Solvent extraction of oil from three cultivars of Nigerian mango seed kernel: Process modeling, GA - optimization, nonlinear kinetics and comparative characterization

Abstract

This work investigated the physicochemical and instrumental characterization of oil optimally extracted from three species of mango kernels (Alphonso, Glenn and Fazli) by highlighting their isolated qualities. The effect of temperature (40-58 °C), dosage (0.0033-0.0267 g/mL) and time (0-360 min) was varied at the course of experiment. It was observed that while temperature increment had a corresponding positive impact on mango kernel oil extraction efficiency, the influence of dosage produced a quadratic effect, reaching maximum efficiency at 0.017 g/mL, beyond which an undesirable decline was recorded. Analysis of variance (ANOVA) of process factors gave an F-value of > 80.5 for temperature, indicating that temperature was the most important parameter that influenced the extraction process, while kernel dosage having F-value < 20 was the least influential process parameter. Process optimization by response surface methodology coupled genetic algorithm (RSM-GA) gave an optimum validation yield of 13.62%, 14.7% and 16.1% for Fazli, Glenn and Alphonso, respectively, at temperature of 56.61 °C, dosage of 0.021 g/mL and extraction time of 275 min. Error function indices obtained from comparative kinetic modeling illustrated that the extraction process was best described by pseudo second order model (R2 > 0.96, Adj-R2 > 0.95). Also, Elovich kinetics highlighted the dominance of rate diffusion over washing mechanism in the extraction process. Physicochemical characterization showed that while all the mango kernel oil (MKO) species exhibited stability against oxidative rancidity, Alphonso species having an acid value of 2.74 mg KOH/g and 1.37% free fatty acid value, highlighted its superior physicochemical qualities over Fazli and Glenn mango kernel oil. GC-MS analysis portrayed the dominance of stearic and palmitic saturated fatty acids in all the three species while myristic acid was only detected in Alphonso mango kernel oil (MKO), emphasizing its application in food and cosmetics industries. X-ray florescence (XRF) demonstrated the significant presence of molybdenum (Mo) element in Glenn mango kernel oil, revealing its unique suitability for application in synthesis of special purpose industrial lubricants. For Alphonso mango kernel oil, XRF revealed that while this oil species has potential application in the production of lubricants with high detergent properties, caution must be taken in the utilization due to the presence of sulphur element in the sample.