Rheological characterisation of cell walls from wheat flour and endosperm: effects of diferulate crosslink hydrolysis

The crosslinking of arabinoxylan chains with ferulic acid dimers in wheat endosperm cell walls is hypothesised to limit the swelling and solubilisation of cell wall polysaccharides. In this study, we report the changes in the rheological and chemical properties of cell walls isolated from wheat flour and purified endosperm after treatments intended to cleave the dimers using enzyme (feruloyl esterase) and alkali (NaOH). Treatment with enzyme at the studied amount released less diferulic acid than alkali, and did not release 8–5′ dimers. All treatments markedly altered viscoelastic behaviour. Before enzyme or alkali treatment, cell walls behaved as structured soft solids with elastic modulus (G′) greater than loss modulus (G″) and limited frequency dependence. Both G′ and G″ decreased following enzyme or alkali treatments, and at higher frequencies, the resulting suspension changed behaviour from solid-like to more liquid-like, with G’’ > G′. The alteration of rheological properties and loss of ferulic acid and dimers correlated with the microscopic observation after enzyme/alkali treatment that cell walls lose their structural integrity, as well as releasing more polysaccharide into solution. These results suggest that the breakage of ferulic acid crosslinks can be used as a technique to alter the rheological behaviour of cell wall polysaccharides in wheat flour with consequences for both nutritional as well as processing functionality.