Sonophotocatalysis for Enhanced Extraction of Corn Cob Xylan and Simultaneous Production of Xylose and Xylooligosaccharides

Corncob biomass (CCB), an agricultural residue having highest xylan content forms a potential source of platform chemicals such as xylooligosaccharides (XOS) and xylose. This study aims at evaluating the synergistic effect of Sonophotocatalysis (SP) for enhanced extraction of corncob xylan. The effect of different pretreatment methods namely Sonocatalysis (US + ZnO), Photocatalysis (PC), Ultrasonication at 20% amplitude (US 20) and Sonophotocatalysis at amplitude of 20% (SP 20) were studied. Amongst, SP 20 resulted in two folds and five folds enhanced xylan extraction compared to US 20 and PC, respectively. The temperature change from 30 +/- 2 to > 90 +/- 2 degrees C by varying sonication amplitude (20%, 50%, 70% and 90%) and extraction time (15, 30 and 60 min) were studied. The results indicated that 90.1 +/- 1.8% of CCB xylan could be extracted within 15 min of extraction when pretreated with SP 90. This reaction condition resulted in 14.59 +/- 1% of xylose and 84.5 +/- 2.01% of total XOS relative to the initial xylan content. The CCB pretreated with SP 90 resulted in 36% and 83% increased xylan extraction compared to US and PC, respectively. The thin layer chromatography analysis substantiates the result obtained in quantitative analysis. The compositional analysis of pretreated CCB with SP 90 showed higher cellulose (52.5 +/- 1.5%), lignin (15.1 +/- 0.9%) content and reduced hemicellulose (3.5 +/- 0.7%). FTIR studies revealed that variation in the peak band at 1730 cm-1 which is characteristic peak for hemicellulose proved breakage of ester linkage between lignin and hemicellulose when CCB pretreated by SP 90. The particle size distribution of US and SP 90 pretreated reduced from 417 +/- 1.5 to 170 +/- 1.2 mu m. SEM analysis revealed distinguished difference in the structure of CCB between untreated and pretreated samples. From our study it was evident that combination of US and PC resulted in enhanced extraction of CCB xylan with reduced time and mild reaction condition without the use of additional chemicals. Further the extracted xylan was simultaneously hydrolyzed into xylose and XOS of DP (2-4) i.e. X2, X3 and X4. This shows that SP could be a promising process for one pot production of XOS and xylose from CCB xylan.