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MICROBIAL CONTAMINATION OF YOGHURT

Format: MS WORD  |  Chapter: 1-5  |  Pages: 58  |  2314 Users found this project useful  |  Price NGN3,000

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CHAPTER TWO
LITERATURE REVIEW
2.1   PRODUCT DESCRIPTION
Yoghurt is a smooth, fermented milk product that evolved empirically some centuries ago through the growth of thermophilic (heat loving). Lactic acid, bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus which ferment the milks lactose to produce lactic acid. It has a characteristic acidic taste possessing 0.95 -1.5% and PH ranging from 3.7-4.2 with viable and abundant fermenting microorganisms.  
2.2   PRODUCTION OF YOGHURT
MATERIALS: In yoghurt preparation the following essential materials are use in processing the product: milk or concentrated skimmed or partly concentrated skimmed milk or milk product and the starter culture Lactobacillus bulgaricus and Streptococcus thermophilus. In. the absence of pure culture one to two spoonful of commercially purchased yoghurt can be used for the inoculation. Also, there are optional ingredients like milk powder, skimmed milk powder, flavour, colours, sugar, wheat, edible casein, preservatives, stabilizers (gelatin, locust bean gum, pectin, starch) etc.
EQUIPMENT: They include refrigerator or cooler, boiler or heater, thermometer.
PROCEDURES: The milk to be fermented is first heated to 70°c for 15 -30 minutes the concentrate or skimmed milk powder is added and the mixture is heated to about 80°c with continuous stirring for 5 minutes so as to kill the microorganisms which are contaminants, lower the redox potential of the mixture and produce factors and condition favourable to the development of the bacteria to be inoculated. Also, the added skimmed milk prior inoculation raises the nutritive value of yoghurt and gives a product of better body and consistency. The product is cooled to about 43°c by dipping in container containing cold water and inoculate with 3% selected strains of actively growing microbial starter (Lactobacillus bulgaricus and Streptococcus thermophilus) or with 1.5% of each culture separately maintain the temperature of 42 -44°c for approximate 5 hours until desired degree of acidity is achieved. Then cool rapidly to 8-10°c and refrigerate as you store till the next morning to check for curd formation. The addition of - stabilizers, flavours, colour, sugar, fruit or honey etc may be added before packaging if desired. The final product usually contains some 10 cells per milliliter of each bacteria specie while the' characteristic flavour is due to the lactic acid and trace amount of ethanol, dimethyl propanol, ethanoic acid and other volatiles products by bacteria fermentation.  
2.3   VARIETIES IN YOGHURT PRESENTATION
Yoghurt has been described as a notoriously balanced food, containing almost the nutrients present in milk but in a more assimilable form. The can be produced from whole or skimmed milk (Ojokoh, 2006). There are large ranges of flavours enhancer available commercially (Anthar, 1996) that can be used in the production of yoghurt and yoghurt is typically categorized as follows:
1.     SET YOGHURT: This type of yoghurt is incubated and cooled in the final package and is characterized by a firm Jelly-like texture.
2.     STIRRER YOGHURT: This type of yoghurt is incubated in a tank and the final coagulum is "broken" by stirring prior to cooling and packaging. The texture of stirred yoghurt will be less firm than a yoghurt not stirred which is some what like a very thick cream. There is some slight reformation of the coagulum after the yoghurt has been packed, however this is slight and can not be relied upon.
3.     DRINKING YOGHURT: This type of yoghurt is very similar to stirred yoghurt, having the coagulum "broken" prior to cooling. In drinking yoghurt, the agitation used to "break" the coagulum is severe. Little care is applied if any reformation of the coagulum will reoccur after packing.
4.     FROZEN YOGHURT: This is inoculated and incubated in the same manner as stirred yoghurt. However, cooling is achieved by pumping through a whipper/chiller/freezer in a fashion similar to the cream. The texture of the finished product is mainly influenced by the whipper/freezer and the size and distribution of the ice crystals produced.
5.     CONCENTRATED YOGHURT: This type is inoculated and fermented in the same way as stirred yoghurt, following the "breaking" of the coagulum. The yoghurt is concentrated by boiling off some of the water. This is often done under vacuum to reduce the yoghurt often lead to protein being totally denatured and producing rough and gritty texture. This is called strained yoghurt due to the fact that the liquid that is released from the coagulum upon heating used to be "strained" off in a manner similar to making of soft cheese.
6.     FLAVOURED YOGHURT: Yoghurt with various flavours and aromas has become very popular. The following are usually added at or just prior to filling into pots. Common additions are fruits or berries, usually as a pure or as whole fruit in syrup. These additives often have" as much as 50% sugar in them. However, with the trend towards healthy eating gained momentum many manufacturers offer a low sugar and low fat version of their products. Low or no sugar yoghurts are often sweetened with saccharin or more commonly aspartame. The use of a "fruit sugar" in the form of concentrated apple juice is sometimes found as a way of avoiding' "additional sugar" on the ingredients declaration. This tends to be a market ploy and has no real added benefits.
