Enhancement of starch-pulp separation in centrifugal-filtration process: Effects of particle size and variety of cassava root on free starch granule separation

• Bound starch granule remains in cassava pulp and is difficult to separate.
• Free starch granule is not bound inside the pulp complex structure.
• Centrifugation and filtration are main mechanisms for starch-pulp separation.
• Semi-bound starch granule is released by centrifugal force acting on cassava pulp.
• Pressure drop drives free starch granule from pulp during filtration process.

Cassava root and starch are used for human food consumption, animal feed and raw material for various industries, including the renewable energy industry. The composition and structure of cassava root depend on variety, age, environmental conditions and planting season. Starch granules following rasping step are divided into free and bound starch; the latter remains in the pulp and is difficult to separate, while the former is not bound inside the pulp complex structure. In a starch extractor, cassava starch granules are separated from pulp through the mechanisms of centrifugation and filtration. This research aimed to study the effects of particle size and variety of cassava root, centrifugation and filtration mechanisms on free starch granule separation efficiency. Three cassava root varieties, Rayong 9, Rayong 11 and Kasetsart 50, were classified by particle size after grinding and sieving. Experiments were conducted at various relative centrifugal forces (RCF: 0–487 × G) and pressure drops (2.5–12.0 kPa). The free starch separation efficiency increased with decreasing particle size of all cassava root varieties. The grinding of cassava root into small pieces caused cell wall breakage, facilitating free starch separation from the pulp. As the RCF increased, some bound starch granules were released due to the force acting on the cassava pulp. The pressure drop in filtration process drove the free starch granules to pass through the screen although this force was insufficient to separate the bound starch granules from the fiber.