Probiotic Levilactobacillus brevis GH1 from baijiu Daqu enhanced γ-aminobutyric acid and antioxidant ability in Cordyceps militaris fruiting body extract and brown rice beverage

γ-Aminobutyric acid (GABA) is a functional amino acid with various physiological activities. Increasing the concentration of GABA in foods and enhancing dietary supplementation are important for health benefits. <i>Baijiu</i>, a traditional Chinese liquor, is one of the oldest and most consumed fermented beverages. <i>Daqu</i>, the fermentation starter of <i>Baijiu</i>, contains functional lactic acid bacteria. However, whether these lactic acid bacteria have the potential to prepare functional beverages enriched with GABA is not clear. In this study, <i>Daqu</i> was used as a screening resource, and fruiting body extracts of <i>Cordyceps militaris</i> and germinated brown rice were used as fermentation materials to obtain <i>Levilactobacillus brevis</i> GH1, which can endogenously produce GABA. <i>Levilactobacillus brevis</i> GH1 demonstrated strong probiotic properties and the ability to survive in a simulated stomach and intestinal conditions, as well as tolerate osmotic pressure and bile salts. The optimal fermentation conditions were 30.83 g/L sucrose, 1.04 g/L corn steep liquor powder, and 52.74 % <i>Cordyceps militaris</i> fruiting body extraction solution at pH 4.06 and culture at 34.40 °C. The GABA concentration reached 16.83 g/L. The DPPH scavenging ability, Fe²⁺ chelating ability, and hydroxyl free radical scavenging ability increased by 1.7, 3.2, and 2.7 times, respectively. Moreover, the beverage is rich in lactic acid, acetic acid, oxalic acid, succinic acid, citric acid, and malic acid. These properties demonstrate that <i>Levilactobacillus brevis</i> GH1 derived from <i>Daqu</i> can be utilized in the development of functional beverages rich in GABA and is suitable for use in functional food products.