Abstract: This study systematically compared the effects of low-inoculum (3%) and high-inoculum (5%) monoculture fermentation with Lactiplantibacillus pentosus, as well as mixed-culture fermentation with L. pentosus and L. plantarum (1:1, 5%), on the quality of fermented Shuidong mustard (Brassica juncea var. foliosa), using naturally fermented samples as the control. The quality of fermented Shuidong mustard was evaluated by measuring pH, total acidity, nitrite content, lactic acid bacterial (LAB) count, color parameters, texture properties, and sensory attributes. The differences in flavor compounds of the fermented mustard samples were further analyzed using high performance liquid chromatography (HPLC) and gas chromatography-ion mobility spectrometry (GC-IMS). The results showed that inoculated fermentation significantly accelerated the acidification process. During the middle and late stages of fermentation, the pH remained below 4.0, while the LAB count was maintained at 107–108 CFU/mL, effectively suppressing nitrite accumulation and the growth of coliform bacteria. Compared with the natural fermentation group, the inoculated treatments exhibited significantly lower residual sugar levels at the end of fermentation. Among them, the high-inoculum monoculture treatment showed the lowest residual glucose concentration ((0.13 ± 0.07) mg/mL), whereas the mixed-culture treatment demonstrated greater metabolic stability. Texture analysis revealed that inoculated fermentation promoted moderate softening of Shuidong mustard, with the low-inoculum single-strain fermentation group exhibiting smaller changes in hardness and chewiness, indicating better texture stability. Regarding non-volatile flavor compounds, mixed-culture fermentation significantly promoted the accumulation of organic acids and taste-active substances, including lactic acid, succinic acid, glutamic acid, and alanine. GC-IMS analysis identified multiple classes of volatile compounds. Alcohols and ketones were dominant in the naturally fermented samples, whereas inoculated fermentation significantly increased the abundance of esters and organic acids. In particular, the high-inoculum monoculture treatment exhibited relatively high levels of ethyl valerate, ethyl lactate, and isovaleric acid and had the most balanced aroma profile and the highest sensory score. In conclusion, an appropriate inoculation strategy can ensure the safety of fermented Shuidong mustard while improving its texture and flavor quality. The high-inoculum monoculture fermentation provided the most harmonious flavor profile, whereas the mixed-culture fermentation showed distinct advantages in organic acid accumulation and color retention.

Key words: Lactiplantibacillus pentosus; Shuidong mustard; inoculated fermentation; textural properties; flavor compounds