Effect of different mild-washing conditions on walnut protein concentrate composition and properties

The agro-food system must transition to a more sustainable paradigm to meet the demand. Shifting to plant protein and reducing food waste are key levers. However, valorizing side-stream plant protein into sustainable and functional ingredients remains challenging. In this study, washing processes were implemented to obtain sustainable walnut protein concentrates from walnut flour. The impact of solvents and temperature was studied on the protein yield and purity. To better understand the protein enrichment mechanism, emphasis was put on the fate of non-protein components during these processes. Two-step processes resulted in concentrates with protein purity between 56.6 and 65.0% with nitrogen yield between 77.0 and 97.7%. The protein enrichment was positively correlated with non-protein compound elimination. The latter was impacted by solvent polarity, temperature, and washing sequence. Thus, the use of hot 96% ethanol to remove lipids, up to 89.2%, and of water at pH 5 to eliminate carbohydrates, phenolic compounds, and phytic acid seemed fundamental. The addition of a third step in an EtOH-EtOH-H 2 O process resulted in higher protein purity (70%). The amino acid composition was not changed by the washing strategy. However, oil holding capacity (increased by 86%), the colour, and the in vitro digestibility (reduction by 50%) were impacted according to the washing sequence, raising questions about the compromise between protein purity and quality. To conclude, washing processes were proven to be efficient for walnut protein concentrate production, paving the way for the use of tree nuts as an alternative sustainable protein ingredient.