Quality Mapping of Tigernut Oil and the Extraction Efficiency Between n-Hexane and Petroleum Ether Solvents

Abstract

Edible Tigernut (Cyperus esculentus) oil samples were separately extracted using n-hexane and petroleum ether solvents. This study aimed at comparing the extraction efficiencies of both solvents and the quality and colour of oil produced with a view for large scale industrial application.  The quality parameters tested included moisture content, saponification value (SV), iodine value (IV), peroxy value (PV), free fatty acid content (FFA), unsaponifiable matter, total fatty matter (TFM), titre (^oC), impurity, and colour.. Results showed that n-hexane extraction efficiency was 86% and significantly higher (p<0.05) than that of petroleum ether which gave 75%. n-Hexane produced 17.10g or 19.01±0.11cm³ of oil yield from 20g of powdered tigernut seed, while petroleum ether produced 15.05g or 16.72±0.12 cm³ of oil from 20g of powdered tigernut seed. The mean SG of oil samples was 0.8917±0.011 at 40^oC. The appearance of oil extracted with n-hexane was brighter and golden yellow, when compared to that of pet ether which gave a brownish-yellow tint. The colour on Lovibond Scale (R*Y*B*N) using 5¹/₄” cell, showed n-hexane extracted oil to be 0.9R, 10Y, 0B, 0N, while the pet ether extracted oil gave 1.2R 12Y, 0.5B, 0N. There was no significant difference in moisture content of both oil samples. The mean values of chemical quality parameters for both oil samples gave saponification value 209.33±0.58, iodine value 91.33± 0.58 , peroxide value 1.06±0.01, ester value 208.33±1.16, moisture content 0.23± 0.021%, free fatty acid content 0.24±0.0058%, impurity content 0.013±0.0058%, unsaponifiable matter 0.11±0.01% and total fatty matter 95.03±0.027%. GC-MS analysis gave seven major fatty acids of the oil samples after conversion to fatty acid methyl esters (FAMEs). Five of these fatty acids were saturated (SFA) and include  lauric acid (1.32±0.08%); myristic acid (31±1.0%); palmitic acid (14.6±0.1%); stearic acid (3.37±0.15%); crotonic acid (0.53±0.068%), giving a total SFA content of 44.77 ±0.29%. The other two were unsaturated fatty acids (UFA), and included oleic acid (45.9±1.83%) and linoleic acid (9.37±0.15%), giving a total of (55.17±0.76%) UFA content. Therefore, the ratio of UFA:SFA gave 1.18±0.0058, suggesting that the oil may be categorized as an ω-6 edible oil. The quality parameters tested, established the quality mapping for quality control, standardization and regulatory activities of future tigernut oil industry in Nigeria.

Keywords: Tigernut,  Oil quality, extraction efficiency, fatty acid, ω-6 edible oil.