Inglingstad R A, Steinshamn H, Dagnachew B S, Valenti B, Criscione A, Rukke E O, Devold T G, Skeie S B, Vegarud G E
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, NO-1432 Ås, Norway.
Norwegian Institute for Agricultural and Environmental Research (Bioforsk), Organic Food and Farming Division, Gunnars veg 6, NO-6630 Tingvoll, Norway.
J Dairy Sci. 2014;97(6):3800-14. doi: 10.3168/jds.2013-7542. Epub 2014 Apr 3.
Two different types of pasture (cultivated and rangeland) and 2 different hay qualities (high and low quality) were examined for their effects on goat milk composition and rennet coagulation properties. Furthermore, the effect of dietary treatments in both the early and late grazing season was studied. As lactation stage is known to influence milk composition, the goats in the early and late grazing season were in the same lactation stage at the start of the experiment. The milk composition was influenced both by dietary treatment and season. Milk from goats on pasture was superior to those on hay by containing a higher content of protein and casein, and the goats on cultivated pasture had the highest milk yield. Casein composition was significantly influenced by forage treatment. Goats grazing on cultivated pasture had higher contents of αs1-casein and also of κ-casein compared with the other treatments, whereas goats grazing on rangeland had the highest content of β-casein. Factors such as milk yield, casein micelle size, αs2-casein, and calcium content were reduced in late compared with early season. More favorable rennet coagulation properties were achieved in milk from the early grazing season, with shorter firming time and higher curd firmness compared with milk from the late grazing season, but the firming time and curd firmness were not prominently influenced by forage treatment. The content of αs2-casein and calcium in the milk affected the firming time and the curd firmness positively. The influence of season and forage treatment on especially milk yield, casein content, and rennet coagulation properties is of economic importance for both the dairy industry and goat milk farmers.
研究了两种不同类型的牧场（人工种植牧场和天然牧场）以及两种不同品质的干草（高品质和低品质）对山羊奶成分和凝乳酶凝固特性的影响。此外，还研究了在放牧早期和晚期日粮处理的效果。由于已知泌乳阶段会影响奶的成分，因此在实验开始时，放牧早期和晚期的山羊处于相同的泌乳阶段。奶的成分受日粮处理和季节的影响。牧场上的山羊所产的奶在蛋白质和酪蛋白含量方面优于干草喂养的山羊，并且人工种植牧场上的山羊产奶量最高。酪蛋白组成受草料处理的显著影响。与其他处理相比，在人工种植牧场上放牧的山羊的αs1-酪蛋白和κ-酪蛋白含量更高，而在天然牧场上放牧的山羊的β-酪蛋白含量最高。与季节早期相比，季节晚期的产奶量、酪蛋白胶粒大小、αs2-酪蛋白和钙含量等因素有所降低。与放牧晚期的奶相比，放牧早期的奶具有更有利的凝乳酶凝固特性，凝固时间更短，凝乳硬度更高，但凝固时间和凝乳硬度受草料处理的影响不显著。奶中αs2-酪蛋白和钙的含量对凝固时间和凝乳硬度有积极影响。季节和草料处理对特别是产奶量、酪蛋白含量和凝乳酶凝固特性的影响对乳制品行业和山羊奶农户都具有经济重要性。
