Betalains from vegetable peels: Extraction methods, stability, and applications as natural food colorants

Betalains are hydrophilic pigments naturally present in a limited number of plants and fungi. In addition to providing pigmentation, ranging from yellow to red, they show potential for replacing artificial food colorings. Betalains can be obtained from agri-food waste like vegetable peels through conventional and emerging extraction methods; however, they are susceptible to chemical changes due to various degradation factors, such as the presence of oxygen, light, and increased temperature. In this context, encapsulation can be used as a strategy to stabilize and reduce the pigment degradation rate for later industrial application in processed foods. This study reviews data from the last five years on the production and relevance of valuing agri-food waste, in addition to research carried out on betalains obtained from vegetable peels, such as extraction methods, encapsulation as a method of controlling stability and applications as colorant in food matrices, highlighting news insights for the field of pigments from plant sources. This review shows that encapsulation techniques using mixtures of wall materials offer superior protection than isolated materials. Despite advances in applicability, gaps still persist regarding stability in food matrices, especially on an industrial scale. However, future investigations should focus on filling the gaps regarding the maintenance of the properties of betalains for application in food industries as natural food coloring based on the precepts of circular economy and sustainable technology.