A techno-economic perspective on a microwave extraction process for efficient protein recovery from agri-food wastes

Different agri-food wastes (brewers spent grain (BSG), spent coffee ground (SCG) and kale stems) have been proposed as excellent sources of protein-enriched extracts with an antioxidant capacity. The optimization of the microwave-assisted hydrothermal and alkali extraction has been compared in this study. From a technical and economic point of view, the extraction of BSG under optimal conditions (110 degrees C, 10 min and 0.5 M NaOH) provided the best extract with a content of 14.6 kg protein/100 kg BSG (dry matter), 13.8 g/L of total sugars and an antioxidant activity (DPPH method) of 17.1 mg trolox equivalents (TE)/g BSG. This extract had the lowest production cost (29.9 (sic)/kg) and a minimum selling price of 51.7 (sic)/kg, estimated for an extraction pilot plant of 15 kg/h of BSG. The microwave-assisted hydrothermal extraction of kale stems, a novel waste in the biorefinery context, also provides bioactive and green extracts of commercial interest. There is a need for specific research studies related to biorefining of agri-food wastes to produce proteins for food, contributing to the development of a future sustainable and climate-neutral agriculture. The proposed techno-economic assessment represents an important advance in research and scaling-up of microwave-assisted extraction processes for protein recovery from agri-food wastes.