How <i>in vitro</i> gastrointestinal digestion impacts the phenolic profile and bioactivities of North American sea buckthorn fruit and seeds

North American sea buckthorn (<i>Hippophae rhamnoides</i> L.) shows great commercial potential as a bioactive-rich fruit. The pomace and seeds of sea buckthorn fruit are rich sources of a variety of polyphenols with promising antioxidant and biological potential. However, the modification of these phenolics through the gastrointestinal tract is unknown and can significantly affect their bioactivities. Therefore, the pomace and seeds of Newfoundland cultivated sea buckthorn were subjected to <i>in vitro</i> simulated gastrointestinal (GI) digestion and their phenolic composition was monitored across oral, gastric, small and large intestine digestion. Moderate phenolic bioaccessibility was recorded for sea buckthorn pomace and seeds, with phenolic release rates of 35.34 and 44.86% after small intestinal digestion. This fraction contained a variety of proanthocyanidins, while phenolic acids and their derivatives were generally released at the earlier oral and gastric digestion. The phenolic profile of sea buckthorn digestion products was considerably different from undigested samples, reflecting on improved rate of inhibition of metabolic enzymes linked to type 2 diabetes and obesity in some cases, as well as oxidative protection to supercoiled DNA against the action of hydroxyl radicals. However, the capacity of samples to protect LDL-cholesterol from oxidative damage was decreased after digestion. These results represent an estimate of physiological effects, pending validation through <i>in vivo</i> human studies. Further research should concentrate on investigating the absorption and transport of polyphenols involved across the human gut by using relevant physiological models.