The Four Basic Four Molecules
Dissertations Gratuits : The Four Basic Four Molecules. Recherche parmi 300 000+ dissertationsPar Maelle1995 • 22 Juin 2013 • 1 057 Mots (5 Pages) • 846 Vues
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
...