Cell wall hydrolysis in netted melon fruit (Cucumis melo var. reticulatus L. Naud) during storage

Abstract

The object was to investigate the change of texture, cell wall hydrolases and cell wall components in muskmelon fruit (Cucumis melo var. reticulatus) during storage. The fruit were stored at 25±3°C for 8 days. Ethylene production, texture and cell wall hydrolases, namely pectinmethylesterase (PME), polygalacturonase (PG), β-galactosidase (β-Gal), and galactanase, and cell wall components such as, uronic acid and non-cellulosic neutral sugars content were determined. The typical ethylene production as a climacteric fruit was shown. The firmness decreased significantly throughout storage (p ≤ 0.05). A decrease in PME activity was detected throughout storage. PG and β-Gal activities increased during storage. A marked increase in galactanase activity was detected during storage (P≤ 0.05). A single isoform of β-Gal (isoform I) was found in unripe fruit (day 0), whilst two isoforms (isoform I and II) were present in ripe fruit (day 8). High galactanase activity was associated with β-Gal isoform II; whereas galactanase activity associated with isoform I was low and similar in both the unripe and ripe fruit. Uronic acid in CDTA-soluble fraction increased significantly whilst those of Na2 CO3-soluble fraction decreased significantly during storage (P ≤ 0.05). A high proportion of galactose was detected in all fractions and it declined during storage. These indicate that the loss of muskmelon texture is associated with the modification of pectin polymers and galactanase activity might be a key cell wall hydrolase in the fruit softening.