Journal of Chromatography A, 1209 (2008) 238–245 Contents lists available at ScienceDirect Journal of Chromatography A journal homepage: www.elsevier.com/locate/chroma Development of a rapid method to determine phenolic and other polar compounds in walnut by capillary electrophoresis–electrospray ionization time-of-flight mass spectrometry Ana M a Gómez-Caravaca a , Vito Verardo b , Antonio Segura-Carretero a,∗ , Maria Fiorenza Caboni b , Alberto Fernández-Gutiérrez a,∗ a Department of Analytical Chemistry, University of Granada, c/Fuentenueva s/n, 18003 Granada, Spain b Dipartimento di Scienze degli Alimenti, Università di Bologna, Piazzale Goidanich 60, 47023 Cesena (FC), Italy article info Article history: Received 19 May 2008 Received in revised form 18 August 2008 Accepted 20 August 2008 Available online 7 September 2008 Keywords: CE MS Phenolic compounds TOF Walnut abstract The aim of this work was to develop a capillary electrophoresis–mass spectrometry (CE–MS) method to identify and quantify phenolic and other related polar compounds in walnut samples. The extraction capacity of several solvent mixtures of phenolic compounds from walnut by conventional solid–liquid extractions was tested, and CE and electrospray ionization MS parameters were optimized. The finalized procedure is able to determine many well-known phenolic compounds present in walnuts and pro- vide relevant information about the presence of minor polar compounds. A new compound in walnut ((2E,4E)-8-hydroxy-2,7-dimethyl-2,4-decadiene-1,10-dioic acid 6-O--d-glucopiranosyl ester, [M-H] - 403.161 m/z) with a structure similar to glansreginins was also identified. Phenolic compounds correspond to 14–28% of total polar compounds quantified. Aglycone and glycosylated ellagic acid represent the prin- cipal components and account for 64–75% of total phenols in walnuts. However, the sum of glansreginins A, B and (2E,4E)-8-hydroxy-2,7-dimethyl-2,4-decadiene-1,10-dioic acid 6 ′ -O--d-glucopiranosyl ester was in the range of 72–86% of total quantified compounds. In addition, this is the first time that separation by CE with detection by electrospray ionization time-of-flight MS has been applied to the analysis of phenolic and other polar compounds in walnut samples, providing results in less than 15min. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Nuts, including walnuts, are a traditional food in the Mediter- ranean, South America and Asia, and are ingredients in sauces, stuffing, entrees, snacks, appetizers and desserts. Walnuts are one of the oldest tree foods known to humans, with historical references dating back to Persia in 7000 B.C. [1]. Walnuts are very rich in fats (52–70%) (oleic, linoleic and linolenic acid are predominant), proteins (14–24%) [2] and contain free amino acids [3]. Walnuts are also good sources of antioxidants including vitamin E and other compounds with biological activity such as flavonoids, other polyphenols and sterols [4]. Walnuts are stable, especially in shells. When walnuts are kept in a cool, dry environment they have a shelf life of 12 months [5]. Walnuts are also a rich source of phenolic compounds [6] which contribute to their antioxidant capacity; they inhibit the oxidation of human plasma and low-density lipoproteins (LDLs) in ∗ Corresponding authors. Tel.: +34 958243296; fax: +34 958249510. E-mail address: ansegura@ugr.es (A. Segura-Carretero). vitro [7] and may influence the low mortality rates from coronary heart disease and cancer in Mediterranean populations as walnuts are important constituents of the daily Mediterranean diet [8] as already mentioned. In addition to the favorable lipid profile of nuts, their phenolic content must be considered as a potential contribu- tor to their apparent antiatherogenic effect. Additionally, phenolic compounds have anti-inflammatory and anti-mutagenic activities [7]. The phenolic content of walnut may affect the storage sta- bility, and could be used as important criteria for evaluation of walnut quality [9]. The presence of phenolic compounds has also been related to the slightly astringent flavor of walnut fruits [10]. Analysis of phenols, polyphenols, and pigments in foods is funda- mental to evaluate both the food and raw material due to their contribution to the color, taste, flavor characteristics and health benefits. Most phenolic compounds commonly identified in walnut are phenolic acids and condensed tannins, and ellagic acid and flavonoids potentially have serum cholesterol-modulating effects [11]. Different phenolic acids and flavonoids have been identified in walnut fruit extracts by high-performance liquid chromatogra- phy (HPLC) [12–14], and in recent studies of walnuts some authors 0021-9673/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2008.08.117