Sweet sorghum bagasse powder was used as the substrate for the treatment studies. Sweet sorghum variety CSSH-45 was obtained from the Department of Plant Science of McGill University. The plants were harvested, defoliated and stems were crushed to extract sweet juice from it. The bagasse obtained was immediately cold washed to remove the free sugars present on it (Hou-min Chang, Richard Phillips et al. 2013). It was then dried in a hot air oven at 500C for 72 hours to obtain constant dry mass. The dried bagasse was chopped using scissors to 1-2 cm long pieces and powdered to small particles using a blender-grinder (Homeland Housewares, LA, USA). The grinding time was two minutes and sample mass was ten grams for all samples in order to obtain uniform particle size distribution in all the samples used for the treatments. The powder was used as such without any further sieving in order to obtain samples containing all parts of the stem because sieving of the pulverised samples will separate the more fibrous bark portions of the stem from the springy pith portions of the stem (Billa, Koullas et al. 1997). The powder from each grinding operations were put into and stored in an air-tight container. The powder was mixed well before taking samples for each experimental treatment and analyses.
Hydrothermal treatment of sweet sorghum bagasse powder
Hydrothermal treatment of the SSB powder was carried out using tap water in an autoclave (DSE-8000, NAPCO, USA). The treatment temperature was selected as 394 K since the significant quantity of heat required to achieve this temperature can be recovered through proper process design (Teramoto, Lee et al. 2009) and will be more effective than simple boiling for the treatment of lignocellulosic biomass. Hydrothermal conditions are created in aqueous media above 1000C and 1 atmospheric pressure. These conditions are conducive to the solubilisation of reactants which are difficult to dissolve in less severe treatment conditions (Rabenau 1985). In the experimental treatments, 10-20 g SSB powder was mixed with 80-90 g water to obtain 10, 15 and 20 % (g bagasse/g aqueous mixture) concentrations and the mixture was kept in an autoclave for the hydrothermal treatment at 394 K. The autoclave was already saturated with steam and therefore the temperature reached 394 K in about 5 minutes. Once the temperature reached 394 K, the mixture was kept at that temperature for 30, 75 and 120 minutes. The treatment was stopped by releasing the steam pressure and keeping the mixture under cold tap water to bring the temperature of the mixture to the room temperature. The mixture was separated using nylon cloth to obtain solid and liquid samples for further analyses and studies. The wet solid samples were dried in a hot air oven and then used for compositional analyses. The liquid samples (hydrolysate) were refrigerated at 40C and were used for the compositional analyses.
The effect of independent...