Microalgae are acknowledged for their potential as a sustainable protein source in diets. Our research explores various microalgae species, evaluating their potential value as protein sources. This study aims to evaluate the protein quality determined by amino acid composition and protein digestibility followed by a peptidomic analysis of algal digesta.
In-vitro digestion analysis was conducted to analyse protein digestibility in 8 microalgae species sourced from the Australian National Algae Culture Collection, CSIRO. Peptides from the digested and undigested fractions were analysed using data-dependent acquisition (DDA) on a SCIEX ZenoTOF 7600 and identified using Peaks Studio.
To determine the quality of proteins in microalgae species, the DIAAS values (In vitro digestible indispensable amino acid score) were measured based on the in vitro digestibility of amino acids and reference requirement values for adults recommended by FAO. Our results indicated that not only was the protein digestibility in some of the species high, their DIAAS values suggest that they can be considered as source of quality protein. Peptidomic analysis of distinct fractions of peptides derived from in vitro digestibility assays suggested most of the peptides in the digested fraction were either single amino acids or small peptides with the mass range of 246.1-668.4 (m/z) and peptide length range between 2 to 6 amino acids. As expected, a higher number of unique peptides were identified in the pellet fractions considered as undigested peptides.
Several novel bioactive peptides with potential anti-inflammatory properties were identified in microalgal peptide digesta. Digestion-resistant peptides were characterized, revealing a predominant association with photosynthetic proteins (GO:0015979). Using in-silico methods, few putative allergenic proteins were identified in the undigested fraction. In conclusion, mass spectrometry analysis of digested and undigested peptides in an in-vitro model can provide further insights into their properties, including potential health benefits and possible allergenicity.