A novel process line for the valorization of industrial spent coffee grounds through coffee roasting technology and ultrasonic‐assisted extraction

Abstract

BACKGROUND:The main by-product of the coffee industry is spent coffee grounds (SCG). To the best of our knowledge, this is the first occasion where industrial SCG has been used to build a batch-valorization line combining barrel coffee roasters as an innovative drying process and ultrasound-assisted extraction technology under the biorefinery concept, seeking to extract chlorogenic acids (CGA).RESULTS: A Probat Sample Barrel Roaster were used to determine the optimal temperature, volume flow of fan, and time for a novel drying method. Drying optimization was carried out in order to reach 5.0% moisture content, reduce water activity and maximize total CGA content. Optimal conditions of 140 °C, 160.0 m 3 h −1 and 11.43 min for temperature, volume flow of fan, and time, respectively, were obtained with a desirability of 70%. Likewise, the optimal temperature, power and frequency settings for an ultrasonic extraction procedure of CGA from dried SCG were evaluated. To maximize the total CGA content, the ultrasonic technique was optimized. Temperature 50 °C, frequency 37 kHz and power 100 W with a desirability of 80% were necessary for optimality. The study was completed with a kinetic analysis using a second-order rate model, Peleg's kinetic model and the phenomenological model. CONCLUSION: Industrial coffee by-products can be processed and valorizing using barrel coffee roasters as a novel technique. For process design, the kinetic parameters of ultrasound-assisted extraction are a helpful tool. A new mathematical model is presented that takes into account the impact of changing temperature on the ultrasonic process.