Studies On The Metabolism Of Fruit Organic Acids In Postharvest Citrus

To inrestigate the metabolism of fruit organic acids in postharvest citrus,changes of organic acids, reducing carbohydrates in the fruits of Newall navel orange ( Citrus sinensis Osbeck cv. Newhall) , Hongjiang cheng (C. sinensis Osbeck cv. HongJing) , HB pummelo(C, grandis Osbeck. Hirado Buntan ) during storage were studied by capillary electrophoresis. The main results were as follows:1. Capillary electrophoresis methods for the determination of organic acids and reducing carbohydrates from citrus fruit flesh, which reducing carbohydrates can be determined within 25 min and organic acids can be determined within 11 rain, were established with good reproducibility and sensitivity. The parameters for separating and determining reducing carbohydrates are the following with an uncoated silica capillary of 75/μm I.D and 50 cm in total length (40 cm of efficient length): running buffer is 75 mmol/L of borax (pH10.5), the segregation voltage is 15 kV and a UV detection wave-length is 214 nm. The experimental conditions for organic acids are: running buffer is 50 mmol/L sodium phosphate and 0.3 mmol/L CTAB (pH 5.75), the segregation voltage is 20 kV, the capillary temperature is at 25℃and the detection wavelength was 200 nm.2. When the fruits of the three cultivars were stored at low temperature, the storing time of HB pummelo fruits is the longest, then Newall navel orange fruits, and Hongjiang cheng fruits are the least.3. Contents of organic acids and reducing carbohydrates of fruits in Newall navel orange, Hongjiang cheng and HB pummelo were analyzed in this study when the fruits were stored at low temperature 4℃. The results showed that the main organic acid was citric acid in fruits of the three citrus cultivars during storage. In the fruits of Newall navel orange and Hongjiang cheng, Contents of citric acid and malic acid showed a decreasing trend in the whole period of storage, while the cis-aconitate and fumaric acid, located downstream of citric acid in the tficarboxylic acid cycle, had the reverse trends of citric acid. However, the pyruvic acid was increased at first, and then declined in the late storage time. The changing model of organic acid in fruits of Newall navel orange and Hongjiang cheng were similar except that the time of significant change was different. The concentration acute change of organic acid in fruit of Newall navel orange fruit was from November 19th, 2005 to December 11th, while between December 27th, 2005 and January 11th, 2006 in Hongjiang cheng fruit.4. After storing 49 days, the content of organic acids were high in HB pummelo ,and during the middle storage, the citric acid and malic acid in HB pummelo had a significant accumulation peak, which was different from other two cultivars. However, cis-aconitic acid, fumaric acid and pyruvic acid in HB pummelo had decreasing trend.