Wheat grains contain a lot of starch (around 75%-80% of the dry weight), which is the main carbohydrate. Soft wheat has more starch than hard wheat, and this is usually true for grains with less protein. There are two types of granules in wheat: A-type (larger, 20-35 mm diameter) and B-type (smaller, 2-8 mm diameter).
|Flour Component (%)
|Starch and other carbohydrates
Properties of wheat starch are closely linked to the appearance, structure, and quality of many food products. Its major uses in food application are connected with gelatinization, pasting, and retrogradation, which underlie starch functionality. Native starch granules are insoluble in cold water, but when temperature is increased, starch loses its molecular organization and undergoes irreversible changes. Indeed, during processing, starch dispersions are subjected to combined heating and shearing effects that affect their rheology and the final characteristics of the product (Cornell, 2004; Mason, 2009).
The gelatinization temperature is about 53-64°C in wheat starch, which is lower than that in most other starches (BeMiller and Whistler, 1996); it depends on the concentration, granule type, and heterogeneity within the granule population (Atwell et al., 1988). Pasting is defined as the state following gelatinization of starch. The starch paste is described as a two-phase system where swollen granules are dispersed in a continuous phase of entangled amylose molecules (Ring, 1985; Mason, 2009). Pasting properties of starch are governed by the concentration, the heating rate, and the presence of other food components (Mariotti et al., 2005).
Another phenomenon upon cooling is called retrogradation, which represents the gel form by the reassociation of amylose chains. This process involves formation of ordered structures during storage (Atwell et al., 1988). Retrogradation is important as it can be a desired end point in certain applications, but it also causes bread/cakes staling and instability in starch pastes. Lots of factors could influence the rate of retrogradation such as the botanical sources (cereal starch in contrast to tuber starch), the amylopectin structure (chain length and distribution), and the amylose-to-amylopectin ratio.
Starch is used in a wide range of foods for a variety of purposes including thickening, gelling, adding stability, and replacing or extending costlier ingredients. It has a range of roles in a variety of foods, as shown in Table 2. An understanding of the mechanism underlying each effect is necessary to make the best use of starch in these functions. However, the changes that starch undergoes during pasting and cooling could impact the structures of foods. Moreover, it is important to recognize how the cooked starch paste changes during storage and the resulting effects on the texture and appearance of the foods. The selection of starch for a given use depends on the desired food properties and the processing and distribution stresses involved.
|Battered and breaded foods
|Formed meat and snack seasonings
|Fried and baked foods, snacks
|Chewing gum, bakery products
|Flavors, beverage clouds
|Ice cream, salad dressings, spreads
|Gum drops, jelly gum centers
|Gravies, pie fillings, soups
Bakery products remain the predominant application for wheat starch. The wheat flour is the major ingredient around which bakery formulas and processes have been developed.
Gelatinization during baking plays a significant role in the formation of the product structure and the changes that subsequently occur as the product is cooled and stored. However, gelatinization does not occur in all baked products, and the degree to which it occurs depends on the availability of water. In low-moisture recipes, such as for biscuits and pastes, the water level is generally too low and the competition for that water too high for significant gelatinization to occur.
In yeast-leavened dough, wheat starch dilutes the wheat gluten to an appropriate consistency, provides maltose for fermentation, and provides a surface for strong bonding with wheat gluten. During baking, it provides flexibility for loaf expansion during partial gelatinization and sets the loaf structure. When it comes to cooling stage, it provides a rigid network to prevent the loaf from collapsing, giving structural and textural properties to the baked product.
Different authors have investigated the influence of granule size distribution on bread characteristics (Shinde et al., 2003; Larsson and Eliasson, 1997). Larsson and Eliasson (1997) showed that the extensibility of the dough increased by the small granules, whereas the resistance to extension decreased by large granules. Park et al. (2004, 2005) showed that the texture was highest when the flour was reconstituted with 30% small granules and 70% large granules in straight dough bread.
In other bakery products (pies, cakes, biscuits, crackers, and meringues) as reviewed by Hahn (1969), the use of starch showed an improvement of product quality by addition of wheat flour. Dubois (1959) showed significant improvements in volume, grain, texture, eating quality, and freshness retention when replacing 30% of the cake flour with wheat starch in angel-food and other foam-type cakes.
In pastries, substitution of wheat starch for 30% of the flour in such hig-hfat products increases product tenderness with a possibility of 17%-20% reduction in shortening as reported by Maningat et al. (2009).
In biscuits and warping of wafers, wheat starch at a level of 5%-30% based on flour is added to prevent cracking. In cookies, the wheat starch remains ungelatinized and does not form a continuous structure after baking (Kulp et al., 1991). Contrary to other baked products (bread and cakes), staling by retrogradation of wheat starch cannot occur during cookie storage. However, textural changes observed during cookies storage come from the moisture interchange among cookie components.
Regarding staling process, in breads, the crumb firming was linked to amylopectin recrystallization within swollen wheat starch granules (Hebeda and Zobel, 1996; Gray and BeMiller, 2003). Some type of modified starches could be used to decrease the staling of baked products as shown by Seyhun et al. (2005) and Hesso et al. (2014).