Read Online Catching Fire: How Cooking Made Us Human by Richard Wrangham - Free Book Online Page B
Authors: Richard Wrangham
Tags: General, science, Social Science, History, Evolution, Cooking, Political Science, Anthropology, Cultural, Technology & Engineering, Life Sciences, Popular Culture, Public Policy, Agriculture & Food, Cultural Policy, Fire Science
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ileostomy patients, digestibility of raw eggs was measured at a meager 51 percent. It was a little higher, 65 percent, in the healthy volunteers whose protein digestion was estimated by the appearance of stable isotopes in the breath. The results showed that 35 percent to 49 percent of the ingested protein was leaving the small intestine undigested. Cooking increased the protein value of eggs by around 40 percent.
The Belgian scientists considered the reason for this dramatic effect on nutritional value and concluded that the major factor was denaturation of the food proteins, induced by heat. Denaturation occurs when the internal bonds of a protein weaken, causing the molecule to open up. As a result, the protein molecule loses its original three-dimensional structure and therefore its natural biological function. The gastroenterologists noted that heat predictably denatures proteins, and that denatured proteins are more digestible because their open structure exposes them to the action of digestive enzymes.
Even before the Belgian egg study, there were indications that cooking can be responsible for enough denaturation to strongly influence digestibility. In 1987 researchers chose to study a beef protein, bovine serum albumin (BSA), selected because it is a typical food protein. In cooked samples, digestion by the enzyme trypsin increased four times compared to that of uncooked samples. The researchers concluded that the simple process of denaturation by heat (causing the protein molecule to unfold and lose its solubility in water) explained its greatly increased susceptibility to digestion.
Heat is only one of several factors that promote denaturation. Three others are acidity, sodium chloride, and drying, all of which humans use in different ways.
Acid is vital in the ordinary process of digestion. Our empty stomachs are highly acidic thanks to the secretions of a billion acid-producing cells that line the stomach wall and secrete one to two liters of hydrochloric acid a day. Food entering the stomach buffers the acidity and causes a more neutral pH, but the stomach cells respond rapidly and secrete enough acid to return the stomach to its original intense low pH, less than 2. This intense acidity has at least three functions: it kills bacteria that enter with the food, activates the digestive enzyme pepsin, and denatures proteins. Denaturation looks particularly important.
Marinades, pickles, and lemon juice are acidic, so if applied for sufficient time they can contribute to the denaturing of proteins in meat, poultry, and fish. It is no surprise that we like seviche, raw fish marinated in a citrus juice mixture, traditionally for a few hours. Hunter-gatherers have likewise been reported mixing acidic fruits with stored meats. The Tlingit of Alaska stuffed goat meat with blueberries and stored salmon spawn mashed with cooked huckleberries. Many other North American groups made pemmican by mixing dried and pounded meat with various kinds of berries, and Australian aborigines mixed wild plums with the pounded bones and meat of kangaroo. While pleasing flavors and improved storage might be enough to account for such mixtures, increased digestibility could also contribute to explaining the broad use of these acidic preparations. Animal protein that has been salted and dried, such as fish, is likewise denatured and thereby made more digestible. Increased digestibility from denaturation also helps account for our enjoyment of dried meats such as jerky or salted fish.
Although gelatinization and denaturation are largely chemical effects, cooking also has physical effects on the energy food provides. Research on the topic began with a misfortune almost two hundred years ago. On June 6, 1822, twenty-eight-year-old Alexis St. Martin was accidentally shot from a distance of about a meter (three feet) inside a store of the American Fur Company at Fort Mackinac, Michigan. William Beaumont, a young, war-hardened surgeon,
The Belgian scientists considered the reason for this dramatic effect on nutritional value and concluded that the major factor was denaturation of the food proteins, induced by heat. Denaturation occurs when the internal bonds of a protein weaken, causing the molecule to open up. As a result, the protein molecule loses its original three-dimensional structure and therefore its natural biological function. The gastroenterologists noted that heat predictably denatures proteins, and that denatured proteins are more digestible because their open structure exposes them to the action of digestive enzymes.
Even before the Belgian egg study, there were indications that cooking can be responsible for enough denaturation to strongly influence digestibility. In 1987 researchers chose to study a beef protein, bovine serum albumin (BSA), selected because it is a typical food protein. In cooked samples, digestion by the enzyme trypsin increased four times compared to that of uncooked samples. The researchers concluded that the simple process of denaturation by heat (causing the protein molecule to unfold and lose its solubility in water) explained its greatly increased susceptibility to digestion.
Heat is only one of several factors that promote denaturation. Three others are acidity, sodium chloride, and drying, all of which humans use in different ways.
Acid is vital in the ordinary process of digestion. Our empty stomachs are highly acidic thanks to the secretions of a billion acid-producing cells that line the stomach wall and secrete one to two liters of hydrochloric acid a day. Food entering the stomach buffers the acidity and causes a more neutral pH, but the stomach cells respond rapidly and secrete enough acid to return the stomach to its original intense low pH, less than 2. This intense acidity has at least three functions: it kills bacteria that enter with the food, activates the digestive enzyme pepsin, and denatures proteins. Denaturation looks particularly important.
Marinades, pickles, and lemon juice are acidic, so if applied for sufficient time they can contribute to the denaturing of proteins in meat, poultry, and fish. It is no surprise that we like seviche, raw fish marinated in a citrus juice mixture, traditionally for a few hours. Hunter-gatherers have likewise been reported mixing acidic fruits with stored meats. The Tlingit of Alaska stuffed goat meat with blueberries and stored salmon spawn mashed with cooked huckleberries. Many other North American groups made pemmican by mixing dried and pounded meat with various kinds of berries, and Australian aborigines mixed wild plums with the pounded bones and meat of kangaroo. While pleasing flavors and improved storage might be enough to account for such mixtures, increased digestibility could also contribute to explaining the broad use of these acidic preparations. Animal protein that has been salted and dried, such as fish, is likewise denatured and thereby made more digestible. Increased digestibility from denaturation also helps account for our enjoyment of dried meats such as jerky or salted fish.
Although gelatinization and denaturation are largely chemical effects, cooking also has physical effects on the energy food provides. Research on the topic began with a misfortune almost two hundred years ago. On June 6, 1822, twenty-eight-year-old Alexis St. Martin was accidentally shot from a distance of about a meter (three feet) inside a store of the American Fur Company at Fort Mackinac, Michigan. William Beaumont, a young, war-hardened surgeon,
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