Polyphenols from macroalgae: extraction, characterization, delivery systems and future exploitation

Macroalgae or seaweeds offer huge potential as a source of new ingredients and bioactives for food applications, and thus, the identification and evaluation of the most promising biomass could help us define their future applications in multiple industries. Thereby, algal biomass is rich in polyphenols, which are powerful bioactives and their extraction, purification, and characterization will help to broaden the use of these molecules as nutraceuticals and functional foods. Moreover, within this field, Pickering emulsions are emerging systems for an efficient delivery of functional ingredients, helping to protect valuable compounds during gastrointestinal digestion. Water-insoluble macroalgal polyphenols have potential as stabilizers of Pickering emulsions, however, the full potential of these compounds for this application has not been explored thoroughly to date. Each chapter of this thesis correspond to a different research objective: Chapter 1 seeks to review the recent research performed on the extraction and biological activities of polyphenols from macroalgae, as well as applications of chitosan-seaweed polyphenols Pickering emulsions. Chapter 2 aims to provide a complete analysis of the chemical composition and nutritional potential of 12 brown macroalgal samples currently commercialised in China, being the most promising macroalgal species selected for further polyphenol extraction in Chapter 3. Chapter 3 focuses on elucidating the use innovative technologies, such as ultrasound-assisted enzyme extraction (UAEE) to extract polyphenols from the brown macroalga Ascophyllum nodosum and further explore its potential antioxidant potential in vitro. Chapter 4 aims to use the purified brown macroalgal polyphenol extracts as new compounds for the stabilization of Pickering emulsions together with chitosan using layer-by-layer electrostatic deposition technology. Chapter 5 seeks to determine the effect of multiple environmental factors on the morphology, droplet size distribution, rheological properties, microstructure, physical stability, turbiscan stability index (TSI) of Pickering emulsions. Chapter 6 explores the applicability of chitosan- polyphenol Pickering emulsion systems for the delivery of β-carotene, analysing their chemical stability to heat treatments, ultraviolet irradiation, in vitro digestion and 8-week storage. Chapter 7 focuses on the generation of β-carotene loaded Pickering emulsion microcapsules via spray-drying technology, analysing also the effects of spray-drying and rehydration on the morphology, encapsulation efficiency, redispersibility and stability of the emulsions and elucidating their stabilization mechanisms. Chapter 8 provides a summary the main findings of this thesis and seeks to elucidate the significance of the results achieved in the thesis, aiming provide answers to improve the future application of macroalgae and polyphenols derived from this biomass as functional ingredients contributing to the further development and expansion of both the seaweed and the food industries.