Online Shear Viscosity Measurement of Starchy Melts Enriched in Wheat Bran

Abstract

Incorporation of wheat bran, a readily available and low cost by-product, in extruded puffed foods is constrained due to its negative effect on the product texture. Understanding the effect of wheat bran on rheological properties of extruded melts, driving the final product properties, is essential to provide solutions to the food industry and enhance its use.

Process, structure and texture of extruded whole wheat

“…This is consistent with previous findings reported in the literature (e.g. Della Valle et al, 1996;Robin et al, 2011c). The decreasing effect of barrel temperature and water content can be explained by their plasticizing effect on the starch matrix.…”

“…Regardless of the extrusion conditions, the melt showed a pseudoplastic behavior with a power law index n ranging from 0.14 to 0.29. These values were close to those reported by Robin et al (2011c) for extruded wheat flour supplemented with wheat bran. Increasing the barrel temperature, water content or screw speed significantly decreased the shear viscosity of the melt at a shear rate of 30 s À1 (Fig.…”

Expansion mechanism of extruded foams supplemented with wheat bran

“…The rheological properties of the matrix surrounding the bubbles determine their resistance to growth. The shear viscosity of the melt was determined with the twin-slit rheometer at similar thermomechanical history of the ingredients as with the die (Robin et al, 2011b) and compared to the expansion data obtained with the same die. As the range of apparent shear rates achieved with the current rheometer (between 10 and 30 s À1 ) was much lower than the theoretical ones at the die exit (an apparent shear rate of about 600 s À1 would be expected), only the trends between the shear viscosity and the expansion will be discussed.…”

“…However, the composition of the bran was not specified and the effect of bran on the flow behavior was not characterized. In a recent study, Robin et al (2011b) showed a significant effect of wheat bran on the melt shear viscosity of extruded wheat flour only at the highest wheat fiber concentration (24.4%), indicating a threshold bran volume fraction. Adding dietary fibers to the extruded melt may also modify the distribution of water between the different phases as shown in a previous work for unprocessed wheat flour supplemented with wheat bran (Robin et al, 2011a).…”

“…doi:10.1016/j.jfoodeng.2011.05.041 ingredient thermomechanical history in the extruder (see e.g. Vergnes et al, 1993;Lach, 2006;Robin et al, 2011b). On-line capillary rheometers were used in several studies to obtain both the shear viscosity and the expansion data, enabling direct comparison between these data and explaining the changes of expansion properties using the rheological data (see e.g.…”