Quality Characteristics and Antioxidant Potential of Lemon (Citrus limon Burm. f.) Seed Oil Extracted by Different Methods

Lemon (Citrus limon Burm. f.) is one of the most widely produced and consumed fruits in the world. The seeds of lemon are generally discarded as waste. The purpose of this study was to investigate the quality characteristics and antioxidant potential of lemon seed oil obtained by four extraction methods (roasted-pressing at 170°C, RP-170; roasted-pressing at 100°C, RP-100; cold-pressing, CP; and supercritical fluid, SF). No significant differences in the viscosity, density, and refractive index were observed in the oil obtained from different methods. In the case of Hunter's value, L (lightness) and b (yellowness) values of SF were higher than those of the others. The oil obtained by the CP method exhibited higher levels of Ca (252.17 mg/kg), Cu (2.38 mg/kg), K (225.98 mg/kg), and Mo (0.47 mg/kg) than that of other methods. The highest contents of total phenols (165.90 mg/mL) and flavonoids (21.69 mg/mL) were significantly high in oil obtained by the SF method. Oleic and linoleic acids consisted of principal fatty acids, which were significantly higher in oil obtained by RP-170. Higher amounts of volatile flavor compounds, such as γ-terpinene, sabinene, and limonene, were observed in CP compared to those observed for the other methods. This study elucidates the effects of different methods of oil extraction on the composition of lemon seed oil and highlights potential applications of these benefits in the food, cosmetic, pharmaceutical, and/or fragrance industries.

Impact of lemon oil composition on formation and stability of model food and beverage emulsions

Lemon oil is a complex organic compound isolated from citrus peel, which is commonly used as a flavouring agent in beverages, foods, cosmetics, and household products. We have studied the influence of lemon oil fold (1×, 3×, 5× and 10×) on the formation and properties of oil-in-water emulsions. Initially, the composition, molecular characteristics, and physicochemical properties of the four lemon oils were established. The main constituents in single-fold lemon oil were monoterpenes (>90%), whereas the major constituents in 10-fold lemon oil were monoterpenes (≈35%), sesquiterpenes (≈14%) and oxygenates (≈33%). The density, interfacial tension, viscosity, and refractive index of the lemon oils increased as the oil fold increased (i.e., 1×<3×<5×<10×). The stability of oil-in-water emulsions produced by high pressure homogenisation was strongly influenced by lemon oil fold. The lower fold oils were highly unstable to droplet growth during storage (1×, 3×, and 5×) with the growth rate increasing with increasing storage temperature and decreasing oil fold. Droplet growth was attributed to Ostwald ripening, i.e., diffusion of lemon oil molecules from small to large droplets. The highest fold oil (10×) was stable to droplet growth, which was attributed to the presence of an appreciable fraction of constituents with very low water-solubility that inhibited droplet growth through a compositional ripening effect. This study provides important information about the relationship between lemon oil composition and its performance in emulsions suitable for use in food and beverage products.