Colored avocado (Persea americana Mill.) seed extract using a natural deep eutectic solvent for potential sustainable food coloring applications: towards a circular bioeconomy

Abstract

Avocado (Persea americana Mill.) production and consumption are rapidly increasing worldwide, with the global yield expected to reach 12 million tons by 2030. This growth generates substantial amounts of agro-industrial residues, mainly seeds and peels, which can pose environmental issues but also represent a rich source of bioactive compounds. Valorizing these byproducts through cascade biorefineries and green processing methods supports the sustainable production of high value-added bioproducts and fosters a circular bioeconomy. This study explores the extraction of natural colorants from avocado seeds as potential eco-friendly substitutes for synthetic orange-reddish food colorants. Colored avocado seed extracts (CASEs) from Fuerte and Hass cultivars were produced using hot distilled water, 70% ethanol (reflux), and glycerol : sodium acetate (Gly : NaOAc, 3 : 1) natural deep eutectic solvent (NADES). Prior to extraction, the seed paste was exposed to air for 35 min to enable polyphenol oxidase-mediated color development. Aqueous and ethanolic extractions yielded dried powders, and the Gly : NaOAc (3 : 1) NADES produced a stable, ready-to-use liquid CASE/NADES with high recoveries (88.6% Hass and 88.2% Fuerte), calculated as the mass of the final liquid system relative to the initial dry seed mass. CASEs showed maximum absorbance at 480 nm and tartrazine-equivalent quantification. The CASE/Gly : NaOAc NADES formulation exhibited pH-dependent color stability across pH 3–7 and maintained chromatic integrity under varied storage and light conditions. Antioxidant capacity, expressed in µmol copper reducing equivalents (CRE) per mL, was the highest in ethanolic extracts (3980.33 for the Fuerte variety and 1980.33 for the Hass variety), followed by NADES extracts with 934.61 and 736.56 CRE per mL, respectively. The CASE/(Gly : NaOAc 3 : 1) system exhibited color intensification under basic conditions and remained stable under both light and dark storage conditions. Total phenolic content (TPC) reached 203.45 mg GAE/100 g fresh weight for the Hass variety and 171.92 mg GAE/100 g fresh weight for the Fuerte variety when extracted with the Gly : NaOAc (3 : 1) NADES. Cytotoxicity assays (MTT) on human skin fibroblasts confirmed that the CASE/(Gly : NaOAc) 3 : 1 NADES systems were non-toxic and potentially suitable as natural food-coloring alternatives. The green valorization of avocado seeds into functional colorants offers a promising route for waste reduction, sustainable bioproduct development and new industrial value chains, supporting the advancement of a resilient circular bioeconomy.