Comparative study on the composition, antioxidant and antibacterial abilities of essential oils from different varieties of grapefruit peel
Citrus maxima belongs to the subfamily Citrus of the Rutaceae family, and has been cultivated in China for over 4000 years. Its main production areas include Guangxi, Guangdong, Chongqing, Fujian, Hunan, etc. The main varieties include Shatian pomelo, Wendan pomelo, and Guanxi honey pomelo, with an annual output of over 5 million tons. Yuzu peel is a byproduct of grapefruit, accounting for 40% to 55% of the total weight of grapefruit. It contains various active substances such as essential oil, pectin, limonin, dietary fiber, etc. It has antioxidant, antibacterial, anti-tumor, blood pressure lowering, and blood sugar lowering effects. It can be used to treat cardiovascular diseases, relieve phlegm and cough, and nourish blood and spleen. Developing and utilizing over 2 million tons of pomelo peel produced annually in our country can not only avoid environmental pollution, but also produce high-value products such as pomelo peel essential oil, pectin, dietary fiber, flavonoids, and limonin. Yuzu peel essential oil can be prepared by methods such as cold pressing, supercritical CO2 extraction, steam distillation, and ultrasound assisted extraction. The antibacterial performance of D-limonene in grapefruit peel essential oil has been reported in literature. Zhang et al. found in their study that Shatian pomelo and Xiangyou, which have the highest content of D-limonene, have higher antibacterial activity than Wendan pomelo and Liangping pomelo, which have lower content of D-limonene. Lan phi et al. also found a correlation between the antibacterial activity of Vietnamese grapefruit peel essential oil and the content of D-limonene in their research.
Although the antibacterial ability of limonene in grapefruit peel essential oil has been proven, other terpenoid compounds in grapefruit peel essential oil also have potential contributions to antioxidant and antibacterial abilities. At present, there is no systematic study on the contribution of various components in grapefruit peel essential oil to antibacterial and antioxidant effects, so it is not possible to classify and utilize grapefruit peel essential oils with different compositions. The purpose of this study is to determine the composition of essential oils from different varieties of grapefruit peel, compare the differences in essential oil composition, and analyze the components with significant antioxidant and bacteriostatic effects in grapefruit peel essential oils based on the results of antibacterial and antioxidant experiments, in order to provide technical support for the classification and development of grapefruit peel essential oils.

This article uses steam distillation to extract 12 types of grapefruit peel essential oils, and compares the essential oil components using GC-MS analysis. A total of 35 chemical components were identified, mainly terpenes and terpene oxides. The highest content of terpenes is D-limonene, followed by β – laurene, α – pinene, and β – pinene. Terpene oxides mainly include linalool, geraniol, neryl alcohol, and neryl acetate. Through antioxidant and antibacterial testing experiments, combined with PCA and hierarchical clustering analysis, it was determined that the components with the most antioxidant and antibacterial effects were D-limonene, citral, and linalool, respectively. Caryophyllene, geraniol, and α – carvacrol had certain antioxidant and antibacterial abilities.
In recent decades, plant essential oils have attracted much attention due to their natural pharmacological effects such as antioxidant, antibacterial, anti-tumor, and anti-inflammatory properties, as well as their pollution-free nature. However, the composition of plant essential oils from different sources varies greatly, and the differences in composition will be reflected in the differences in product activity. The main component of essential oils from citrus species in the Rutaceae family, such as orange peel and grapefruit peel, is D-limonene. The antibacterial and antioxidant effects of limonene have been extensively documented, and the differences in the activity of essential oils from different varieties of citrus species are influenced by the type and content of non limonene components. This study screened out citral, linalool, and a series of compounds with antibacterial and antioxidant activities such as caryophyllene, geraniol, and α – carvacrol. However, the types of citrus peel essential oils involved are limited, and the antibacterial experiments target a limited number of microbial species. The activity tests are also limited to antibacterial and antioxidant activities. The next step of research will expand the range of varieties, form a small database of citrus essential oil components, and extend activity testing to common drug activities.