Wheat bran and onion skin waste are agri-food by-products generated in large quantities
annually. Their valorization represents an important opportunity, linked to sustainability, for
obtaining bioactive compounds with beneficial properties. These by-products are notable for
their high content of bioactive compounds, specifically phenolic compounds, among which
quercetin and ferulic acid stand out for their antioxidant activity. The main aim of this work has
been to study the technical feasibility of a combined ultrasound-assisted extraction (UAE) /
nanofiltration (NF) process for the recovery of phenolic compounds present in wheat bran and
onion skin wastes generated as by-products in local food companies.
UAE was firstly performed for the extraction of polyphenols from wheat bran (WB) and onion
skin waste (OSW) using an acetate buffer at pH 5 and an aqueous ethanol solution (70 vol.
%) as solvents, respectively, under the optimum operating conditions. A final WB extract was
obtained with a total polyphenol content (TPC) of 3.56 ± 0.18 mg GAE/g WB and an antioxidant
activity (AA) of 7.75 ± 1.20 µmol Fe2+/g WB. An OSW extract was also obtained, with a TPC of
44.47 ± 0.83 mg GAE/g OSW, a total flavonoid concentration (TFC) of 19.22 ± 0.35 mg QE/g
OSW, and an AA of 28.38 ± 2.70 mg Trolox/g OSW. Ferulic acid is the main component of
wheat bran extract, while quercetin and its glycosylated derivatives are the main components
of onion skin extract.
Both extracts were then concentrated by nanofiltration (NF) in a high pressure stirred cell,
using a NF270 flat polyamide membrane (270 Da cut-off), under optimal operating conditions
reaching a volume concentration ratio (VCR) of 5 after 7,5 and 1,8 h for WB and OSW extracts,
respectively, with minimal loss of polyphenols in the permeates and recoveries of AA, TPC,
and TFC in the concentrates higher than 99% in all cases.
The results obtained in this study could contribute to the valorization of agri-food waste using
environmentally friendly techniques, demonstrating the potential o
