Multiscale assessment of food lipid structures

Abstract

Establishing structure-function relationships is a key step in the development of novel sustainable food formulations and processing technologies. In the manufacturing of lipid-based foods, critical functionalities (shelf life stability, texture and mouth feel) are governed by underlying multiscale lipid structures. Understanding the dynamics of multiscale structural changes in lipid systems under processing conditions will allow for production of food products with desired functionalities. The aim of this thesis was to develop and apply novel complementary methodologies to characterize and quantify multiscale structures of food lipids under static and dynamic processing conditions. The focus is on investigation of micronized fat crystal (MFC) networks and phospholipid liquid crystalline (LC) structures formed after degumming. Non-invasive multiscale assessment under shear was enabled by rheo-microMRI and rheo-SAS techniques specifically developed for the structural characterization of complex lipid dispersions. Chapter 2 describes the implementation and application range of rheo-microMRI in millimeter gap sized concentric cylinder (CC) geometries at high magnetic field and strong magnetic field gradients which allows for temporal and spatially resolved flow measurements with high sensitivity. Precautions needed to be taken to perform experiments at low shear on lipid systems which have dispersed chemical shifts. Subsequently it was shown that rheo-microMRI measurements can provide information about position- and time-dependent flow behaviour. This allowed for quantitative assessment of local constitutive laws. Chapter 3 presents the design of a versatile temperature controlled rheo-SAS cell. It was shown that this concentric cylinder (CC) rheo-cell can be used with both X-ray sources from a high-end synchrotron facility as well as with lab-based equipment. The application of the designed CC rheo-SAS cell for quantitative assessment of multiscale fat crystal networks under a wide range of shear rates was demonstrated. Structural anisotropy, crystal growth, phase transition and changes in spatial distribution of crystals could be monitored in a real-time manner. These rheo-microMRI and -SAS methodologies together with complementary techniques (confocal Raman-imaging, rheology, SFC NMR X-ray diffraction and scattering techniques) were subsequently used for dynamic assessment of multiscale micronized fat crystal (MFC) structures. Chapter 4 reveals that MFCs form a weak-link network of aggregates connected by a continuous net of dispersed nanoplatelets. The rough surface of MFC nanoplatelets hampers stacking into large aggregates indicating that particle–cluster aggregation was dominant. Application of shear released nanoplatelets from the weak-link continuous net, which subsequently aligned along the flow direction. Moreover, shear induced rapid recrystallisation of the thinner MFC nanoplatelets. In Chapter 5 the investigation of the coupling between the recrystallization and network formation MFC nanoplatelets is pursued by rheo-microMRI, rheo-SAXD and confocal Raman-imaging. Variation of oil composition, temperature and shear provided a means to manipulate MFC recrystallization rate and thus network strength. Chapter 6 presents results of multiscale assessment of crude oil gums obtained under industrial relevant conditions by water degumming (WD) and enzymatic degumming (ED). Mesostructural (SANS, SAXS) and compositional (NMR) assessment of these compositional heterogeneous lipid systems allowed structural quantification of lamellar LC phases in these gums. Partial incorporation of non-polar lipids (diglycerides (DGs) and free fatty acids (FFAs)) into gum bilayers occurred. This affected the dynamics at molecular scale as seen by 1H time-domain (TD) NMR T2 relaxometry. The results showed that both the total amount of gum as well as the amount of amphiphilic lipids in the gum can be determined by means of FID-CPMG measurements, which opens the opportunity to assess the efficiency of degumming treatments.