Elucidation of density profile of self-assembled sitosterol plus oryzanol tubules with small-angle neutron scattering

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Small-angle neutron scattering (SANS) experiments have been performed on self-assembled tubules of sitosterol and oryzanol in triglyceride oils to investigate details of their structure. Alternative organic phases (deuterated and non-deuterated decane, limonene, castor oil and eugenol) were used to both vary the contrast with respect to the tubules and investigate the influence of solvent chemistry. The tubules were found to be composed of an inner and an outer shell containing the androsterol group of sitosterol or oryzanol and the ferulic acid moieties in the oryzanol molecule, respectively. While the inner shell has previously been detected in SAXS experiments, the outer shell was not discernible due to similar scattering length density with respect to the surrounding solvent for X-rays. By performing contrast variation SANS experiments, both for the solvent and structurant, a far more detailed description of the self-assembled system is obtainable. A model is introduced to fit the SANS data; we find that the dimensions of the inner shell agree quantitatively with the analysis performed in earlier SAXS data (radius of 39.4 ± 5.6 Å for core and inner shell together, wall thickness of 15.1 ± 5.5 Å). However, the newly revealed outer shell was found to be thinner than the inner shell (wall thickness 8.0 ± 6.5 Å). The changes in the scattering patterns may be explained in terms of the contrast between the structurant and the organic phase and does not require any subtle indirect effects caused by the presence of water, other than water promoting the formation of sitosterol monohydrate in emulsions with aqueous phases with high water activity

Temperature responsive colloidal particles from non-covalently interacting small molecular weight natural bioactive molecules

We report generation of temperature responsive colloidal particles based on the spontaneous interactions of two small molecular weight actives of natural origins. This finding is an important step towards the development of controlled colloidal structures from natural and sustainable materials for food and drug delivery applications

Manipulation of Recrystallization and Network Formation of Oil-Dispersed Micronized Fat Crystals

A detailed investigation was carried out on the modulation of the coupling between network formation and the recrystallization of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear, and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. During MFC dispersion production at high shear, a significant increase in the average crystal thickness (ACT) could be observed, pointing to recrystallization of the MFC nanoplatelets. More rapid recrystallization of MFC occurred in the SF dispersion than in the BO dispersion, which is attributed to higher solubility of MFC in the SF oil. When the dispersions were maintained under low shear in narrow gap Couette geometry, we witnessed two stages of recrystallization (measured via rheo-SAXD) and the development of a local yield stress (measured via rheo-MRI). In the first stage, shear-enabled mass transfer induces rapid recrystallization of randomly distributed MFC nanoplatelets, which is reflected in a rapid increase in ACT (rheo-SAXD). The formation of a space-filling weak-link MFC network explains the increase in yield stress (assessed in real time by rheo-MRI). In this second stage, recrystallization slows down and yield stress decreases as a result of the formation of MFC aggregates in the weak link network, as observed by confocal Raman imaging. The high fractal dimension of the weak-link network indicates that aggregation takes place via a particle-cluster mechanism. The effects of oil type and shear on the recrystallization rate and network strength could be reproduced in a stirred bowl with a heterogeneous shear stress field, which opens perspectives for the rational manipulation of MFC thickness and network strength under industrial processing conditions.</p

Manipulation of Recrystallization and Network Formation of Oil-Dispersed Micronized Fat Crystals

A detailed investigation was carried out on the modulation of the coupling between network formation and the recrystallization of oil-dispersed micronized fat crystal (MFC) nanoplatelets by varying oil composition, shear, and temperature. Sunflower (SF) and bean (BO) oils were used as dispersing media for MFC nanoplatelets. During MFC dispersion production at high shear, a significant increase in the average crystal thickness (ACT) could be observed, pointing to recrystallization of the MFC nanoplatelets. More rapid recrystallization of MFC occurred in the SF dispersion than in the BO dispersion, which is attributed to higher solubility of MFC in the SF oil. When the dispersions were maintained under low shear in narrow gap Couette geometry, we witnessed two stages of recrystallization (measured via rheo-SAXD) and the development of a local yield stress (measured via rheo-MRI). In the first stage, shear-enabled mass transfer induces rapid recrystallization of randomly distributed MFC nanoplatelets, which is reflected in a rapid increase in ACT (rheo-SAXD). The formation of a space-filling weak-link MFC network explains the increase in yield stress (assessed in real time by rheo-MRI). In this second stage, recrystallization slows down and yield stress decreases as a result of the formation of MFC aggregates in the weak link network, as observed by confocal Raman imaging. The high fractal dimension of the weak-link network indicates that aggregation takes place via a particle-cluster mechanism. The effects of oil type and shear on the recrystallization rate and network strength could be reproduced in a stirred bowl with a heterogeneous shear stress field, which opens perspectives for the rational manipulation of MFC thickness and network strength under industrial processing conditions.</p

