The purpose of this paper was to study the extraction conditions of hemp proteins from undelipidated press-cakes. The effects of different hydration conditions on protein recovery yield and polypeptide profile were evaluated: pH (2 to 12), ionic strength (0 to 500 mM NaCl) and press-cake/liquid weight ratio (2% to 22%). pH was the most impacting factor. At acidic pH (2 to 7) the extraction yields were low and quite constant (<7%), corresponding mainly to hemp albumins solubilization. The extraction of globulins started to increase significantly from pH 8, with protein extraction yield varying from 8.3% at pH 8 to 67.1% at pH 12 for a 10% press-cake/liquid weight ratio. The addition of NaCl in press-cake suspensions did not increase the total nitrogen content in aqueous extracts at alkaline pH while the lowest press-cake/liquid weight ratios (5% to 10%) were revealed optimal regarding protein recovery rate. The intense coloration observed on the aqueous extracts above pH 8 was assigned to solubilization and oxidation of phenolic compounds whose concentration increased about sevenfolds from pH 2 to 12. At the highest applied pH (11 to 12), the formation of covalent complexes between phenolic compounds and some hemp polypeptides was hypothesized. Aqueous extraction at strong alkaline pH (>9) without salt addition and respecting a 10% press-cake/liquid weight ratio should be retained to optimize protein extraction yield. However, further purification steps are required to evaluate the nutritional, organoleptic, and techno-functional properties of hemp proteins extracted in such conditions. PRACTICAL APPLICATION: The traditional extraction process of hemp proteins by alkaline solubilization and isoelectric precipitation, mostly from delipidated hemp press-cake, leads to limited quantity and poor solubility of extracted proteins, and data related to extraction conditions are insufficiently available to optimize this process. This article aims to find optimal hydration conditions (pH, ionic strength, press-cake to liquid ratio) for protein extraction from undelipidated hemp press-cake, allowing high protein recovery and preserving protein quality. The results obtained represent very useful data for developing an economically viable and sustainable extraction process of proteins from raw hemp press-cake.
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