Semi-dynamic in vitro digestion of honey chlorella vulgaris reveals biochemical and structural insights during gastro-intestinal transit

Concerns about current food systems have prompted increased exploration of sustainable alternative protein sources, such as microalgae. This study investigated honey Chlorella vulgaris, a chlorophyll-deficient mutant, distinguished by its consumer-friendly honey colour, milder flavour and improved texture. To facilitate the nutritional transition towards this source, a standardised in vitro semi-dynamic INFOGEST digestion model was employed to analyse the digestive behaviour of C. vulgaris, focusing on the biochemical and structural changes during in vitro digestion. Gastric digestion was conducted over 67.5 min with dynamic fluid addition and gastric emptying. Results indicated slow gastric digestion of C. vulgaris due to the initially low pepsin activity and low protein solubility. Significant protein breakdown commenced when the pH dropped to 3.5. By the end of the gastric phase, 11.8 % of the protein and 3.0 % of free amine groups were released, generating new peptides of 0.3–1 kDa. Followed by 2 h static intestinal digestion, some cell structures remained intact, indicating a barrier to nutrient release. Pancreatic enzymes caused substantial protein hydrolysis, generating a higher fraction of 0.1–0.3 kDa peptides, with a notable release of essential amino acids as well as phenolic compounds. This study highlighted that protein insolubility and the cell wall structure of C. vulgaris may impede enzyme effectiveness, leading to a reduced protein breakdown. Furthermore, introduction of processing steps may enhance bioaccessibility in microalgae-derived foods, thereby contributing to the development of nutritional and sustainable food productions.