Pectic polysaccharides extracted from pot marigold (Calendula officinalis) industrial waste

Abstract

Residues from the essential oil and the natural pigment industry are cheap, abundant and insufficiently investigated wastes with a great valorization potential. Such underexplored biomass is derived from the pot marigold (Calendula officinalis) used industrially for lutein extraction and obtaining of essential oil. The aim of the present work was to investigate the potential of two pot marigold wastes as a source of polysaccharides: the first obtained after 1,1,1,2-tetrafluoroethane (freon R134a) extraction of marigold (F-waste), and second obtained after hydrodistillation (HD-waste). The potential of wastes as a source of polysaccharides was estimated by dilute hydrochloric acid extraction whereupon the F and HD yielded 9.81 ± 0.58% and 3.12 ± 0.24% of polysaccharides, respectively. The chemical composition, physicochemical properties and infrared spectroscopy data suggested that they were acidic pectic type polysaccharides with galacturonic acid content 632.86 ± 2.30 μg mg−1 and 617.99 ± 3.15 μg mg−1 polysaccharide, degree of methoxylation 63.7 ± 1.5% and 48.9 ± 2.5%, and degree of acetylation 3.5 ± 0.1% and 3.3 ± 0.1% for F and HD polysaccharides, respectively. The rheological properties of acid-extractable polysaccharides were investigated and it was found that F-polysaccharide yielded strong gel. The polysaccharides were investigated by differential thermal analysis and the analyses revealed that they start decomposing significantly after 230–240 °C. Consecutive fractional extraction with four extractants was performed for the first time, and information about the polysaccharide content and the different polysaccharide fractions present in the wastes was obtained. The overall polysaccharide yield of 14.35 ± 1.01% and 20.01 ± 0.56% from HD and F marigold waste respectively, suggested that marigold waste could be an alternative source of pectic polysaccharides.