Abstract
Since there is little information about the relationship between glycosidases and avocado fruit softening, we assayed some glycosidase activities during avocado fruit softening. β-Galactosidase, α-L-arabinofuranosidase and β-glucosidase activities increased during ripening ; that of β-galactosidase activity closely paralleled the trend in fruit softening. Therefore, β-galactosidase was fractionated into three isoforms using hydrophobic chromatography and cation exchange chromatography ; the isoforms were labeled AV-GAL I, AV-GAL II or AV-GAL III. AV-GAL III activity in the fruit, which was detected 4 days after harvest, increased with fruit softening, whereas AV-GAL I and II activities were detectable throughout the ripening period with little change. When the activities against four fractions of cell wall polysaccharides prepared from avocado fruit were assayed, AV-GAL III released a significant amount of monomeric D-galactose from guanidine thiocyanate (GTC) soluble cell wall polysaccharide, compared with AV-GAL I and II. AV-GAL I did not release detectable D-galactose from the four isolated cell wall polysaccharides, indicating that, among three β-galactosidase isoforms, AV-GAL III plays the most important role on the softening of avocado fruit.
