Chips are not equally chips!The term „chips“ is used in German-speaking countries as shorthand for potato chips. These are raw potatoes sliced thin and then fried in oil. But even the small, usually triangular shaped cornmeal salt biscuits - the tortilla chips, the Indonesian crackers from manioc flour, salt and grinded shrimp - grab chips or slices of dried fruit such as bananas and apple chips are popular snacks with this name. They are all very tasty. It can be easy to forget what kind of "calories bomb" just as there may be eaten. And faster than we wanted, is the entire pack empty.

A comparison of these four types of chips offers pupils interesting options for analytical investigations. Of course, the chips depending on the manufacturer differ somewhat from each other. However, a comparison between potato, tortilla, crab and apple chips shows most differences (see Tab. 1 and Fig. 1). These results could even help, to think about the consumption of chips a little bit more and ultimately to buy these snacks more deliberately.

This article makes suggestions, which are suitable both for individual lessons at different grade levels and for a project-oriented and multi-disciplinary approach. A qualitative analysis of food components (proteins, carbohydrates, fats) into chips lends itself to both the chemistry and biology classes. A qualitative determination of fat content is already possible with simple means in the early stages of teaching chemistry as example to the separation of substance mixtures. But it also works for something more complicated and much more exact, using a Soxhlet apparatus. In addition, it can also reveal more components (eg vitamin C, chloride, magnesium and calcium ions) and determine qualitatively and quantitatively.

If a slide is prepared with the crushed chips and is examined under the microscope very interesting images can be observed. Additionally, single constituents can be stained specifically. Thus, it's possible to assign certain structures.

Tab. 1: ! The composition of the chips was based on 100 g. The values were taken from the package information of different manufacturers and can vary around this average.

Type Potato chips Tortilla chips Crab chips Apple chips

Energy [ kJ ]

Proteins [ g ]

Carbohydrates [ g ]

which sugars [ g ]

Fat [ g ]

Others [ g ]

2300 2050 2150 1250

7 8 4 2

50 65 63 68

0.4 0.9 6.2 61.8

38 23 27 2

5 4 6 28

Fig. 1: ! The composition of the four types of chips is illustrated graphically.

C. Kummer, D. Nippa, J. Viehweg chips project.pdf

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Potato chipsProteinsCarbohydratesFatOthers

Tortilla chips Crab chips Apple chips

Activities

1. Detection of food components

The main components can be determined semi-quantitatively by simple test-tube experiments (Fig. 2 and Tab. 2). This requires that the chips are first crushed. A coffee-mill is perfect for this.

A A spatula full sample was suspended in a test tube with 1 mL of demineralised water and then 1 mL of conc. nitric acid was added. The mixture was heated for about 5 minutes. After cooling, the supernatant can be decanted and neutralised with ammonia solution.

The yellow color is based on the nitration of aromatic amino acids (xanthoproteic reaction) and is a sensitive detection of proteins.

Hint: The wastes can be disposed in the sink.

B! A spatula full sample was suspended in a test tube with 1 mL of demineralised water and then with one drop of Lugol's reagent (iodine-potassium iodide solution) was added.

A blue color is usually a positive indicator for starch (see Fig. 4).

Hint: The wastes can be disposed in the sink.

C! A spatula full sample was suspended in a test tube with 1 mL of demineralised water. The supernatant was filtered off. The filtrate was mixed with 1 mL of Benedict's reagent and heated in boiling water for 5 minutes.

In the presence of reducing sugars, a brick-red color of copper-oxide or a reddish-brown precipitate of elemental copper appears.

Hint: The residues are disposed in the collecting tank for dissolved heavy metal salts.

D! A spatula full sample was suspended in a test tube with 1 mL of petroleum ether. After vigorous shaking and brief heating in a water bath a few drops of the supernatant were transferred onto a filter paper.

The positive detection of fats is possible, if a transparent grease spot is to be seen after evaporation of the petroleum ether.

Hint: The residues of extraction are disposed in the collecting tank of non-halogenated organic solutions, the solids in household garbage.

Fig. 2: ! Shown are the results of different detections. In the test tubes A to C a negative control is each on the left side. Potato, tortilla, crab and apple chips were suspended in the next test tubes and were investigated after the same way. At D the grease spot samples for potato and tortilla chips are in the top and for crab and apple chips are in the lower row.

Tab. 2: "The intensity of test reactions was rated as "strong" (+), "weak" (±) or "not detectable" (!).

Test \ Sample Potato chips Tortilla chips Crab chips Apple chips

Xanthoproteic test

Starch test

Test on reducing sugars

Grease spot test

+ + ± ±

+ + ( + ) !

! ! ! +

+ + + !

C. Kummer, D. Nippa, J. Viehweg chips project.pdf

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2. Determination of fat content

The fat content can be determined after extraction with a lipophilic solvent by determining experimentally the mass difference (Fig. 3 and Tab. 3).

Variant A25 mL of petrolium ether were added to an exactly weighed amount of sample (about 1.5 g of the crushed chips) in a large test tube. This is closed by a stopper in a glass tube (length about 50 cm). The mixture is

then heated for about one hour so that the condensation zone in the air-cooled glass tube not is exceeds the middle region. A magnetic stirrer with magnetic bars in the test tube and the water bath are helpful (Fig. 3 A). After cooling, the mixture was filtered and the filtrate was dried over night. Finally, the mass is determined.

Variant BOf course, it is also possible to use a Soxhlet apparatus for extraction (Fig. 3 B). The amount of sample and of solvent is determined by the size of the Soxhlet apparatus. The fat is extracted under reflux for 1-2 h.

Tab. 3: !The values for the fat extraction using a Soxhlet apparatus are shown exemplary for crab and for apple chips.

3. Microscopic investigations

The crushed chips are also suitable for microscopic investigations (Fig. 4).

A spatula full sample was suspended in 2-3 drops water. The slide was covered. It can be stained if necessary.

Fig. 4: ! First the microscopic picture of the crushed crab chips

shows that here with Lugol's reagent a polysaccharide but not starch, but chitin is stained blue (compare Fig. 2B). The ornament-like patterned surfaces in some very bizarre structures are parts of the shrimp. In addition, at 200 times magnification, small lipid droplets can be clearly seen.

C. Kummer, D. Nippa, J. Viehweg chips project.pdf

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A B

Fig. 3 The pictures show the different equipment that was used for the quantitative determination of fat content: Variant A is obtained by simple means; B is a Soxhlet apparatus for

extractions.

Fig. 3 The pictures show the different equipment that was used for the quantitative determination of fat content: Variant A is obtained by simple means; B is a Soxhlet apparatus for

extractions.

Fat extraction Crab chips Apple chips

m(Sample)start [ g ] 4.5945 4.5945

m(Sample)finish [ g ] 3.3632 4.5182

! m = m(Fat) [ g ] 1.2313 0.0763

ω(Fat) [ % ] 26.8 1.7