TTILE: FERMENTATION OF DAIRY PRODUCT OBJECTIVE
Production of yogurt and carry out the sensory test and measure the acidity until desired pH reach. INTRODUCTION
Certain foods such as yogurt are made by introducing into milk organisms such as lactobacilli that ferment the milk. The fermented foods are often heat-treated after initial pasteurization to kill the fermenting organisms and to increase the shelf-life of the products. The labels of such products indicate whether they contain live fermenting organisms. If you make yogurt at home, be sure to purchase a live-culture brand of yogurt to use as your starter (Black, 2012). Yogurt is made by adding Streptococcus thermophilus and Lactobacillus bulgaricus Lactobacillus bulgaricus to to milk. These organisms release still other products, and so yogurt has a different texture and flavor flavor (Black, 2012). Several species of bacteria bacteria are used in the commercial production of yogurt. Most formulations include combinations of two or more species to synergistically enhance growth and to produce the optimum balance of flavor and acidity. One common pairing of organisms in commercial yogurt is that of Lactobacillus delbrueckii subsp. delbrueckii subsp. bulgaricus and bulgaricus and Streptococcus thermophilus . Yogurt gets its unique flavor from acetaldehyde, diacetyl, and acetate produced from fermentation of the milk sugar lactose. The proportions of products, and ultimately the flavor, in the yogurt depend upon the types of enzyme systems possessed by the species used. Both species mentioned above contain constitutive b-galactosidase systems that break down lactose and convert the glucose to lactate, formate, and acetate via pyruvate in the Embden-Meyerhof-Parnas (glycolysis) pathway. Lactose is a disaccharide composed of glucose and galactose. S. thermophilus does not possess the enzymes needed to metabolize galactose, and L. delbrueckii preferentially delbrueckii preferentially metabolizes glucose. This results in an accumulation of galactose, which adds sweetness to the yogurt. Acetaldehyde is produced directly from pyruvate by S. thermophilus and thermophilus and through the conversion of proteolysis products threonine and glycine by L. delbrueckii . Some strains of S. thermophilus also thermophilus also produce glucose polymers, which give the yogurt a viscous consistency (Leboffe & Pierce, 2012). The application and potential of fermentation milk products can be obtained from the study in making commercial yogurt that was success in the physical properties as well in chemical properties.
APPARATUS AND MATERIAL 1. Fresh milk. 2. Yogurt starter. 3. Small container. 4. Parafilm. 5. Pipette. 6. Phenolphthalein. 7. Retort stand. 8. Beaker. 9. NaOH. 10. Dropper. METHOD
1. The 500ml milk is pasteurized at 80oC and let it rest for 15-20 minutes. 2. The milk was then cooled by the flow of water. Care must be taken so that the milk was not contaminated by the tap water. After the temperature of the milk was reached 45oC, 20ml yogurt starter was added as the starter culture. Every transfer must be done aseptically to prevent contamination. 3. The milk was then incubated at 45oC. Analysis: 1. The initial acidity of the titration was measured for every 30 minutes by using 5ml milk and a few drops of phenolphthalein was added. 2. Incubation stopped when the acidity reached 0.90-0.95%. 3. The yogurt was tested in terms of its colour, aroma, mouth feel perception and texture. 4. The lactic acid percentage was plotted in order to see the changes along the production of the yogurt. RESULT Hours
1
2
3
4
pH
6.08
6.04
4.74
4.27
0.360
0.369
0.667
0.921
Acidity (%)
Table 1 : Percentage (%) Of Acidity and pH of Milk.
Attribute
Description Before incubate
After incubate
Color
White
Milky or creamy white
Texture
Less viscosity.
High viscosity.
Dilute.
Thicken. Formation of curd.
Mouth feel
Aroma
Creamy.
Extremely creamy.
Bitter taste.
More sour and less bitter
Strong milk odour
Strong sour smell, slight milk odour
Table 2 : Sensory Evaluation.
Percentage % Lactic Acid Against Time (Hour) Percentage of bacteria %
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1
2
3
4
Time (Hour) Percentage % of Lactic Acid
Graph 1 : Percentage Of Lactic Acid (%) against Time (Hour). DISCUSSION
For the first hour the pH value of the yogurt was 6.08 then it decrease through time 4 hours has past were the pH value is 4.27. Streptococcus thermophilus starts to grow where it drops the milk pH from 6.08 to 6.04 and as a result it produced carbon dioxide and lactic acid. Next, these products stimulate the Lactobacillus bulgaricus to grow and also further drop the pH to 4.74. Yogurt fermentation involves the conversion of lactose to lactic acid by bacteria, resulted in pH reduction. The decreased of pH may be attributed to the
increase percentage of lactic acid during fermentation (Shima, Salina, Masniza, & Atiqah, 2012). Lactic acid is one of major product of lactose degradation in milk and milk products due to the bacterial fermentation. Depending on the microorganisms involved, fermentation of milk proceeds via glycolysis pathway will produce lactic acid while via pentose phosphate pathway with formation of lactic and acetic acids (Burghagen, Hadziyev, Hessel, Jordan, & Sprinz, 1999) and (Urbienė & Leskauskaitė, 2006). The lactic acid in the study showed increasing in percentage. For the first two hours there was slight increase from 0.360% to 0.369%. After the first two hours the percentage of lactic acid increases tremendously from 0.369% to 0.921% from 2 hours until 4 hours. The increase in lactic acid bacteria count (LABC) will lead to the increase in lactic acid content. The present experimental study showed the changes occur in yogurt making. Before incubation process the color of milk was white. The texture was less viscosity and more dilute. The mouth feel was creamy and tasted bitter. The aroma was strong milk smell. After incubation the colour changed to milky or creamy white. The texture changed to high viscosity, thicken and there were formation