Molecular Gastronomy: Exploring the Science of Flavor (51 page)

m y os in: Along with actin, an essential protein for muscle contraction.

neurons: The brain contains nerve cells, or neurons, that transmit and receive signals

in the form of neurotransmitter molecules. Once a certain excitation threshold is ex-

ceeded, an electrical impulse is propagated through a prolongation of the cell, known

as an axon, triggering the release of neurotransmitters, which traverse a synaptic cleft

and activate other neurons.

nuclear magnetic resonance (nmr): A nondestructive method for determin-

ing molecular composition that exploits the magnetic properties of certain atomic nu-

clei along with radio waves. No radioactivity is involved.
See also
Magnetic resonance

imaging.

odor: A sensation that occurs in cooking when one puts one’s nose above a pan on the

stove: The heated foods release volatile molecules that attach themselves to the recep-

tors of olfactory cells in the nose—hence the invention of the cover, which retains heat

and traps the odorant molecules inside.

odorant compounds: Molecules that are sufficiently volatile to reach receptor pro-

teins, located on the surface of olfactory cells in the nose. Volatility by itself is not suf-

ficient: A molecule is aromatic only if it binds to one of these receptors, thus triggering

the excitation of the olfactory cell, which signals to the brain that an aroma (or an odor)

has been detected.

oil: In cooking, a liquid whose molecules are almost exclusively triglycerides.

olfact ion: The faculty that permits us to detect the presence of molecules in the air

above a dish that have evaporated from it and that contribute to the flavor of the food.

osmazome: A mistaken notion that arose toward the end of the eighteenth century. Alco-

hol was believed to extract a well-defined principle peculiar to meats—the osmazome—

that was responsible for their flavor. Why was this idea mistaken? Because the alcoholic

extract in question is composed of many sorts of molecules and because the principle

changes depending on the meat.

osmosis: A remarkable physicochemical phenomenon that used to be demonstrated with

the aid of a pig’s bladder immersed in a volume of water. A bladder partly filled with

sweetened water was observed to swell up: The sugar is unable to escape the bladder,

and more water seeps in from outside. The underlying reason for this phenomenon is

the tendency of concentrations of various molecules on either side of a permeable bar-

rier to be equalized.

346 | gloss ar y

oxidation: An important reaction that has been insufficiently explored in cooking. In

recent years it has often been said that the browning of the surface of meats is caused

by a chemical transformation known as the Maillard reaction. It is more accurate to say

that the Maillard reaction contributes to browning together with other reactions, among

them the Strecker degradation and various oxidizing reactions.

papillae: Drink a glass of milk, stick out your tongue in front of a mirror, and you will be

able to make out small round projections on the tongue. These papillae (usually called

gustatory, although I prefer to say sapictive because they detect tastes rather than flavor)

are composed of cells whose surface supports proteins known as receptors. When a

taste molecule interacts with these receptors, the cells are electrically activated and send

a signal to the brain indicating that they have detected this particular molecule. The

papillae tell us when we ought to stop eating.

pectin: Chemists consider it a d-galacturonic acid polymer, a complex definition that

can be simplified by observing, first of all, that it is a sugar. The properties of this mol-

ecule result from a long chain of atoms consisting of hydroxyl (–oh) groups, a methyl

(–ch ) group, carboxylic acid (–cooh) groups, and methyl ester (–cooch ) groups.

3

3

The carboxylic acid groups are important in cooking because they electrically repel one

another in a basic medium, with the result that pectins are unable to combine with one

another. Therefore in making preserves (which is to say gels created by the association

of pectins) the acid groups must be neutralized by h+ ions. In other words, the cooking

medium must be sufficiently acidic.

pectinases: Enzymes that degrade pectin. If you want to make apple juice without wear-

ing yourself out, simply add pectinases to an apple and let them act for a while at room

temperature.

peptides: Molecules formed by the bonding of certain amino acids.

pH: A measure of the acidity or alkalinity of a given environment. The scale runs from 0 to

14. Values between 0 and 7 correspond to acid environments and values between 7 and

14 to alkaline (basic) environments. It is inexcusable that pH paper is not commonly

found in kitchens today. How else can one determine a solution’s relative acidity?

phenolics.
See
Polyphenols.

phospholipids: We could not live without these molecules because, along with glycero-

lipids, they constitute the double molecular layers that form the membranes of living

cells. They have a lipid part and a phosphate part (a phosphorus atom surrounded by

oxygen atoms), but most owe their distinctive properties to the presence of an electri-

cally charged part and a hydrocarbon part (composed solely of carbon and hydrogen

atoms).

physics: One of the pillars of gastronomy, involving not particle physics or astrophysics

but the physics of “soft” or “condensed” matter. Emulsions, foams, and gels are best

studied collaboratively by physicists and chemists.

