A Comprehensive Review: Exploring Bioactive Compounds of Citrus Fruit Peels for Therapeutic and Industrial Applications

Citrus fruit peel has recently been highlighted as one of the major wastes and by-products of the citrus industry, which offers a plethora of health benefits and industrial uses. In addition to the common micronutrients present in the whole fruits (including carbohydrates, fibre, vitamin C, potassium, folate, calcium, thiamin, niacin, vitamin B6, phosphorus, magnesium, copper, riboflavin, and pantothenic acid), albeit in different proportions, citrus peels contain high amounts of pectin, vitamin C, and phytochemicals. The major phytochemicals present in citrus fruit peel include phenolic acids (caffeic, p-coumaric, ferulic, and sinapic acid), flavanones (naringin and hesperidin), and polymethoxylated flavones (nobiletin and tangeretin), which are important bioactive compounds. The phytochemical and therapeutic efficacies of citrus fruit waste are documented in several early studies; however, detailed information on the industrial uses of these bioactive components is limited. This article aims to highlight recent advancements in the diverse range of applications of citrus fruit peel, including its use as a natural flavouring, an essential oil, and a source of dietary fibre in preventing metabolic and infectious diseases. Moreover, this review discusses the processing methods (drying and extraction) of citrus fruit peel for industrial uses, offering insights that enhance the understanding of the importance of citrus fruit peel not only as a by-product but also as a substance of immense value to human health.