Functional Properties of Sunflower Flour as a Function of Food-grade Thiols and pH

Abstract

Sunflower (Helianthus annuus) flour is a promising non-GMO and allergen-free protein source with increasing relevance as an alternative to conventional oilseed soy proteins. However, a significant challenge that limits its industrial application is the undesirable greening that occurs during alkaline extraction. This greening is primarily caused by the oxidation of chlorogenic acid (CGA), which reacts with protein amino groups, to form green trihydroxybenzacridine (TBA) pigments. This study evaluated the effect of two food-grade thiol compounds: Cysteine (Cys) and Glutathione (GSH), at concentrations of 0.0, 2.8, and 5.6 mM and two pH levels (9 and 11), on the color, functional properties, protein content, chlorogenic acid content, and Maillard reaction products of sunflower protein powders. A Factorial Complete Randomized Design (CRD) was used to evaluate the effect of thiol type, thiol concentration and pH on greening (-a* values), browning index (BI), functional properties, CGA content, protein content, and Maillard reaction products, including advanced glycation end-products (AGEs), hydroxymethylfurfural (HMF), and Fluorescence of Advanced Maillard Products and Soluble Tryptophan (FAST) Index. Compositional analysis for protein content (73.10-84.8%) and CGA remained unchanged. Results showed that 5.6 mM cysteine at pH 11 effectively lowered greening and enhanced browning. Functional properties such as water and oil holding capacities, nitrogen solubility, and surface hydrophobicity were not significantly affected, as well as Maillard reaction products. These findings support the use of thiol-assisted extraction to improve the visual quality of sunflower protein without compromising functionality.