Molecular Gastronomy: Exploring the Science of Flavor (26 page)

tion. Their hydrosoluble part can react with oxygen as well.

Proof by Reaction

At the Institut National de la Recherche Agronomique station in Nantes,

Gilles Gandemer, Anne Leseigneur, and their colleagues studied the role of

phospholipids in triggering Maillard reactions in simplified systems. To an

aqueous solution of cysteine (an amino acid chosen because it contains a sulfur

atom and creates molecules crucial for the formation of the aroma of cooked

meat) and ribose (a sugar known for its activity in cooking that can be released

in nucleotides) they added either fatty acids found in phospholipids (linoleic

acid, palmitic acid, and ethanolamine) or the principal phospholipids in meats

(phosphatidylcholine and phosphatidylethanolamine), producing concentra-

tions of various molecules comparable to those found in meats. These mix-

tures were then heated to 140°c (284°f).

Because the products of Maillard reactions are too numerous to be test-

ed in a controlled way, chemists have sought instead to study changes in

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chromatographic profiles, focusing on the heterocyclic compounds, which

have a meaty taste, and on the products of lipid oxidation. Observing the ap-

pearance of new peaks on the chromatograms and the falling off from certain

peaks generated by systems modeled without lipids, the chemists were able

to confirm that phospholipids have a greater effect than triglycerides. They

also showed that the aromas of cooked meat caused by phospholipids arise

mainly from two effects: a fatty note created by the presence of carbonylated

compounds (which contain the c = o chemical group), the result chiefly of the

oxidation of fatty acids, and the interaction of lipids and their degradation prod-

ucts with the direct and intermediate products of Maillard reactions, which

leads to the synthesis of a few new molecules and a reduction in the formation

of other compounds.

It was also known that the nonvolatile products of Maillard reactions impede

the oxidation of lipids. Further analysis showed that the odors of the modeled

systems resulted more from a disturbance of Maillard reactions than from lipid

oxidation. Although lipids do not come into contact with compounds dissolved

in the aqueous phase, phospholipids, because of their polar head, are partially

soluble and can react with the intermediate products of Maillard reactions.

172 | investigations a nd mod el s

49

Tenderizing Meats

Why a meat that is well suited to boiling is not good for roasting.

m e a t i s a g r e e a b l e t o e a t o n l y w h e n it has been aged for a sufficient

period of time. After an animal is slaughtered its meat begins to toughen (for

twenty-four hours in the case of beef). This toughness can be reduced by as

much as 80% by aging, which lasts for several days (ten in the case of beef).

Can this period be shortened, or is it at least possible to determine the mini-

mum amount of time needed to preserve carcass and muscle so that a given

cut of meat will be properly tenderized? Ahmed Ouali and his colleagues at

the Institut National de la Recherche Agronomique (inra) station for meat

research in Clermont-Ferrand analyzed the characteristics of muscle tissue in

order to predict the length of time needed for aging different kinds of meat.

The first stage in the transformation of animal muscles into meat is the

onset of cadaveric rigidity. Muscle cells continue to contract and relax imme-

diately after death because they still contain adenosine 5´-triphosphate (atp), a

molecule that stores energy. The chemical cycles of muscle cells regenerate atp

for a certain time, but when it is produced only by the degradation of glycogen

(which serves as a reserve supply of glucose) the muscle is no longer able to

relax and remains in a contracted state.

During this phase the degradation of glycogen and glucose produces lactic

acid, whereas the degradation of atp releases phosphoric acid, with the result

that the muscles are acidified. The swiftness of acidification depends chiefly

on the type of muscle: Red (or slow-contracting) muscles, which derive their

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energy from oxygen carried by the blood, are acidified less and less quickly

than white (or fast-contracting) muscles, which do not consume oxygen, mak-

ing them more vulnerable to alteration by microorganisms.

Tenderizing and Degradation

The conditions under which cadaveric rigidity occurs determine the course

of the next phase, tenderizing, which probably results from the degradation

of structural elements. A distinction has long been made between the sort

of toughness associated with collagen (the protein that sheathes muscle cells,

grouping the muscle cells into bundles and the bundles into muscles) and the

sort associated with myofibrils (the proteins responsible for the contraction of

muscles). It has recently been observed that collagen, which is mostly unaf-

fected by the tenderizing process, provides an index, or baseline, for measur-

ing toughness. Collagen varies according to its concentration in muscles and

determines the preferred cooking method for different cuts of meat. Pieces

with high concentrations of collagen are best boiled, whereas ones with low

concentrations of collagen are better suited to roasting.

Two types of mechanisms seem responsible for tenderizing myofibrils. Cer-

tain proteolytic enzymes decompose proteins, breaking down the filaments

and fibrils, and an increase in osmotic pressure dissociates the constituent

proteins of the filaments.

The inra biochemists studied three groups of enzymes capable of de-

grading myofibrillar proteins: cathepsins, calpains, and a complex of proteins

known as proteosomes, less well known than the other two because it has only

recently been discovered. The activity of these enzymes in muscles depends

on acidity, the concentration of calcium ions and atp, and so on. In living

animals it is limited by various inhibitors that prevent the decomposition of

muscles, but enzymatic regulation is suppressed after slaughter, largely as a

consequence of acidification. Furthermore, the increase in the osmotic pres-

sure of muscle cells that occurs after death facilitates and reinforces the action

of the enzymes: The accumulation of small molecules and free salts in the in-

tracellular liquid dissociates the protein complexes, permitting the proteolytic

enzymes to penetrate to their substrates more easily.

