Natural colorants from vegetable food waste: Recovery, regulatory aspects, and stability-A review

Worldwide, approaches inspired by the Circular Economy model have been increasing steadily, generating new business opportunities such as the recovery of high-added value molecules (e.g., pigments) from vegetable food waste that may be applied as food additives (e.g., colorants). Indeed, food waste is a global problem that does not seem to be decreasing, leading to economic, environmental, and social issues. Moreover, synthetic dyes have been associated with adverse effects on human health, encouraging research to explore much safer, natural, and eco-friendly pigments. This state-of-the-art review gives a brief overview of the regulatory aspects concerning food waste, Circular Economy, and natural versus synthetic colorants. We have critically reviewed the recent advances in pigment recovery from vegetable food waste bringing back the green/unconventional extraction methods. Among them, enzyme-assisted extraction as a depth feature technique is highlighted, given that it allows the recovery of pigments in a mild, selective, efficient, and sustainable way. Furthermore, the stability issue of the different natural colorants has been critically discussed in relation to the extraction and application conditions. Several and tailored stabilization methods have been described and reported for each pigment although additional research is necessary on their long-lasting stabilization and utilization in food matrices. Practical Application This review focuses on the main types of natural pigments in vegetable food waste, their legislative framework, extraction technologies and strategies to improve the stability , as well as their possible applications.