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W. Kalt

Fruit extract of the European blueberry, or bilberry (Vaccinium myrtillus), is a major component of a great number of pharmaceutical and food supplement products. Compared to most small fruits, bilberry has a high concentration of anthocyanin pigments. Anthocyanins are of biomedical interest due to their properties as antioxidants and protein cross linkers. The major clinical applications for anthocyanins are in ophthalmology, blood vessel and connective tissue disorders, and diabetes. Bilberries are harvested from wild stands throughout Scandinavia, Eastern Europe, and at higher altitudes in southeastern France. Because they are wild, a wide array of genotypes make up the commercial product. As part of an investigation of the nutraceutical components of North American wild lowbush blueberries (Vaccinium angustifolium), we are comparing the anthocyanins and other phenolic components from fruit of commercially available Vaccinium species. We are particularly interested in the variation in composition among Vaccinium clones and species.

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W. Kalt and J. McDonald

Fruit composition can be affected by genetic and environmental factors during development and ripening. Red-ripe strawberries were harvested at regular intervals during the harvest season to determine how early or later ripening fruit may vary in composition. The cultivars `Cavendish', `Honoeye', and `Kent' were harvested twice weekly over a 3-week period and FW, %DW, and sugar, acid, and anthocyanin pigment content was measured. The study was repeated for 2 years. Fresh fruit weight declined over the harvest period, while the %DW increased in all cultivars. Although the content of sucrose and glucose (mg/g DW) did not vary among the harvest dates, their content was different among the cultivars. Citric and malic acid content (mg/g DW) was lower in the later harvests, although their content was similar among the cultivars. Total anthocyanin content increased and then declined during the harvest season. Pelargonidin 3-glucoside, the major strawberry anthocyanin, was highest in `Honoeye', while cyanidin 3-glucoside content was similar among the three cultivars.

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W. Kalt and J. McDonald

Sugars, pigments, and organic and phenolic acids were examined in three name clones of lowbush blueberries (V. angustifolium Aiton) during two seasons. Between the two seasons, glucose and fructose content was not different, but anthocyanin content differed by 40%. Also, titratable acidity differed by 40%, and total acid content (as measured by HPLC) by 60%. Differences in total acid content between the two seasons could be attributed to changes in some, but not all, acids. Acid content of berries of different maturities suggested that some, but not all, acids decreased as fruit ripened. Although the acid profile was different in the 2 years of the study, overall the lowbush blueberry profile was distinct from that recently reported for highbush and rabbiteye blueberries [Ehlenfeldt et al., HortScience 29(4):321–323]. Succinic acid was absent in lowbush fruit, and there was a higher level of quinic acid than found in highbush or rabbiteye blueberries. Citric acid was present in lowbush fruit at a level intermediate between the other Vaccinium species.

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W. Kalt, C. Lawand and C.F. Forney

Highbush blueberry (Vaccinium corymbosum) fruit of the cultivars `Bergitta', `Bluegold', and `Nelson' were harvested at six stages of maturity and evaluated for their antioxidant capacity and anthocyanin and phenolic content. Fruit of the four earliest maturities were also stored at 20 °C for up to 8 days. At the time of harvest, fruit of different maturities had substantial differences in their anthocyanin content, and less marked differences in phenolic content and antioxidant capacity. Substantial anthocyanin synthesis occurred in under-ripe fruit during 20 °C storage, and varied depending on fruit maturity at harvest. Total phenolic content changed very little during storage, and there was no change in fruit antioxidant capacity. The results suggest that anthocyanin phenolics are formed on or off the plant, primarily from other pre-existing phenolic components. Whether phenolics are present as anthocyanins or other colorless forms, has relatively little impact on antioxidant capacity.

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W. Kalt, J.E. McDonald and S. MacKinnon

Fruit and vegetable components that possess antioxidant capacity are being actively investigated because of the purported impact of dietary antioxidants on human health. Phenolic components, including anthocyanins, are believed to be major contributors to the antioxidant capacity of many small fruit species. Various horticultural factors have been examined with respect to anthocyanin and phenolic content, and antioxidant capacity of small fruit, especially Vaccinium species. Vaccinium species, and certain other fruits, had a high antioxidant capacity compared to strawberries and raspberries. However, genotypic variation in these characteristics was substantial among wild blueberry clones. Fruit maturity did not influence antioxidant capacity, although phenolic profiles changed dramatically during ripening. Fresh storage of certain ripe fruit at 20 °C led to increased anthocyanin content and increased antioxidant capacity. Certain food processing factors, such as heat and oxygen, decreased the antioxidant capacity of blueberry products.

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A. Howell, W. Kalt, J.C. Duy, C.F. Forney and J.E. McDonald

It is now widely held that the antioxidants contained in fruit and vegetables can provide protection against certain human degenerative conditions that are associated with oxygen free radical damage. This view is supported by epidemiological, in vitro, and more recently, in vivo evidence. Phenolics (polyphenolics) contribute substantially to the antioxidant complement of many small fruit species whose ripe fruit are red, purple or blue in color. Fruit containing high levels of phenolic antioxidants would be attractive to health conscious consumers, therefore optimization of production and processing factors affecting small fruit antioxidant capacity is desirable. In many small fruit crops, antioxidant activity [measured as oxygen radical absorbing capacity (ORAC)] is positively correlated with their content of anthocyanins and total phenolics. Genera, species, and genotypes vary with respect to phenolic content. Both annual and geographical factors appear to influence ORAC, although many years of study are needed to distinguish these effects from other biotic and abiotic factors that influence fruit phenolic content. Antioxidant capacity due to phenolics is decreased by food processing practices, such as heat or aeration.