Fat and Salt in Food

Determination of fat and salt in potato chips, french fries, and/or hash browns

Recently, there has been a lot discussion of calories and fats in our foods in the news media. Most food labels list recommended serving sizes, sometimes with unrealistic quantities, of the food product and then lists the nutritional information based on that serving, assuming a 2,000 calorie per day diet. Nutritional information usually includes calories, total fat, saturated fat, cholesterol, sodium, total carbohydrate (with separate listing of dietary fiber and sugars), and protein. The label information may also include vitamins and minerals.
Nutritionists recommend that no more than 30% of our daily 2000 calories come from fat.
However, in our snack food and fast food world, we often eat a diet that contains a larger percentage of fat. So, the question arises, how much fat is in a snack bag of a food such as potato chips, or a standard serving of French fries? Hash browns?
In this experiment, you will determine the fat content and salt of several different fat laden salty foods that you probably eat by the handful. You will be performing an extraction of the fats by putting the sample in a non polar solvent, petroleum ether. Fats are not water soluble, unlike carbohydrates and proteins. By using a non polar solvent, only the fats will dissolve in the liquid. This liquid will then be separated from the solid and the mass of fat ‘extracted’ will be measured. You can then compare this to the mass of the original sample and determine the % of fat in the in original sample.

The 'Other' part of the lab is going to determine how much salt is in the sample (and we will also compare this to the value on the food 'label') In this case we are going to extract the salt (which dissolves into sodium ion and chloride ion) with water. We are going to assume all the chlorine we determine via titration is in the form of sodium chloride.
This method you will use for this part involves chemical volumetric analysis. You will use a silver nitrate (AgNO₃) solution of known concentration and use it to precipitate out the chloride in the food sample. The procedure is complicated by the fact that the dense white precipitate, silver chloride (AgCl), does not settle rapidly. It is impossible to tell when all the chlorides have been removed from the seawater unless an indicator is used to signal complete precipitation by a visual color change. The indicator in the analysis is chromate ion. When all of the chloride ion is exhausted, the chromate ion reacts with silver ions and produces silver chromate, which is red. The instant a permanent orange tinge appears in the solution (one that doesn’t vanish with mixing), the addition of silver nitrate is stopped. The final solution color should look like that of orange juice.
The chemical reactions are:
Cl^-(aq) + Ag⁺(aq) → AgCl(s) (white precip)
2 Ag⁺(aq) + CrO₄^2-(aq) → Ag₂Cr₂O₄(s) (red-brown precip)

Before you come to lab, you must print off the Lab Data Sheet which you will turn in (as well as your calculations sheet and graded pre-lab) before you leave lab.

Fat content procedure in brief:
Place ~0.5 g of crushed up chips (or torn up fries/hash browns) into a 13x100 mm test tube. Add ~3mL of petroleum ether, stopper, and shake the solution. Use the centrifuge to settle the solid to the bottom. Pour off the liquid into a pre-weighed 25 mL flask. Add another 3 mL of petroleum ether and stir/centrifuge. Again, pour of the liquid into the flask. Carefully heat the flask to remove the petroleum ether. Determine the mass of fat in the flask and calculate the % of fat in the substance.

Sodium (as measured by sodium chloride) procedure in brief:
Place ~15 g of food (whatever it is) into a beaker with 50 mL of water. With a stirring rod (or other such tool) break up the food and swirl it in the water for 5 min. Filter off the food-goop using a tool provided by your instructor (small strainer). Titrate the sample with 0.1 M AgNO₃. At the end point, you should be able to calculate the moles of Cl in the sample. From there:
moles Cl Śmoles NaCl Śmoles Na in sampleŚg of Na in sampleŚg Na per g of 'food'

Prelab Questions:
1. Find a bag of chips and look at the nutritional facts label. Calculate the % of fat in the chips. This can be done by comparing the mass of a serving size to the total mass of fat (see Total Fat on the label) in one serving. This is the calculation you will be doing in this lab.
2. Find the nutritional facts for McDonalds French fries and Burger King hash browns. (These are both easily found with a google search) Calculate the g of sodium per g of food. What is the % sodium in the food? This is the value you will be comparing your experimental data with.
3. Bring a chip (or other fatty/salty food that can be crushed up easily) sample to lab to be tested. Brownie points to the person who brings is the product that has the HIGHEST fat content.

~MEO 12.3.07