2.2. Characterization of the root powder
The swelling index of the powder was determined according to Ghanem et al. (2010) on a half gram of powdered material incubated in a 25 mL ground glass stoppered cylinder graduated over a height of 130 mm in 0.5 mL divisions. The powder was moistened with 1 mL of ethanol (96% v/v), distilled water was added up to 25 mL, and the cylinder was closed and shaken over 20 min at room temperature. It was then allowed to stand for 2 h. The volume occupied by the disintegrating agent including adhering mucilage was recorded.
The crude mucilage was extracted from roots (5 g DW) with 500 mL water under stirring for 40 h at room temperature (Classen and Blaschek, 1998). The extract was centrifuged at 20,000g during 5 min at 4◦C. The aqueous supernatant was concentrated to 150 mL by evaporation and the mucilage solution was poured into 600 mL of a mixture of 96% ethanol and 1% acetic acid. The dry weight of the lyophilized crude mucilage was determined.
Concentration of lignin and structural polysaccharides (cellulose and hemicellulose) were determined according to Van Soest et al. (1991). The root dry matter was crushed and exposed successively to a neutral detergent solution during 1 h at 100◦C to obtain by filtration the NDF (neutral detergent fibers), then to an acid detergent solution during 1 h at 100◦C to get the ADF fraction (acid detergent fibers), and then to sulfuric acid 72% during 3 h to obtain the ADL fraction (acid detergent lignin). The ADL fraction was incinerated at 550◦C during 3 h, and the mass loss allowed us to calculate the lignin percentage. The difference between ADF and ADL provided the percentage of cellulose, and the difference between NDF and ADF the percentage of hemicelluloses.
Scanning electron microscopy was performed using a SEM Phillips XL20: powder sputter coated with gold in a preparation chamber for 75 s under 1.2 kV at −150 to −170◦C. Specimens were viewed under 2–5 kV at −170 to −190◦C.