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

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.