Rennet coagulation properties of milk in the presence of oil droplets stabilised by a combination of sodium caseinate and whey protein isolate

Abstract

This manuscript describes the in situ investigation of the rennet-induced aggregation of skim milk recombined with emulsion droplets stabilised with whey protein isolate (WPI) and sodium caseinate (NaCas) in isolation or in combination. The experiments were conducted with two levels of rennet as well as with and without added CaCl₂. Diffusing wave spectroscopy and small deformation rheology were used to follow the gelation behaviour. In addition, scanning electron microscopy was employed to observe changes in the aggregation state of the oil droplets. We report that the presence of WPI-stabilised droplets did not alter the gelation behaviour of the casein micelles in recombined milks, even in the presence of added CaCl₂. In contrast, NaCas-stabilised droplets in solution impaired the rennetability of the recombined milk, even after the addition of CaCl₂. The mixture of both proteins at the interface was also investigated. When the WPI covering the fat droplets was gradually and systematically substituted by NaCas, any amount over 30% also impaired the rennetability of the milks. It was speculated that the increased steric repulsion of the oil droplets in conjunction with an increase in NaCas present in the serum phase in the recombined milks were the most likely contributors to the impaired rennetability of the casein micelles.

酪蛋白酸钠和分离乳清蛋白粉结合的油滴稳定剂对乳的凝乳特性的影响摘要

本文描述了通过现场考察用分离乳清蛋白粉(WPI)和酪蛋白酸钠(NaCas)在独立和结合条件下的乳滴稳定剂调制的脱脂乳的诱导凝乳聚合特性。实验分成两种情况,一种是添加 CaCl₂,一种是不添加 CaCl₂。该实验用扩散光谱仪(DWS)和小变形流变仪追踪凝胶变化特性。另外,扫描电镜被用来观察油滴聚合状态的变化。在 WPI-稳定液滴单独存在的条件下,不会改变调制乳酪蛋白胶束胶凝特性,即使添加了 CaCl₂ 也不影响。相反,以酪蛋白酸钠-稳定液滴溶液会破坏调制乳的凝乳能力,即使后来添加 CaCl₂,效果也一样。如果将分离乳清蛋白粉和酪蛋白酸钠两种蛋白在分界面混合进行研究,当分离乳清蛋白粉(WPI)覆盖了脂肪液滴后,会逐渐的、有规律地被酪蛋白酸钠所取代,当酪蛋白酸钠量超过 30%以后也会破坏凝乳能力。据此推测增加油滴的空间排斥,同时增加调制乳乳清相中酪蛋白酸钠的量,将两者协同起来可以最大程度的破坏酪蛋白胶束的凝乳能力。