The glass transition temperature (T-g) of a dry ultrafiltrated pectinlyase (PL) preparation decreased from 56 to 24 degreesC when water content increased to 20%. The thermal transition temperature (T-p) for protein denaturation decreased greatly up to 40% moisture; above 40% no further changes in T-p were observed. In the glassy state, a lag period of approximately 7 days with no PL activity loss was observed; after that, PL activity was lost. Above T-g, the rates of PL inactivation greatly increased. In the glassy state E-a was 16.6 kJ/mol. When the system was in a higher mobility state (rubbery), E-a increased to 66.5 kJ/mol.