Superficial scald and ascorbic acid content of "Granny smith" and "Imperial double red delicious" apples: effect of postharvest treatments and storage conditions

The effect of different postharvest treatments (diphenylamine, vitamin C and CaCl2) and storage conditions namely, regular storage, ultra low oxygen atmosphere (ULO), and modified atmosphere (MA) at 0 C and 90 reletive humidity (RH) were evaluated on "Granny smith" and "Imperial double red delicious" apples for different storege periods following which, fruits were transferred to 20 C for one or five days. "G. Smith" apples were subjected to ULO storage on the same day of harvest; "I.D.R. Delicious" apples were stored for 10 days in air before transfer to ULO atmospheres. Fruits were stored for 6 and 7 months and sampled every 45 and 30 days for "G.Smith" and "I.D.R. Delicious" respectively. "G.Smith" apples treated with 2000ppm diphenylamine (DPA) developed a smalll percentage (7.91) of superficial scald symptoms compared to 32.84 of the control. The same apple variety treated with vitamin C 4000ppm applied as prestorage dip developed only 26.50 superficial scald. "I.D.R. Delicious: apples treated with 1500ppm DPA developed 35.25 superficial scald compared to 56.87 on the control. Treatment with vitamin C 4000ppm + CaCl2 0.125M slightly reduced the incidence of superficial scald (49.90). Apple ascorbic acid content was not significantly affected by postharvest treatments. Fruit colour and soluble solid content at harvest in both cultivars varied considerably with the stage of maturity but much of this variation disappeared during storage. No superficial scald symptoms developed on late-harvested "G.Smith" apples; little were observed on "I.D.R. Delicius" apples. The ULO-stored "G. Smith" did not develop superficial scald during subsequent shelf life compared to 33.51 scald on MA-stored fruits however, "I.D.R. Delicius" apples stored under similar conditions developed 26.21 superficial scald during subsequent shelf life but, preserved more ascorbic acid (7.1mg) during storage than fruit stored in air (6.5mg). ULO-stored friuts, generally had better fresh firmness, colour and higher titratable acidity. Fruits stored in modified atmosphere were softer and developed more superficial scald, but had higher soluble solid content. The sensitivity to scald incidence appeard to be related to variety, maturity at harvest, and storage conditions. More effective control over superficial scald was achieved with ULO storage and slightly with DPA used as prestorage chemical treatment.