The Four Basic Four Molecules

THE FOUR BASIC

FOOD MOLECULES

Water is the major component of

nearly all foods-and of ourselves! It's

also a medium in which we heat foods

in order to change their flavor, texture, and stability. One particular

property of water solutions, their

acidity or alkalinity, is a source of

flavor, and has an important influence on the behavior of the other

food molecules.

•

Fats, oils, and their chemical relatives

are water's antagonists. Like water,

they're a component of living things

792

Fats and Heat 801

Emulsifiers: Phospholipids,

Lecithin, Monoglycerides 802

Carbohydrates 803

Sugars 803

0 ligosaccharides 803

Polysaccharides: Starch, Pectins,

Gums 804

Proteins 805

Amino Acids and Peptides 806

Protein Structure 806

Proteins in Water 808

Protein Denaturation 808

Enzymes 809

and of f o ods, and they're also a cooking medium. But their chemical nature

is very different-so different that they

can't mix with water. Living things

put this incompatibility to work by

using fatty materials to contain the

watery contents of cells. Cooks put

this quality to work when they fry

foods to crisp and brown them, and

when they thicken sauces with microscopic but intact fat droplets. Fats also

carry aromas, and produce them.

•

Carbohydrates, the specialty of

plants, include sugars, starch, cellulose, and pectic substances. They

generally mix freely with water. Sugars give many of our foods flavor,

while starch and the cell-wall carbo-

McGee, H. (2004) On Food and Cooking: The Science

and Lore of the Kitchen. Scribner: New York, NY.

WATER

793

hydrates provide bulk and texture.

•

Proteins are the sensitive food molecules, and are especially characteristic of foods from animals: milk and

eggs, meat and fish. Their shapes and

behavior are drastically changed by

heat, acid, salt, and even air. Cheeses,

custards, cured and cooked meats,

and raised breads all owe their textures to altered proteins.

WATER

Water is our most familiar chemical companion. It's the smallest and simplest of

the basic food molecules, just three atoms:

H20, two hydrogens and an oxygen. And

its significance is hard to overstate. Leaving

aside the fact that it shapes the earth's continents and climate, all life, including our

own, exists in a water solution: a legacy of

life's origin billions of years ago in the

oceans. Our bodies are 60% water by

weight; raw meat is about 75% water, and

fruits and vegetables up to 95%.

0

H H

+

WATER CLINGS STRONGLY

TO ITSELF

The important properties of ordinary water

can be understood as different manifestations of one fact. Each water molecule is

electrically unsymmetrical, or polar: it has

a positive end and a negative end. This is

because the oxygen atom exerts a stronger

pull than the hydrogen atoms on the electrons they share, and because the hydrogen

atoms project from one side of the oxygen

to form a kind of V shape: so there's an

oxygen end and a hydrogen end to the

water molecule, and the oxygen end is more

negative than the hydrogen end. This polarity means that the negative oxygen on one

water molecule feels an electrical attraction to the positive hydrogens on other

water molecules. When this attraction

brings the two molecules closer to each

other and holds them there, it's called a

hydrogen bond. The molecules in ice and

liquid water are participating

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