Citrus is a globally significant economic crop with the largest cultivation area and highest production yield. Currently， its processed products are still dominated by juice， canned goods， and similar items， resulting in relatively low comprehensive utilization of citrus resources. Citrus peels， pomace， physiological fruit drops， and other by-products are rich in high-value bioactive components such as pectin， flavonoids， and essential oils， which have wide applications in food， pharmaceuticals， chemical engineering， and other fields. This article reviews the status and technological bottlenecks in the citrus processing industry， systematically outlines the properties， biological activities， and advancements and limitations of traditional extraction technologies for key functional components in citrus resources. It also summarizes the technical advantages of synthetic biology in the green manufacturing of natural products， with a focus on recent progress in microbial biosynthesis of citrus flavonoids. In line with the demands for resource recycling and green， low-carbon development， synthetic biology is expected to open new pathways for obtaining high-value active ingredients from citrus， thereby promoting the industry's transition toward higher added value and sustainable development.

citrus processing  /  high-value utilization  /  flavonoids  /  synthetic biology  /  microbial cell factories