Chitosan/Alginate Polyelectrolyte Complexes (PECs) for Bioactive Peptide (BAP) Delivery

Short bioactive peptides (BAPs) have gained significant traction given their potential health benefits, particularly, to aid in mitigating hypertension and diabetes. Hence, their potential application as functional food ingredients, supplements, or nutraceuticals, has been recognised, though not yet realised. However, BAPs are highly susceptible to degradation and instability when considering aspects of the product development process, and the most critical concern remains their susceptibility to hydrolysis in the gastrointestinal tract during digestion that compromises their bioaccessibility and bioavailability. One promising strategy to address this limitation is to encapsulate BAPs in a suitable encapsulation vehicle.

Polyelectrolyte complexes (PECs) obtained by electrostatic self-assembly of oppositely charged chitosan (CS) and alginate (ALG) represent a simple to prepare, sustainable and versatile biopolymer platform for bioactive compounds association and oral delivery. CS+ALG PECs protect against acid, salt hydrolysis, and proteases degradation. However, key underpinning factors such as the role of charge ratio (nˉ/n+) that can contribute to the PEC formation, stability and delivery, need further investigation.

This thesis focuses on studying CS+ALG PECs for the gastrointestinal delivery of BAPs derived from fish, with emphasis in understanding the role of the complexation charge ratio (nˉ/n+). The CS (Mw 111 kDa, degree of acetylation 10%) and two distinct ALG (Mw 21 kDa; M/G 1.4, and Mw 8 kDa; M/G 5.1), were selected to prepare PECs at varying (nˉ/n+). Then their biophysical characteristics were investigated using dynamic light scattering (DLS), small angle X-ray scattering (SAXS), and micro-viscosimetry measurements. The selected PECs (based on size/Rh and stability/z-potential) were then loaded with the BAPs, and the encapsulation efficiency was quantified using HPLC-UV.