Low degree of polymerization xylooligosaccharides production from almond shell using immobilized nano-biocatalyst.

In this work, the effect of particle size on alkali pretreatment of the almond shell was evaluated for recovery of hemicellulose. Further, endoxylanase from Thermomyces lanuginosus was immobilized on Fe-based magnetic nanoparticles to enable reuse of enzyme. Reduction in particle size significantly influences the recovery of hemicellulose as particle size below 120 µm enable recovery of 97% available hemicellulose in 1 h at 121 °C with 2 M alkali. The enzyme could retain 93.3% of enzymatic activity upon immobilization onto magnetic support using glutaraldehyde (25 mM) and was at par with the free enzyme in terms of pH and temperature profile. The measurement of reaction kinetics (Km and Vmax) indicates similar values for free and immobilized enzyme. The structural and morphological analysis indicates presence near spherical magnetic core and successful cross-linking of the enzyme without alteration of the magnetic core. The immobilized enzyme was able to hydrolyze hemicellulose to produce XOS, the yield equivalent to 67.4% of that obtained using free enzyme at 50 °C. The comparison of XOS production ability at 50 and 60 °C, suggests that the immobilized enzyme retains activity as similar yield was obtained at both temperatures, whereas, the yield for free enzyme decreases significantly. The XOS yield on recycling of immobilized enzyme for three successive cycles was found to reduce to 41% of the initial cycle. However, in all cycles of enzymatic hydrolysis, the percentage of xylobiose was found to be above 90%.

Production and faecal fermentation of pentose oligomers of hemicellulose: Study of variables influencing bioprocess efficiency.

Almond shell, a by-product obtained from the nut industry, was valorised into low degree of polymerisation xylooligosaccharides using alkaline pretreatment and enzymatic hydrolysis. The effect of particle size on hemicellulose recovery upon pretreatment was studied using 1 and 2 M NaOH. It was observed that particle size significantly influences hemicellulose recovery, as particles below 120 µm resulted in near complete recovery at 2 M NaOH. Enzymatic hydrolysis of hemicellulose was optimised using response surface methodology, to obtain efficient xylooligosaccharides production at low enzyme dose and high substrate concentration. For higher XOS yield, an enzyme dose of 10 U and substrate concentration <2% was optimal. The in-vitro human faecal fermentation study revealed no significant difference in gas and short chain fatty acid level among substrates evaluated. It was observed that short chain oligosaccharides produce higher level of acetate than medium chain oligosaccharides.