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Physicochemical and Rheological Characterization of an Acidic Milk Product: Kefir Concentration Effect



Author(s)

Jorge Octavio Virues Delgadillo, Miguel de Jesús Luna Lara, Claudia Karina Lozada Santillan, Carmen Bulbarela Sampieri and López del Castillo Lozano Micloth

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DOI:10.17265/2159-5828/2017.02.003

Facultad de Ciencias Químicas, Universidad Veracruzana, Lomas del Estadio S/N, Xalapa, Veracruz 91000, México

The main objective of this study was the analysis of physicochemical and rheological behavior of a drinkable beverage prepared with different concentrations (5%, 10% and 20% w/w) of Kefir. Several rheological models were also evaluated to determine the model that better fit experimental data. Apparent viscosity was measured with a Brookfield Viscometer within shear rates of 0.26 rad/s to 2.09 rad/s; and with an Ar-2000ex TA Instruments Rheometer within shear rates of 0.01 rad/s to 1,000 rad/s. Physicochemical tests, such as titratable acidity, chloride percent, fat concentration, color, humidity, syneresis, and total solids, were determined using laboratory equipment. The main result observed in all samples tested with Brookfield viscometer was that Kefir drink behaved as a Newtonian Fluid within shorter strain rates (0.26 rad/s to 2.09 rad/s). However, when the same samples were tested with Ar-2000ex Rheometer, a different behavior was observed: Over a wider range of shear rates, the fully non-Newtonian behavior of Kefir samples was discovered. Besides, additional variables such as shear and normal stresses, and loss and storage modulus, were analyzed with Ar-2000ex Rheometer. The rheological model that better fitted the experimental data was Cross model, followed by Power Law Model. Statistical analysis of viscosity data acquired with Brookfield Viscometer from all Kefir concentrations was not significant (p values greater than 0.05); which demonstrated that the effect of Kefir concentration over shorter strain rates was not significant, and thus, the samples behave as a Newtonian fluid. On the other hand, p values lower than 0.05 were observed in most of the different Kefir concentration samples tested with Ar-2000ex Rheometer; which indicates that a statistical significant effect was observed and thus a non-Newtonian behavior of Kefir samples. All statistical analysis was performed with SPSS v.16 software, selecting a Duncan Test with a confident interval of 95% to accept or reject the variances compared of the different Kefir concentration samples.

Food rheology, viscosity, shear rate, kefir concentration.