Analytical Methods Rapid quantification of muscle fat content and subcutaneous adipose tissue in fish using MRI Guylaine Collewet a,b,⇑ , Jérôme Bugeon c , Jérôme Idier d , Stéphane Quellec a,b , Benjamin Quittet e , Mireille Cambert a,b , Pierrick Haffray e a Irstea, UR TERE, 17 avenue de cucillé, CS 64427, 35044 Rennes, France b Université Européenne de Bretagne, France c INRA, UR1037, SCRIBE, IFR140, F-35000 Rennes, France d IRCCyN CNRS, F-44300 Nantes, France e SYSAAF, F-35000 Rennes, France article info Article history: Received 23 January 2012 Received in revised form 17 September 2012 Accepted 23 September 2012 Available online 15 November 2012 Keywords: MRI Fish Fat content Subcutaneous fat abstract The potentiality of MRI to quantify fat content in flesh and subcutaneous fat in fish cutlets was investi- gated. Low measurement time was aimed at in a view to handling large number of samples needed in selective breeding programs for example. Results on fresh and frozen–thawed cutlets were compared to assess this way of conservation. As MRI generates unwanted spatial variations of the signal, a correc- tion method was developed enabling the measurement on several cutlets simultaneously in less than 3 min per sample. For subcutaneous fat, the results were compared with vision measurements. High cor- relations between both techniques were found (R 2 = 0.77 and 0.87 for the ventral and dorsal part). Fat in flesh was validated vs NMR measurements. No statistical difference was found between fresh and frozen– thawed cutlets. RMSE was respectively 0.8% and 0.89%. These results confirmed the potentiality of MRI for fat measurement in fish particularly for a large number of samples. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The quantity and the anatomic distribution of lipid in fish are of major importance for the quality of the product. Subcutaneous adi- pose tissue is directly linked to fillet yields because it is discarded during fillet trimming, while the quantity of lipid in flesh highly influences the sensory perception and the gustative aspects. In or- der to optimize the quality of fish products, improvement by ge- netic selection could be seen as a promising strategy (Gjedrem, 1997) that needs estimations of genetic parameters of subcutane- ous fat and the lipid content of the flesh. Considering the several thousand individuals to phenotype in a selective breeding pro- gram, a rapid and accurate method of the measurement of lipid in fish is needed. The measurement of both fat content in flesh and subcutane- ous fat can be achieved if the spatial resolution of the sensor is high enough to separate the different parts of the fish. Another requirement is to obtain images with a good contrast between muscle and fat to distinguish both tissues. Computer vision, X-rays computer tomography and magnetic resonance imaging (MRI) meet such requirements and have been used for estimation of fat content in fish (Mathiassen, Misimi, Bondo, Veliyulin, & Ost- vik, 2011). Analysis of images acquired with a CCD camera (Marty-Mahe et al., 2004) or with a desk-top scanner (Kause et al., 2008) has been successfully used for characterization of rainbow trout. In these cases, thanks to the color of the flesh, the contrast between fat and muscle enables the segmentation of the different tissues such as the red muscle, white muscle, lipid stripes and dorsal fat depot (Stien, Kiessling, & Marine, 2007; Stien et al., 2006). These methods have the advantage to use cheap sensors and to achieve very high spatial resolution such as 0.127 mm 2 per pixel. However they are restricted to fish with pigmented flesh and they are inva- sive since fish have to be cut before analysis. Moreover, intermedi- ate correlations (0.77) were estimated between visual traits measured and the muscle fat content (Marty-Mahe et al., 2004). On the contrary X-rays and MRI are more expensive but non- invasive and suitable for all kinds of fish since they provide a con- trast between fat and muscle whatever the color of the flesh. X-rays have been tested for prediction of carcass composition in rainbow trout (Gjerde, 1987), Atlantic salmon (Rye, 1991), Atlantic halibut (Kolstad, Vegusdal, Baeverfjord, & Einen, 2004), common carp (Hancz et al., 2003) and common carp, grass carp, silver carp and pike perch (Romvari, Hancz, Petrasi, Molnar, & Horn, 2002). For 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.09.131 ⇑ Corresponding author at: Irstea, UR TERE, 17 avenue de cucillé, CS 64427, 35044 Rennes, France. E-mail address: guylaine.collewet@irstea.fr (G. Collewet). Food Chemistry 138 (2013) 2008–2015 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem