Compost as a soil supplement increases the level of antioxidant compounds and oxygen radical absorbance capacity in strawberries

Compost as a soil supplement significantly enhanced levels of ascorbic acid (AsA) and glutathione (GSH) and ratios of AsA/dehydroascorbic acid (DHAsA) and GSH/oxidized glutathione (GSSG) in fruit of two strawberry (Fragaria x ananassa Duch.) cultivars, Allstar and Honeoye. The peroxyl radical (ROO(*)) as well as the superoxide radical (O(2)(*)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radical (OH(*)), and singlet oxygen ((1)O(2)) absorbance capacity in strawberries increased significantly with increasing fertilizer strength and compost use. The planting medium (compost) x fertilizer interaction for phenolics and flavonoids was significant. Fruit from plants grown in full-strength fertilizer with 50% soil plus 50% compost and 100% compost yielded fruit with the highest levels of phenolics, flavonol, and anthocyanin content. A positive relationship between antioxidant activities and contents of AsA and GSH and ratios of AsA/DHAsA and GSH/GSSG existed in fruit of both strawberry cultivars. Correlation coefficients for the content of antioxidant components versus antioxidant activity against ROO(*), O(2)(*)(-), H(2)O(2), OH(*), or (1)O(2)] ranged from r( )()= 0.7706 for H(2)O(2) versus GSH/GSSH in cv. Allstar to r = 0.9832 for O(2)(*)(-) versus total flavonoids in cv. Allstar.