Changes in the catechin and epicatechin content of grape seeds on storage under different water activity (a w ) conditions Efimia Hatzidimitriou, Nikolaos Nenadis, Maria Z. Tsimidou * Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece Received 2 February 2007; received in revised form 11 May 2007; accepted 11 May 2007 Abstract Storage effect on antioxidant content and capacity of grape seeds under different a w conditions (a w 0.33; 0.53; 0.75/50 days, 25 °C) was examined. Total phenol content (determined by the Folin–Ciocalteu method) decreased during storage though changes were trivial for samples stored at 33% or 53% RH. High level of humidity (75%) accelerated degradation and resulted in a 50% reduction of total phe- nol content. Minor loss of the DPPH radical scavenging activity (%RSA) of the extracts was observed. Catechin and epicatechin content monitored by RP-HPLC was reduced during storage, particularly at 75% RH. Epicatechin content proved to be less sensitive to water activity conditions than catechin content. Results of various in vitro assays (Folin–Ciocalteu, FRAP, DPPH, ABTS, CBA, ORAC and copper induced liposome oxidation) did not support difference in terms of resistance to oxidation. Based on the continuous release of gallic acid, our finding was related to hydrolytic reactions. Control of a w of grape seeds can be of practical importance for the wine industry. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Grape seeds; Catechin; Epicatechin; Degradation; Water activity; Antioxidant activity 1. Introduction Among the different parts of the grape, seeds accumu- late the majority (60–70%) of phenolic compounds (Ribe ´- reau-Gayon, Glories, Maujean, & Dubourdieu, 2000), and have for that reason been thoroughly studied for more than 10 years (Shi, Yu, Pohorly, & Kakuda, 2003). Fractionation, characterization and identification of low and high molecular weight grape seed phenolics (Escrib- ano-Bailo ´n, Gutie ´rrez-Ferna ´ndez, Rivas-Gonzalo, & San- tos Buelga, 1992; Labarbe, Cheynier, Brossaud, Souquet, & Moutounet, 1999; Oszmianski & Sapis, 1989), revealed that monomeric flavan-3-ols (catechin, epicatechin and epi- gallocatechin) and their acylated forms (esters with gallic acid) (epicatechin gallate and epigallocatechin gallate), phenolic acids (gallic acid in particular) and dimeric B1, B2 procyanidins are the characteristic phenolic constituents of grape seeds (De Freitas and Glories, 1999; Fuleki and Da Silva, 1997; Guendez, Kallithraka, Makris, & Kef- alas, 2005a,2005b; Palma and Taylor, 1999; Shi et al., 2003; Yilmaz and Toledo, 2004b). The presence of dimeric B3, B4, B5, B6, B7, B8, trimeric C1, tetrameric and polymeric procyanidins has also been reported (Escribano-Bailo ´n et al., 1992; Oszmianski & Sapis, 1989; Santos-Buelga, Francia-Aricha, & Escribano-Bailo ´n, 1995). Based on quantitative information catechin–epicatechin monomers seem to be the two principal compounds, at about equal amounts, depending on the grape variety. Their levels vary from a few to some hundreds of mg/ 100 g of dry seeds. Epicatechin content is slightly higher in red varieties. During vinification, only a portion of catechins and procyanidins is extracted from seeds and is diffused to the 0308-8146/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2007.05.032 Abbreviations: FRAP, ferric reducing antioxidant power; DPPH, 1,1- Diphenyl-2-picrylhydrazyl; ABTS, 2,2 0 -Azinobis(3-ethylbenzothiazoline- 6-sulfonic acid)diammonium salt; CBA, crocin bleaching assay; ORAC, oxygen radical absorbance capacity; TPTZ, tripyridyltriazine. * Corresponding author. Tel.: +30 2310997796; fax: +30 2310997779. E-mail address: tsimidou@chem.auth.gr (M.Z. Tsimidou). www.elsevier.com/locate/foodchem Food Chemistry 105 (2007) 1504–1511 Food Chemistry