| Carambola(Averrhoa carambola L.) is thinly peeled, crisp and angulate, very easy to damage and highly perishable. Therefore, it is of great significance to study the postharvest preservation technology and its effect on the fruit quality of carambola.In this study, the preservation effects of different kinds of film packing, fresh-keeping agents and low temperature on the fruit quality, the changes of sugar acid content, and cell structure of ‘Xiangmi’ carambola fruit were investigated. Meanwhile, the effects of different preservation treatments and related enzyme activity on the types of organic acid metabolism were also analyzed. The main results were as follows:1. At room temperature(25°C), the weight loss rate of packed carambolafruit significantly decreased, and the storage period was greatly extended. The microporous anti-fog film bag could effectively decrease the weight loss rate and condensation phenomenon in the bag; shrinkable wrap could reduce the interaction between the individual but the operation was complex; PE packaging could reduce the water loss of the fruit, but its poor permeability could promote fruit yellowing or even cause disease. In general, the microporous anti-fog film bag and shrinkable wrap were the best, which could extend the storage time by 5 days at room temperature.The pulp cell structure gradually disintegrated as the carambola fruit ripened and deteriorated.2. Both1-MCP and ethylene absorbent could extend the storage time of carambola. The effect of 1-MCP treatment on reducing ethylene release rate and inhibiting fruit softening was significantly better than that of ethylene absorbent. The ethylene absorbent could only delay fruit yellowing but showed little effect on the control of fruit softening. The treatment of 1-MCP combining with microporous anti-fog film bag could prolong the shelf life of carambola fruit from 7 days to 16 days.3. Cold storage(7°C) could significantly inhibit thephysiological metabolism of the fruit, including color index, firmness, ethylene production and respiration rate. Cold storage could significantly prolong the preservation period to 40 days while the fruit could be stored for only 2 weeks at room temperature.4.The sugar components of carambola were glucose, fructose and sucrose, mainly as monosaccharides. During storage at room temperature and low temperature, the variation trend of fructose and glucose content was consistent; the fructose/glucose ratio close to 1:1, and both were 2 to 3 times of sucrose content.5. An HPLC analysis method for the determination of oxalic acid, malic acid, ascorbic acid and citric acid of carambola was established. The optimized chromatographic conditions were: the column was Agilent Eclipse Plus C18, the mobile phase was 99.0% 0.015 mol·L-1potassium bicarbonate(p H=3), 1.0% of HPLC grade methanol, the injection volume was 15 μL, the injection time was 10 min, the flow rate was 0.8 m L·min-1, and the column temperature was 25°C. DAD detection wavelength was 215 nm.During the storage, the main acid components of carambola were malic acid and oxalic acid, followed by citric acid and ascorbic acid. Malic acid and oxalic acid accounted for 90% of the organic acid in carambola. Based on the gradual decrement trend of oxalic acid content and low activity of oxalate oxidase during preharvest and postharvest, we speculated that oxalic acid might exist as a metabolic end product in the fruit. The content of malic acid was accumulated before harvest, and significantly correlated with titrable acid and respiration rate, it was suggested that the type of organic acid metabolism of carambola fruit was malic acid metabolism. |
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