Texas A&M University, Food Science & Technology Department, College Station, TX 77843, USA.
Texas A&M University, Food Science & Technology Department, College Station, TX 77843, USA; Texas A&M University, Soil & Crop Sciences Department, 2474 TAMU, College Station, TX 77843, USA.
Food Res Int. 2021 Jul;145:110426. doi: 10.1016/j.foodres.2021.110426. Epub 2021 May 19.
Whole grain polyphenols are associated with structure-specific bioactive properties. However, the phenolic profile of grain ingredients can be significantly altered by processes like fermentation. This study investigated how polyphenol profiles in different cereal grains respond to microbial metabolism during sourdough fermentation. Whole grain wheat (white and red), sorghum (white and lemon-yellow), and teff (white and brown) flours were subjected to natural sourdough fermentation for 48-96 h, and phenolic profiles and their metabolites monitored using UPLC-tandem quadrupole MS. Flavonoid O-glycosides (dominant in sorghum) were rapidly metabolized (66% reduction in 48 h) to release aglycones (2.5 fold increase). O-Glycoside groups in mixed O/C-glycosides (dominant in teff) were selectively hydrolyzed, but more slowly (11-32% reduction in 48 h) than homo-O-glycosides, suggesting steric hindrance from the C-glycoside groups. Flavonoid C-glycosides (dominant in wheat) and aglycones (white sorghum) were generally stable to microbial degradation. Extractable phenolic acids and their esters (most abundant in white sorghum) were extensively degraded (80% reduction in 48 h) with few metabolites detected at the end of fermentation. Thus, extractable phenolics in sorghum were generally most extensively metabolized, whereas those in wheat were the least impacted by sourdough fermentation. New microbial metabolites, putatively identified as O-methylcatechol-vinyl-isoflavans, were detected in all fermented samples, with levels increasing with fermentation time. Based on structure, these compounds were likely derived from cell wall C-C linked diferulic acid metabolism. As expected, Folin reactive phenols and antioxidant capacity increased in fermented samples, but the extent was distinctly smaller in sorghums (1.3-1.9 fold) vs teff (2.4-3.2 fold) and wheat (2.0-6.1 fold), likely due to higher presence of easily metabolizable phenolics in sorghum. The phenolic profile of a cereal grain affects the products of microbial metabolism during fermentation, and may thus alter phenolic-dependent bioactive properties associated with a specific grain.
全谷物多酚与特定结构的生物活性特性相关。然而，谷物成分的酚类谱可以通过发酵等过程发生显著改变。本研究调查了不同谷物在酸面团发酵过程中微生物代谢对多酚谱的影响。全谷物小麦（白麦和红麦）、高粱（白高粱和柠檬黄高粱）和埃塞俄比亚画眉草（白画眉草和棕画眉草）面粉经过自然酸面团发酵 48-96 小时，使用 UPLC-串联四极杆 MS 监测酚类谱及其代谢产物。在 48 小时内，高粱中含量较高的类黄酮 O-糖苷（占主导地位）迅速代谢（减少 66%），释放出糖苷配基（增加 2.5 倍）。混合 O/C-糖苷中 O-糖苷基团（在埃塞俄比亚画眉草中占主导地位）选择性水解，但速度较慢（48 小时内减少 11-32%），这可能是由于 C-糖苷基团的空间位阻。在小麦中含量较高的类黄酮 C-糖苷和糖苷配基（白高粱）一般不易被微生物降解。可提取的酚酸及其酯（在白高粱中含量最丰富）在发酵结束时检测到的代谢产物很少，在 48 小时内被大量降解（减少 80%）。因此，高粱中的可提取酚类通常被微生物代谢得最广泛，而小麦中的酚类受酸面团发酵的影响最小。在所有发酵样品中都检测到了新的微生物代谢产物，推测为 O-甲基儿茶酚-乙烯异黄酮，其水平随发酵时间的增加而增加。根据结构，这些化合物可能来自细胞壁 C-C 连接的二芳基醚酸代谢。不出所料，发酵样品中的福林反应酚和抗氧化能力增加，但高粱中的增加幅度明显较小（1.3-1.9 倍），而埃塞俄比亚画眉草（2.4-3.2 倍）和小麦（2.0-6.1 倍），这可能是由于高粱中更容易代谢的酚类含量较高。谷物的酚类谱会影响发酵过程中微生物代谢的产物，从而可能改变与特定谷物相关的依赖酚类的生物活性特性。
