A Review on Innovative Biotechnological Approaches for the Upcycling of Citrus Fruit Waste to Obtain Value-Added Bioproducts.

The cultivation of citrus fruits has increased significantly around the globe due to rising consumer demand. The citrus fruit processing industry produces approx. 110 to 120 million tonnes of citrus fruit waste worldwide every year. This in turn contributes to landfills and environmental pollution, and poses a risk to human health and the ecosystem. Proper recycling of citrus waste helps reduce pollution and also serves as a sustainable source for the production of different bio-based products. Abundant bioactive compounds in citrus waste offer immense economic value for the production of various useful products. Moreover, bioactive compounds found in citrus wastes have various biological properties, including antioxidant, anticancer, antimutagenic, antiplatelet, cardioprotective and antiviral activities. Instead of disposing of them directly, citrus wastes can be upcycled into various value-added products, including single-cell proteins, biopolymers, pectin, biofuel, biofertilizer and bioenergy. Citrus peels serve as a cost-effective reservoir of nutraceuticals and provide an affordable dietary option for the treatment of degenerative diseases. The citrus waste, which is used as a biofertilizer and is a rich source of phenolic compounds and carotenoids, helps to extend the shelf life of food. The aim is to maintain economic viability and sustainability with the help of recent innovations in the industry. This review discusses recent advances in the valorization of citrus fruit waste and presents innovative biotechnological approaches to extract valuable bioactive compounds such as limonene, flavonoids and pectin. These compounds are used in different sectors, from the food and pharmaceutical industries to bioenergy. Techniques such as microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) are characterized by high yields and energy efficiency. Techniques for sampling, pretreatment, extraction of phytochemicals, purification and identification of citrus fruit waste are also studied. Additionally, this review highlights the environmental benefits of waste valorization as part of a circular economy approach that contributes to both economic sustainability and pollution reduction.