Valorization of kaffir lime peel through extraction of essential oil and process optimization for phenolic compounds

BACKGROUND: Kaffir lime peel is a food waste which contains good aromatic essential oil and phenolic compounds. Extraction of essential oil from kaffir lime peel is conducted to obtain the extract for using as biological ingredients in various products. After essential oil extraction, kaffir lime peel residue has been remained, and it can be considered as another by-product. Therefore, it is interesting to evaluate the contents of phenolic compounds in the kaffir lime peel residue to understand the possibility of valorization of kaffir lime peel wastes at a practical level. In this study, extraction of essential oil from fresh kaffir lime peel was conducted by hydrodistillation, and phenolic compounds were extracted from the kaffir lime peel residue by process optimization of an ethanolic extraction method. RESULTS: Through hydrodistillation and gas chromatography-mass spectrometry analysis, essential oil of kaffir lime peel contained terpinene-4-ol (19%), beta-pinene (15.8%) and d-limonene (15.6%) as the major volatile compounds. In extraction of phenolic compounds from kaffir lime peel residue, all investigated parameters had significant linear effects on the yield of phenolic compounds, but no interaction effects among the extraction parameters were observed. Optimal conditions for the extraction were 120 min, 60 ? and 1:20 g mL(-1), resulting in phenolic compounds of 8.6 mg GAE g(-1) sample. The phenolic compound yield extracted from fresh kaffir lime peel at the optimal conditions was close to that extracted from the kaffir lime peel residue. CONCLUSIONS: Through hydrodistillation, only essential oil was extracted from kaffir lime peel, while phenolic compounds are still remained in the solid residue of the kaffir lime peel at high concentration as the fresh sample. Results of this study are useful for maximizing extraction yield of phenolic compounds from kaffir lime peel. The results of this study also revealed the possibility of maximizing the utilization of kaffir lime peel wastes at the practical stage through extraction of both essential oils and phenolic compounds.(c) 2023 Society of Chemical Industry (SCI).