Title: Interactions and reactions between different types of proteins and their importance in wheat-based model and noodle systems
Other Titles: Interacties en reacties tussen verschillende typen proteïnen en hun belang voor tarwegebaseerde model- en noedelsystemen
Authors: Lambrecht, Marlies
Issue Date: 15-Nov-2016
Abstract: Proteins impact the structural quality of wheat-based food products. The main proteins of wheat are gluten proteins. These consist of monomeric gliadin and polymeric glutenin. They form a network when wheat flour is mixed with water and polymerize even further upon heating, mainly through disulfide bond formation. Gluten network formation is responsible for inter alia the visco-elastic properties of wheat-based dough, the crumb structure of bread and the cooking properties of pasta or noodles.
In many wheat-based food products including some cake, cookie, pancake, waffle, bread, tortilla, pasta and noodle systems wheat proteins coexist with globular proteins from egg, soy or milk. Under specific conditions, different proteins interact or react differently than similar proteins. Literature provides examples of changes in food systems as a result of the impact of different types of proteins on each other which are called “co-protein effects”. These can be either synergistic or antagonistic. For example, when speaking about polymerization of proteins, a synergistic (or antagonistic) effect occurs when more (or less) proteins polymerize in mixtures of two proteins than expected based on observations made with separate proteins. Even though interactions and reactions between proteins impact on food systems, the occurrence of co-protein effects is not well understood. This is unfortunate as more fundamental knowledge on the impact of egg, soy or whey proteins on protein network formation in wheat dough and later processing steps, can open perspectives for creating cost-effective food products with enhanced properties.
Against the above background, this doctoral work aimed to study interactions and reactions between different types of proteins and their importance for wheat-based food products.
In a first part, the impacts of different co-solvents in extraction and elution media on non-size effects in size-exclusion chromatography were studied. Most techniques for studying proteins require them to be soluble. Egg, soy and whey proteins are soluble in water or salt solutions while wheat gluten proteins are not. Co-solvents are necessary to solubilize gluten proteins but these in some cases interact with size exclusion resins altering the separation and apparent molecular weight distribution. An in-depth study indicated that the use of sodium dodecyl sulfate (SDS) containing medium as extraction and elution medium minimized non-size effects. A method for studying heat-induced covalent network formation of different protein types was developed. It is based on their loss in extractability in SDS containing medium and changes in molecular weight distributions during heating.
In a second part, heat-induced polymerization (100 °C) was studied in model systems for isolated wheat, egg, soy and whey protein (fractions) in water or aqueous ethanol. Proteins polymerized to a larger extent in water than in aqueous ethanol. The results of isolated protein (fractions) were compared with those of their mixtures with gluten proteins. A synergistic co-protein effect was observed in some cases, namely when proteins polymerized to a larger extent in their mixture with gluten than what would be expected based on the weight-averaged results of the isolated proteins. Phase-separation of proteins did not limit the occurrence of synergistic co-protein effects. Both in water and aqueous ethanol different protein types impacted each other’s denaturation and/or polymerization. A model was developed to predict co-protein effects between globular and wheat gluten proteins during heating at 100 °C in water. The amount of hydrophobic protein sites and accessible sulfhydryl groups of unfolded globular proteins are key parameters determining co-protein effects in their mixtures with gluten.
In a third part, non-covalent interactions were found to dominate the properties of fresh noodles while covalent cross-links and hydrogen bonds mainly determined the properties of cooked noodles. Ionic and hydrophobic interactions had some impact on cooked noodles but probably by hindering covalent network formation. The addition of whole egg positively impacted the properties of wheat-based noodles even more than that of egg white and egg yolk. Protein (fractions) with a high amount of accessible sulfhydryl groups rapidly initiated disulfide bond formation which reduced the flexibility of the protein network to cope with starch swelling during cooking. However, insufficient cross-linking during cooking lead to noodles with a weak structure and high levels of material leaching into the cooking water.
In conclusion, different types of protein can impact each other’s network formation through non-covalent interactions and covalent cross-links. High amounts of accessible sulfhydryl groups and hydrophobic protein sites in globular protein enhance the rate of gluten protein incorporation in the protein network. However, fast and excessive polymerization can reduce noodle quality. An optimal extent of protein network formation is necessary in wheat-based noodles to obtain superior quality. Addition of whole egg or bovine serum albumin enhanced the properties of cooked noodles.
Publication status: accepted
KU Leuven publication type: TH
Appears in Collections:Teaching Support Unit, Faculty of Bioscience Engineering
Centre for Food and Microbial Technology

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