Dynamic volume change measurements of cereal materials by environmental scanning electron microscopy and videomicroscopy

Abstract

SummaryMoisture migration induced volume change in cereal materials was studied by environmental scanning electron microscopy, videomicroscopy and stereoscopy. It is shown that the in situ volume change can be monitored by the changes of projection area with the assumption of isotropic swelling/shrinkage. The projection area change from videomicroscopy matches well with the volume change by stereoscopy after dimensional normalization. The arbitrary volume values in between two relative humidity levels are available by interpolating the equilibrium volumes at beginning and ending. The sorption/desorption curves were fitted by the 'parallel exponential kinetics' model, which described two independent, parallel processes as 'slow' and 'fast'. In the low relative humidity range, sorption curves match well with the 'parallel exponential kinetics' model and the two parallel processes tend to be identical when relative humidity increases. The diffusivity of water moisture in a cracker, which was estimated by the half-equilibrium principle, has a strong dependence on relative humidity.

The water vapor sorption behavior of flax fibers—Analysis using the parallel exponential kinetics model and determination of the activation energies of sorption

“…As adsorption occurs, the cell wall expands due to the presence of water molecules occupying space inside the nanocapillaries. The volume change of plant material has been measured on an environmental scanning microscope and has also been shown to obey the PEK model 14…”

“…When the RH is changed, the plant cell wall responds to this by establishing a new equilibrium MC value, but this takes a finite time to achieve. It has been found that the so‐called ‘parallel exponential kinetics’ (PEK) model provides exceptionally good fits to adsorption and desorption curves for foodstuffs, pharmaceutical materials, and both natural and regenerated cellulose fibers 8–14. The PEK equation is a double exponential of the form: where MC is the moisture content after infinite time of exposure of the sample to a constant RH and MC 0 is the moisture content of the sample at time zero.…”

The water vapour sorption behaviour of three celluloses: analysis using parallel exponential kinetics and interpretation using the Kelvin-Voigt viscoelastic model

“…It has been demonstrated that the water vapour sorption behaviour of natural fibres (Kohler et al 2003;Hill et al 2010a;Xie et al 2010a), regenerated cellulose fibres (Okubayashi et al 2004(Okubayashi et al , 2005a, microcrystalline cellulose (Kachrimanis et al 2006), wood flour (Hill et al 2010b, c;Jalaludin et al 2010;Xie et al 2010b, c) and some foodstuffs (Madamba et al 1996;Rahman et al 1998;Tang et al 2008), can be accurately described using the parallel exponential kinetics (PEK) model (Eq. 1).…”

Analysis of the water vapour sorption behaviour of Sitka spruce [Picea sitchensis (Bongard) Carr.] based on the parallel exponential kinetics model

“…(1)x of natural fibres (Kohler et al 2003), regenerated cellulose fibres (Okubyashi et al 2004(Okubyashi et al , 2005a, microcrystalline cellulose (Kachrimanis et al 2006), and some foodstuffs (Madamba et al 1996;Rahman et al 1998;Tang et al 2008).…”