Abstract: This study was designed in order to scientifically evaluate the health benefits of Porphyra haitanensis harvested at different times and its phenolic compounds. The bioaccessibility and antioxidant activities of phenolic compounds in P. haitanensis harvested at different growth stages (early, middle and late) were evaluated after being cooked and subjected to in vitro oral and gastrointestinal digestion and the modulatory effect of cooked P. haitanensis on the gut microbiota in vitro was investigated. The results showed that the bioaccessibility of total polyphenols and total flavonoids were 104.80%–117.03% and 35.21%–59.60% after in vitro digestion, respectively, and the content and release after digestion of polyphenols in P. haitanensis at the early growth stage were higher than those at the middle and late stages. In vitro colonic fermentation of P. haitanensis could promote the production of propionic acid and n-butyric acid, and effectively inhibit the production of isobutyric acid and isovaleric acid. According to 16S rRNA gene sequencing, P. haitanensis could promote the growth of Bacteroidetes, Megamonas, Lactobacillus and other beneficial bacteria. In conclusion, P. haitanensis is a good source of polyphenols, and polyphenols in P. haitanensis still have good antioxidant activity and bioaccessibility after digestion in gastrointestinal tract. P. haitanensis has a significant regulatory effect on the gut microbiota. Young P. haitanensis seems to be a better choice for consumers.

Key words: Porphyra haitanensis; harvest time; in vitro digestion; phenolic substances; bioaccessibility; gut microbiota