Molecular Gastronomy: Exploring the Science of Flavor (24 page)

the highest seal of quality, for the meat of Spanish pigs is marbled with fat that

contains many such acids.

Spanish Hams
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44

Foie Gras

It melts less and tastes better when it is cooked immediately after the geese

are slaughtered.

b o t h a l s a c e a n d t h e s o u t h w e s t e r n r e g i o n of France claim to

have been the first to invent foie gras, but it is not a new delicacy: The Ro-

mans are known to have force-fed geese with figs. The manner in which it is

prepared is changing, however. Goose livers traditionally were cooked several

hours after the animals had been slaughtered, but a revision of food industry

regulations in France has led to a centralization of local slaughterhouses and,

with it, the practice of immediate evisceration and cooking. What effect has

this had on the quality of the livers?

In the early 1990s, a team headed by Dominique Rousselot-Paillet and Gé-

rard Guy at the Institut National de la Recherche Agronomique (inra) sta-

tion in Artiguères succeeded in showing that livers obtained by on-the-spot

(
à chaud
) evisceration lost less fat than ones that had been allowed to cool

down before cooking. Producers were delighted, but they worried that the new

method would have adverse consequences from the point of view of taste. To

resolve the matter, which concerns one of the glories of French cuisine, Sylvie

Rousset-Akrim and her colleagues at the inra station in Clermont-Ferrand

analyzed the sensory characteristics of canned foie gras prepared under both

conditions.

Thirty geese were raised and force-fed at Artiguères. After immediate evis-

ceration the large lobe of the livers was cut lengthwise into two parts. One

sample was sterilized at once at 105°c (221°f) for 50 minutes, and a second

158 |

sample, taken from the other half of the lobe, was prepared following the same

procedure, only
à froid,
which is to say after several hours of cold storage. Then

the two samples were tested by trained tasters.

Earlier studies comparing goose and duck foie gras revealed a great dispar-

ity between livers and helped researchers develop the protocol for later tests.

The tasters were instructed to grade the intensity of eighteen aspects of the

cooked livers on a scale of 0 to 20: appearance (compact, smooth, veined),

odor (chicken liver, foie gras), texture (sticky, compact, firm, tender, granular,

plump, smooth, crumbly), taste (sour, bitter), and aroma (defined as a detect-

able part of flavor: foie gras, chicken liver, rancid). Statistical analysis of the

results yielded the desired information.

First, the Clermont-Ferrand team showed that human beings are reliable

measuring instruments when one knows how to use them. In many cases it

was possible to distinguish the two modes of preparation. In particular, the

livers that had been cooked at once were both more veined and more tender,

plumper and smoother, less granular, less friable, and less bitter, with a foie

gras aroma that was more developed than that of livers prepared after a few

hours’ delay. The sticky livers were the plumpest and the least crumbly. The

compact livers were the firmest and smoothest and, again, resisted crumbling.

Finally, the most granular ones were the most friable and also the least plump

and smooth.

More Tender, More Fragrant

Similarly, the statistical analysis showed a correspondence between odors

and aromas, the aromas of chicken liver and rancidity being opposed to the

aroma of foie gras. Acidity varied inversely with the intensity of the aroma of

foie gras. But to a greater degree than either odor or taste, the various aspects

of texture were positively correlated with aroma: In addition to smoothness of

appearance and the odor of foie gras, tenderness, compactness, plumpness,

and smoothness were associated with the aroma of foie gras.

Without making any prior assumptions, the tasting distinguished two

groups. The first consists mainly of livers prepared
à froid,
which have a granu-

lar, friable texture and an aroma of chicken liver with a note of rancidity; the

second group is composed of livers prepared
à chaud
(along with a few livers

from the first group), which are plumper, more tender, and smoother.

Foie Gras
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What accounts for this division? The fact that the lipid melting rate (the rate

at which fatty matter is released during cooking) is far higher for livers pre-

pared
à froid
(21%) than for ones prepared
à chaud
(9%) suggests that rapid re-

moval and cooking of the liver after slaughter prevents the postmortem change

of hepatic tissue, limiting membranous lesions and the escape of lipids.

The melting rate depends on the mass of the livers in the case of prepara-

tion
à froid
but not in the case of preparation
à chaud.
And no matter which

mode of preparation is used, warm or cold, compactness and firmness vary

inversely with the weight of the liver: The heaviest ones were found to be less

compact and less firm. But when the melting rate increases, as in the case for

the livers prepared
à froid,
the foie gras seemed more granular, friable, rancid,

and also less smooth, tender, compact, plump, and aromatic.

Producers have no reason to worry, because the new method of cooking

livers immediately after the geese have been slaughtered does not harm their

product—quite the opposite. Cooks will draw the same conclusion: The best

foie gras is made from livers obtained directly from the slaughterhouse.

160 | investigations a nd mod el s

45

Antioxidant Agents

Aromatic plants prevent the oxidation of dietary fats.

bu t t er a nd o t h e r f o od s c o n t a i n i n g f a t s turn rancid on contact

with air as a result of a chain reaction: the autoxidation of fatty acids. Arresting

this degradation, which produces disagreeable tastes and odors and creates

free radicals, has long been an elusive goal. Eliminating oxygen from foods and

to protecting them from light is not enough. Antioxidant compounds are also

needed to combat the precursors of autoxidation that are already present.

