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首页> 外文期刊>Journal of dairy research >Modelling casein aggregation and curd firming in goats' milk from backscatter of infrared light
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Modelling casein aggregation and curd firming in goats' milk from backscatter of infrared light

机译：模拟山羊乳中酪蛋白聚集和凝乳紧实的红外光反向散射

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摘要

A kinetic model was proposed for describing the curd assembly of skimmed goats' milk during enzymic coagulation. The enzymic coagulation of milk was monitored using an optical sensor that measured diffuse reflectance (light backscatter) at 880 nm. The appearance of a shoulder, at low temperatures and protein concentrations, in the diffuse reflectance ratio profile after the inflection point of the curve (T_(max)) appeared to separate the aggregation and curd firming steps. The diffuse reflectance ratio profile after T_(max) was attributed to the overlapping of casein micelles aggregation and curd firming reactions. The developed kinetic model combined a second order reaction model to describe aggregation reactions and a first order reaction model to describe firming processes reactions. A completely randomised block design with three replications was used to determine the effect of protein concentration and temperature on kinetic constants. Milk was adjusted to three levels of protein (30, 50 and 70 g/kg), and coagulated at five temperatures (20, 25, 30, 35 and 40℃) to test a wide range of processing conditions. Data points from each profile after T_(max) were fitted to the proposed model using non-linear regression. The average R~2 and standard error of prediction (SEP) for 45 tests conducted were in the range of 0.9975 +- 0.0027 and 0.0081 +- 0.0037, respectively. A significant increase in characteristic times for aggregation (τ_2) and curd firming processes (τ_1) were found when temperature decreased or protein increased. Theoretical asymptotic value of reflectance ratio, R_∞, increased with increasing level of protein and temperature (P<0.05). The parameter β_1, which represented the fraction of diffuse reflectance ratio attributed to aggregation, decreased with increasing temperature and decreasing protein.
机译：提出了动力学模型来描述脱脂山羊乳在酶促凝结过程中的凝乳组装。使用光学传感器监测牛奶的酶促凝结，该光学传感器在880 nm处测量漫反射率（反向散射光）。在曲线的拐点（T_（max））之后，在漫反射率分布中，在低温和蛋白质浓度下，肩膀的出现似乎将聚集和凝乳固化步骤分开。 T_（max）后的漫反射率分布归因于酪蛋白胶束聚集和凝乳固化反应的重叠。开发的动力学模型结合了描述聚集反应的二阶反应模型和描述固化过程反应的一阶反应模型。具有三个重复的完全随机区组设计用于确定蛋白质浓度和温度对动力学常数的影响。将牛奶调节至三种蛋白质水平（30、50和70 g / kg），并在五个温度（20、25、30、35和40℃）下凝结，以测试各种加工条件。使用非线性回归将T_（max）之后每个轮廓的数据点拟合到建议的模型中。进行的45个测试的平均R〜2和预测标准误（SEP）分别在0.9975±0.0027和0.0081±0.0037的范围内。当温度降低或蛋白质增加时，发现凝集特征时间（τ_2）和凝乳固化过程（τ_1）显着增加。反射比的理论渐近值R_∞随蛋白质水平和温度的升高而增加（P <0.05）。代表归因于聚集的漫反射率的比例的参数β_1随着温度的升高和蛋白质的降低而降低。

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