但它确实有一个潜在的缺点。这是因为一些耐冷属在不完全增殖的情况下具有蛋白水解活性，这可能会对凝乳凝结和常规奶酪成熟产生负面影响。此外，在奶酪制作之前，无论是在农场收集点还是在向乳品厂转移的过程中，牛奶都可能发生正或负的偶然温度变化。本研究由一家主要的新鲜奶酪生产公司直接委托进行，包括一项工厂试验。在该试验中，故意采用了从 4°C 到 13°C 的温度梯度，随后进行了反转，以：(a)验证不同成熟阶段的产物的感官变化，(b)同时使用来自相同样本的 DNA 提取和 16S-代谢组测序进行分析，以确定存在于牛奶和奶酪样本中发现的群落中的所有细菌的丰度和相应的分类学身份。总的来说，检测到 1714 个不同的变体，并分为 394 个已识别的分类群。奶酪中观察到细菌群落的显著变化，这与牛奶冷藏温度有关，随后与感官测试中得分改变的样本有关。特别是，在 13°C 的峰值温度下，蛋白酶解嗜冷菌被肠杆菌目和其他分类群所淘汰，但在牛奶冷却到 7°C 时，它们在下降阶段迅速增加。已经收集了相关线索，以便更好地预测热滥用的影响或参数变化，从而允许奶酪制造行业更好地处理技术处理条件。
