Future Industries Institute, UniSA STEM, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095, Australia.
Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, 381 Royal Parade, Parkville, VIC 3052, Australia; BioSAXS beamline, Australian Synchrotron, ANSTO, 800 Blackburn Road, Clayton, VIC 3168, Australia.
J Colloid Interface Sci. 2022 Feb 15;608(Pt 3):2839-2848. doi: 10.1016/j.jcis.2021.11.008. Epub 2021 Nov 8.
Dairy emulsions contain an intrinsically heterogeneous lipid phase, whose components undergo crystallisation in a manner that is critical to dairy product formulation, storage, and sensory perception. Further complexity is engendered by the diverse array of interfacially-active molecules naturally present within the serum of dairy systems, and those that are added for specific formulation purposes, all of which interact at the lipid-serum interface and modify the impact of lipid crystals on dairy emulsion stability. The work described in this article addresses this complexity, with a specific focus on the impact of temperature cycling and the effect of emulsifier type on the formation and persistence of lipid crystals at lipid-solution interfaces. Profile analysis tensiometry experiments were performed using single droplets of the low melting fraction of dairy lipids, in the presence and absence of emulsifiers (Tween 80 and whey protein isolate, WPI) and during the temperature cycling, to study the formation of monoacylglycerol (MAG) crystals at the lipid-solution interface. Companion experiments on the same lipid systems, and at the same cooling and heating rates, were undertaken with synchrotron small angle X-ray scattering, to specifically analyse the effect of emulsifier type on the formation of triacylglycerol (TAG) crystals at the lipid-solution interface of a model dairy emulsion. These two complementary techniques have revealed that Tween 80 molecules delay MAG and TAG crystal formation by lowering the temperature at which the crystallisation occurs during two cooling cycles. WPI molecules delay the crystallisation of MAGs and TAGs during the first cooling cycle, while MAG crystals form without delay during the second cooling cycle at the same temperature as MAG crystals in an emulsifier free system. The crystallisation of TAGs is inhibited during the second cooling cycle. The observed differences in crystallisation behaviour at the interface upon temperature cycling can provide further insight into the impact of emulsifiers on the long-term stability of emulsion-based dairy systems during storage.
乳制品乳液含有内在不均匀的脂质相，其成分以对乳制品配方、储存和感官感知至关重要的方式结晶。进一步的复杂性是由乳系统血清中天然存在的各种界面活性分子以及为特定配方目的添加的那些分子引起的，所有这些分子都在脂质-血清界面相互作用，并改变脂质晶体对乳制品乳液稳定性的影响。本文所述的工作解决了这种复杂性，特别关注温度循环的影响以及乳化剂类型对脂质-溶液界面处脂质晶体形成和持久性的影响。使用乳制品脂质低熔点部分的单个液滴，在存在和不存在乳化剂（吐温 80 和乳清蛋白分离物，WPI）的情况下，并在温度循环过程中，进行了轮廓分析张力测量实验，以研究单酰基甘油（MAG）晶体在脂质-溶液界面处的形成。在相同的冷却和加热速率下，对相同的脂质系统进行了同步辐射小角 X 射线散射的伴随实验，以专门分析乳化剂类型对模型乳制品乳液脂质-溶液界面处三酰基甘油（TAG）晶体形成的影响。这两种互补技术表明，吐温 80 分子通过降低两次冷却循环中结晶发生的温度来延迟 MAG 和 TAG 晶体的形成。WPI 分子在第一次冷却循环中延迟 MAG 的结晶，而在相同温度下，第二次冷却循环中 MAG 晶体没有延迟形成，而在没有乳化剂的体系中，MAG 晶体形成没有延迟。TAG 的结晶在第二次冷却循环中受到抑制。在温度循环时界面上结晶行为的观察到的差异可以进一步深入了解乳化剂对储存过程中基于乳液的乳制品系统长期稳定性的影响。
