the most active sites, giving rise to higher energy of interaction
between the sorbate and the sorption sites. As these
active sites become occupied, sorption subsequently occurs
on the less active sites giving lower heats of sorption (Iglesias
& Chirife, 1982). The net isosteric heat of sorption ranged
from 5.01 kJ/mol at moisture content of 1 g/g dry
matter to 1.10 kJ/mol at a moisture content of 9 g/g dry
matter for instant tea powder and the corresponding value
for tea granules was 4.43 kJ/mol at moisture content of
0.2 g/g dry matter and 0.58 kJ/mol at moisture content of
1.4 g/g dry matter.