Plant-based meat alternatives of high quality and digestibility could be a way to reduce meat consumption and, consequently, the environmental impact. Many plant-based proteins are deficient in specific indispensable amino acids, but by combining different sources, complete protein-mixes can be produced that meet human body requirements. In the present work, the protein quality of beef burgers, known to be an excellent source of protein, was compared to the protein quality of highly transformed veggie burgers made from soy as the sole plant source (soy burgers) and from combined protein sources (pea-faba burgers). The different burgers were digested according to the INFOGEST in vitro digestion protocol. After digestion, total protein digestibility was determined, either based on total nitrogen (Kjeldahl) analysis, or after acid hydrolysis based on total amino groups (o-phthalaldehyde method) or total amino acids (TAA; by HPLC). The digestibility of individual amino acids was also determined, and the digestible indispensable amino acid score (DIAAS) was calculated based on in vitro digestibility. The impact of texturising and grilling on in vitro protein digestibility and the digestible indispensable amino acid ratio (DIAAR) was evaluated at the level of the ingredients and the finished products. As expected, the grilled beef burger had the highest in vitro DIAAS values (Leu 124 %), and grilled soy protein-based burger reached in vitro DIAAS values that could be rated as a good protein source (SAA 94 %), according to the Food and Agriculture Organization. The texturing process did not significantly affect the total protein digestibility of the ingredients. However, grilling led to a decrease in digestibility and DIAAR of the pea-faba burger (P <0.05), which was not observed in the soy burger, but led to an increase in DIAAR in the beef burger (P <0.005).
