Диханбаева Ф.Т, Опабекова Н.С.

Казахстан, Алматинский Технологический Университет, факультет Пищевых Производств

Bio life of yoghurt.

Yogurt is undeniably healthy food - you'll get great benefit by making it part of daily eating habits. Eating yogurt allows you keeping easily within recommended limits. According to Food Standard Agency the fat content in yoghurt may vary from 0.5 to 5% and the total solids from 9 to 20%. Depending on the fat content yoghurt can be categorized as: full fat (6% - 10% fat), medium fat content (3% - 5%), yoghurt with low fat (1% - 3%) and the last one- skimmed (0% fat). With at most 5 g of fat per serving, yogurt is pure health food, one that is not just low fat, but also contains protein, vitamins and minerals.

Yogurt (also spelled yogourt or yoghurt) is a semi-solid fermented milk product which originated centuries ago in Bulgaria. Its popularity has grown and is now consumed in most parts of the world. It was originally produced to extend the keeping qualities of milk but now is enjoyed simply for its taste and versatility in cooking. The production has shown tremendous increase during the past few years mainly due to the introduction of wide variety of flavours and added fruits and other sweeteners. Yoghurt is one of the most popular fermented dairy products all over the world. Over the past 10 years new bacteria have been used in yogurt-making, to make 'bio yoghurts', these are reputed to aid digestion. All yoghurt is made from milk using bacteria. The milk is heated up and a sample of bacteria is added to the milk while it’s cooling. The bacteria live off the lactose in the milk and they convert it into a substance called ‘lactic acid’. And it’s this lactic acid that makes the yoghurt set.

Nowadays different forms of yoghurt are available in the market:

· soy yogurt, a dairy-yogurt alternative, is made from soy milk.

· Greek sheep's milk yogurt. It is a rich and creamy Greek set yogurt made from sheep's milk.

· Greek yogurt, it has a deliciously thick and creamy texture. The original variety is made from whole cow's milk and cream.

· natural yogurt. A smooth yogurt made from traditional cultures. It has no added flavours or sweeteners. Natural yogurt can be added to fresh fruit and cereals for breakfast. It can be used to make dips and salad dressings, as a garnish for soups and used to add a creamy taste and texture to sauces and curries. It can be used as a substitute for cream or ice cream or as a topping for fresh fruit, meringues or gateaux.

· non "bio" yoghurt, is made using bacteria that are killed off by the acid environment of stomach as soon as they get there. This might seem like a good idea if customer doesn’t like the idea of having bugs inside - but in fact the bacteria used to make yoghurt are very good, not harmful to health.

· natural bio live yogurt is a smooth live yogurt made with active bio cultures for a mild and creamy taste. With bio-yoghurts, the bacteria used in the production process aren’t killed by the acid inside. The bacteria avoid being digested themselves and stick to gut wall and they help digestion of other foods. They also boost immune system by reducing the amount of bad bacteria in gut, which immune system normally has to kill to protect. Unfortunately, the bacteria used to make bio-yoghurts, Lactobacillus acidophilus, don’t grow very quickly. It takes a day or two to produce a significant amount of yoghurt. And that’s why bio-yoghurt is normally much more expensive than normal yoghurt.

Common types of yoghurt in everyday:

Set Yogurt - natural set yogurt. It is made with traditional cultures and is sometimes known as French yogurt, which is fermented in the pot that it is sold in. It is produced when fermentation at controlled temperatures sets the yogurt in tubs. Easily identified by its flat surface with a thin ‘skin’ on top. Set yogurt can be natural or vanilla flavoured or with fruit or flavourings at the base, and fairly thick in texture and devoid of whey separation.

Stirred Yogurt is made when fermentation is carried out in bulk in a large vat, not in individual containers. Once the fermentation reaches the desired level the yogurt is pumped through a cooler to stop the fermentation. Then the added fruit or flavouring is stirred into the yogurt.

Drinking Yogurt is produced similarly to stirred yogurt.  The body is then diluted and mixed with a blend of flavours, fruit or berry juices. This product is enjoyed as a delicious, nutritious drink.

Flavoured Yogurt. There are many varieties of yogurts in the market - vanilla and honey are the most popular. Most have added sugar or artificial sweeteners to enhance the flavours.

• fruit yogurt - includes fresh fruit pieces or sweetened fruit pulps. Most are contained in stirred yogurt while some have fruit on the bottom with naturally set yogurt on top. In some cases fruit jam is used instead of raw fruit pieces in yoghurts to allow storage for weeks.
• yogurt combination packs - these are available in split containers with fruit, nuts or muesli to combine with yogurt for a snack or meal.

Yoghurt is a dairy product produced by bacterial fermentation of whole or skimmed milk. Fermentation of the milk sugar (lactose) produces lactic acid, which acts on milk protein to give yoghurt its texture and its characteristic tang. Yoghurt is made by introducing specific harmless bacteria strains into milk; traditionally they are Lactobacillus bulgaricus and Streptococcus thermophilus, which are subsequently fermented under controlled temperatures and environmental conditions. Most of the yoghurts shops are made using of these two bacteria. They are used because they grow very quickly and turn milk into yoghurt in just a few hours.

