Study on the Properties and Drying Kinetic Analysis of Sarawak Sago Starch

Maswida, Mustafa Kamal (2024) Study on the Properties and Drying Kinetic Analysis of Sarawak Sago Starch. PhD thesis, Faculty of Engineering.

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Abstract

The study covers the properties, drying kinetics, and drying models of Sarawak sago starch. Properties analyzed include the composition, morphology, size, color, viscosity, chemical bond and thermal stability. The properties were compared for sago starch produced from different sources. The first sample was the commercial sago flour, bought from Kota Samarahan supermarket, the second sample was lemantak, bought from local producer, which was prepared using traditional method, and the third sample was prepared in the laboratory. Effect of drying was analyzed using the sago starch that was prepared in the laboratory, dried using an oven at temperatures of 50 to 80°C and fan speed of 0 to 0.95 m/s, microwave at 200W, freeze dryer at -92°C, and sun drying. In addition, the effect of sample thickness of 0.5 to 2 cm, and different location within the oven was also assessed. For oven drying, sago starch was dried continuously and intermittently; continuous drying refers to drying without interruption, and for the intermittent drying, a drying schedule that involves switching the oven `on’ and `off’ for certain period. The drying models assessed were thin layer models of empirical concept, simplified Fickian model and Characteristic Drying Curve concept. Results show that there were differences in the measured properties for sago starch prepared using different methods. It was found that lemantak and starch prepared in the laboratory have quite similar properties, but quite significant differences observed for the commercial sago flour, which has lower in total starch content of 29.79%, resistant starch content of 8.19% , viscosity of 7.45% as well as broken granules. Drying at 60°C for 15 hours increased the whiteness and thermal stability and decreased the moisture content of the sago starch. Increase in whiteness was observed based on increment in whiteness index of 46.89%, while moisture content decrease of 75%. It was also found that the final moisture content of samples dried intermittently was higher than those dried continuously, but below than 13%, which is considered within the quality required. The intermittent oven drying is considered more effective drying than continuous drying in terms of energy saving; the drying period for intermittent drying (10.8% at 12 hour) was almost similar with the period of continuous drying (9.2% at 12 hour). The use of fan was found to increase the drying process. It was observed that drying at lower temperature of 60oC with fan velocity of 1 m/s gives estimated diffusivity of 5.77 x10-9 m2/s, which is higher than that observed for drying at 80°C without fan gives estimated diffusivity of 1.27x10-9 m2/s, suggesting that drying at lower temperature with added fan can be a good option for drying starch. It was also found that lower sample thickness results in faster drying. The diffusivity for sample thickness of 0.5 cm was estimated to be about 8.2 x 10-10 m2/s, which is 200% higher than that estimated for sample thickness of 2 cm with diffusivity of 2.5 x 10-9 m2/s. Meanwhile, the sample position within the oven showed insignificant drying effect. Most drying models able to illustrate the drying kinetics of starch satisfactorily except drying characteristics curve model. The empirical model gives the lowest standard error of 0.006. The fitted parameters for drying at 50 to 80 ºC were drying constant estimated between 0.043 to 0.225, diffusivity between from 7.086x10-10 to 1.268x10-9 m2/s and activation energy of 17.7 to 19.4 kj/mol.

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