bacterial growth in milk experiment
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Free resources to assist you with your university studies! To export a reference to this article please select a referencing stye below: If you are the original writer of this essay and no longer wish to have your work published on UKEssays.com then please: Our academic writing and marking services can help you! The test tube with the methylene blue is your test sample. Quarters from infected cows have the potential to shed in excess of 10,000,000 bacterial cfu/ml of milk produced. Copyright © 2003 - 2020 - UKEssays is a trading name of All Answers Ltd, a company registered in England and Wales. Reference this. The most common bacteria found in milk were the lactobacilli. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream Among the four types of milk left in the fridge, the chocolate milk and the butter milk were the only samples that went through a slight colour and appearance change. Experiments were conducted using a simplified human milk spoilage model based on goat's milk as a human milk surrogate, spiked with a single bacterial strain (Staphylococcus epidermidis ), in which pH and carbon dioxide (CO 2) concentration were measured along with bacteria count over 160 hr. The rate of the curdling of milk is caused by both the warm temperature and acidic conditions in the cupboard milk samples. Using your calibrated eye dropper or pipette, measure 1 ml methylene blue. Clinical Focus: Nataliya, Resolution. It could be concluded that several factors influenced the bacterial growth rate in milk. The pH levels of all the milk samples excluding the buttermilk, were very close the neutral, therefore they encouraged bacterial growth. Based on the sugar content of the milks, it was shown that the rate of bacterial reproduction in the chocolate milk was faster than the other types of milk because of its high sugar content which was about double the sugar content of the other types of milk. Take the lid off of the Petri dish (the lid is larger than the dish) and carefully cover the bottom-half of … This process allowed new gene combinations to be introduced which may provide the daughter cells a better chance of adapting to the changing conditions. If turmeric is applied to foods, then the growth of bacteria and fungi will be suppressed. at 55C on the growth of microorganisms in the 0.1 m MF systems used for milk protein fractionation. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. Finally, a distinct cell wall would be formed between the two DNA molecules splitting the original call into two smaller genetically identical daughter cells (Bailey, 2014). The factors that control the rate of bacterial growth discovered in this experiment could be applied to everyday life. All science fair projects This experiment was testing how effective natural plant extracts are as antibiotics by placing a mixture of the bacteria and natural plant extract combined together with milk and measured the diameter of the bacterial colony in the agar plate and compared it a mixture of only milk and the bacteria without the plant extract to see if the plant extract was effective in killing the bacteria. Any scientific information contained within this essay should not be treated as fact, this content is to be used for educational purposes only and may contain factual inaccuracies or be out of date. Registered office: Venture House, Cross Street, Arnold, Nottingham, Nottinghamshire, NG5 7PJ. Do you have a 2:1 degree or higher? Bacteria could obtain energy from various sources. The growth of all microbes was characterized by the appearance of logphase after 12 hours in all the milk types tested, which shows that the optimal time period for growth of the tested isolates is ranging between 12 – 48 hours and this means provision of enzymes for … The bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. Data representative of the results obtained in manyexperiments are presented in tables 1 and 2. Or, you can press a variety of common objects like coins, combs, etc. Whereas, the milk samples in the fridge had less amount of lactic acid present and produced a faint or no sour odour (Chua, 2008). Many micronutrients such as vitamins and micro-minerals are also available. Therefore, after a while the cupboard samples would slowly increase in pH level; become more basic, as all the bacteria die due the extremely acidic environment and thus the bacterial growth rate would decrease drastically. It was concluded that milk is an ideal setting for the reproduction of bacteria due to its high water content, pH value close to 7, and ingredients. The milk samples kept in the cupboards for