Title : Establishment of a lactic acid bacteria fermentation system for grape marc: Exploring microbial metabolism of phenolics and their changes during simulated in vitro digestion
Abstract:
Grape marc (GM) is a waste product produced during the winemaking process. The enormous volume of wine production worldwide creates a significant amount of GM annually. GM is rich in nutrients and has excellent antioxidant properties. Lactic acid fermentation is a popular food preparation method, and by using GM as a substrate for fermentation, the pomace is preserved and the health benefits are improved, thus being a potentially valuable method that allows efficient management of pomace. An optimized fermentation system was developed using red GM as a substrate for lactic acid bacteria (LAB). This study investigated the effects of different LAB strains on the content and antioxidant capacity of phenolic compounds during fermentation, as well as bioaccessibility of these fermented bioactive compounds under simulated gastrointestinal digestion. Additionally, it explored the metabolism of phenolics by LAB and the potential health benefits of fermented GM after in vitro digestion. The results indicated that GM supplemented with exogenous glucose and yeast extract served as a more effective substrate for LAB fermentation compared to unmodified GM. During fermentation, flavonoids and tannins were significantly degraded, while anthocyanin content exhibited a marked increase. LC-ESI-QTOF-MS/MS analysis was employed to identify changes in specific phenolics during degradation and transformation. During the in vitro digestion, fermented GM demonstrated significantly higher total phenolic content (TPC), total anthocyanin content (TATC), total condensed tannin content (TCTC), and antioxidant activity (DPPH), along with improved bioaccessibility, compared to unfermented samples. Notably, the intestinal-phase TPC and DPPH reached 24.6 mg/g gallic acid equivalents and 23.8 mg/g Trolox equivalents, respectively. The metabolic performance of LAB strains varied during the intestinal phase; however, most strains exhibited robust potential for phenolic metabolism, particularly for anthocyanins and tannins, warranting further investigation. These findings highlight the role of fermentation and digestion in enhancing the functionality of phenolics, underscoring the immense potential of LAB-fermented GM as a phenolic-rich functional ingredient for health-promoting applications. This approach offers a highly cost-effective pathway for advancing such products in the food, pharmaceutical, and cosmetic industries, while also contributing sustainably development.
