Analysis of physicochemical properties of cold brew Robusta and decaffeinated coffee prepared via ultrasound-assisted soaking and extraction

This study investigated the effects of ultrasound-assisted soaking and extraction on the physicochemical and flavour characteristics of cold brew Robusta and decaffeinated Arabica coffee. During soaking, ultrasound promoted the penetration of D-xylose and L-leucine into green beans, facilitating the formation of flavour-active Maillard compounds during roasting, whereas ultrasound-assisted extraction enhanced the subsequent release of these compounds into the cold brew. Ultrasound treatment significantly increased lightness while decreasing pH, droplet size, and viscosity ( p < 0.05). Thirty-two volatile compounds were identified, and their total abundance increased with ultrasound duration ( p < 0.05). D-xylose treatment elevated furfural derivatives associated with fruity and sweet aromas, whereas L-leucine treatment enhanced pyrazines responsible for roasted and nutty notes. Extended sonication mitigated the formation of undesirable intermediates such as α-dicarbonyl compounds and furans. These findings demonstrate that ultrasound-assisted soaking and extraction can enhance flavour-related chemical composition while reducing harmful Maillard reaction products in cold brew coffee.