Riddet Institute, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand.
School of Food and Advanced Technology, Massey University, Auckland 0632, New Zealand.
Food Funct. 2023 Jul 31;14(15):6985-6997. doi: 10.1039/d3fo01126g.
The effect of Ca on pepsin-induced hydrolysis of κ-casein and subsequent coagulation of casein micelles was studied in a micellar casein (MC) solution at pH ≈ 6.0 at 37 °C without stirring. An NaCl-supplemented MC solution was used as a positive control to assess the effect of increased ionic strength after CaCl addition. Quantitative determination of the released -κ-casein during the reaction using reverse-phase high-performance liquid chromatography showed that specific hydrolysis of κ-casein by pepsin was little affected by the addition of either CaCl or NaCl. However, rheological properties and microstructures of curds induced by pepsin hydrolysis depended markedly on the addition of salts. Addition of CaCl up to 17.5 mM facilitated coagulation, with decreases in coagulation time and critical hydrolysis degree, and increases in firming rate and maximum storage modulus ('); further addition of CaCl (22.5 mM) resulted in a lower '. Increased ionic strength to 52.5 mM by adding NaCl retarded the coagulation and resulted in a looser curd structure. In a human gastric simulator, MC, without the addition of CaCl, did not coagulate until the pH decreased to ≈5.0 after ≈50 min of digestion. Addition of CaCl facilitated coagulation of casein micelles and resulted in more cohesive curds with dense structures during digestion, which slowed the emptying rate of caseins. At the same CaCl concentration, a sample with higher ionic strength coagulated more slowly. This study provides further understanding on the effect of divalent (Ca) ions and ionic strength on the coagulation of casein micelles and the digestion behavior of milk.
在 pH 值约为 6.0、37°C 且不搅拌的条件下，研究了 Ca 对胃蛋白酶诱导κ-酪蛋白水解以及随后酪蛋白胶束凝结的影响。在添加 CaCl 后评估离子强度增加的影响时，使用添加 NaCl 的胶束酪蛋白溶液作为阳性对照。使用反相高效液相色谱法定量测定反应过程中释放的 -κ-酪蛋白，结果表明，胃蛋白酶对 κ-酪蛋白的特异性水解受 CaCl 或 NaCl 的添加影响很小。然而，胃蛋白酶水解诱导的凝乳的流变特性和微观结构明显取决于盐的添加。添加高达 17.5 mM 的 CaCl 可促进凝结，降低凝结时间和临界水解程度，增加固化速率和最大储能模量（ '）；进一步添加 CaCl（22.5 mM）会导致较低的 '。通过添加 NaCl 将离子强度增加至 52.5 mM 会延迟凝结，并导致凝乳结构较松散。在人类胃模拟器中，未添加 CaCl 的胶束在消化约 50 分钟后 pH 值降至约 5.0 时才凝结。添加 CaCl 可促进酪蛋白胶束的凝结，并在消化过程中形成更具凝聚力的凝乳，具有致密的结构，从而减缓了酪蛋白的排空速度。在相同的 CaCl 浓度下，具有较高离子强度的样品凝结速度较慢。本研究进一步了解了二价（Ca）离子和离子强度对酪蛋白胶束凝结以及牛奶消化行为的影响。
