Chocolate rheology is important for the efficiency of mixing, pumping and transportation during processing, with consequential effect on the textural properties of both molten and molded finished products. However, the extent to which dark chocolate rheology is influenced by particle size distribution (PSD), fat and lecithin content during industrial processing and their interrelationships with the textural properties of finished chocolate is not fully understood. The objective of this study was to evaluate the relationship between rheological and textural properties of dark chocolate systems as influenced by PSD of its inherent solids and composition during processing. A 4 x 3 x 2 factorial experiment was conducted with varying PSD (D90 of 18ìm, 25ìm, 35ìm and 50ìm), fat (25%, 30% and 35%) and lecithin (0.3% and 0.5%). Rheological properties (yield stress and apparent viscosity) and textural properties (firmness, viscosity index and hardness) of the dark chocolates were measured respectively using shear rate-controlled rheometer (ThermoHaake ViscoTester 550) and TA.HD Plus Texture Analyzer (Stable Micro Systems). The results indicated that PSD, fat and lecithin content significantly (P<0.05) affected all the rheological and textural properties. Increasing particles sizes resulted in significant reductions in yield stress (920.7-35.5 Pa), apparent viscosity (61.0-3.4 Pas), firmness (7.8-1.6 kg), viscosity index (4.8-1.6 kg/sec) and hardness (7.8-4.2 kg) of the chocolates with the greatest effect occurring in the products containing 25% fat and 0.3% lecithin, which reduced further with increasing fat and lecithin contents. Correlation and regression analysis showed high correlation coefficients (r = 0.9783-0.9977) and regression coefficients (R2 = 0.9768-0.9977) among the rheological and textural properties indicating their interrelationships. Principal component analysis of the data showed that the rheological and textural properties of the dark chocolates were highly related with PSD, fat and lecithin accounting for 95.4% of the variability in their data.
- particle size distribution
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