The effect of emulsifier and/or sucrose on the swelling of an 8% wheat starch dispersion was evaluated by microscopy. Visual observations of smeared starch pastes under the light microscope, image analysis of the starch granule sizes and viscosity measurements of the starch paste during heating were combined to explain the effects of the added ingredients. Sucrose (12 or 24%, w/w) was shown to delay the swelling of the granules at least up to 50 °C. Above this temperature, the leakage of amylose and granule fragmentation were delayed, but the swelling itself seemed to be accelerated. The polyglycerol ester emulsifier (PGE/MG) at concentrations of 0.5 and 4.0% hindered amylose leakage completely up to 90 °C, followed by a sudden granule rupture. The size of the granules increased up to about 70 °C, but not above this temperature. The monoglyceride (MG) emulsifier in α‐form already had a restrictive effect on the swelling at low temperatures, while the same emulsifier in β‐form did not restrict the swelling until higher temperatures were reached. The emulsifier itself converted into the lamellar state at between 55 and 70 °C, irrespective of the initial form, but the final viscosity was higher in the paste with MG in β‐form. Thus, the initial physical state of the emulsifier was shown to have an influence on the final properties of the gel.

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Cereal Chem. 79(4):546-552The microstructure of a-gel and b-crystalline emulsifiers and their effects on cake batter foam have been studied with polarized light microscopy, confocal laser scanning microscopy (CLSM) and image analysis, freeze-etching, and transmission electron microscopy (TEM). The emulsifiers Colco and Aroplus, which are commercial a-gels, and the monoglyceride Dimodan P in its a-gel and b-crystalline forms were added to the batter in concentrations of 0.8, 2.0, 3.1, and 4.2%. Dimodan P a-gel was also prepared with three NaCl concentrations (0.05, 0.67, and 1.35‰). The distribution of air in the foam was evaluated with density measurements and with image analysis of bubbles in optically sectioned batter. In the cake batter, all the a-gel emulsifiers decreased the density, thereby increasing the incorporation of air, more than the b-crystalline emulsifier, which did not have any effect on the density. There were noticeable differences in microstructure between the different a-crystalline emulsifiers. Large, regular a-structures seemed to increase the batter volume and interfacial area more than smaller aggregates. Adding salt in the emulsifier gel changed the structure, probably into a-lamellar liposomes, which impaired the aerating effect at lower concentrations.Emulsifiers are widely used products in the food industry. The most apparent field of application is the dispersion of air into a foam or an emulsion, since the surfaces are stabilized by either proteins or emulsifiers. In the baking industry, the emulsifiers are also used for other effects. A sponge cake batter with emulsifier can be whipped in a one-stage process, simplifying the production. The incorporation and stability of air bubbles are improved, and a finer dispersion gives a better cake quality. The emulsifiers may also improve the shelf life by interactions with starch, slowing down the recrystallization process.One way of studying the foam stability and air incorporation is to measure the air bubbles with some kind of microscopy. Cauvain and Cyster (1996) showed a bubble size diagram in which the air bubbles in the batter decrease from 25 to 10 mm as the emulsifier level rises. Unfortunately, they did not reveal how this measurement was performed. Shepherd and Yoell (1976) squashed the batter under a cover glass to make the measurements under a light microscope. A more gentle variant of transmission microscopy was used by Brooker (1993). This did not include any squashing, but the analyzed layer was 1-2 mm thick and several bubbles were on top of each other. It would be more practical to use a method that makes optical sections of the foam, such as confocal laser scanning microscopy (CLSM). In combination with image analysis, the method should give information about the bubble size distribution and the stability. The theories about image analysis and the interpretation of two-dimensional images are well described by Russ (1990).The performance of an emulsifier in a foam will depend on factors such as the chemical content, the h...

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