Preparation and Characterization of Hydroxypropylated Sago Starch
Sailin @ Stalin, Malini (1998) Preparation and Characterization of Hydroxypropylated Sago Starch. Masters thesis, Universiti Putra Malaysia.
Sago starch was hydroxypropylated with propylene oxide at 40°C in an alkaline medium containing sodium sulphate. In this study, the level of propylene oxide (0-14%), sodium hydroxide (0-2%), sodium sulphate(0-30%), reaction time (8-24 hrs) and reaction temperature (20-50°C) were varied to produce various samples of hydroxypropylated sago starch. The molar substitution (MS), which is the amount of substitution that has occured during hydroxypropylation and the pasting properties were measured for each sample. Increase in the amount of propylene oxide, sodium sulphate and sodium hydroxide, reaction temperature and reaction time progressively increased the molar substitution of the modified peak viscosity and the hot paste viscosity. However, the gelatinization temperature, the consistency of the hot paste viscosity after holding at 95°C and the setback value was decreased. Highest molar substitution of 0.41 was observed at 1.5% sodium hydroxide at which the highest peak viscosity and breakdown with the lowest setback value was also observed. The peak viscosity, cold paste viscosity and breakdown was highest at 25% sodium sulphate concentration. The maximum level of hydroxypropylation was observed at 10% propylene oxide, 1.5% sodium hydroxide, 25 % sodium sulphate, at 24 hours reaction time and at 40°C. In another study, hydroxypropylated sago and corn starch were prepared by reaction with propylene oxide in an alkaline medium containing sodium sulphate at 40°C and its physicochemical characteristics were studied and compared with the native starches. Some of the physicochemical characteristics evaluated were : pasting properties, molar substitution, swelling power and solubility, water holding capacity, gel strength, sediment value, light transmittance, acid and heat stability, starch damage and freeze-thaw stability. In addition, the morphology of the starch granules were also observed.Hydroxypropylation increased the swelling power and solubility, water holding capacity and freeze-thaw stability of both starches. The swelling power of sago starch increased from 33.69 ± 3.92 % to 60.44 ± 2.72% when it was hydroxypropylated. As for com starch the swelling power increased three times higher from 8.67 ± 0.056 % for native com to 24.99 ± 1.039% for hydroxypropylated com. The water holding capacity of native sago was 11.00 ± 0.12% and it further increased to 17.23 ± 0.25% when it was hydroxypropylated. As described in the literature, it was found that hydroxypropylation increased the freeze-thaw stability of the sago and com starches. The gel strength of the starches decreased when it was hydroxypropylated and the values were 56.5 ± 2.12%, 11.5 ± 0.71%, 84.5 ± 2.12% and 46 ± 1.42% for native sago, hydroxypropylated sago, native com and hydroxypropylated com respectively. The percentage of starch damage was only 0.02% when sago starch was hydroxypropylated but for com the starch damage was 2.64% when it was hydroxypropylated. The sediment value of native sago (96.25 ± 1.0%), was the highest followed by hydroxypropylated sago starch (94.54 ±0.57%), hydroxypropylated com starch (67.17 ±0.57%) and native com starch (27.0 ± 2.6%) respectively. Both starches when hydroxypropylated showed no improvements in their acid and heat stability.
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