Rheological Behavior of Processed Mustard. I: Effect of Milling Treatment

Abstract

The inJuence of milling level on the rheological behavior of processed mustard was investigated using three different particle sizes (slightly-coarse, standard, and fine) prepared according to a standard formulation and pilot-plant replication of the commercial methodology. All samples showed unimodalpopulationbased particle size distributions which were described by the population-mode (dpoJ. On a volume basis, all milling levels had well-defined bimodal distributions consisting of a smaller-and a larger-size group of particles described by their modes (d and D ) . The most important particle size index in relating milling level to rheological behavior was not the population mode (dpop) but the larger-size volume mode (0) from the bimodal distribution. The coarser the milling, the higher the larger-size volume mode (D), and higher the values of: a ) Apparent viscosity of nonmixed samples (qJ, b ) Bingham yield stress ((T,) and plastic apparent viscosity (qp), c ) Shear stress constant ( A ) and coefficient of thixotropic breakdown ( B ) from the Weltman stress decay model, d ) Yield stress (go) and consistency index ( K ) from the Herschel-Bulkley model, and e ) Storage (GI) and loss (G") moduli. As indicators of structure-texture relationship, the above rheological parameters can be profitably utilized to study the effect of manufacturing practices on long term storage stability of the product.

Rheological properties of commercial mustards

“…Although all investigated mustards exhibited non-Newtonian, pseudoplastic flow with a yield stress and a thixotropy hysteresis loop (Figs. 1 and 2), which confirms earlier observations on the rheology of mustards (Aguilar et al, 1991a;Bhattacharya et al, 1999;Gerhards & Schubert, 1993), there were Values followed by the same letter in the same column are not significantly different (p ¼ 0:05). * Mean value of two repetition.…”

“…For the Herschel-Bulkley model the degree of fit (R 2 > 0:94) was poorer than that obtained by Bhattacharya et al (1999). Nonetheless, this model is recommended by some authors for describing the flow curves of mustard (Aguilar et al, 1991a;Bhattacharya et al, 1999;Gerhards & Schubert, 1993). Although all investigated mustards exhibited non-Newtonian, pseudoplastic flow with a yield stress and a thixotropy hysteresis loop (Figs.…”

“…The values of the two parameters mentioned depend on the temperature of measurement, the range of shear rate or stress and the kind of sample. According to Aguilar et al (1991a), one of the most important factors determining the rheological properties of mustard is the milling degree of mustard seeds which affects the size of solid particles in the final product. Gerhards and Schubert (1993) found that the stirring of a sample before measurement leads to a drop in the value of both yield stress and flow behaviour index but practically does not influence the value of the consistency index.…”

“…It is known that mustard, a semi-solid food, exhibits a non-Newtonian, pseudoplastic flow with a distinct yield stress and thixotropy (Aguilar, Rizvi, Ramirez, & Inda, 1991a, 1991bBhattacharya, Vasudha, & Krishna Murthy, 1999;Gerhards & Schubert, 1993;Yoo, Rao, & Steffe, 1995).…”

“…As shown by Aguilar et al (1991a), the rheological properties of processed mustard are determined by the size of solid phase particles. Those properties can be created or modified by controlling the particle size distribution (milling degree) in the manufacturing process.…”