# Brewer’s Spent Yeast as a Biosorbent for the Synthetic Dye Tartrazine Yellow

## TL;DR

This study explores using brewer's spent yeast to safely stabilize and control the release of the food dye tartrazine, making it safer for use in food products.

## Contribution

The novel use of brewer’s spent yeast as a biosorbent for tartrazine under food-relevant and gastrointestinal conditions is presented.

## Key findings

- Brewer’s spent yeast showed highest adsorption of tartrazine at pH 2 and 25 °C (4.23 mg·g–1).
- Adsorption was best described by the Temkin model at pH 2 and the Dubinin–Radushkevich model at pH 7.
- Simulated gastrointestinal conditions showed lower dye desorption, indicating potential for controlled release.

## Abstract

Tartrazine is a synthetic
dye commonly used in the food
industry
to enhance the visual appeal of food products. However, its instability
under specific conditions, such as changes in pH, exposure to UV or
sunlight, or increased temperature, may lead to adverse effects, raising
concerns about its toxicity. Thus, ensuring the safety, controlled
release, and stability of these colorants in food matrices remains
a significant challenge. This study aimed to evaluate inactivated
brewer’s yeast (Saccharomyces cerevisiae) as a promising biosorbent matrix for the adsorption and stabilization
of tartrazine, thereby developing a safer, more stable delivery system
for this food additive. Unlike previous studies that focus primarily
on wastewater treatment, this work uniquely investigates tartrazine–yeast
interactions under food-relevant and simulated gastrointestinal conditions,
highlighting the yeast’s ability to stabilize the dye and control
its release. Adsorption experiments were conducted at different pH
levels (2 and 7) and temperatures (10, 25, 37, and 90 °C). Samples
of the dye alone, the yeast alone, and the dye adsorbed onto the yeast
were analyzed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric
analysis (TGA), and scanning electron microscopy (SEM). The system
comprising the yeast with the highest adsorption percentage was investigated
for its stability at various pH and temperature conditions, as well
as simulated gastrointestinal degradation. The highest adsorption
was observed at pH 2 and 25 °C (4.23 mg·g–1). The kinetic data fit a pseudo-second-order model, suggesting that
chemisorption is driven by electron-sharing or valence interactions
between the dye and the yeast surface. FTIR analysis revealed characteristic
bands of Brewer’s spent yeast related to hydroxyl groups (around
3271 cm–1), C–H stretching vibrations (1398
and 2916 cm–1), carbonyl groups (1633 cm–1), and aromatic residues (between 669 and 536 cm–1). No significant disappearance of S=O bands was observed after adsorption.
Still, shifts and the appearance of peaks indicate chemical interactions
between dye molecules and yeast cell wall components under different
pH conditions. TGA results showed an increase in the thermal stability
of the adsorbed dye, with lower mass loss than free tartrazine. Isotherm
modeling revealed that the Temkin model best described adsorption
at pH 2, indicating a decreasing interaction energy with increasing
surface coverage, whereas the Dubinin–Radushkevich model provided
the best fit at pH 7, suggesting a physical adsorption mechanism on
a porous biosorbent surface. Simulated gastrointestinal conditions
revealed lower dye desorption (2.37 mg·g–1)
from the biosorbent at pH 7 and 37 °C, indicating potential for
controlled release. This study aims to demonstrate a novel role for
residual beer yeast as a stabilizing matrix and controlled-release
system for tartrazine under simulated gastrointestinal conditions.
It highlights the importance of brewer’s yeast as a sustainable,
functional, and promising biosorbent for the formulation of future
food compounds, mitigating the adverse effects and toxicity associated
with free tartrazine and thereby contributing to safer applications
of food additives.