A textural additive for restructuring meats.
WHY DO THE FRENCH EAT LESS BEEF than they did only ten years ago? In part it is because the quality of the meat does not justify its high price. Tender cuts that can be cooked rapidly (various types of steak, for example) are expensive because they constitute only 20–30% of bovine muscle tissue. What can be done with the other cuts that used to be tenderized by long, slow cooking?
The meat processing industry has proposed a solution in the form of restructured products such as ground beef and meats sliced into thin sheets. Both techniques—cutting fresh meats into very small pieces and cold-hardened meats into very thin slices—destroy the collagen networks that form the majority of the muscles in the anterior half of the animal. Yet once it has been destructured, meat must be put back together: The butcher in your supermarket reshapes ground beef with a press, for example, but there isn’t always much left of the reformed product after cooking.
Cooks know that cooking an egg white produces a gel that can trap dispersed particles; this is the principle of fish loaves, clafloutis (a custard made with cherries or plums), and quiches. Drawing on this principle in order to restore cohesiveness to destructured meats, the processing industry has introduced various textural additives with increased binding power, such as sodium alginate, an extract of algae. However, the use of dairy and vegetable compounds makes it impossible to advertise the product as pure beef.
Many researchers have looked for ways to extract such additives from meat itself, particularly from the scraps that remain on the bones after butchering. Teams led by Joseph Culioli and Ahmed Ouali at the Institut National de la Recherche Agronomique (INRA) stations in the Clermont-Ferrand area have shown that, at least in the laboratory, myosin can be used as an effective binding agent.
Myosin is an abundant protein, accounting for 20% of the dry matter in the striated skeletal muscles that can be processed by mechanical means. Proteins in the muscle mass of the animal fall into three categories: myofibrillary proteins, sarcoplasmic proteins, and connective tissue proteins. Myosin is the principal protein of the myofibrillary system, where it is found in the form of thick fibers. In the presence of calcium ions and adenosine triphosphate (ATP), the fuel of living cells, these fibers combine with more delicate fibers composed mainly of actin, giving rise to muscle contraction when the two sorts of fiber slide past one another.
Myosin Gels
Because the properties of proteins depend on their amino acid sequences, they do not all have the same gelatinizing effect. The thermal gelatinizing properties of myosin, which are also involved in the preparation of cooked hams, pâtés, sausages, and so on, are greater than those of actin. To determine which combination of factors yields the firmest gel, the INRA biologists developed new extraction methods to compare the effect of myosin proteins from two different types of muscle (fast white muscles, which are responsible for brief spurts of intense effort, and slow red muscles, which function in the presence of oxygen) removed from animals at different times after death. Initially myosin was extracted from muscles in rabbits because they are unmixed, being either red or white.
Protein samples were extracted by grinding up the muscles and then placing them in solutions with different concentrations of salt. The thermal gela-tinization of the protein suspensions in these solutions was studied with the aid of a rheometer (an instrument for measuring the flow of fluids), which revealed both the viscous and elastic characteristics of the gels.
A Hot Gel
These measurements showed that thermal gelatinization occurs even at very weak myosin concentrations (0.1–0.5%) and that the firmness of the resulting gels strongly increases with the myosin concentration.
The gelatinization of pure myosin begins at 40°C (104°F), with the rigidity of the gels increasing up to 80°C (176°F).The purer the myosin solution, the greater the rigidity. As with other gels, the rigidity of myosin gels depends on the salt concentration and the acidity of its environment. The myosins that form the firmest gels are found in the fast white muscles, with a pH of about 5.8, and in the presence of salt, which favors the dissociation of macromolecular chains.
Subsequent analysis confirmed the suitability of bovine myosin for the restructuring of meat. The gels are firmer when the myosin is extracted just after slaughter, before the onset of rigor mortis (a consequence of irreversible bonds being established between the actin and myosin). Sodium pyrophosphate, a molecule belonging to the same family as ATP, dissociates the actin–myosin complexes and so makes it possible to obtain firmer gels. The incorporation of these myosin extracts in meats that are then sliced into thin sheets has made it possible to increase their cohesion while limiting the loss of juices, which are trapped in the gel.