Abstract
The nutritional characteristics of fatty acid (FA) containing foods are strongly dependent on the FA’s chemical/morphological arrangements. Paradoxically the nutritional, health enhancing FA polyunsaturated fatty acids (PUFAs) are highly susceptible to oxidation into harmful toxic side products during food preparation and storage. Current analytical technologies are not effective in the facile characterization of both the morphological and chemical structures of PUFA domains within materials for monitoring the parameters affecting their oxidation and antioxidant efficacy. The present paper is a review of our work on the development and application of a proton low field NMR relaxation sensor (1H LF NMR) and signal to time domain (TD) spectra reconstruction for chemical and morphological characterization of PUFA-rich oils and their oil in water emulsions, for assessing their degree and susceptibility to oxidation and the efficacy of antioxidants. The NMR signals are energy relaxation signals generated by spin–lattice interactions (T1) and spin–spin interactions (T2). These signals are reconstructed into 1D (T1 or T2) and 2D graphics (T1 vs. T2) by an optimal primal-dual interior method using a convex objectives (PDCO) solver. This is a direct measurement on non-modified samples where the individual graph peaks correlate to structural domains within the bulk oil or its emulsions. The emulsions of this review include relatively complex PUFA-rich oleosome-oil bodies based on the aqueous extraction from linseed seeds with and without encapsulation of externally added oils such as fish oil. Potential applications are shown in identifying optimal health enhancing PUFA-rich food formulations with maximal stability against oxidation and the potential for on-line quality control during preparation and storage.
Highlights
Polyunsaturated fatty acids (PUFAs) such as α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are important nutrients that regulate a wide variety of biological functions, from blood pressure to the development and functioning of the brain and nervous system [1,2,3,4]
The linseed oil (LSO) samples oxidized at low temperatures (25 and 40 ◦C) have a T2 vs. D curve with a negative slope, which can be rationalized by the slow LSO oxidation rate, and formation of low MW products, which decrease viscosity
In addition to individual PUFA molecules having specific molecular structures, their material functionality and their response to oxidants are strongly dependent on their aggregate structures in food oils or within aqueous emulsions
Summary
Polyunsaturated fatty acids (PUFAs) such as α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are important nutrients that regulate a wide variety of biological functions, from blood pressure to the development and functioning of the brain and nervous system [1,2,3,4]. In the present paper we review our work using 1H LF NMR energy relaxation technology with modified signal reconstruction algorithms for characterizing PUFA and their triglyceride oils and oil in water (O/W) emulsions with respect to their internal chemical and morphological arrangement. This correlates to their susceptibility to oxidation and antioxidant efficacy in food preparation and storage. OOxxiiddaattiioonn ooff PPUUFFAA--RRiicchhOOiillssaannddOO//WWEEmmuulslsioionnssFFooooddPPrroodduucctsts In the present review paper, we show how the complex arrangement of the different phases and components of emulsions can be further characterized using a novel 1H LF NMR energy relaxation time domain (TD) sensor including an optimized reconstruction program for generating chemical morphological fingerprinting maps. The potential to characterize an emulsion’s complex morphological structures including the interface using novel 1H LF NMR and reconstruction algorithms is described in subsequent sections
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