In-situ Micro-FTIR Spectroscopic Observation On The Hydration Process Of Polyporaceae Fungi

Auricularia and poria cocos are both valued as edible and medicinal resources.Their hydration is a fundamental process when eaten. In order to know the effect ofwater on the structure of auricularia and poria cocos, the Micro-Fourier transforminfrared spectroscopy (Micro-FTIR) technique has been used and the gained IRspectra are measured and analyzed in detail.The IR peak of water as well as that of auricularia was found to be sensitive tohydration. By the band fitting at3258cm-1at low relative humidity (RH), it wasfound that strong hydrogen bonds were formed between water molecules andpolysaccharide. In detail, strong hydrogen bonding was formed between the watermolecules and the carboxyl C=O groups of polysaccharide at first at RH22%, whichwere reflected by a red shift of the C=O stretching band from1735to1730cm-1. Withincreasing RH from22to37%, the strong hydrogen bonding was formed betweenwater molecules and carboxyl C-O groups, exhibiting a blue shift from1245to1250cm-1for the C-O(H) stretching band. With further increase of RH, the watermolecules continuously bonded with OH groups of polysaccharide and evenaggregated to form clusters with spectral characteristic of bulk water.In Poria cocos, Triterpene compound and polysaccharides are main compositionin poria cocos. The heteropolysaccharide was identified as a linear chain of β-(1�'3)-D-glucan. Because of strong overlaps between some bands, the difference spectraand band decompositions has been applied to analysis the structural change. IRspectra show the transform of hydrogen bonds with the RH. It means that the=CH2groups (1417cm-1) form strong hydrogen bond with water molecules at lower RH,and then some transfer to weak hydrogen bond with the increase in RH. The furtherstudy suggests that the C1-OH、C2-OH、C3-OH groups from polysaccharide bond toform C1-OH···H2O、C2-OH···H2O、C3-OH···H2O steady modes, respectively, withwater molecules.