Leaf protein concentrate from paunch grass and green waste: A technoeconomic analysis and lifecycle assessment

Abstract

The global supply of food and feed protein needs to double during the first half of the 21st century. At present, food and feed protein is produced by livestock and arable crop farming. Further expansion of this protein production model is unsustainable in many countries due to overallocated water resources, limited availability and accessibility of new farmlands, and the environmental impacts of widespread fertiliser and fossil fuel use in agriculture. Alternative sources of food and feed protein are therefore needed to meet growing demand. One potential source of protein is leaf protein concentrate (LPC) manufactured from negative value paunch grass (PG) and leafy green waste (GW). The chemical compositions PG and GW have therefore been determined for the first time in New Zealand. Their protein contents (15.2 to 16.2 DM%) are comparable to those of alfalfa and ryegrass, making them suitable LPC feedstocks. The optimal manufacturing method uses two passes through a screw press with intermediary maceration to extract the PG and GW leaf proteins into a liquor; the liquor is then acidified with hydrochloric acid and the protein coagulated by steam injection (85°C, 30 seconds), to achieve 45.9 to 62.0 mass percent protein recovery. The industrial-scale manufacture of leaf protein concentrate from these waste materials is technologically and financially viable when it is co-sited with a meat processing facility or rendering plant, and the fibre fraction is treated as a valuable co-product instead of a waste stream. The LPC has a crude protein content (~37 DM%) and essential amino acid profile that is comparable to other plant protein products used for animal feed. Its Global Warming Potential (2094 kg CO- e / M- LPC) is relatively high when compared with those of other animal feed protein sources; the Blue Water Footprint (39.3 m³ H₂O / MT LPC) is relatively low. Both impacts are within the range of protein sources already supplied to the animal feed industry. The fibre co-product has great potential; it could be used as a bulking agent for composting processes, a feedstock for anaerobic digestion, and a fuel for process heat. Further work in understanding the drying, extrusion, and palletisation properties of the LPC is needed for industrial-scale production and commercialisation.