O'Connell A, Ruegg P L, Jordan K, O'Brien B, Gleeson D
Teagasc, Livestock Systems Research Department, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland; Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
J Dairy Sci. 2016 May;99(5):3367-3374. doi: 10.3168/jds.2015-10495.
The dairy industry in Ireland is currently undergoing a period of expansion and, as a result, it is anticipated that milk may be stored in bulk tanks on-farm for periods greater than 48 h. The objective of this study was to investigate the effects of storage temperature and duration on microbial quality of bulk tank milk when fresh milk is added to the bulk tank twice daily. Bulk tank milk stored at 3 temperatures was sampled at 24-h intervals during storage periods of 0 to 96 h. Bulk tank milk samples were analyzed for total bacterial count (TBC), psychrotrophic bacterial count (PBC), laboratory pasteurization count (LPC), psychrotrophic-thermoduric bacterial count (PBC-LPC), proteolytic bacterial count, lipolytic bacterial count, presumptive Bacillus cereus, sulfite-reducing Clostridia (SRC), and SCC. The bulk tank milk temperature was set at each of 3 temperatures (2°C, 4°C, and 6°C) in each of 3 tanks on 2 occasions during two 6-wk periods. Period 1 was undertaken in August and September, when all cows were in mid lactation, and period 2 was undertaken in October and November, when all cows were in late lactation. None of the bulk tank bacterial counts except the proteolytic count were affected by lactation period. The proteolytic bacterial count was greater in period 2 than in period 1. The TBC and PBC of milk stored at 6°C increased as storage duration increased. The TBC did not increase with increasing storage duration when milk was stored at 2°C or 4°C but the PBC of milk stored at 4°C increased significantly between 0 and 96 h. The numbers of proteolytic and lipolytic bacteria, LPC, or PBC-LPC in bulk tank milk were not affected by temperature or duration of storage. Presumptive B. cereus were detected in 10% of all bulk tank milk samples taken over the two 6-wk periods, with similar proportions observed in both. In bulk tank milk samples, a greater incidence of SRC was observed in period 2 (20%) compared with period 1 (3%). Milk produced on-farm with minimal bacterial contamination can be successfully stored at 2°C and 4°C for up to 96h with little effect on its microbial quality.
爱尔兰的乳制品行业目前正处于扩张阶段，因此预计农场散装罐中的牛奶储存时间可能会超过48小时。本研究的目的是调查当每天两次向散装罐中添加新鲜牛奶时，储存温度和持续时间对散装罐牛奶微生物质量的影响。在0至96小时的储存期内，每隔24小时对储存在3个温度下的散装罐牛奶进行采样。对散装罐牛奶样品进行总细菌数（TBC）、嗜冷菌数（PBC）、实验室巴氏杀菌菌数（LPC）、嗜冷耐热菌数（PBC-LPC）、蛋白水解菌数、脂肪分解菌数、蜡样芽孢杆菌疑似菌、亚硫酸盐还原梭菌（SRC）和体细胞数（SCC）分析。在两个6周期间，分两次在3个罐中的每一个中将散装罐牛奶温度设定为3个温度（2°C、4°C和6°C）中的每一个。第1阶段在8月和9月进行，此时所有奶牛处于泌乳中期，第2阶段在10月和11月进行，此时所有奶牛处于泌乳后期。除蛋白水解菌数外，其他散装罐细菌数均不受泌乳期影响。第2阶段的蛋白水解菌数高于第1阶段。储存在6°C的牛奶的TBC和PBC随储存时间的增加而增加。当牛奶储存在2°C或4°C时，TBC不会随着储存时间的增加而增加，但储存在4°C的牛奶的PBC在0至96小时之间显著增加。散装罐牛奶中蛋白水解菌和脂肪分解菌的数量、LPC或PBC-LPC不受温度或储存时间的影响。在两个6周期间采集的所有散装罐牛奶样品中，10%检测到蜡样芽孢杆菌疑似菌，两个阶段的比例相似。在散装罐牛奶样品中，第2阶段（20%）的SRC发生率高于第1阶段（3%）。农场生产的细菌污染极少的牛奶可以成功地储存在2°C和4°C下长达96小时，对其微生物质量影响很小。
