Temperature-dependent Microstructure and Rheology of Fat in Adipose Tissue in Pork, Beef and Lamb

Matching the texture of fat in plant-based meat alternatives requires an in-depth understanding of the structure and rheology of animal adipose tissue which, to-date, remains under-studied. We investigated the temperature-dependent microstructure and thermal properties of adipose tissue from pork, beef and lamb. Microstructural characterisation via electron, confocal and light microscopy showed that the back fats were structurally similar and consisted of fat dispersed in discrete units within a protein matrix akin to a closed cell foam. Differential scanning calorimetry showed distinct fat melting profiles in each of the tissues, which were ascribed to differences in fatty acid profile. Fat crystal organisation, melting and re-solidification signatures unique to each adipose tissue were found via X-ray diffraction and Raman spectroscopy. The dynamic rheological behaviour of the back fats was characterised via frequency and amplitude sweeps as well as texture analysis via puncture tests. At 20 °C, prior to heating, the small and large deformation properties of adipose tissue were dominated by the solid fat phase in the adipose cells. Upon heating to 80 °C, with the fat phase molten, the protein network underpinning the structure of the back fats conferred elastic behaviour to the tissues, and the now-molten oil partly leaked from the adipocytes into the surrounding interstitial space. Upon re-cooling, a bicontinuous network of fat crystals and protein contributed to back fat rheology. Large deformation rheology revealed animal species-specific differences in back fat rheology. Overall, we found that the temperature-dependent microstructure of adipose fat was intricately linked to the fat phase melting behaviour, and importantly, to its protein matrix at elevated temperatures. Such understanding is necessary to provide the required insights to effectively replicate the functionality of adipose tissue using plant-based materials.