Extraction and Characterization of Bioactive Compounds from Diverse Marine Microalgae and Their Potential Antioxidant Activities.

This study compared free and bound phenolic compounds in various marine microalgae species. It assessed total phenolic content (TPC), total flavonoid content (TFC) and total condensed tannin content (TCT) and their antioxidant capacities using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS⋅+ ) radical cation-based assay and ferric ion reducing antioxidant power assay. Liquid chromatography-mass spectrometry (LC-MS) was also employed to characterize the phenolic profiling. Results showed that free phenolic compounds ranged from 1.83-6.45 mg GAE/g d. w., while bound phenolic compounds ranged from 4.03-26.03 mg GAE/g d. w., indicating significant differences. These variations were consistent across assays, highlining unique profiles in different species. A total 10 phenolics were found in these seven microalgae, including 1 phenolic acid, 6 flavonoids, 1 other polyphenol and 2 lignans. 4'-O-methyl-(-)-epigallocatechin 7-O-glucuronide and chrysoeriol 7-O-glucoside in microalgae were firstly reported in microalgal samples. These findings have implications for future applications in industries.

Bioaccessibility and bioactivities of phenolic compounds from microalgae during in vitro digestion and colonic fermentation.

Microalgae are a developing novel source of carbohydrates, phenolic compounds, carotenoids and proteins. In this study, in vitro digestion and colonic fermentation were conducted to examine the total phenolic content and potential antioxidant activity of four microalgal species (Chlorella sp., Spirulina sp., Dunaliella sp., and Isochrysis sp.). The bioaccessibility of targeted phenolic compounds and the short-chain fatty acid (SCFA) production were also estimated. Particularly, Spirulina sp. exhibited the highest total phenolic content (TPC) and free radical scavenging (2,2'-diphenyl-1-picrylhydrazyl, DPPH) capacity after gastrointestinal digestion of 7.93 mg gallic acid equivalents (GAE) per g and 2.35 mg Trolox equivalents (TE) per g. Meanwhile, it had the highest total flavonoid content (TFC) of 1.07 quercetin equivalents (QE) per g after 8 h of colonic fermentation. Dunaliella sp. and Isochrysis sp. showed comparable ferric reducing antioxidant power (FRAP) of 4.96 and 4.45 mg QE per g after 4 h of faecal reaction, respectively. p-hydroxybenzoic and caffeic acid almost completely decomposed after the intestine and fermented in the colon with the gut microflora. In Dunaliella sp. and Isochrysis sp., these phenolic acids were found in the colonic fermented residual, probably due to the presence of dietary fibre and the interactions with other components. All four species reached the highest values of SCFA production after 16 h, except Spirulina sp., which displayed the most increased total SCFA production after 8 h of fermentation. It is proposed that Spirulina sp. could be more beneficial to gut health.

The complex of whey protein and pectin: Interactions, functional properties and applications in food colloidal systems - A review.

This review describes the mechanism of non-covalent/covalent interaction of whey protein-pectin (WPP) complexes, including electrostatic interaction, steric hindrance, cross-linking and Maillard reaction. The interaction between whey protein and pectin determines the form of the complex in the system, i.e. co-dissolution, precipitation, separation, complex coacervation and compounding. The interaction of WPP is affected by environmental conditions and its own properties, including several factors such as pH, polymer concentration and ratio, temperature, and ionic strength. In addition, the functional properties of WPP complexes are discussed through illustrative examples. The complexes with good emulsification, heat stability, gelling properties and biological activity have promising application prospects. WPP complexes have been widely studied for application in food colloidal systems, including protein beverages, delivery systems for bioactive substances, fat substitutes and food preservation films/coatings. The understanding of the interaction and functional properties of WPP complexes provides theoretical support for the improvement and design of new food colloidal systems.