Quantitative analysis of antiradical phenolic constituents from fourteen edible Myrtaceae fruits

Kurt A. Reynertson,^a,^§ Hui Yang,^a Bei Jiang,^a Margaret J. Basile,^b and Edward J. Kennelly^a,^*

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Abstract

Many species of Myrtaceae are cultivated in home gardens throughout the tropics for their edible fruit, and have been used in traditional medicine to treat several inflammatory conditions. Fruit phenolics are important dietary antioxidant and anti-inflammatory constituents. We have investigated the antiradical activity, total phenolic content (TPC), and total anthocyanin content (TAC) of 14 underutilized Myrtaceae fruits, namely Eugenia aggregata, E. brasiliensis, E. luschnathiana, E. reinwardtiana, Myrciaria cauliflora, M. dubia, M. vexator, Syzygium cumini, S. curranii, S. jambos, S. javanicum, S. malaccense, S. samarangense, and S. samarangense var. Taiwan pink. An HPLC-PDA method was developed to quantify the amounts of cyanidin 3-glucoside (1), delphinidin 3-glucoside (2), ellagic acid (3), kaempferol (4), myricetin (5), quercetin (6), quercitrin (7), and rutin (8) present in MeOH extracts of the fruit. TPC ranged from 3.57 to 101 mg/g, TAC ranged from undetectable to 12.1 mg/g, and antiradical activity, measured as DPPH˙ IC₅₀, ranged from very active (19.4 μg/ml) to inactive (389 μg/ml).

Keywords: HPLC-PDA, quantitative analysis, Myrtaceae, Myrciaria, Eugenia, Syzygium, antioxidant, flavonoid, anthocyanin, Folin-Ciocalteu, DPPH, polyphenolic

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1. Introduction

According to the Centers of Disease Control and Prevention, over half of all deaths in the United States are caused by diseases of the heart and malignant neoplasms (Minino, Heron & Smith, 2006). Epidemiological evidence suggests that diets high in fruits and vegetables are linked to a reduced incidence of heart disease, cancer, and some neurodegenerative disorders (; ; ; ). Reactive oxygen species (ROS) are produced naturally in mammalian systems as a result of oxidative metabolism. However, ROS damage cell membranes and DNA, causing cancerous mutations, and the oxidation of low-density lipoprotein is a major factor in the promotion of heart disease. ROS are also implicated in activating redox-responsive pro-inflammatory transcription factors, nuclear factor (NF)-κB and activator protein (AP)-1 (). Inflammation is a major factor in the promotion of chronic inflammatory diseases, as well as the etiology of cancers and heart disease (Middleton, Kandaswami & Theoharides, 2000; Hu et al., 2002). Oxidative damage is balanced by endogenous antioxidants, but additional protection, provided by nutritive and non-nutritive elements from food, is critical for disease chemoprevention.

Colourful fruits are a potentially rich source of many dietary phenolic antioxidants and are believed to play an important role in the prevention of many oxidative and inflammatory diseases (Arts et al., 2005). The anthocyanin pigments are responsible for many of the bright fruit and flower colours, and act as strong antioxidants and anti-inflammatories, with antimutagenic and cancer chemopreventative activities (; ). Anthocyanins often account for much of the phenolic content of these fruits, but flavanols, procyanidins, phenolic acids, and ellagitannins may be the most predominant phenolics in some taxa. Polyphenolic compounds inhibit several oxidative and inflammatory enzymes (Middleton et al., 2000), and have shown antiallergenic, antiviral, antibacterial, antifungal, antitumor, and antihemorrhagic activities (). Flavonoids also inhibit the inflammatory transcription factors NF-κB and AP-1 (Rahman et al., 2006).

The plant family Myrtaceae is pan-tropical in occurrence, with concentrations in South America, Southeast Asia, and Australia. The fleshy-fruited subfamily, Myrtoideae, includes many economically important food plants, agricultural crops, and ornamentals, including the Mediterranean genus Myrtus (myrtle), spices such as clove (Syzygium aromaticum), allspice (Pimenta dioica), and bay rum (Pimenta racemosa), and the fruits of Psidium (guavas), Myrciaria, Eugenia, Syzygium, Plinia and Luma.

In this report, we have analyzed the phenolic content and antiradical activity of 14 edible fruits from 13 species of Myrciaria, Eugenia and Syzygium, namely Eugenia aggregata Kiaersk., E. brasiliensis Lam., E. luschnathiana Klotzsch ex O.Berg, E. reinwardtiana (Bloom) DC, Myrciaria cauliflora (Mart.) O.Berg, M. dubia (Kunth) McVaugh, M. vexator McVaugh, Syzygium cumini (L) Skeels, S. curranii (C.B.Rob.) Merr., S. jambos (L) Alston, S. javanicum Miq., S. malaccense (L)Merr. & L.M.Perry, S. samarangense (Bloom) Merr. & L.M.Perry and S. samarangense var. Taiwan pink.

These fruits are mostly red to purple drupes, 2-4 cm in diameter, although some species produce larger or less pigmented fruit. In the tropics, these species are often cultivated in home gardens, small-scale agricultural plots, or wild-harvested. They are primarily eaten fresh or used to make jams, desserts, wines, liquors, and vinegars, and can be found in local markets. In addition to their use as food, many of these fruits have been used in divergent traditional medical practices for a variety of illnesses and conditions. Most notably, the seeds of the jamun (S. cumini) are an important Ayurvedic medicine for diabetes. The rose apple (S. jambos) has been used in India as a tonic for the brain and for liver problems, as an astringent, and digestive (Kirtikar & Basu, 1988), and distilled to make rosewater (Morton, 1987). In Brazil, E. brasiliensis leaves have been used for gastrointestinal disorders and rheumatism, and the jaboticaba fruit (M. cauliflora) has been used as a treatment for hemoptysis, asthma, diarrhea, and chronic inflammation of the tonsils (Morton, 1987). Leaves of S. malaccense have been used for a wide variety of inflammatory conditions in Western Samoa ().

The majority of the phytochemical literature for these species has focussed on the aromatic terpenoid compounds found in the leaves (Wong & Lai, 1996), but phenolics have also been identified in some species. We previously reported flavonols, phenolic acids, anthocyanins, and depsides from M. cauliflora (), as well as the occurrence of catechin and epicatechin in E. aggregata (Reynertson, Basile & Kennelly, 2005). Myrciaria dubia was reported to contain cyanidin 3-glucoside and delphinidin 3-glucoside (). Several flavonoids, ellagitannins, and phenolic acids have been identified from the fruits, seeds, and aerial parts of S. cumini (Bhatia, Bajaj & Ghangas, 1971; ; ), and flavonoids and ellagitannins have been found in the fruits of S. samarangense (Okuda, Yoshida, Hatano, Yazaki & Ashida, 1982; Nonaka, Aiko, Aritake & Nishioka, 1992; Srivastava, Shaw & Kulshreshtha, 1995; Nair, Krishnan, Ravikrishna & Madhusudanan, 1999). Ellagic acids and an anthocyanin were reported from S. malaccense (). To the best of our knowledge, however, the phenolic constituents of Eugenia brasiliensis, E. luschnathiana, E. reinwardtiana, Myrciaria vexator, Syzygium curranii, S. javanicum, and S. samarangense var. Taiwan pink have not been reported in the literature, despite their widespread consumption in the tropics.

Here we report on the HPLC-PDA quantification of eight phenolic compounds in 14 fruits. Cyanidin 3-glucoside (1), delphinidin 3-glucoside (2), ellagic acid (3), kaempferol (4), myricetin (5), quercetin (6), quercitrin (7), and rutin (8) .

With cancers and heart disease being the leading causes of death in the United States, studies indicate that diets high in naturally occurring antioxidants and anti-inflammatories are important as a first-line strategy of chemoprevention (Youdim et al., 2001; Hu et al., 2002; Arts et al., 2005; ). We have shown that edible fruits in the Myrtaceae are a rich source of biologically active phenolic compounds, which is similar to other well-studied berries and fruits ().

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Wednesday 12 December 2012