of curd. The mouth feel was extremely creamy and tasted sourer and less bitter. The aroma was strong sour smell and has slightly milky smell. Sugar found in milk is called lactose. When starter cultures added into milk it breaks lactose into glucose. Then as the sugar glucose is formed, it will be fermented into lactic acid by the microorganism. It also produced acetaldehyde where it refers to colourless liquid of chemical compound that creates the tart and sour taste of plain yogurt. The lactic acid caused the pH of milk to decrease and cause the casein which is protein found in milk to denature and stick together and formed curdles to produce yogurt. UHT milk is milk that has been heated to an ultra high temperature. UHT milk is theoretically the best type of milk to make yogurt with as there are no bacteria to compete with the yogurt formers. More subtle changes of heat treatment include effects of heat on milk protein (helps to improve the thickness), milk enzymes (reduces rancid and bitter off flavours), milk sugar (reduces pH and contributes to flavour) and fat (fatty chemicals help to improve flavour). On the negative side, heat treatment of milk will reduce the vitamin content. On the study we used UHT milk for yogurt making The milk is usually clarified and separated into cream milk and skim milk and then standardized to achieve the desired fat content before the addition of the starter cultures. The commercial starter cultures of yogurt production are composed of a symbiotic mixed culture of S.thermophillus and L.bulgaricus. If the initial concentration of starter culture is
too low, other micro-organisms may grow. Too high a concentration is wasteful. The most effective starter cultures are simply a dose of readymade yogurt.These starter organisms are ultimately responsible for the formation of typical yogurt flavour and texture. Although they can grow independently, the rate of acid production is much higher when used together than either of the two organisms grown individually. In yogurt processing, pasteurization of milk is very important. This is because at high heat treatment the whey (serum) is denatured. Milk is pasteurized at the temperature 80oC for 15 to 20 minutes. Proteins will form more stable gel that can avoid division of water during storage. Furthermore, it reduces the number of spoilage microorganisms in milk. This purpose is to provide a better environment so that the starter cultures can grow. Apart from that, pasteurization helps to ensure that the cultures remain actives in the yogurt after fermentation. Enzymes speed up chemical reactions which would otherwise happen very slowly. The enzymes in the yogurt making bacteria cause milk to turn into yogurt. The enzymes controlling the metabolism of the bacteria will work best at a particular temperature. If it is too cold the enzymes work very slow, so little yogurt is made. The name Streptococcus thermophilus tells you that this bacterium is a thermophile. It loves heat. The optimum temperature for yogurt production is 46°C. The milk cooled until the temperature reached 45oC to bring the yogurt to the ideal growth temperature for the starter cultures. At 45oC, it allows formation of a soft gel and characteristics flavor of yogurt. In order to form a very good quality of yogurt, the pH of yogurt must be in the range of 4.4 to 4.7. Streptococcus thermophilus and Lactobacillus bulgaricus are heat resistance and can survive at 80oC for 15 to 20 minutes. The key to commercial development of fermented milk products is the consistent and predictable rate of acid development by lactic acid bacteria. Furthermore, the rate and extent of pH decrease during manufacture, retention of coagulants, loss of minerals and electrochemical interactions between protein molecules. Hence, in turn, it has consequences or the development of flavour and physical properties (Lee & Lucey, 2010). Streptococcus thermophilus played a major role in producing the sour taste in yogurt. Meanwhile, Lactobacillus bulgaricus is instrumental in producing the scent through the production of lactic acid and acetaldehyde. The uses of both types of bacteria are intended to accelerate the process of acid production, increase the amount if lactic acid, improve the consistency of the coagulant and also improve the flavour. The amount of lactic acid is one of the important parameters because the core product expected in the yogurt is lactic acid levels produced by a microorganism capable of being used.
Food provides a source of energy and the raw materials for growth of the bacteria. Milk contains a sugar called lactose and protein which makes the yogurt thick when heated. Depending on the milk used, the food provided and possible competition from other bacteria will be different. Different types of milk will affect the flavour and thickness. CONCLUSION
The fermentation of yogurt to produce yogurt was done successfully. The pH for the milk to become yogurt was reached in the specific range of standard commercial yogurt which was 4.4 to 4.7. The sensory test was carried out and it’s achieved the consistency of typical commercial yogurt. REFERENCES
Black, J. G. (2012). Microbiology Principles and Explorations. New Jersey: John Wiley & Sons. Burghagen, M. M., Hadziyev, D., Hessel, P., Jordan, S., & Sprinz, C. (1999). Milk and dairy products. In H. -D. Belitz, & W. Grosch, Food Chemistry (pp. 470-512). New York : Springer-Verlag. Leboffe, J. M., & Pierce, E. B. (2012). Microbiology Laboratory Theory & Application. Englewood: Morton Publishing Company. Lee, W. J., & Lucey, J. A. (2010). Formation and Physical Properties of Yogurt. Asian-Aust. J. Anim. Sci. Vol.23, No.9 , 1127-1136. Shima, A. R., Salina, H. F., Masniza, M., & Atiqah, A. H. (2012). Viability of Lactic Acid Bacteria in Home Made Yogurt Containing Sago Starch Oligosaccharides. International Journal of Basic & Applied Science Vol:12 No: 01 , 58-62. Urbienė, S., & Leskauskaitė, D. (2006). Formation of some organic acids during fermentation of milk. Pol. J. Food Nutr. Sci. , 277-281.
