Changes in the Cell Wall Components of Kiwifruit During Storage in Air or Controlled Atmosphere

Abstract

Abstract Eight-one percent of the harvest firmness in kiwifruit (Actinidia chinensis Planch.) was lost during the first 8 weeks of storage in air at 0°C. As softening proceeded, a solubilization of uronic acids and the neutral sugar residues usually associated with pectic polymers (galactose, arabinose, and rhamnose) was detected. No consistent changes were noted in cellulose or the neutral sugars usually associated with hemicelluloses. Starch degradation also occurred coincident with softening. The amount of cell wall components soluble in water following fruit homogenization and the proportion of ethanol-precipitable pectic neutral sugars in this fraction increased during the first 8 weeks of storage. Once the rate of softening slowed (8 to 20 weeks), an equilibrium situation apparently was established between the amounts of the sugars formed in the ethanol-precipitable (i.e., polymeric) and ethanol-soluble fractions, suggesting that digestion of wall components continues after their excision from the insoluble wall matrix. Controlled atmosphere (2% O2+ 5% CO2; CA) storage retarded flesh softening relative to that measured in fruit held at 0° in air. A comparison of the changes in the cell wall components of air-stored and CA-stored kiwifruit suggests that, in addition to cell wall degrading processes contributing to fruit softening, starch degradation (possibly causing cell turgor changes) also may be involved in low-temperature softening of kiwifruit. The losses in water-insoluble cell wall pectic neutral sugars and uronic acids in air and CA storage were similar during the first 8 weeks of storage. Once softening slowed in CA, small but consistent reductions in the amount of cell wall turnover were observed as compared to air storage.