Super market products:
| instant mashed potato powder (ingredients: potato, emulgator 471, antioxidation agent,
ascorbylpalmitate, dye curcumin)
| paprica (ingredients: paprica, separating agent, cellulose, silicium dioxide)
| edible oil (ingredients: sun flower oil, lemon oil, vitamin A, vitamin D) | |
Glass wares:
| 2 gas washing bottles 250 mL (without head), fitted with a stopper
| beaker 50 mL
| 2 beakers 100 mL
| 2 beakers 250 mL
| glas funnel d = 10 cm | |
Experimental procedure:
3 g of paprica are dissolved in 80 mL of edible oil. The solution is distributed in two gas washing bottles. 200 mL of water is added. When the phases have separated, 20 g of potato powder are poured into one of the two bottles. Now the two bottles are stoppered and shaken.
Results:
When shaking is stopped the liquids in one of the two bottles will separate again regenerating a red colored layer on top of the water. In the other bottle a homogenous, orange colored mixture is formed.
Video clip (Download RealPlayer .rm file)
Discussion and background:
The insolubility of oil in water is due to the fact that oil is non polar and hydrophobic. The oil is less dense, so it will be in the upper layer. Paprica is soluble in oil.
The emulgator in instant mashed potato powder consists of mono- and diglycerides of fatty acids. In the case of a diglyceride the two fatty acid "tails" on the molecule are lipophilic. The glycerin backbone is hydrophilic.
Diglyceride
Emulgators are used in situations where fats or oils must form for a certain time a stable mixture in aqueous media. Therefore they are a component of foods, detergents, and cosmetics.
Lecithin is often used as an additive in such processed foods as ice cream, margarine, and salad dressings, because it helps blend or emulsify fats with water.
Lecithin is a natural emulgator. With lecithin's hydrophobic and hydrophilic portions, it can simultaneously interact with both oil and water, making it an effective emulsifier. The hydrophobic "tail" contains two long hydrocarbon chains of two fatty acids. The hydrophilic head consists of carbonyl groups, a glycerol bridge and a phosphatidylcholine region:
Lecithin - Space filling model
(Source: http://www.web-books.com/MoBio/Free/Ch1B2.htm)
The word "lecithin" is derived from the Greek term "lekithos", which means "yolk of an egg", where it was first discovered. But soybeans are the most important source of commercial lecithin.
Reference:
Schwedt, G.: Experimente mit Supermarktprodukten, Wiley-VCH-Verlag, Weinheim 2001
Index of Lecture Experiments
