State diagrams of arabinoxylan-water binaries

Since Arabinoxylans are natural polysaccharides that seem promising candidates as cryostabilizers, the state diagram (i.e. the representation in the temperature-composition plan of the macroscopic phases) of their aqueous solutions seemed worth determining.

Two lots of purified water extractable arabinoxylans (WEA) of different molecular mass (56 and 410 kDa labeled as LMW-AX and HMW-AX, respectively) were used to prepare aqueous solutions of various composition. These were cooled below their freezing point and annealed for 2 h at a suitable temperature before a DSC 5°C min⁻¹ heating run aimed at determining their primary glass transition temperature, T_g′, and the onset of ice fusion. Once the corresponding composition, C_g′, was assessed, the main curves of the corresponding state diagram were drawn.

As expected, the T_g′ value drawn for HMW-AX was higher (−17°C) than for LMW-AX (−35°C). The C_g′ was instead found close to 75% w/w for both HMW-AX and LMW-AX. The fictitiousness of this coincidence could be easily recognized by expressing the solute concentration in molar fraction, X: it was then possible to verify that, as expected, X_g′ for LMW-AX was one order of magnitude larger than for HLW-AX.     

Structural elucidation of new ferulic acid-containing phenolic dimers and trimers isolated from maize bran

Four new phenolic dimers and trimers that contain ferulic acid moieties were isolated from the alkaline hydrolyzate of insoluble maize bran fiber and their structures were established by 1D/2D NMR and mass spectrometry. The biological role of one dimer remains unclear whereas the dimeric vanillin-ferulic acid-cross-product probably represents an oxidative degradation product from the corresponding diferulate. Both ferulic acid dehydrotrimers are able to cross-link polysaccharide chains. However, the 5-5/8-O-4(H₂O)-triferulic acid may be a cross-link in its identified structure whereas we assume that the identified 8-O-4/8-5(non-cyclic)-triferulic acid arose from a natural 8-O-4/8-5(cyclic)-triferulate analog during the saponification process.