In recent years, the trend toward the utilization of plant proteins in food development has become increasingly popular owing to their healthfulness, affordability, and environmental sustainability (Lindberg, McCann, Smyth, Woodside, & Nugent, 2024). Soy protein isolate (SPI) is one of the most widely used high-quality plant proteins in the food industry because of its excellent gelling, foaming, and emulsifying properties and ideal amino acid pattern (García, Torre, Marina, Laborda, & Rodriquez, 1997). Flavor is an important influencing factor in the food processing industry, and the practical application of SPI in food processing is limited by its beany flavor (Su et al., 2024). This flavor originates from the storage and processing of unsaturated fatty acids via automatic oxidation, photosensitized oxidation, and enzymatic oxidation accompanied by the generation of hexanal, hexanol, 1-octen-3-one, and other aldehydes and ketones with unpleasant flavors (Jiang, Yang, & Li, 2024; Nedele, Schiebelbein, Bär, Kaup, & Zhang, 2022). Such volatile compounds affect the overall flavor of SPI, limiting consumer acceptance and hindering the development of the SPI processing industry. Therefore, modulation of the beany flavor of soybean isolate proteins is important to extend the application of the proteins.

Different SPI processing and modification techniques can significantly affect the food flavor. Multiple studies have been conducted to remove the SPI soybean flavor via biological and chemical methods, e.g., Pei (2022) used Lactobacillus rhamnosus to ferment pea flour and found that the fermentation effectively attenuated the undesirable flavor of pea protein, with significant reductions in nonanal, octanal, and 2-ethyl-1-hexanol. Wang, Guldiken, Tulbek, House, and Nickerson (2020) deodorized pea proteins by aqueous solvent washing. 50 % and 80 % concentrations of ethanol and isopropanol were effective in removing odor compounds from the proteins but resulted in lower amino acid scores. In addition, these methods are costly, difficult to control, and not always safe (Damodaran & Arora, 2013). Therefore, it is imperative to explore green strategies for modifying protein structure to reduce beany flavor.

Dry heating treatment is an essential step in the production of SPI and its products and plays a key role in dry heat sterilization, the passivation of anti-nutritional factors, and protein powder processing (Brytan & Padrela, 2023). Dry heating treatment can inhibit the activity of lipoxygenase (LOX) and promote the unfolding of the protein structure, disrupting the forces between protein molecules and altering the binding of proteins to flavor compounds (Wang et al., 2021; Xu et al., 2024). For example, Guo, He, Wu, Zeng, and Chen (2019) investigated the effect of preheated SPI on the interaction of aroma compounds with proteins. They found that the interaction with hexyl acetate and heptyl acetate was weakened and the binding with linalool formate, linalool acetate, linalool, and geraniol was enhanced after SPI preheating. This suggests that heat treatment can alter the interaction between flavor compounds and proteins. Wen et al. (2023) investigated the effect of dry heating temperature on the spatial structure of SPI and oxidative modification of the side chains of amino acid residues. The results showed that oxidation of SPI occurred after dry heating and promoted the formation of intermolecular disulfide bonds in the protein. However, the effect of dry heating temperature on the structure of soy protein and its relationship with changes in beany flavor has not been reported.

In this study, the dry heating treatment method was selected to reduce the beany flavor of SPI. The physicochemical properties of SPI were characterized by the particle size, potential, solubility, sulfhydryl, disulfide, and carbonyl groups at different dry heating temperatures (80, 100, 120, and 140 °C). The protein structure was determined by circular dichroism (CD), Fourier transform infrared (FT-IR), fluorescence spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and scanning electron microscopy (SEM). The flavor of SPI was determined via gas chromatography–mass spectrometry (GC–MS), and the effects of different dry heating temperatures on the SPI flavor were investigated. Variable importance in projection (VIP) was combined with odor activity value (OAV) analysis, and the key beany flavor of SPI was screened out. To reveal the relationship between molecular conformational changes in dry heating treatment SPI and key beany flavor. The results of this work offer a theoretical basis for dry heating technology aimed at reducing the beany flavor of SPI and provide important guidance for the preparation of SPI with the desired flavor.