six days produced a pungent sour odour while the samples in the fridge had no or a faint sour smell. A physical property of acids was sourness, therefore considering that there were more lactobacilli bacteria in the cupboard samples breaking down sugar and producing lactic acid as a by-product, there was a greater quantity of acid in the samples forming the strong sour smell. A small sample of the different types of milk (~50mL) was poured in the corresponding labeled glass cups. Furthermore, the lactobacilli bacteria existent in milk produced lactic acid by fermenting the sugars in milk. All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. These errors affected the analysis greatly since the information wasn’t specific and accurate. All samples of milk dropped in pH levels and it seemed like by the fourth day, all samples kept in the cupboards had produced a cheese-like solid substance that was surrounded by a thin liquid residue. Milk contained various compounds, the main ones being fat, protein, and sugar. 353. Bacteria reproduce when one cell splits into two cells through a process called binary fission. The greenish yellow liquid residue surrounding the floating clump was a solution of translucent whey. Pathogenic bacteria induced food poisoning such asBacillus cereus whereas spoilage bacteria were only capable of producing pungent odours, unappetizing flavours, and changes in texture and appearance of milk. This suggests that non- refrigerated milk increases the growth of bacteria in milk, compared to refrigerated milk. Here: α-hemolysis (S. mitis, L); β-hemolysis (S. pyogenes, M); γ-hemolysis (also called non-hemolytic, S. salivarius, R). The pH level was taken for each milk sample and recorded in the appropriate observation table. The protein in milk also provides a source of carbon the bacteria can use, in addition to lactose, as a fuel source. This coincides with fact that experiment 4 had the greatest amount of heat applied to the milk treatment and experiment 2 coincides with the least amount of heat being applied to the milk treatment. During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. Generation time is the time required for a bacterium to give rise to two daughter cells under optimum conditions. This was because of the difference in the amounts of lactic acid present in the two groups of samples. In this lab everything went as originally planned. Fission occurs rapidly in as little as 20 minu… The other 4 glass cups were labeled as; whole, skim, butter, and chocolate as well. Oct. 1, 1925 Bacterial Count of Milk and Cream 699 In contrast with centrifugally separated cream, gravity separated cream shows a much higher percentage increase in bacterial count over whole milk. The curdling process of milk occurred more quickly at warmer temperatures compared to cold temperature, therefore only the samples in the cupboard developed curd (Moncel, 2014). The results after the six day observation period showed that the four types of milk which are kept in the fridge underwent little to no changes in appearance, odour, pH level or colour, whereas the milk that were left in the cupboards presented drastic changes in all aspects. This was because both the warm temperature and the close to neutral pH level provided the bacteria in milk, lactobacilli, with a favourable environment for reproduction allowing more bacteria to ferment lactose which produced more lactic acid and increased the acidity of the milk (“Microbiology,” 2014). 2 . Warm temperature provided bacteria a favourable environment for reproduction which caused them to multiply quickly as opposed to cooler temperatures. Bacteria were the only living organisms that existed on Earth for approximately 3.5 billion years implying that these prokaryotic organisms were able to survive through all the harsh climate changes in Earth’s history. of bacterial growth while experiment 2 had the least amount of bacterial growth. The drop of the pH values in the milk caused by the lactic acid resulted in various different alterations of the milk, appearance and texture wise producing different fermented dairy products (“Milk,” 2014). Place the methylene blue in one of the test tubes. These protein molecules repelled each other, however when the pH level decreases, the molecules suddenly became attracted to each other forming chunks. A population of bacteria could increase greatly in a fairly little amount of time considering that they reproduce exponentially. The donor bacterium would transfer all or part of its chromosome to the receiving bacterium. The pH values also affected the bacterial growth rate. The results of the experiments showed that primarily heat treatment and, to a minor extent, fat content of milk influenced the growth parameters of both bacterial strains, especially Lb. The Kingdom Bacteria consisted of anaerobic unicellular microorganisms with exceptional abilities of adapting to wide ranges of environment conditions. Subsequently, the model was extended with the average competition coefficients (E-BR–GD model) that represented quantitative relations among the populations. 