Centro de Investigacion en Alimentacion y Desarrollo A.C., Unidad Cuauhtemoc, Av. Rio Conchos S/N, Parque Industrial, Ciudad Cuauhtemoc, Chihuahua, Mexico, C.P. 31570.
Universidad Autonoma de Chihuahua, Facultad de Ciencias Quimicas, Chihuahua, Chihuahua, Mexico, C.P. 31570.
J Dairy Sci. 2020 Apr;103(4):3088-3094. doi: 10.3168/jds.2019-16998. Epub 2020 Feb 7.
Milk curds are a semisolid structure resulting from the enzymatic coagulation of milk, consisting mainly of paracasein micelles, fat globules, and whey. This gel undergoes a series of changes in its composition and structure during setting and curing, affecting curd density. The present study investigated the composition and density of inoculated and noninoculated milk curds during a 60-min curing period conducted at 30, 35, and 40°C. The purpose of the study was to determine the density changes occurring in the protein phase of curds during curing under different conditions of temperature and pH to understand the nature of the structural changes happening in the paracasein matrix. Noninoculated curd density values oscillated between 1.0247 and 1.0294 g/cm after 60 min of curing, whereas inoculated treatments showed values between 1.0222 and 1.0321 g/cm. This small difference in density between the studied samples was surprising because the whey content of samples differed greatly. Density of the protein phase reached values of 1.8002 and 1.4388 g/cm for noninoculated and inoculated curds, respectively, after 60 min of curing. Two independent mechanisms involved in the development of the protein-based structure of curds were identified upon comparison of the development of protein phase density in inoculated and noninoculated curds. Although the larger increase in protein phase density observed in noninoculated curds was probably due to the concurrent action of calcium-mediated electrostatic bonds and temperature-dependent hydrophobic bonds, inoculated curds showed a lower protein phase density caused by calcium solubilization and by a decrease in the net charge of paracasein micelles induced by pH reduction.
奶豆腐是一种半固态结构，由牛奶的酶促凝固形成，主要由副酪蛋白胶束、脂肪球和乳清组成。在凝固和熟化过程中，这种凝胶的组成和结构会发生一系列变化，从而影响凝块的密度。本研究在 30°C、35°C 和 40°C 下进行 60 分钟的凝固过程中，研究了接种和未接种牛奶凝乳的组成和密度。研究目的是确定在不同温度和 pH 条件下，凝乳的蛋白质相密度变化，以了解副酪蛋白基质中结构变化的性质。未接种凝乳的密度值在 60 分钟的凝固后在 1.0247 到 1.0294 g/cm 之间波动，而接种处理的密度值在 1.0222 到 1.0321 g/cm 之间。研究样品之间的密度差异很小，这令人惊讶，因为样品的乳清含量差异很大。未接种和接种的凝乳在 60 分钟的凝固后，蛋白质相的密度分别达到 1.8002 和 1.4388 g/cm。通过比较接种和未接种凝乳中蛋白质相密度的发展，确定了参与凝乳蛋白质结构发展的两个独立机制。尽管未接种凝乳中观察到的蛋白质相密度的较大增加可能是由于钙介导的静电键和温度依赖性疏水键的共同作用，但接种凝乳的蛋白质相密度较低是由于钙的溶解以及 pH 降低导致副酪蛋白胶束的净电荷减少所致。
