Influence of extrusion conditions on the colour of millet-legume extrudates using digital imagery

peer-reviewedColour acts as one of the triggers for acceptance of snack foods. Digital imaging in conjunction with Adobe Photoshop can help identification of variations in the colour of extruded products. Response surface methodology-based central composite rotatable designed experiments were conducted to understand the colour components and overall acceptability (OAA) of extruded snacks made from millet–legume blends, 12–28% legume, at different moisture content (MC) of 12–24% wet basis (w.b.), extruded at varying die head temperatures (DHT) from 160–200 °C, barrel temperatures from 100–140 °C and screw speeds of 100–140 rpm. A simple digital camera was used for capturing the images of the extrudates. An L*a*b* colour model (where L* is the black/ white element, a* is green/red and b* is blue/yellow) was used for colour characterisation and OAA was determined by a hedonic scale. It was inferred from the analysis of the resulting statistically valid second order models for the responses that all the colour components were significantly affected by the amount of legume in the extruder feed and by the DHT. It was also observed that DHT, synergistically with other processing parameters, had a significant effect on all the responses. The OAA was highest for the extrudates with higher L* values. Optimum processing conditions were derived while the responses adhered to constraints. The responses of the extrudates prepared under optimum conditions exhibited no significant variation from model predicted values

Time variability of viscosity parameter in differentially rotating discs

We propose a mechanism to produce fluctuations in the viscosity parameter ($\alpha$) in differetially rotating discs. We carried out a nonlinear analysis of a general accretion flow, where any perturbation on the background $\alpha$ was treated as a passive/slave variable in the sense of dynamical system theory. We demonstrate a complete physical picture of growth, saturation and final degradation of the perturbation as a result of the nonlinear nature of coupled system of equations. The strong dependence of this fluctuation on the radial location in the accretion disc and the base angular momentum distribution is demonstrated. The growth of fluctuations is shown to have a time scale comparable to the radial drift time and hence the physical significance is discussed. The fluctuation is found to be a power law in time in the growing phase and we briefly discuss its statistical significance.Comment: 22 pages, 3 figures; Accepted versio