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Epidemiological studies have indicated that a diet high in fresh and processed fruits is correlated with lower incidences of chronic cardiovascular, degenerative, and proliferative diseases. Specifically, plant-derived vitamin C (L-ascorbic acid) is a critical component of the human diet and has been shown to have important antioxidant power in both in vitro and in vivo conditions. As with vitamin C, numerous health benefits (e.g. anti-cancer properties, treatment of diabetic retinopathy, benefits towards reduced blood pressure, protection against LDL oxidation, and boosts to the immune system including reduced inflammation) have been attributed to specific anthocyanin extracts from pigmented plant tissues. Anthocyanins are naturally occurring flavonoid compounds that impart red to purple colours to skins of dozens of different fruits such as apples, grapes, blueberries, and raspberries. Over 600 different anthocyanins have been identified in plants. Previous studies have shown that fruits from different plant species preferentially accumulate particular types of anthocyanins, resulting in significantly different bioactive capacities as well as variable pigment intensities and hues. For example, “cane” fruits such as raspberries accumulate anthocyanins derived from a dihydroquercitin precursor that have superior antioxidant properties to those synthesized to a greater degree in commercially important European wine grape varieties, which are predominantly dihydromyricetin-type. While previous work has been devoted to characterizing antioxidant activities of total anthocyanin extracts from cane fruits and grape berries, the molecular biology underlying the predominant production of the apparently healthier types of anthocyanin compounds in cane fruits remains unknown. Furthermore, interactions between vitamin C and flavonoid phytochemicals have been previously indicated; for example, published data showed reduced oxidative degradation of the major anthocyanins in elderberry juice cultivars that also contained high vitamin C content. One hypothesis arising from this finding is that anthocyanins may help stabilize the bioavailability of red fruit-derived vitamin C to animals. The genes and metabolic pathways underlying both ascorbate and anthocyanin biosyntheses are well-characterized in plants. For these reasons, the nutritional quality of fruit, particularly red berries such as raspberries and some grapes, has become increasingly relevant and molecular breeding approaches are now viable for enhancing the content of specific healthy phytochemicals in fruits.
Genetic background plays an essential role in the nutritional qualities of fruit, but until recently, it has essentially been ignored in fruit breeding programs. Recently, a report compared a number of phytochemical parameters in a selection of genotypes from the Italian strawberry breeding program and found significant differences among genotypes for total antioxidant capacity but very poor correlation between antioxidant capacity and horticultural attributes (e.g. yield and fruit size); however, when crosses were made between clones with desirable horticultural attributes and those with high antioxidant capacity, they were able to select progeny that had both desirable commercial attributes and high antioxidant capacity. These data further indicate that breeding of “functional” fruits with improved nutritional properties is feasible and can be coupled with selections for more traditional agronomic traits of economic importance.
 More than 80% of Canada's red raspberries are grown in BC in just 5,000 acres with a domestic market value in 2006 of $10 million. Raspberries are an important source of antioxidant phytochemicals. Consuming just one cup of raspberries can provide 40% of the recommended daily intake of vitamin C. As mentioned above, raspberries are also a rich source of anthocyanin flavonoids, chiefly cyanidins. Little work to date has been done in raspberry breeding for antioxidant traits. We were not able to find any reports of co-selection (i.e. “stacking”) of antioxidant characteristics with other economically important traits in raspberry. One study determined that four Spanish raspberry cultivars differed significantly in vitamin C content and anthocyanidin glycosylation but did not report any heritability data for these traits. These findings suggest that sufficient variability in antioxidant phytochemicals are present in different raspberry genotypes to incorporate this phenotype in selection schemes in raspberry breeding programs. An important consideration specifically for the flavonoids is that in ripe raspberries, anthocyanins have been shown via oxygen radical absorbance capacity (ORAC) assays to have a greater role in determining antioxidant capacity than the flavan-3-ols (tannins).
The Pacific Agri-food Research Centre’s (PARC’s) Small Fruit Breeding Program in Agassiz, BC, has a long tradition of releasing cultivars that are very adaptable, thereby setting new standards in fruit quality, appearance, and combined resistance to pests and diseases. Some examples are the raspberry cultivars, Chilliwak, Tulameen, and the latest two releases from the program, Chemainus and Saanich, which are recognized worldwide for their high fruit quality and improved resistances to pests and diseases. The PARC program provides a rich genetic resource to mine and exploit to further improve BC raspberries for enhanced vitamin and anthocyanin contents and increase the market for BC raspberries and cultivars internationally.
Through the new FNH Vitamin Research Fund at UBC, we are launching in April 2008 a collaboration between my lab and the labs of Dr. David Kitts (UBC Food Science) and Chaim Kempler (lead geneticist on the PARC Small Fruit Breeding Program) in which we plan to use metabolite profiling and antioxidant assays of several PARC raspberry genotypes to make initial parental selections for improving antioxidant capacity. In support of this goal, we plan to develop trait-associated SNP and/or random SSR markers to assist in selections of genotypes exhibiting superior antioxidant properties in order to more rapidly co-select for this trait and other economically important traits in raspberry.
Through a 2007 NSERC Discovery grant to my lab, we are also exploring the biochemical genomics of flavonoid-3’5’-hydroxylase (F3’5’H). We hypothesize that expression of flavonoid-3’5’-hydroxylase transcripts is fundamental to determining dihydroquercitin-type and dihydromyricetin-type in grape berries in comparison to raspberries. We are examining the potential to manipulate F3’5’H expression in order to engineer improved anthocyanin composition in grape berries and wines for human health applications.
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