Revisiting extraction of bioactive apocarotenoids from Crocus sativus L. dry stigmas (saffron)

An ultrasound assisted extraction method is proposed for the recovery of bioactive glycosides (i.e. crocins and picrocrocin) from Crocus sativus L. dry stigmas using aqueous methanol. Response surface methodology (RSM) was employed to optimize the extraction parameters, namely, the percentage of methanol (%), the duration (min) and the duty cycles (s) of sonication. Optical microscopy, spectrophotometry and RP-HPLC-DAD were employed to follow pros and cons of the process. Additional experiments were conducted to compare recoveries with those under other agitation conditions (e.g. magnetic stirring according to ISO 3632-2 standard). The percentage of methanol, the sonication duration and duty cycles combination that can be recommended as optimum for the recovery of crocins and picrocrocin were 50%, 30 min, 0.2s and 0.44%, 30 min, 0.6s, respectively. Picrocrocin levels were not influenced dramatically under the optimum conditions for crocins extraction (11±2 instead of 12±1 mg kg(-1) dry stigmas, respectively) so that these can be considered optimum for both categories of tested compounds. Ultrasound assisted extraction speeded up further recovery of these precious apocarotenoids. Our findings for extraction conditions are useful for both industrial and analytical applications and should be considered in a forthcoming revision of the ISO 3632-2 technical standard.