Sustainable process intensification for ferulic acid recovery from Allium cepa by-product: Ultrasound-assisted alkaline extraction and statistical optimization

In the era of the circular bioeconomy, the systematic upcycling of agro-industrial residues such as onion peels (Allium cepa) represents a sustainable frontier for recovering high-value bioactive phenolic compounds. Among them, Ferulic acid is a key phenolic precursor of vanillin (a flavoring agent) with antimicrobial and antioxidant properties, and it has widespread applications in the food and cosmetic industries. In this study, the valorization of onion peels for bioprospecting and sustainable recovery was investigated. Ferulic acid was extracted using four methods: alkaline hydrolysis, alkaline hydrolysis combined with ultrasonic-assisted extraction, DES extraction, and hydrothermal extraction with cellulase. The yields of ferulic acid obtained by these methods were compared. The ultrasonic-assisted hybrid extraction was the most efficient method. Additionally, predictive statistical modelling was conducted to enhance efficiency. In the Plackett-Burman method, key parameters affecting the yield were identified. Further RSM optimization resulted in a 2.7-fold increase in yield, achieved at 1 g substrate concentration, 2.5 M NaOH molarity, and 40 min of sonication time, with a significant R² value of 0.96. The extracted compound was successfully identified and characterized. Overall, the study demonstrates that ultrasound-assisted alkaline extraction, combined with statistical optimization, provides an effective approach for process intensification and the sustainable valorization of onion peel waste into value-added phenolic compounds.