Changes in the cell wall network during the thermal dehydration of alfalfa stems.

The effects of heat treatments used to dry alfalfa stems were investigated. Heating at 70 or 100 degrees C caused no major change in the cell wall composition, but xylanase had lower activity on the cell wall of heated material and the amount of xylose released varied with the temperature used. Chemical fractionation of cell wall carbohydrates showed that the main changes occurring during stem dehydration concerned pectic polymers and probably hemicelluloses. There was less material soluble in ammonium oxalate from alfalfa heated at 100 degrees C than from fresh alfalfa. The results suggest that heat processing causes some changes in the cell wall network. Environmental scanning electron microscopy was used to examine fully hydrated tissues at high resolution. There was cell distortion without disruption of cell walls as water was lost.