Polyphenol content, antioxidant activity and surface colour of asparagus spears cultivated under different conditions of sunlight

The polyphenol content and DPPH radical-scavenging activity of asparagus spears cultivated under different conditions of sunlight have been investigated. In spring harvest on open field cultivation, the surface colour of spears was lightened by shading through application of black netting. Application of eight sheets of netting, causing a reduction of 95% of photosynthetic photon flux density (PPFD) compared to open field, was especially effective for lightness of spears. The sunlight intensity with shading corresponds to that under asparagus fern of mother stalk cultivation method. The polyphenol, rutin, ascorbic acid and chlorophyll contents, as well as DPPH radical-scavenging activity decreased with the shading of sunlight. Similar results were obtained for both green and purple asparagus.