Antioxidants are compounds that can delay or inhibit the oxidation of lipid or other molecules by inhibiting oxidizing chain reactions and they play an important role in health protection (Velioglu et al., 1998). In addition to being rich in folate, potassium, and fiber, fruit of the cultivated strawberry (F. ×ananassa) are a good source of a variety of natural antioxidants (Heinonen et al., 1998; Wang et al., 1996). Antioxidants in strawberry fruit include vitamin C and phenolic compounds such as phenolic acids and flavonoids, including flavonols and anthocyanins.
Important phenolic acids in strawberries are the ellagitannins and ellagic acid glucosides, which break down to pure ellagic acid, also present in the fruit (Cerdá et al., 2005). Ellagic acid is valuable to human health because it is antimutagenic and has anticarcinogenic activity against chemical-induced cancers (Okuda et al., 1989). Ellagitannins in strawberries are primarily located in the achenes (Maas et al., 1991). The ellagic acid, glucosides, and pure ellagic acid are present in the red fleshy receptacle. Ellagic acid in pure form is poorly absorbed through the bowel and is mostly biologically unavailable whereas the ellagitannins and ellagic acid glucosides are easily available for absorption in mammalian systems (Okuda et al., 1989). In general, the content of ellagic acid glucoside of strawberry cultivars is higher than that of ellagic acid (Cerdá et al., 2005; Daniel et al., 1989).
Beneficial effects of flavonoids have been described for diabetes mellitus, allergies, cancer, viral infections, headache, stomach and duodenal ulcers, paradentosis, and inflammatory diseases (Kuehnau, 1976). Flavonoids in strawberry include the flavonols quercetin and kaempferol (Wang and Zheng, 2001). These and other polyphenols play a protective role in carcinogenesis by reducing the bioavailability of carcinogens (Starvic et al., 1992). Clegg and Morton (1968) reported that, of the flavonols, quercetin had the greatest antioxidant activity, followed by dihydroquercetin > kaempferol > quercitrin > chlorogenic acid = p-coumaric acid.
The anthocyanins are a group of flavonoids with exceptionally good scavenging activities. Pelargonidin-based anthocyanins such as pelargonidin 3-glucoside, pelargonidin 3-rutinoside, and pelargonidin 3-glucoside–succinate are the predominant anthocyanins in cultivated strawberry fruit (Gil et al., 1997; Wang and Zheng, 2001). Strawberry fruit generally contain much lower levels of cyanidin-based anthocyanins, cyanidin 3-glucoside and cyanidin 3-glucoside–succinate, than pelargonidin-based anthocyanins (Gil et al., 1997; Wang and Zheng, 2001). These anthocyanin compounds have shown protection against harmful free radicals and have been associated with lower incidence and mortality rates of cancer and heart disease in addition to a number of other health benefits (Ames et al., 1993; Dragsted et al., 1993; Velioglu et al., 1998; Wang et al., 1996). Antioxidant efficacy in preventing oxidation of human low-density lipoprotein among anthocyanins is as follows: delphinidin > cyanidin > malvidin > pelargonidin (Satué-Gracia et al., 1997).
The levels of antioxidants and antioxidant capacity in strawberry extracts from whole fruits vary considerably among genotypes (Wang and Lin, 2000; Zheng and Wang, 2003). This may be true partly because the cultivated strawberry (F. ×ananassa) is a hybrid of two very different wild species (Darrow, 1966). Accessions of the progenitor species are valued by strawberry breeders as sources of novel traits, especially pest resistance and abiotic stress tolerance. Because strawberry is a relatively new crop, dating to the 1700s (Darrow, 1966), as few as three backcrosses can yield selections of cultivar quality (J.F. Hancock, pers. comm.). Therefore, if found to be of value in improving antioxidant capacity or the balance of specific phenolic compounds, accessions from these progenitor species could be readily incorporated into a strawberry breeding program.
No accession from either of the progenitor species has been evaluated for antioxidant capacity or levels of phenolic compounds. A core subset of the Fragaria L. collection maintained at the U.S. Department of Agriculture National Clonal Repository, Corvallis, OR, has been constructed to contain a group of native F. virginiana and F. chiloensis thought to be of value to strawberry improvement. This core subset is being characterized for many horticultural traits useful to breeders (Hancock et al., 2001a, b), including resistance to black root rot, common foliar diseases, and nematodes (Hancock et al., 2001b, 2002; Pinkerton and Finn, 2005), but not for antioxidant activity.
There is some antioxidant information on another wild strawberry species, F. vesca L. This species is generally considered to be a progenitor of the genome of F. virginiana and F. chiloensis, and therefore F. ×ananassa. Sondheimer and Karash (1956) showed that the major pigments of F. vesca are the anthocyanins pelargonidin 3-monoglucoside and cyanidin 3-monoglucoside, and that the ratio of pelargonidin 3-glucoside to cyanidin 3-glucoside for this species was much lower (1 pelargonidin 3-glucoside : 1 cyanidin 3-glucoside) than for cultivated strawberries (1 pelargonidin 3-glucoside : 0.05 cyanidin 3-glucoside).
The objectives of this study are 1) to evaluate the antioxidant contents and antioxidant activities in representatives of F. virginiana and F. chiloensis in comparison with representatives of the cultivated strawberry species (F. ×ananassa), 2) to determine which strawberry compounds are more closely correlated with antioxidant capacity among these three species, and 3) to identify wild strawberry genotypes with high antioxidant activity and bioactive compounds for use in cultivar development.
