Rheological and optical properties of commercial chocolate milk beverages

Flow behaviour and colour of nine commercial samples from three different lots of chocolate flavoured milk beverages were analysed. Experimental shear stress-shear rate relationships, obtained at 25degreesC, fitted mostly to the Newton model, as for plain milk, though some samples fitted better to Ostwald-de Waale and Bingham models. Newtonian viscosity values ranged from 2.67 to 18.68 mPa s for samples of one lot. At 5degreesC. as expected, Newtonian viscosity of samples was higher and pseudoplasticity increased (n values were lower). Six of the nine samples showed consistent viscosity values through the lots. Main differences in colour of samples were detected for parameter L* (brightness), ranging from very light (L* = 53.5) to dark (L* = 18.3) samples. Except for two samples brightness values were consistent through the lots. Hue (h*) values were consistent for all samples. However, chromaticity (C*) values differed from one lot to the other. except for two other samples, showing the difficulty in controlling this attribute in industry. (C) 2001 Elsevier Science Ltd. All rights reserved.