Meat-like texture

Thermoplastic extrusion technology has been used to texturize many defatted vegetable protein ingredients, and produce many fibrous structures and meat-like textures. Such processes have been used extensively to prepare meat analogs (1, which have found their widest application in formulation of foods for institutional markets (3). A primary disclosure of extrusion texturization of vegetable proteins was made by Atkinson ( ). General descriptions of various extrusion processes have also been reported (1, 5-14). ... 

Meat-like texture relied upon the presence of a few limited bubbles within the structure providing failure sites for breakage during chewing. Not surprisingly, these products tended to have a pasty texture rather than exhibiting meat-like fibrosity. 

As well as rmderstanding meat itself, in the recent past the ability to copy or synthesise meatlike structure has had an economic benefit, because of the high cost of meat as a protein source. Most recently, pressure from animal welfare concerns, vegetarianism, and the need to reduce saturated fat intake has led to a prohferation of products which provide some kind of meat-like textures by processing. What are the structural elements, and how should they be assembled Much of the story can be pieced together from the published literature. 

Tempeh is widely believed to have originated in Indonesia many centuries ago. Although relatively unknown in the surrounding countries, such as Thailand, China, and Japan, where soybeans form an important part of the diet, tempeh continues to be one of the most popular fermented foods in Indonesia. Because of its meat-like texture and mushroom flavor, tempeh is well suited to Western tastes. It is becoming a popular food for a number of vegetarians in the United States and other parts of the world (Nout Kiers, 2005). 

Canned-type animal foods, on the other hand, are generally received very favorably by animals, apparently due in part to their meat-like texture, consistency and aroma. However, the elevated moisture content of such products necessitates thermal processing in sealed containers to obtain a conmercially sterile product, thereby adding considerably to product cost. Furthermore, once such a can is opened, it must be quickly consumed since the product is quite conducive to supporting microbial growth and hence will deteriorate very rapidly unless stored... 

Tofu has long been a source of protein in the Orient. It has much the same importance to the people of the Orient that meats, eggs and cheese have for the people in Western Countries. Tofu is usually sold in the form of a wet cake with a creamy-white color, smooth custard-like texture and a bland taste. It is highly hydrated and, depending on the water content, tofu products with different characteristics can be produced. The typical oriental type of tofu has a water content about 85%. Japanese prefer tofu having a smooth, fragile texture that contains about 88% water. The Chinese, on the other hand, produce many types of firm products with a chewy meatlike texture and a water content as low as 50-60%. Western consumers like tofu with a firm texture therefore, tofu found in the U.S. supermarkets contains 75-80% water. 

Tofu can be kept frozen or freeze-dried to prevent microbial deterioration. However intemolecular interactions occur during frozen storage. As a result, the texture of tofu is changed from soft, smooth to sponge-like with a meat-like chewiness. 

Textured Soy Proteins. Textured vegetable proteins, primarily textured flours and concentrates (50% protein and 70% protein, dry basis, respectfully) are widely used in the processed meat industry to provide meat-like structure and reduce ingredient costs (3-6, 9-10). Available in a variety of sizes, shapes, colored or uncolored, flavored or unflavored, fortified or unfortified, textured soy proteins can resemble any basic meat ingredient. Beef, pork, seafood and poultry applications are possible 03, 4-7, 15, 19) Proper protein selection and hydration is critical to achieving superior finished product quality. Textured proteins have virtually no solubility and, thus, no ability to penetrate into whole muscle tissue Therefore, textured soy proteins are inherently restricted to coarse ground (e.g. sausage) or fine emulsion (e.g. weiners and bologna) products, and comminuted and reformed (i.e. restructured) meat products. None are used in whole muscle absorption or injection applications (2-4, 6, 11). 

The female emu begins to breed between 18 months and 3 years of age, and may continue to produce eggs for more than 15 years. The emu grows to full size within 2 years, when it is 1.5-1.8m and weighs up to 65-70kg. Emu products include leather, meat and decorative eggshells. Emu oil is sold for cosmetic and pharmaceutical purposes. Emu meat, like ostrich meat, is similar in texture and colour to beef. 

Texturization. In a recent review, Kinsella (100) described texturized food proteins as those in protein-rich products whose structure, shape, texture, flavor, and appearance are modified to resemble those of conventional food products. Most attention has been given recently to producing meat-like materials from plant proteins, and meat extenders and fillers are now common and accepted by many consumers. In fact, the idea of such foods is not a new one. John Harvey Kellogg, whose name appears on a number of familiar products, attempted to produce palatable meat-free foods as long ago as 1880. 

