BIOCHEMICAL AND PHYSICAL EVALUATION OF TEXTURAL CHARACTERISTICS OF NECTARINES EXHIBITING WOOLLY BREAKDOWN - NMR IMAGING, X-RAY COMPUTED-TOMOGRAPHY AND PECTIN COMPOSITION

Woolly breakdown of cool-stored nectarines (Prunus persica) has been m onitored using both destructive (pectin composition) and non-destructi ve (NMR imaging, and X-ray computed tomography) methods. Breakdown was less severe after storage at 2 degrees C in air than at 0 degrees C a nd was almost completely prevented by CA-storage (10% O-2 + 10% CO2 at 0 degrees C). Fruit developing woolliness exhibited little depolymeri sation of pectins in comparison with healthy fruit where the water-sol uble pectins underwent a 60% increase. Woolly breakdown was detectable by NMR imaging as dark areas corresponding to low proton density. How ever, the development of woolliness did not affect the mobility of wat er in the tissues. X-ray computed tomography indicated that the lower proton density of injured tissues observed with NMR corresponded in fa ct to the presence of gas spaces. It is therefore concluded that the b iochemical changes in pectin composition observed in nectarines exhibi ting woolly breakdown occur without noticeable modification of the wat er status of the tissue and that the woolly texture could, at least pa rtly, result from the inclusion of intercellular gas spaces in injured tissues.