Evaluation of phlorotannin bioaccessibility and antioxidant capacity stability of a safe and sustainable brown seaweed extract: role of age-related digestion changes and matrix composition

Addressing age-related health challenges through improved nutrition is increasingly important as the global population ages. Concurrently, sustainable food systems are focusing on low-impact ingredients, such as brown seaweed, which require minimal resources and offer promising health benefits. However, concerns about heavy metal accumulation in brown seaweed highlight the challenges associated with its safe use. After confirming the safety of a sustainable Durvillaea incurvata extract, containing phlorotannins from trimers to octamers and mannitol, through an 80% reduction in heavy metals, this study evaluated the bioaccessibility of phlorotannins and the stability of antioxidant capacity during in vitro gastrointestinal digestion in both standard and older adult models. It also compared these results with two commercially available seaweed products: micronized capsules and rehydrated salad. Crude extract exhibited the highest phlorotannin level before digestion for both Folin-Ciocalteu (22.5 mg PhE/g dw) and DMBA (0.8 mg PhE/g dw) assays. Phlorotannin bioaccessibility indices reached 1005% and 332% in the standard and older adult models, respectively, when total soluble polyphenol values were used for measurement. The DMBA assay confirmed an increase in phlorotannin content after digestion, likely due to the release of compounds previously bound to the food matrix; however, the differences observed between the two digestion models did not exhibit the same magnitude of change. The antioxidant capacity (DPPH assay) was highest in the micronized seaweed; however, it decreased after digestion. Conversely, the digested crude extract retained its antioxidant capacity under older adult conditions. These results support the use of brown seaweed extracts as safe and effective ingredients in foods for older adults.