Enzymatic hydrolysis and ethanol production using xyloglucanase and Debaromyces hansenii from tamarind kernel powder: Galactoxyloglucan predominant hemicellulose

Abstract

The hydrolysis and ethanol production from tamarind kernel powder (TKP), a rich source of galactoxyloglucan (GXG) was investigated for the first time using xyloglucanase and thermotolerant Debaromyces hansenii. The acid hydrolysis of TKP with 2N H 2SO 4 at 120 °C for 30 min yielded an overall saccharification of 94% based on the total available carbohydrate content and further fermentation at 40 °C with thermotolerant D hansenii produced an ethanol yield of 0.35 g/g. A maximum hydrolysis of 55 and 78% for GXG was obtained in 48 h at 50 °C using Thermomonospora xyloglucanase (TXy) and accellerase™1000, respectively. The synergistic effect of β-galactosidase and xyloglucanase was demonstrated by the exogenous addition of β-galactosidase to TXy which improved the overall hydrolysis of GXG by 30%. The rate of hydrolysis of GXG with TXy and accellerase was increased by 15–20% in the presence of chemical surfactants (tween 80 and toluene) or protein additive (BSA). The fermentation of enzymatic hydrolysates of GXG by TXy and accellerase with free cells at 40 °C produced an ethanol yield of 0.39 and 0.41 g/g whereas with immobilized cells produced 0.45 and 0.43 g/g, respectively, with a theoretical conversion efficiencies of 78–88%. The immobilized yeast cells were reused six times at 40 °C with 100% fermentation efficiency.