RHEOLOGICAL BEHAVIOR OF PROCESSED MUSTARD .1. EFFECT OF MILLING TREATMENT

The influence 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 unimodal population-based particle size distributions which were described by the population-mode (d(pop)). 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 (d(pop)) but the larger-size volume mode (D) 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 (eta-ap), b) Bingham yield stress (sigma-o) and plastic apparent viscosity (eta-p), c) Shear stress constant (A) and coefficient of thixotropic breakdown (B) from the Weltman stress decay model, d) Yield stress (sigma-o) and consistency index (K) from the Herschel-Bulkley model, and e) Storage (G') 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.