Basic Concepts of Culinary Chemistry Harriet G. Friedstein Rochester Institute of Technology, 50 W. Main Street, Rochester, NY 14614 Cooking and chemistry have had separate histories, and while a cook may not consider himself or herself a chemist, the cooking process is just one method of producing a chemical change. The chemical and physical changes that take place in foods during cooking depend upon energy source, time, temperature, and cooking method (baking, frying, etc.). Food texture, color, composition, moisture content, and taste are affected in various ways. There are chemical and structural changes in muscle fihers and cmnective tissue of meats, and fruits and vegetables undergo chemical and structural changes h .;m;~lle*rrh,iny(, In i t mper.~iurt.. wvn r ~ r thr Even i f 3 Imsic a.hemi.;trv roura. includrs .fi unit ~ , I Iiwd. th? unit usually deals only with the chemical composition of fats and lipids, carbohydrates, proteins, vitamins, and additives. It is unfortunate that the subject of food and the changes that occur in food is usually left to home econnmics courses. Following are some examples of culinary chemistry suitahle for a beginning chemistry course. How Does Bread Become Toast? Nonenzymatic hrowning not only occurs in the toasting of bread hut also is responsible for the dark brown color and the flavor produced by roasting raw cocoa beans. The reaction was studied by Maillard from 1912 to 1917. As stated by Garard ( I ) (and reiterated by Kirk (2)),"Foods are complex chemical systems and the Maillard reaction has never heen completely explained." A general example of the Maillard reaction, in which an aldehyde of the sugar and the amine group of the acid react, is
What is the green color that results when these precautions are not taken? Iron, in the form of iron (11) ions, reacts with sulfide ions from the white to form iron(I1) sulfide: Fez+
FeS
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Why Do Cooked Vegetables Vary in Quallty? Although there are a number of reasons for variation in quality of cooked vegetables, including changes in the cell structure, here we will he concerned with the chemical changes that occur in the chlorophyll of the green vegetables. It is desirable to cook vegetables as fast as possible to preserve their bright green color. Clydesdale and Francis (3) found that the chlorophyll molecule is very unstahle. Briefly, magnesium is replaced by hydrogen during heating; this is called pheophytinization. During this process, the bright green chlorophylls form dull, olive-green pheophytins. The general equation (4) is
+ COOC?,,Hx
What Causes the Greenish Color around the Yolk of Hard-boiled Eggs? Many times when eggs are boiled, they appear to have a greenish color around the volk. Ex~eriencedcooks know that eggs nwd I,) h~ I N N I I slonly, ~ that Ini1111gneed>i t , he
