Lipoxygenase and hydroperoxide lyase activities in ripening tomato fruit
John C. M. Riley, Claude Willemot and John E. Thompson
Postharvest Biology and Technology Vol: 7 Issue: 1-2 Pages: 97-107.
1996
บทคัดย่อ
Volatile flavor compounds of lipid origin are produced by the sequential actions of lipoxygenase (LOX) and hydroperoxide lyase (HPL). The activities of these enzymes and their subcellular localization were determined in ripening tomato fruit (Lycopersicon esculentum L. cv. Match W42). Enzyme activity was measured in the microsomal fraction, a post-microsomal pellet (PMP) and a cytosolic fraction obtained from tomatoes at the mature-green, breaker, and red stage. LOX activity was predominantly (~80% of the total) in the PMP fraction for all stages of fruit development, and gel filtration of this fraction indicated that this represents soluble LOX that had been pelleted by centrifugation. For all of the subcellular fractions at all stages of development, LOX activity was higher at pH 6 than at pH 7 or 8. The microsomal form of LOX showed the greatest change in activity with fruit development, increasing by ~69% between the mature-green and breaker stages of development and declining again as the fruit turned red. In contrast, HPL was predominant (~73% of the total) in the microsomal fraction at all stages of fruit development, proved to be insensitive to pH over the range 6 to 8 and did not show any significant change in activity as the fruit ripened. Moreover, although most of the LOX was found in the PMP fraction, more lipid hydroperoxide is produced by microsomal LOX than is consumed by microsomal HPL. These observations suggest that the microsomal compartment is the site at which volatile flavor formation is initiated in tomato fruit.