Phenolic Content During Healing of ‘Valencia’ Orange Peel Under High Humidity1

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Abstract
Free phenolic constituents increase more than 2-fold in injured peel of oranges (Citrus sinensis Osbeck) cv. Valencia after 48 hr at 30°C and 96 to 98% relative humidity (rh). Concomitantly, conjugated phenolic compounds decrease to near depletion as a heavily lignified layer forms on injured cells. At 5°C all wound healing processes slow down. Infection of injured tissue by Penicillium digitatum Sacc. at 27°C inhibits lignin synthesis and the disappearance of conjugated phenolic compounds, but does not interfere with the usual increase in free phenolics. Mycelium of P. digitatum contributes little to the level of phenolic compounds of decayed fruit tissue. Extracts of free phenolic substances from healed tissue d) not exhibit fungistatic activity on P. digitatum spores, Lignin formation provides a mechanical barrier which retards or inhibits penetration of injured tissue by P. digitatum.

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