Whole Grains and Health. Группа авторов
of sourdough processing to reduce starch digestibility is assumed to be mainly due to formation of organic acids, especially lactic acid, during fermentation (Liljeberg et al. 1995).
Specific modifications in baked product texture can be achieved by development of new sourdough cultures, and by optimizing acidity and interactions with grain components. As reported by Katina et al. (2005), the changes in dough structure over time can not only be detected by small deformation viscoelastic measurements, but also by confocal laser‐scanning microscopy. The protein fraction of the gluten‐free sourdough is degraded over time, although this process is more obvious in wheat sourdough (Clarke et al. 2004). However, the addition of sourdough to gluten‐free batters does lead to an improvement of the gluten‐free‐bread (Katina et al. 2005).
1.7.3 Cakes
Cakes are characterized by high levels of sugar and fat in the formula. Since they also contain relatively high levels of water, the molar sugar concentration is not high enough to prevent starch gelatinization during baking. Because of that, cakes set when baked, giving a light product. The presence of α‐crystalline emulsifiers increases the incorporation of air and the batter volume (Richardson et al. 2002). During conventional baking, cake batter undergoes structural transformations, including starch gelatinization, protein denaturation, volume increase, liberation of carbon dioxide from leavening agents, water evaporation, crust formation and non‐enzymatic browning. Sucrose regulates starch gelatinization and protein denaturation during baking, causing a shift towards higher temperature values (Kim and Walker 1992). Partial or total substitution of sucrose has been studied using sorbitol, wheat starch and inulin (Baeva et al. 2003; Rodríguez‐García et al. 2014). However, the replacement of sucrose in sponge cake batters with other water‐retaining agents may affect the physical and chemical transformations in the sponge cake system (Rodríguez‐García et al. 2014).
Rice flour, which does not contain gluten, is one of the alternatives to wheat flour in order to obtain gluten‐free cereal products. However, due to its low gas retention capacity, rice products have some quality problems such as low volume, poor texture, color and crumb structure. Gums such as xanthan, guar, κ‐carrageenan can be added to gluten‐free cake formulation in order to emulate the viscoelastic properties of glutenin. Different effects on the porosity are obtained depending on the gum type (Turabi et al. 2010).
1.7.4 Pasta
Two important transformations in the main components of durum wheat pasta take place during cooking: gluten polymerization and starch gelatinization. The competition of both components for water determines the final texture properties of the product (Fuad and Prabhasankar 2010). Microscopy techniques such as scanning electron microscopy and light microscopy of stained sections have helped to increase knowledge regarding the induced structural changes of pasta during cooking (Heneen and Brismar 2003). There is a moisture distribution gradient from the surface to the center due to the penetration of water and the progress of starch gelatinization. This moisture gradient is essential for the texture properties of pasta. In this way, the ideal texture of pasta, known as “al dente” is characterized by a soft outer region and a very thin hard core (Sekiyama et al. 2012). Pasta is usually made from durum wheat semolina and is a good source of low glycaemic index carbohydrate (Brennan 2008). Bran and germ particles in semolina produce a less homogeneous mixture and the particles can physically interfere with gluten development (Manthey and Schorno 2002). For this reason, bran and germ, commonly referred to as pollard, are largely removed during milling of durum wheat. However, nutritionally‐enriched pasta is also available commercially, prepared using wholemeal, semolina/flour or ground whole‐wheat. Although negative effects in the cooking and sensory properties of whole‐wheat or bran enriched pasta have been frequently reported, spaghetti dried at high temperature can be prepared with pollard, with 10% substitution of semolina, causing minimal impact on sensory and technological properties (Aravind et al. 2012). High molecular weight inulin can also be incorporated with minimal effect on the technological and sensory properties below 20% incorporation (Aravind et al. 2012b).
Nuclear magnetic resonance imaging (MRI) is a non‐invasive and nondestructive method to visualize the water distribution and to study its influence in the properties of pasta (Bonomi et al. 2012). It has proved particularly useful in combination with microscopy techniques such as light microscopy or epifluorescence. This way, the water distribution has been related to differently cooked zones in pasta (Sekiyama et al. 2012) and the influence of raw materials in the microstructure of cooked pasta (Steglich et al. 2014). In pasta, the gluten network is continuous throughout the whole tissue encapsulating starch granules and fibre particles. However, according to the study carried out on spaghetti by Steglich et al. (2014), microstructure is not homogeneous throughout the product after cooking since starch granules are affected by heat differently depending on their distance to the surface. Starch granules in the core region did not gelatinize, while granule distortion and amylose leakage increased towards the surface (Figure 1.5A). The MRI and microscopy results of this study proved that the local water content and microstructure differed due to locally varying raw materials. The whole grain pasta showed lower (darker) T2 * values, which was attributed to faster exchange of water protons with exchangeable fibre protons or to less swelled starch granules in the areas close to the fibre particles or both (Figure 1.5 B–D). Rice, being low in protein, has relatively poor technological properties for interacting and developing a cohesive network for gluten‐free pasta products. Severe parboiling, extrusion cooking and/or addition of pre‐gelatinized flour are required in order to obtain the desired texture and avoid excessive leaching of solids during cooking (Marti et al. 2013).
Figure 1.5 Representative cross‐sections of 10‐min cooked spaghetti made of 100% fine durum wheat semolina (DS) and durum whole grain flour (DS+WG). A: Bright field light micrographs at high magnification from three regions; B–D: Bright field light micrographs (B), polarized light micrographs (C), and T2* maps (D) of cross‐sections at lower magnification. Sections in A and B were stained with Light Green and Lugol’s iodine solution for observation of protein (green) and starch (blue/violet), respectively, while fibre particles were not stained
(Source: (B) and (D): Modified from Steglich et al. 2014).
1.8 Starch network‐based products
Most ready‐to‐eat cereals (RTEC) possess a starch network‐based structure. These products are processed cereals suitable for human consumption with or without further cooking at home and are usually eaten at breakfast or as snacks. RTEC constitutes an important contribution to daily nutrient intake and breakfast quality according to recent analyses on previous studies and evidence (Kosti et al. 2010; Williams 2014). RTEC are typically grouped by cereal form rather than the type of grain used. Apart from rolled cereals, the main types are whole grain flakes, puffed grain cereals and extruded cereals. Unlike rolled cereals, the later types of RTEC go through a step that cooks the grain in combination with flavor materials, sweeteners and/or nutritional fortifying agents. Gelatinization of the starch grain fractions is the main purpose of the cooking stage and is essential for the development of the desired textural and organoleptic properties of these products.
Crispbread, which traditionally has been elaborated with rye flour, have a continuous starch network which encapsulates the protein, due to the