Phenylalanine ammonialyase and invertase activities in strawberry fruit during ripening progress

Strawberry fruit (Fragaria × ananassa Duch.) is one of the most consumed fruits worldwide due to its nutritional properties and health promoting effects. The ripening of strawberries is a highly synchronized, genetically programmed and irrevocable phenomenon encompassing a chain of physiological, biochemical and organoleptic alterations. The first aim of the study was to determine phenylalanine ammonialyase (PAL) activity in the fruits of two cultivars of strawberries, i.e., 'Rubygem' and 'Fortuna', which were at different stages of ripening. Phenylalanine ammonialyase (PAL, E.C. 4.3.1.5) is a key enzyme that initiates phenylpropanoid metabolism via which anthocyanins are synthesized. In turn, the second goal of the study was to determine invertase (β-fructosidase; EC 3.2.1.26) activity. The enzyme catalyses the conversion of sucrose to its monosaccharide constituents glucose and fructose in fruits during ripening process. The results revealed significant differences in PAL and invertase activities of 'Fortuna' and 'Rubygem' during ripening stages. The activity of these enzymes increased in relation to the fruit ripening time.