On Food And Cooking Part 9

3.5 3.5.

Ovomucin

1.5 1.5.

Avidin

0.06 0.06.

Others

10 10.

Protein

Natural Functions Natural Functions

Ovalb.u.min

Nourishment; blocks digestive enzymes? Nourishment; blocks digestive enzymes?

Ovotransferrin

Binds iron Binds iron

Ovomucoid

Blocks digestive enzymes Blocks digestive enzymes

Globulins

Plug defects in membranes, sh.e.l.l? Plug defects in membranes, sh.e.l.l?

Lysozyme

Enzyme that digests bacterial cell walls Enzyme that digests bacterial cell walls

Ovomucin

Thickens alb.u.men; inhibits viruses Thickens alb.u.men; inhibits viruses

Avidin

Binds vitamin (biotin) Binds vitamin (biotin)

Others

Bind vitamins (2+); block digestive enzymes (3+)... Bind vitamins (2+); block digestive enzymes (3+)...

Protein

Culinary Properties Culinary Properties

Ovalb.u.min

Sets when heated to 180F/80C Sets when heated to 180F/80C

Ovotransferrin

Sets when heated to 140F/60C or foamed Sets when heated to 140F/60C or foamed

Ovomucoid

Globulins

Sets when heated to 170F/75C; stabilizes foam Sets when heated to 170F/75C; stabilizes foam

Lysozyme

Enzyme that digests bacterial cell walls Enzyme that digests bacterial cell walls

Ovomucin

Stabilizes foam Stabilizes foam

Avidin

Others

A few of the dozen or so egg-white proteins are especially important for the cook and worth knowing by name.

Ovomucin accounts for less than 2% of the total alb.u.men protein, but has by far the greatest influence on the fresh egg's commercial and culinary value. It makes fried and poached eggs compact and attractive by making the thick white thick - 40 times more so than the thin white. Ovomucin somehow pulls together the otherwise soupy protein solution into an organized structure; gently tear a piece of hard-cooked white and you can see its laminations along the edge of the tear. This structure is thought to help cus.h.i.+on the yolk and slow the penetration of microbes through the white. It gradually disintegrates with age in the raw egg, which may make the white more digestible for the developing chick, and certainly makes the egg less useful for the cook. accounts for less than 2% of the total alb.u.men protein, but has by far the greatest influence on the fresh egg's commercial and culinary value. It makes fried and poached eggs compact and attractive by making the thick white thick - 40 times more so than the thin white. Ovomucin somehow pulls together the otherwise soupy protein solution into an organized structure; gently tear a piece of hard-cooked white and you can see its laminations along the edge of the tear. This structure is thought to help cus.h.i.+on the yolk and slow the penetration of microbes through the white. It gradually disintegrates with age in the raw egg, which may make the white more digestible for the developing chick, and certainly makes the egg less useful for the cook.

Ovalb.u.min, the most plentiful egg protein, was the first protein ever crystallized in the laboratory (in 1890), yet its natural function remains unclear. It seems related to a family of proteins that inhibit protein-digesting enzymes, and may be a mainly nutritional relic of ancient battles against a now-extinct microbe. It is the only egg protein to have reactive sulfur groups, which make decisive contributions to the flavor, texture, and color of cooked eggs. Interestingly for the cook, ovalb.u.min's heat resistance increases for several days after laying, so that very fresh eggs need less cooking for a given consistency than eggs a few days old.

Ovotransferrin holds tightly onto iron atoms to prevent bacteria from using them, and to transport iron in the developing chick's body. It is the first protein to coagulate when an egg is heated, and so determines the temperature at which eggs set. The setting temperature is higher for whole eggs than for egg white, because ovotransferrin becomes more stable and resistant to coagulation when it binds the abundant iron in the yolk. The color of ovotransferrin changes when it latches onto metals, which is why egg whites whipped in a copper bowl turn golden; you can also make a pink meringue by dosing the whites with a pinch of ground-up iron supplement. holds tightly onto iron atoms to prevent bacteria from using them, and to transport iron in the developing chick's body. It is the first protein to coagulate when an egg is heated, and so determines the temperature at which eggs set. The setting temperature is higher for whole eggs than for egg white, because ovotransferrin becomes more stable and resistant to coagulation when it binds the abundant iron in the yolk. The color of ovotransferrin changes when it latches onto metals, which is why egg whites whipped in a copper bowl turn golden; you can also make a pink meringue by dosing the whites with a pinch of ground-up iron supplement.

