Department of Molecular Sciences, Swedish University of Agricultural Sciences, Box 7015, SE-750 07 Uppsala, Sweden.
Department of Molecular Sciences, Swedish University of Agricultural Sciences, Box 7015, SE-750 07 Uppsala, Sweden.
J Dairy Sci. 2021 Aug;104(8):8595-8609. doi: 10.3168/jds.2020-19651. Epub 2021 Apr 23.
This study investigated the influence of monthly variation on the composition and properties of raw farm milk collected as part of a full-scale cheese-making trial in a region in northern Sweden. In our companion paper, the contribution of on-farm factors to the variation in milk quality attributes is described. In total, 42 dairy farms were recruited for the study, and farm milk samples were collected monthly over 1 yr and characterized for quality attributes of importance for cheese making. Principal component analysis suggested that milk samples collected during the outdoor period (June-September) were different from milk samples collected during the indoor period. Despite the interaction with the milking system, the results showed that fat and protein concentrations were lower in milk collected during May through August, and lactose concentration was higher in milk collected during April through July than for the other months. Concentrations of free fatty acids were generally low, with the highest value (0.86 mmol/100 g of fat) observed in February and the lowest (0.70 mmol/100 g of fat) observed in June. Plasmin and plasminogen-derived activities varied with sampling month without a clear seasonal pattern. The pH of farm tank milk ranged from 6.60 to 6.82, with the lowest and highest values in September and February, respectively. The highest somatic cell count was observed in August (201 × 10 cells/mL) and the lowest in April (143 × 10 cells/mL). The highest value of gel strength, was recorded in December (88 Pa) and the lowest in July (64 Pa). Rennet coagulation time and gel strength were inversely correlated, with the lowest rennet coagulation time value observed in December. Orthogonal projections to latent structures (OPLS) and discriminant analysis adaptation of OPLS identified casein micelle size and total proteolysis as the milk quality attributes with major responses to sampling month, with smaller casein micelle size and higher total proteolysis associated with the outdoor months. Using discriminant analysis adaptation of OPLS to further investigate causes behind the variation in milk traits revealed that there were factors in addition to feeding on pasture that differed between outdoor and indoor months. Because fresh grass was seldom the primary feed in the region during the outdoor period, grazing was not considered the sole reason for the observed difference between outdoor and indoor periods in raw milk quality attributes.
本研究调查了每月变化对瑞典北部地区全面奶酪制作试验中收集的生牛乳组成和特性的影响。在我们的相关论文中，描述了农场因素对牛奶质量属性变化的贡献。总共有 42 个奶牛场参与了这项研究，每月采集一次农场牛奶样本，并对其重要的奶酪制作质量属性进行了特征描述。主成分分析表明，在户外期间（6 月至 9 月）采集的牛奶样本与在室内期间采集的牛奶样本不同。尽管与挤奶系统存在相互作用，但结果表明，5 月至 8 月采集的牛奶的脂肪和蛋白质浓度较低，4 月至 7 月采集的牛奶的乳糖浓度较高，而其他月份的浓度较低。游离脂肪酸的浓度通常较低，最高值（0.86mmol/100g 脂肪）出现在 2 月，最低值（0.70mmol/100g 脂肪）出现在 6 月。蛋白酶和蛋白酶原衍生的活性随采样月份而变化，没有明显的季节性模式。农场罐内牛奶的 pH 值范围为 6.60 至 6.82，分别出现在 9 月和 2 月。体细胞计数最高出现在 8 月（201×10 个细胞/ml），最低出现在 4 月（143×10 个细胞/ml）。凝胶强度的最高值记录在 12 月（88Pa），最低值记录在 7 月（64Pa）。凝乳时间和凝胶强度呈负相关，12 月的凝乳时间值最低。正交投影到潜在结构（OPLS）和 OPLS 的判别分析适应确定了酪蛋白胶束大小和总蛋白水解度是对采样月份有主要响应的牛奶质量属性，较小的酪蛋白胶束大小和较高的总蛋白水解度与户外月份有关。使用 OPLS 的判别分析适应进一步研究导致牛奶性状变化的原因表明，除了放牧之外，还有其他因素在户外和室内月份之间存在差异。因为在户外期间，新鲜草很少成为该地区的主要饲料，所以放牧不能被认为是生牛乳质量属性在户外和室内期间出现差异的唯一原因。
