Once pasteurized donor milk is thawed for its administration to a preterm or sick neonate, and until it is administered, it is kept refrigerated at 4 to 6°C for 24 h. After this time, unconsumed milk is discarded. This time has not been extended, primarily because of the concern of bacterial contamination. The aim of this study was to determine the changes in pH and bacterial count when pasteurized donor milk was kept under refrigeration for a prolonged period (14 d). In this prospective study, 30 samples of pasteurized donor milk from 18 donors were analyzed. Milk was handled following the regular operating protocols established in the neonatal unit and was kept refrigerated after thawing. pH measurements and bacteriology (on blood agar and MacConkey agar plates) were performed on each sample at time 0 (immediately after thawing) and then every day for 14 d. Changes in pH of samples over time were evaluated with linear mixed-effects regression models. A slow but gradual increase in milk pH was observed starting from the first day [mean (±SD) pH of 7.30 (±0.18) at time 0 and 7.69 (±0.2) on d 14]. No bacterial growth was observed in any of the samples throughout the complete trial except in one sample, in which Bacillus flexus was isolated. In conclusion, pasteurized human donor milk maintains its microbiological quality when properly handled and refrigerated (4–6°C). The slight and continuous increase in milk pH after the first day could be due to changes in the solubility of calcium and phosphate during refrigerated storage.

将经过巴氏消毒的供体奶解冻后用于早产或患病的新生儿，直到给药前，将其在4至6°C下冷藏24小时。在这段时间之后，将未消费的牛奶丢弃。这段时间没有延长，主要是因为担心细菌污染。这项研究的目的是确定巴氏灭菌的供体奶长时间冷藏（14天）时pH和细菌数量的变化。在这项前瞻性研究中，分析了来自18个捐赠者的30份巴氏灭菌捐赠者牛奶。按照新生儿部制定的常规操作规程处理牛奶，解冻后保持冷藏。pH测量和细菌学（血液）在0时（解冻后立即）对每个样品进行琼脂和MacConkey琼脂平板），然后每天进行14天。用线性混合效应回归模型评估样品的pH值随时间的变化。从第一天开始观察到牛奶pH值缓慢但逐渐增加[在第0天的时间0和7.69（±0.2），平均pH为7.30（±0.18），在第14天为7.69（±0.2）]。在整个整个试验中，在任何一个样品中都没有观察到细菌生长，除了一个分离了弯曲芽孢杆菌的样品。总之，经过适当处理和冷藏（4–6°C），巴氏杀菌的人类供体乳可以保持其微生物质量。在第一天之后，牛奶pH值会出现轻微且连续的升高，这可能是由于冷藏过程中钙和磷酸盐的溶解度发生了变化。