When the lactic acid concentration was decreased
to 10 mmol/L and further to 1 mmol/L, the RS III yields
approached or exceeded those from cassava starch suspended
in water (Table 1). Partial acid hydrolysis and thermal
treatment improves RS III yields by inducing partial depolymerisation
of amylose chains which results to increased
polymer mobility for molecular rearrangement
Excessive hydrolysis of the glycosidic bonds, as may
have occurred in the 100 mmol/L lactic acid treatment, may
limit amylose recrystallisation during subsequent incubation.
The viscosities of the slurries gave an indication of
the extent of hydrolysis. The viscosity of autoclaved cassava
starch suspended in water or 1 mmol/L lactic acid was 1390
and 2140 mPa s, respectively. Both values were significantly
higher (P < 0.05) than the viscosities of starch suspended
in 100 mmol/L (20 mPa s) or 10 mmol/L lactic acid
(68 mPa s).