36D-23 |
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G. GUNES and A. Sokmen. Food Engineering, Istanbul Technical Univ., ITU Kimya-Metalurji Fak., Gida Muh. Bol., Maslak, Istanbul, 34469, Turkey Chocolate with reduced calories (light chocolate) has become popular among consumers and manufacturers. Light chocolate can be produced by replacing sucrose with substitutes such as sugar alcohols. Replacement of sucrose with sugar alcohols would affect rheological properties, which in turn affects the processing and quality. The objective of this study was to investigate effects of different sugar alcohols (maltitol, isomalt, and xylitol) and different particle size distributions on rheological properties of molten chocolate. Three different particle size intervals (106-53µm, 53-38µm ve 38-20µm) were obtained by grinding and sieving the sugar powders to different sizes and measured by a particle size analyzer. Chocolate samples were made in our laboratory with the following ingredients mixed on weight to weight basis: sucrose or sugar alcohols (43.40%), cocoa butter (32.83%), cocoa powder (23.47%) and lecithin (0.3%). Shear stress values of chocolate samples were measured at 40 o C in the shear rate range of 5 to 60 s-1 using a rheometer. The data were applied to some of the known rheological models (Casson, Bingham and Herschel-Bulkley models) that have been proposed for chocolate. The best results were obtained with the Herschel-Bulkey model. Flow behavior index (m) of all chocolate samples were within the range 0.99 to 1.05. Chocolate with isomalt showed significantly higher plastic viscosity (1.83 Pa.s) compared to other samples. This was associated with isomalt's lower density. Chocolate with maltitol had higher yield stress (5.51 Pa), which was associated with its smaller particles size distributions. Both the plastics viscosity and the yield stress for all chocolate samples increased as the particle size decreased. In conclusion, sucrose substitutes used in chocolate can change rheological properties of chocolate depending on their physical and chemical nature. The processing and quality may be affected by sucrose substitutes and should be further studied for optimization of process and quality.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |