Chapter 3: Status of carbohydrates and dietary fibre in the gluten-free diet
3.4 Nutritive value of gluten free breads currently on the market
The cereal group provides important amounts of most nutrients and plays a major role in human nutrition. Carbohydrates have a special significance in cereal products such as breads. In the course of this study, 95 gluten free bread products were purchased and their nutritive value with respect to calories, carbohydrate and dietary fibre content was evaluated. The products were grouped into white breads, brown breads, multi-seed breads and pumpernickel style breads. The average values for provided energy as well as carbohydrate and fibre content were calculated for each bread group and compared to the values for a standard wheat bread of the same category. The data for the reference wheat breads was sourced from the United States Department of Agriculture (USDA) National Nutrient Database for Standard Reference. Energy is required to sustain the body’s various functions, including respiration, circulation, physical work, and maintenance of core body temperature. In the gluten free products reviewed, the energy content (kcal/100g) varies from 178 kcal/100g for a multi-seed gluten free bread to 311 kcal for white rolls as well as a sunflower containing bread. In this respect the origin of the calories is interesting. Appendix Ia shows the calorie content as well as the amount of carbohydrates and the amount of sugar of the gluten free products. The primary role of carbohydrates (sugars and starches) is to provide energy to cells in the body. They can be classified into two broad categories: the available and unavailable ones. Available carbohydrates are those digested and absorbed by humans, which include starch and soluble sugar. Dietary fibres are carbohydrates which are not digested by the endogenous secretion of the human digestive tract (Southgate 1995). Starch is the most abundant cereal polysaccharide and is a major food reserve providing a bulk nutrient and energy source in the human diet (Dewettinck 2008). The carbohydrate content of most gluten free products is lower than the standard gluten-containing ones. This is probably due to the fact that in addition to flour or starch, nearly all gluten free formulations contain oil and a protein source such as milk or whey powder, soy protein concentrate, egg albumin, rice or lupine protein.
Another value to be considered is the content of simple carbohydrates or “sugars”. On food labels “sugars” is defined as all monosaccharides and disaccharides present, excluding polyols. The intake of mono- and disaccharides should be limited as much as possible since they increase the caloric value of a product without providing vitamins or minerals. Several products (21 out of 95) did not give information on the sugar content. In the other products the sugar content varied widely from trace amounts to substantial amounts of 8.8 g/100g for white rolls (of 46.7 g/100g carbohydrates) and 12.4 g/100g sugar for a sweet white bread (of 52.2 g/100g carbohydrates). The white wheat bread included into the study as a wheat referecence contained 4.3 g of sugar per 100g bread.
The importance of a sufficient dietary fibre intake has long been recognized. This substance group includes resistant starch, cellulose and other complex polysaccharides, such as arabinoxylans, β-glucans, pectins, arabinogalactans and lignin. Dietary fibre can be divided into soluble and insoluble portion. Soluble dietary fibre slows down glucose absorption, reduces plasma cholesterol concentrations and is useful in the management of diabetes and heart diseases. Insoluble fibre increases faecal weight, bulk and softness as well as the frequency of defecation and reduces the intestinal transit times. These effects probably play a role in preventing colon cancer and other bowel disorders (Dewettinck et al. 2008). The analysis of ingredients of the gluten free breads showed that a high number of them are fibre enriched. The substances used for this purpose include sugar beet fibre, psyllium husk, citrus fibre, pea fibre, cellulose and derivates (e.g. Hydroxypropylmethylcellulose HPMC), inulin, apple fibre, and bamboo fibre. Table 3.3 shows the amount of total, soluble and insoluble fibre as well as colour and the water holding capacity of some commercially available fibres. Regarding the dietary fibre content of the products, only 74 out of 95 stated the levels on the packaging. As shown in appendix Ia, big variations of this value could be observed. As expected, the white breads showed the lowest fibre contents, ranging from 0.1 g to 9.7 g per 100 g bread, with an average of 4.0 g per 100 g. However, compared to its gluten containing counterparts, the
majority of gluten free white breads (25 out of 32) contained a higher amount of fibre. The brown breads showed a similar average fibre content to the white bread category, with an average of 4.8 (1.3 g minimum and 9.3 g maximum). This is probably due to the fact that in several cases brands market the same product formulation twice. In many cases the white bread is transformed into brown bread, simply by adding food colouring, i.e. molasses or caramel. Seventeen out of the 54 products (brown, multi-seed or pumpernickel style breads) contained caramel, dark syrup or treacle among the ingredients. The pumpernickel style breads show a higher fibre content between 4.0 g and 7.0 g per 100 g with an average of 5.3 g per 100 g. Therefore these breads lie only slightly below the average for gluten containing pumpernickel style bread (6.5 g). The highest fibre content showed the breads containing multi-seeds, with values ranging from 3.9 g to 14.2 g and an average of 7.7 g per 100 g. The standard reference for this type of bread, containing gluten, is 7.4 g per 100 g. Summarising this data, it can be seen that the dietary fibre content of the gluten free breads is generally higher than that of the gluten-containing counterparts. However, there is some uncertainty to the data; since there is a substantial amount of samples (22 %) that did not give any information on the fibre content. It is possible that these samples were very low in dietary fibre.
Table 3.3 Several commercially used fibres and some of their physiologically and technologically important properties Fibres Total dietary fibre
[g/100 g] Soluble [g/100 g] Insoluble [g/100 g] Colour WHC [g water/g solid] References
Apple fibre 60-90 8-15 45-81 brownish 6.1 Product Specification sheet Rettenmeier (Germany) Bamboo fibre 97 0 97 white 4.8 Rossel, Santos, Collar (2009)
Cellulose 98 1 97 white 5.6 Rossel, Santos, Collar (2009)
HPMC 100 100 0 white n.a. Rossel, Santos, Collar (2009)
Citrus fibre 44-68 5-10 38-62 white - light yellow
n.a. Figuerola et al. (2005) Inulin 97 97 0 white 11.1 Rossel, Santos, Collar (2009)
Pea fibre 65-75 >0.5 >65 white - beige 6-9 Product Specification sheet Rettenmeier (Germany) Psyllium husk 77-80 >75 2-5 brownish 20 Product Specification sheet Rettenmeier
(Germany); Goni et al. (1998)