Department of Food Science, Cornell University, Northeast Dairy Foods Research Center, Ithaca, NY 14853, USA.
J Dairy Sci. 2010 Dec;93(12):6000-11. doi: 10.3168/jds.2010-3601.
Our objective was to determine the effect of commonly used milk preservatives on the accuracy of fat, protein, and lactose content determination in milk by mid-infrared (mid-IR) milk analysis. Two producer raw milks (Holstein and Jersey) and 2 pasteurized modified milks, 1 similar to Holstein milk and 1 similar to Jersey milk were used as the 4 different milk sources. Seven different milk preservative approaches (K(2)Cr(2)O(7) and 6 different bronopol-based preservatives) and a portion of unpreserved milk for each of the 4 different milks sources were tested for fat B, lactose, protein, and fat A. The experiment was replicated 3 times (28 d each) for a total of 84 d. Two mid-infrared (mid-IR) transmittance milk analyzers (an optical and a virtual filter instrument) were used. A large batch of pilot milk was prepared from pasteurized, homogenized, unpreserved whole milk, split into vials, quick frozen by immersion in liquid nitrogen, and transferred into a -80 °C freezer. Pilots were thawed and analyzed on each testing day during the study. Significant increases were observed in all uncorrected readings on the pilot milks over the 84 d of the study, but the increases were gradual and small on each instrument for all components. Results from the study were corrected for these changes. A significant difference in mid-IR fat A readings was observed, whereas no differences were detected for fat B, lactose, or protein between unpreserved and preserved milks containing 0.02% K(2)Cr(2)O(7.) Therefore, K(2)Cr(2)O(7) has little or no effect on mid-IR test results. All bronopol-based preservative approaches in this study differed in mid-IR test results compared with K(2)Cr(2)O(7)-preserved and unpreserved milks, with the largest effect on protein results. Mid-IR uncorrected readings increased with time of refrigerated storage at 4°C for all preservative approaches, with the largest increase for protein. The rate of increase in uncorrected readings with time of storage was always higher for raw milks than for pasteurized milks, and the stability of instrument zero was lower for raw milks than for pasteurized milks. The largest economic effect of a systematic bias caused by a preservative occurs when the milks used for calibration and routine testing for payment do not contain the same preservative or when calibration milks are preserved and milks for routine testing are unpreserved. These effects can create errors in payment for large dairy processing plants ranging from several hundred thousand to over a million dollars annually.
我们的目的是确定常用牛奶防腐剂对中红外（中红外）牛奶分析中牛奶脂肪、蛋白质和乳糖含量测定准确性的影响。使用两种原奶（荷斯坦和泽西）和 2 种巴氏杀菌改良奶，1 种类似于荷斯坦奶，1 种类似于泽西奶，作为 4 种不同的牛奶来源。测试了 7 种不同的牛奶防腐剂方法（K 2 Cr 2 O 7 和 6 种不同的溴硝醇基防腐剂）和每种牛奶防腐剂方法下的部分未保存牛奶，以确定脂肪 B、乳糖、蛋白质和脂肪 A。该实验共重复了 3 次（每次 28 天），总计 84 天。使用了 2 台中红外（中红外）透射奶分析仪（光学和虚拟滤波器仪器）。从巴氏杀菌、均化、未保存的全脂牛奶中制备了一批大量的试验奶，将其分装在小瓶中，通过浸入液氮快速冷冻，并转移到-80°C 冷冻库中。在研究期间的每个测试日，对试验奶进行解冻和分析。在研究的 84 天中，所有未经校正的读数在所有未经校正的读数上都观察到了显著增加，但对于所有成分，每种仪器的增加都是渐进的和小的。对研究结果进行了校正，以消除这些变化的影响。观察到中红外脂肪 A 读数存在显著差异，而在含有 0.02% K 2 Cr 2 O 7 的未保存和保存牛奶中，脂肪 B、乳糖或蛋白质的中红外测试结果无差异。因此，K 2 Cr 2 O 7 对中红外测试结果几乎没有影响。与 K 2 Cr 2 O 7 保存和未保存的牛奶相比，本研究中所有溴硝醇基防腐剂方法的中红外测试结果均存在差异，对蛋白质结果的影响最大。对于所有防腐剂方法，冷藏储存时间的中红外未校正读数随时间的增加而增加，蛋白质的增加最大。与巴氏杀菌奶相比，原料奶的储存时间与未校正读数的增加率总是更高，原料奶的仪器零稳定性也低于巴氏杀菌奶。当用于校准和常规测试的牛奶不含相同的防腐剂或当校准牛奶被保存而常规测试的牛奶未被保存时，防腐剂引起的系统偏差的最大经济影响就会出现。这些影响可能会导致大型乳制品加工厂的付款出现错误，每年从几十万到上百万美元不等。
