Effects of calcium chloride treatments on wheat grain peroxidase activity and outer layer mechanical properties

Wheat grain soaking in calcium solutions was used as a tool to enhance endogenous peroxidase activities and follow potential changes in outer layer mechanical properties and cell wall phenolic profile. Treatment with 10 mmol L -1 calcium chloride was found to increase peroxidase activities in grains from two cultivars differing in kernel hardness, but at a different level. Concomitantly, mechanical properties of the outer layers from treated grains, assessed by uniaxial tension tests, showed significant stiffening depending on wheat cultivar. These changes were also observed in tissues after removal of the outer pericarp but not in each of the isolated layers, suggesting that modification of the mechanical properties occurs at the interface between the aleurone layer and the surrounding tissues. Analyses of the outer layer phenolic acid composition after mild or severe alkaline hydrolysis and of released lignin monomers after thioacidolysis appeared in accordance with the observed changes in tissue mechanical properties and suggest modification of cell wall compound interactions.