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 monitored using both destructive (pectin composition) and non-destructive (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 and was almost completely prevented by CA-storage (10% O-2 + 10% CO2 at 0 degrees C). Fruit developing woolliness exhibited little depolymerisation of pectins in comparison with healthy fruit where the water-soluble pectins underwent a 60% increase. Woolly breakdown was detectable by NMR imaging as dark areas corresponding to low proton density. However, the development of woolliness did not affect the mobility of water in the tissues. X-ray computed tomography indicated that the lower proton density of injured tissues observed with NMR corresponded in fact to the presence of gas spaces. It is therefore concluded that the biochemical changes in pectin composition observed in nectarines exhibiting woolly breakdown occur without noticeable modification of the water status of the tissue and that the woolly texture could, at least partly, result from the inclusion of intercellular gas spaces in injured tissues.