Aims This study aimed to screen the γ-aminobutyric acid (GABA) producing lactic acid bacteria (LAB) from kimchi, and investigate the glutamate decarboxylase (GAD) activity of the highest GABA-producing strain. Methods and Results Seven strains of LAB were screened from kimchi with GABA-producing activity. Strain Levilactobacillus brevis F109-MD3 showed the highest GABA-producing ability. It produced GABA at a concentration of 520 mmol l^-1 with a 97.4% GABA conversion rate in MRS broth containing 10% monosodium glutamate for 72 h. The addition of pyridoxal 5’-phosphate had no significant effect on the GAD activity of L. brevis F109-MD3. The optimal pH range of GAD was 3.0-5.0 and the optimal temperature was 65 ºC. The D value of GAD at 50 ºC, 60 ºC, and 70 ºC was 7143 min, 971 min, and 124 min, respectively, and Z value was 11.36 ºC. Conclusions Seven strains isolated from kimchi, especially F109-MD3, showed high GABA-production ability even in the high concentrations of MSG at 7.5% and 10%. The GAD activity showed an effective broad pH range and higher optimal temperature. Significance and Impact of the Study These seven strains could be potentially useful for food grade GABA production and the development of healthy foods.

To address the challenge of high sodium in paocai, this study evaluated the partial substitution of NaCl with KCl during radish paocai fermentation, focusing on microbial kinetics and flavor. The methodology integrated microbial growth modeling with comprehensive flavor analysis (HS-SPME-GC-MS, HS-GC-IMS, E-tongue) and Random Forest (RF) machine learning. Substituting 30% NaCl with KCl (K30) significantly increased mannitol and glutamic acid, enhancing desirable fresh, sweet, and umami tastes. RF modeling identified erucin, 1-hexanol, 3-methylbutan-1-ol, and 2-methoxy-4-vinylphenol as potential key aroma compounds. The K30 treatment also improved the aroma profile by increasing volatile compounds associated with cabbage, fruit, and sweet notes. Conclusively, sensory analysis confirmed that K30 paocai exhibited superior sourness, sweetness, umami, and overall acceptability. These findings support that 30% NaCl substitution with KCl is a valuable strategy for producing low-sodium radish paocai with an enhanced flavor profile, offering a practical framework for sodium reduction across traditionally fermented foods.

Chinese spicy cabbage (CSC) is a common traditional fermented vegetable mainly made of Chinese cabbage. In addition to eating raw, boiling and stir-frying are the most common cooking methods for CSC. To identify the impacts of boiling or stir-frying on the quality of CSC, the physicochemical properties, flavor compounds, and sensory properties of CSC were analyzed. A total of 47 volatile flavor compounds (VFCs) were detected by gas chromatography–mass spectrometry. Sulfide was determined as the main flavor compound of CSC, mainly contributed by cabbage, garlic, and onion odors. The content of sulfide decreased significantly after cooking. Nonanal, geranyl acetate, and linalool were newly generated after boiling with odor activity value (OAV) > 1, and contributed fatty, sweet, fruity, and floral odors to BL-CSC. 1-Octen-3-one, 1-octen-3-ol, octanal, nonanal, and (E)-2-nonenal were newly generated after stir-frying with OAV > 1, and contributed mushroom, fatty, and green odors to SF-CSC. Diallyl trisulfide, nonanal, (E)-β-ionone, β-sesquiphellandrene, and (E)-2-decenal were considered as the potential key aroma compounds (KACs) to distinguish the CSCs after different heat treatment. After cooking, the total titratable acidity of CSC increased and the sensory properties changed significantly. This study provides valuable information and guidance on the sensory and flavor changes of thermal processing fermented vegetables.