Dairy whipping cream : synergistic roles of fat crystallisation and partial coalescence : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Food Technology, Massey University, Palmerston North, Manawatū, New Zealand

Abstract

The study of fat crystallisation and shear-induced partial coalescence mechanisms has been crucial for the development of aerated colloidal food products like whipping cream, whipped toppings, and ice cream. This research examines the interdependent effects of these factors on the stability, foam structural properties, and underlying mechanisms of oil-in-water (O/W) emulsions in the recombined dairy whipping cream made using anhydrous milk and stabilised by sodium caseinate.

Partial coalescence in O/W emulsions can be influenced by factors such as droplet sizes, shear, air incorporation, and the addition of emulsifiers. This study investigates the impact of fat droplet sizes and emulsifiers on the development of stable whipped cream, with the aim of understanding the complex physico-chemical properties affected by these interrelated factors. The study is divided into three parts: 1) development of a novel technique using a rheometer to monitor the primary mechanism of whipping in the presence of air, 2) investigation of the influence of fat droplet sizes, and 3) examining the effect of different types and concentrations of emulsifiers on whipping properties.

In Chapter 4, a rheological setup and methodology were developed to systematically explore the influence of shear-induced partial coalescence in the presence of air in whipping cream systems. This methodology integrates rotational rheology with starch spindle to investigate the kinetics of partial coalescence in the presence of air by examining the viscosity, particle size, and microstructure of foam and fat droplets in the analysed creams.

In Chapter 5, the study found that fat droplet size has a strong influence on emulsion stability and modulates the crystallisation of emulsified milk fat. Large droplets induce faster nucleation and crystal formation on the inner surface of the fat droplet interface, thus triggering nucleation events more quickly than smaller droplets. In contrast, smaller droplets have slower nucleation rates, potentially resulting in delayed or absent crystal formation within the droplets, hindering aggregation and subsequent fat crystallisation, and consequently, partial coalescence within the emulsion. The study also demonstrated that larger fat droplets have lower shear resistance than smaller fat droplets, resulting in shorter whipping times for aerated emulsions. Conversely, smaller fat droplets improve stability by hindering fat crystallisation and partial coalescence, thus extending the whipping time. When evaluating aerated emulsions, larger fat droplets were found to efficiently entrap air cells and encapsulate them with partially coalesced fats, resulting in maximum stability and overrun. Conversely, smaller fat droplets delay crystal nucleation within the droplets, resulting in a less cohesive and stable foam structure.

In Chapter 6, research also examined how different types and concentrations of emulsifiers affect homogenised milk creams and their whipping properties. The investigation focused on understanding the effects of low molecular weight (LMW) emulsifiers on fat crystallisation, polymorphic transitions, whipping properties, and foam structure in O/W emulsions. It was found that lipophilic emulsifiers such as MDG and LACTEM showed better adsorption and interfacial displacement compared to hydrophilic emulsifier (Tween 80), resulting in reduced protein adsorption at the O/W interface and mitigating phase separation.

In summary, the study highlights the crucial role of fat droplet size and emulsifiers in determining emulsion stability, crystallisation kinetics, and whipping properties. The insights gained provide valuable information for refining dairy product formulations and processing techniques and contribute to a deeper understanding of fat crystallisation and partial coalescence in emulsified systems. The successful development of this methodology has highlighted its potential for reliable and real-time use of this technique in the future. These results provide an interesting starting point for further work on controlling the partial coalescence of fat droplets and fat crystallisation behavior by selecting appropriate emulsifier formulas according to their different functionality to achieve betrer stability in the aerated emulsions of dairy and non-dairy products.