Practical implications of the phase‐compositional assessment of lipid‐based food products by time‐domain NMR

Abstract

The objective of this work is to determine the solid fat content (SFC) of the fat-oil phase in oil-in-water (O/W) emulsions, i.e., the droplet SFC, using transverse relaxation decay deconvolution (TRDD) analysis. The TRDD NMR experiment classifies protein protons as mobile, semimobile, and nonmobile. Hence, protein contributes more or less to the solid content detected by TRDD as a function of pH, protein content, and protein denaturation. By taking into account the protein contribution to the overall solid content, one can estimate the droplet solid content in O/W emulsions. The SFC can then be deduced if one converts the ingredients' mass fraction into ingredients' proton fraction using the ingredients' proton densities.Paper no. J11392 in JAOCS 83, 905-912 (November 2006). KEY WORDS:O/W emulsions, SFC, solid content, transverse relaxation decay deconvolution (TRDD), whey proteins.The key to understanding many functional properties of food products and materials is in the physical state of their ingredients (1). Texture (hardness) and melting behavior of margarine and chocolate, for example, are determined by the phase behavior of their lipid component, i.e., the balance between the solid/liquid state and the effects of crystal polymorphism (1,2). For many cereal materials, the phase composition of the carbohydrate components determines processing and textural properties. The various phases comprise different crystalline starch polymorphs, gel states, mesomorphic phases, and liquid-like dissolved phases (3,4). For the assessment of crystal polymorphism of food materials, one traditionally deploys X-ray diffraction and thermal analysis (mostly DSC) (5). These techniques are unsurpassed in addressing specific phase-compositional details of lipid and carbohydrate materials, such as polymorph identification. However, they mostly fall short when the phase composition of complex foods products needs to be assessed in a quantitative manner. For this purpose, NMR relaxometry currently presents the most powerful option. Strong advantages of NMR over other methods are that it probes molecular mobility of the different phases, and that the obtained signals directly relate to corresponding proton densities. For this purpose, dedicated low-field NMR relaxometers have been designed that are relatively cheap and easily operated by nonexperts. The earliest example of a widespread application within the foods community is the determination of solid fat content (SFC) of lipids by NMR (6). This methodology uses rather crude acquisition and data treatments of the free induction decay (FID). More recent sophisticated NMR line-shape analysis procedures (7-9) were introduced to derive detailed quantitative phase-compositional information on polysaccharides (10,11) and on lipids (12). Even thermal denaturation of proteins (13) was investigated. This type of analysis also can be applied to complex food products (8,9,14,15). In our implementation for lipid-based products, we denoted this approach as transverse relaxation decay deconvolu...

Nanostructuring fiber morphology and solvent inclusions in 12-hydroxystearic acid / canola oil organogels

“…Solid fat crystals have relaxation times below 70 μs [30]. Also, for β and β′ fat crystal's T 2 relaxations are less than 45 μs and α crystals relax at 12 μs [31]. It is observed that at lower concentrations there is a significant (P N 0.05) decrease in the free induction relaxation times at 30°C when compared to 5°C (Fig.…”

“…130 ms and 200 to 500 ms in the temperature range studied. Duval, van Duynhoven and Bot [31] reported that mobile oil has T 2 relaxations greater than 2 ms. Hence, the aforementioned relaxations are attributed to the oil phase.…”

Investigations of food colloids by NMR and MRI

“…Following the work of Van Duynhoven et al [1], Trezza et al [2] recently, demonstrated that greater accuracy in the measurement of the solid fat content could be achieved from combined FID and CPMG acquisition and when the signal is analysed with semi-empirical mathematical functions for solid, semi-solid and liquid components. An extension of this method has also been proposed in order to adapt the method to nonanhydrous fat products such as emulsions [3]. Indeed, in emulsions the contribution of non-fat solid-like protons such as non-echangeable protein protons to the solid phase has to be taken into account.…”

Crystalline stability of self-assembled fibrillar networks of 12-hydroxystearic acid in edible oils

“…Hence, the aforementioned relaxations are attributed to the oil phase. Duval, van Duynhoven, and Bot (2006) reported that mobile oil has T 2 relaxations greater than 2 ms. Given this, the relaxations in the range of 50-70 ms are attributed to the immobilized or entrained oil (less mobile oil) and those in the range of 200-500 ms to the mobile liquid oil.…”