Comparison of analytical methods for the quality control of a new formulation containing soy extract and melatonin

Abstract

Three analytical methods have been developed and compared for the quality control of a new formulation (Soymen GN(R) capsules) containing soy extract and melatonin for the treatment of menopausal symptoms. The first method is based on MEKC with diode-array detection, using a mixture of basic carbonate buffer (95%) and methanol (5%), containing 55 mM SDS, as the BGE. The second method is an HPLC method with UV detection at 260 nm. The third method is an HPLC method coupled to amperometric detection which is carried out at an oxidation potential of +0.8 V. In both HPLC systems, the chromatographic separation is obtained on an RP C18 column using a mixture of ACN and an acidic phosphate buffer (25:75 v/v) as the mobile phase. A feasible pretreatment procedure with a methanol/water mixture has been implemented to achieve the quantitative extraction of the main soy isoflavones and of melatonin from the capsules. The results obtained with the three methods are in good agreement with each other and satisfactory in terms of linearity (r(2) >0.9996), precision (RSD <5.4%) and accuracy (recovery >97%). Thus, each of the three analytical methods seems to be suitable for the simultaneous analysis of the main soy isoflavones and melatonin in the new commercial formulation.

Quality control and determination of melatonin in food supplements

“…Few studies have developed and validated analytical methods for determination of melatonin in food supplements (3 20 mg/tablet or capsule) (Costantini & Paoli, 1998;Saracino et al, 2008). However, our method presents higher precision and repeatability in standard solution (< 1%) than the abovementioned methods (1-4.3%) under the same conditions.…”

“…Recently, the European Commission has authorized two health claims for food containing melatonin (Regulation (EU) 432/2012) regarding alleviation of jetlag (0.5 mg/day) and as an aid to sleep (1 mg/day) based on the positive scientific opinion of the European Food Safety Authority (European Food Safety Authority 2010; 2011). However, the Food and Drug Administration (FDA) has not evaluated the claims for melatonin supplements (Food and Drug Administration 2002;2006;2008). Instead, a disclaimer on the label declaring "these statements have not been evaluated by the FDA" is mandatory.…”

“…Despite the European Commission clearly establishing a minimum melatonin content per quantified portion to fulfil the authorized health claims (Regulation (EU) 432/2012), literature focused on determination of melatonin in food supplements for quality control is highly scarce and was published before this regulation entered into force (Costantini & Paoli, 1998;Saracino et al, 2008).…”

“…The main limitation of melatonin determination in foods and plants is its low concentration (pg to µg per g or mL), which make necessary the use of sophisticated and highly sensitive detectors. However, as far as we know, only a few studies have developed and validated simple analytical methods (capillary electrophoresis, thin-layer Page 7 of 27 A c c e p t e d M a n u s c r i 7 chromatography, LC with UV detector and LC with amperometric detector) for the determination of melatonin in food supplements at higher concentrations (3 20 mg/tablet or capsule) (Costantini & Paoli, 1998;Saracino et al, 2008).…”

“…Page 9 of 27 A c c e p t e d M a n u s c r i 9 Melatonin was extracted from supplements following the method of Saracino et al (2008) with slight modifications. A total of 3 tablets, 3 capsules or 2 sachets of each supplement were used for each analysis.…”