Cell Wall Characteristics of Pithiness Tissues in 'Niitaka' Pears during Storage

We examined physiological and chemical characteristics of pithiness disorder occurred in stored ‘Niitaka’ pears (Pyrus pyrifolia Nakai). Pithiness disorders were increased as low temperature storage time passes and those were prominent in the fruits of full ripe which increased disorder up to 80% for 4 months of storage. Anatomical changes observed by stereomicroscope in damaged tissues showed an extent of cell collapse and cavity formation. The weights of disordered fruits were lower than those of unaffected ones when compared with fruit size. Analysis of pithiness tissues showed almost 40% of firmness drop when we compared to sound tissue. The amount of water-, trans-l,2-cyclohexanediamine-N,N,N',N'-tetra-acetic acid (CDTA)-, and sodium carbonate-soluble pectic polysaccharides and 4% KOH soluble hemicellulosic fraction increased as pithiness disorder extended. But the depolymerizations of high molecular-mass cell wall pectic-and hemicellulosic polysaccharides were not prominent in the disordered tissues while a slight difference was found between unaffected and disordered fruits. Results indicated that the depolymerization of cell wall components were not the major cause of pithiness disorder during low temperature storage in ‘Niitaka’ pears.