• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17
  18. 18
    18
  19. 19
    19
  20. 20
    20

The comparison of bacterial content in a range of milks.

Extracts from this document...

Introduction

Yasmin White 1210 The comparison of bacterial content in a range of milks Introduction Milk is a nutritious food. It is an excellent source of calcium, phosphorus, riboflavin, and vitamin D and a good source of protein, vitamin A, potassium, and several B vitamins. These constituents differ widely in molecular size and solubility, therefore milk is a complex physiochemical system. The enzymes found in cow's milk are: protease, amylase, lactase, lipase, xanthine oxidase, phosphatase, aldolase, catalase, and peroxidase. It's the lipase here that can cause hydrolytic rancidity. The smallest molecules, those of salts, lactose, and water-soluble vitamins, are in 'true solution'. The proteins, including the enzymes, are in the colloidal state (suspension in the liquid) because of the large size of their molecules. Lactose (milk sugar) is a white crystalline disaccharide, it has the same molecular formula as sucrose (C12H22O11) but it differs in structure, making it an isomer. It contains the simple sugars, glucose and galactose. Galactose is catalysed by lactase. When milk sours, the lactose is converted by bacteria to lactic acid, this causes a change in the milk's consistency. Milk is often naturally contaminated with bacteria. Lactobacillus and Streptococcus Lactis (the two most common lactic acid bacteria) produce lactic acid during fermentation: Bacteria: Bacteria are very small organisms, each being a living cell. Most bacteria are between 0.0005mm to 0.002 mm long and they rarely exceed 0.01mm in length. Whether or not the bacteria move, all must respire; most use oxygen, respiring aerobically, while others, including several of the pathogenic or disease-causing bacteria, respire anaerobically. Anaerobic respiration: Anaerobic respiration is the release of energy from food material by a process of chemical breakdown that does not require oxygen. The food e.g. Carbohydrate, is not broken down completely to carbon dioxide and water but to intermediate compounds such as lactic acid or alcohol. C6H12O6 ? ?CO2 ? ?C2H3OH ? (118KJ) Some bacteria derive all their energy from anaerobic respiration, and the end products are frequently lactic acid; the processes know as fermentation. ...read more.

Middle

0.0351 0.0360 0.0585 55 0.0576 0.0396 0.0405 0.0630 75 0.0468 0.0927 0.0495 0.0801 80 0.0720 0.0450 0.0270 0.0540 100 0.0675 0.0603 0.0360 Unspecified 105 0.0630 0.0540 0.0450 Unspecified (Graph overleaf) Analysis of the results The results show a number of conclusions. To begin with, the raw milk seems to have proved my hypothesis accurately. The levels of lactic acid started at 0.0225cm� and rose in a relatively steady rate up to a level of 0.0270cm� after just five hours of exposure to room temperature. It then leveled out at this amount for a further 20 hours. These results suggest that the first stage of growth was happening- the lag phase-the cells are active but there is little growth as they are taking up water and starting to produce enzymes. The next phase of growth is outlined after 25 hours of exposure-the exponential (or log phase)-the population increases rapidly-from just 0.0207cm� of lactic acid present in the milk, to 0.0585cm�-a total increase of 0.0378cm� in just 25 hours. Surprisingly it seems the bacteria endure another lag phase-the cells are still active but again there is little growth. Without looking at the results following these, you might assume that the bacteria are progressing towards the stationary phase-bacterial cells are dying more or less at the same rate, as they were produced-however looking at the results at 75hours-80hours it seems that this stage is highlighted here. After 50 hours the levels of lactic acid, production seems to decrease-only a slight increase of lactic acid content-from 0.0585cm� - 0.0801cm� (an increase of 0.0216cm�). If you compare this to the increase of lactic acid content from a similar time difference there is an obvious decline in production, for example between 25 hours and 30 hours there is an increase of content of 0.00450cm�-almost double the rate of production. Finally, the levels of lactic acid after 55hours suggest that the bacteria are now progressing through the second exponential phase (log phase)-an increase from 0.0630cm� to 0.0801cm� in just 20 hours. ...read more.

