Sustainable Protein Processing of Flaxseed By-Product: Nutritional Quality and Functional Properties

Overcoming environmental, food security, and growing global population challenges requires exploring sustainable protein production. Promisingly, agro-industrial by-products emerge as alternative sources. This study hypothesizes that processing methods can significantly improve the nutritional quality and functional properties of flaxseed meal (FSM) by reducing anti-nutritional factors and enhancing protein digestibility. This study assessed the chemical and nutritional quality of FSM after oil extraction, focusing on its composition, anti-nutritional factors, in vitro protein digestibility (IVPD), and amino acid score. Different processes and processing parameters were assessed based on an experimental design. A central composite design supported evaluating the impact of conventional heating, microwave, and ultrasound on the nutritional quality of this meal. Unprocessed FSM exhibited a protein content of 39% and an IVPD of 88%. Through processing, IVPD was elevated to 95% for the conventional heating, with 87.8°C, 37 min, and pH 8.0 as the best conditions. Protein solubility of the FSM significantly improved at pH 8 and 9 (up to 98%). Thermal processing proved effective in completely inactivating phytic acid, while ultrasound reduced trypsin inhibitory activity by 50%. Lysine was the first-limiting amino acid (AAS = 86%–90%) for all processes and parameters. Processing also enhanced the functional aspects, affirming that treated FSMs represent potential protein sources for the food industry due to their high nutritional quality and viable improvement due to processing.