Difference between revisions of "Yogurt"
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Revision as of 06:26, 27 August 2008
Higher order taxa:
Introduction of Yogurt Niche
Description of Niche
Other Niches Affecting Microbes in Yogurt
Influence by Adjacent Communities
The yogurt niche and its environment overlap its similarity between some of the other dairy niches, specifically being the milk niche which is the root of all dairy niches. The making of yogurt is first through the transition of the milk niche. Firstly, yogurt is made from fermented milk. Milk is rich in sugars, more specifically the sugar being lactose. An environment rich in sugars is an environment that microbes love to thrive in; thus, milk is a great feast for microbes. The following are a list of microbes that thrive in milk. Of all the microbes that live in milk, the Bacillus family and the Streptococcus family is the one that overlaps into the yogurt niche. However, there are only two particular microbes that feast in yogurt which are Lactobacillus bulgaricus and Streptococcus thermophilus. So, as we can see there is a similarity between the microbes that thrive in milk to the ones that thrive in yogurt.
Related Microbes in Adjacent Communities
1. Streptococcus lactis
Purpose: Souring Method: Lactose-lactic acid precipitation
2. Streptococcus bulgaricus
Purpose: Souring Method: Lactose-lactic acid precipitation
3. Lactobacillus casei
Purpose: Cheese ripening Method: Controls altermentation.
4. E coil
Purpose: Souring & gassiness Method: Lactic acid & gases and affects cheese ripening.
5. Bacillus substallis
Purpose: Protecolysis Method: flavors change.
6. Alkaligenes viscus
Purpose: Ropiness Method: Ropi milk
7. S Streptococcus liquifiecence
Purpose: Bitter Flavour Method:Bitter flavour to cream &butter.
8. Bacillus substallis
Purpose: Sweet curdling Method: Curd formation
9. Streptococcus paracitrovorus
Purpose: Attacks citric acid Method: Flavors curd.
Conditions under which the environment changes
In the process of using the lactose sugar from the milk, Lactobacillus produces acid which makes the yogurt sour and a less suitable place for other microbes. This is why there is a dramatic decrease in the amount of microbes that live in the yogurt niche when compared to the milk niche. Thus the essential conversion between milk to yogurt is the acidic levels. The increase in acidic levels is the sourness that is tasted in yogurt which lacks in milk, another characteristic difference. Lactic acid also known as lactate is not good for bacteria. So, as a response to this change in environment, they excrete lactate into their environment. This again is what causes the pH to fall to become more acidic. Another affect of excreting lactate is that the protein molecules in the milk become denatured. What this means is that the protiens unfold from their normal structures and become disordered. After becoming distroted, the protein molecules begin to stick to each other forming a semi-solid matrix. Thus, this is what gives the yogurt a semi-solid state, another characteristic different from the liquid-milk.
Microbes Specific to Yogurt
Which microbes are present?
Are there any other non-microbes present?
Do the microbes that are present interact with each other?
Microbe Metabolism and Its effect on environment and human body
Lactobacillus is found to be living in highly acidic environments of pH 4-5 or lower, thereby altering the pH and suppressing pathogens by producing lactic acid. Under the optimal temperature of 37°C, it derives the energy, such as ATP, by converting the glucose to lactic acid through homolactic fermentation. Nevertheless, it is unable to breakdown complex sugars, like ribose, under the optimal temperature. In addition, Lactobacillus secretes nonbacteriocin antibacterial substances. In humans, Lactobacillus is found in the gut and vagina. In the vagina, it plays an important role by keeping the pH low to deter infection.
Under the optimal temperature of 42°C, Streptococcus thermophilus, can generate ATP through fermentation. In contrast to Lactobacillus, it is also able to produce ATP through aerobic respiration in the presence of oxygen. Through fermentation, it converts lactose to lactic acid at the optimal pH of 4.6. In humans, Streptococcus thermophilus is found in the upper part of the intestine and can help people with lactase-deficiency to digest lactose due to the low level of lactase they produce.
Milk fermented with yogurt cultures and Lactobacillus casei compared with yogurt and gelled milk: influence on intestinal microflora in healthy infants
Consuming fermented dairy products have profound health effects, such providing the minerals and vitamins to humans. They regulate the equilibrium and metabolism of microflora in healthy infants. The experiment was based on comparing the effects of consumption of regular yogurt, milk fermented with yogurt cultures and Lactobacillus casei (YC), and nonfermented gelled milk on the fecal microflora of healthy 39 infants who were divided in three groups, and each group received one of three products. The results show indexes, such as anaerobes, bifidobacteria, bacteroides were not modified during supplementation period. However, in the yogurt group, the number of enterococci in fecal samples had increased. In the YC group, the number of fecal lactobacillus had increased in the colon in which lactobacillus may provide physiological benefits. This may prove that Lactobacillus can used for preventing infectious diseases and stimulating the immune system.
(1.)Virginia Vadillo-Rodríguez, Henk J. Busscher, Willem Norde, Joop de Vries, and Henny C. van der Mei1. "Dynamic Cell Surface Hydrophobicity of Lactobacillus Strains with and without Surface Layer Proteins". Bacteriol. 2004 October; 186(19): 6647–6650.doi: 10.1128/JB.186.19.6647-6650.2004.
(3.)LYN C. RADKE-MITCHELL and W. E. SANDINE. "Influence of Temperature on Associative Growth of Streptococcus therrnophilus and Lactobacillus bulgaricus". Journal of Dairy Science Vol. 69, No. 10, 1986
Edited by [Chung Abbott, Ibukun Osindele, Anusha Sridharan, Jerry Wang], students of Rachel Larsen