THE THERMOMECHANICAL PROPERTIES OF CARROT CELL-WALL MATERIAL

The effect of temperature and moisture on the fabrication of pressed c arrot cell wall specimens for Dynamic Mechanical Thermal Analysis was assessed. Results obtained from the water extractability of the materi al showed that more cell wall material became solubilised when moistur e 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 monos accharides were observed, represented principally by galactose, rhamno se, arabinose and glucose. Pectic polysaccharides became more water so luble when isolated carrot cell wall was pressed at 100 degrees C with a water content 800 g kg(-1) (wet weight basis). A molecular weight f raction centred at 100 000 Da was observed in the severely pressed mat erial (100 degrees C, 800 g kg(-1) water) but was barely present in th e mildly pressed (30 degrees C, 500 g kg(-1) water) and unpressed spec imens, consistent with depolymerisation and solubilisation. In contras t to the chemical modifications, the bending modulus, E', of the press ed carrot cell wall material remained unchanged for the cell wall spec imens moulded under different conditions, consistent with small change s in molecular weight. Pressed cell wall material was stiffer than pre ssed freeze-dried carrot which could be due to the plasticising role o f the intracellular components. The stiffness of both cell wall and fr eeze-dried carrot specimens decreased with plasticisation by water in the range 10-500 g kg(-1). (C) 1998 Society of Chemical Industry.