Quantitative Assessment of Triacylglycerol Crystallite Thickness by ¹H Spin-Diffusion NMR

Properties and consumer appreciation of fat containing food products are greatly influenced by the growth of the fat crystalline domains and their morphology. Various analytical methods can be exploited to provide insight into the multilength scale microstructure of fat networks, but very few are able to discriminate structural features between different ways of processing fats. We selected in this work methods that highlight the mesostructure of fat crystalline systems. In this respect, ¹H spin-diffusion NMR and XRD methods were employed to determine the fat crystallite thicknesses (crystalline domain size). This is the first attempt to quantify the mesostructure domains of triglyceride-based fat crystals by means of ¹H spin-diffusion NMR experiments. The crystalline domain sizes determined by spin-diffusion NMR were found to be in good agreement with the crystallite thickness determined by the Scherrer analysis of the first order diffraction line from SAXS data. These results demonstrate the ability of the NMR technique to characterize the mesostructure of fats in a quantitative manner. This method is of particular interest for the structure analysis of fats, especially because of the possibility to quantify the size of the crystalline domains in diluted systems where scattering techniques struggle with the amount of diffracting material

Exploring how changes to the steroidal core alter oleogelation capability in sterol: γ-oryzanol blends

Oleogels based on sterols such as β - sitosterol blended with the sterol ester γ-oryzanol are a very interesting class of systems, but there are aspects of their formation and structure that remain elusive. It has previously been shown that a methyl group on the C30 position of the sterol-ester plays an important role in gelation. This work explored the effect that having C30 methyl groups on both the sterol and the sterol-ester had on the the gelation process and subsequent gel structure. Lanosterol and saponified γ-oryzanol (which was synthesised as part of this study) were identified as materials of interest, as both feature a methyl group on the C30 position of their steroidal cores. It was observed that both sterols formed gels when blended with γ-oryzanol, and also that lanosterol gelled sunflower oil without the addition of γ-oryzanol. All of these gels were significantly weaker than that formed by β-sitosterol blended with γ-oryzanol. To explore why, molecular docking simulations along with AFM and SAXS were used to to examine these gels on a broad range of length scales. The results suggest that saponified γ-oryzanol - γ-oryzanol gels have a very similar structure to that of β-sitosterol - γ-oryzanol gels. Lanosterol- γ-oryzanol gels and pure lanosterol gel, however, form with a totally different structure facilitated by the head-to-tail stacking motif exhibited by lanosterol. These results give further evidence that relatively slight changes to the molecular structure of gelators can result in significant differences in subsequent gel properties

SANS and SAXS: A Love Story to unravel structural evolution of soy proteins and polysaccharide fibres during high moisture extrusion for meat alternatives

Plant-based meat alternatives are seeing considerable interest due to their potential to reduce environmental burden and enhance population health. The food industry, therefore, seeks routes to provide the consumer with whole-cut plant-based products that closely resemble meat products. High-moisture extrusion (HME) of plant proteins enables the industrial manufacturing of meat-like products with highly hierarchical structural organisation of fibres. The major bottleneck in serving the growing market for these products is a lack of insight intohow multiscale structures evolve during shear processing. Furthermore, it remains an open question of how two biopolymers, one being a plant protein and the other being a polysaccharide, contribute to the anisotropic structure formation during HME. This study shows how the complementary use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) can add clarity to these matters, benefiting from the different contrasts in scattering length density (SLD) encountered with each of these methods. It is demonstrated that twobiopolymers have differences in the development of structural anisotropy. The protein fibril alignment starts in the extruder section with its further development along the cooling die. On the other hand, for polysaccharide fibres, the strongest local alignment has been found in the transition zone. RST/Neutron and Positron Methods in Material