Department of Agronomy, Food, Natural Resources, Animals and Environment (DAFNAE), University of Padova, Viale dell'Università 16, 35020 Legnaro (PD), Italy; Department of Veterinary Science, University of Parma, Via del Taglio 10, 43126 Parma, Italy.
Department of Veterinary Medicine, University of Sassari, Via Vienna 2, 07100 Sassari, Italy.
J Dairy Sci. 2018 Jul;101(7):5832-5837. doi: 10.3168/jds.2017-14256. Epub 2018 Apr 19.
The importance of milk coagulation properties for milk processing, cheese yield, and quality is widely recognized. The use of traditional coagulation traits presents several limitations for testing bovine milk and even more for sheep milk, due to its rapid coagulation and curd firming, and early syneresis of coagulum. The aim of this technical note is to test and improve model fitting for assessing coagulation, curd firming, and syneresis of sheep milk. Using milk samples from 87 Sarda ewes, we performed in duplicate lactodynamographic testing. On each of the 174 analyzed milk aliquots, using 180 observations from each aliquot (one every 15 s for 45 min after rennet addition), we compared 4 different curd firming models as a function of time (CF, mm) using a nonlinear procedure. The most accurate and informative results were observed using a modified 4-parameter model, structured as follows: [Formula: see text] where t is time, RCT (min) is the gelation time, CF (mm) is the potential asymptotical CF at an infinite time, k (%/min) is the curd firming rate constant, and k (%/min) is the curd syneresis rate constant. To avoid nonconvergence and computational problems due to interrelations among the equation parameters, CF was preliminarily defined as a function of maximum observed curd firmness (CF, mm) recorded during the analysis. For this model, all the modeling equations of individual sheep milk aliquots were converging, with a negligible standard error of the estimates (coefficient of determination >0.99 for all individual sample equations). Repeatability of the modeled parameters was acceptable, also in the presence of curd syneresis during the lactodynamographic analysis.
牛奶凝固特性对牛奶加工、奶酪产量和质量的重要性已得到广泛认可。传统的凝固特性在测试牛乳时存在一些局限性，在测试绵羊乳时甚至更多，因为绵羊乳的凝固和凝块固化迅速，凝块早期排乳清。本技术说明的目的是测试和改进评估绵羊乳凝固、凝块固化和排乳清的模型拟合。使用 87 只萨丁岛母羊的奶样进行了两次乳动学法测试。在 174 个分析的奶样中，每个奶样重复两次（在添加凝乳酶后 45 分钟内每 15 秒一次），我们比较了 4 种不同的凝块固化模型作为时间（CF，mm）的函数，使用非线性程序。使用如下结构的改良 4 参数模型观察到最准确和信息丰富的结果：[公式：见正文]其中 t 是时间，RCT（min）是凝胶时间，CF（mm）是无限时间的潜在渐近 CF，k（%/min）是凝块固化速率常数，k（%/min）是凝块排乳清速率常数。为了避免由于方程参数之间的相互关系而导致的非收敛和计算问题，CF 被初步定义为在分析过程中记录的最大观察到的凝块硬度（CF，mm）的函数。对于该模型，所有个体绵羊乳样的模型化方程都收敛，估计的标准误差可忽略不计（所有个体样本方程的决定系数>0.99）。即使在乳动学法分析期间发生凝块排乳清，模型化参数的可重复性也是可以接受的。
