Viscoelastic Properties and Air-bubble Structure of Bread Containing Gelatinized Rice Porridge

Abstract

The effect of the addition of gelatinized rice porridge was investigated on the following bread qualities : loaf volume, viscoelastic properties and air-bubble structure. Four kinds of bread were prepared : bread containing rice porridge (rice porridge bread), bread containing gelatinized rice flour (gelatinized rice flour bread), wheat flour bread and rice flour bread. Evaluation of qualities of the breads was carried out by volume measurement of loaf samples, creep test and digital image analysis on the air-bubble structure of crumb specimens. Rice porridge bread showed a maximum specific volume of 4.51cm³/g, and gelatinized rice flour bread also showed 4.30cm³/g, which was larger than rice flour bread. The viscoelastic moduli values of gelatinized rice flour bread and rice porridge bread were significantly smaller (p<0.05) than those of wheat flour and rice flour breads, which indicates that the addition of gelatinized rice flour or rice porridge to bread dough made breads softer. Bubble parameters such as mean air-bubble area, number of air-bubbles, and air-bubble area ratio (ratio of bubble area to whole area) were not significantly different among the bread crumb specimens. Therefore, the bubble structures of the bread samples seemed similar, which implied that differences in viscoelasticity resulted from the air-bubble wall (solid phase of bread crumb) rather than the air-bubble. This study showed that a 15% addition of gelatinized rice to bread dough produces bread with larger loaf volume and soft texture without improving agents such as gluten.