The objective of this study was to measure the effect of different milk cooling rates, before entering the bulk tank, on the microbiological load and composition of the milk, as well as on energy usage. Three milk precooling treatments were applied before milk entered 3 identical bulk milk tanks: no plate cooler (NP), single-stage plate cooler (SP), and double-stage plate cooler (DP). These precooling treatments cooled the milk to 32.0 ± 1.4°C, 17.0 ± 2.8°C, and 6.0 ± 1.1°C, respectively. Milk was added to the bulk tank twice daily for 72 h, and the tank refrigeration temperature was set at 3°C. The blend temperature within each bulk tank was reduced after each milking event as the volume of milk at 3°C increased simultaneously. The bacterial counts of the milk volumes precooled at different rates did not differ significantly at 0 h of storage or at 24-h intervals thereafter. After 72 h of storage, the total bacterial count of the NP milk was 3.90 ± 0.09 log₁₀ cfu/mL, whereas that of the precooled milk volumes were 3.77 ± 0.09 (SP) and 3.71 ± 0.09 (DP) log₁₀ cfu/mL. The constant storage temperature (3°C) over 72 h helped to reduce bacterial growth rates in milk; consequently, milk composition was not affected and minimal, if any, proteolysis occurred. The DP treatment had the highest energy consumption (17.6 ± 0.5 Wh/L), followed by the NP (16.8 ± 2.7 Wh/L) and SP (10.6 ± 1.3 Wh/L) treatments. This study suggests that bacterial count and composition of milk are minimally affected when milk is stored at 3°C for 72 h, regardless of whether the milk is precooled; however, milk entering the tank should have good initial microbiological quality. Considering the numerical differences between bacterial counts, however, the use of the SP or DP precooling systems is recommended to maintain low levels of bacterial counts and reduce energy consumption.

这项研究的目的是在进入大容量储罐之前，测量不同的牛奶冷却速度对牛奶的微生物负荷和组成以及能量消耗的影响。在牛奶进入3个相同的散装牛奶罐之前，先进行了三种牛奶预冷处理：无板式冷却器（NP），单级板式冷却器（SP）和双级板式冷却器（DP）。这些预冷却处理将牛奶分别冷却至32.0±1.4°C，17.0±2.8°C和6.0±1.1°C。每天两次向大容量储罐中添加牛奶72小时，并将储罐的冷藏温度设置为3°C。每次挤奶事件发生后，每个大罐内的混合温度都会降低，因为3摄氏度时的牛奶量会同时增加。在储存0小时或之后的24小时间隔内，以不同速率预冷的牛奶体积的细菌计数没有显着差异。储存72小时后，NP牛奶的细菌总数为3.90±0.09 log₁₀ cfu / mL，而预冷牛奶的体积为3.77±0.09（SP）和3.71±0.09（DP）log ₁₀cfu / mL。超过72小时的恒定存储温度（3°C）有助于降低牛奶中的细菌生长速率；因此，牛奶的成分没有受到影响，发生了最小的蛋白水解作用（如果有的话）。DP处理的能耗最高（17.6±0.5 Wh / L），其次是NP（16.8±2.7 Wh / L）和SP（10.6±1.3 Wh / L）处理。这项研究表明，将牛奶在3°C下储存72小时后，无论牛奶是否经过预冷，细菌的数量和组成的影响都降至最低。但是，进入水箱的牛奶应具有良好的初始微生物质量。考虑到细菌计数之间的数值差异，建议使用SP或DP预冷系统以保持较低的细菌计数水平并减少能耗。