Hemicellulose based biorefinery from pineapple peel waste: Xylan extraction and its conversion into xylooligosaccharides

Pineapple peel waste was utilized as an unexplored source of hemicellulose (31.8 +/- 1.9%) for value addition. Hemicellulose was extracted by an alkali-based method, where the peels were incubated at different alkali concentrations (5%, 10% and 15% w/v) at temperatures ranging from 35 degrees C to a maximum of 65 degrees C for a fixed period of 16 h. A maximum recovery of hemicellulose (95.9 +/- 2.0%) was observed after incubating extractive-free pineapple peels in 15% (w/v) alkali solution for 16 h at 45 degrees C. Higher incubation temperatures (65 degrees C) for 16 h, resulted in a lower yield of hemicellulose (81.7 +/- 3.7%) which can be attributed to the disintegration of the hemicellulose structure due to large severity factor (temperature-time combination). With low severity factor, it was noted that higher yields (96.6 +/- 0.3%) were obtained 65 degrees C, 4h). Hydrothermal-assisted alkali extraction was also evaluated for maximizing the recovery of pineapple peel hemicellulose. The maximum relative recovery of (8) over tilde7.6% was obtained with 10% (w/v) alkali at the end of 1.5 h of hydrothermal pretreatment (121 degrees C and 15 psi pressure). The hemicellulose extracted by hydrothermal-assisted alkali pretreatment was enzymatically hydrolyzed to produce XOS and the process was optimized in terms of enzyme dose (U), temperature (degrees C), pH and time (h). Direct hydrolysis of pineapple peels with dilute nitric acid produced xylose-rich liquor ((9) over tilde1% xylose yield) at 0.5% nitric acid, reaction time of 1 h and solid-liquid ratio of 1:20. The xylose-rich liquor could be converted to potential chemicals such as xylitol. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.