Functionality and Structural Properties of Arabinoxylan during Frozen Storage of Yeasted Bread Dough Enriched with Wheat Fiber
The use of frozen yeasted dough in the baking industry is rising and is expected to increase in the coming years. Maintaining the stability of the dough upon freezing and prolonged frozen storage is, however, a challenge to the industry. Arabinoxylan (AX) has been known to impact dough water behaviour but, little or no information is available regarding its functionality in frozen dough. This thesis therefore aimed at understanding the functionality of wheat fiber as rich sources of AX in frozen dough and most importantly the changes in AX structure as well as its impact on the final bread product. Wheat aleurone or bran was used to replace 15% refined flour and dough made from composite flour (flour plus fiber) samples was frozen stored for 28 weeks. Frozen dough bread with added wheat fiber had higher loaf volume throughout the 28 weeks storage period compared to refined and whole wheat flour. Wheat fiber increased bound water and reduced water movement in frozen dough stored for 9 weeks. In addition, wheat fiber lessened negative changes in frozen dough strength, extensibility and stickiness. The properties of AX in frozen dough stored for 9 weeks were also investigated. Water soluble AX (WSAX) content increased for frozen dough up to the first 3 weeks of frozen storage while the degree of branching on the xylan backbone reduced suggesting removal of arabinose residues. WSAX molecular characteristics indicated a reduction in molecular weight (MW), intrinsic viscosity and radius of gyration with storage time. In this particular study, bread volume equally increased with storage time for the first 3 weeks of frozen storage. This suggested that during frozen storage of dough, WSAX levels increased due to hydrolytic activity of endogenous enzymes in the dough resulting in an increased viscosity of the dough aqueous phase. Consequently there was less water movement and little damage to gluten network structure. Enzyme modification of AX in wheat fiber enhanced frozen dough bread similar to that of unmodified AX. The findings demonstrated that the structure of AX in dough impacts its functionality during frozen storage and thus, the final bread quality.