Effect of frozen storage and microwave reheating on some physical attributes of fresh bread containing hydrocolloids

The effect of frozen storage and subsequent thawing under microwave heating on fresh bread quality was investigated. Two different flour types were used. Xanthan and guar gum were also added at ‘low’ and ‘high’ concentration (0.16 and 0.65 g/100 g flour, respectively). The specific volume, the porosity using a pycnometer, the crust firmness (puncture experiments) and the crumb viscoelastic behaviour (relaxation experiments) were evaluated. After thawing a significant shrinkage was observed, a porosity reduction in all samples, a major softening of the crust in control samples, a viscous crumb in most samples. A more rubbery crust especially in samples containing guar gum was also noticed, which can be ascribed to gums water binding capacity or to gums/water interactions and/or because gums can inhibit gluten-starch interactions influencing the plasticity of the bread. At high gum concentration destabilization effects were observed. Guar gum resulted generally in less desirable, final bread quality considering that it was not so efficient as concerning the maintenance of the gluten matrix after frozen storage, whereas xanthan addition gave better bread properties at ‘low’ concentration. Differences in respect to the flour type used were mainly observed after microwave heating. Textural attributes could be correlated to structural characteristics of the crumb (porosity and specific volume), indicating their mutual dependence.