Mechanical, microstructure and permeability properties of a model bread crust: Effect of different food additives

• Crust layer is proposed as a model for studying moisture barrier and migration properties.
• Additives modify water vapor permeability, sorption isotherms and mechanical properties.
• Functional properties are correlated with microstructural changes due to additives.
• Additives promoting discontinuities within the structure decrease fracture hardness.

The aim of this study was to understand the action of different additives on the crust properties using a layer crust as a model. Moisture content, water vapor barrier properties, water sorption isotherms and mechanical properties were evaluated. Crust model showed multilayer internal structure. Glycerol (10% and 20%) and HPMC-10% increased moisture content, whereas linolenic acid and beeswax, glycerol-1%, HPMC-0.5% and citric acid significantly decreased it. Water vapor permeability (WVP) decreased with lipids and citric acid, due to their hydrophobic nature and crosslinking action, respectively. Hydrophobic additives lowered the WVP of the crust and provided water barrier properties and brittle texture. Crust mechanical properties were greatly correlated with water present as well as with composition of crust layer. Barrier properties of the crust layer were greatly dependent on the hydrophilicity or hydrophobicity of the additives, which determined the internal interactions between starch and proteins and the microstructure and mechanical properties.