Dietary tannins improve lamb meat colour stability G. Luciano a , F.J. Monahan c , V. Vasta b , L. Biondi b , M. Lanza b , A. Priolo b, * a Dottorato di Ricerca in Scienze delle Produzioni Animali, University of Catania, Via Valdisavoia 5, 95123 Catania, Italy b DACPA Sezione di Scienze delle Produzioni Animali, University of Catania, Via Valdisavoia 5, 95123 Catania, Italy c School of Agriculture, Food Science and Veterinary Medicine, Agriculture and Food Science Centre, University College Dublin, Dublin 4, Ireland article info Article history: Received 22 February 2008 Received in revised form 3 July 2008 Accepted 10 July 2008 Keywords: Lamb Lipid oxidation Colour stability Dietary tannins abstract Fourteen male Comisana lambs were divided into two groups at 45 days of age: lambs fed a concentrate diet (C), or lambs fed the same concentrate with the addition of quebracho (Schinopsis lorentzii) tannins (T). Sheep were slaughtered at 105 days of age. Lipid oxidation, colour coordinates, haem pigment con- centration, and metmyoglobin percentages were measured on minced semimembranosus muscle (SM) over 14 days of refrigerated storage in a high oxygen modified atmosphere. Tannin supplementation increased (P < 0.01) a * values and reduced (P < 0.01) b * values of the SM when compared to C. Lower hue angles (P < 0.001) and metmyoglobin formation (P = 0.07) were observed in lamb from T-fed com- pared to C-fed sheep during the 14-days storage period. Furthermore, feeding T resulted in greater (P < 0.001) haem pigment concentrations in the SM during refrigerated storage; however, diet had no (P = 0.28) effect on lipid oxidation. Therefore, including quebracho tannins in sheep diets can improve meat colour stability of fresh lamb during extended refrigerated storage. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction A number of meat palatability attributes are considered of importance by consumers. Among these, flavour and colour play a major role, being sensory properties by which meat quality is readily assessed (Liu, Lanari, & Schaefer, 1995). In red meats, it has been established that both colour and flavour are negatively af- fected by oxidative processes. Lipid oxidation products contribute to the development of off-flavours, especially during storage (Gray, Gomaa, & Buckley, 1996), while myoglobin oxidation leads to meat discoloration (Greene, 1969). Lipid oxidation and colour deteriora- tion are believed to be linked, with haem pigments serving as cat- alysts of lipid peroxidation (Baron & Andersen, 2002). On the other hand, high levels of vitamin E in bovine muscles were shown to de- lay meat discoloration (Faustman et al., 1989) and vitamin E addi- tion to in vitro model systems, containing oxymyoglobin and phospholipids, reduced both lipid oxidation and metmyoglobin formation (Yin, Faustman, Riesen, & Williams, 1993). These results suggest a role of lipid oxidation in promoting myoglobin oxidation and colour deterioration in meat. Tannins are a complex group of water-soluble polyphenolic compounds arising from the metabolism of plants. Tannins are classified into two main groups, hydrolysable tannins and con- densed tannins. The latter are oligomers and polymers of (epi)cat- echin or (epi)gallocatechin with widely varying degrees of polymerization (Manach & Donovan, 2004). Tannins are present in several feed resources used for ruminant feeding (Vasta, Nudda, Cannas, Lanza, & Priolo, 2007). Phenolic compounds are known to have antioxidant properties. Tang, Kerry, Sheehan, Buckley, and Morrissey (2001) demonstrated an effect of dietary tea catechins in controlling lipid oxidation in chicken meat. However, the antiox- idant activity of a dietary compound depends primarily on the pos- sibility of it being absorbed through the gastrointestinal tract. The degree of polymerization greatly affects the absorption of dietary flavonoids (Déprez, Mila, Huneau, Tome, & Scalbert, 2001). Although monomeric compounds can be absorbed, no studies have detected the presence of tannins with degrees of polymerization greater than dimers in plasma (Manach & Donovan, 2004; Manach, Williamson, Morand, Scalbert, & Rémésy, 2005; Scalbert, Morand, Manach, & Rémésy, 2002). Controversial results have been pro- vided by in vivo studies using 14 C-labelled tannins to follow their metabolism in the gastrointestinal tract of rats and ruminants (Abia & Fry, 2001; Perez-Maldonado & Norton, 1996; Terrill, Waghorn, Woolley, McNabb, & Barry, 1994). Ruminal microbial population can adapt to tannins, protecting the animals from their antinutritional effects (Smith, Zoetendal, & Mackie, 2005). However, Makkar, Becker, Abel, and Szegletti (1995) demonstrated that rumen microbes do not hydrolyse condensed tannins. Con- versely, in vivo and in vitro studies provided evidence for the active metabolism of condensed tannins by the intestinal microflora of both humans and rats (Abia & Fry, 2001; Déprez et al., 2000; Rios et al., 2003). These results suggest that tannins do not remain inert along the whole gastrointestinal tract; rather, tannins could 0309-1740/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2008.07.006 * Corresponding author. E-mail address: a.priolo@unict.it (A. Priolo). Meat Science 81 (2009) 120–125 Contents lists available at ScienceDirect Meat Science journal homepage: www.elsevier.com/locate/meatsci