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J. Agric. Food Chem. 2008, 56, 8874–8878
Synephrine Content of Juice from Satsuma Mandarins (Citrus unshiu Marcovitch) KLAUS DRAGULL, ANDREW P. BREKSA III,*
AND
BRIAN CAIN
Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, California 94710
Synephrine, the main protoalkaloid in Citrus species, is commonly analyzed as the active component in citrus peel-containing herbal supplements, but the edible parts of mandarins have been largely ignored. The synephrine concentration has been determined in the juices of Citrus unshiu mandarins harvested from 10 different groves located in a major growing region in California. For comparison, the physicochemical properties of the juices, including pH, conductivity, soluble solids content, and titratable acidity, were also measured. The synephrine values among 10 groves ranged from 73.3 to 158.1 mg L-1. Repeat sampling of fruit from the 10 locations showed that the intragrove variability in synephrine concentrations ranged from 1.0 to 27.7% CV and was grove dependent. Among the physicochemical properties, titratable acidity weakly correlated with synephrine, and for one sample a low maturity index was linked to high synephrine content. The overall mean synephrine concentration of 92.8 mg L-1 is up to 6-fold higher than values previously determined for orange juices and suggests that mandarin juice could constitute a significant dietary source of synephrine. Furthermore, the results suggest that grove location and maturity affect synephrine content. KEYWORDS: Citrus; juice; synephrine; Citrus unshiu; Citrus reticulata; mandarin; tangerine; Satsuma; variability
INTRODUCTION
Synephrine (Figure 1) is a phenolic amine that was initially isolated as synthetic product and used pharmacologically as a vascoconstrictor and bronchiectatic agent (1). The presence of synephrine in citrus leaves was first reported in 1964 by Stewart et al. (2), who in the course of evaluating the micronutrient contents of several hundred varieties determined that the greatest synephrine concentrations were found in mandarin and orange leaves. No synephrine was detected in the leaves from grapefruit, pummelo, or shaddock trees; neither was it detected in roots of any of the citrus varieties tested or in leaf samples taken from trees suffering from Mn deficiencies (2). Results obtained in a follow-up study examining the juice concentrations of synephrine corresponded well with those observed for leaves, but were at concentrations 10-20 times less than those found in leaves (3, 4). A subsequent analysis of the phenolic amine content of Citrus and another 187 plant species demonstrated that Citrus possessed the greatest concentrations of synephrine and that the highest concentrations in citrus were at least 10fold higher than those in the other plants evaluated (5). Citrus spp. are the only known plants having synephrine in the edible portions. It was not until recently, when sour orange (Citrus aurantium L.) derived botanicals and extracts were introduced to consumers as alternatives to the FDA-banned ephedrine-containing prod* Corresponding author [telephone (510) 559-5898; fax (510) 5595849; e-mail
[email protected].
10.1021/jf801225n
ucts, that the presence of synephrine in citrus fruits and products became of interest (6-13). With the resurgence in the interest in synephrine, multiple analytical methods for the quantitation of synephrine have been reported, and a review of these methods was recently completed by Pellati et al. (14). A direct comparison of the synephrine concentrations reported among all these papers is difficult due to the ambiguous sample descriptions found in some and differences in sample preparation. However, as a whole, they support the original observations made by Stewart et al. (2) and have additionally contributed by identifying sour orange as a citrus with synephrine concentrations comparable to those found in mandarins (Citrus reticulata Blanco, Citrus unshiu Marcovitch). As indicated above, the literature contains a number of papers detailing the development and demonstration of analytical methods for determining synephrine concentrations. The emphasis on method development has resulted in a wide breadth of Citrus samples analyzed and within those samples the identification of those cultivars with the highest synephrine concentrations. However, the variability in synephrine concentrations within the cultivars tested is still largely unknown because in most cases only single representative samples were used. The main objective of this study was to close this gap. An understanding of the variability in concentration, and eventually the effects of environment and agricultural practices, will be essential if citrus growers and processors are to capitalize on the economic potential of
This article not subject to U.S. Copyright. Published 2008 by the American Chemical Society Published on Web 09/05/2008
Synephrine in Mandarin Juices
J. Agric. Food Chem., Vol. 56, No. 19, 2008
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Table 1. Summary of Physicochemical Properties and Synephrine Concentrations (n) 30) soluble solids total titratable maturity conductivity, content (SSC), acidity (TTA), index synephine, pH mS °Brix % (w/v) (SSC/TTA) mg L-1
Figure 1. Chemical structure of synephrine.
delivering dietary levels of synephrine through their fresh fruits and products. Tangerine or mandarin oranges are ideally suited to be utilized in this way because they already possess many properties important to consumers (e.g., easy peeling, seedless, etc.) and have some of the highest reported synephrine concentrations (i.e., Cleopatra, 280 mg L-1) (3). For this study, we chose to characterize the synephrine concentrations found in peeled fruit from commercial groves located in Placer County (California) of the Owari selection of Satsuma mandarin (C. unshiu Marcovitch). Placer County is a major mandarin-producing region in the state. To gain better insight into the variations in synephrine concentration found within and across the groves, mandarins were obtained from 10 different groves. Physicochemical properties of the harvested fruits were measured in addition to the synephrine concentrations to facilitate comparison of the samples. MATERIALS AND METHODS Materials and Chemicals. ACN (HPLC grade), ammonium acetate (enzyme grade), and water (HPLC grade) were purchased from Fisher Scientific (Fair Lawn, NJ). Alternatively, water was deionized to g18.1 MΩ/cm resistance using a Barnstead NANOpure Deionization System (Dubuque, IA) and filtered through a 0.45 µm type HA membrane filter (Millipore, Billerica, MA) prior to use. The (()-synephrine standard was purchased from ChromaDex (Santa Ana, CA). Plant Materials. Fruits [Owari selection of Satsuma mandarin (C. unshiu Marcovitch)] were harvested from each of 10 different groves located in Placer County, CA. Harvesters were instructed to pick mature fruits of random sizes from throughout the entire grove. Fruits were harvested in mid-November 2007 and stored for
