# Conjugation of Microalgal Phenolics and Protein for Bioactivity and Bioaccessibility Enhancement

## TL;DR

This study shows that combining microalgal proteins and phenolics improves their stability, antioxidant activity, and bioaccessibility, making them more useful for food and nutraceutical products.

## Contribution

The study demonstrates that conjugation enhances the bioactivity and bioaccessibility of microalgal compounds through structural changes and chemical reactions.

## Key findings

- Conjugation significantly increased antioxidant activity by up to 644% and ACE inhibitory activity by up to 19.7%.
- The 2.5% conjugate showed the highest bioaccessibility, 2.5 times that of free phenolics.
- FTIR and NMR analyses confirmed covalent bond formation through Schiff base and Michael addition reactions.

## Abstract

Microalgae are rich in protein and phenolics, thereby having great potential for production of functional foods and nutraceuticals. However, despite featuring high nutritional value, these compounds often suffer from low stability and bioaccessibility. In this study, phenolics and protein extracted from Chlorella vulgaris were conjugated at different ratios (2.5–10%) and the structure and bioactivity of the conjugates were comprehensively characterized. The fluorescence intensity of protein decreased from 340 to 130–98 a.u. after conjugation and the UV-vis absorbance dropped from 1.6 to 0.5 a.u., which confirms the alteration of the chromophore area. The FTIR spectra revealed shifts in the C=O, N-H, and C-N bands, and the 1H NMR spectra showed the broadening of signals and appearance of new peaks, indicating covalent bond formation through the Schiff base and Michael addition reactions. Conjugation significantly increased the antioxidant activities, in terms of ABTS inhibition by 644%, 257%, and 97%, as well as the ACE inhibitory activity, by 13.5%, 17.5%, and 19.7% for the 2.5%, 5% and 10% conjugates, respectively. The 2.5% conjugate showed the highest bioaccessibility (144%), which was 2.5 times that of free phenolics. Overall, this study proves that conjugation is an effective approach to enhancing the bioactivity and bioaccessibility of microalgae-derived compounds and unravel the structure–activity relationship of conjugates. The findings can promote the valorization of microalgae for product development in the food and nutraceutical industries.