A proton NMR relaxation study of hen egg quality Luca Laghi a , Mauro A. Cremonini a , Giuseppe Placucci a , Stanislav Sykora b , Kevin Wright c , Brian Hills c, T a Department of Food Science, University of Bologna, Via Ravennate 1020, 47023 Cesena, Italy b Extra Byte, Via R. Sanzio 22C, 20022 Castano Primo, Italy c Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, UK Accepted 8 December 2004 Abstract A quantitative analysis of NMR proton relaxation in hen egg albumen and yolk is undertaken to research the causes of quality loss during the first few days of storage and to access the feasibility of an on-line NMR sensor of internal egg quality. It is shown that the change in the transverse relaxation in thick egg albumen mainly results from an increase in proton exchange rate resulting from a pH increase attributed to loss of carbon dioxide by diffusion through the eggshell. The results suggest that the low-field T 1 is the best relaxation time indicator of albumen quality. D 2005 Elsevier Inc. All rights reserved. Keywords: Egg’s quality; Low-resolution NMR; NMRD; Model-free analysis 1. Introduction Quality deterioration in hen eggs during the first few days of storage has been the subject of several biochemical investigations and has been reviewed [1]. Being noninva- sive, MRI is a potentially valuable technique for monitoring these internal quality changes. Jayasundar et al. [2] showed that all the major structures including the yolk, egg white, the chalaza, latebra and airspace could be clearly identified in MR images of raw hen eggs. Even the white and yellow rings inside the egg yolk could be discerned in T 1 -weighted images [2,3]. These MRI studies are not merely of academic interest but have potentially important commercial signifi- cance for automated egg grading. Modern egg grading machines sort eggs according to size at rates of up to 120,000 eggs per hour, but internal egg quality is usually assessed by random sampling and human visual inspection by shining light through the egg in a process called bcandling.Q To try to circumvent this labor-intensive operation, there is an intense research effort underway to develop noninvasive on-line sensors of both internal and external egg quality [4]. Being noninvasive and capable of revealing internal structure, an on-line MRI sensor is a potential candidate, provided, of course, that it can be developed as a low-cost sensor and useful correlations between image parameters and egg quality can be found. A hint that such correlations exist can be found in the work by Capozzi et al. [5] who showed that the proton longitudinal relaxation time of the egg white measured at 700 kHz follows a pseudoexponential decay with time after laying. More recently, Schw7gele et al. [6] showed that the water proton transverse relaxation time of raw egg white measured at 7.5 MHz decreased with increasing storage time over a 40-day period. However, Jayasundar et al. [2], working at a higher proton frequency of 200 MHz, found no MRI-measurable changes in their relaxation-weighted images of either the egg white or yolk during storage of raw eggs over 5 days. They did however see an almost linear increase in the size of the airspace caused by evaporation of water through the shell. Potentially useful NMR–egg quality correlations can also be explored by in vitro relaxation time measurements on separated egg albumen and yolk, but there have been surprisingly few such studies to date. Klammer and Kimmich [7] found that there were no apparent changes in the transverse relaxation times of resolved spectral compo- nents (water and lipid peaks) in the yolk of fertilized hen egg but did not report on the relaxation behavior of the egg albumen. An earlier paper of Koenig and Brown [8] reported 0730-725X/$ – see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2004.12.003 T Corresponding author. Tel.: +44 0 16032 55378; fax: +44 0 1603 507723. E-mail address: brian.hills@bbsrc.ac.uk (B. Hills). Magnetic Resonance Imaging 23 (2005) 501 – 510