Conclusion

0.0360 0.0360 0.0360 Raw Hours exposed to the air: 100 Amount of lactic acid present in the milk: g Type of milk Trial one Trial two Trial three Average Whole Pasteurised 0.0630 0.0630 0.0630 0.0630 Semi-skimmed Pasteurised 0.0540 0.0540 0.0540 0.0540 UHT 0.0450 0.0450 0.0450 0.0450 Raw Hours exposed to the air: 105 Results of 'experiment to investigate the relationship between bacterial content and pasteurization' Cooled for 1 minute Amount of NaOH needed to titrate the milk/ml Time the milk was heated for/mins Temperature the milk reached/ ?c Test 1 Test 2 Test 3 Average 0 24 2.70 2.70 2.70 2.70 1 32 2.50 2.50 2.50 2.50 2 50 2.30 2.30 2.30 2.30 3 57 2.20 2.30 2.30 2.30 4 61 2.00 2.00 2.00 2.00 5 80 1.50 1.50 1.50 1.50 6 105 1.50 1.40 1.40 1.40 Cooled for 1 minute Amount of lactic acid present in the milk/ml Time the milk was heated for/mins Temperature the milk reached/ ?c Test 1 Test 2 Test 3 Average 0 24 0.0243 0.0243 0.0243 0.0243 1 32 0.0225 0.0225 0.0225 0.0225 2 50 0.0207 0.0207 0.0207 0.0207 3 57 0.0198 0.0207 0.0207 0.0207 4 61 0.0180 0.0180 0.0180 0.0180 5 80 0.0135 0.0135 0.0135 0.0135 6 105 0.0135 0.0126 0.0126 0.0126 Cooled for 2 minutes Amount of NaOH needed to titrate the milk/ml Time the milk was heated for/mins Temperature the milk reached/ ?c Test 1 Test 2 Test 3 Average 0 24 2.70 2.70 2.70 2.70 2 55 2.30 2.30 2.30 2.30 4 75 1.90 1.90 1.90 1.90 6 90 1.50 1.40 1.40 1.40 8 110 0.90 0.90 0.90 0.90 Cooled for 2 minutes Amount of lactic acid present in the milk/ml Time the milk was heated for/mins Temperature the milk reached/ ?c Test 1 Test 2 Test 3 Average 0 24 0.0197 0.0197 0.0197 0.0261 2 55 0.0167 0.0167 0.0167 0.0167 4 75 0.0139 0.0139 0.0139 0.0139 6 90 0.0110 0.0102 0.0102 0.0102 8 110 0.00657 0.00657 0.00657 0.00657 ?? ?? ?? ?? 1 ...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

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

    4 star(s)

    and recorded the values in a table. 16. I carried out this experiment 2 more times and then used the results to obtain an average set of results. Safety and Precautions The safety and precautions I took while I carried out this experiment were that: * I washed my hands

  2. This assignment is about planning and designing practical experiment to carry out an investigation ...

    perfect circle of clear zone and measurable, but if I had irregular circles I would have measured area of clear zone using colony counter pen, which measure an area accurately. Concentration of E.coli used in practical was unknown and haemocytometer could have been used to measure the concentration of the E.coli.

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

    Pour the 10cm of each sample into separate test tubes. Mark on each of the test tubes, which samples are refrigerated and which are at room temperature. Also differentiate between the different types of milk used by marking each test tube.

  2. Investigating Seed Germination. Hypothesis If there is water, oxygen and a suitable ...

    --> Overall time taken for germination - The amount of time given for each seed to germinate must remain the same, as if the time given for the seeds to germinate varied, some seeds would be able to have more time to grow than the others, which in turns affect the length of the seedlings.

  1. An investigation into the antibiotic effects of penicillin and streptomycin on the bacterium Escherichia ...

    Number of times to repeat. 4. Control disc. 5. Number of impregnated discs to put in each Petri dish. 6. Concentration of antibiotic. 7. Method of measurement. 8. Sterile techniques Temperature to incubate at: It is important to incubate all the Petri dishes at the same temperature, so that

  2. Testing the effectiveness of various anti microbial agents.

    However if this is not possible then they need to be stored for a longer period of time at room temperature. If this is done however the results may not be as good as they could be. *At the end of the incubation period you can now need to record

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

    Petri dish as far from the edges as possible, closing the cover as soon as possible. 12) Heat the forceps again pick up another paper disc and immerse it in the 100% non-branded bleach solution. Deposit the disc in the same Petri dish away from both the other disc and the edges.

  2. 'Bacteria. Friend or Foe?' Bacteria is something we are all reminded of ...

    it has the ability to colonize their lungs causing serious infection if inhaled (5). This begs the question, who is really at fault, the bacteria or the host? Having evolved in their presence humans have serious difficulty with a relatively small number of bacteria so why do we persist in filling our homes with bacteria killing products?

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