Controlled Foaming on Cereal Protein

Abstract

Foamed materials are used today in many applications such as packaging, insulation, protection, construction materials and in food as well. What differentiates them, in addition to the physical and chemical properties of the materials, is their cell structure giving different foam properties, like porosity, density, strength and texture. Thus, keeping the foaming process under control is fundamental. It can yield to different products, characterized by their own structure, but made up with the same materials. In this project a model foam system of a cereal prolamin protein, starch, plasticizer and foaming agents, with applications in gluten free food and insulation foams, was developed and characterized. The protein zein was mixed with maize starch, plasticizer and foaming agent into a composite protein melt, which was heated in a hot mould (two parallel, heat controlled plates) to initiate the gas formation and foaming process. A mathematical model for the foam density, based on the main ingredients and the mould temperature, was developed and verified. Analysis on both dough and foams were performed. Specific measurements were performed on two different mixtures, identified by the model in having equal density but quite different structure. Foam characteristic (geometry, mean volume-weighted star volume, surface density and compression test) and rheological properties of the melt (extensional viscosity and strain hardening index) of these two were analyzed to further elucidate the relationship between the ingredients, and the process parameters and the foam and melt properties. The percentage of zein/starch amount was the most important factor followed by the presence of foaming agent and the mould temperature respectively, while plasticizer was not important for the foam structure, even if it was necessary to form a melt at the process temperature. The foaming process of dough with lower amount of zein was influenced by the swelling of starch, whose rate was related to the mould temperature, where the foaming agent was necessary to develop gas bubbles.