Improvement of sponge cake baking test procedure and characteristics of soft wheat flour desirable for making sponge cake
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While the sponge cake (SC) baking test involves a lengthy, complicated procedure and requires experienced personnel to properly conduct the test, it provides the most informative and reliable estimation of overall end-use quality of soft white and club wheat especially for their uses in many Asian countries. Understanding of soft white wheat quality traits affecting SC baking is lacking and in great need of improvement. The objectives of this research were to develop a simple, fast and reliable baking test for predicting flour quality for use on sponge cakes and to identify functional properties of soft white wheat flour important for making acceptable sponge cakes. A simpler and comparably reliable SC baking test procedure was developed by making considerable modifications to the conventional test procedure at the egg foam whipping and batter mixing stages. Foam density, SC volume and crumb grain comparable to that of the conventional procedure were obtained with modifications, including extension of whipping time without heat input using a 5-liter KitchenAid® mixer, one time water addition at 3 min before the completion of egg whipping instead of twice, and flour incorporation into the egg foam using a KitchenAid® wire whisk or a Beater Blade®. The modified method of using Beater Blade® or wire whisk for batter mixing exhibited significant correlations in SC volume with the conventional procedure (r=0.931, P<0.001, r=0.925, P<0.001, respectively). Significance of flour particle size on SC baking performance was determined using flours of different particle size prepared by re-grinding and sieving. Particle size reduction of flour by re-grinding improved SC volume (0.8-15.0%) and crumb grain, with little change in density and viscosity of the flour-water batter despite increases in flour starch damage (0.1-0.2%) and sodium carbonate retention capacity (4.8-13.9%). Flour fractions of small (< 55 µm) particles produced the largest SC volume, ranging from 1353-1450 mL. Even with comparable or higher protein content, flour fraction of intermediate particle size produced larger volume (1040-1195 mL) of SC than did flour fractions of large particle size (955-1130 mL). The qualitative and quantitative roles of starch on SC baking potential of wheat flour were investigated using flours of various amylose content as well as different quantities and proportions of starch in the baking formula. Normal and single-null partial waxy flours produced SCs ranging from 1093 to 1335 mL in volume, while double-null partial waxy and waxy wheat flours produced SC of 828 to 895 mL. Both amylose content and pasting properties (final viscosity and setback) of wheat flour exhibited significant positive relationships with SC volume. Amylose content of normal and waxy starch blends was significantly related with their SC volume (r=0.975, P<0.05). Pure wheat starch of over 80 g or more than 75% starch in 100 g starch-gluten blends in replacement of 100 g wheat flour in the SC baking formula were needed to produce SC having the maximum volume potential.