Thermal-induced interactions between soy protein isolate and malondialdehyde: Effects on protein digestibility, structure, and formation of advanced lipoxidation end products

Thermally processed lipid- and protein-rich foods have sparked widespread concern since they may degrade food nutrition and even risk food safety. This study investigated soy protein isolate (SPI) alterations of digestibility and structure, as well as the formation of potentially hazardous chemicals, i.e., advanced lipoxidation end products (ALEs), after interacting with malondialdehyde (MDA, a lipid oxidation product) under high-temperature cooking conditions (100–180 °C, up to 60 min). In-vitro protein digestion of the SPI-MDA mixtures suggested that their room-temperature interactions damaged SPI digestibility, and increasing the temperature and the duration of the thermal treatment exacerbated the adverse effects. Protein oxidation, covalent aggregation of subunits, and changes in secondary and tertiary structures were revealed using thiol quantification, gel electrophoresis, fluorescence spectroscopy, and circular dichroism (CD) spectra, which could explain reduced protein digestibility. High-resolution mass spectrometry (HRMS) identified seven non-crosslinked ALEs and two crosslinked ALEs. Increased MDA concentrations promoted the generation of ALEs. Moreover, the acrolein-derived ALEs with reactive carbonyl groups were prone to further reacting into crosslinked ALEs, potentially responsible for the subunit aggregation.