Ultrasound-assisted maillard reaction: a novel strategy for debittering, flavor enhancement, and antioxidant activity improvement of walnut peptides

Walnut peptides (WP) show excellent antioxidant, anti-inflammatory, antihypertensive, and immunomodulatory activities, making them promising for functional foods and nutritional supplements. However, hydrophobic amino acids formed during enzymatic hydrolysis cause severe bitterness, limiting their application. This study investigated the debittering effect of ultrasound-assisted Maillard reaction (US-MR) on WP by applying ultrasonic pretreatment at different amplitudes followed by Maillard reaction. Results indicated that US-MR promoted WP-glucose conjugation, increased browning intensity and free amino acid content, and enhanced antioxidant activity. Treatment at 30% amplitude achieved the best performance, with the highest fluorescent compound content, the largest reduction in bitter amino acids, and abundant volatile flavors such as aldehydes, ketones, furans, and pyrazines. Sensory evaluation confirmed improved aroma, umami, and texture with significantly reduced bitterness. US-MR thus provides an effective strategy to mitigate WP bitterness and facilitate the development of high-value walnut peptide products. • Ultrasound-assisted Maillard reaction (US-MR) reduces walnut peptides' bitterness, promotes glucose conjugation, and boosts browning. • It enriches volatile flavor compounds (aldehydes, ketones, pyrazines) and improves sensory attributes. • US-MR enhances walnut peptides' antioxidant activity, offering a promising strategy for high-value product development.