Effects of various protein- and polysaccharide-based clarification agents on antioxidative compounds and colour of pomegranate juice Betül Erkan-Koç a , Meltem Türkyılmaz b , Oktay Yemis ß c , Mehmet Özkan d,⇑ a Turkish Statistical Institute, Çankaya, Ankara 06650, Turkey b Institute of Food Safety, Ankara University, Dıs ßkapı, Ankara 06110, Turkey c Department of Food Engineering, Faculty of Engineering, Sakarya University, Serdivan, Sakarya 54187, Turkey d Department of Food Engineering, Faculty of Engineering, Ankara University, Dıs ßkapı, Ankara 06110, Turkey article info Article history: Received 16 December 2014 Received in revised form 14 March 2015 Accepted 18 March 2015 Available online 24 March 2015 Keywords: Natural sedimentation Gelatin Albumin Casein Chitosan Xanthan gum Phenolics abstract The effects of natural sedimentation and clarification agents [protein-based (albumin, casein and gelatin) and polysaccharide-based (chitosan and xanthan gum)] on total phenolics, hydrolysable tannins, antho- cyanins and antioxidant activity of pomegranate juice were investigated. While protein-based agents led to higher reductions in the contents of total phenolics (7.2–17.2%), hydrolysable tannins (16.7–59.5%) and anthocyanins (11.7–23.7%) (p < 0.05) than natural sedimentation, polysaccharide-based agents had simi- lar effects on these compounds, like natural sedimentation (p > 0.05). The stabilities of b-punicalagin and a-punicalagin (the major hydrolysable tannins) against clarification were similar. Moreover, antioxidant activities of the samples clarified with polysaccharide-based agents were higher (2.4–26.6%) than those of the protein-based agents. For both high total phenolic, hydrolysable tannin and anthocyanins contents, as well as high antioxidant activity, we suggest that polysaccharide-based agents be used for the clarifica- tion of pomegranate juice. In fact, chitosan is especially recommended for this purpose since chitosan (10.3 NTU) led to lower turbidity as compared to xanthan gum (20.0 NTU). Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Pomegranates are generally processed into juice with their rinds, constituting 48% of the whole fruit (Kulkarni & Aradhya, 2005). During pressing of pomegranates, hydrolysable tannins (e.g. punicalagins and punicalin), which are the main phenolic group in the rinds, pass from the rinds into juice (Muhacir-Güzel, Türkyılmaz, Yemis ß, Tag ˘ı, & Özkan, 2014). And, they cause the for- mation of cloudy appearance as well as astringency and bitterness in juice (Spanos & Wrolstad, 1992). The cloudy appearance nega- tively affects consumer attitude toward pomegranate juice since consumers question the safety and quality of turbid products. The removal of hydrolysable tannins should be targeted to pro- duce a clear pomegranate juice (Muhacir-Güzel et al., 2014; Turfan, Türkyılmaz, Yemis ß, & Özkan, 2011) because pomegranates contain insignificant amounts of the other compounds (pectin and protein) causing the turbidity in juices (Benk, 1971). For the removal of tan- nins, cold-clarification of pomegranate juice with only gelatin is suggested (Özkan, Yemeniciog ˘lu, Asefi, & Cemerog ˘lu, 2002). However, gelatin removes the significant amounts of not only hydrolysable tannins (74% reduction, Muhacir-Güzel et al., 2014) but also anthocyanins (19% reduction, Turfan et al., 2011), which are responsible for the attractive red colour of pomegranate juice, from the juice. Therefore, the effects of different clarification agents [polyvinylpolypyrolidone (PVPP) (Vardin & Fenerciog ˘lu, 2003) and albumin (Valero, Vegara, Martí, & Saura, 2014)] and clar- ification methods [natural sedimentation (Vardin & Fenerciog ˘lu, 2003), laccase treatment (Neifar et al., 2011) and microfiltration (Mirsaeedghazi, Emam-Djomeh, Mousavi, Aroujalian, & Navidbakhsh, 2010)] on tannin and anthocyanin contents of pome- granate juice have been extensively investigated in various studies. However, an efficient clarification agent or a method removing tannins, but at the same time preventing anthocyanin loss from pomegranate juice, has not still been found. New clarification methods and different clarification agents should be investigated to solve the clarification problems in pome- granate juice. Although the removal effects of chitosan (Fang, Zhang, Du, & Sun, 2007; Imeri & Knorr, 1988), casein (Cosme, Ricardo-da-Silva, & Laureano, 2008) and xanthan gum (Fang et al., 2007) on haze precursors in various fruit juices (apple and bayberry juice) and white wine were determined in previous stud- ies, the effects of these clarification agents on the turbidity of pomegranate juice have not been investigated. In literature, there are conflicting statements about clarification mechanism of chitosan. While Bassi, Prasher, and Simpson (2000) http://dx.doi.org/10.1016/j.foodchem.2015.03.064 0308-8146/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +90 (312) 203 3300/3621; fax: +90 (312) 317 8711. E-mail address: mozkan@ankara.edu.tr (M. Özkan). Food Chemistry 184 (2015) 37–45 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem