Journal of Food and Nutrition Research Vol. 50, 2011, No. 2, pp. 73–85 REVIEW Arbutus unedo L. and its benefits on human health IVO OLIVEIRA – PAULA BAPTISTA – ALBINO BENTO – JOSÉ ALBERTO PEREIRA Summary Arbutus unedo has been long used in folk medicine, throughout Mediterranean countries, with the employment of infusions and decoctions of almost all parts of this plant: leaves, fruits, barks and roots. The application of these tra- ditional remedies arises from several health-promoting characteristics, for treatment of gastrointestinal and urological problems, hypertension and cardiac diseases, diabetes and as anti-inflammatory agent, among other interesting proper- ties. Antioxidant ability of A. unedo shrub is also known, and antimicrobial activity has also been reported. Several compounds present in different parts of the plant may be linked to these properties. Included in those are carotenoids, flavonoids, phenolic acids and vitamins (C and E). Other bioactive compounds may be also found in different parts of A. unedo, like terpenoids and organic acids. This review will focus on the known composition of several parts of A. unedo, their antioxidant ability and traditional use, and the available data sustaining the rationality of the use as part of folk medicine. Keywords Arbutus unedo; chemical composition; biological properties; folk medicine In the recent years there has been an increased phase of the fruits usually comprises two periods. interest in natural products, leading to an exten- The first starts in the middle of October and ends sive search for bioactive compounds, namely plant in the beginning of December, while the second antioxidants, and their significance in medicine, happens around New Year’s Eve [4]. The leaves food industry and human nutrition [1]. are alternate, simple, with oblanceolate form and Arbutus unedo L., the strawberry-tree, belongs a dark green colour, leathery, short-stalked and to the family of Ericaceae and is an ever-green toothed [5]. There are several qualities associated shrub (Fig. 1A), native in the Mediterranean re- with this plant, such as ornamental, ecological and gion. In Europe, it grows mostly in the Mediter- economical value, as well as therapeutic and me- ranean basin (Portugal, Spain, France, Italy, Al- dicinal properties. It is a popular ornamental tree, bania, Greece, Bosnia and Herzegovina, Croatia, producing red fruits and pinkish-white flowers, Macedonia, Montenegro, Serbia and Slovenia) which appear during winter months and increase including some Mediterranean islands (Balear- the value for planting and ornamental purposes ic, Corsica, Sardinia, Sicily and Crete), mainly in [5]. This plant also has an important role from the coastal and inland areas where climate is adequate ecological point of view. It helps to maintain the to its development [2]. It has also been able to diversity of the fauna, avoids erosion of the soils, adapt to conditions of the south-western coast of it regenerates rapidly after fires, grows in poor Ireland [2] (Fig. 2). Although occasionally reach- soils [6] and it may be used for phytoremediation, ing a height of 12 m, it is normally between 1.5 m namely against arsenic contamination [7]. The to 3 m tall [3]. The fruits are conspicuous, globu- fruits, even though edible, are usually consumed lar, orange-red when ripe, growing up to 2 cm in as jams, marmalades or distilled into liquors [4]. diameter (Fig. 1B, 1C). The flower is a clump of Strawberry-tree honey is popular for its strong little cream-coloured lanterns. The maturation and distinctly bitter taste and has also been subject Ivo Oliveira, Paula Baptista, Albino Bento, José Alberto Pereira, Mountain Research Centre (CIMO), School of Agriculture, Polytechnic Institute of Bragança, Campus Sta Apolónia, Apartado 1 171, 5301-854 Bragança, Portugal. Correspondence author: José Alberto Pereira, tel.: +351-273-303277, fax: +351-273-325405, e-mail: [email protected] © 2011 VÚP Food Research Institute, Bratislava 73 Oliveira, I. et al. J. Food Nutr. Res., 50, 2011, pp. 73–85 A B C Fig. 1. Arbutus unedo. A – tree, B – unripe fruits, C – ripe fruits. Fig. 2. Approximate distribution of Arbutus unedo L. Tab.1. Traditional medicinal uses of different parts of A. unedo plant. Part used Medicinal use Reference Gastrointestinal disorders, urological problems, dermatologic problems, cardio- Leaves vascular application, kidney diseases, hypertension, cardiac diseases, diabetes, 12, 14, 15, 16, 49 antihae morrhoidal, diuretic, anti-inflammatory, anti-diarrheal Gastrointestinal disorders, urological problems, dermatologic problems, kidney Fruits 12, 14, 15 diseases, cardio-vascular application Gastrointestinal disorders, urological problems, dermatologic problems, cardio- Bark 16 vascular application Gastrointestinal disorders, urological problems, dermatologic problems, cardio-vascu- Roots lar application, hypertension, cardiac diseases, diabetes, diuretic, anti-inflammatory, 17, 18, 19, 49 anti-diarrheal 74 Arbutus unedo L. and its benefits on human health to some studies [8, 9]. Organic acid composition, a