Optimizing protein recovery from plant substrate using ultrafiltration: A case study on wheatgrass

Abstract

Providing the world's population with valuable food and proteins is considered as one of the greatest challenges of the upcoming decade. In this study, a process to recover nitrogen/protein concentrates from wheatgrass using a cascaded ultrafiltration was investigated. First, washing of wheatgrass during a mechanical extraction was examined with a ratio up to 1:2 (press cake/washing fluid, w/w). This was followed by a statistical investigation (full factorial experimental design) on the influences of substrate storage conditions (SSC), pre-shredding (PS) and washing conditions (WC) on the protein content of the resulting fraction, expressed by a nitrogen recovery rate (NRR). Washing of wheatgrass during the mechanical extraction was found to increase NRR by up to 29%–67.8% at a 1:2 ratio (1:0–46.0%, 1:0.5–53.0%, 1:1–58.0%). Significant effects (p-value <0.05) were found in the resulting crude juice for the variation of SSC between fresh and frozen/thawed wheatgrass (NRR 80.5%/62.8%) and for washing/non-washing during the mechanical extraction (NRR 76.1%/67.2%). These significant influences were detected in almost all subsequent fractions, whereas no significant effect was found for the influence of pre-shredding (p-value >0.05). An optimal process consisting of processing freshly harvested wheatgrass and a washing ratio of 1:2 during mechanical extraction led to a protein-rich fraction by ultrafiltration with a NRR of 34.4%. This NRR is comparable to recovery rates achieved with established substrates and processes. The protein-rich fraction can meet the daily requirements of protein quantities and macro minerals such as potassium, magnesium and phosphorous, providing more than 100% of the recommended intake. It was noted that 41.6% of the nitrogen in wheatgrass fell to by-product streams that need to be utilized to increase economic potential (biorefinery).