Extraction and phytochemical profile of garlic metabolites and its use as alternative source of cycteine and glutathione

Abstract

Compounds that contain sulphur are known as thiols or sulfhydryl compounds. Cysteine and glutathione (GSH) which are sulphur-containing antioxidants are classified in this group. Apart being powerful antioxidants, they are widely used in food, pharmaceutical and cosmetic industries. Production of cysteine and GSH can be achieved through several methods such as chemical synthesis, enzymatic catalysis, microbial fermentation, and genetic/metabolic engineering. Although cysteine and GSH are abundantly present in plants but less was focused on extracting these compounds from plant sources. Therefore, this study intended to explore the potential of garlic as an alternative source for both compounds. Garlic was chosen based on the pungent smell produced by garlic which is correlated to high sulphur contents. Waterbased extraction assisted by sonication was used to obtain cysteine and GSH. This method was considered as it was simple, safe and cost effective for extractingthiols. Optimization of process conditions was performed using One Factor at a Time (OFAT) design. Cysteine and GSH were quantified as thiols/sulfhydryl compoundsusingEllman's reagent method. Global metabolites analysis approach using gas chromatography mass spectrometry (GCMS)and principal component analysis (PCA)was applied to study the effect of process conditions on the metabolites as a means to achieve optimal cysteine and GSH production. With respect to OFAT study, the optimum concentration of extracted thiols (0.1700 mM) was obtained at garlic concentration of 100 %w/v with 100 % amplitude of sonicator for 15s of extraction time and process temperature at 25 ºC. Based on GCMS analysis, it showed metabolites present in garlic which are amino acids and its derivatives, sugars, sugar alcohols, and organic acids. PCA successfully grouped garlic samples based on sample preparation and solvent extraction used, however it was unable to discriminate the garlic sample based on different process conditions since most of the metabolites presented are conserved. In conclusion, garlic is found to be a potential source for cysteine and GSH production. Future studies are warranted to further investigate in more detail the optimal process conditions for extracting thiols from garlic.