2.4   HEALTH BENEFITS OF YOGHURT
Dairy products such as yoghurt; contains probiotic cultures e.g. Lactobacilli which are currently among the best known examples of "functional food" (Oyeleke, 2009). Their associated health claims include. a.   Yoghurt is easier to digest than milk and so many people including children who can not tolerate milk, either because of a protein allergy' or lactose intolerance can enjoy yoghurt more digestible than milk. The live active cultures create lactose, the enzymes lactose intolerant people lack and another enzymes contained in some yoghurts (beta-galactosidae) also improve lactose in lactase deficient persons. Breaking down the milk sugar lactose into glucose and galactose two sugars that are easily absorbed by lactose intolerant persons. However, bacterial enzymes created by the culturing process partly digest the milk protein casein making it easier to absorb and less allergenic (Witton, 2004). b.  Yoghurt contributes to colon health: There is a magical truism that state "you are as healthy as your colon" when we drink yoghurt we care for our colon in two ways:
a.    Yoghurt contains lactobacteria: Intestine friendly bacteria culture that fosters a healthy colon and lowers the risk of colon cancer by promoting the growth of healthy bacteria and there by deactivate harmful substances which can cause problem in the colon.
b.   Yoghurt is rich in calcium which contributes colon health and decreases the risk of colon cancer (Gray, 2007).
c.   It improves the bioavailability of other nutrients culturing of yoghurt increase the absorption of calcium, and vitamins B, the presence of lactic acid in it aids the digestion of le milk calcium, making it easier to absorb Maltock, 2007).
d.  Yoghurt can boosts immunity: The regular consumption of live cultured yoghurt produces a higher level of immunity boosting interferon as his bacteria cultures stimulates infection fighting white cells in the blood stream with anti tumor effects (Maltock, 2007).
e.   Yoghurt aids healing: After intestinal, infection like diarrhea which injures the lining of the intestines especially the cells that produce' lactase which results to temporal lactose mal- absorption problem, yoghurt however because it contains less lactose and more lactase is usually well tolerated by healing intestine and is a popular healing food for diarrhea (Gray, 2007).
f.    Protection against ulcers: Helicobacter pylori the bacterium responsible for most ulcer, can be shut down by yoghurt.
g.   Yoghurt can decrease yeast infection eating eight ounces of yoghurt that contains live and active cultures daily reduces the amount of yeast colonies in the vagina and decreases the incidence of vaginal yeast infection as show from research (Gray, 2007). h.  Yoghurt is a rich source of calcium. An 8 ounce serving of most yoghurts provides 450mg of calcium, one half of a child's RDA and 30- 40% of the adult RDA for calcium. Because the live active cultures in yoghurt increase the absorption of calcium, an 8 ounce serving of yoghurt gets more into the body than the same volume of milk can.
i.    It is an excellent source of protein. Plan yoghurt contains around 10-14 grams of protein percent 8- ounces, which amounts to twenty percent of the daily protein requirement for most persons. i.e it contains more percent than the same volume of milk also the culturing of the milk protein during fermentation makes it easier to digest.
j.    Yoghurt can lower cholesterol -Daily consumption of ounces (100g) of yoghurt significantly improved the cholesterol while raising HDL (good) cholesterol which may be because of the ability of the live culture in it to assimilate cholesterol or because yoghurt binds the bile acids which lower' cholesterol (Maltock, 2007).
k.  Yoghurt help prevent and treat Arthritis; Lactobacillus a probiotic (friendly) bacteria found in yoghurt offers "remarkable preventive and curative effects on arthritis.
l.    Improve fresh breath and a healthy mouth. Consuming just 3.2 ounces of yoghurt twice a day not only lowers levels of hydrogen sulfide and other volatile sulfide compounds responsible for bad breath, but may also eliminate tongue-coating bacteria and reduce dental plaque formation, cavities and' risk for gingivitis, Research backed by the international Association for dental research shows that eating plain live -yoghurt for six weeks can reduce levels of oral bacteria by up to 80% so yoghurt is a traditional bad breath cure (Okpalugo et al., 2008),  
2.5   NUTRITIONAL PROFILE OF YOGHURT
Yoghurt as a dairy food can be consumed in form of snack, thirst quenching beverages and as a desert, but it's nutritional value cannot be over emphasized. It is a good source of iodine, calcium, phosphorus, zinc, riboflavin, vitamin B5 and vitamin B12. It is also nutritionally rich in protein, molybdenum and Pantothenic acid (Ensminger, et al., 1986). The food rating system adopted as the government  standard for food labeling that are found in the U.S food and drug administration allow yoghurt to be rated as one of the world's healthiest food. Table II shows the nutrient for which yoghurt is rated. The absence of a particular nutrient does not necessarily mean that it is absent, rather the nutrient is not provided in a sufficient amount or concentration to meet the rating criteria.

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