Physical Changes in Bamboo (Bambusa phyllostachys) Shoot During Hot Air Drying: Shrinkage, Density, and Porosity

The apparent density of bamboo (Bambusa phyllostachys) shoot was investigated at a moisture content range of 10-92% wet basis by weighing the product in air and determining the buoyancy force in toluene. An analysis of variance (ANOVA) unveiled that moisture content significantly affected apparent density at 95% confidence level. The true density of the bamboo shoot was determined by grinding the dried sample to exclude all internal pores and using density bottles. The experimental data fitted well to a general density equation for fruits and vegetables proposed by Lozano et al. (1983) and to a second order polynomial (SOP) model. The internal porosity generated during drying varied in a nonlinear (quadratic) fashion. Shrinkage at different moisture content levels was measured by evaluating the dimensional changes in bamboo shoot slabs (5.0 × 3.2 × 1.8 cm) by drying in a convection oven and a tray dryer operating at 70°C and 7.2% relative humidity. Shrinkage was affected statistically by decreasing moisture content at 95% confidence level. Shrinkage was compared with available models in literature and found to be oriented based on fiber direction and distinctly different from the isotropic volume change in fruits and vegetables.