Teagasc Food Research Centre Moorepark, Fermoy, Co. Cork, P61 C996, Ireland; Department of Chemistry, Maynooth University, Maynooth, Co. Kildare, Ireland.
Teagasc, Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, P61 C996, Ireland.
J Dairy Sci. 2019 Oct;102(10):8630-8647. doi: 10.3168/jds.2018-15884. Epub 2019 Aug 1.
Low-heat skim milk powder (LHSMP) was manufactured on 3 separate occasions in mid lactation (ML, July 4-20) and late lactation (LL, September 27 to October 7) from bulk milk of 3 spring-calving dairy herds on different feeding systems: grazing on perennial ryegrass (Lolium perenne L.) pasture (GRO), grazing on perennial ryegrass and white clover (Trifolium repens L.) pasture (GRC), and housed indoors and offered total mixed ration (TMR). The resultant powders (GRO-SMP, GRC-SMP, and TMR-SMP) were evaluated for composition and color and for the compositional, physicochemical, and processing characteristics of the reconstituted skim milk (RSM) prepared by dispersing the powders to 10% (wt/wt) in water. Feeding system significantly affected the contents of protein and lactose, the elemental composition, and the color of the LHSMP, as well as the rennet gelation properties of the RSM. The GRO and GRC powders had a higher protein content; lower levels of lactose, iodine, and selenium; and a more yellow-green color (lower a* and higher b* color coordinates) than TMR powder. On reconstitution, the GRO-RSM had higher concentrations of protein, casein, and ionic calcium, and lower concentrations of lactose and nonprotein nitrogen (% of total N). It also produced rennet gels with a higher storage modulus (G') than the corresponding TMR-RSM. These effects were observed over the combined ML and LL period but varied somewhat during the separate ML and LL periods. Otherwise, feeding system had little or no effect on proportions of individual caseins, concentration of serum casein, casein micelle size, casein hydration, heat coagulation time, or ethanol stability of the RSM at pH 6.2 to 7.2, or on the water-holding capacity, viscosity, and flow behavior of stirred yogurt prepared by starter-induced acidification of RSM. The differences in the functionality of the LHSMP may be of greater or lesser importance depending on the application and the conditions applied during the processing of the RSM.
低脂奶粉（LHSMP）是在泌乳中期（ML，7 月 4 日至 20 日）和泌乳后期（LL，9 月 27 日至 10 月 7 日），从三个不同的春季产奶牛群的牛奶中制造的，这些牛奶分别来自于三种不同的喂养系统：在黑麦草（Lolium perenne L.）牧场上放牧（GRO）、在黑麦草和白三叶草（Trifolium repens L.）牧场上放牧（GRC）以及室内饲养并提供全混合日粮（TMR）。对所得粉末（GRO-SMP、GRC-SMP 和 TMR-SMP）进行了成分和颜色分析，并对通过将粉末分散在水中至 10%（wt/wt）制备的再制脱脂乳（RSM）的组成、物理化学和加工特性进行了评价。喂养系统显著影响了 LHSMP 的蛋白质和乳糖含量、元素组成和颜色，以及 RSM 的凝乳酶凝胶特性。GRO 和 GRC 粉末的蛋白质含量较高，乳糖、碘和硒含量较低，颜色呈黄绿色（较低的 a和较高的 b颜色坐标），而 TMR 粉末的颜色则较深。再制时，GRO-RSM 的蛋白质、酪蛋白和离子钙浓度较高，乳糖和非蛋白氮（总氮的%）浓度较低。它还产生了具有较高储能模量（G'）的凝乳酶凝胶，高于相应的 TMR-RSM。这些影响在 ML 和 LL 整个时期都有观察到，但在单独的 ML 和 LL 时期略有不同。否则，喂养系统对 RSM 中个别酪蛋白的比例、血清酪蛋白的浓度、酪蛋白胶束大小、酪蛋白水合作用、热凝固时间或 pH 值为 6.2 至 7.2 时的 RSM 的乙醇稳定性、或通过 RSM 的起始酸化制备搅拌酸奶时的持水能力、粘度和流动行为几乎没有影响。LHSMP 功能的差异可能根据应用和 RSM 加工过程中的条件而具有更大或更小的重要性。
