Purpose:
To see if starch is present in different mediums
Materials:
– White paper
– Popcorn
– Plain Cheerios
– Crackers
– Rice
– Unknown substances A, B, C, D, E
Apparatus: – Petri dish
– Iodine
– Dropper
– White paper
Method:
- A small piece of white paper was ripped off and one – two drops of iodine was dropped on it, the white paper (that is coated with starch), and the positive test for amylose (starch) was observed.
- A Petri dish with popcorn, cheerios, crackers and rice is placed on a white piece of paper so it could be more easily observed. On each material one – two drops of iodine were dropped on each to see if each material contained amylose (starch).
- The Petri dish was cleaned with water, dried and the five unknown substances were placed on the dish in separate locations and the dish was placed on a piece of white paper for better visibility. On each material one – two drops of iodine was dropped to see if each substance contained amylose (starch).
Observations:
| Material | Description Before Iodine Drops | Description After Iodine Drops |
| White Paper | Bright white piece of paper covered in amylose (starch) | White color turns a bluish/purple color (indicates the presence of amylose, (starch)) |
| Cheerios | Light brown, textured, in the shape of a ring | Slight change in color to a bluish/purple |
| Rice | Individual, short, white pieces | Rice absorbs iodine, turns a bluish/purple |
| Popcorn | Puffy, large pieces
of white popcorn, slightly buttered |
Iodine shrivels popcorn shrinking pieces, changes color into a bluish/purple |
| Crackers | Yellowish/white tint, with rough edges and fairly smooth surface | Cracker dissolves slightly, changes color to a bluish/purple but color change does not last long |
| Unknown Substance A | Many small white crystals, not thick in texture | Iodine makes substance wet, but does not change color. |
| Unknown Substance B | White crystals found in small granules, thin in texture | Iodine makes the crystals gel like in texture but does not change their color. |
| Unknown Substance C | Beige powder with small granules, thin in texture. | When mixed with iodine substance gains a dough like texture and becomes a darker shade of beige, not changing color. |
| Unknown Substance D | White powdered substance, thick in texture. | When iodine dropped on the color immediately changes into the bluish/purplish color. |
| Unknown Substance E | Many small crystals, yellow colored substance | Crystals do not change color, iodine just makes substance more liquid like in texture |
Explanation:
Through the test with white paper, it was learned that when iodine is dropped on a substance containing amylose (starch) the color of the substance changes into a bluish/purple color rather than staying the original color when no amylose is present. When the iodine was dropped on all of the food substances (plain cheerios, rice, popcorn, and cracker) all of the substances turned to a bluish/purple color thus proving that amylose was present in all of them. The only food substance which reacted differently was the small color change in the cheerio. Instead of changing for a long time it changed briefly showing that a small amount of amylose is present. The result for the unknown substances was much different than that of the food items. When the iodine was dropped onto the five substances (unknown substances A, B, C, D, and E) all but unknown substance D did not show the bluish/purple color indicating amylose. Unknown substance D turned the bluish/purple color which shows that it contains amylose (starch). The others (unknown substances A, B, C, and E) did not change into this bluish/purple color thus showing that they do not contain amylose (starch).
Conclusion:
Throughout this experiment many different items were tested using iodine to see if they contained amylose (starch). This experiment has taught us that the liquid iodine can be used as an apparatus to show if the polysaccharide amylose is present in different items. When the material turned a bluish/purple color it showed that this item contained amylose and thus could be broken down by salivary amylase. The gained knowledge of its amylose content lets us know if this object can be broken down inside of the mouth through hydrolysis (with the aid of salivary amylase) or must wait until later on in the process of digestion (the stomach or small intestine) to be broken down.
