Effects of 6-methyl-5-hepten-2-one vapor on peel browning of ‘Delicious’ and ‘Granny Smith’ apples: open vs. closed system

Abstract

Abstract An open and a closed system were used to evaluate the effects of 6-methyl-5-hepten-2-one (MHO) vapor on peel browning or scald development of ‘Delicious’ and ‘Granny Smith’ (scald susceptible) or ‘Fuji’ and ‘Gala’ (scald resistant) apples. In the open system, fruit were placed on the top of a beaker containing MHO and held in a ventilation hood with airflow of 0.56 m s−1 at 20 °C for 4 days. In the closed system, an open beaker containing MHO, together with 30 apples, was sealed in a 30-l jar, which was opened for 1 h every 2 days for 7 days at 20 °C. Differing scald susceptibilities for ‘Delicious’ and ‘Granny Smith’ were created using fruit at harvest (least susceptible), fruit stored in regular air (RA) for 4 months or controlled atmosphere (CA) for 6 months 0 °C (most susceptible), or fruit treated with DPA at harvest and then stored in RA for 4 months or CA for 6 months at 0 °C (less susceptible). At harvest, MHO induced peel browning over 100% of the treated area of the four cultivars in the open system but induced no browning on fruit in the closed system. Fruit treated similarly with acetone or ethanol showed peel browning in the open system but not in the closed system. Scald developed after 4 months RA storage in ‘Delicious’ and ‘Granny Smith’ and after 6 months CA storage in ‘Granny Smith’. Scald increased in these fruit after 7 days at 20 °C. DPA treatment inhibited scald both during storage and during the poststorage period at 20 °C. In the open system, MHO treatment increased MHO concentrations in fruit peel by 100-fold and induced uniform peel browning in the treated area within 24 h in both cultivars regardless of storage condition or DPA treatment. The severity of the symptom increased with time. In the closed system, although MHO treatment increased MHO concentration in fruit peel by 3–10 fold compared with untreated controls, it did not change scald development regardless of cultivar, storage condition, or DPA treatment.