In most processes, some expansion by puffing of the flow stream by water vapour pressure is required to achieve low-density expanded products. Bubble expansion has been comprehensively reviewed recently by Kokini and Moraru (2003). The extent and nature of expansion of the structures so formed are critical to their subsequent use and in-mouth texture. Highly expanded stmetures (0.1 g/ml), when eaten dry, give crisp textures, which melt in the mouth as plasticisation by saliva causes their cell walls to collapse. Hardness increases as bulk density increases, but many of the denser products are designed to be eaten in a rehydrated state as meat-like analogue products. Not surprisingly, the rate of stmeture collapse on hydration also increases as bulk density decreases, since these materials are both hydrophilic and porous. 

A frozen SPI filament product, with fiber-like texture, was sold in the United States for improving textural characteristics of fabricated foods, including structuring mechanically deboned meat and poultry. The manufacturer s specifications for the product include >93% protein (N x 6.25, mfb), <0.2% crude fiber, 65% moisture, 0.9% ash, and <0.1% fat. 

The meat-like appearance in spun protein isolates results from strands of parallel fibers, but in extruded SFs, SPCs, and SPI, the meat-like structure is created from multi-laminate palisade layers. Extruder-texturized proteins are readily acceptable to... 

Rossello et al. (1995) have described the production process of Sobrasada, which is typically produced in the Balearic Island off the coast of Spain. It usually contains approximately 50% fresh raw lean pork, 40% fresh pork fat, 5% paprika, 2% salt, and 5% white pepper. The lean and fat are finely ground and kneaded together until the mixture has a paste-like texture, after which the paprika, salt, and white pepper are mixed with the meat and stuffed into natural casings. The mbcture is held at about 4°C for 24 hr and ripened at ambient winter temperature of about 8-15%°C and a relative humidity of 60-85% for about 4 months. 

Traditionally, extrusion texturization of soy protein has been used to create meat analogues. Addition of sodium hydroxide during extrusion does not aid in texturization, with worse product quality at high pH (Dahl and Villota, 1991). Precipitation within the extruder at the soy isoelectric point may be necessary for adequate texturization. Huang and colleagues (1995) at Iowa Sate University devised a process in which soy protein isolate could be extruded into textile fibers. Brittleness was offset by addition of glycerol during extrusion and by various chemical treatments post-extrusion. A similar process could be developed to produce superior meat-like fibers. 

There has also been a great amount of discussion relative to providing iron-fortified milk formulas for infants. However, these formulas may be too expensive for low-income families. Also, pediatricians and nutritionists usually advise parents to start feeding meats, cereals, and other iron containing foods to infants by the time they are 3 months of age (when the iron stores from birth may be depleted). Like the iron used to enrich flour and bread, the iron used to fortify cereals htis a low bioavailability. Meats provide the most available form of iron, but their cost sometimes limits their use. Perhaps some of the newly engineered foods, like textured vegetable protein, will provide suitable vehicles for iron fortification. 

Vaisey et al. ( ) evaluated the performance of fababean and field pea concentrates as ground beef extenders. Sensory attributes of broiled meat patties containing the protein concentrates were more acceptable to taste panelists when these products were added as texturized flakes than as flour. The extended products had significantly less drip loss than all-meat controls but had softer textures. Texturizing the concentrates by drum-drying and flaking reduced their fat retention properties but produced patties more like the all-beef control. 

Recently, processes using extreme pressures (e.g., 400 MPa) have been applied to meat in all its product forms (Hayashi and Bahiy 1996). Just as in heat processing, vegetative cells of microorganisms are destroyed, so the process is equivalent to pasteurisation. However, the sensitivity of muscle proteins to pressure denaturation is different from in heat treatment so, while the same safety status is achieved, a product whose appearance, colour and texture is more like that of an uncooked meat is obtained. 

Such traditional soybean foods as tofu (soybean curd) and tempeh have little flatus activity (42). In the case of tofu, oligosaccharides are presumably eliminated during the course of its preparation, and, in the case of tempeh, enzymes produced by the mold (Rhizopus) during fermentation probably hydrolyze the oligosaccharides. As might be expected because of their low carbohydrate content (< 1%), soy protein isolates are devoid of flatus activity (43). It follows that textured meat analogs made from isolated soy protein are most likely free of flatus activity. 

Tempeh, or tempe in some literature, is made by fermenting dehulled and cooked soybeans with mold, Rhizopus sp. Freshly prepared tempeh is a cake-like product, covered and penetrated completely with white mycelium, and has a clean, yeasty odor. When sliced and deep-fat fried, it has a nutty flavor, pleasant aroma, and crunchy texture, serving as a main dish or meat substitute. In recent years, tempeh has been found to provide some health benefits, including antimicrobial and antioxidant effects and protection against diarrhea (Hachmeister Fung, 1993 Nout Kiers, 2005). 

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