36D-10 |
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N. RAHARITSIFA, Food Science and Technology Dept., Laval Univ., Comtois Bldg. - FSAA, Québec, QC G1K7P4, Canada, D. B. Genovese, Laboratorio de Alimentos - PLAPIQUI, UNS - CONICET, Camino "La Carrindanga" Km 7, CC 717, Bahía Blanca, 8000, Argentina, and C. Ratti, Soils Sci and Agri-Food Engineering, Laval Univ., Comtois Bldg. - FSAA, Québec, QC G1K7P4, Canada. Foam mat drying is a good way of dehydrating liquid foods in short times. Due to the porous structure of the foamed materials, mass transfer is enhanced leading to shorter dehydration times. Although a simple and promising technology, drainage of the liquid phase causes the structure of foams to change upon time. The intrinsic instability of foams represents thus an important problem to be solved prior to foam processing. We determined to characterize stability of apple juice foams as a function of their composition, properties and process conditions. Apple juice foams were prepared using egg white powder or methylcellulose (0.1 to 3 %) at different whipping times (3 to 7 min). Stability (through drainage), rheological properties (using a SR5000 Rheometer, Rheometrics, in oscillatory and transient modes) and physical properties such as foam density and bubble size, were measured in order to evaluate the effect of foaming agents and whipping times on foam stability and characteristics. Foams made with egg white powder showed lower density (that is, better capacity of the continuous phase to include air) than those made with methylcellulose. However, the methylcellulose foams were more stable (from drainage results), more uniform and with smaller bubble diameter (from 54 to 187ìm) at equal concentrations and whipping times. Density curves presented a minimum value as the foaming agent concentration increased, being 2% (w/w) for egg white powder and 0.2% (w/w) for methylcellulose at all whipping times. Preliminary rheological tests showed that viscoelastic behaviour of foams depended on the foam density range (higher or lower than the minimum density value). This project on foam characterization and stability is expected to help in the further processing of foams (such as foam-mat drying) and also to contribute to the production of "tailor-made" food products through manipulation of the initial material characteristics.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |