SUBCELLULAR GENERATION AND DISTRIBUTION OF LIPID-DERIVED VOLATILES INTHE RIPE TOMATO

The flavour volatile pathway in ripe tomato has been examined by quant itation of the volatile CG aldehydes, hexanal and trans-2-hexenal, in three subcellular fractions, a microsomal (membrane) fraction, the cel l cytosol, and a lipid particle fraction isolated from the cytosol by floatation centrifugation. The lipid particles comprise a hydrophobic compartment within the cytosol, range from 10 to 100 nm in diameter an d appear to be derived from membranes. They are distinguishable from m embranes, however, in that they have a higher (3.3 fold) free: esterif ied fatty acid ratio. Isolated microsomal membranes proved capable of generating hexanal in vitro upon incubation with exogenous substrate f or lipoxygenase. However, when ripe tomato fruit were fractionated, mo st (similar to 90) of the hexanal and trans-2-hexenal was found in the cytosolic fraction. Indeed the microsomal and lipid particle fraction s contained only 6.5 % and 4.3 %, respectively, of the volatile aldehy des. As well, the hexanal and trans-2-hexenal in the lipid particle fr action did not coelute with fatty acids during,eel filtration of the p article fraction indicating that the volatiles are solvated in the buf fer in which the particles are suspended. These observations support t he contention that lipid particles and key flavour volatiles are both derived from membranes. They also raise the possibility that blebbed l ipid particles serve as a vehicle for moving flavour volatiles out of membranes, and that the volatiles subsequently partition out of the pa rticles into the cytosol in accordance with partition coefficients.