Konuklar Gül, Gunasekaran Sundaram
Cereal Products and Food Science Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, USDA, 1815 N. University Street, Peoria, Illinois, 61604, USA.
J Colloid Interface Sci. 2002 Jun 1;250(1):149-58. doi: 10.1006/jcis.2002.8321.
The effect of continuous steady shear stress (CSSS) on rennet-induced coagulation of milk was studied by measuring the change in viscosity of the system with time. Continuous shear stress (< or =0.5 Pa) applied during coagulation did not counteract the network formation at standard cheese-making conditions. In fact, CSSS of 0.2 Pa promoted coagulation by possibly increasing diffusion, collision, and hydrolization rates due to near-field, attractive hydrodynamic reactions. This was evidenced by the high viscosity of the resultant coagulum. However, the viscosity profile of the coagulum formed in the presence of CSSS followed the same trend as that formed in the absence of CSSS. Viscosity versus time profiles in both cases displayed an initial lag phase followed by a steady increase until a plateau value. The viscosity plateau reached under CSSS was marked with several sudden peaks, indicating the dynamic structure of the coagulum. These peaks in viscosity profiles began to appear after about 1380 s since rennet addition at standard cheese-making conditions. The time at which viscosity first exceeds 40 kPa s was verified to coincide with manual determination of the time at which the coagulum is cut (i.e., cutting time) during cheese making.
通过测量体系粘度随时间的变化，研究了连续稳态剪切应力（CSSS）对凝乳酶诱导的牛奶凝固的影响。在标准奶酪制作条件下，凝固过程中施加的连续剪切应力（≤0.5 Pa）并未抵消网络结构的形成。事实上，0.2 Pa的CSSS可能通过近场吸引流体动力反应提高扩散、碰撞和水解速率，从而促进凝固。这一点由所得凝块的高粘度得到证明。然而，在有CSSS存在的情况下形成的凝块的粘度曲线与在没有CSSS的情况下形成的凝块的粘度曲线遵循相同的趋势。两种情况下粘度随时间的曲线均显示出初始滞后阶段，随后稳定增加直至达到平稳值。在CSSS下达到的粘度平稳值有几个突然的峰值，表明凝块的动态结构。在标准奶酪制作条件下，从添加凝乳酶起约1380 s后，粘度曲线中的这些峰值开始出现。经证实，粘度首次超过40 kPa·s的时间与奶酪制作过程中人工确定的凝块切割时间（即切割时间）一致。
