2.1. Herbal Preparation

Dried root of P. lobata in powdered form was purchased from the medical supply store of Dongguk University International Hospital (Ilsan, Goyang-si, Gyeonggi-do, Korea). To prepare the PR extract, 500 g of PR powder was mixed vigorously with 5 L of 30% ethanol (v/v), and the resultant mixture sonicated in a water bath for 1 h at room temperature. The mixture was then centrifuged at 1200× g for 15 min at room temperature following which the supernatant was filtered through a Whatman^® Grade 4 filter paper (Whatman, Maidstone, Kent, UK). The residue was subjected to the above-mentioned extraction procedure twice using 40 mL of 30% ethanol (v/v) each time. The collected extract was evaporated to dryness using a rotary evaporator (EYELA N-1200A, EYELA, Tokyo, Japan) and subsequently freeze-dried using a lyophilizer (Bondiro, IlshinBioBase, Dongducheon-si, Gyeonggi-do, Korea). The resultant product was kept at −80 °C until further use.

The B. breve used in this study as a starter for PR fermentation was obtained from Cellbiotech (Gimpo, Gyeonggi-do, Korea). Selected pure B. breve was incubated in MRS broth media (BD Difco ^™, Franklin Lakes, NJ, USA) at 37 °C for 24 h. The broth was then centrifuged at 12,000× g at room temperature for 3 min and the supernatant discarded. The cell pellet was washed with PBS (pH 7.4) three times. Finally, the bacterial cells were resuspended in PBS and inoculated to a PR extract prepared in distilled water for 24 h.