Department of Agronomy, Food, Natural Resources, Animals and the Environment, University of Padova, Viale dell'Università 16, Legnaro (PD), Italy 35020.
Department of Agronomy, Food, Natural Resources, Animals and the Environment, University of Padova, Viale dell'Università 16, Legnaro (PD), Italy 35020.
J Dairy Sci. 2020 Sep;103(9):7951-7956. doi: 10.3168/jds.2019-17847. Epub 2020 Jul 16.
We used 20 mid-lactating Holstein cows, housed in 4 pens according to a Latin square design, to evaluate the effects of dietary protein restriction (crude protein: 12.3 vs. 15.0% dry matter) and conjugated linoleic acid supplementation (CLA: 6.34 g/d of C18:2cis-9,trans-11 and 6.14 g/d of C18:2trans-10,cis-12) on milk composition, coagulation, curd firming and syneresis modeling, and cheese yield and quality (96 small cheeses). Dietary crude protein restriction, suggested as a way to reduce N excretion in farming, caused a reduction in milk protein content (-4%,), milk casein (-3.8%), lactose (-1%), cheese soluble protein (-16.8%), and the cheese maturation index (-15%), and a correlated increase in cheese fat content (+7.5%) and the fat to protein ratio (+18%). A modest reduction (-0.9%) in milk fat recovery in the curd did not affect cheese yield. The addition of CLA to the cows' diet, suggested as a way to improve N use efficiency and the nutritional value of dairy products, caused substantial alterations to the milk composition, cheese-making process, and cheese quality. The CLA reduced the fat (-12.3%), protein (-2%), casein (-2.2%), lactose (-1.0), and total solids (-4%) contents of milk, tended to delay coagulation, and weakened curd firming. The CLA reduced the fresh cheese yield (-7.5%) and cheese solids (-8.2%) because of the lower nutrient content of the milk, but also because of a lower recovery of milk protein in the curd (-0.9%) and lower total solids (-4.5%). It also reduced the fat content in the ripened cheese (-11.8%), as well as the fat to protein ratio (-19.4%) as a result of having increased the protein content (+9.3%). Last, it increased the lightness of the paste of the ripened cheeses (+3.3%), and especially the shear force (+16.3%). Dietary crude protein restriction, and CLA addition in particular, substantially altered the milk composition, cheese-making process, and cheese quality, and therefore needs to be carefully evaluated. Further studies are required to shed light on the causes of these modifications.
我们使用 20 头泌乳中期荷斯坦奶牛，根据拉丁方设计将其饲养在 4 个围栏中，以评估日粮蛋白质限制（粗蛋白：12.3%对 15.0%干物质）和共轭亚油酸（CLA）补充（18:2cis-9,trans-11 的 CLA 为 6.34 g/d 和 18:2trans-10,cis-12 的 CLA 为 6.14 g/d）对牛奶成分、凝结、凝乳固化和排乳率建模以及奶酪产量和质量（96 小块奶酪）的影响。日粮粗蛋白限制被建议作为减少农业中氮排泄的一种方法，导致牛奶蛋白含量降低（-4%）、牛奶酪蛋白降低（-3.8%）、乳糖降低（-1%）、奶酪可溶性蛋白降低（-16.8%）和奶酪成熟指数降低（-15%），同时奶酪脂肪含量增加（+7.5%）和脂肪与蛋白质比例增加（+18%）。凝乳中牛奶脂肪回收率适度降低（-0.9%）并不影响奶酪产量。CLA 添加到奶牛日粮中被建议作为提高氮利用效率和乳制品营养价值的一种方法，对牛奶成分、奶酪制作过程和奶酪质量产生了重大影响。CLA 降低了牛奶中的脂肪（-12.3%）、蛋白质（-2%）、酪蛋白（-2.2%）、乳糖（-1.0%）和总固形物（-4%）含量，使凝结时间趋于延迟，并削弱了凝乳固化。CLA 降低了新鲜奶酪的产量（-7.5%）和奶酪固体（-8.2%），这是由于牛奶中的营养成分较低，以及凝乳中牛奶蛋白回收率较低（-0.9%）和总固形物减少（-4.5%）所致。它还降低了成熟奶酪中的脂肪含量（-11.8%）以及脂肪与蛋白质的比例（-19.4%），这是由于蛋白质含量增加（+9.3%）所致。最后，它增加了成熟奶酪的糊状物的亮度（+3.3%），特别是剪切力（+16.3%）。日粮粗蛋白限制，特别是 CLA 的添加，极大地改变了牛奶成分、奶酪制作过程和奶酪质量，因此需要仔细评估。需要进一步的研究来阐明这些变化的原因。
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