Application of modern extraction methods for determining toxic phytochemical compounds contained in Solanum plants

Abstract

The Solanum genus is among the most diverse and valuable in terms of agricultural utility and vegetable crops. This study was directed at the characterization of toxic metabolites contained in Solanum retroflexum and Solanum mauritianum following extraction by aqueous two phase extraction (ATPE), microwave assisted extraction (MAE) and pressurized hot water extraction (PHWE) with the aid of UHPLC-qTOF-MS. The application of qTOF-MS offered unprecedented sensitivity for thorough identification of similar metabolites such as solanelagnin, solanine, solamargine, solasonine and solasodine following ATPE. Furthermore, the application of ATPE in the presence of precipitating agents in a form of kosmotropes and chaotropes enabled simultaneous extraction of multiple glycoalkaloids in a single step. The ATPE technique was also observed to be a versatile technique which saw it being compatible with PHWE and MAE. In particular, the application of microwave assisted aqueous two-phase extraction (MA-ATPE) was quantitatively shown to be a better extractant of solasonine and solamargine compared to MAE and MAE+ATPE. Additionally, the synergy of microwaves and salting-out in the ‘one-pot’ MA-ATPE technique was a contributing factor for enhanced extraction of glycoalkaloids at shorter extraction periods. Multivariate chemometric studies were designed using Design Expert 11 for optimizing the extraction of solasodine (m/z 414 → 396) and solanine (m/z 868 → 722) based on MRM quantification in MA-ATPE, ATPE and PHWE-ATPE. Comparison of ATPE and PHWE-ATPE for the extraction of solasodine from Solanum mauritianum indicated that ATPE was a better extractor of solasodine by a factor of approximately 1.5. The effect of temperature in PHWE-ATPE was shown to be insignificant (p > 0.05) and could account for the lower extraction of solasodine compared to ATPE. Furthermore, the effect of mass of plant powder during ATPE was a statistically significant (P < 0.05) parameter behind the enhanced extraction of solasodine. Quantification studies based on MRM transition showed that the kosmotrope-Na2CO3 was a better extractant than the chaotrope-NaCl for solanine in MA-ATPE and solasodine in ATPE and PHWE-ATPE. This observation, herein, was due to the greater negative charge density of the divalent carbonate ion from Na2CO3, which was pivotal in salting-out of the analyte (solanine or solasodine) through the formation of strong hydrogen bonds among water molecules surrounding the solute. As a prototype, ATPE and MA-ATPE could be quick, green purification and enrichment methods for phytochemicals with strong pharmaceutical relevance, which could meet the insatiable appetite for affordable medicines in the market.