The sensitivity of myofibrils to proteolytic enzymes greatly varies according

to the type of muscle. The myofibrils in red muscle, for example, differ greatly

174 | investigations a nd mod el s

from the ones in white muscle. These differences have to do not only with

the identity of the myofibrillar proteins but also with the structure and exten-

sion properties of the myofibrils themselves: The more rapidly the muscles

contract, the more rapid their enzymatic alteration. This observation explains,

at least in part, the well-known relationship between the age of cattle at the

time of slaughter and the tenderness of their meat after aging. The aging time

ranges from 4–5 days for calves to 8–10 days for steers because the muscles of

the older animals are redder than those of the younger ones.

Understanding these mechanisms will allow government researchers and

commercial food technologists to concern themselves with the tenderness

and, more generally, the quality of meat and to incorporate these properties

in the criteria they apply, which today are geared mainly to shortening the

time needed for animals to reach maturity. One of the chief objections to this

practice is that the very white meat of animals subjected to artificially acceler-

ated growth is also less flavorful and less juicy than the meat of animals from

the same breed that have been raised by traditional methods. What is needed

above all is patience.

Tenderizing Meats
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50

Al Dente

The right way to cook pasta.

a n y on e w h o p u t s s p a g h e t t i i n h o t w a t e r for ten minutes or so

and expects a good result is bound to be disappointed. Simple though it is, the

cooking of pasta raises a number of questions. The first has to do with salt:

Must it be added to the cooking water and, if so, why? Is it really necessary to

add oil to the cooking water? How can pasta be prevented from sticking?

At home one can quickly make good pasta from scratch by mixing flour

(usually made from wheat, but corn or chestnut flour may also be used), a bit

of salt, water, oil, and eggs. Long kneading gives body to the pasta, which is

then rolled and cut up before being cooked for three to six minutes. During

cooking the starch granules absorb water and expand, and the proteins in the

egg and flour form an insoluble network that binds the starch granules tightly

together, limiting the extent to which they are washed into the cooking water.

Cooks can prevent homemade pasta from sticking by increasing the propor-

tion of egg. If the protein network is formed before the starch swells up, the

pasta remains firm during cooking and doesn’t stick; if the starch swells up

before the protein network forms and the pasta is cooked, part of the starch

(chiefly one of two types of molecule called amylose) has time to diffuse in the

cooking water, so that the surface of the pasta is coated with the other type of

molecule (amylopectin) and its strands stick together. After straining, a chunk

of butter or a bit of olive oil will keep the hot pasta from sticking on the plate.

176 |

To improve commercial manufacturing techniques, Pierre Feillet, Joël

Abecassis, Jean-Claude Autran, and their colleagues at the Institut National

de la Recherche Agronomique (inra) Laboratoire de Technologie des Céré-

ales in Montpellier sought to determine which proteins give pasta its distinc-

tive culinary qualities.

Hard-Grain Wheat Gluten

Commercial producers make pasta from hard-grain wheat. In the absence

of egg the protein network is formed by proteins in the wheat and, more

precisely, in its gluten. If one takes the mass obtained after kneading flour

and water for a long time and then rinses it under a stream of running water,

the elastic matter that remains is composed of gluten proteins. Because this

substance is more abundant in hard wheats than soft ones, laboratories such

as the one in Montpellier are interested in the composition and genetic vari-

ability of hard-wheat proteins and in methods of making of pasta that favor

the formation of a protein network.

The quality of a good commercial pasta is judged by its yellow-amber

color and its culinary properties, which is to say the likelihood that it will

not stick after cooking (or even after being slightly overcooked). Plant ge-

neticists therefore have looked to develop hard wheats with firm and elastic

gluten. The inra biochemists showed that this latter characteristic is as-

sociated with the presence of a particular protein, gamma-45 gliadin, com-

mon to varieties of hard wheat that are rich in glutenins of low molecular

mass.

The Montpellier team also investigated the optimal conditions for making

pasta and showed that drying it at a high temperature (about 90°c [194°f]) as-

sists the formation of a network of proteins that is more rapidly insolubilized

during cooking. This heat must be applied at the end of the drying process

in order not to damage the starch granules. Kneading the dough and pulling

it through an extrusion press with the aid of an Archimedean screw must

also be done in such a way that these granules are preserved. The application

of high temperatures acts on the color because it inactivates both lipoxygen-

ases (enzymes that destroy yellow pigments) and peroxidases (enzymes that

darken organic material).

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Oil, Water, and Acidity

How, then, should pasta be cooked? The first thing to keep in mind is that

the proportion of proteins must be high. If hard wheat is not used then one

must add eggs to develop the gluten network or else patiently work the dough

and carefully roll it out, using enough water to hydrate the proteins so that

they are able to bind together. Whatever its composition, pasta must be put

into boiling water so that cooking time is reduced and loss of starch content

minimized.

Is there any reason to add oil to the cooking water? Batches of spaghetti

that have been overcooked, either with or without the addition of oil, show no

differences with regard to stickiness as long as the pasta does not pass through

the surface layer of oil at the end. Oil is useful mainly because it coats the pasta