Midwest Dairy Foods Research Center, Department of Dairy and Food Science, South Dakota State University, Brookings 57007.
Midwest Dairy Foods Research Center, Department of Dairy and Food Science, South Dakota State University, Brookings 57007.
J Dairy Sci. 2018 Apr;101(4):2921-2926. doi: 10.3168/jds.2017-14028.
Flow of milk through the plate heat exchanger (PHE) results in denaturation of proteins, resulting in fouling. This also accelerates bacterial adhesion on the PHE surface, eventually leading to the development of biofilms. During prolonged processing, these biofilms result in shedding of bacteria and cross-contaminate the milk being processed, thereby limiting the duration of production runs. Altering the surface properties of PHE, such as surface energy and hydrophobicity, could be an effective approach to reduce biofouling. This study was conducted to compare the extent of biofouling on native stainless steel (SS) and modified-surface [Ni-P-polytetrafluoroethylene (PTFE)] PHE during the pasteurization of raw milk for an uninterrupted processing run of 17 h. For microbial studies, raw and pasteurized milk samples were aseptically collected from inlets and outlets of both PHE at various time intervals to examine shedding of bacteria in the milk. At the end of the run, 3M quick swabs (3M, St. Paul, MN) and ATP swabs (Charm Sciences Inc., Lawrence, MA) were used to sample plates from different sections of the pasteurizers (regeneration, heating, and cooling) for biofilm screening and to estimate the efficiency of cleaning in place, respectively. The data were tested for ANOVA, and means were compared. Modified PHE experienced lower mesophilic and thermophilic bacterial attachment and biofilm formation (average log 1.0 and 0.99 cfu/cm, respectively) in the regenerative section of the pasteurizer compared with SS PHE (average log 1.49 and 1.47, respectively). Similarly, higher relative light units were observed for SS PHE compared with the modified PHE, illustrating the presence of more organic matter on the surface of SS PHE at the end of the run. In addition, at h 17, milk collected from the outlet of SS PHE showed plate counts of 5.44 cfu/cm, which were significantly higher than those for pasteurized milk collected from modified PHE (4.12 log cfu/cm). This provided further evidence in favor of the modified PHE achieving better microbial quality of pasteurized milk in long process runs. Moreover, because cleaning SS PHE involves an acid treatment step, whereas an alkali treatment step is sufficient for the modified-surface PHE, use of the latter is both cost and time effective, making it a better surface for thermal processing of milk and other fluid dairy products.
牛奶在板式换热器（PHE）中的流动会导致蛋白质变性，从而造成结垢。这也会加速细菌在 PHE 表面的附着，最终导致生物膜的形成。在长时间的处理过程中，这些生物膜会导致细菌脱落，并交叉污染正在处理的牛奶，从而限制了生产运行的持续时间。改变 PHE 的表面特性，如表面能和疏水性，可能是减少生物污垢的有效方法。本研究旨在比较原生不锈钢（SS）和改性表面[Ni-P-聚四氟乙烯（PTFE）]PHE 在巴氏杀菌生奶过程中的结垢程度，以实现 17 小时不间断的加工运行。对于微生物研究，在不同时间间隔从 PHE 的进口和出口无菌收集生奶和巴氏杀菌奶样品，以检查牛奶中细菌的脱落情况。运行结束时，使用 3M 快速拭子（3M，圣保罗，明尼苏达州）和 ATP 拭子（Charm Sciences Inc.，劳伦斯，马萨诸塞州）从巴氏杀菌器的不同部分（再生、加热和冷却）的板上取样，进行生物膜筛选，并分别估计原位清洗的效率。对数据进行方差分析，并比较平均值。与 SS PHE 相比，改性 PHE 在巴氏杀菌器的再生部分经历了较低的嗜温菌和嗜热菌附着和生物膜形成（平均 log 1.0 和 0.99 cfu/cm）。同样，与改性 PHE 相比，SS PHE 观察到更高的相对光单位，表明在运行结束时 SS PHE 表面存在更多的有机物。此外，在 h 17 时，从 SS PHE 出口收集的牛奶显示出 5.44 cfu/cm 的平板计数，明显高于从改性 PHE 收集的巴氏杀菌牛奶（4.12 log cfu/cm）。这进一步证明了改性 PHE 在长时间的工艺运行中能够获得更好的巴氏杀菌牛奶的微生物质量。此外，由于清洁 SS PHE 需要进行酸处理步骤，而改性表面 PHE 只需进行碱处理步骤，因此使用后者既具有成本效益，又节省时间，是热加工牛奶和其他液态乳制品的更好表面。
