Steam explosion pre-treatment of alkali-impregnated lignocelluloses for hemicelluloses extraction and improved digestibility.

The application of steam explosion pre-treatment to extract xylan-rich biopolymers from alkali-impregnated lignocelluloses, while simultaneously increasing the enzymatic digestibility of cellulose, was investigated. Steam-enhanced extraction of xylan from sugarcane trash (SCT) and aspen wood (AW) was performed at varying temperatures (176-204 °C) and retention times (3-17 min) after the impregnation of biomass samples with sodium hydroxide at 1:20 (w/w) solid loading ratio. Xylan extraction and cellulose digestibility results were statistically analysed to fix the condition/s for significantly enhanced values. Accordingly, maximum xylan yields of 51 and 24%, and highest cellulose digestibility of 92 and 81%, were attained for SCT and AW respectively following their pre-treatment at 204 °C for 10 min. At this most-severe condition, neither xylose nor furfural - a degradation product from xylose - were observed in the hemicellulose extract, indicating steam explosion pre-treatment with alkali impregnation of lignocelluloses as viable biorefinery approach to co-produce xylan biopolymers and bioethanol.

Single-step microwave-assisted hot water extraction of hemicelluloses from selected lignocellulosic materials - A biorefinery approach.

The viability of single-step microwave-induced pressurized hot water conditions for co-production of xylan-based biopolymers and bioethanol from aspenwood sawdust and sugarcane trash was investigated. Extraction of hemicelluloses was conducted using microwave-assisted pressurized hot water system. The effects of temperature and time on extraction yield and enzymatic digestibility of resulting solids were determined. Temperatures between 170-200°C for aspenwood and 165-195°C for sugarcane trash; retention times between 8-22min for both feedstocks, were selected for optimization purpose. Maximum xylan extraction yields of 66 and 50%, and highest cellulose digestibilities of 78 and 74%, were attained for aspenwood and sugarcane trash respectively. Monomeric xylose yields for both feedstocks were below 7%, showing that the xylan extracts were predominantly in non-monomeric form. Thus, single-step microwave-assisted hot water method is viable biorefinery approach to extract xylan from lignocelluloses while rendering the solid residues sufficiently digestible for ethanol production.

Cytogenetic characterization of two laboratory colonies of Anopheles arabiensis Patton from Ethiopia.

Polytene chromosome analysis was carried out in samples of Anopheles arabiensis from two colonies originating from different sites in the Rift Valley, Ethiopia. Both colonies were found to maintain the main chromosomal inversion variations existing in wild populations. Changes in karyotype frequencies were documented as well as excesses of heterokaryotypes.