Preparation of Plant Extracts as Prebiotic Sources

Two plants, Jerusalem artichokes (H. tuberosus; hereafter referred to as artichoke) and white button mushrooms (A. bisporus; hereafter referred to as mushroom), procured from a private company in Iran, were used as sources of prebiotics. The plant materials were repeatedly washed with tap water to remove the presence of any dirt and then allowed to dry until the water droplets disappeared from their surface. Each one of the artichokes and the mushroom was cut into small slices. The slices were then dipped in a 0.5% (w/v) citric acid solution for 15min to avoid browning (Mahore and Shirolkar, 2018) and dried in an oven at 50°C for 48h. The dried samples were ground in a household grinder. The extraction process was performed by the soaking method as previously described (Harborne, 1980). Briefly, 100g of each dry powder was added in 1l of distilled water, and the mixture was kept in dark for 48h. After that, the concentrated liquid was centrifuged (10, 000 x g at 4°C, 15min; Sobye et al., 2018), and the resulting precipitate was discarded. Finally, the supernatant was then filtered using a 0.22μm syringe filter and used for preparing the desired prebiotic concentrations (2, 25, 50, 75, and 100%). In this assay, glucose was removed from all culture media (broth/agar) containing extracts as previously described (Hoseinifar et al., 2017).