Characterization of two Moroccan watermelon seeds oil varieties by three different extraction methods

Abstract

The purpose of this study is to assess and evaluate the physicochemical properties of the seed oils of two Moroccan varieties of watermelon “Citrullus lanatus” extracted by three different techniques, a mechanical process using cold press, and two chemical processes using a Soxhlet apparatus and a sonotrode ultrasound assisted extraction (UAE) using n-hexane. The total phenolic compounds (TPC) and antioxidant properties against the DPPH radicals (2,2-diphenyl-1-picrylhydrazyl) were also studied. The seed oils of both varieties of watermelon exhibited high concentrations of unsaturated fatty acids with the predominance of linoleic and oleic fatty acids. The primary sterol was β-sitosterol, and high levels of total tocopherols were observed. Ɣ-tocopherol was the predominant tocopherol in all tested oils. TheCitrullus lanatus var. lanatusvariety seeds oil exhibited the highest TPC value (89.5 ± 0.06 mg EGA/100 g; EGA: gallic acid equivalent), with 82.4 ± 0.03% DPPH free radical inhibition efficiency. Nevertheless, all tested seeds oils showed a significant amount of total phenolic compounds and a good inhibition against DPPH radicals ranging from 51.1 ± 0.1% to 84.8 ± 0.04%. In addition, the influence of the ultrasonic extraction parameters was studied using two different solvents (n-hexane and the methanol-chloroform mixture), with different particle sizes (500–300 µm), duration (10 and 20 minutes), cycle (1–0.5), amplitude (80–100%) and solvent/seed ratios (1:5 and 1:10), and the seed roasting parameter was also studied. The oil yield was mainly affected by the extraction solvent, then the solvent/seed ratio and the duration, respectively.