Chemical profile and antioxidant capacities of tart cherry products
Introduction
Current animal research suggests that tart cherry consumption may confer multiple health benefits (Seymour et al., 2008). However, there is conflicting information about the phytochemistry of anthocyanins and other flavonoids in different cultivars of tart cherry (Prunus cerasus L) and in industrially-processed tart cherry products, such as dry fruits, powders from individually quick frozen (IQF) cherry, frozen cherries, juices, and juice concentrates (Blando et al., 2004, Bonerz et al., 2007, Chandra et al., 2001, Seeram et al., 2001). As such, it is unknown if these products have similar phytochemical profiles. This information is critical in order to facilitate and validate further studies on the health effects of consumption of tart cherry products.
Recently, tart cherry has had increasing impact upon the edible fruits market, due to the suspected health benefits associated with regular intake of anthocyanins and related polyphenolics (Beattie et al., 2005, Kim et al., 2005, Piccolella et al., 2008). The major anthocyanins in tart cherries are derivatives of cyanidin, while in other berries, such as strawberries, pelargonidin glycosides predominate. It is noteworthy, however, that anthocyanins may not be stable during processing or storage. As a result, some anthocyanin derivatives may be rapidly formed which may impact bioavailability and bioactivity.
The finding that tart cherries contain significant levels of anthocyanins may also suggest significant antioxidant activity. One of the best known properties of anthocyanins, in general, is their strong antioxidant activity in metabolic reactions, due to their ability to scavenge oxygen free radicals and other reactive species (ROX). This feature makes anthocyanins a potential tool for use in studies on oxidative stress and its related pathologies. For example, it has been reported in animal studies that tart cherry-enriched diets reduce oxidative stress and inflammation (Seymour et al., 2008). Importantly, these effects were achieved using physiologically relevant amounts of the whole fruit (Seymour et al., 2008).
The antioxidant, melatonin (N-acetyl-5-methoxytryptamine), has been identified in fresh-frozen fruits of ‘Balaton’ and ‘Montmorency’ tart cherries, suggesting that sufficiently high levels of melatonin could alter blood levels of this indole and provide protection against oxidative damage (Burkhardt, Tan, Manchester, Hardeland, & Reiter, 2001).
The biological effectiveness of tart cherries may be due to phytochemical interactions which accomplish complementary effects. Thus, it is not surprising that whole cherry fruit products or mixtures of tart cherry secondary metabolites could be biologically more active than individual components. Such a synergistic effect refers to cases when combinations of bioactive substances exert effects at target sites that are greater than the sum of individual components (Cseke et al., 2006, Lila and Raskin, 2005).
In the present study, we aim to identify and quantify the anthocyanins and other flavonoid phytochemicals, as well as melatonin, in various tart cherry products from two cherry cultivars, namely ‘Montmorency’ and ‘Balaton’. Secondly, we aim to determine their respective antioxidant capacities using the common trolox equivalent antioxidant capacity (TEAC) assay.
Section snippets
Chemicals
Solvents employed for extraction and HPLC analysis were obtained from Fisher Scientific Co., Pittsburgh, PA. Folin-Ciocalteu phenol reagent, quercetin, kaempferol, melatonin, gallic acid, and propyl gallate were purchased from Sigma Chemical Co., St. Louis, MO. Anthocyanins (cyanidin, cyanidin-3-glucoside, cyanidin-3-rutinoside, cyanidin 3-glucosylrutinoside, cyanidin 3-sophoroside, peonidin-3-glucoside, peonidin, and pelargonidin) and other flavonoids (isorhamnetin and
Analysis of the levels of total anthocyanins and total phenolics in various tart cherry products
Our results show that all tart cherry products analysed have substantial amounts of total anthocyanins and total phenolics. Generally, tart cherry products contain higher levels of total phenolics than total anthocyanins (Table 1). More total anthocyanins are present in tart cherry products obtained from ‘Balaton’ cultivar than from ‘Montmorency’ cultivar. However, ‘Montmorency’ tart cherry products show higher levels of total phenolics. Our results reveal that frozen tart cherries derived from
Discussion
In the present study, we compared the antioxidant activities of commercially available tart cherry fruit products as well as the antioxidant activities of individual standard constituents in these products. Some compounds, particularly cyanidin derivatives, kaempferol, quercetin, and melatonin, showed higher antioxidant activities than the other compounds analysed (Fig. 2). Each of these compounds could contribute to the antioxidant effects attributed to tart cherry fruit crude extracts.
Acknowledgements
This study was supported by an unrestricted grant provided by The Cherry Marketing Institute (Lansing, MI USA).
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