• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

An investigation to determine the rate of bacterial growth in milk under different conditions.

Extracts from this document...

Introduction

An investigation to determine the rate of bacterial growth in milk under different conditions. Aim Fresh milk contains many microorganisms including the bacteria lactobacillus. Pasteurisation is the process where the milk is heated to a 72�c for 15 seconds, which kills most but not all of the bacteria. Under suitable conditions these bacteria reproduce rapidly. In anaerobic conditions i.e. when there is a lack of oxygen in the milk, the bacteria respire to produce lactic acid. The aim of the investigation is to determine the rate at which bacteria reproduce and therefore the rate at which they respire. This will enable us to determine how different sets of milk, react under different conditions. Although the rate of each bacterium does not change, as the density of bacteria increases through cell multiplication, the overall rate of oxygen uptake will increase. It is the rate of uptake that gives the colour changes in the rezararurin dye. The colour changes from blue to lilac to mauve to pink and finally it goes colourless. The rate of bacterial growth in the samples of milk is measured by the rate of microbial respiration, which is indicated by a fall in pH. A fall in pH is due the accumulation of lactic acid. The accumulation of lactic acid occurs when the density of bacteria increases through cell multiplication. As the density of bacteria increases the demand for oxygen increases, once all the oxygen is used up the conditions turn anaerobic, thus resulting in the production of lactic acid. ...read more.

Middle

Skimmed Semi-skimmed Full fat refrigerated Ultra heat treated 5 Lilac Lilac Pink Light blue 10 Lilac Lilac Light pink Light blue 15 Pink Light pink Cream Light blue 20 Pink Light pink Cream Light blue 25 Pink Light pink Cream Light blue 30 Pink Pink Cream Light blue Refrigerated Colour Time (Min) Skimmed Semi-skimmed Full fat refrigerated Ultra heat treated 5 Blue Light blue Light blue Light blue 10 Blue Light blue Light blue Light blue 15 Blue Light blue Light blue Light blue 20 Blue Light blue Light blue Light blue 25 Blue Light blue Light blue Light blue 30 Blue Light blue Light blue Light blue Room temperature Milk sample pH Skimmed 5.8 Semi skimmed 6.6 Full fat 6.0 UHT 6.4 Refrigerated Milk sample pH Skimmed 6.4 Semi skimmed 6.4 Full fat 6.4 UHT 6.2 Day 4 Room temperature Colour Time (Min) Skimmed Semi-skimmed Full fat refrigerated Ultra heat treated 5 Slightly turbid yellowish liquid White White Light blue 10 Slightly turbid yellowish liquid White White Light blue 15 Slightly turbid yellowish liquid White White Light blue 20 Slightly turbid yellowish liquid White White Light blue 25 Slightly turbid yellowish liquid White White Light blue 30 Slightly turbid yellowish liquid White White Light blue Refrigerated Colour Time (Min) Skimmed Semi-skimmed Full fat refrigerated Ultra heat treated 5 Blue Light blue Light blue Light blue 10 Blue Light blue Light blue Light blue 15 Blue Light blue Light blue Light blue 20 Blue Light blue Light blue Light blue 25 Blue Light blue Light blue Light blue 30 Blue Light ...read more.

Conclusion

Skimmed milk at room temperature was the slowest of the three pasteurised samples to change colour. This means that the rate of bacterial respiration and multiplication in this sample of pasteurised milk was the slowest. However the most significant fall in pH occurred between day 2 and day 3 where the pH fell from 7.0 to 5.8. This means that the rate of bacterial multiplication and hence respiration between these two day was the fastest for this sample. The results obtained for these samples of milk can be justified by the relative amounts of bacteria left in each sample after they undergo pasteurisation. The full fat sample of milk has the most bacteria left in it as pasteurisation occurs over the shortest amount time of the three samples of milk. Therefore the rate of bacterial multiplication will be more rapid then the other two samples because initially there was more bacteria in the sample. Once the density of bacteria increases the demand by bacteria for oxygen will increase and this will increase the production of lactic acid, as the conditions will turn more anaerobic. The colour change of the rezasurin dye will also change the quickest. The skimmed milk sample is the most pasteurised sample, therefore it will have the least amount of bacteria in it initially. The rate of reproduction will be the same as the full fat sample however the density will be lower. This means that the demand for oxygen by the bacteria will not be as great as in the full fat sample ant equivalent times. Therefore the rate the colour of the dye will change will be slower. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our GCSE Living Things in their Environment section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Living Things in their Environment essays

  1. Marked by a teacher

    The effects of disinfectants and antibacterial soap on bacterial growth

    5 star(s)

    However, this might have encouraged the other kind of bacteria (from the environment, rather than from the body) to grow. Obviously, this does not make much sense, because we encouraged the growth of one kind of bacteria. tested that bacteria, and then regrew it in conditions suitable for another kind of bacteria.

  2. Marked by a teacher

    A2 Biology Coursework -Investigation into the effect of different concentrations of antibiotics on the ...

    4 star(s)

    Table My control which didn't contain any antibiotic solution what so ever had the highest absorbance value in all 3 experiments suggesting and proving the fact those bacteria has grown without the presence of antibiotic. Graph (On a separate Paper)

  1. Marked by a teacher

    In this experiment, mung bean seedlings and Brine shrimp eggs were used to study ...

    4 star(s)

    From the experiment on the rate of hatching of Brine shrimp eggs, the optimum temperature in which the rate of hatching is the highest is found to be at 25oC as well. The total number of eggs in observation was counted.

  2. Marked by a teacher

    An Investigation into a Woodlice's Preferred Choice of Environment.

    3 star(s)

    I then put black card over one side of the lid of the choice chamber, and by putting muslin in between the bottom and the lid I ensured that no woodlice would touch the cotton wool or the empty section.

  1. Investigation - Examination of bacterial sensitivity on antibiotics.

    Ecoli - This was first isolated by Eschecheria in 1885 from the feces of an infant. It was found later to be a normal inhabitant of the intestinal tract of the human body. The longevity of Ecoli is reduced outside the animal body.

  2. The comparison of bacterial content in a range of milks.

    They usually are not pathogenic. Lactobacilli also create problems. They sometimes are responsible for spoilage of beer, milk and meat. A variety of gram-positive bacteria produce lactic acid as their major or sole fermentation product and are sometimes collectively called lactic acid bacteria.

  1. Branded Bleach is more effective at killing E. coli than Non branded bleach - ...

    Seal the Petri dish using sellotape. 14) Complete stages 11-13 for all the required concentrations of bleach. 15) Put the Petri dishes in an incubator for a set time of 48 hours at 25�C. 16) After said time remove the dishes from the incubator.

  2. To see how Blowfly larvae (Calliphora) react to light.

    The reason for this is due to the larvae needing to get out of the light as quickly as they can, reducing the amount of time that they exposed to potentially threatening situations. NULL HYPOTHESIS Due to information that I have seen about the way in which woodlice behave in

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work