The thermomechanical properties of carrot cell wall material

Abstract

The effect of temperature and moisture on the fabrication of pressed carrot cell wall specimens for Dynamic Mechanical Thermal Analysis was assessed. Results obtained from the water extractability of the material showed that more cell wall material became solubilised when moisture and temperature of the different treatments were increased. Chemical analysis revealed that this involved an increase in the water-soluble uronic acid components. Furthermore, more water-soluble neutral monosaccharides were observed, represented principally by galactose, rhamnose, arabinose and glucose. Pectic polysaccharides became more water soluble when isolated carrot cell wall was pressed at 100°C with a water content 800 g kg−1 (wet weight basis). A molecular weight fraction centred at 100000 Da was observed in the severely pressed material (100°C, 800 g kg−1 water) but was barely present in the mildly pressed (30°C, 500 g kg−1 water) and unpressed specimens, consistent with depolymerisation and solubilisation. In contrast to the chemical modifications, the bending modulus, E′, of the pressed carrot cell wall material remained unchanged for the cell wall specimens moulded under different conditions, consistent with small changes in molecular weight. Pressed cell wall material was stiffer than pressed freeze-dried carrot which could be due to the plasticising role of the intracellular components. The stiffness of both cell wall and freeze-dried carrot specimens decreased with plasticisation by water in the range 10–500 g kg−1. © 1998 Society of Chemical Industry.