Effects of bed volumes and moisture contents on the textural parameters of individual puffed cereal particles

This work is an investigation of the effects of bed volumes and moisture contents on the textural properties of puff cereals. The first study, two commercial puffed cereals were compressed both individually and in cells of different diameters and heights. Their force-displacement curves were jagged, irregular and irreproducible. The jaggedness of those curves were expressed in terms of their apparent fractal dimension determined from the Richardson plot and the box counting (Kolmogorov dimension) and in term of the mean magnitude of their Fourier power spectrum of their normalized residuals. Three dimensional plots of jaggedness measures versus cell diameter and height produced approximately planar relationship and could be described by the non linear models. Their extrapolation to the individual particle characteristic dimension gave jaggedness values in agreement with those determined experimentally on the individually particle. These results indicated that at least in a certain cereal products, it is possible to assess the brittleness of individual particles from their bulk compressibility pattern. Moreover, this procedure could also be used to estimate the particle stiffness expressed in terms of the fitted force at preselected displacement level (e.g. 15% or 25%) or in terms of the slope of peak force-displacement curve. The second study was moisture content effects on the textural properties of three puffed cereals having various moisture contents. The jaggedness of the force displacement relationship of these cereals was determined in terms of the apparent fractal dimension and the mean magnitude of the power spectrum of their normalized residuals. The plots of these jaggedness measures versus moisture contents yielded a characteristic sigmoid shape very similar to the plots of corresponding sensory crispness or crunchiness versus moisture contents relationships. This close similarity illustrates that the jaggedness measures of the force displacement relationship is manifestation of the same failure events that produce the crispness and crunchiness sensation. In all three products, moisture toughening were detected instrumentally but only in two products, moisture toughening was a clearly corresponding increase in the sensory hardness scores. This indicates that at least in certain cereal products moisture toughening can be perceived simultaneously with brittleness loss