Effects of Freeze-Dried Burdock Root and Ultrasonic Treatment on the Growth and β-Glucosidase Activity of Lactiplantibacillus plantarum FEL112 in the Fermentation of Black Soymilk

Burdock (Arctium lappa L.) root, rich in inulin and polyphenols, has physiological activities and can serve as a nutritional source for microorganisms. The aim of this study was to investigate the effects of freeze-dried burdock root powder (BP) and ultrasonic treatment (US) on the growth and β-glucosidase activity (β-GA) of Lactiplantibacillus plantarum FEL112 (Lp-FEL112) in the fermentation of black soymilk (BS). The viable cell counts and β-GA of Lp-FEL112 incubated in different amounts of BP in BS (x% BP/BS, w/v) without US or using US (40 and 120 kHz) for 1% BP/BS were evaluated. The total phenolic content (TPC), antioxidant activity, and isoflavones in the fermented product extract (FE) for 1% BP/BS were analyzed. The β-GA of Lp-FEL112 for 1% BP/BS without US at 24 h was 16.01 ± 1.88 U/mL, higher than those in 3% BP/BS and 7% BP/BS, and was enhanced to 18.62–26.86 U/mL using US. The antioxidant activities, TPC, and the isoflavone aglycones (daidzein and genistein) ratio in the FE of 1% BP/BS were improved with US. This study demonstrated that adding a limiting amount of BP to BS combined with US in the fermentation of BS by Lp-FEL112 could eliminate the need for an extraction step while achieving enhancement in the functionality of the fermented products.