Table 1 shows the yields of RS III obtained from cassava
starch suspended in distilled water, 1, 10 or
100 mmol/L lactic acid then autoclaved at 121 C for
1 h and incubated at different temperatures and times.
We considered the quantities of RS III in the raw cassava
starch (0.44 g/100 g) to be negligible and did not account
for them in the determination of RS III in the subsequent
experiments. Preliminary studies performed using lactic
and citric acid concentrations exceeding 100 and
50 mmol/L, respectively, were unsuitable as these concentrations
excessively acidified the starch slurries (pH < 3.0)
and created unfavourable conditions for enzymatic activity
in the subsequent isolation of RS III.
Irrespective of the incubation temperature or time, lower
amounts of RS III were formed from cassava starch suspended
in 100 mmol/L lactic acid compared to suspensions
in water. 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 (Thompson,
2000). 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
Table 1 shows the yields of RS III obtained from cassava
starch suspended in distilled water, 1, 10 or
100 mmol/L lactic acid then autoclaved at 121 C for
1 h and incubated at different temperatures and times.
We considered the quantities of RS III in the raw cassava
starch (0.44 g/100 g) to be negligible and did not account
for them in the determination of RS III in the subsequent
experiments. Preliminary studies performed using lactic
and citric acid concentrations exceeding 100 and
50 mmol/L, respectively, were unsuitable as these concentrations
excessively acidified the starch slurries (pH < 3.0)
and created unfavourable conditions for enzymatic activity
in the subsequent isolation of RS III.
Irrespective of the incubation temperature or time, lower
amounts of RS III were formed from cassava starch suspended
in 100 mmol/L lactic acid compared to suspensions
in water. 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 (Thompson,
2000). 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
การแปล กรุณารอสักครู่..
