POSTHARVEST STORAGE OF BLACKBERRY FRUIT DOES NOT INCREASE ANTIOXIDANT LEVELS

Authors: Perkins Veazie, Penelope; WILHELMINA, K. - AG CANADA

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2001
Publication Date: 8/10/2002
Citation: Perkins Veazie, P.M., Wilhelmina, K. 2002. Postharvest storage of blackberry fruit does not increase antioxidant levels. Acta Horticulturae. 585:521-524.

Interpretive Summary: Antioxidants are found in many plants and have been found to be medically beneficial to humans in prevention of cancer and atherosclerosis. Small fruits contain several types of antioxidants such as the anthocyanin pigments which give fruit their color, and procyanidins which impart bitter or astringent taste. One of the measures of the total antioxidant capacity yof the fruit is called ORAC (oxygen radical absorbing capacity). ORAC has been found to increase when small fruit (blueberries, raspberries, strawberries) are stored after harvest. Blackberry fruit of 5 varieties were stored for 9 days at 2 C and for 7 days at 2 C plus 2 days at 20 C to determine how storage affects ORAC. There were large differences among the varieties. Kiowa had the highest ORAC and Shawnee the lowest. Stored blackberries did not increase in ORAC. These results indicate that the antioxidant levels in blackberry fruit may not be increased by storage.

Technical Abstract: Blackberries (Rubus subgenus rubus) are a rich source of anthocyanins and other polyphenolic antioxidants. Because of their antioxidant properties, dietary polyphenolics have been associated with a reduced risk of various degenerative conditions including certain cancers and coronary heart disease. A number of studies have been done to identify germplasm high in ORAC (oxygen radical absorbing capacity) in Rubus species. The present study was done to determine how the ORAC and total phenolic content in fruit of erect-type blackberries was affected by fruit storage. Blackberries of five cultivars, originating from the University of Arkansas breeding program (all tetraploids), grown in Lane, Okla. and harvested in 1998 at the shiny black and dull black stages of ripeness were held at 2 C, 95% relative humidity for 7 days plus 2 days at 20 C. Non-decayed berries were freeze-dried and powders of drupelet and receptacle tissue (no seeds), ,were extracted with acidified methanol. Samples were analyzed for ORAC using a COBAS-FARA II spectrofluorometric centrifugal analyzer. 'Arapaho' had higher ORAC values in shiny black fruit. ORAC values were highest in 'Kiowa' and lowest in 'Shawnee' fruit (4.05 and 2.69 mmol trolox/g freeze dried tissue, respectively). Average ORAC values of stored blackberries were slightly lower than those of fresh berries (3.11 vs 3.39 mmol trolox eq./g dwt, respectively). With the exception of 'Navaho', and 'Shawnee', total anthocyanin and phenolic contents were similar or lower in stored blackberries. These results indicate that ripeness stage and cultivar affect ORAC values of blackberries more than postharvest storage.