Biorefinery Approach Applied to the Valorization of Purple Corn Cobs

The increased demand for textile products and the use of synthetic dyes have contributed to making dye wastewater one of the main causes of severe pollution problems. The use of natural dyes is therefore attracting big interest among the dyeing industries. Besides this, natural pigments need to be of low cost, with implications for the extraction methods used. Recovering pigments from waste materials and proposing a biorefinery approach can be a solution, reducing total costs and increasing the total revenue, within the green economy. This work reports a biorefinery approach to recover anthocyanins by setting up a quick and cheap extraction method, starting from dried purple corn cobs, to obtain pigments used to dye natural fibers. The residues of the cobs were extracted, recovering anthocyanins for nutraceutical purposes. The exhausted residue was proposed as animal bedding, closing the loop with zero waste produced, that is, residual animal bedding is collected with food waste, producing compost and/or biogas and fertilizers. Water extraction allowed the recovery of 36.3% of anthocyanins, mainly composed of cyanidin derivatives (glycosylated and mainly monoacylated). The use of the first extract to dye fabrics gave good results in terms of color strength and fastness. The subsequent extraction with ethanol allowed the recovery of additional 33.2% of residual anthocyanins. The anthocyanin-rich extract exhibited very good anti-inflammatory activity with high nutraceutical potential. Residual exhausted ground-up cobs are recommended to be used as animal bedding since the fiber content and water retention ability were very similar to those of a homologous commercial product. Moreover, the residual anthocyanins (183 ± 15 mg 100 g–1), recalcitrant to extraction, conferred interesting properties to the proposed animal bedding.