Sustainable upcycling of brewers' spent grain by thermo-mechanical treatment in twin-screw extruder

Thermo-mechanical treatment of brewers' spent grain (a by-product of beer manufacturing) was successfully performed via the extrusion process. The impact of temperature (from 30 to 180 degrees C), throughput (from 1 to 5 kg/h) and screw speed (from 75 to 375 rpm) on particle size, color, chemical structure, antioxidant activity and thermal stability of resulting material, as well as correlations between particular properties, were investigated. The color of treated brewers' spent grain was strongly influenced by particle size and the extent of Maillard reactions occurring during extrusion, responsible for the browning of material. Moreover, products of these reactions, melanoidins, enhanced the antioxidant activity of brewers' spent grain, which after extrusion at 180 degrees C was increased by even 100%. Thermo mechanical treatment of brewers' spent grain at 120 and 180 degrees C increased its thermal stability investigated by thermogravimetric analysis. It was also observed that temperature treatment above 100 degrees C also led to the reduction in friction inside the extruder barrel and reduced by at least 20% specific mechanical energy required to brewers' spent grain modification, which positively affects the economic aspect of the process. The results confirm that a proper adjustment of extrusion parameters allows easy tailoring of the appearance (color, particle size distribution) and performance properties (thermal stability, antioxidant activity) of brewers' spent grain, which significantly extend applications of this cellulosic-rich waste in wood polymer composites technology. (c) 2020 Elsevier Ltd. All rights reserved.