Identification and distribution of lignans in Punica granatum L. fruit endocarp, pulp, seeds, wood knots and commercial juices by GC–MS

The lignans isolariciresinol, medioresinol, matairesinol, pinoresinol, secoisolariciresinol and syringaresinol were detected and quantified for the first time in pomegranate (Punica granatum L.) and in commercial pomegranate juices by means of GC–MS. The total lignan content in the different plant parts was estimated as follows: 36.1 ± 0.3 μg/g in seeds, 17.8 ± 0.2 μg/g in wood knots, 11.2 ± 0.2 μg/g in fruit pulp, 3.3 ± 0.1 μg/g in endocarp. Secondary metabolite distribution varied greatly in the evaluated samples, with syringaresinol being the most abundant contributor in seeds (23.5 ± 0.4 μg/g) and pinoresinol in knots, pulp, endocarp and juice (8.9 ± 0.3, 7.4 ± 0.2, 3.3 ± 0.1 and 2.1 ± 0.2 μg/g, respectively). A survey on two concentrated juices and three commercial pomegranate beverages evidenced the presence of lignans in all of them, with values ranging from 0.4 ± 0.1 to 4.4 ± 0.1 μg/g. Lignans may be relevant contributors to the purported dietary beneficial properties of pomegranate juice and their considerable abundance in agro-industrial waste materials could render P. granatum by-products an inexpensive and renewable natural source of these healthy compounds.