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

Abstract

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.

Anthocyanins from Agro-Industrial Food Waste: Geographical Approach and Methods of Recovery—A Review

“…There are widely used methods of extracting bioactive compounds from food waste, including steam distillation, solvent extraction, CO 2 extraction, and Soxhlet extraction [ 57 ]. Even though conventional organic solvent extraction techniques are easy to use, low-cost, and do not require special equipment, they have many disadvantages [ 58 ]. These disadvantages include the restricted type and a large amount of solvent required for extraction.…”

“…Furthermore, it is not expensive, and most importantly, it is not toxic and does not cause bioactive compounds to undergo significant chemical changes, maintaining their biological characteristics [ 60 , 61 ]. The main disadvantage of this method is that the solvent is non-polar, so this technique is more suitable for extracting non-polar pigments, such as carotenoids or chlorophylls, rather than polar ones as betalains and anthocyanins [ 58 ]. However, in the case of anthocyanins, a co-solvent is used to promote the extraction of polar compounds.…”

“…Microwave absorption excites molecules to upper rotational levels, dissipating this excess energy to the medium in the form of heat. This method relies on rapid heating by microwave radiation, which causes the plant cell walls to break down as the cell structure expands [ 58 ]. As a result, the technique is based on focused or non-focused applications on a sample of non-ionizing electromagnetic waves of frequency ranging from 300 MHz to 300 GHz [ 12 ].…”

Impacts of turmeric and its principal bioactive curcumin on human health: Pharmaceutical, medicinal, and food applications: A comprehensive review

“…The colorants are used to regain the natural color lost during processing and storage, to strengthen the weak color, to color the colorless food, and to meet consumer acceptance by hiding low quality (274). Since the additives are chemicals, their excess is harmful to health.…”

Bioactive Natural Pigments’ Extraction, Isolation, and Stability in Food Applications

“…Natural colorants derived from anthocyanins, carotenoids, and/or chlorophylls have low stability due to their sensitivity to factors such as light, pH, temperature, and oxygen, among others; therefore, these pigments may degrade during the extraction and storage processes [ 137 ]. In the food industry, there are different encapsulation processes to avoid such degradation, through which it is necessary to coat the active substance (core) with some coating material (encapsulant), thus obtaining various forms of capsules, such as films, spheres, or irregular particles, as well as various types of structures (porous, compact, amorphous, or crystalline).…”