Some important steps have to be followed before the extraction of the starch from the potato tubers.
3. Weighing v2
Select a potato with an appropriate mass. Weigh it to obtain an initial mass of the tuber. Potato tubers with a total weight of approximately one kilogram were used in the extraction in order to get the best result. Note that the ratio of the impurities on the potato affects the weight too.The ratio of the impurities to the potato was then determined by the difference in the weighing before and after washing.
Wash the selected potato with water to remove the contaminants which could otherwise affect the final output of the tuber. Rubbing is an important step since this step will determine the purity factor of the potato. Proper washing need to be done to fully avoid any contamination.
The potato is then weighed again in order to compare with the weight obtained initially, making sure that the ratio of impurities does not affect the final result.
Peel the potato with care by using a knife in order to prevent the peeling of additional potato cells. This would cause loss of starch granule from the potato resulting in starch loss. Damaged starch granules could lead to alteration in the physiochemical properties of the starch , resulting in an undesired result.
The peeled potato was then diced to small regular cubes of similar size .Again, care was taken to avoid damage of the starch granule in the sweet potato.
Blend the diced potato in a blender with water
Filter the solution with a cloth (cheesecloth would be the best choice).This is to separate the starch granules extract from the residue of the potato. Your end result would be a starch solution. Redo this step to obtain more starch.
Dry the starch solution to obtain solid starch.
Production of starch based bioplastic
1. Add 25cm^3 water into the beaker and add 2.5g potato starch, along with 3cm^3 of 0.1M hydrochloric acid and 2cm^3 of glycerol and stir it with a glass rod.
2. Place the beaker on the tripod and heat it using the Bunsen burner and boil it gently for 15 minutes.
3. Turn the Bunsen burner off after 15 minutes and leave it to cool.
4. Dip the glass rod into the mixture and apply it onto the universal indicator to measure the
pH. Add sodium hydroxide to neutralise the mixture and test it with universal indicator again.
5. Pour the mixture from the beaker into the petri dish and spread the mixture evenly.
6. Leave the petri dish for it to dry.
Since starch is made of 2 types of glucose molecules , amylose and amylopeptin , amylopeptin being a branched molecule with complicated bonds. Dilute hydrochloric acid is added to the aqueous solution of starch to break down the branched amylopectin molecules into straight chained amylose molecules.Then, it is heated to 100 celcius. As the solution is heated, the starch becomes soluble in the water and the starch granules will swell with water. This creates a paste that is highly viscous and the process is known as gelatinization. As the paste cools, the water is expelled and the amylose molecules hydrogen bond to
form a structure resulting in a brittle plastic film. To improve the flexibility of the samples, glycerol can be added to the solution before heating. Glycerol is a small molecule that is hydrophilic. When glycerol is added to the starch mixture, it traps water in the starch chains making it less crystalline, and consequently less brittle.