规定方法的原理是使用乙酸乙酯从试验部分提取棒曲霉素，然后用碳酸钠水溶液分配提取物，通过使用紫外线检测器的高效液相色谱法定性和定量测定棒曲霉素含量。基于5毫升即饮苹果汁，检测限为10μg/l。

The principle of the method specified is extraction of patulin from a test portion using ethyl acetate followed by partitioning of the extract with aqueous sodium carbonate solution, qualitative and quantitative determination of the patulin content by means of high-performance liquid chromatography using an ultraviolet detector. The limit of detection is 10 μg/l, based on 5 ml of ready-to-drink apple juice.