The effect of postharvest calcium and heat treatments on apple (Malus Domestica Borkh.) fruit quality and enzymes of the ethylene biosynthetic pathway

The objectives of this research were as follows: 1) to study the effect of heat treatment on apple fruit quality, 2) to clarify the effect of heat on enzymes of the ethylene biosynthetic pathway, 3) to determine the effect of calcium pressure infiltration on the enzymes of ethylene biosynthesis, and 4) to examine the effect of heat and calcium treatment in combination on apple fruit quality and ethylene production. 'Delicious' and 'Braebum' apples (Malus domestica Borkh.) were treated with heat (three days at 38 C) and calcium (2% CaCl₂, 103 kPa, 5 minutes) alone and in combination. The fruit quality parameters measured were firmness, respiration and ethylene production rates, soluble solids content (on ‘Delicious' apples only) and calcium content. To investigate the effects of the treatments on the enzymes involved in ethylene biosynthesis, assays for 1-aminocyclopropane-1-carboxylic acid (ACC), l-(malonylamino)cyclopropane-1-carboxylic acid (MACC), and ethylene forming enzyme (EFE) (on 'Braebum' apples only) were performed.

In experiment one, ‘Delicious' apples were treated with heat and subsequently put into cold storage at 0 ± 1 C for two weeks or two months. Soluble solids content, respiration rate, and calcium content were unaffected by the treatment. The heat-treated apples were softer than the control fruit at both removal times. Ethylene production was inhibited in the heat-treated fruit by 47% and 36% at two weeks and two months respectively. ACC and MACC concentrations were not statistically different in the heat-treated fruit when compared to the control. A large amount of fruit to fruit variation was present.

In experiment two, 'Braebum' apple fruit were heat-treated and calcium infiltrated individually and in combination, prior to storage at 20 C for 2, 7, 14, or 30 days or 0 C for two months. The heat plus calcium treatment was the only treatment which affected fruit firmness. At seven days post treatment at 20 C, the heat plus calcium treated fruit were firmer than all other treatments. In the 20 C stored fruit, all treatments significantly lowered the respiration rate at seven days. However at 0 C, the calcium only treatment was the only treatment to affect the respiration rate. All treatments in both storage conditions lowered ethylene production. At 20 C, the heat and heat plus calcium treated fruit had lower ACC concentrations than the control at two days. At seven days, the calcium treated fruit showed an accumulation of ACC. Similarly at 0 C, the calcium plus heat treated fruit exhibited an accumulation of ACC. An assay for EFE activity was performed on the fruit stored at 0 C. The heat, heat plus calcium, and calcium plus heat treated fruit showed an inhibition of EFE activity while the calcium only treated fruit were not affected.