Porphyran and oligo-porphyran originating from red algae Porphyra: Preparation, biological activities, and potential applications

• The source, structure, and preparation approaches of porphyran are summarized. • Porphyranase hydrolysis is the promising strategy to prepare oligo-porphyran. • Catalytic characteristics of different porphyranases are reviewed for the first time. • Porphyran and oligo-porphyran play excellent roles in human nutrition and health. Porphyra is one of the most economically important red algae in the world. The functional components extracted from Porphyra such as porphyrans, proteins, lipids, and minerals have strong physiological activities. Porphyran, a sulfated galactan, is composed of alternating 1,4-linked α- l -galactopyranose-6-sulfate (L6S) and 1,3-linked β- d -galactopyranose (G). Porphyran and oligo-porphyran have a series of pharmacological and biological functions, such as antioxidation, anticancer, antiaging, antiallergic, immunomodulatory, hypoglycaemic, and hypolipidemic effects. Thus, red algae Porphyra -derived porphyran and oligo-porphyran have various potential applications in food, medicine, and cosmetic fields. For better application, this review introduces and summarizes the structure and source of porphyran as well as the preparation methods, biological activities, and potential applications of porphyran and oligo-porphyran. Moreover, the future research directions and emphasis of porphyran and oligo-porphyran preparation as well as their functional activities and applications are highlighted and prospected.