Ripening Physiology in `Navaho' Thornless Blackberries: Color, Respiration, Ethylene Production, Softening, and Compositional Changes

Abstract

Fruit were harvested from an erect, thornless blackberry (Rubus L. subgenus Rubus Watson, `Navaho' to study ripening changes. Soluble solids content increased between the red (unripe) and dull-black (overripe) stages of ripening while titratable acidity decreased sharply between the mottled and shiny-black ripeness stages. Anthocyanin content increased sharply between the mottled and shiny-black stages. Firmness of drupelet and receptacle tissues decreased between the mottled and shiny-black stages of ripeness. In whole blackberries, total uronic acids decreased, and water soluble uronic acids increased between the green-red and shiny-black ripeness stages. Volatile production paralleled ripening changes, and was highest in dull-black fruit, with alcohols and aldehydes predominating. Respiration of intact fruit maintained in water decreased between the green and red ripeness stages and increased at the mottled (part-black) and black ripeness stages. Ethylene production remained below 10 nmol·kg-1·h-1 until the dull-black (overripe) stage of maturity. Free 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC oxidase did not increase in berries until the shiny-black stage, corresponding with the onset of detectable ethylene production. ACC oxidase activity decreased in the drupelet tissue (0.5 to 0.01 μmol·kg-1·h-1) and increased in the receptacle tissue (2 to 3.8 μmol·kg-1·h-1) as fruit changed from red to dull black. These results indicate that ripening in blackberries may be initiated in the receptacle tissue. Ripening in blackberries is likely independent of ethylene, but ethylene may regulate berry detachment from pedicels, thus controlling timing of fruit harvests.