Functional property enhancement of walnut flower melanin by lysine modification: Structural characterization, stability, and bioactivity studies

This study utilized an ultrasound-assisted alkaline extraction and acid precipitation approach to isolate WFM, which was then modified with Lysine to produce Lysine-modified WFM (L-WFM). The experimental results demonstrated that the maximum extraction yield of WFM reached 16.13 % under optimized conditions: 0.80 mol/L NaOH, 82 W ultrasonic power, 60 min ultrasonic time, 1:25 (<i>w</i>/<i>v</i>) solid-to-liquid ratio, and 75 °C ultrasonic temperature. Lysine modification induced a 3 nm blue shift in the UV-vis absorption maximum of WFM, transformed its morphology from irregular aggregates to smooth crystalline flakes, reduced thermal stability, and significantly increased the color value of WFM. Notably, compared to WFM, L-WFM exhibited a significant increase in color value, along with markedly improved solubility, thermal, light, and pH stability. Additionally, its antioxidant and antimicrobial activities were also significantly enhanced. This study provides a theoretical basis for improving the functional properties of WFM. <b>Keywords:</b> Walnut flower; Melanin; Lysine modification; Physicochemical properties; Structural characterization.