Processing of value-added products from underutilised oilseeds: African oil bean (Pentaclethra macrophylla Benth) and melon (Citrullus colocynthis) seeds

African oil bean (AOB) and melon seeds are edible oil seeds found in Nigeria, sub-Saharan regions and other West African countries. Both seeds are underutilised and information on their potential benefits is scarce. Also, there is a hunger challenge and a high rate of malnutrition in these regions where AOB and melon seeds are found. Therefore, identifying routes for the exploitation of those seeds could aid at handling challenges such as food insecurity and poverty in developing countries of Africa, where AOB and melon seeds are indigenous. The main aim of this research was to assess the chemical properties of AOB and melon seeds, evaluate appropriate methods for protein extraction and build our knowledge on the relationship between the extraction method, the protein structure and its functionality. Lipid and protein were the predominant components of AOB and melon seeds. In AOB, lipid accounted for 42% (w/w) and protein for 26% (w/w), whereas in melon, the respective values were 53% (w/w) for lipids and 32% (w/w) for protein. A control extraction method was used to extract the protein in the defatted oil seeds at pH 11, 50 ˚C and for 30 min. Ultrasound-assisted protocol was also adopted and investigated at different durations and intensities while the temperature and pH were kept constant. The protein extracts were precipitated at their isoelectric points and protein isolates were neutralised and freeze dried. The amino acid profile of the protein isolates was investigated, as well as the protein secondary structure by FTIR and surface hydrophobicity to assess any conformational changes of proteins during extraction. Also, the functional properties of AOB and melon seed protein isolates were determined. From the control extraction method, AOB seeds had 32.5 % (w/w) recovery yield while melon seeds had 48.2% w/w recovery yield. The use of ultrasonication for 30 min and 10 μm intensity led to increased recovery yields compared to the control extraction method, from 32.5 to 41.8% w/w for AOB and more than 100% for melon seeds. All nine essential amino acids were found in AOB protein isolates, although tryptophan was in trace amounts (0.4 g/ 100g). In melon seed protein isolates, eight of the essential amino acids were present and tryptophan was not detected. The amino acid profile of AOB and melon isolates indicate a hydrophobic nature of the extracted proteins. Both protein isolates had satisfactory emulsifying properties. It was noted that the amino acid composition of the proteins and the extraction conditions influenced the secondary structure and functional properties of the protein isolates. In conclusion, this research can serve as a baseline for the efficient valorisation of AOB and melon seeds as sources of protein for the fortification and formulation of food products.