567 Proc. VII th IS on Kiwifruit Eds.: G. Costa and A.R. Ferguson Acta Hort. 913, ISHS 2011 Study of Anaerobic Metabolism of Kiwifruits in ULO, LO, or Regular CA at Room Temperature R. Botondi, V. Russo and F. Mencarelli Department of Food Science and Technology Postharvest Lab (LAPO) University of Viterbo Italy Keywords: kiwifruit, ethanol, acetaldehyde, PDC, ADH, LDH, GPT Abstract Kiwifruits were picked at an early ripening stage with firmness of 105 N and soluble solids content (SSC) of 6 °Brix. Fruits were placed in air (CK), ULO (ultra- low oxygen) with 0.25% O 2 , LO (low oxygen) with 1% O 2 , or regular CA (controlled atmosphere) 2% O 2 + 5% CO 2 , all maintained at 20°C and 90% relative humidity (RH). After 19 days, fruits were removed from the atmospheres to SL (shelf life) in air at 20°C for 12 days. Kiwifruit kept in the modified atmospheres produced little ethylene and had reduced respiration during the atmosphere treatments while control fruit showed a typical climacteric curve. At the time of shift to SL, kiwifruit in ULO showed reduced rise of both ethylene, and respiration compared to LO and CA fruit. Softening occurred during the atmosphere treatment but fruit in ULO were firmer than in other treatments. Control fruit softened rapidly and continuously. During SL, atmosphere treated fruits did soften but after 19 days they were slightly firmer than control fruit. PDC (pyruvate decarboxylase), lactate dehydrogenase (LDH), and ADH (alcohol dehydrogenase, for the reaction ethanol to acetaldehyde) activities in atmosphere-treated fruits were low but two times higher than control fruit during storage; at the time of shift to SL, there was a large, rapid, burst for PDC and LDH while, slightly later, ADH increased, at the same extent. Control fruit showed a much lower increase in enzyme activities and the increase was delayed compared with atmosphere treatments. Ethanol increased initially at the time of the shift and then declined while acetaldehyde continued to rise. The potential role of anaerobic respiration on rapid softening of kiwis during SL is discussed. INTRODUCTION Kiwifruit is usually stored for long periods by controlling the atmosphere or by normal refrigeration (Manolopoulou and Papadopoulou, 1998) but its high sensitivity to ethylene requires care during harvest and postharvest handling. Kiwifruit soften steadily during storage depending on atmosphere used. Even when ethylene is undetectable it has been shown that invisible postharvest structural changes occur during ripening (Taglienti et al., 2009). After CA storage kiwifruit soften rapidly in parallel with the rise of ethylene and if physical injuries affect fruit, softening rapid and fruit temperature plays an important role (Mencarelli et al., 1996). Kiwifruit is usually stored in 5% CO 2 + 2% O 2 but recently an ultra-low oxygen (ULO) storage with 1% O 2 + 1% CO 2 has been proposed to increase storage life compared with conventional storage (Antunes, 2007). Reduction in oxygen is a positive method to control ethylene production and to delay softening, but it is risky as it may lead to development of anaerobic metabolites such as ethanol, acetaldehyde and lactic acid. PDC, ADH, and LDH are three important enzymes responsible for acetaldehyde, ethanol and lactate production, respectively. ADH genes are expressed in plant tissues in a developmentally regulated manner, particularly during fruit ripening (Manriquez et al., 2006). Induction of ADH isozymes in response to hypoxic stress is commonly reported for various plant tissues, including ‘Hass’ avocado fruit (El-Mir et al., 2001) but no data has been reported on the changes of anaerobic enzymes (PDC, LDH, ADH) and relative