A new Density Functional Theory (DFT) based method for supporting the assignment of vibrational signatures of mannan and cellulose—Analysis of palm kernel cake hydrolysis by ATR-FT-IR spectroscopy as a case study

Attenuated Total Reflectance (ATR) FT-IR spectroscopy gives in situ information on molecular concentration, organization and interactions in plant cell walls. We demonstrate its potential for further developments by a case study which combines ATR-FT-IR spectroscopy with a recently published DFT method for polysaccharide IR band assignments.Palm kernel cake is enzymatically hydrolyzed and fermented, which targets cellulose and mannan in particular. The DFT method helps to identify their spectral changes and gives new knowledge on their spectral signatures. This method thus provides a prerequisite for FT-IR analysis. The removal of mannan is identified and correlates with positional shifts of both the mannan glycosidic linkage vibration at 1180 cm−1 and the 896 cm−1 cellulose exocyclic C6H2 vibration. This indicates a cellulose environment change, and for mannan the theoretical results show a decreasing degree of polymerization to be a plausible cause, although others may interfere.