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Sci Tech
This can't be yogurt!
Mr. SANJIT BAGCHI REPORTS in the July 29 issue of The Telegraph, Kolkata on a recent scientific finding involving yoghurt. Apparently some Swedish scientists have found that a modified form of curd or yoghurt is good to protect your teeth against caries, the affliction that you get eating too much chocolate and other sweetmeats. I found it interesting for two reasons. Firstly, making sweet curds (mishti doi) is a Bengali specialty.
Secondly, south Indians like me grew up with the admonition at home that curd and buttermilk are excellent for health while chocolates are bad for teeth. Indeed, each region in India is branded, often dismissively, with one food item dhokla with the Gujaratis, gongura with Andhras, sarson ka saag with Punjabis, and curd rice and thayir vadai with the Tamilians. Well, while the rice part and the vadai part combinations with curd may be Tamilian inventions, curd itself is universal. Note for example the mishti doi of the Bengalis and the lassi of Punjabis; and dhokla downed with buttermilk (chaas) is saaroo che.
One cannot sing the praise of curd enough. Indeed very early Vedic poems talk of it, and praise curd as the "food of the Gods". Dr. K. T. Achaya points out that a blended curd-rice dish is mentioned in the Rigveda as karambha (a name still in use in Gujarat). Kautilya's Arthasastra refers to the profession of curd sellers as mathitika. Tamil literature poetically compares the pat of starter curd used to "a white mushroom". Fermenting milk was known in the Middle East as long as 2000 BC. Yoghurt itself is thought to have originated among the nomadic tribes of Eastern Europe and Western Asia. The word yoghurt (or yogurt, both spellings are ok) is Turkish in origin, and used interchangeably with curd, while the ancient Assyrian word for yogurt, lebeny, meant `life'.
A legend associated with the 12th century Mongol Chief Genghis Khan (or his messenger) has it that while journeying across the desert, he stopped at a newly conquered village. The villager filled his leather satchel (or a container made of hollowed gourd) with milk, sure that it will spoil under the heat of the sun, leaving the horseman to die in the desert. Instead, the constant agitation of the ride and the warm temperature gave birth to a delicious white, custardy substance, which the man drank and enjoyed. Much fortified, he continued his arduous journey!
Another is the study by Elie Metchenikoff (who won the Nobel in 1908 for his early work on immunology), who concluded that the Bulgarians, Azerbaijanis and tribes from the Caucasus mountains owe their extraordinary longevity (many centurions even today) and good health to their habit of making and eating curds, and a related fermented drink called kefir. Metchnikoff showed rightly, that curd is formed from milk upon the action of microorganisms; he isolated the primary yoghurt culturing microbe as Lactobacillus bulgaricus (after the Bulgarians).
Indeed it is the lactobacillus microbes that do the major job. The actual subspecies vary from region to region, but all of them act on the lactose sugar present in milk and convert it into the sweetly mild acid called lactic acid. The longer you ferment, the more lactic acid - a taste not acceptable to the finicky Tamilian. (if there is no other go, he adds salt and water and drinks it up as buttermilk). The other major species of microbe present in milk is streptococcus lactis. These microbes first break down the milk sugar lactose, using one enzyme, into glucose and galactose, and then through a series of enzyme steps, break down these sugars into lactose acid.
Mitochondria, present not inside these microbes but in our cells as symbiotic partners, crack the lactic acid, and its relatives, further into carbon dioxide and release energy in a storable form in the cell. But all this conversion by the mitochondria need oxygen gas, which we breathe in. When we exert too much with vigorous activity we gasp for breath. The drop in the oxygen level in the blood and muscles leads to the accumulation of unburnt lactic acid, which makes its presence felt as pain. Stop a while and gather breath- the lactic acid is oxidised, the pain is gone and energy regained.
One of the first steps in the digestion of milk is to break down the lactose sugar present. This is done by the enzyme lactase. Lactobacillus abounds in this, but we humans too produce this enzyme in the villi or bristly projections of the intestine. But in many ethnic groups, notably among some people in Punjab, the gene that produces this enzyme in the body is defective. As a result, these people cannot digest milk well and suffer upset stomach when they take milk. Termed lactose intolerance, this condition is easily taken care of by substituting milk with curd. The lactobacilli there pitch in and break down the lactose. Now we know why lassi is just as popular as, if not more than, milk in Punjab.
Lactobacillus does more than just ferment milk for us. It produces important vitamins, including B1, B{-2}, B{-3}, B{-5}, B{-6}, B12, A and K all of which are essential for us. It helps fight infection by secreting antibacterial and antifungal substances. It also helps with protection and restoration of useful bacteria that live in our body as symbiotic partners. Lactobacillus is thus a friendly bug, unlike helicobacter pylori, the nasty that causes ulcers, migraines and so forth. There is in fact a report that eating yoghurt during a full course of antibiotic treatment would provide added benefit. (I cannot but recall how this friendly bug came to the rescue of my daughter Katyayani, when she was a newborn baby, hardly a week old. Her mother had inadvertently passed on to her through the placental route, the nasty pathogen E.histolytica. A couple of days after birth, Katya went through a dangerous period of diarrhoea and weakness. The very able and alert pediatrician, Dr. Chikarmane of Baroda, diagnosed it right and purged her of the pathogen using antibiotics. Right then and there, he also administered to her a vial of lactobacillus, to help her digest milk, build body defence and health. She is a healthy, beautiful damsel now, thanks to Dr. Chikarmane, and thanks to lactobacillus.)
Now to Sanjit Bagchi and his report on how a special yogurt formulation fights tooth cavities caused by sugar staying in the mouth. Dental cavity, or caries, is caused by a bacterium called streptococcus mutans. This cousin of S. lactis in milk feeds on sugar left in the mouth after we eat sweets (and not clean our mouth and teeth) and breaks it down to, you guessed it, lactic acid. If left long on the teeth enamel, this acid caused erosion of the enamel causing cavities. Of course, the wisest thing to do is to brush your teeth and rinse your mouth well after every meal, or at least twice a day.
In the instance, Bagchi reports on a recent paper by Dr. L. Hammarstrom and colleagues at the Centre for Oral Biology of the Karolinska Institute in Sweden, that appeared in the July 2002 issue of Nature Biotechnology. They noted that the caries-causing S. mutans makes an adhesive molecule (call it SAI/II), which enables it to stick on to the tooth enamel in order to feed on the sugar coating the tooth surface. They decided to generate an antibody to SAI/II that bind stick to this adhesive and strip it off the tooth. To this end, they obtained the gene that makes the business part of the antibody and inserted it into lactobacillus. As the microbe grew it also produced the antibody against SAI/II. This transgenic lactobacillus was then administered into experimental rats that were afflicted with caries. The S. mutans counts as well as the severity of the caries reduced markedly. What the Swedish group has done is, in effect, deliver passive immunity on the spot against caries causing pathogens.
The idea is applicable to other situations. Lactobacilli are "generally regarded as safe" (or GRAS) microbes, we can use them as vehicles to immunise people against H. pylori (the ulcer-causing bug), rotavirus (causing severe diarrhoea in children) and so on. When such engineered lactobacilli are added to yoghurt, the dish will be doubly beneficial. Until now, we have had low-calorie or fat-free yoghurts. We have fruit- flavoured frozen yoghurts that are like ice creams, and a company sells these with the slogan "This can't be yoghurt!" Now we can also expect vaccine-fortified flavours!
D. Balasubramanian
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