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Home HortScience Hot Weather Raspberries Heat Up the Competition
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PROVO, UT - Recent reports about the powerful antioxidants in colorful fruits like raspberries and blueberries have prompted scientists to investigate fruits' antioxidant "capacity", a measure of their phytochemical content. Research has proven that phenolic acids, anthocyanins, and other flavonoids - compounds responsible for most of a fruit's antioxidant capacity - are at their peak when fruit is ripest. Ripe raspberries have a particularly high antioxidant capacity and total phenolic content compared with most other berries and are a good source of ellagic acid, a potent phytochemical being studied for its ability to fight human pathogens.

Tory L. Parker from the Department of Nutrition, Dietetics and Food Science at Brigham Young University described a recent study in HortScience that measured the antioxidant capacity and total phenolic content of six raspberry varieties. "While most raspberries grown in temperate environments are harvested in the spring from "floricane" (second year spring bearing) plants, raspberries grown in hot, dry conditions are harvested in the fall from "primocane" (first year bearing) plants that have been nourished from irrigation and fertilization throughout the summer," Parker explained. "The dry climate results in berries that can lose moisture more quickly. Particularly late in the season, as the weather begins to turn cold, some cultivars produce significantly smaller, darker berries, whereas other cultivars do not."

Parker and a team of researchers compared six cultivars of raspberries grown on a farm in Utah ('Autumn Bliss', 'Caroline', 'Jaclyn', 'Joan J', 'Polana', and 'Polka'). Samples from all cultivars were collected every two weeks from mid-August until mid-October. The analyses showed that 'Autumn Bliss' had the highest overall oxygen radical absorbance capacity (ORAC) and total phenolic content across the season, while 'Caroline' had the lowest ORAC and phenolic content when fresh.

The researchers also tested the raspberries after refrigeration and freezing. The data showed no significant ORAC difference between fresh and refrigerated berries, but did reveal a significant difference in ORAC between refrigerated and frozen storage. Fresh and frozen berries showed no significant difference in total phenolics, but a significant increase in total phenolics occurred during refrigerated storage.

"Averaging all cultivars and pickings, refrigerated berries had a significantly higher total phenolic content than fresh or frozen berries, although some moisture loss occurred during refrigeration," Parker noted.

The team's final experiments compared the primocane raspberries to three cultivars of fall bearing California raspberries purchased at local supermarkets. Both the ORAC values and total phenolic values were significantly lower in the supermarket raspberries than in the dry climate cultivars.

Parker summarized the extensive research project, noting: "Antioxidant capacity and total phenolic content of primocane raspberries grown in hot, dry conditions vary between cultivars, on average do not change significantly after storage, are higher later in the season, and are higher than supermarket cultivars."

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The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/cgi/content/abstract/46/2/236

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org


 

Original Article:

Antioxidant and Phenolic Changes Across One Harvest Season and Two Storage Conditions in Primocane Raspberries (Rubus idaeus L.) Grown in a Hot, Dry Climate
Brenner L. Freeman, Janet C. Stocks, Dennis L. Eggett, and Tory L. Parker
HortScience 46:236–239. [Abstract] [Full Text] [PDF]

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