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Title: Understanding ingredient functionality in pound cake making and storage
Other Titles: De rol van ingrediënten tijdens de bereiding en bewaring van pound cake
Authors: Luyts, Annelies; M0323358
Issue Date: 18-Nov-2014
Abstract: Pound cake, a common European cake type, is prepared from equal portions of flour, sugar, fat and eggs. During baking, both starch and egg components form a gel. This results in water binding and structure setting. Temperature gradients during conventional pound cake batter baking cause structure setting to take place at different times in different regions of the batter. As a result, crumb of conventional cake is heterogeneous in terms of moisture content and starch and protein properties. During storage, cake crumb firms through mechanisms that, when this work started, were still poorly understood. Still, most authors agreed that crumb to crust moisture migration has a large impact on crumb firming. We here set out to study the mechanisms by which crumb firming occurs. In a first experimental chapter, model systems of different complexities, i.e. flour-water, flour-sugar-water, egg-water, egg-sugar-water and flour-egg-sugar-water models, were analyzed by proton (1H) nuclear magnetic resonance (NMR) to provide a basis for studying proton mobility in pound cake and its crumb. Crumb proton populations were assigned to (A) non-exchanging CH protons of crystalline starch, proteins and crystalline fat, (B) and (C) non-exchanging CH protons of amorphous starch and gluten, which are in little contact with water, (D) exchanging protons of water, starch, gluten, egg proteins and sugar and (E) protons of lipids from margarine and egg yolk.In a next chapter, electrical resistance (ER) heating was used to produce cakes with minimal moisture gradients. In the further experimental work, this technique was applied to study processes other than moisture migration during storage of cakes. The baking process in an electrical resistance oven (ERO) was first compared with that in a conventional oven. In an ERO, the structure setting of cakes, which is the result of both starch and egg gel formation, progressively and uniformly takes place throughout the entire cake batter and ultimately results in homogeneous cake crumb. For conventional cakes, a batter moisture content of 26.9% was sufficient to gelatinize all starch in the center crumb. More moisture evaporation during baking in the ERO resulted in the need to increase the batter moisture content to 30.0% to allow all starch to gelatinize in these cakes (further referred to as ERO cakes). Minimal temperature gradients during baking in the ERO resulted in cakes with minimal moisture gradients. Furthermore, starch gelatinization and protein network formation by covalent linkage formation occurred in a similar way during both conventional and ERO baking. All in all, ERO baking allows producing homogeneous cake samples, with starch and protein properties similar to those of the center of conventional cakes. Only in the outer crumb layer, i.e. at a distance of up to 1 cm from the side walls in the ERO, starch and protein properties may be slightly different because of the small temperature gradient close to the surface. Moisture migration from crumb to crust contributes to firmingof crumb of conventional cakes and evidently not to that of ERO cakes. DSC and 1H NMR measurements showed that the contribution of amylopectin retrogradation to crumb firming was rather small but significant in both cake types. To further study the importance of amylopectin retrogradation for pound cake crumb firming, amylases were included in the recipe. The texture of the resultant ERO cakes was monitored during storage. First, activity of amylases with varying modes of action, i.e. maltogenic, maltotetraose forming and endo-amylases, was measured in different sucrose concentrations and at different temperatures. To work properly during cake baking, the amylases should be active at high temperature (85 °C) and in high sucrose concentrations. Our results showed that the maltotetraose forming amylase was the least sensitive to both high temperature and high sucrose concentrations. Based on the results, different amylases with varying working mechanisms, i.e. two maltogenic amylases, an endo-amylase and a maltotetraose forming amylase, were selected for cake making and enzyme dosages appropriate for cake making were determined based on dose-response curves for cake volume. In the last part of this study, the amylases selected in the previous chapter were added to the recipe of ERO cakes in doses determined as described above. The crumb texture evolution of these cakes during storage was monitored and related to changes in amylopectin retrogradation and proton mobility. The impact of amylases on cake firming during storage depends on their mode of action and the effects on cake crumb firming resemble those found for bread crumb firming. Since starch in cake batter is much more diluted than in bread dough, and because of the high levels of sugar in cake batter, it is hypothesized that starch in pound cake is present in more or less intact swollen granules, surrounded by a limited amount of leached amylose, and embedded in a protein network. Exo-amylases limit crystallization of the side chains of amylopectin inside the granular structures. In contrast, endo-amylases had only a limited impact on amylopectin retrogradation. The anti-firming effect of exo-amylases was more pronounced than that of endo-amylases in line with what is known for bread systems. All in all, we conclude that some exo-amylases are effective anti-firming agents in cake. Their anti-firming properties very likely result from inhibition of amylopectin retrogradation. Although amylopectin retrogradation was reduced to a great extent in cakes baked with (some) amylases, crumb firming of these cakes was much less affected. Therefore, we conclude that the firming of ERO cakes during storage is also influenced by processes other than amylopectin retrogradation.In conclusion, comparison of the changes in crumb properties of conventional and ERO cakes during storage allowed putting forward a crumb firming mechanism maintaining that crumb to crust moisture migration is the dominant and amylopectin retrogradation is only a minor factor in cake crumb firming.Further work will be needed to unravel the role of other components such as amylose, protein and lipids in cake crumb firming during storage.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Centre for Food and Microbial Technology

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