Gluten-free bread and other products are used by sufferers of coeliac disease, who experience digestive problems as a result of consuming gluten. Long term consumption of gluten can cause damage to the small intestine.
It is estimated that around one in 200 people suffer from the condition, but only a fraction of these are diagnosed because there are any number of atypical forms. As it gains greater recognition delivering appropriate, nutritionally valuable and appealing foods is a challenge for food manufacturers.
Typically, gluten-free products contain starch from corn, rice, soy and buckwheat flours - but as the authors of the new study pointed out, these are lacking in important nutrients and dietary fibre.
Moreover, the weaker structure of gluten-free bread compared with conventional bread makes it difficult to add in additional nutrients.
"It seems… that the easiest way to increase the content of dietary fibre in gluten-free bakery products is to introduce it as usually used ingredients or to replace standard ingredients with analogues rich in fibre," wrote researcher Jaroslaw Korus and colleagues in the study write-up, which has been accepted for publication in the journal Food Hydrocolloids.
Korus set out to investigate the use of resistant starch as a partial replacer for corn starch in gluten-free bread, since it aids functioning of the digestive tract, microbial flora, blood cholesterol levels and can help in diabetes management.
On the other hand, preparations using resistant starch are "less prone to pasting". Since the structure of bread depends on starch gelatinisation, it was thought that this could affect loaf quality.
Korus and team prepared gluten free breads containing corn starch, potato starch, guar gum, pectin, freeze dried yeast, sucrose, salt, plant oil and water.
In each loaf, a proportion of the corn starch (10, 15, 20 and 50 per cent) was replaced by corn resistant starch, and the same proportions of potato starch were replaced by tapioca resistant starch.
The researchers then compared the rheological properties. The tapioca resistant starch was seen to have the most positive effect on gelatinisation and decreased viscosity, which may explain the lower hardness of the bread.
The effect on other rheological parameters appeared limited. For instance, the resistant starch was seen to have no significant impact on crumb texture. Sensory evaluation was also comparable, "which proves that partial replacement if starch in recipes for gluten free bread with resistant starch preparation doesn't significantly influence organoleptic quality of the obtained bread," wrote Korus in the conclusion.
The team stressed, however, that use of the resistant starches meant the amount of water in the formulations had to be adapted according to absorption and to get the right dough consistency.
However on a nutritional level, the breads with resistant starch were seen to have much high dietary fibre content, as well as insoluble and soluble fractions.
The highest total dietary fibre achieved was 6.30g per 100g. This led the researchers to conclude that "such a bread could be advised for technological practice".
Food Hydrocolloids (Elsevier) - online ahead of printDOI: 10.1016/j.foodhyd.2008.07.010"The impact of resistant starch in characteristics of gluten-free dough and bread"Authors: Jaraslaw Korus, Mariusz Witczak, Rafal Ziobro and Leslaw Juszczak