Answering a few chemistry questions based on provided data on page one. Also, there is an article need to be read in order to respond to the last three questions
YOGURT by Gwendolyn D. Evans* For many of us, yogurt is an unusual -tasting food, but its history is even more unusual: ♦ Many centuries ago the Mongols of Asia were reported to eat a strange food that had medicinal properties, and it was said that they enhanced its flavor by mixing the sour -tasting food with the blood of horses. ♦ When the secret recipe of this food, which was believed to extend from Constantinople to France, King Francis I bought the formula for a large sum. ♦ In 1931 a Spanish businessman, Isaac Carasso, produced the food and sold it in pharmacies throughout Europe. With the advent of World War II, Carass o’s son, Daniel, brought the formula to the United States. The food — then named Danone, after Daniel — was slow to catch on because people thought the sourness meant it had spoiled. When fruit was added to balance the sourness, sales of the product — rena med Dannon Yogurt — improved. ♦ In the 1970’s, yogurt became known as a health food. Some people concluded that it must be good for you if health -conscious people were willing to eat something so sour. ♦ In 1985, television advertisements for Dannon Yogurt showed happy Asians eating lots of yogurt. They looked healthy and very old. The ads reinforced the notion that yogurt promotes longevity. Long life: Scientific -sounding claims that yogurt is good for you can be traced to the turn -of-the -century theories o f Elie Metchnikoff, a respected Russian biologist who won the Nobel Prize for medicine in 1908. Metchnikoff believed that our life span is limited by bacteria. In his book The Prolongation of Life, he stated that the intestinal tract harbored great numbers of bacteria that produced toxins that slowly poisoned the body and caused premature death. He called this process “autointoxication by putrefactive bacteria” and believed that surgical removal of the colon where the bacteria lived would extend human life. However, because colon surgery carried considerable risk, he recommended another treatment that he believed would rid the human intestine of harmful bacteria. Metchnikoff had studied the culinary practices of French, Russian, and Bulgarian peasants and no ted that the Bulgarians, who consumed about three quarts of yogurt a day, had remarkable longevity. He concluded that the lactobacilli bacteria, which are present in yogurt, establish colonies in the intestine and displace the harmful bacteria. Although it was unproved, Metchnikoff wrote books that popularized his theory. He also ate lots of yogurt and announced that he expected to live to the age of 150. Later, tests showed that the Lactobacillus bulgaricus bacteria do not colonize in the human intestine, leaving Metchnikoff with no scientific basis for his beliefs. When we are born, our intestines are relatively sterile and free of bacteria. As daily food is consumed, the intestines quickly adopt colonies of bacteria. Adult intestines contain a vast range of flora, lactobacilli, streptococci, staphylococci, coliform bacteria, and yeast. In this competitive environment, the yogurt bacteria are unable to establish colonies. To be fair to Metchnikoff, the idea that intestinal bacteria can be harmful may have some merit. Today, medical experts say that there is a correlation between bowel cancer and the high dietary intake of animal fat and protein. It is possible that the putrefactive bacteria (those that consume protein) may somehow produce carcinogenic compou nds from cholesterol and bile salts. But even if this is so, eating lots of yogurt is not likely to be much of a remedy, because the bacteria in yogurt don’t colonize in our digestive tract, and yogurt contains animal fat and protein.Where does this leave the health claims of yogurt? Is it good for you even if it doesn’t make you live longer? Is it a good diet food? Let’s look at how yogurt is made. Making it all gel: Yogurt is fermented milk, a product that can easily be made at home. From the cook’s point of view, two major changes take place when milk is converted to yogurt: It turns from sweet to sour and from liquid to a semisolid gel.
These ch anges are caused by the bacteria Lactobacillus bulgaricus and Streptococcus thermophilus . Cows’ milk contains about 4.8% lactose and the bacteria consume much of this sugar, producing the sour -tasting lactic acid, CH3CH (OH)COOH. It is this acid that cause s protein in the milk to coagulate. Milk contains many types of protein, and the type known as casein is involved in making yogurt. Casein molecules are normally packed into microscopic bundles called micelles. At milk’s normal pH of 6.5, the micelles are dispersed throughout the liquid. As the lactic acid builds up, the pH gradually drops to 4.5, and the acid alters the casein molecules so that the micelles link together in chains and clusters.
The linked micelles form a semisolid network known as a gel. T he other ingredients of the milk, such as vitamins, enzymes, unfermented lactose, fat, and water, remain in the spaces of the gel -like protein network. During the conversion of milk to yogurt the amount of lactose is reduced, but the food value of the other components in milk is largely unchanged. Eat yourself skinny: Many dieters have turned to yogurt in response to television advertisements showing stylish and skinny people eating yogurt instead of hamburgers. Some low -fat yogurt is advertised as having on ly 1% fat. Although true, the implication that it is diet food may be misleading. Some popular brands are low in fat, but added sugar, fruit, and flavorings raise the caloric count. Yogurt has the calories of the milk it was made from, plus the calories of the milk solids that are often added to give it firmer “body”, plus the calories of any added sugar and fruit. An 8 -ounce cup of fruit -flavored yogurt averages about 250 calories — the same as a small salad and an apple. Yogurt is nutritious because it is high in protein, riboflavin, and calcium, but compared to other diet foods it is not especially low in calories. If you are on a diet, be sure to check the calories listed on the label. Lactose intolerance: The sugar present in milk — lactose — is the all -important source of energy for nursing calves and babies. Lactose is a disaccharide; a sugar of two rings that cannot be absorbed into the bloodstream until it has been broken into two smaller sugars by the enzyme lactase. The amount of lactase in your bo dy is not constant. It reaches its maximum level in the human intestine shortly after birth, then declines between the ages of 1.5 and 3.5, when babies no longer need to drink milk. For most people, lactase production ceases by age three. However, due to genetic differences, most people of European ancestry (or any location where people drink the milk of cows, goats, yaks, etc.) continue producing lactase at a lower level for the rest of their lives. This means that, as adults, they can drink moderate amoun ts of milk and easily digest the milk sugar. However, some adults can’t drink milk products without discomfort. In the absence of lactase, the sugar passes through the small intestine without being absorbed and reaches the colon intact. There it nourishes b acteria that produce carbon dioxide and water. The gas and excess water cause severe abdominal cramps and bloating; the lactose and lactic acid increase osmosis within the colon, leading to water retention and diarrhea. This condition called lactose intole rance, causes real abdominal distress. Lactose intolerance was not recognized by western medical science until the 1960s.
This relatively late recognition of a common problem probably occurred because in the United States only about 10% of Caucasians of Eu ropean descent have lactose intolerance, compared to 70% of African Americans . Most lactose -intolerant adults can consume only about a pint of milk per day without intestinal distress, but they can consume larger amounts of yogurt. This is because yogurt co ntains 25 -50% less lactose than milk. Shortfall: Should you eat yogurt? Sure...if you like it. Will it help you lose weight?
Perhaps, if you read the label and buy only the varieties that have fewer calories than the food you’ve been eating. Is it good for you? You bet — just like milk and fruit. Will it make you live longer? That brings us back to Elie Metchnikoff. Metchnikoff, you recall, was the Russian biologist who popularized the notion that the lactobacilli in yogurt promote lon gevity and announced that he would live to be 150 years old. He continued to eat yogurt and write books until he died of old age at 71 — just 79 years short of his goal. *Reprinted with permission from Chem Matters. Copyright 1989 American Chemical Society.
