Extraction Conditions Optimization of Main Organic Acids from Fruits

【Objective】This study aimed at investigating an effective extraction method of main organic acids(citric acid, tartaric acid, malic acid, succinic acid) from fruits.【Method】Using citrus, grapes and other fruits as test materials, the aqueous ethanol solution as the extraction agent, and using ultrasonic extraction method, the effect of extraction on the extraction agent(ethanol concentration, ratio of water extraction and organic acid stability, different concentrations of ethanol extraction, effect of 10% ethanol soluble extractant and the main organic acid stability and so on), extraction conditions(extraction method, ultrasonic extraction time and so on) were studied for optimization. Technical parameters for optimized extraction conditions(the detection limit, precision, repeatability, accuracy) were tested. The measuring results by using this method were compared with analytical results with the existing national standard method.【Result】The suitable method for organic acid extraction in fruits is the ethanol ultrasonic extraction method: Samples were extracted for 30 min with 10% ethanol solution in ultrasonic extractor. Then sulfuric acid solution was added, the concentration of sulfuric acid contained in solution was the same as in flow consistent solution. Finally constant volume was made with ethanol solution, then mixed and filtered. The filtrate was filtered by 0.22 μm aqueous membrane needle filter for ion chromatography analysis. All the main organic acids could be extracted completely. The main organic acids didn't change to lactic acid and acetic acid at least in 15 days when the extract was placed under natural conditions. The optimized extraction method is high precision(RSD 0.28%-1.20%), repeatability(variation coefficient of 0.236%-3.02%(n=5)) and high accuracy(recovery 88.9%-101.2%). The method of organic acids in the determination results was significantly higher than the existing national standard results.【Conclusion】The method was rapid, simple, accurate, reproducible, and suitable for the determination of the contents of main organic acid in fruits.