The untapped industrial crop, Cucumeropsis mannii: dry oil extraction, characterization and potential use as biodiesel feedstock and heavy metal sink

Abstract

Due to the quest to meet a basic need – food, vast potentials of numerous African crops have remained unexplored. Cucumeropsis mannii, an invaluable West African melon, is cultivated for its edible proteinous oil-rich seeds. Here, we report for the first time, its potential use for biodiesel production over an uncommon heterogeneous nanocatalyst, and for wastewater treatment. An identification of the untapped species’ seed was made, for disambiguation. Oil (CMO) was expressed from the C. mannii seeds (CMS) and characterized. The CMS was found composed of 53.5% lipids, while 46.1% of the full-fat CMS flour was recovered as vegetable oil. Transesterification experiments were performed using a specially-prepared heterogeneous nanocatalyst derived from Eobania vermiculata shells, by varying successively: methanol/oil ratio, temperature, and reaction time. Maximum biodiesel (CMOME) yield of 86.2% was achieved at catalyst concentration of 5.4%, methanol to oil molar ratio of 9:1, reaction temperature of 60 °C, after 3 h of reaction. Furthermore, part of the polyunsaturated CMO was sulphur-functionalized and utilized at different dosage levels for extraction of Ag+ from 600 to 1500 ppm simulated water. The modified CMO exhibited desirable sorption properties – sinking 100% of Ag+ from 900 ppm water, after 7-h-phase-contact at 6.9 g (20 mL)− 1 dosage. Stagewise operation (multi-staging) was found capable of improving the extraction efficiency in highly concentrated wastewater. Although CMOME conformed to EN-14214 and ASTM D-6751 standards, it had low oxidation stability; making wastewater treatment a more faithful application. Regarding the crop’s food value, residual CMS cake remained edible, even with longer shelf-life (relative to the full-fat flour) – encouraging commercial flour-defattening and consequent availability of CMO for industrial applications. Lastly, it was concluded (with some relevant recommendations) that CMO has great potentials for use as biodiesel feedstock and as heavy metal removal agent.

Flour nutritional profile, and soxhlet-extracted oil physicochemical breakdown-storage performance of white melon (Cucumeropsis mannii Naudin) seed varieties from Southeast Nigeria

“…The defatted large melon seed obtained the maximum carbohydrate content (16.26%), followed by the defatted miniature melon seed (12.36%). Overall, the approximate composition in this document competes well with previously reported data [ 2 , 7 , 9 , 21 – 23 ]. Various proximate trends have been previously reported especially for resembling defatted flour samples.…”

“…Elsewhere, varying IVs have been reported, like 132.6 g I 2 /100g for C . mannii [ 7 ], 108.33 g / 100 g for watermelon, 104.45 mg /100g for pumpkin oil [ 33 ], as well a range from 15.10 to 45.80 in five varieties of melon [ 34 ]. This specific acid value suggests the edibility of oil and its food processing suitability [ 19 ].…”

“…This would suggest that C . mannii oil will not require pretreatment before transesterification for biodiesel production [ 7 , 24 ]. Interestingly, both high flash and fire points of the different Soxhlet-extracted oils significantly differed ( p< 0.05) but not so for specific gravity ( p> 0.05).…”

“…It is a member of the Cucurbitaceae family, which includes groups of cultivars that produce seeds that have a juicy pale yellow or green flesh that tastes bitter and is commonly mistaken for Citrullus spp . (lanatus, mucosospermus , Vulgaris or colocynthis [ 5 – 7 ]. A tendril climber, white melon is a typically annual creeping herb with hairy stems and a lobed leaf plant with a fibrous and shallow root system that thrives throughout the Savannah belts of Nigeria as a subsidiary crop [ 8 ].…”

“…Seeds of C . mannii are not limited to food and medicinal purposes alone [ 10 ], but are also relevant in cosmetics [ 11 ], serving also as a potential biodiesel feedstock [ 7 , 12 ].…”