Some foods naturally contain antioxidant compounds that protect them

from turning rancid, such as the tocopherols (vitamin E) found in virgin olive

oil and the ascorbic acid (vitamin C) of lemon. To extend the shelf life of their

products, food processing companies began using these natural compounds

more than twenty years ago while seeking ways to synthesize substances with

greater antioxidant action. However, consumers feared the unknown toxicity of

synthesized products, causing research to be confined to natural compounds.

Understanding the autoxidation of fatty acids nonetheless is important for

studies of such compounds. This reaction occurs when light breaks the –c–h

bonds of a lipid by forming unstable –c• free radicals that react with the oxy-

gen in the air to form other –coo• free radicals. These radicals then react with

other –c–h bonds to create a new –c• radical that propagates oxidation.

Phenols, the antioxidants used by the food processing industry, are mol-

ecules containing a benzene ring composed of six carbon atoms at the apices

of a hexagon, at least one of which is bound to an –oh hydroxyl group. The

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antioxidant activity of phenol acids and their esters depends on their structure

and, more particularly, on the delocalization of the electrons in their aromatic

core: Some of their electrons are shared by all the atoms of the benzene ring.

When these compounds react with the free radicals formed by the autoxidation

of fats, they are transformed into free radicals, but they remain stable because

the nonmatching electrons are delocalized, which limits their reactivity. Thus

the propagating reaction is blocked, with the result that foods are prevented

from turning rancid.

Despite its well-defined purpose, research on antioxidants was a tedious

business because the reaction needing to be avoided appears only slowly; for-

tunately, it takes time for food to go bad. Systematic investigation using tradi-

tional tests of rancidity, which lasted several days, was impracticable because

it took much too long.

A new test devised in the 1990s by Hubert Richard and his colleagues at the

École Nationale Supérieure des Industries Agricoles et Alimentaires in Massy

resolved the problem by indicating the antioxidant power of a compound in

a matter of only a few hours. They bubbled oxygen into a lipophilic solvent,

dodecane, in which methyl linoleate (the fat to be tested) and the candidate

antioxidant were dissolved at 110°c (230°f). Gas chromatography revealed that

half of the methyl linoleate is oxidized in three hours. The antioxidant power of

a compound is measured in terms of its ability to lengthen this half-life.

The new faster method was then used to elucidate the chemical character-

istics of antioxidant compounds (in order to predict which ones would be the

most effective) and to determine which aromatic plants are the best sourc-

es of these compounds. Comparison of several plant phenol acids with four

antioxidants commonly used in the food processing industry—butylated hy-

droxyanisole (bha), butylated hydroxytoluene (bht), 2-tertbutylhydroquinone

(tbhq), and propyl gallate—disclosed the strong antioxidant effect of many

compounds. In particular it became apparent that the antioxidant activity of a

given molecule seems to depends on how many –oh hydroxyl groups it has

and on the degree of stabilization created by the delocalization of electrons.

These findings made it easier to predict the antioxidant efficiency of different

compounds and to determine in which natural substances the most potent

antioxidants are present.

Tests devised at the Massy laboratory for analyzing various extracts from

aromatic plants confirmed the long-suspected antioxidant activity of rosemary,

162 | investigations a nd mod el s

sage, cloves, thyme, oregano, ginger, and capsicum, but not of nutmeg. The

extracts from rosemary, sage, cloves, and ginger exhibited a degree of activ-

ity similar to that of alpha-tocopherol, roughly one-tenth that of bha and of

gamma-tocopherol. Although neither pepper, parsley, celery, Indian celery,

nor basil was found to display antioxidant properties, contrary to what earlier

studies suggested, benzoin and vanilla act in a way similar to that of alpha-

tocopherol. These two plants contain vanillin, which first attracted interest as

an antioxidant in 1989.

The most promising plants undoubtedly are rosemary, cloves, sage, ginger,

and benzoin. Sage may be a particularly good source, for it has been shown

to contain six powerful antioxidant compounds: carnasol, carnosic acid, and

isorosmanol, all present in large quantities, as well as rosmadial, rosmanol,

and epirosmanol.

Antioxidant Agents
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46

Trout

Variable quality has prompted physical chemists to take a closer look.

w h a t m a k e s s e a t r o u t t a s t e s o g o o d ? Is the pink color of its flesh a

sign of quality? How should it be cooked to satisfy gourmets? And how should

it be raised to suit processing requirements, particularly in connection with

smoking, a technique in which French companies have long specialized?

Although France is among the world leaders in trout production, the study

of trout aquaculture is almost thirty years behind the study of beef and other

kinds of meat. One of the chief problems is inadequate genetic selection,

which causes unwanted variability in the quality of farm-raised fish. Benoît

Fauconneau, Michel Laroche, and their colleagues at the Institut National de

la Recherche Agronomique stations in Rennes and Nantes, in collaboration

with the Institut Français de Recherches sur la Mer and several private com-

panies, have been exploring the physicochemical characteristics and sensory

properties of trout filets in an attempt to determine the causes and effects of

differences in quality.

It was known that the gustatory qualities of the large salmonids and their

susceptibility to treatment by means of techniques such as smoking and mari-

nating depend principally on the concentration of lipids—molecules that dis-

solve aromatic compounds and that also can communicate tastes when they

are heated or oxidized—in the flesh of the fish. Preliminary analysis of fario

trout (
Salmo trutta
) raised in the sea by Elsamer S.A., in collaboration with

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food technologists in Camaret, revealed that the filets obtained from these fish

contained 65–70% water, 20–24% proteins, and 2–12% lipids.