Bioactive Phytochemicals: Sources, Production, and Delivery of Betalains, Carotenoids, Organosulfur Compounds, Phenolics, and Phytosterols

Bioactive compounds are naturally occurring food constituents with potentially health-promoting properties, although no official daily intake recommendations have currently been established for them. Among these, phytochemicals—such as betalains, carotenoids, organosulfur compounds, phenolics, and phytosterols—stand out due to their biological relevance. Interdisciplinary collaboration is crucial for advancing phytochemical research, from identifying novel sources and optimizing production to evaluating their biological functions and potential applications. This review summarizes conventional and emerging sources of these key phytochemicals, including wild edible plants, microorganisms, algae, insects, and food industry by-products, emphasizing their potential under sustainability and climate change contexts. Advances in extraction technologies and the use of green solvents are also discussed. Furthermore, genetic and agronomic strategies to enhance bioactive content are considered. The article also addresses formulation approaches focused on delivery systems to improve dispersibility, stability, and bioavailability.