The food industry is highly regulated by government authorities, all food chains and supplies are evaluated according to international standards to control and assure quality. Milk is an essential food all over the world. So in order to meet the milk requirements, composition and characteristics analysis of milk is necessary. In lab experiment proximate analysis technique is used. In proximate analysis percentage of fats, protein and carbohydrates is determined. During laboratory activity, the percentage of proteins carbohydrates and water can be analyzed. Determination of the composition is necessary to calculate food value. Laboratory results can be compared with the expected values. Purpose of the lab activity is to allow us to use their knowledge of macromolecules and designing a whole line of experiments to evaluate the composition of milk. Understating of the macromolecules assay is very useful in analysis of milk composition. In this course we are challenged to advance and test our skills scientific reasoning, formulating a hypothesis and schematically run experiments. Any kind of unknown substance is evaluated to identify its chemical nature and macromolecular assay. It is anticipated that milk includes carbohydrates, fats and proteins. According to pervious literatures major part of milk composition are proteins. There are numerous kind of proteins in milk.it is predicted that fats are most important portion of milk. Milk composition and percentages of different macromolecules in milk can give us knowledge about physical and chemical properties of milk.
Material and methods:
The food we eat is made of cells. We digest our food and obtain energy and the raw materials from which to build our own cells. We can use chemical indicator tests to determine which kinds of macromolecules particular foods contain. Each food sample is considered an unknown because its exact molecular composition is not known. In order to investigate our unknowns using chemical indicator tests, we must first find out how the indicator chemicals react with each type of macromolecule. As an example, in order to test for the presence of starch, we need to know what color the indicator chemical produces when it is combined with starch versus the color it produces when there is no starch. Therefore, before you test your unknown foods, you must perform each chemical test on a substance known to contain the macromolecule you are testing for (positive control) and a substance that definitely does not contain the macromolecule (negative control).
There are four basic components of organic food. The composition of these four macromolecules in milk was evaluated in laboratory using standard protocol. Availability of the material and utensils was also kept under consideration. Following are the procedure used in the analysis of milk macromolecules.
Test for carbohydrates: carbohydrates are divided into two basic types, starch and simple sugar
Test for starch: lugol’s reagent or iodine solution is used to test starch. Iodine solution is yellowish brown to dark purplish in color.
Material: two test tubes, Iodine solution, Milk sample
- Take two separate test tube one with milk sample other containing control (distilled water)
- Add 3 drops of iodine solution in both tubes separately.
- Record the result in both test and control
- Change in the color is an indication of starch presence.
Benedict’s solution: This is used to test simple carbohydrates in sample. Benedict’s solution is blue color liquid with copper ions. When benedicts solution and simple sugar solutions are heated for a while, color changes from blue to brick red.
Materials: Two test tubes, milk, distilled water, water bath, benedict’s solution.
- Add 3 drops of Benedict’s solution to 5 ml of milk in a test tube.
- Add 3 drops of Benedict’s solution to 5 ml of distilled water in another test tube as control.
- Now place both test tubes in a beaker half-full of water. Heat this water bath on a hot plate until the water in the beaker has boiled for 2-3 minutes.
- Record the change in color as an indicator of simple sugar presence or absence.
2. Testing for lipids:
Grease spot test: Put a small drop of milk on a paper. Next to it put a small drop of water. Allow both to dry. Record what happened to both the spots.
Water will evaporate but milk will leave an oil spot due to fats.
3. Testing for proteins using the CuSO4 test
Materials: Cuso4, milk, 40% NaOH, dropper, test tube holder.
- Take small amount of 40% NaOH in a dropper.
- Add few drop of 40% NaOH in test tube containing 5ml milk.
- With the help of a dropper take 1% CuSO4 solution
- Add few drops in the same test tube containing milk.
Shake well note the change in color.
4. Testing pH using pH indicator paper. pH can easily be checked with an electronic device called pH meter. Sometimes for more convenience pH paper are also used to check ph. pH paper is quite easy to use just dip a side of paper in milk solution and after drying for a second match the color with the chart. Neutral pH is 7 above this pH is basic and below is acidic.