PHYSICAL AND CHEMICAL TREATEMENTS OF ZEIN TO IMPROVE GLUTEN-FREE BREAD QUALITY
thesisposted on 25.02.2021, 04:40 by Enrico Federici
Gluten is a complex mixture of proteins imparting unique viscoelastic properties to doughs. However, despite its outstanding role in producing high quality baked goods, gluten is also associated with health disorders such as celiac disease or gluten sensitivity. This generated an increased demand of gluten-free products as individuals suffering of gluten-related disorder need to follow a strict gluten-free diet. Zein is a gluten-free storage protein from corn possessing promising features for gluten replacement in breadmaking. Although numerous studies attempted to improve zein dough rheological properties to improve its breadmaking performance, zein bread making potential remain inferior if compared to gluten. When it is incorporated into a dough, zein can form fibrils which confers extensibility, however, it does not possess a strain hardening behavior, a fundamental feature to produce high quality bread.
To improve zein dough strain hardening we hypothesize that structures formed by zein are not large enough to generate an elastic response, however the application of physicochemical treatment can induce the formation of broader structures better suited to store energy and therefore generate elasticity. Thus, the objective of this dissertation is to determine if dough viscoelastic properties essential for bread production can be obtained through the application of treatment favoring the formation of larger zein structures.
Zein was electrospun using aqueous ethanol or acetic acid as solvent to form nanofibrils. Several additives were tested to enhance fibrils mechanical properties. Zein electrospun fibers were then incorporated into a dough and the extensional properties of the resulting dough were assessed with a texture analyzer. Results indicated that, the addition of electrospun fibrils into dough did not improve the generation of elasticity, suggesting that fibrillar morphology is not an essential feature for the generation of elasticity.
The effect of extrusion and thermal treatment on zein were tested. The formation of zein large assemblies has been assessed with the use of SDS-PAGE, showing the formation of larger aggregates for either treatment. FTIR and a texture profile analysis were performed to assess the secondary structure and elasticity of zein viscoelastic masses. Results indicated an increased amount of β-sheet structure together with increase of springiness and cohesiveness from 0.56±0.01 and 0.43±0.01 of untreated zein to 0.87±0.01 and 0.77±0.01 of samples treated at 190℃. Treated zein was then added to a dough which was tested for extensional properties with a texture analyzer. Results indicated the generation of strain hardening behavior in dough, a fundamental property for dough gas retention, both in extruded zein and thermally treated samples at 160℃. Finally, extruded zein and thermally treated zein were incorporated into a dough and baked into a loaf of bread. Despite improvement in rheological properties, incorporation into bread did not show improvement in bread quality.
The findings of this dissertation showed that the use of zein extrusion and thermal treatment is an effective tool to improve the elasticity and strain hardening behavior of zein dough, potentially finding application as a substitute of gluten. Furthermore, this study showed that it is possible to form a gluten-free dough which is extensible and possess a strain hardening behavior.