Glossary
| 347

polyphenol oxidases: Enzymes that oxidize molecules of the polyphenol class, form-

ing quinones that react to produce brown compounds. These enzymes are responsible

for the discoloration one sees in apples that have been cut up and left out, exposed to

the air.

polyphenols: Molecules containing at least one benzene ring (a hexagonal ring with

six carbon atoms attached to hydrogen atoms) and hydroxyl (–oh) groups. Tannins are

polyphenols, as are many of the molecules that give foods their color.

polysaccharides: Another name for complex sugars.

potato: A vegetable whose cells have the peculiar property of containing small granules

of starch, which absorb water and swell during cooking.

precipitation: The French humorist Alphonse Allais used to say that water is a danger-

ous liquid because a single drop is enough to cloud the purest absinthe. This cloudiness

is caused by the precipitation of anethol, a component of absinthe. Precipitation is a

phenomenon that has been studied by chemists for centuries and that could be put to

better use by cooks.

preserves: Pectin molecules in fruits are joined together by cooking, forming a net-

work—or gel—that traps water, sugar, and the various molecules that give fruits their

good taste.

proteases (including proteinases): Enzymes that degrade proteins. Fresh pineapple, for

example, contains the protease bromelin; papaya, papain; figs, ficin. These enzymes are

our enemies when we try to make pineapple, papaya, and fig jellies.

proteins: Chains of amino acids that are longer than peptides.

rancidity: The result of leaving fat exposed to air.
See
Autoxidation.

receptors: Proteins on the surface of cells that react by means of weak forces with com-

pounds in the cellular environment and trigger various physiological reactions: detec-

tion of an odor, a taste, and so on.

rennet: An extract from the abomasum of calves that permits the formation of certain

cheeses made from milk: Casein micelles, once chemically modified by rennet, cease to

repel one another and combine to form a gel that traps fats.

retro-olfaction: As food is chewed in the mouth it is very slightly heated and releases

volatile molecules that rise up through the retronasal fossae at the rear of the mouth

and reach the nose, where they are detected by olfactory receptors.

salt: The kind you find in the kitchen is sodium chloride. As one would expect, its taste is

usually salty, but in its unrefined state it may contain other salts that give it a bitter taste.

sal t y: The sensation produced by salt and certain other compounds.

sapict ion: Both French and English ought to adopt this word, which is much more

precise than
gustation.
If the physiology of flavor (not taste) is to make further progress

we must take into account what we have learned so far. Just as we have abandoned er-

roneous notions such as phlogiston and caloric, should we not adopt other more useful

ones in their place?
See also
Taste molecules.

348 | gloss ar y

sauces: Remarkable physicochemical systems that accompany a great variety of dishes.

Traditionally they are softer than the meats and vegetables they accompany, but their

viscosity must be greater than that of water. Mastery of the rheological behavior of sauc-

es is one of the great challenges of cooking.

sodium bicarbonate: Also known as bicarbonate of soda, or baking soda, it is a valu-

able base in cooking, used to soften lentils and to accelerate the cooking of vegetables.

soufflé: A foam that expands not because its air bubbles are dilated by the heat of the

oven but because a portion of its water evaporates.

sour.
See
Acidity.

starch: Dough is made by mixing flour with water. If the dough is then kneaded under a

thin stream of water, a white powder composed of minute granules appears. This mate-

rial, starch, is also found in the cells of potatoes and other vegetables.

starches: Foods that contain starch. They can be identified by a test familiar to children:

Pour a little tincture of iodine on them and see whether a purple stain appears that then

turns blue.

starching: A process by which starch granules heated in water lose some of their amy-

lose molecules and swell up, forming a starch paste.

strecker reac t ion: Amino acids react when carbonyl compounds (which have a

–c=o group) are present, producing a degradation named after the German chemist

Adolph Strecker (1822–1871). This reaction often occurs in cooking because Maillard

reactions are sources of carbonyl compounds.

sucrose: Ordinary sugar, composed of a glucose molecule joined together with a fructose

molecule (both molecules lose their identity during bonding, however). Sucrose is the

prototype sugar molecule, but there are many others.

sugars: Some are made up of small molecules, such as glucose, fructose, and lactose.

Others are made up of large molecules, such as cellulose and pectin.

suspension: A physicochemical system obtained by the dispersion of solid particles in

a liquid. India ink is an example of a suspension. Custard, in which aggregates of egg

proteins are suspended in the water contained in the milk, is another.

sweet: The taste produced by sucrose and other sugars. The sensation varies, depending

on the sugar.

tannins: Extracted from various kinds of vegetable matter, including wood, they have the

property of combining with proteins and iron. For example, a sheet of (protein) gelatin

soaked in strong tea (a solution containing tannins) causes the tea to become cloudy.

taste molecules: Certain food molecules dissolve in water and then become attached

to receptors on the surface of the papillary cells in the mouth. It is sometimes said that

excitation of these cells causes a signal to be sent to the brain that a flavor has been

detected. But this terminology is confused, for taste receptors register the sensation of

specific tastes. The perception of a food’s flavor is the product of a whole set of sensa-

tions in addition to the sensation of tastes: perceptions of smell, texture, temperature,

Glossary
| 349

and so on. It would be more helpful if the term
sapiction
were used to refer to the detec-

tion of a particular taste by sapictive receptors that are carried by sapictive cells in the

papillae.

tastes: It was long thought that only four existed (salt, sweet, sour, bitter), but recent ad-

vances in neurophysiology have shown that monosodium glutamate, for example, has

a distinctive taste (called umami) and that various bitter molecules stimulate different

papillary cells. But consider licorice. Is it salty? No. Is it sweet? No. Sour? No. Bitter? No.

Umami? No. Well, then, what is it?

tensioactive molecules: Laundry detergents contain molecules that adhere to the

surface of greasy stains, enveloping and detaching them from soiled fabrics. The drop-

lets of water-insoluble matter coated with these tensioactive molecules are dispersed in

water and then carried off during the rinse cycle. In cooking, molecules of the same

type coat droplets of oil introduced into water to form emulsions. See for yourself and

try making an emulsion with a drop of liquid detergent, but don’t eat it.

triglyceride: An ester of glycerol, attached to three fatty acids. These molecules, which

have the shape of a comb with three teeth, make up dietary fats. The teeth—the fatty

acids—come in different lengths, and some have carbon atoms that are joined together