Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2010
Publication Date: 8/1/2010
Citation: Tsuchida, H., Kozuke, N., Han Gyeong, P., Choisuk, H., Levin, C.E., Friedman, M. 2010. Low-temperature Storage of Cucumbers Induces Changes in the Organic Acid Content and in Citrate Synthase Activity. Postharvest Biology and Technology. 58:129-134. Interpretive Summary: The cucumber (cucurbits) is an important fruit vegetable belonging to the family Cucurbitaceae. Cucumbers contain approximately 95% water, 3.6% carbohydrates, and 0.65% protein, and are low in calories (150 kcal per Kg). They are a good source of the following nutrients (in mg per Kg): pantothenic acid (B5) (0.026); vitamin C (0.28); magnesium (1.3). Cucumbers are among a number of tropical and subtropical crops that are sensitive to above-freezing cool temperatures. Low temperature storage of cucumbers may induce damage associated with chilling injury resulting in compositional as well as in morphological (structural) and microbiological changes. Using radio labeling techniques, gas chromatography, and enzyme assays, we observed in the present collaborative study carried out in Japan and Korea, changes in the distribution of organic acids and reduction in the activity of the enzyme citrate synthase in cucumber tissues stored at 1 °C and 20 °C for up to 12 days. The results of the present study suggest that increased synthesis of alanine and pyruvic acid and reduced activity of citrate synthase could serve as biomarkers of stress-induced changes during storage of chilled cucumbers and possibly other fruits and vegetables.
Technical Abstract: To elucidate the cause of reported pyruvate accumulation in chilled stored cucumbers (Cucumis sativus L.) cv. ‘Toppugurin’, we have examined differences in the extent of incorporation of acetate-1,2-14C into the tricarboxylic acid (TCA) cycle and the specific activity of the enzyme citrate synthase between healthy and chilling-injured cucumber tissues stored in the dark for 0, 3, 6 and 12 days at 1 °C and 20 °C. Radioactive tracing, gas chromatography, and enzyme analysis suggest that the incorporation of acetate into citrate, the distribution of organic acids in the tricarboxylic acid cycle, and the specific activity of citrate synthase in the cold-storage (chilling-injured) cucumber tissues differed from those in the healthy tissues. The observed decrease in citrate synthase activity may be the cause of the observed increase in pyruvate accumulation in the chilling injured cucumber fruit tissue compared to tissues stored at 20 °C. The results also suggest that the increased formation of pyruvate and reduced activity of citrate synthase during cold storage observed in the present study could serve as indicators (biomarkers) of stress-induced changes in chilled cucumbers. Possible mechanisms of the described effects are discussed.