Analysing the effects of frozen storage and processing on the metabolite profile of raw mullet roes using 1 H NMR spectroscopy Cristina Piras, Paola Scano, Emanuela Locci, Roberta Sanna, Flaminia Cesare Marincola ⇑ Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, Cittadella di Monserrato, SS 554, 09042 Monserrato, CA, Italy article info Article history: Received 23 September 2013 Received in revised form 12 February 2014 Accepted 27 February 2014 Available online 12 March 2014 Keywords: 1 H NMR Metabolomics Mullet roes Frozen storage Processing abstract 1 H NMR spectroscopy was used to investigate changes in the low molecular weight metabolic profile of raw mullet (Mugil spp.) roes during frozen storage and upon processing. NMR data were analysed by Prin- cipal Component Analyses (PCA). In the model constructed using frozen roes, no statistical significant metabolic modifications were observed in the first six months of storage, while choline derivatives, dimethylamine, lactate, and most of the free amino acids were identified as changing with statistical sig- nificance (p < 0.05) in response to frozen storage time of twelve months. The PCA model comparing the metabolic profiles of roes before and after processing showed that the major modifications occurring upon manufacturing were the increase of the choline derivative compounds, uracil, and free amino acids, and a large decrease of taurine, glucose, lactate, and creatine/phosphocreatine. All of the above men- tioned modifications reflect the occurrence of chemical/biochemical reactions arising from degradation processes such as lipolysis and proteolysis. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Salted-dried fish roes are one of the most popular forms of roe products in many countries. Among these, the best-known is the salted-dried mullet (Mugil spp.) roe, called ‘‘karasumi’’ in Japan, ‘‘avgotaracho’’ in Greece, and ‘‘bottarga’’ in Italy. Dried mullet roe is considered a stable natural source of health beneficial n-3 fatty acids (Barra et al., 2008; Kalogeropoulos, Nomikos, Chiou, Fragop- oulou, & Antonopoulou, 2008; Scano, Rosa, Locci, Dessì, & Lai, 2009; Scano et al., 2008), such as eicosapentaenoic acid (EPA, 20:5 n-3) and docosahexaenoic acid (DHA, 22:6 n-3). Its lipid frac- tion is characterised by a high portion of wax esters (ca. 50–65% of lipid classes), triacylglycerols, phospholipids, and cholesterol (Rosa, Scano, Melis, Deiana, Atzeri, & Dessì, 2009; Scano et al., 2009). Furthermore, mullet roe is a source of high quality proteins. Recently, preliminary results have also shown remarkable nutra- ceutical properties of bottarga lipids, qualifying bottarga as a food with potential benefits in colon cancer prevention (Rosa, Scano, Atzeri, Deiana, & Falchi, 2013). However, one must remember that the composition of bottarga may change according to both manu- facturing and storage conditions, due to hydrolysis and oxidation processes affecting mainly the lipid components (Rosa et al., 2009; Scano et al., 2009; Rosa, Scano, Atzeri, Deiana, Mereu, & Dessì, 2012) and, to a lower extent, the global profile of low molec- ular weight metabolites (Locci, Piras, Mereu, Cesare Marincola, & Scano, 2011; Scano, Rosa, Locci, Manzo, & Dessì, 2012; Ziaeian, Moini, & Jamili, 2008). Differently from salted-dried mullet roes, a limited amount of data is available on unprocessed mullet roes (Chiou & Konosu, 1988; Scano et al., 2009). In particular, to our knowledge, no study has been performed on the frozen storage impact on their compo- sition before and after processing. This topic is of current interest since most of the commercial salted-dried mullet roes are manu- factured starting from frozen raw material. This is the case of bot- targa produced in Sardinia (Italy). Bottarga has become so increasingly popular in international markets that mullets of the Mediterranean sea are not enough to satisfy the request of this product. As a result, the Sardinian manufacturers must turn their attention to other fishing areas located in different regions of the globe for roe supplies. Indeed, raw roes are purchased from distrib- utors located mainly in the Atlantic Ocean, namely in FAO fishing areas 31 (central-western), 34 (central-eastern), and 41(south- western). As a consequence, imported mullet roes must travel far- ther distances and, being not possible the processing at the time after catching, they are kept frozen to alleviate the deterioration caused by microorganisms and slow down other processes such as activity of endogenous enzymes and oxidations. However, although fish storage at subzero temperatures may extend shelf life, measurements of sensory, chemical, and physical properties http://dx.doi.org/10.1016/j.foodchem.2014.02.160 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +39 070 675 4389; fax: +39 070 675 4388. E-mail address: flaminia@unica.it (F. Cesare Marincola). Food Chemistry 159 (2014) 71–79 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem