Using volatile emissions and chlorophyll fluorescence as indicators of heat injury in apples

Volatile emissions and chlorophyll fluorescence were investigated as potential signals of heat injury for apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit. 'McIntosh','Cortland','Jonagold', and 'Northern Spy' apples were exposed to 46 degreesC for 0, 4, 8, or 12 hours (heat treatments). Following treatments, fruit were kept at 20 degreesC and evaluated after 1, 2, 4, or 7 days. Heat treatments induced volatile production including ethanol and ethyl acetate. The 8 and 12 hours heat treatments increased ethanol and ethyl acetate production in all four cultivars by as much as 170- and 11-fold, respectively, I day after treatments. Heat treatments also reduced ethylene production and chlorophyll fluorescence. Heat for 12 hours caused serious flesh browning. Among the cultivars investigated, 'Northern Spy' and 'McIntosh' were most susceptible to heat stress based on the degree of flesh browning. Correlation coefficients of heat stress induced ethanol emission and chlorophyll fluorescence with flesh browning were 0.82 and -0.66, respectively. The nondestructive measurements of ethanol emission and chlorophyll fluorescence have potential to identify stressed fruit with reduced quality or compromised storage life.