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).