Magnetic resonance imaging of single rice kernels during cooking Ales ˇ Mohoric ˇ a,1 , Frank Vergeldt a,1 , Edo Gerkema a,1 , Adrie de Jager a,z , John van Duynhoven b,1 , Gerard van Dalen b,1 , Henk Van As a, * ,1 a Laboratory of Biophysics and Wageningen NMR Centre, Wageningen University, Dreijenlaan 3, 6703 HA Wageningen, The Netherlands b Unilever Research Vlaardingen, Olivier van Noortlaan, P.O. Box 114, 3130 AC Vlaardingen, The Netherlands Received 29 June 2004; revised 18 August 2004 Available online 17 September 2004 Abstract The RARE imaging method was used to monitor the cooking of single rice kernels in real time and with high spatial resolution in three dimensions. The imaging sequence is optimized for rapid acquisition of signals with short relaxation times using centered out RARE. Short scan time and high spatial resolution are critical factors in the investigation of the cooking behavior of rice kernels since time and spatial averaging may lead to erroneous results. The results are confirming the general pattern of moisture ingress that has been suspected from previous (more limited) studies. Water uptake as determined by analysis of the MRI time series recorded during cooking compares well with gravimetric studies. This allows using these real-time MRI data for developing and validating models that describe the effect of kernel microstructure on its cooking behavior. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Hydration; Gelatinization; Rice; Cooking; RARE; Magnetic resonance imaging 1. Introduction Cooking is one of the most important processing steps in the preparation of foods. It involves transport of heat and mass (water) and commonly several ingredi- ents in the cooked food material undergo phase transi- tions, such as gelatinization of starch. To a large extent the rates of these processes are governed by the initial phase-composition and microstructure of the material. MRI has been deployed successfully to study the interaction between structure of a food material, and the dynamic transport (heat, mass) and phase tran- sition events that occur during cooking [1]. MRI is ide- ally suited for such studies since it can detect both molecular mobility and localization in a dynamic and non-invasive manner. Typically, the deployed MRI techniques were based on conventional spin-echo meth- ods. For many materials, however, conventional spin- echo techniques do not provide sufficient spatial and temporal resolution. An important example where the conventional MRI approaches fall short in resolving power is cereals like rice. Rice kernels typically have spa- tial dimensions of millimeters, cooking times in the tens of minutes during which glassy and crystalline starch becomes gelatinized. To be able to make useful obser- vations with spin-echo MRI, investigators either empha- sized spatial or time-resolution, sacrificing one feature in favor of the other. An example is given by Takeuchi et al. [2] who ac- quired structural information in only one spatial dimen- sion in order to obtain sufficient time-resolution to monitor moisture distribution in a rice kernel in real time during cooking. This approach is valid if one can assume that the object under study is structurally 1090-7807/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jmr.2004.08.013 * Corresponding author. Fax: +31 317 482725. E-mail address: henk.vanas@wur.nl (H. Van As). 1 We were deeply saddened by the death of P. Adrie de Jager on July 13, 2004. z Deceased. www.elsevier.com/locate/jmr Journal of Magnetic Resonance 171 (2004) 157–162