| Essential oils have been the key natural raw material in flavor and fragrance industry since its inception (Dugo et al., 2002). Citrus essential oil, as the largest essential oil group, comprises 70% of imported oils in US (Dugo et al., 2002). Their unique sensory properties have been widely accepted and applied in beverage, confectionary, perfume, house care and other fields. However, due to relatively simple chemical composition and tremendous price differences among citrus species, unscrupulous players have been tempted to practice adulteration in citrus oils for a long time. Addition of key aromatic chemicals into low-grade stripped oil or oil fractions is one way to lower the oil cost. Extending high quality citrus oil with oil fractions from a cheaper source is also taking place on regular basis. As they become increasingly sophisticated, perpetrators are capable of making blends that are almost indistinguishable from authentic oils through conventional GC analysis. As a consequence, essential oil industry is demanding definitive, sensitive, and efficient approaches to grade commercial citrus oils and keep adulterated oil from entering the finished products. A reversed-phase HPLC method was developed for compositional study of essential oils from major citrus species (i.e., orange, mandarin, tangerine, lemon, lime, and grapefruit). Majority of the oxygenated heterocyclic components in citrus oils were identified by HPLC-MS and confirmed by previous literatures. Two hydroxylated PMFs (polymethoxyflavone) have been identified from cold pressed orange and tangerine oils for the first time. A comprehensive database of major PMF compounds is built with data collected from a large pool of industrial orange, tangerine and mandarin oil samples. Numerical ranges of PMF compounds for sample approval were extrapolated from the database. Meanwhile, principle components analysis (PCA) was carried out for sample classification. Based on the numerical limits and statistical analysis results, detailed information regarding the origin and history of oil samples can be revealed. Similar study will be performed on lemon, lime and grapefruit oil samples as well. The author is hoping this analysis procedure will be serving as a routine quality control test for authenticity evaluation and adulteration detection in citrus essential oils. |
