Mechanical properties of food products are regularly analysed by tensile tests. The aim of this study was to demonstrate the potential of using advanced tensile testing techniques to better understand the mechanical properties of anisotropic food products, such as meat analogues and certain dairy products. The effects of various tensile testing parameters, including tensile gauge length and deformation rate, on the interpretation of mechanical properties of meat analogues was studied. Additionally, digital image correlation, an image analysis technique, was used for true distance recording and analysis of fracturing behaviour of the products. An isotropic product was prepared from solely soy protein isolate, and an anisotropic product was prepared from soy protein isolate and pectin using the shear cell technology. The tensile properties of the products were studied with four different moulds with varying gauge lengths of 17.5, 15, 11.5, and 8.5 mm, and at three deformation rates of 46.2, 23.1, and 11.6 mm/min. A smaller gauge length and slower deformation rate improved visualization and interpretation of the multi-stage descending branch in force – distance curves of anisotropic products. Additionally, tensile parameters, specifically toughness, proved to be more accurate at small gauge length and slow deformation rate, because overestimation due to rapid crack propagation was prevented. True distance data obtained with digital image correlation further improved the interpretation of the fracturing behaviour of the products. Inhomogeneous strain distribution in anisotropic products was shown with digital image correlation, in contrast to the homogeneous strain distribution observed in isotropic products. Furthermore, the Poisson's ratio, obtained through digital image correlation, explained inherent differences in structure and plasticity between isotropic and anisotropic meat analogues. This study shows the importance of careful selection of testing parameters and techniques. Moreover, it advises the use of digital image correlation for better measurement of fracture mechanics and strain distribution.

Pronounced fibres are formed through simple shearing of a dense calcium caseinate dispersion. Both mechanical tests and scanning electron microscopy images demonstrate that the material is anisotropic. It is hypothesised that calcium caseinate aggregates, under shear, align into micro-fibres and bundle further into a hierarchical structure. Yet no direct evidence at the sub-micron length scale can support the assumption. Small angle neutron scattering (SANS) experiments were conducted on calcium caseinate samples prepared at different conditions. Analysis of the SANS data revealed that the micro-fibres have a diameter of ∼100nm and a length of ∼300nm. The addition of enzyme and air contributed to longer and thinner micro-fibres. Furthermore, the extent of fibre alignment at the micro-scale and the macroscopic anisotropy index followed the same trends with varying processing conditions. It is concluded that the material does indeed possess a hierarchical structure and the micro-fibres are responsible for the anisotropy on the macro-scale.

Calcium caseinate dispersions can be transformed into anisotropic, fibrous materials using the concept of shear-induced structuring. The aim of this study is to further investigate the relative importance of air bubbles and protein on the mechanical anisotropy of calcium caseinate material. In this study, the effect of air on mechanical anisotropy of these fibrous materials was described with a load-bearing model, with the void fraction, and the bubble length and width as input parameters. The anisotropy of the protein phase was estimated using materials obtained from deaerated dispersions after shearing at different shear rates. We concluded that the deformation of air bubbles can only partly explain the mechanical anisotropy; the anisotropy of the protein phase is more important. Based on all results, we further concluded that the anisotropy of the protein phase was affected by the air bubbles present during the structuring process. This effect was explained by locally higher shear rate in the protein matrix during the structuring process.

Dense calcium caseinate dispersions can be transformed into hierarchically fibrous structures by shear deformation. This transformation can be attributed to the intrinsic properties of calcium caseinate. Depending on the dispersion preparation method, a certain amount of air gets entrapped in the sheared protein matrix. Although anisotropy is obtained in the absence of entrapped air, the fibrous appearance and mechanical anisotropy of the calcium caseinate materials are more pronounced with dispersed air present. The presence of air induces the protein fibers to be arranged in microscale bundles, and the fracture strain and stress in the parallel direction are larger compared with the material without air. The effects can be understood from the alignment of the fibers in the parallel direction, providing strain energy dissipation. This study shows that creation of anisotropy is the result of interactions between multiple phases.

We present an investigation of the dynamics of calcium caseinate as a function of hydration, solvent isotope (H₂O and D₂O) and drying methods (roller drying and spray drying), using quasi-elastic neutron scattering (QENS). These factors are key to the formation of fibres in this material which makes it a potential candidate as a next-generation meat analogue. Using a phenomenological model, we find that the relaxation times of the dry spray dried powder decrease with increasing temperatures, while they do not change for the roller dried powder. The spectra of the hydrated samples reveal two independent picosecond processes, both reflecting localized re-orientational motions. We hypothesize that the faster motion is due to the external protein groups that are hydrophilic and the slower motion is due to the internal groups that are hydrophobic. The solvent effect of D₂O is not limited to the external groups but prevails to the internal groups where less protons are mobile compared to the H₂O hydrated samples. Higher temperatures narrow the number difference in mobile protons, possibly by altering the weak interactions inside the protein aggregates. These findings suggest that a harsh and longer drying process contributes to less active protein side-groups and highlight the hydrophobic effect of D₂O on the fibre formation in calcium caseinate.