Recovery of crude polysaccharides from peel and mesocarp of pomegranate: the Wonderful and Laffan cultivars

Natural polysaccharides from plants are, biocompatible, and water soluble compounds that shown antioxidant, anti-bacterial, anti-virus, activities making them suitable for pharmaceutical and biomedical uses. Even if the tannins of pomegranate (Punica granatum L.) have been extensively studied and the fruit is well known in folk medicine of several countries, to date only few reports are available on the polysaccharides of this fruit. A galactomannan of pomegranate with mw of 110 kDa, a β-1→3 galactopyranose backbone and β-D mannopyranose and α-D mannopyranose as side chains, has shown in vivo anticancer activity in mice[1]. Moreover no data has been published on the polysaccharides of mesocarp, usually the main by-product of the juice production. Our work is focused to isolate crude polysaccharides from two pomegranate cvs (Laffan and Wonderful) applying different temperatures and extractive steps. The fruits from Laffan were collected in Syria 2011, the Wonderful ones from Grosseto, Italy in 2013. The extractive method was optimized in terms of yield and time consuming applying different steps, extraction times and water/dried material ratios. The final procedure was as follows: 5g of lyophilized was soaked in 200 mL of distilled water then decocted according to methods applied in the Chinese traditional medicine and recently proposed for pomegranate peel [2] . The extract was cooled, centrifuged and the solid residue was re-extracted once again using the same process. The supernatants were combined, concentrated (about 1/2 of initial volume) then added of cold ethanol and kept overnight at 4 ºC to induce the precipitation of the crude polysaccharides. The precipitate was then re-dissolved in distilled water and added again with ethanol to remove the solution containing tannins and other impurities[2]. The optimum experimental parameters were as follows: extraction temperature 100 °C, extraction time 60 min, water/raw material ratio 1g /40 mL, and only one extractive step. Under these conditions the percentage yields range from 8% to 10% of crude polysaccharide on dried mesocarp, while a minor content was obtained for the dried peel with values from 4.5% to 5%. As expected, the % of polysaccharides recovered from peel has shown an higher variability (RSD from 11% to 25%) mainly related to the non homogeneous thickness of this material. A very good reproducibility (RSD below 3,5%) of the extractive method was obtained for the mesocarp. These preliminary data help to improve the knowledge of these typical by-products of pomegranate fruit having an high content of crude polysaccharides that could be used as natural gelling products in food chemistry but also to evaluate their health properties to date not investigated