Oxygen Concentration: Oxygen is not required by the bacteria producing yogurt
Duration of fermentation: Specific chemicals are required to give the yogurt its flavour. Too short fermentation, and these will not be produced; too long a fermentation and the product become more acidic. Other micro – Organisms may invade and produce off flavors.
Manipulating Variables
* PH
*Temperature
* Concentration of starter culture
Concentration of starter culture
Commercially, starter cultures of 1-2 % of the milk are used. Concentrations of, say, 1-5 % would be best used in laboratory.
Controlling Variables
* Starter concentration: An initial concentration of 1% is suitable
* Type of milk
* Oxygen concentration: No aeration should be carried out.
* PH: Milk ph is 6.7 to 6.9, but lower PHS will encourage the growth of lactobacilli
These are the variables that need to be controlled so this is classed as a fair test
Time: Commercial fermentation is about is about 3-5 hours. In the laboratory this could be carried out overnight or over one day
Monitoring the fermentation
Qualitative and Quantitative qualities
* Qualitative – tasting it
* Quantitative – pH measurement – final yogurt pH is 4.6
* Quantitative- bacterial growth can be demonstrated using a redox indicator such as resazurin or methylene blue
Safety Points
* Sterilized equipment to avoid contamination
* Wash hands before and after experiment
* Minimize contact with micro-organisms used
Materials And Method
First of all I measured out precisely a well-known volume of milk then I used a graduated pipette. Then I transferred milk to the 100-cm3 beaker. I then measured accurately a known volume of live yogurt. I then transferred yogurt to the milk. After that I inserted a ph probe into a log it data logger. I placed the ph probe into the milk, and then I placed the beaker into a 250-cm3 beaker so that the probe didn’t cause me any difficulties. I then got my data logger to record readings at appropriate intervals and start logging. After that I placed the beaker into a incubator at the desired temperature.
Results 1
Method 2
I began by measuring out accurately the milk by using a pipette. Then I transferred the milk into a beaker, and then I measured out exactly a known volume of live yogurt. After that I transferred the yogurt to the milk, then I checked the finished product.
Conclusion
Enzymes inside bacteria catalyze yogurt process. The efficiency of an enzyme is influenced by temperature; an enzyme has an optimum temperature where it can work to its most competent. The higher the temperature the more efficient the enzyme is. This is because the enzyme and substance are combining more often. above a certain temperature the could drop significantly. This is because the active site of the enzyme is being destroyed so the substrate is no longer fits in. the enzyme has become denatured
Further Analysis
* Yogurt is deemed complete when set at 4.6
* The efficiency of the enzymes involved can be measured by how quickly the yogurt reaches 4.6 degrees C
* The optimum temperature was 4 degrees
* From my data I found out the optimum temperature was between 40 degrees and 50 degrees this is because the data is fairly similar
* I could have correctly established the optimum temperature by carrying out more experiments between 40 degrees and 50 degrees for my second experiment I will use the optimum temperature of 45 degrees
Results 2
The optimum condition was 45degrees, the ph started at 6.9 degrees and ended on 4.6 degrees
Evaluation
Design error:
* When I placed the water bathes to the incubator, the contents properly didn’t reach the desired temperature immediately.
*Bacterial growth could have been detected if I was using resazurin or blue methylene.
Human error:
* Masses and volumes could have been mis calculated
* There could have been errors in cell counting
* Errors may have been made whilst making buffer solutions
* Yogurt and milk are difficult to measure and is also viscous
Equipment error:
*The measurement I received from the thermometers properly wasn’t absolutely accurate
*ph meter could have been defective
Vocational Aspects
Yogurt production demonstrates fermentation by Streptococcus thermophilum and Lactobacillus bulgaricus. Heated milk is inoculated and maintained at a given temperature causing bacteria to grow and ferment lactose, the sugar in milk. The bacteria produce lactic acid, which causes the milk to coagulate and adds a sour flavor.
Be sure to follow aseptic technique and use only food-grade containers for this experiment. You must submit a proposal on what your experimental group(s) will entail before beginning this laboratory work.
Kamran Masood
