TESTING FOODS FOR STARCH AND LIPIDS BY MARIA CORDERO

HOW TO DETECT LIPIDS IN FOODS USING ALCOHOL

                                                                                                              What are lipids?

 Lipids are organic biomolecules formed mainly of carbon, hydrogen and oxygen. They accumulate large amounts of energy and perform many functions in living things. They make up biological cell membranes, protect some organs, regulate body functions, in the case of sex hormones and vitamins A,D,K,E. They are excellent thermal insulators. Some are essences and others are plant pigments.

Lipids are insoluble in water but soluble in organic solvents such as alcohol. This property was used in this experiment.

 María put samples of food in different beakers and added alcohol. She let the mixture stand for a few minutes. 

 When this is done, a clear liquid should float on top. If the liquid is white it is that too little food or alcohol has been used.

 After a while she took some of this clear liquid and with the use of a pipette and put it into a test tube. Now she added a few drops of water and observed. In some test tubes the liquid remained clear and in others it became cloudy. The cloudy samples indicate the presence of lipids. The samples that remained clear indicate that the sample does not have lipids or at least not significant amounts.

 Alcohol dissolves lipids present in food samples. When water is added the liquid becomes cloudy. It is because a lipid emulsion, in which water and alcohol act as an emulsifier agent, are formed. The emulsifier causes the lipids to remain suspended in the water in the form of drops. Due to the suspension the mixture takes on a cloudy whitish appearance indicating the presence of lipids in the sample.

HOW TO DETECT STARCH IN FOOD USING IODINE.

 Iodine changes colour when in contact with starch. Using a pipette María added a few drops of iodine to different food samples. The foods that contain starch, such as bread, pasta or rice, turned black or dark blue. 

 Starch comes from plants, it is a carbohydrate and is therefore made up of carbon, hydrogen and oxygen. It consists of a large number of glucose molecules joined together. This polysaccharide is produced by most green plants. It is the most common carbohydrate in human diets and is contained in large amounts in foods like potatoes, wheat, rice etc.