The Composition of Volatile Aroma Components, Flavanones, and Polymethoxylated Flavones in Shiikuwasha (Citrus depressa Hayata) Peels of Different Cultivation Lines

Citrus peels are important sources of various pleasant aroma compounds and valuable bioactive substances. To investigate differences in the composition and content of Shiikuwasha (Citrus depressa Hayata) peels from different cultivation lines, the composition of volatile aroma components, flavanones, and polymethoxylated flavones (PMFs) in four Shiikuwasha cultivation lines was examined. The composition of volatile aroma components in cold-pressed extracts of Shiikuwasha peels was analyzed using gas chromatography–flame ionization detection and gas chromatography–mass spectrophotometry. The extracts contained mainly monoterpene hydrocarbons (93.40–97.25%), including limonene (46.52–68.26%) and γ-terpinene (21.48–30.52%). Differences in the composition of volatile aroma compounds in the Shiikuwasha cultivation lines were revealed using principal component analysis. Additionally, the composition of flavanones and PMFs was determined using high-performance liquid chromatography methods. Neohesperidin (96.58%) was the predominant flavanone in 'Izumi kugani' peel, while the other peels had high hesperidin contents (89.26–98.66%). Moreover, the PMFs of Shiikuwasha peels were composed of nobiletin (56.74–64.77%) and tangeretin (23.17–34.70%).