Advancing sustainable practices based on UV-C radiation for valorising downgraded date fruit residues from date syrup production

Date fruit pomace from syrup production represent a significant by-product with potential for valorization. This study investigated the physicochemical and functional properties of residues generated through microwave-assisted (MWR), ultrasound-assisted (USR), and water bath (WBR) extraction methods. Additionally, the dates pomaces remaining after green extractions (MWR, USR and WBR) were irradiated with ultraviolet C (UV-C) (5, 10, 20 and 40 min). The effects of these UV-C treatments on soluble carbohydrates, polyphenol profile, and antioxidant capacity were thoroughly examined. Microwave-assisted extraction retained the highest amounts of insoluble dietary fiber (24.31 g/100 g) and total dietary fiber (29.22 g/100 g). The ratio of insoluble to soluble dietary fiber was the closest to the optimum (3:1) in USR (2.96), compared to WBR (2.85) and MWR (4.95). Carbohydrate content was highest in WBR (50.23 g/100 g), followed by MWR (44.43 g/100 g) and USR (34.32 g/100 g), and remained largely unaffected under UV-C treatment. Regarding polyphenol profile, the UV-C irradiation of date syrup residues for 20 min optimally enhanced these compounds, with MWR yielding the highest content, followed by WBR and USR. Total polyphenol content assessed using both the Fast Blue and Folin-Ciocalteu methods, significantly increased after UV-C treatment. While ferric reducing antioxidant power and oxygen radical absorbance capacity remained relatively unchanged. However, the half maximal effective concentration required to inhibit 50 % of the 2,2-diphenyl-1-picrylhydrazyl radical was augmented. Summarizing, date syrup pomace is a valuable source of dietary fiber and polyphenols, and UV-C irradiation appears to be a promising method for preserving and enhancing their nutritional and functional properties, offering potential for the development of value-added ingredients from date processing waste, and contributing to the economic and environmental sustainability of the date industry.