INHIBITION OF ETHYLENE VIA DIFFERENT WAYS AFFECTS LOX AND ADH ACTIVITIES, AND RELATED VOLATILES COMPOUNDS IN PEACH (CV. ´ROYAL GEM´)

Abstract

Peach aroma depletion is the main reason for the reduced consume of peaches in the market. The reason of this low aroma development is the early harvest and the use of low temperature. In previous papers we showed a relationship of volatiles development with ethylene production of peaches. Here we studied the influence of different treatments to inhibit ethylene production on ethylene production, commercial quality characteristics, and volatiles in relationships to enzymatic activities. Peaches (cv. 'Royal Gem') were picked at early ripening stage (10-11% SSC and 60-68 N firmness) in July and successively separated to be treated with N 2 (100%) for 44 h at 20°C + in air at 20°C and 80% RH until day 9, or 1 ppm 1-MCP for 20 h at 20°C + in air at 20°C until day 9, or at 3° in air for 7 d + at 20°C for 2 d, or for 9 d in air at 20°C (control). Ethylene was reduced greatly by nitrogen and low temperature. 1-MCP had intermediate values between these two treatments and the control. This ethylene response affected firmness and deformation of peaches but not the SSC (soluble solids content). Even volatiles, mainly esters, were affected by ethylene level. Control fruits showed the highest volatiles content (peak area) after 2 days in parallel with the rise of ethylene for the climacteric peak. 1-MCP treated fruits showed the highest volatiles value after 6 days when the ethylene production reached a value of 4 μL kg -1 h -1 slightly lower than the level reached by the control 4 days before. Nitrogen and low temperature-treated fruits showed very low ethylene production even after the shift to normal atmosphere (nitrogen treatment); consequently the total volatiles were lower. Nitrogen treated peaches developed an aroma with sweet nuance due to the high content of ethanol and acetate esters. Alcohol dehydrogenase (ADH) activity was related to alcohol formation. Lypoxygenase (LOX) activity was high in nitrogen-treated fruits but C6 compounds were partially related to the enzyme activity. Low temperature treated peaches increased the lactones production when transferred to higher temperatures but the esters content remained lower. Nitrogen can represent a good postharvest treatment for the peach distribution.