In-situ XRD Case Study: Using variable temperature XRD to understand polymorphic changes in milkfat

Selecting blends of fish oil with a high percentage of long chain poly-unsaturated fatty acids, and milkfat with a high percentage of saturated fatty acids, could potentially demonstrate desirable characteristics such as increased omega-3 fatty acids and melting point, as well as improved crystallisation and oxidative stability. In this work, in-situ variable temperature XRD with various cooling rate, annealing and ageing processes was used to study the effect of various milkfat concentrations on thermal properties and crystalline structures of these blends.

Long-chain omega-3 polyunsaturated fatty acids (LCPUFA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which exist in fish oil, are important nutrients. Incorporating these LCPUFAs into food products is a challenge for the food industry, because LCPUFAs are extremely unstable toward oxidation. Milkfat is a potential carrier, as well as a stabilising agent for other oils/bioactives via spray chilling. With polymorphs that can affect texture, milkfat could have three forms of crystals (α, β’ and β) based on the crystallisation conditions. The β’ crystals, followed by α crystals, are the dominant forms, with the α crystals producing the desired texture in ice cream. The small needle-like crystals of β’ impart good plasticity that make milkfat suitable for the production of margarine, shortening, and other dairy products.

The Monash X-ray Platform’s D8 Advance diffractometer can be fitted with different chambers to perform a range of in-situ XRD applications for materials such as polymers, new functional and energy materials, lipids, proteins, pharmaceutical and biological samples. Roughly 25% of the diffractometer’s beamtime is being dedicated to in-situ and in-operando XRD studies.

In this case the diffractometer was fitted with a wide range temperature chamber allowing temperature range from -150°C to 450°C in vacuum, or up to 300°C with inert gas purging. Diffraction patterns were collected after a range of designated heating/cooling rates, or annealing and ageing times and used to identify the different polymorphs formed after these specific processing conditions.

Data and images courtesy of Mitra Nosratpour, Yong Wang, Meng Wai Woo, Cordelia Selomulya 2020, Characterisation of thermal and structural behaviour of lipid blends composed of fish oil and milkfat', Food Research International, 137 (2020) 109377. https://doi.org/10.1016/j.foodres.2020.109377