Investigation of the effect of gelatine, egg albumin and cross-flow microfiltration on the phenolic composition of Pinotage wine A. Oberholster a,b,⇑ , L.M. Carstens a , W.J. du Toit a a Department of Viticulture and Oenology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa b Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616, USA article info Article history: Received 19 July 2012 Received in revised form 31 August 2012 Accepted 25 September 2012 Available online 15 November 2012 Keywords: Egg albumin Gelatine Cross-flow microfiltration Phenols Tannins Mouth-feel abstract The effect of fining and cross-flow microfiltration on the phenolic composition of red wine was investi- gated. Both gelatine (G) and egg albumin (EA) fining decreased the mean degree of polymerisation (mDP) of tannin significantly by 26.4% and 25.2%, respectively, compared to the control (C). Cross-flow microfil- tration (CF) also decreased the mDP significantly by 25%. Thus, the fining agents and cross-flow microfil- tration selectively removed the highly polymerised phenols. After 3.5 months of bottle ageing, differences between the different treatments and the control decreased. CF had the most significant effect on the fla- van-3-ol and polymeric phenol (tannin) content of the wines compared to the control followed by G fin- ing. CF and EA treatments significantly decreased the total pigment content compared to C. CF was also the only treatment that could be distinguished from the other treatments by sensory analysis. All treat- ments improved clarity of the wines with cross-flow microfiltration having the largest effect. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Phenolics are important contributors to wine quality, ageing po- tential and sensory characteristics. Phenolic compounds are responsible for the differences observed between white and red wine and are extracted from grape skins and seeds during wine- making. The concentration of phenols can be influenced by grape variety, viticultural practices and winemaking processes and trans- formation that can take place during wine ageing (Castillo-Sanchez et al., 2008). The main flavonoid compounds present in grapes and wine are anthocyanins, flavan-3-ols and their polymerised products (Aron & Kennedy, 2007). Flavan-3-ols can be present as monomers, oligo- mers and polymers in red wine, also known as proanthocyanidins or condensed tannins (Ribéreau-Gayon, Glories, Maujean, & Dubourdieu, 2006). Anthocyanins originate from skins in grapes and are responsible for the red colour of red grapes and wine (Harbertson, Picciotto, & Adams, 2003). Polymeric pigments are more stable to pH changes and bisulphite bleaching than monomeric pigments (Ribéreau- Gayon et al., 2006). Thus, monomeric anthocyanins and polymeric pigments can be distinguished by these characteristics (Harbertson et al., 2003). During the first year of storage rapid changes take place in the colour composition of the wine. The purple–red colour of a young red wine changes to orange–red with aging. These changes occur when the monomeric pigments are replaced with oligomeric forms which are more stable through direct and indi- rect polymerisation reactions (Cheynier et al., 2006). Fining agents are used to eliminate or reduce undesirable sub- stances in wine. The main purpose of using a protein based fining agent in particular is to soften the wine and to reduce wine astrin- gency through complexation of the proteins with the phenolic compounds in the wine and removal thereof through precipitation (Sarni-Manchado, Deleris, Avallone, Cheynier, & Moutounet, 1999). Protein fining agents differ in several physico-chemical ways. The different characteristics are molecular weight distribution, iso- electric point and the surface charge density (Cosme, Ricardo- Da-Silva, & Laureano, 2009). Fining agents such as egg albumin, casein, gelatine and PVPP re- duces the phenolic content of wines and may decrease the colour of some wines (Castillo-Sanchez, Mejuto, Garrido, & Garcia-Falcon, 2006; Castillo-Sanchez et al., 2008; Cosme, Ricardo-Da-Silva, & Laureano, 2008; Cosme et al., 2009; Sarni-Manchado et al., 1999). Several authors found that there is increased interaction between proteins and more polymerised proanthocyanidins and proantho- cyanidins esterified with gallic acid than less polymerised proanthocyanidins (Cosme et al., 2009; Ricardo-Da-Silva et al.,1991; Sarni-Manchado et al., 1999). Cosme et al. (2009) stated that egg albumin and low molecular weight gelatine only 0308-8146/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2012.09.128 ⇑ Corresponding author at: Department of Viticulture and Enology, University of California, One Shields Avenue, Davis, CA 95616, USA. Tel.: +1 530 754 4866; fax: +1 530 752 0382. E-mail address: aoberholster@ucdavis.edu (A. Oberholster). Food Chemistry 138 (2013) 1275–1281 Contents lists available at SciVerse ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem