Modelling the enzymatic softening of apples in relation to cultivar, growing system, picking date and season

The postharvest softening of four apple cultivars cv. Idared, Liberty, Pilot and Pinova coming from an organic and an integrated experimental orchard was studied to compare the effects of cultivar, growing system, picking date and season. The stiffness of apples was examined monthly by acoustic impulse‐response technique. The activity of β‐galactosidase (β‐Gal) and polygalacturonase (PG) causing cell wall breakdown was investigated at harvest and during storage. A mechanistic model approach was developed to interpret the integral set of data on softening as a function of the measured enzyme activities. No consistent differences were observed in β‐Gal or PG activity during storage of apples coming from either organic or integrated orchards, whereas their stiffness behaved comparably. In general, the effect of cultivar and season was higher than the effect of production system. Using the developed model, postharvest stiffness changes were described in relation to the observed changes in β‐Gal and PG activity during storage.