Acrylamide (AM) is produced as a by-product of the Maillard reaction during the thermal processing of baked goods. Research has indicated that the addition of fermented sourdough significantly reduced the AM content in baked products. This study investigated the main metabolites of sourdough fermented by single strains of Pediococcus pentosaceus (PP), Saccharomyces cerevisiae (ST), and their combinations. Additionally, the inhibitory effect of sourdough on AM in both bread and asparagine/glucose (Asn/Glc) chemical simulation system was examined, and the potential inhibitory mechanism was systematically elucidated. The key findings revealed that at an ST-to-PP ratio of 1:1, the 2 strains exhibited synergistic growth. The sourdough samples fermented with this mixed combination (MF-s) for 12 h exhibited the highest content of organic acids, resulting in a lower pH value than those of samples fermented with only PP sourdough (PP-s) or ST sourdough (ST-s). The MF-s samples exhibited higher contents of maltose, Glc, fructose, sucrose, and total free amino acid than ST-s and PP-s. After 12 h of fermentation, the inhibition rate of AM in wheat bread and the Asn/Glc system reached the highest level. Particularly, MF-s exhibited the highest inhibition rate of AM (49.66%), followed by PP-s (42.23%) and ST-s (38.22%). These rates were significantly higher than those in the naturally fermented group (P < 0.05). The kinetic model analysis results indicated that the logistic exponential kinetic model was considered highly suitable for describing the kinetic process of AM.

A variety of spectroscopic techniques were used to study the inhibitory effect and mechanism of rutin and quercetin on starch-digesting enzymes and their combined effect. The results showed that the types of inhibition of rutin and quercetin on α-amylase were competitive, mainly driven by hydrophobic interactions and hydrogen bonds, and the half maximum inhibitory concentrations (IC₅₀) were 0.36 and 0.22 mg/mL, respectively. The inhibition of α-glucosidase by rutin and quercetin was of mixed type, driven by hydrogen bonds, and the IC₅₀ were 1.30 and 0.362 mg/mL, respectively. Moreover, both flavonoids could combine with α-amylase and α-glucosidase at only one/kind of action site to form a complex, thus inhibiting the activity of the enzymes, and their combinations in different proportions had a synergistic inhibitory effect on α-amylase and α-glucosidase. When the concentration ratio between rutin and quercetin was 7:1 and 3.6:18, the combination index for α-amylase and α-glucosidase was 0.20 and 0.22, respectively, showing the best synergistic inhibitory effect. This study provides a theoretical basis for further research on the interaction mechanism between flavonoids and starch-digesting enzymes, is meaningful for guiding the processing and utilization of edible and medicinal plants rich in flavonoids, and helps to promote the virtuous cycle of the tartary buckwheat industry.

In this study, the changes in the viable count of lactic acid bacteria and the contents of major organic acids in sourdough were explored during spontaneous and inoculated fermentations with the typical sourdough starter cultures Lactobacillus plantarum (Lp), Lactobacillus paralimentarius (Lpa) and Lactobacillus fermentum (Lf) separately and in combination: Lpa + Lp (1:1), Lp + Lf (1:1) and Lpa + Lf (1:1), and the effect of co-fermentation with yeast on bread quality was evaluated. The results demonstrated that Lf grew fastest in sourdough among the single cultures, while the highest number of bacterial colonies of 9.20 (lg(CFU/g)) was observed in sourdough fermented with Lpa + Lp + Lf for 10 h. From 16 h onward, the number of bacterial colonies remained stable. Furthermore, the rate of inoculated fermentation (for both single and mixed culture fermentation) was always faster than that of natural fermentation, and the sourdoughs fermented with Lf and Lpa + Lp + Lf reached the desired pH 4.0 after 16 h. Moreover, at this time, the maximum contents of lactic acid and acetic acid in sourdough were obtained (9.05 and 2.31 mg/g, respectively). Compared with ordinary dry yeast fermented bread (OFB), the specific volume of Lpa + Lp + Lf fermented sourdough bread increased by 19.43%, the hardness decreased by 38.21%, and the resilience rose by 29.17%. In the case of flavor quality, Lpa + Lp + Lf fermented sourdough bread contained the largest number (49) and amount (352.39 μg/kg) of flavor compounds including four unique esters, namely ethyl lactate, ethyl palmitate, phenethyl 2-methylpropionate and ethyl caproate. In addition, anti-aging properties of the bread were evaluated, revealing that after 7 days of storage, the quality did not remarkably deteriorate, the hardness increased by only 1.93 times, and the rate of water migration was slow during storage. In summary, Lpa + Lp + Lf fermented sourdough can significantly improve the taste of bread and extend its shelf life.

In this study, Lactobacillus plantarum (Lp), Lactobacillus fermentum (Lf) and Weissella confusa (Wc) were selected as exogenous strains for the fermentation of sourdough. The growth of lactic acid bacteria, the distribution of major metabolites such as organic acid and sugar, and the distribution of protein in sourdough were evaluated by high performance liquid chromatography (HPLC) and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Finally, the sourdough was applied to the production of frozen dough bread. The results showed that in the sourdough, the bacteria entered the logarithmic growth phase at 4–12 h, and mixed cultures grew better than individual ones, showing synergism. Particularly, the colony count of Lf + Wc in sourdough was as high as 9.18 (lg(CFU/g)) after 12 h fermentation, and a large amount of fructose (11.82 mmol/kg) and extracellular polysaccharide (EPS) (3.132 g/kg) were generated. Compared with the other groups, Lf + Wc exhibited moderate acid production rate, lower protease activity and slower protein degradation rate. The baking quality of bread made from Lf + Wc fermented sourdough frozen and stored for 13 weeks decreased slightly, and the baking loss rate decreased only by 5.3%. In addition, GC-MS analysis showed that the number of volatile compounds in frozen dough bread fermented with Lf + Wc increased by eight after 13 weeks of frozen storage. In conclusion, Lf and Wc have a good synergistic effect when used together. Notably, metabolites such as exopolysaccharides generated during metabolism are of great significance for delaying and controlling the deterioration of frozen dough bread quality. This study provides a certain theoretical basis for the application of multigrain sourdough as a natural antifreeze agent in the large-scale preparation of frozen dough.