Enzyme release of phenolics from muscadine grape (Vitis rotundifolia Michx.) skins and seeds Changmou Xu a , Yavuz Yagiz a , Wlodzimierz Borejsza-Wysocki a , Jiang Lu b , Liwei Gu a , Milena M. Ramírez-Rodrigues a , Maurice R. Marshall a,⇑ a Department of Food Science and Human Nutrition, University of Florida, Gainesville, FL 32611, United States b Center for Viticulture and Small Fruit Research, Florida Agricultural & Mechanical University, Tallahassee, FL 32317, United States article info Article history: Received 4 October 2013 Received in revised form 24 January 2014 Accepted 30 January 2014 Available online 13 February 2014 Keywords: Muscadine grape Enzyme Hydrolysis Phenolics DPPH abstract Enzyme degradation of plant cell wall polysaccharides can potentially enhance the release of bioactive phenolics. The aim of this study was to evaluate various combinations of solvent and enzyme, enzyme type (cellulase, pectinase, ß-glucosidase), and hydrolysis time (1, 4, 8, 24 h) on the release of muscadine grape skin and seed phenolics, and their antioxidant activities. Results showed that pre-treated musca- dine skins and seeds with enzymes decreased total phenolic yield compared with solvent (50% ethanol) alone. Enzyme release of phenolics from skins of different muscadine varieties was significantly different while release from seeds was similar. Enzyme hydrolysis was found to shorten extraction time. Most importantly, enzyme hydrolysis modified the galloylated form of polyphenols to low molecular weight phenolics, releasing phenolic acids (especially gallic acid), and enhancing antioxidant activity. Ó 2014 Published by Elsevier Ltd. 1. Introduction Muscadine grape (Vitis rotundifolia Michx.) is an important grapevine species native to southeastern United States and Mexico, and has been extensively cultivated since the 16th century. Musca- dine grapes are rich sources of bioactive phenolics and other nutri- ents studied for their potential health benefits. The compounds identified in muscadine seeds included hydroxybenzoic acid, hydrolyzable tannins, flavan-3-ols and condensed tannins, ellagic acid derivatives, and quercetin rhamnoside; the skin contained hydroxybenzoic acid, hydrolyzable tannins, flavonoids, including anthocyanin 3,5-diglucosides, ellagic acid derivatives, quercetin, myricetin, and kaempferol glycosides (Sandhu & Gu, 2010). Cell culture studies have suggested that phenolics from muscadine grapes have strong anticancer activities, such as inhibiting prolifer- ation of colon and prostate cancer cells by inducing apoptosis (Hudson et al., 2007; Mertens-Talcott, Lee, Percival, & Talcott, 2006). Therefore, muscadine grape pomace is a potential source of bioactive phenolics, which could be used in the food and phar- maceutical industries. In grape, phenolics in general can be classified as (1) cell-wall phenolics, which are bound to polysaccharides by hydrophobic interactions, hydrogen bonds and covalent bonds, and (2) non-cell-wall phenolics, encompassing phenolics confined in the vacuoles of plant cells and phenolics associated with the cell nucleus (Liyama, Lam, & Stone, 1994; Pinelo, Arnous, & Meyer, 2006). The cell wall of grape fruit is a complex network composed of about 30% neutral polysaccharides (cellulose, xyloglucan, arab- inan, galactan, xylan and mannan), 20% acidic pectin substances (of which 62% are methyl esterified), 15% insoluble proanthocy- anidins, and <5% structural proteins (Lecas & Brillouet, 1994). Degradation of cell wall polysaccharides, which eliminates this physical barrier and opens up the cell, is a fundamental step in improving the release of phenolics from grape fruit. Research has focused on the application of cell wall hydrolyzing enzymes, such as cellulases, glucanase, and pectinases, to release phenolics from grape fruit and pomace. Kammerer, Claus, Schieber, and Carle (2005) reported that pectinases and cellulases could result in nota- bly higher recovery rates of phenolics from Vitis vinifera L. grape pomace. Pectinases and macerating enzymes also were reported to promote anthocyanin extraction and improve the quality of red wines (Haight & Gump, 1994). However, others have found that pectinases and macerating enzymes can cause a decrease in the total yield of anthocyanins and a loss of wine color, or the pectinases have no apparent benefit (Wightman & Wrolstad, 1996; Wrolstad, Wightman, & Durst, 1994). Cellulase treatment was reported not effective for phenolic release from grape http://dx.doi.org/10.1016/j.foodchem.2014.01.128 0308-8146/Ó 2014 Published by Elsevier Ltd. ⇑ Corresponding author. Tel.: +1 3523921978x405; fax: +1 352 392 1988. E-mail addresses: unclemarty_2001@ufl.edu, martym@ufl.edu (M.R. Marshall). Food Chemistry 157 (2014) 20–29 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem