Mechanical properties
The parboiling temperature and duration has the significant
influence on the hardness of the kernel. The hardness of the paddy
decreases with the increasing soak water temperature (Pillaiyar
and Mohandoss, 1981b) and it increases with increasing steaming
time (Kar et al., 1999). Parboiling also increases the ultimate tensile strength (by about four to five times) and modulus of elasticity
of the rice kernel. These strength values are directly proportional to steaming duration and the degree of starch gelatinisation (Saif
et al., 2004). The increase in strength may be the reasons why there
is less breakage of parboiled rice when milled and why parboiled
rice has altered texture than non-parboiled rice when cooked.