An investigation into the functionality of kafirin from a high digestible, high-lysine sorghum in a composite dough and bread system
Abstract
Sorghum proteins are unable to form the viscoelastic protein networks necessary for the creation of high quality leavened bread products. It is thought that the main contributing factor to this lack in functionality is the formation of the kafirins into rigid protein bodies during grain development. The discovery of a high digestibility, high-lysine (HDHL) sorghum cultivar that is freed from the conventional protein body may prove to be the answer to sorghum use in breadmaking. The aim of this study was to determine whether protein body-free kafirins in HDHL sorghum flour can participate as viscoelastic proteins in sorghum-wheat composite dough and bread. Dough extensibility tests revealed that maximum resistance to extension (g) and time to dough breakage (sec) at 35°C for HDHL sorghum-wheat composite doughs were substantially greater (p<0.01) than for normal sorghum-wheat composite doughs at 30 and 60% substitution levels. Functional changes in HDHL kafirin occurred upon exceeding its Tg. Normal sorghum showed a clear decrease in strain hardening at 60% substitution, whereas HDHL sorghum maintained a level similar to wheat dough. Significantly higher loaf volumes resulted for HDHL sorghum-wheat composites compared to normal sorghum-wheat composites at substitution levels above 30% and up to 56%, with the largest difference at 42%. HDHL sorghum-wheat composite bread exhibited lower hardness values, lower compressibility, and higher springiness than normal sorghum-wheat composite bread. Finally, HDHL sorghum flour mixed with 18% vital wheat gluten produced viscoelastic dough while normal sorghum did not. The use of sourdough fermentation allowed for an increase in bread volume of the 36% HDHL sorghum-wheat composite bread by 35cm3, bringing it within the standard deviation of a 20% HDHL sorghum-wheat composite bread. This is in contrast to the 36% normal sorghum-wheat composite bread which only increased by 5 cm3. Pre-gelatinization of the sorghum flour before addition to the composite dough allowed for an increase in volume for the HDHL sorghum-wheat composite bread by 25cm3, whereas the normal sorghum-wheat composite bread increased by 10 cm3. Finally, the addition of vital wheat gluten greatly aided in the volume and overall bread quality of the HDHL sorghum-wheat composite bread, allowing for the production of a 36% HDHL sorghum-wheat composite bread with a volume that was not significantly different from the 100% wheat flour control. These results clearly show that kafirin in HDHL sorghum flour contributes to the formation of an improved protein network with viscoelastic properties that leads to better quality composite doughs and bread.
Degree
M.S.
Advisors
Hamaker, Purdue University.
Subject Area
Food Science
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