Metabolomic analyses of plasma and liver of mice fed with immature Citrus tumida peel

Supplementing food with functional small molecules has been shown to prevent diseases and improve the quality of life, especially in elderly people. Citrus fruits and citrus fruit-products are popular food supplements across the world. In this study, we focused on a Japanese citrus fruit, Citrus tumida hort. ex Tanaka (C. tumida), and elucidated the effects of supplementation of the peels of immature C. tumida (PIC) on food intake, body and fat tissue weights, and metabolic profiles of plasma and liver in mice. Supplementation with 5% (w/w) PIC for 4 weeks significantly suppressed body weight gain and decreased adipose tissue weight, including that of the epididymal, perirenal, and subcutaneous fats. Metabolome analyses using capillary electrophoresis time-of-flight mass spectrometry showed that the level of 2-hydroxyvaleric acid was reduced in the blood plasma of mice fed with PIC. Supplementation with PIC significantly elevated the levels of dipeptides (Thr-Asp, Ser-Glu, and Ala-Ala), glucuronic acid (and/or galacturonic acid-2), and S-methylglutathione, and significantly reduced the levels of betaine aldehyde in the liver. In conclusion, PIC supplementation affects the metabolism of fatty acids, pectin, glutathione, and choline. Our study demonstrates the potential beneficial effects of PIC, especially in metabolic syndrome and obesity. PIC may be developed as a functional food and used in the treatment of these diseases. Nutritional and metabolome studies are effective in studying the effects of specific dietary supplements and will contribute to the development of functional foods.