The process of yoghurt making can be shortly described in this way: The bacteria ingest natural milk sugars and release lactic acid as a waste product. The increased acidity causes milk proteins to tangle into a solid mass in a process called denaturation. The increased acidity (pH= 4–5) also prevents the proliferation of potentially pathogenic bacteria. Fermented, partially evaporated, milk prepared by maintaining it at 50°C for 12 hours after the addition of a mixed culture of Lactobacillus bulgaricus, L. Acidophilus, and Streptococcus thermophilus; used as a food. A ratio of 1:1, Streptococcus thermophilus to Lactobacillus bulgaricus, inoculation is added to the milk. A temperature of 43° C is maintained for 4-6 h under quiescent conditions. This temperature is a compromise between the optimums for the two microorganisms (Streptococcus thermophilus - 39° C; Lactobacillus bulgaricus- 45° C).

In an attempt to make their products sound more exclusive, some large manufacturers are creating strains with proprietary names, such as Danon’s L. casei Immunitas™ and Bifidus Regularis™. These strains have no greater functional powers than the publicly-available bacteria.

In most countries, a product may be called yoghurt only if live bacteria are present in the final product. The majority of yogurts sold in the UK are 'live' yogurts - this means that they contain live bacteria when they are sold and up to the use by date. In the United States, to be named yoghurt, the product must contain the bacteria strains Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Often these two are co-cultured with other lactic acid bacteria for taste or health effects. These include L. acidophilus, L. casei and Bifidobacterium species.

Yogurt has traditionally been made from milk that had been partially condensed by evaporation while it had been heated almost to boiling. Coagulation of the milk proteins is induced by thermophilic bacteria which propagate well at an elevated temperature of 40- 45°C. The milk is coagulated by a slowly increasing concentration of lactic acid as the bacteria metabolize lactose. The proteins do not precipitate but form a gel. Its ability to retain all the water present in the milk is the result of a peculiar microstructure of the protein network.

Technology of making yoghurt in industry:

Yogurt is unique from both the structural as well as compositional viewpoints, because it is solid and has the highest water content of all solid milk products. Yogurt that has been stored for a long period of time may show some syneresis as the separation of a liquid phase from a gel is called. This is only a minor cosmetic defect and the liquid soaks back into the body of the yogurt as soon as the yogurt is stirred.

Compared to other milk products such as cheese, ice cream, or butter, yogurt contains most milk constituents except lactose, which the bacteria convert into lactic acid. This acid gives the yogurt a pleasant acidic flavour and, at the same time, the sweetness caused by lactose is reduced. Live 'friendly' lactic acid bacteria protect the yogurt from harmful pathogenic microorganisms and thus give it a longer shelf life. The fat content in some yogurts may be reduced for dietetic reasons.

Milk and dairy products are major sources of calcium, especially yoghurt. Calcium is the most important mineral for building strong bones and teeth. Our bodies can’t make calcium, so we must get it from the foods. An average adult should aim to take in 700mg calcium each day. Babies, children and adolescents require large amounts for growth and development, while pregnant and breast-feeding mothers must have an adequate intake to ensure their own calcium levels are not compromised. Yoghurt has also other medical uses, in particular for a variety of gastrointestinal conditions; making up for a lack of vitamins; healing oral and skin infections such as eczema, ulcers, and abrasions; and in preventing antibiotic-associated diarrhea. One study suggests that eating yoghurt containing L. acidophilus helps prevent vulvovaginal candidiasis, though the evidence is not conclusive.

Japanese researchers found eating the yoghurt reduced levels of hydrogen sulphide - a major cause of bad breath - in 80% of volunteers. The key are active bacteria in yogurt, specifically Lactobacillus bulgaricus and Streptococcus thermophilus. Details were presented at a meeting of the International Association for Dental Research: a total of 24 volunteers who took part in the study were given strict instructions on oral hygiene, diet and medication intake. The volunteers then ate 90 grams of yoghurt a day for six weeks. At the end of the study, researchers took samples. They found hydrogen sulphide levels decreased in 80% of participants. Levels of plaque and the gum disease gingivitis were also significantly lower among yoghurt eaters.

The particular combination of its components makes yoghurt irreplaceable and dispensable for digestion to work well. Undoubtedly, yoghurt is the basis for keeping digestive system in the best way. As a summary for all above said – “the Customer is always right”… So, the choice is up to you!

References:

· A. Y. Tamime and R. K. Robinson: Yogurt - Science and Technology, 2nd edition, published in the UK by Woodhead Publishing Limited, Cambridge, England, 1999

· Varnam, A. H. and Alan H.Va: Milk and milk products: technology, chemistry and microbiology , London : Chapman & Hall, 1994

· P. E. Norris: Yoghurt, Play Press, 1984

· Ramesh C.Chandan: Manufacturing of yogurt and fermented milk, Blackwell Pub Professional, 2006