Valorization of Java citronella (Cymbopogon winterianus Jowitt) distillation waste as a potential source of phenolics/antioxidant: influence of extraction solvents

Solid residues obtained after essential oil extraction from Cymbopogon winterianus Jowitt (Java citronella) was explored as a potential source of phenolics/antioxidant. Both the non-distilled plant materials and their solid residues were extracted with Soxhlet extraction method using solvents of various polarity viz. petroleum ether, chloroform, ethyl acetate, acetone, ethanol, methanol, water and various combination of (50% and 75%) of methanol, ethanol, and acetone in water. Different antioxidant assays like 2,2-diphenyl-1- picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), superoxide anion (SO) radical scavenging assay, ferric-reducing antioxidant power (FRAP) and iron chelating ability along with total phenol (TPC) and flavonoid content (TFC) was measured to evaluate the extract. Compared to distilled materials, the non-distilled plant materials had significantly higher TPC/TFC content and also exhibited higher antioxidant activities. 50% aqueous methanol showed the highest extractive yield, whereas 75% aqueous methanol exhibited the highest TPC and TFC content. The 50% or 75% aqueous methanolic extract also exhibited the highest DPPH, ABTS and SO scavenging activity and ferric-reducing antioxidant power activity. However, ethyl acetate and 75% aqueous acetone extract of non-distilled and distilled plant materials, respectively showed the highest iron chelating activity. The half maximal effective concentration (IC₅₀ = µg/mL) for DPPH, ABTS, SO and metal chelating ability in non-distilled plant extract ranged from 64-387, 92-761, 285-870, and 164-924, respectively, and corresponding value of distilled materials ranged from 144-865, 239-792, 361-833 and 374-867, respectively. The EC₅₀ (µg/mL) for FRAP assay ranged from 118-840 and 151-952 for non-distilled and distilled materials, respectively. The findings of this study indicate the potential of these by-products as a natural antioxidants source.