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Detecting starch and sugars in food

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DETECTING STARCH AND SUGARS IN FOOD Candidate Name: Dai Yangyang Date: June 8th, 2012 Aim: To detect the presence of starch and sugars (glucose and fructose) in different food sources. Background: We have many different foods in daily life and many of them contain nutrients like carbonhydrates which are essential to human life. Starch is a polysaccharide, a group of nutrients known as carbonhydrates. Glucose and fructose are monosaccharides, simpler carbonhydrates which are often refered to as sugars. In order to detect the different carbonhydrates content in ranges of food, we used two theories in our experiment. Firstly, starch can react with iodine to create a blue product. Secondly, glucose and fructose are reducing sugars which can be tested by Benedict’s reagent, because the reducing sugars which contain aldehydes group produce red copper(â ) oxide precipitate when react with Benedict’s reagent. Materials and equipments: 2cm3 of 1% starch solution, 2cm3 of 1% glucose solution, 10 cm3 of 1% iodine solution, 30 cm3 of 1% Benedict’s reagent, small amounts of ...read more.


2.The diagram(fig.1) below shows what I observed directly after the procedure 3 : Food source Color change Mushroom / Potatoes Blue-black Bread piece Blue-black Sweet potatoes Purple-blue Lemon / Onion / Biscuit Blue-black Cucumber / Tomatoes / Peanuts / 3.Then,the diagram(fig.2) below shows what I observed directly after the procedure 4: Food source Color change Lemon Red-orange Lettus Dark purple-red Tomaot sauce Orange Cucumber Red-orange Tomato Orange Dark green vegetable / Milk Light orange Biscuit Orange Cereal Orange Sweet potato Red-orange Analysis: 1. In my whole experiment, the procedure 1 and 2 were used as testing thoeries to give us a standard to testify whether certain food source contained certain kinds of carbonhydrates. If in procedure 3 the food turned color near blue or purple, the food must contain starch inside. What?s more, if in procedure 4 the solution in the test tube turned color near red or orange, the food msust contain reducing sugars glucose or fructose. ...read more.


This time, I controled the water very carefully by pouring it softly along side the walls of the beaker and measuring cylinder to make sure there?s no bubble made during the procedures. My improvement was successful and at the second time we added water accurately to 500cm3. 2. The color of final solution in test tube ?2.5mgdm-3? was as dark as that of the solution with 10mgdm-3and it?s not consistent with the general trend of other solutions. I considered the whole procedure of our experiment thoroughly and thought of two possible errors. Firstly we could have made that firstly we might add more than 5 cm3 standard detergent solution to the test tube. Secondly, because before using the 1000cm3 beaker to heat the test tube we used 500 cm3 beaker at first then we found it too small to hold six test tubes so we removed two test tubes out of the water and then put them into the bigger container. Maybe one of the two previously heated test tube was the ?2.5mgdm-3? one and it?s darker because it has been heated for seconds before others. What?s assay ? ...read more.

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