Chemical changes in the cortical tissue and cell walls of calcium-infiltrated ‘Golden Delicious’ apples during storage

Abstract

‘Golden Delicious’ apples (Malus×domestica Borkh.) were either untreated or pressure-infiltrated after harvest with 0, 1, 2, 3 or 4% CaCl2 solutions (w/v) and stored at 0 °C for up to 6 months. The chemical composition of the fruit cortical tissue and cell walls of the 2–4 mm layer under the epidermis was studied. Storage of untreated fruit resulted in a decrease in K, P, Mg, S and Suc content of the tissue, while Fru and Glc increased. In the cell wall, Ca, Mg and total polysaccharide content increased while S, P, total neutral sugar and protein content decreased. During storage, fruit infiltrated with 0% CaCl2 showed a decrease in total polysaccharide and uronic acid content while neutral sugar content increased. After 6 months, the 0% treated fruit had higher levels of total P, Na and S compared to the untreated fruit. These changes in the cell wall of both untreated and 0% treated fruit resulted in an overall decrease in cell wall content of the apple tissue during storage. Analyses of Ca-infiltrated tissue and cell wall characteristics showed an interaction between CaCl2 treatment and time in storage for total and cell wall-bound minerals, total neutral sugar (Glc, Ara, Gal and Rha), protein and cell wall content. CaCl2 infiltration resulted in an increase in both total and cell wall-bound Ca of the apple tissue during storage, with a maximum reached at 2% CaCl2 for fruit stored 4 or 6 months. Ca-infiltrated fruit had higher levels of total K and Na, cell wall-bound Mg, and reduced loss of Ara and Gal after 6 months storage compared to fruit treated with 0% CaCl2, resulting in reduced cell wall degradation of 2% CaCl2 treated fruit during storage. The major changes in the tissue and cell walls occurred after 6 months storage, indicating that this stage was critical for quality maintenance.