Small angle scattering is frequently applied to study the anisotropy in complex soft matter systems. One emerging application is to probe the multi-scale structure in food matrices; while few models are available to describe the anisotropic scattering pattern in a quantitative, yet simple manner. For this purpose, anisotropy is introduced to the Guinier–Porod model to study the scattering from non-spherical objects with a preferred orientation. This generalised anisotropic Guinier–Porod model can be adapted to approximate the sector scattering from both cylinders and ellipsoids (both prolate and oblate). In practice, it is applied to describe the anisotropic scattering from fibres in a meat analogue made of calcium caseinate. A good agreement is found between fitted dimensions of the fibres and those observed from the microscopy image. The effect of orientation distribution on the shape and intensity of the scattering pattern is further discussed and three means to obtain the orientation distribution of the symmetry axis are proposed. Given the model is straightforward and the fitting remains phenomenological, it provides a novel approach to extract information from complex food systems.

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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.

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In the past decades, neutron scattering techniques have been applied to many soft matter systems and have yielded fruitful results that contribute to a better understanding of their properties. Yet, the techniques were rarely used for studying food materials, probably because they are less well known and less accessible to food scientists. This work fills a small part of the research gap by applying several neutron scattering techniques to the characterisation of a food-relevant protein sample: calcium caseinate. Calcium caseinate can be transformed into pronounced fibres to form the basis for a next generation meat analogue. Given the prospect of the material, the emphasis in this work is on quantifying the size, structure and dynamics of the air bubbles and fibres present in calcium caseinate gels. The main findings are summarised into four chapters.@en

Phospholipid gum mesostructures formed in crude soybean oil after water degumming (WD) and enzymatic degumming (ED) were studied at a range of phospholipid and water concentrations. For ED, phospholipase C (PLC), phospholipase A2 (PLA2) and a mixture of phospholipases Purifine 3G (3G) were used. Both WD and ED resulted in lamellar liquid-crystalline phases, however, of different topology. The dependence of the bilayer spacings (as observed by SANS and SAXS) on the ratio between amount of water and amphiphilic lipids differed for WD and PLA2 ED vs PLC and 3G ED. This difference was also observed for dynamics at molecular scale as observed by time-domain (TD) NMR and attributed to partial incorporation of diglycerides and free fatty acids into gum bilayers after PLC and 3G ED. Feasibility of using TD-NMR relaxometry for quantification of the gum phase and estimation of degumming efficiency was demonstrated.

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Microemulsion systems consisting of D₂O, an alkane, an anionic internal olefin sulfonate surfactant, salt and secondary butyl alcohol (SBA) as co-solvent are studied in a systematic way. In four different sample sets, either the salt content, SBA content or alkane carbon number was varied in order to study the effects of the individual compounds on the structure sizes making up the microemulsion. Using complementary small-angle neutron scattering techniques SANS and Spin-Echo SANS, it was found that the microemulsion systems exhibit the largest structures in the optimum state (domain size of d/2 =144 nm in the model by Teubner and Strey), where the structure is considered bicontinuous. In comparison, at under- and over-optimum states where the structures consist of emulsified spherical droplets, the smallest measured diameter was 2R = 44 nm. Furthermore, the structure sizes in bicontinuous microemulsions decrease exponentially (down to d/2 =15 nm for pentadecane and 5 wt% SBA) as function of both SBA content and alkane carbon number. The observed trends in structure sizes combined with the trends observed in the area per surfactant molecule, are qualitatively explained with the extended Winsor R-ratio, the HLD-NAC model and surfactant film flexibility arguments.

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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.

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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.

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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.

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A versatile cell for X-ray and neutron scattering experiments on samples under shear has been designed. To our knowledge, it is the first shear cell which can be used for both SAXS and SANS in respectively synchrotron or reactor beamlines. The cell is mainly intended for scattering experiments in so-called “1–2 plane geometry” but can also be modified into cone–plate and plate–plate rheological geometries, giving access to the 1–3 scattering plane. The latter two geometries, however, can only be used with neutron scattering. The final cell design is compact, which allows it to be used even with lab-based X-ray sources. A special thermostatic shell allows for the temperature control of the samples under investigation in the range from 5 up to 100 °C. Several X-ray and neutron scattering experiments performed with the cell have helped in better understanding of the structuring under shear of food materials, such as: cellulose suspensions, fat crystal networks and milk proteins.

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