Effect of pH and Concentration of the Anthocyanin-Flavonol Co-Pigment Complex on the Color of ‘Better Times’ Roses1

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Abstract
Flavonoids isolated from ‘Better Times’ rose petals were cyanidin 3,5-diglucoside, the 3-rhamnoside, 3-glucoside, 3-arabinoside, 3-glucuronide of quercetin and the 3-glucoside, and 3-xyloside of kaempferol. The rose pigment, a co-pigment complex of cyanindin 3,5-diglucoside (2.0-2.8 × 10-2M) and quercetin or kaempferol glycosides, (0.8-1.4 × 10-1M, expressed as quercitrin) was present only in epidermal cells. At the pH of freshly harvested tissue (3.70 to 4.15) this pigment was red with a λmax of 539 nm. As the tissue aged the pH increased (4.40 to 4.50) and the pigment became more blue with a λmax of 543 nm. Cornell preservative prevented the increase in pH of commercial cut roses and maintained their original color. The high pigment concn and the phenomenon of co-pigmentation explain the intense color of ‘Better Times’ roses in a pH range where anthocyanins alone are virtually colorless.

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