Extraction method influenced physical, aroma, and antioxidant profiles of Shiikuwasha (Citrus depressa Hayata) pulp essential oil

Essential oil of Shiikuwasha (Citrus depressa Hayata) was obtained by extracting the non-polar phase of its pulp mixture by using cold centrifugation or steam distillation. The extraction methods produced pulp essential oil with different physicochemical and functional properties, including color, optical rotation, aroma components, and antioxidant activity. Heating treatment in steam distillation enhanced the amount of oil extracted by nearly double of that produced by cold centrifugation (6.99 versus 3.64% w/w, respectively). Moreover, compared with cold centrifugation, steam distillation produced an increased amount and diversity of volatile aroma compounds, as determined by GC-flame ionization detection/mass spectrometry (GC-FID/MS) and GC-olfactometry (GC-O). However, the main aroma components of these oils were monoterpene hydrocarbons limonene (57.36-59.78%) and gamma-terpinene (24.88-25.14%), followed by moderate amounts of p-cymene, terpinolene, alpha-pinene, beta-pinene, myrcene, and alpha-thujene (1-2% each) that compositionally differ from other known citrus essential oils, which have less limonene and more gamma-terpinene. Compared with steam distillation, cold centrifugation demonstrated superior 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity and preserved more phenolic content, as demonstrated by the occurrence of orange-yellow phytopigments in the oil. Additionally, the aroma components gamma-terpinene and terpinolene contributed to the overall antioxidant activity of the pulp oils.