Ultrasound treatment enhanced the functional properties of phycocyanin with phlorotannin from Ascophyllum nodosum.

Introduction: Phycocyanin offers advantageous biological effects, including immune-regulatory, anticancer, antioxidant, and anti-inflammation capabilities. While PC, as a natural pigment molecule, is different from synthetic pigment, it can be easily degradable under high temperature and light conditions. Methods: In this work, the impact of ultrasound treatment on the complex of PC and phlorotannin structural and functional characteristics was carefully investigated. The interaction between PC and phlorotannin after ultrasound treatment was studied by UV-Vis, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, fourier transform infrared (FTIR) spectroscopy. Additionally, the antioxidant potential and in vitro digestibility of the complexes were assessed. Results: The result was manifested as the UV-Vis spectrum reduction effect, fluorescence quenching effect and weak conformational change of the CD spectrum of PC. PC was identified as amorphous based on the X-ray diffraction (XRD) data and that phlorotannin was embedded into the PC matrix. The differential scanning calorimetry (DSC) results showed that ultrasound treatment and the addition of phlorotannin could improve the denaturation peak temperatures (Td) of PC to 78.7°C. In vitro digestion and free radical scavenging experiments showed that appropriate ultrasound treatment and the addition of phlorotannin were more resistant to simulated gastrointestinal conditions and could improve DPPH and ABTS+ free radical scavenging performance. Discussion: Ultrasound treatment and the addition of phlorotannin changed the structural and functional properties of PC. These results demonstrated the feasibility of ultrasound-assisted phlorotannin from A. nodosum in improving the functional properties of PC and provided a possibility for the application of PC-polyphenol complexes as functional food ingredients or as bioactive materials.

Polyphenol extracts from Ascophyllum nodosum protected sea cucumber (Apostichopus japonicas) body wall against thermal degradation during tenderization.

To retard the protein degradation during sea cucumber processing, polyphenol extracts from Ascophyllum nodosum (PhE) was used as a potential antioxidant to maintain the structural integrity of sea cucumber body wall. Accordingly, the protection effects of PhE (0, 0.5, 1.0 and 1.5 mg PhE/g SFBW) against thermal degradation of the solid fragments of body wall (SFBW) have been investigated in order to evaluate their impact on the oxidation level and structural changes. Electronic Spin Resonance results showed that PhE could significantly inhibit the occurrence of oxidation by scavenging the free radicals. The effect of PhE on chemical analysis of soluble matters in SFBW was characterized by SDS-PAGE and HPLC. Compared with thermally treated SFBW, samples with PhE presented a decrease in protein dissolution. Thermal treatment resulted in the disintegration of collagen fibrils and fibril bundles in SFBW samples, while the density of collagen fibrils was increased, and the porosity decreased in samples with PhE. The results of FTIR and intrinsic tryptophan fluorescence confirmed that the structures of SFBW were modified by PhE. Besides, the denaturing temperature and decomposition temperature were both improved with the addition of PhE. These results suggested that PhE appeared to have a positive effect on lowering oxidation and improving thermostability and structural stability of SFBW, which could provide a theoretical basis for protecting sea cucumber body wall against degradation during thermal tenderization.