Novel application of NMR relaxometry in studies of diffusion in virgin rape oil A. Rachocki ⇑ , J. Tritt-Goc Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan ´, Poland article info Article history: Received 27 May 2013 Received in revised form 9 October 2013 Accepted 20 November 2013 Available online 28 November 2013 Keywords: Rape oil Molecular dynamics Diffusion coefficient Force-free-hard-sphere model FC NMR relaxometry Pulse gradient spin echo (PGSE) Single point imaging (SPI) abstract Field cycling (FC) proton nuclear magnetic resonance ( 1 H NMR) relaxometry was applied to study the dynamics of rape oil molecules. The spin–lattice relaxation data, measured in the frequency range from 0.01 to 30 MHz, were analysed by applying relaxation theory combined with the force-free-hard-sphere (FFHS) diffusion model. In the low frequency range, the relaxation was dominated by the translational diffusion contribution. Therefore, the diffusion coefficient of rape oil was determined from a linear dependence of the 1 H NMR relaxation dispersion drawn as a function of the square root of Larmor fre- quency. The results are consistent with those obtained from the pulse gradient spin echo (PGSE) NMR method. To estimate the density of oil protons, a parameter required to derive the diffusion coefficient from NMR relaxometry, a single point imaging (SPI) NMR experiment was proposed. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction A problem of differentiation between the authentic vegetable oils from false oils has arisen in recent years. Much effort has been made to develop new methods for authentication of oils. Among them are different analytical methods, including a high-resolution 1 H and 13 C NMR spectroscopies (Agiomyrgianaki, Petrakis, & Dais, 2010; Aids & Hatzakis, 2013; Fang, Goh, Tay, Lau, & Yau Li, 2013; Juan, Bosque-Sendra, Cuadros-Rodriguez, Ruiz-Samblas, & Paulina de la Mata, 2012; Rubel, 1994; Sacchi, Addeo, & Paolillo, 1997). The NMR techniques are totally non-destructive if the experiments are running below the characteristic temperature of the studied sample, e.g., decomposition temperature. Therefore, the measure- ments can be repeated any number of times on the same sample. Possible applications of field cycling (FC) NMR relaxometry (Anorado, Galli, & Ferrante, 2001; Kimmich & Anoardo, 2004; Noack, 1986), for verification of oil samples, evaluation of oil qual- ity and differentiation of oils, as well as for the study of whole oil seeds have recently been reported (Conte et al., 2011; Rachocki, Latanowicz, & Tritt-Goc, 2012). These studies have shown that the dynamic parameters, associated with motions of oil molecules, such as the translational and rotational correlation times derived from FC NMR relaxometry, are specific to particular oils because they depend on a variety of factors, e.g., the chemical composition and the kinematics viscosity of oil, the oil production process, and the geographical growth area of the cultivar. However, the compu- tation of correlation times from FC NMR relaxometry requires the assumption of relaxation theory, which can reproduce the measured spin–lattice relaxation data over a broad frequency range. The calculations can be time consuming (Ballari, Bonetto, & Anorado, 2005; Conte et al., 2011; Rachocki et al., 2012). In this paper we show that FC NMR relaxometry can easily be used to determine the translational diffusion coefficient, which is another dynamic parameter characterising the motion of mole- cules and unique to particular samples. The determination of diffu- sion coefficient from FC NMR relaxometry requires a simple mathematical operation. Thus, this method can be used in a variety of industrial applications in which specification of oil is needed. At first, FC NMR relaxometry was applied to determine the dif- fusion coefficient in molecular liquids (Harmon, 1970; Harmon & Muller, 1969), and of paramagnetic species in solution (Belorizky et al., 1998). Recently, this method was applied to determine the translational diffusion coefficients for a series of simple molecular liquids or polymer melts but with well known chemical formulas (Kruk, Meier, & Rossler, 2011, 2012; Meier, Kahlau, Kruk, & Rossler, 2010; Meier, Kruk, Bourdick, Schneider, & Rossler, 2013). However, to the best of our knowledge, FC NMR relaxometry has never been used to obtain a diffusion coefficient in vegetable oils, where the chemical compositions are more complex than those previously studied. 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.11.112 ⇑ Corresponding author. Tel.: +48 61 8695241; fax: +48 61 8684524. E-mail address: radam@ifmpan.poznan.pl (A. Rachocki). Food Chemistry 152 (2014) 94–99 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem