Characteristic of different thermal treatment-induced dough protein oxidation and its impact on human gut microbiota

The thermal processing methods of flour products are diverse. This study aims to explore the effects of these methods (e.g., steaming, high-pressure, frying, baking, air frying, and microwave) on wheat dough protein oxidation and these oxidized proteins on human gut microbiota composition. We found that the different methods resulted in varying degrees of browning, decreased protein digestibility, and altered water distribution, protein noncovalent interactions, and surface hydrophobicity in the dough; the protein structure changed from α-helix and random coil to β-sheet and β-turn, and showed varying degrees of distinct aggregation and cross-linking. The protein oxidation products demonstrated elevated levels of carbonyl compounds, advanced glycation end products, and Schiff bases to varying extents, accompanied by a reduction in free amino and sulfhydryl group contents. Additionally, decreases in tryptophan and tyrosine concentrations were observed, while oxidation-derived amino acid products-namely dityrosine, kynurenine, and N'-formylkynurenine-displayed an increase in concentration. Under in vitro anaerobic fermentation conditions, thesev oxidized proteins further disrupted the human gut microbiota at different levels, notably raising the abundance of pro-inflammatory bacteria such as Fusobacterium, Bilophila, and Sutterella, and lowering the abundance of anti-inflammatory bacteria including Bacteroides, Phascolarctobacterium, and Oscillibacter. The findings indicate that different thermal processing methods induce protein oxidation to differing degrees, and these oxidative products consumption may lead to varying extents of gut microbiota dysbiosis, with baking and air frying exhibiting the most pronounced effects. Thus, the choice of processing methods for flour-based products should take into account the potential for protein oxidation.