Citrus fruits are consumed in large quantities worldwide due to their attractive aromas and taste, as well as their high nutritional values and various health-promoting effects, which are due to their abundance of nutrients and bioactives. In addition to water, carbohydrates, vitamins, minerals, and dietary fibers are important nutrients in citrus, providing them with high nutritional values. Citrus fruits are also rich in various bioactives such as flavonoids, essential oils, carotenoids, limonoids, and synephrines, which protect from various ailments, including cancer and inflammatory, digestive, and cardiovascular diseases. The composition and content of nutrients and bioactives differ significantly among citrus varieties, fruit parts, and growth stages. To better understand the nutrient and bioactive profiles of citrus fruits and provide guidance for the utilization of high-value citrus resources, this review systematically summarizes the nutrients and bioactives in citrus fruit, including their contents, structural characteristics, and potential health benefits. We also explore the composition variation in different citrus varieties, fruits parts, and growth stages, as well as their health-promoting effects and applications.

Dietary fibers (DFs) regulate host health through various mechanisms related to their dietary sources, specific physicochemical structures, fermentability, and physiological properties in the gut. Considering the numerous types and sources of DFs and their different physicochemical and physiological properties, it is challenging yet important to establish the key mechanisms for the beneficial health effects of DFs. In this review, the types and structures of DFs from different fruits and vegetables were summarized and the effects of different processing methods on DF properties were discussed. Moreover, the impacts of DFs on gut microbial ecology, host physiology, and health were described. Understanding the complex interaction between different DFs and gut microbiota is vital for personalized nutrition. It is also important to comprehend factors influencing gut microbiota and strategies to regulate the microbiota, thereby augmenting beneficial health responses. The exploration of molecular mechanism linking DFs, gut microbiota, and host physiology may allow for the identification of effective targets to fight against major chronic diseases.

Citrus-derived flavonoids play important roles in the regulation of physiological conditions of citrus plants, including color changes of flower and fruit, flavor development, and anti-stress physiology. Moreover, citrus flavonoids possess multiple health-promoting effects in humans, and they are important ingredients for nutraceuticals and functional foods. The biosynthesis of flavonoids in citrus plants is of special significance because it determines the chemical structures and bioaccumulation of these bioactive compounds in the plants, which consequently influences their physiological functions in both citrus plants and human body. This review systematically summarizes: 1) the biosynthesis pathway of citrus-derived flavonoids, 2) the biosynthesis location and distribution of flavonoids in citrus plants, 3) the factors affecting flavonoid biosynthesis, 4) the biological significance of flavonoid biosynthesis in citrus plants, and 5) the health-promoting properties of citrus-derived flavonoids. The collation of this information provides scientific guidance for the development of healthy citrus foods and other health-promoting products containing citrus flavonoids.