The Nutritional Value of Eggs An egg contains everything you need to make a chick, all the ingredients and chemical machinery and fuel. That fact is its strength as a food. Cooked - to neutralize the protective antinutritional proteins - the egg is one of the most nutritious foods we have. (Raw, it causes laboratory animals to lose lose weight.) It's unmatched as a balanced source of the amino acids necessary for animal life; it includes a plentiful supply of linoleic acid, a polyunsaturated fatty acid that's essential in the human diet, as well as of several minerals, most vitamins, and two plant pigments, lutein and zeaxanthin, that are especially valuable antioxidants (p. 255). The egg is a rich package. weight.) It's unmatched as a balanced source of the amino acids necessary for animal life; it includes a plentiful supply of linoleic acid, a polyunsaturated fatty acid that's essential in the human diet, as well as of several minerals, most vitamins, and two plant pigments, lutein and zeaxanthin, that are especially valuable antioxidants (p. 255). The egg is a rich package.

Cholesterol in Eggs Too Too rich for our blood, it's been thought: a belief that contributed to the steep drop in U.S. egg consumption beginning around 1950. Among our common foods, the egg is the richest source of cholesterol. One large egg contains around 215 milligrams, while an equivalent portion of meat has about 50. rich for our blood, it's been thought: a belief that contributed to the steep drop in U.S. egg consumption beginning around 1950. Among our common foods, the egg is the richest source of cholesterol. One large egg contains around 215 milligrams, while an equivalent portion of meat has about 50.

Why is there so much cholesterol in the egg? Because it's an essential component of animal cell membranes, of which the chicken embryo must construct many millions before it hatches. There is some variability in the cholesterol contents of different breeds, and the hen's diet has some effect - a feed high in sitosterol, a vegetable relative of cholesterol, brings egg cholesterol down by a third. But these reductions still leave egg yolk way ahead of most other foods.

Since high blood cholesterol does increase the risk of heart disease, many medical a.s.sociations have long recommended limiting our yolk consumption to two or three per week. However, recent studies of moderate eaters have shown that egg consumption has little influence on blood cholesterol. This is partly because blood cholesterol is raised far more powerfully by saturated fats in the diet than by cholesterol itself, and most of the fat in egg yolk is unsaturated. It also appears that other fatty substances in the yolk, the phospholipids, interfere with our absorption of yolk cholesterol. So there no longer seems to be any reason to bother counting our weekly yolks. Of course, eggs shouldn't displace positively heart-protective fruits and vegetables from the diet; and on a strict regimen to deal with serious heart disease or obesity, it may make sense to avoid egg yolks along with similarly fatty animal foods. Better than 60% of the calories in a whole egg come from fat, a third of them from saturated fat.

Egg Subst.i.tutes Largely impelled by the public desire for cholesterol-free eggs, food manufacturers have come up with formulations that imitate whole beaten eggs, and can be cooked into scrambled eggs or omelets or used in baking. These products consist of genuine egg whites mixed with an imitation of the yolk, which is usually made from vegetable oil, milk solids, gums that provide a thick consistency, as well as colorings, flavorings, and vitamin and mineral supplements. Largely impelled by the public desire for cholesterol-free eggs, food manufacturers have come up with formulations that imitate whole beaten eggs, and can be cooked into scrambled eggs or omelets or used in baking. These products consist of genuine egg whites mixed with an imitation of the yolk, which is usually made from vegetable oil, milk solids, gums that provide a thick consistency, as well as colorings, flavorings, and vitamin and mineral supplements.

Fertilized Eggs Despite folklore to the contrary, there is no detectable nutritional difference between unfertilized and fertilized eggs. By the time a fertilized egg is laid, the single germ cell has divided into tens of thousands of cells, but its diameter has only grown from 3.5 millimeters to 4.5, and any biochemical changes are negligible. Refrigerated storage prevents any further growth or development. In the U.S. grading system, any significant development of the egg - from minute blood vessels (which appear after two to three days of incubation) to a recognizable embryo - is considered a major defect, and automatically puts it in the "inedible" category. Of course this is a cultural judgment. In China and the Philippines, for example, duck eggs containing two- to three-week embryos are boiled and eaten, in part for their supposed contribution to virility. Because embryos obtain some nourishment from the sh.e.l.l, these duck embryos do contain more calcium than the eggs that they developed from. Despite folklore to the contrary, there is no detectable nutritional difference between unfertilized and fertilized eggs. By the time a fertilized egg is laid, the single germ cell has divided into tens of thousands of cells, but its diameter has only grown from 3.5 millimeters to 4.5, and any biochemical changes are negligible. Refrigerated storage prevents any further growth or development. In the U.S. grading system, any significant development of the egg - from minute blood vessels (which appear after two to three days of incubation) to a recognizable embryo - is considered a major defect, and automatically puts it in the "inedible" category. Of course this is a cultural judgment. In China and the Philippines, for example, duck eggs containing two- to three-week embryos are boiled and eaten, in part for their supposed contribution to virility. Because embryos obtain some nourishment from the sh.e.l.l, these duck embryos do contain more calcium than the eggs that they developed from.

The Composition of a U.S. Large EggA sh.e.l.led U.S. Large egg weighs 2 ounces, or 55 grams. In the following table, all weights are given in grams (g) or thousandths of a gram (mg). Fat accounts for about 60% of the calories in an egg, saturated fat around 20%.