Laboratory Services Division, University of Guelph, Guelph N1H 8J7, Ontario, Canada.
J Dairy Sci. 2011 Jul;94(7):3279-87. doi: 10.3168/jds.2010-4102.
Automated electronic milk analyzers for rapid enumeration of total bacteria counts (TBC) are widely used for raw milk testing by many analytical laboratories worldwide. In Ontario, Canada, Bactoscan flow cytometry (BsnFC; Foss Electric, Hillerød, Denmark) is the official anchor method for TBC in raw cow milk. Penalties are levied at the BsnFC equivalent level of 50,000 cfu/mL, the standard plate count (SPC) regulatory limit. This study was conducted to assess the BsnFC for TBC in raw goat milk, to determine the mathematical relationship between the SPC and BsnFC methods, and to identify probable reasons for the difference in the SPC:BsnFC equivalents for goat and cow milks. Test procedures were conducted according to International Dairy Federation Bulletin guidelines. Approximately 115 farm bulk tank milk samples per month were tested for inhibitor residues, SPC, BsnFC, psychrotrophic bacteria count, composition (fat, protein, lactose, lactose and other solids, and freezing point), and somatic cell count from March 2009 to February 2010. Data analysis of the results for the samples tested indicated that the BsnFC method would be a good alternative to the SPC method, providing accurate and more precise results with a faster turnaround time. Although a linear regression model showed good correlation and prediction, tests for linearity indicated that the relationship was linear only beyond log 4.1 SPC. The logistic growth curve best modeled the relationship between the SPC and BsnFC for the entire sample population. The BsnFC equivalent to the SPC 50,000 cfu/mL regulatory limit was estimated to be 321,000 individual bacteria count (ibc)/mL. This estimate differs considerably from the BsnFC equivalent for cow milk (121,000 ibc/mL). Because of the low frequency of bulk tank milk pickups at goat farms, 78.5% of the samples had their oldest milking in the tank to be 6.5 to 9.0 d old when tested, compared with the cow milk samples, which had their oldest milking at 4 d old when tested. This may be one of the major factors contributing to the larger goat milk BsnFC equivalence. Correlations and interactions between various test results were also discussed to further understand differences between the 2 methods for goat and cow milks.
自动化电子牛奶分析仪可快速计数总细菌数 (TBC)，目前被全球许多分析实验室用于原奶检测。在加拿大安大略省，Bactoscan 流式细胞仪 (BsnFC; Foss Electric, Hillerød, Denmark) 是原奶 TBC 的官方基准方法。违规者将被处以与 BsnFC 等效的 50,000 cfu/mL 的罚款，这是标准平板计数 (SPC) 的监管限值。本研究旨在评估 BsnFC 用于原羊奶 TBC 的检测，确定 SPC 和 BsnFC 方法之间的数学关系，并确定羊奶和牛奶 SPC:BsnFC 等效值差异的可能原因。测试程序按照国际乳品联合会公报指南进行。2009 年 3 月至 2010 年 2 月，每月大约对 115 个农场散装奶罐的奶样进行抑制剂残留、SPC、BsnFC、嗜冷菌计数、成分（脂肪、蛋白质、乳糖、乳糖和其他固体、冰点）和体细胞计数的检测。对测试样本结果的数据分析表明，BsnFC 方法将是 SPC 方法的良好替代方法，可提供准确、更精确的结果，且周转时间更快。尽管线性回归模型显示出良好的相关性和预测性，但线性检验表明，这种关系仅在对数 4.1 SPC 以上才呈线性。逻辑增长曲线最能模拟整个样本群体中 SPC 和 BsnFC 之间的关系。SPC 50,000 cfu/mL 监管限值的 BsnFC 等效值估计为 321,000 个个体细菌计数 (ibc)/mL。这一估计与牛奶奶的 BsnFC 等效值（121,000 ibc/mL）有很大的不同。由于山羊养殖场的奶罐抽样频率较低，78.5%的样本在检测时奶罐中最早的挤奶时间为 6.5 至 9.0 天，而牛奶奶样在检测时奶罐中最早的挤奶时间为 4 天。这可能是导致羊奶 BsnFC 等效值较大的主要因素之一。还讨论了各种测试结果之间的相关性和相互作用，以进一步了解羊奶和牛奶两种方法之间的差异。
