The multifunctionality of plant pigments: roles, recovery from by-products and stability challenges

ABSTRACT The growing demand for natural pigments in food, cosmetic, and pharmaceutical applications is driven by increasing concerns over the safety, sustainability, and environmental impact of synthetic dyes. Natural pigments derived from plants, algae, and microbial sources offer functional and health-promoting properties but are often limited by intrinsic instability and challenges related to scalable and sustainable production. This review provides a comprehensive overview of major plant pigment groups - anthocyanins, carotenoids, chlorophylls, and betalains, with particular emphasis on their biological roles, chromatic properties, and stability characteristics focusing on the valorisation of food processing by-products and agro-industrial wastes as abundant and low-cost pigment sources within a circular bioeconomy framework. Recent advances in green and non-thermal extraction technologies, including ultrasound-, microwave-, enzyme-assisted extraction, pulsed electric fields, supercritical fluid extraction, and natural deep eutectic solvents, are critically discussed in terms of efficiency, sustainability, and applicability. In addition, current stabilization strategies, such as microencapsulation, nanoemulsions, and copigmentation, are reviewed as complementary approaches to enhance pigment functionality and application potential. Regulatory inconsistencies and consumer acceptance further shape innovation uptake. Bridging laboratory advances with industrial practice requires pilot-scale validation, techno-economic assessment, and harmonised safety standards.