method to prepare the “drug”. Besides all this its total contents of phenolic compounds, as well facts, this tree still keeps on being underexploited, as its physicochemical and melissopalynological mainly due to the high heterogeneity of the plants. properties are known [8]. The production of jams, All these described medicinal and therapeutical liquors and honey based on A. unedo represent characteristics are linked to the contents of several an economic importance of this shrub in rural biologically active compounds in different parts of areas [10]. There are several reports on the use of A. unedo. This review will focus on the composi- different parts of this plant in traditional medicine tion of different parts of the A. unedo shrub, as (Tab. 1). The plant contains a wide variety of anti- well as on the known biological activity and health- oxidant compounds (Fig. 3). Fruits are used in folk promoting effects of extracts of this plant. medicine as antiseptic, diuretic and laxative agents [11–15]. Leaves of this shrub are used as an infu- sion for their astringent, diuretic, urinary anti- LEAVES septic, anti diarrheal and depurative agents. More recently they are used in the therapy of hyperten- Chemical composition sion, diabetes, and in the treatment of inflamma- In the leaves of A. unedo, different phytoche- tory diseases [11, 16–18]. Other parts of this plant, mical compounds are present, such as terpenoids, such as roots and bark, are also used in traditional -tocopherol, essential oils and phenolic com- medicine, in the treatment of gastrointestinal dis- pounds. The most important phenolics are pre- orders, as well as at urological and dermatologic sented in Fig. 4. The known terpenoids found in problems [15, 19] using decoction of the roots as the leaves are -amyrin acetate, betulinic acid and Fig. 3. Antioxidant compounds present in the Arbutus unedo tree. 75 Oliveira, I. et al. J. Food Nutr. Res., 50, 2011, pp. 73–85 OH OH O HO OH HO O O OH O HO HO OH HO O OH OH OH Arbutin Catechin Ethyl gallate Fig. 4. Chemical structures of the most abundant phenolic compounds in A. unedo leaves. lupeol [20]. The -tocopherol amount present An initial study was performed by PABUÇCUOĞLU varies, depending on the time of collection of the et al. [28], and a more comprehensive study was samples. The highest amount is found when the performed by OLIVEIRA et al. [27]. In the former leaves are collected in March, reaching the con- study, the authors studied the antioxidant activity tent of 132.8 mg of -tocopherol per kilogram of of ethanolic and methanolic extracts of the leaves, dry weight. Although this appears to be a very low using 2.2’-azino-bis(3-ethylbenzthiazoline-6-sul- amount, it is very similar to the quantity present phonic acid) (ABTS•+), and related the activity to in the major industrial source of -tocopherol, the flavonol glycosides and tannins present in the the soya bean [21]. The composition of the essen- leaves [28]. In the latter study, OLIVEIRA et al. [27] tial oil of A. unedo has already been determined studied the antioxidant activity using three differ- by KIVCAK et al. [22], with major components ent methods (reducing power assay, scavenging identified as (E)-2-decenal, -terpineol, hexade- effect on 2.2-diphenyl-1-picrylhydrazyl (DPPH) canoic acid and (E)-2-undecenal. The phenolic radicals and scavenging effect on superoxide radi- fraction of the leaves includes a large variety of cals), and also quantified the total phenolics of the compounds: tannins, flavonoids (catechin gal- leaves [27]. Ethanolic extracts were found to be of late, myricetin, rutin, afzelin, juglanin, avicularin), the highest reducing power (extract concentration phenolic glycosides (quercitrin, isoquercitrin, providing 0.5 of absorbance EC50 of 232.7 μg·ml-1) hyperoside) and iridoid glucosides [5, 23–25]. and the highest DPPH scavenging effect (EC50 of Polyphenols have been identified and quantified 63.2 μg·ml-1). In the scavenging assay on super- by FIORENTINO et al. [26]. This work allowed the oxide radical, methanolic extracts produced the identification of twelve compounds (arbutin, ethyl best results (EC50 of 6.9 μg·ml-1). The amount of gallate, p-hydroxybenzoyl arbutin, galloyl arbu- total phenols was as much as (192.66 ± 1.66) mg tin, gallocatechin, catechin, kaempferol 3-O-- GAE per gram of extract, when the leaves were L-ramnopyranoside, quercetin 3-O--L-ramno- extracted with ethanol [27]. The results demon- pyranoside, myricetin 3-O--L-ramnopyranoside, strated that the leaves of A. unedo possess a high kaempferol 3-O--D-arabinofuranoside, quercetin scavenging effect against DPPH radical and 3-O--D-arabinofuranoside and myricetin 3-O-- a high reducing power, as well as a potent effect D-arabinofuranoside). The major polyphenolic in scavenging superoxide radical, one of the most compound was found to be arbutin (627 mg·kg-1 important free radical, the precursor of several of fresh leaves), followed by catechin (546 mg·kg-1 molecules associated with tissue damage through of fresh leaves) and ethyl gallate (440 mg·kg-1 of oxidation [29].