Antioxidant properties of anthocyanins extracted from litchi (Litchi chinenesis Sonn.) fruit pericarp tissues in relation to their role in the pericarp browning

Abstract :

Anthocyanins were extracted and purified from litchi fruit pericarp and their antioxidant properties were investigated. Effects of exogenous anthocyanin treatments on pericarp browning and membrane permeability of harvested litchi fruit were also evaluated. Anthocyanins from litchi fruit pericarp strongly inhibited linoleic acid oxidation and exhibited a dose-dependent free-radical-scavenging activity against DPPH radical, superoxide anions and hydroxyl radical. The degradation of deoxyribose by hydroxyl radicals was shown to be inhibited by anthocyanins acting mainly as chelators of iron ions rather than directly scavenging hydroxyl radicals. Anthocyanins were also found to have excellent reducing power. The reducing power of anthocyanins, ascorbic acid and butylated hydroxytoluene all at 100 mu g/ml were 3.70, 0.427 and 0.148, respectively, indicating that anthocyanins from litchi pericarp had a strong electron-donating capacity. Furthermore, application of anthocyanins to harvested litchi fruit significantly prevented pericarp browning and delayed the increase in membrane permeability. It was therefore suggested that anthocyanins could be beneficial in scavenging free radicals and reducing lipid peroxidation of litchi fruit pericarp. (c) 2006 Elsevier Ltd. All rights reserved.

1. Introduction

Oxidation is essential to many living organisms for the production of energy necessary for biological processes. Oxygen-centred free radicals, also known as reactive oxygen species (ROS), including superoxide, hydrogen peroxide, hydroxyl (HOradical dot), peroxyl (ROOradical dot) and alkoxyl (ROradical dot), are produced in vivo during oxidation (Bloknina, Virolainen, & Fagerstedt, 2003). ROS are not only strongly associated with lipid peroxidation, leading to food deterioration, but are also involved in development of a variety of diseases, including cellular aging, mutagenesis, carcinogenesis, coronary heart disease, diabetes, and neurodegeneration ( [Halliwell and Gutteridge, 1999] and [Moskovitz et al., 2002]). Although almost all organisms possess antioxidant defence and repair systems to protect against oxidative damage, these systems are insufficient to prevent the damage entirely (Simic, 1988).

Fruits and vegetables contain different antioxidant compounds, such as ascorbic acid, tocopherol, glutathione and carotenoids, which may contribute to protection against oxidative damage (Bloknina et al., 2003). Recent research results have shown that anthocyanins from edible fruits were effective antioxidants in vitro (Einbond, Reynertson, Luo, Basile, & Kennelly, 2004). Antioxidative properties of anthocyanins arise from their high reactivity as hydrogen or electron donors, and from the ability of the polyphenol-derived radicals to stabilize and delocalize the unpaired electron, and from their ability to chelate transition metal ions (termination of the Fenton reaction) (Rice-Evans, Miller, & Paganga, 1997). Thus, anthocyanins may play a role in the antioxidant ability related to fruit browning.

Litchi (Litchi chinensis Sonn.) is a tropical fruit originating from China, with a bright red attractive pericarp surrounding a white aril (Nakasone & Paull, 1998). Litchi pericarp contains a large amount of anthocyanins, which are responsible for the red colour. In our preliminary study, the anthocyanin content of pericarp tissues of harvested litchi fruit was 0.20 mg/g fresh weight (Duan & Jiang, unpublished data). Cyanidin-3-glucoside ( [Lee and Wicker, 1991] and [Zhang et al., 2000]), cyanidin-3-rutinoside ( [Lee and Wicker, 1991] and [Sarni-Manchado et al., 2000]), malvidin-3-glucoside (Lee & Wicker, 1991) and quercetin-3-rutinoside (Sarni-Manchado et al., 2000) were identified as the major monomeric anthocyanins pigments, while cyanidin-3-rutinoside was the most important pigment of litchi (var. Huaizhi) pericarp tissues (Zhang, Pang, Yang, Ji, & Jiang, 2004). However, little information on the antioxidant capability of the anthocyanins from litchi fruit peel is available.

The objective of the current research was to evaluate the antioxidant properties of anthocyanins from litchi fruit pericarp and then investigate the effects of exogenous anthocyanin treatments on the pericarp browning of harvested litchi fruit.

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