Black, B.L., Enns, J.M. & Hokanson, S.C. 2002 A comparison of temperate–climate strawberry production systems using eastern genotypes HortTechnology 12 670 675
Cerdá, B., Tomás-Barberán, F.A. & Espín, J.C. 2005 Metabolism of antioxidant and chemopreventive ellagitannins from strawberries, raspberries, walnuts, and oak-aged wine in humans: Identification of biomarkers and individual variability J. Agr. Food Chem. 53 227 235
Cheng, G.W. & Breen, P.J. 1991 Activity of phenylalanine ammonialyase (PAL) and concentrations of anthocyanins and phenolics in developing strawberry fruit J. Amer. Soc. Hort. Sci. 116 865 869
Clegg, K.M. & Morton, A.D. 1968 The phenolic compounds of blackcurrant juice and their protective effect on ascorbic acid. II. The stability of ascorbic acid in model systems containing some of the phenolic compounds associated with black currant juice J. Food Technol. 3 277 284
Daniel, E.M., Krupnick, A.S., Heur, Y.H., Blinzler, J.A., Nims, R.W. & Stoner, G.D. 1989 Extraction, stability, and quantification of ellagic acid in various fruits and nuts J. Food Chem. Composition Analysis 2 338 349
Dragsted, L.O., Strube, M. & Larsen, J.C. 1993 Cancer-protective factors in fruits and vegetables: Biochemical and biological background Pharmacol. Toxicol. 1 116 135
Gil, M.I., Holcroft, D.M. & Kader, A.A. 1997 Changes in strawberry anthocyanins and other polyphenols in response to carbon dioxide treatments J. Agr. Food Chem. 45 1662 1667
Hancock, J.F., Callow, P.W., Dale, A., Luby, J.J., Finn, C.E., Hokanson, S.C. & Hummer, K.E. 2001a From the Andes to the Rockies: Native strawberry collection and utilization HortScience 36 221 225
Hancock, J.F., Finn, C.A., Hokanson, S.C., Luby, J.J., Goulart, B.L., Demchak, K., Callow, P.W., Serçe, S., Schilder, A.M.C. & Hummer, K.E. 2001b A multistate comparison of native octoploid strawberries from North and South America J. Amer. Soc. Hort. Sci. 126 579 586
Hancock, J.F., Hokanson, S.C., Finn, C.E. & Hummer, K.E. 2002 Introducing a supercore collection of wild octoploid strawberries Acta Hort. 567 77 79
Heinonen, I.M., Meyer, A.S. & Frankel, E.N. 1998 Antioxidant activity of berry phenolics on human low-density lipoprotein and liposome oxidation J. Agr. Food Chem. 46 4107 4112
Huang, D., Ou, B., Hampsch-Woodill, M., Flanagan, J.A. & Prior, R.L. 2002 High-throughput assay of oxygen radical absorbance capacity (ORAC) using a multichannel liquid handling system coupled with a microplate fluorescence reader in 96-well format J. Agr. Food Chem. 50 4437 4444
Lewers, K.S., Enns, J.M., Wang, S.Y., Maas, J.L., Galletta, G.J., Hokanson, S.C., Clark, J.R., Demchak, K., Funt, R.C., Garrison, S.A., Jelenkovic, G.L., Nonnecke, G.R., Probasco, P.R., Smith, B.J., Smith, B.R. & Weber, C.A. 2004 ‘Ovation’ strawberry HortScience 39 1785 1788
Maas, J.L., Wang, S.Y. & Galletta, G.J. 1991 Evaluation of strawberry genotypes for ellagic acid, an antimutagenic and anticarcinogenic plant phenol 115 117 Dale A. & Luby J.J. The strawberry into the 21st century Timber Press Portland, OR
Pinkerton, J. & Finn, C.E. 2005 Responses of strawberry species and cultivars to the root-lesion and northern root-knot nematodes HortScience 40 33 38
Satué-Gracia, M.T., Heinonen, I.M. & Frankel, E.N. 1997 Anthocyanins as antioxidants on human low-density lipoprotein and lecithin-liposome systems J. Agr. Food Chem. 45 3362 3367
Starvic, B., Matula, T.I., Klassen, R., Downie, R.H. & Wood, R.J. 1992 Effect of flavonoids on mutagenicity and bioavailability of xenobiotics in food 239 249 Huang M.T., Ho C.T. & Lee C.Y. Phenolic compounds in food and their effects on health II. Antioxidants & cancer prevention Amer. Chem. Soc. Symp. Ser. 507 Washington, DC
Velioglu, Y.S., Mazza, G., Gao, L. & Oomah, B.D. 1998 Antioxidant activity and total phenolics in selected fruits, vegetables, and grain products J. Agr. Food Chem. 46 4113 4117
Wang, S.Y., Bunce, J.A. & Maas, J.L. 2003 Elevated carbon dioxide increases contents of antioxidant compounds in field-grown strawberries J. Agr. Food Chem. 51 4315 4320
Wang, S.Y. & Lin, H.S. 2000 Antioxidant activity in fruits and leaves of blackberry, raspberry, and strawberry varies with cultivar and developmental stage J. Agr. Food Chem. 48 140 146
Wang, S.Y. & Lin, H.S. 2003 Compost as a soil supplement increases the level of antioxidant compounds and oxygen radical absorbing capacity in strawberry J. Agr. Food Chem. 51 6844 6850
Wang, S.Y., Zheng, W. & Galletta, G.J. 2002 Cultural system affects fruit quality and antioxidant capacity in strawberries J. Agr. Food Chem. 50 6534 6542
Zheng, W. & Wang, S.Y. 2003 Oxygen radical absorbing capacity of phenolics in blueberries, cranberries, chokeberries, and lingonberries J. Agr. Food Chem. 51 502 509