FTIR mapping of peels of <em>Litchi chinensis</em> after acid treatment and its SSF for ethanol production by <em>Pachysolen tannophilus</em> MTCC 1077

Abstract

Pulverized peels of <em>L. chinensis</em> consists of 40 ± 0.38% cellulose, 28 ± 0.18% hemicellulose and 25 ± 0.31% of lignin on dry solid basis. About 1% HNO₃ delignified peels of <em>L. chinensis</em> yielded 46.71% xyloseand 12.42% arabinose under steam explosion, with a hydrolytic efficiency of 78.2 ± 0.45%. Fourier transform infrared (FTIR) spectroscopy results not only indicated the penetration of HNO₃ in the amorphous region of the biomass and degradation of hemicelluloses but also revealed the structural differences before and after pretreatment. Simultaneous saccharification and fermentation (SSF) of pretreated peels of <em>L. chinensis</em> by crude cellulase and immobilized yeast <em>Pachysolen tannophilus</em> MTCC 1077 were investigated in the present study. Important process variables for ethanol production from pretreated peels of <em>L. chinensis</em> were optimized using response surface methodology (RSM) based on central composite design (CCD) experiments. A three level CCD experiments with central and axial points was used to develop a statistical model for the optimization of process variables such as incubation temperature (30°C, 32°C and 34°C) X1, inoculum level (2%, 4% and 6%) X2 and nutrients (1/2/3) X3. Data obtained from RSM on ethanol production were subjected to the analysis of variance (ANOVA) and analyzed using a second order polynomial equation and contour plots were used to study the interactions among three relevant variables of the fermentation process. The processing parameters setup for reaching a maximum response for ethanol production was obtained when applying the optimum values for temperature (30°C), inoculum level (6%) and fermentation medium (ammonium sulphate, KH₂PO₄, peptone and yeast extract) for <em>P. tannophilus</em> MTCC 1077. Maximum ethanol concentration 10.5 g/l was obtained after 72 h from <em>P. tannophilus</em> MTCC 1077 at the optimized process conditions in anaerobic batch fermentation.