Bio-waste of vegetable oil production as a source of natural phenols with antioxidant properties

The aim of the study was to determine phenolic compounds in bio-waste of vegetable oil production and to test the antioxidant/reducing properties of the waste-derived extracts. Ethanol extracts from defatted seedcakes of camelina, milk thistle, hemp, mustard, pumpkin, and sunflower were prepared, the extract composition was characterized using HPLC and MALDI MS methods. Camelina, milk thistle, hemp, mustard, and sunflower seedcakes were found to contain significant amounts of phenolic compounds (6-17 mg/g), with the most abundant phenols being phenolic acids and flavonoids. For various seedcakes, phenolic profiles were shown to differ from each other significantly. For example, in pumpkin and sunflower seedcakes, > 90% of the total mass of phenols fell at hydroxybenzoic and hydroxycinnamic acids, respectively, while in milk thistle extract, the vast majority of phenols were flavonoids. Among flavonoids, flavones/flavonols prevailed in extracts from camelina, hemp, and mustard seedcakes, whereas flavanones were the main flavonoids in milk thistle extract. All the extracts were tested for their antioxidant/reducing properties, and, except the one from pumpkin seedcake, they were found to exhibit very high reactivity in DPPH and Folin-Ciocalteu assays. Besides, all the extracts effectively deactivated NO center dot and OH center dot radicals; camelina and milk thistle extracts were also shown to decelerate biodiesel oxidation. All the extracts demonstrated good performance in green synthesis of silver nanoparticles; camelina extract, rich in flavonols, appeared to be suitable for the preparation of stable nanoparticle colloids. Thus, the above seedcakes, apparently, can be used to extract various natural antioxidants applicable in a variety of redox processes.