Impact of melt rheology on zein foam properties

Abstract

Zein, the main protein fraction in maize, is left as a by-product from bio-ethanol production. The protein has been investigated as a material for a long time, but mainly in the form of films. In contrast, foamed zein is presented in this paper. Zein foams may perhaps be used e.g. as trays for biodegradable food packages or as scaffolds for tissue engineering. A batch method for manufacturing solid foams was successfully developed, the foams being manufactured by evaporation of solvent from zein resins. In order to be suitable for foam formation, a resin must possess gas-retaining properties, which can be predicted by extensional rheology. The presence of plasticizer in some of the resins decreased their extensional viscosity, and this in turn affected the foaming process. Although all the resins displayed strain-hardening behaviour, there was coalescence of pores in all the foams. Insufficient extensional viscosity resulted in the collapse of pore walls during foam expansion. Structure analysis showed e.g. that most pores were elongated along the main axis of the mould in which the foams were manufactured. The plasticizer content in the resins had no significant effect on the mechanical properties of the foams.

Effect of viscoelasticity on foam development in zein–starch dough

“…For the dough formulations prepared in this study, the m-index ranged from a minimum of 0.7 ± 0.3 at the extension rate of 0.01 s À1 to 1.8 ± 0.4 at 1.0 s À1 . These values are consistent with those reported previously (Gillgren et al, 2010) for zein foams. Differences in the strain hardening index Table 1.…”

“…A standard error was then calculated for the measurements for each formulation. The symbols correspond to the formulations listed in Table 1: filled squares, base formulation; empty triangles, CA 0.5; filled triangles, CA 1; empty circles, CA 2. which the cell walls collapse during cell expansion and the foaming process (Gillgren et al, 2010). Since no leavening agent was used and the dough was not proofed, bubble expansion was driven by the phase transition to steam of the water contained in the dough at temperatures between 80 C and 100 C. The dough softens with increasing temperature until drying occurs, concomitant with crosslinking of the zein.…”

“…assuming the validity of the CoxeMerz rule for the zein-based dough (Gillgren et al, 2010). The K and n power law parameters from Eq.…”

“…Subsequent studies investigated bubble growth during the proofing and baking of zein doughs that contained starch, plasticizers, and leavening agents (Andersson et al, 2011;Dobraszczyk, Smewing, Albertini, Maesmans, & Schofield, 2003;Lawton, 2004;Schober et al, 2008). The formation of bubble structures in the crumb, and consequently the texture of the baked products, was found to be related to several physical properties of the dough, such as shear and extensional viscosity (Dobraszczyk & Morgenstern, 2003), strain hardening, and the glass transition temperature (Dobraszczyk & Roberts, 1994;Gillgren, Alv en, & Stading, 2010;.…”

Developments in the Science of Zein, Kafirin, and Gluten Protein Bioplastic Materials

“…The scaffolds had good mechanical properties and were degradable by mammalian proteases. In contrast, Gillgren et al (2010) used molding to produce a solid zein foam by heating a zein resin in a mold. This foam had moderate mechanical properties when compared to commercially available petroleum-and bio-based foams.…”