74 0 obj <>/Filter/FlateDecode/ID[<51743C8C586D7346A2AE8CB8467C70D2>]/Index[57 44]/Info 56 0 R/Length 91/Prev 1615106/Root 58 0 R/Size 101/Type/XRef/W[1 2 1]>>stream That much amount (V1) of the inoculums was pipetted out before adding an equivalent amount of the broth to it, so that the net volume remains constant. Milk contains a significant amount of protein, a nutrient made of nitrogen-rich amino acids. The ability to ferment foods enables communities to safely consume both dairy and vegetables regardless of season and to lengthen shelf life without refrigeration (Steinkr… A few factors were temperature, pH levels, water content, and available food sources. Bacteria require nitrogen to synthesize new proteins as they increase their population during growth. Registered Data Controller No: Z1821391. of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. Various bacteria could grow in an environment with the pH level close to 7; hence in a close to neutral environment, bacteria reproduce rapidly. From simple essay plans, through to full dissertations, you can guarantee we have a service perfectly matched to your needs. However, milk is unique with respect to its sugar. A preliminary experiment showed that two of the powders and one of the syrups had high bacterial counts, and the others had low counts. 354 Bacterial Changes in Milk garded-is proven by careful milk dealers and dairymen every- where, and laboratory studies have amply demonstrated that clean milk, kept cold, is more apt to lose organisms during the first twenty-four to forty-eight hours than to gain them. The receiving cell would then undergo binary fission with the new gene content to produce more cells with this new gene combination. If you need assistance with writing your essay, our professional essay writing service is here to help! and growth. Several food agencies reported that at temperatures between 5 to 60°C several foodborne bacteria were able to grow; this was referred as the “danger zone.” This fact explained the reason behind the extremely slow rate of bacterial reproduction in the fridge milk samples considering that refrigerators were usually kept under 4°C to inhibit rapid bacterial growth in the foods. 8th May 2018 Extreme freezing can stop bacterial growth and/or kill bacteria altogether. Therefore, the greater amount of available food supply, the faster the bacteria multiply in the milk (“What is lactobacillus?,” 2014). h��Yko۸�+�x/����(�w�4MP���-����č_��n�_�gH��C�[g��PH��"yΜ�x+2ᝐy.�*h�p9�BjiE�PZ-��j%���L���5J#�ɍ�C� m%�y���s�60m��"��x4�J� ;�6C?��x�ȭ�Ƣt�exy�3/ �a��x���[��NU�~�V�=����5�G�H�(. The colour of the milk samples were identified and noted in the corresponding observation table. The most common bacteria found in milk were the lactobacilli. In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. At this point, the milk would be more vulnerable spoilage caused by mould and yeast which are able to survive in pH values below 4.5, extremely acid conditions (“What pH is,” 2012). There were also other types of reproduction that bacteria go through such as transformation, transduction, and spore formation (Galbraith et al., 2001). of incubation is indicated (Figure 1). Kitchen utensils and equipment should be kept clean and dry in order to restrict the amount of bacteria produced since moisture level, and the amount of available nutrients are both factors that affect the rate of bacterial reproduction (“Dairy bacteriology,” 2013). The colour of milk was due to the ability of these protein molecules to refract light. From -30 degrees C (-22 degrees F) and below, bacteria growth slows rapidly. Another factor that could’ve influenced the outcome was the different expiry dates for the types of milk. They could be photoautotrophic, photoheterotrophic, chemoautotrophic, or chemo- heterotrophic. If the factors were considered, one would be able to control the growth of bacteria. We're here to answer any questions you have about our services. Chocolate milk had about 10g of sugar per 100mL (“Chocolate milk,” 2014), whole milk had about 5.2 grams (“Nutrition facts,” 2014), skim milk had 4.9g (“Skim milk,” 2014), and buttermilk with a 5 g sugar content per 100mL (“Buttermilk,” 2014). Milk was an emulsified colloid where the protein molecules are suspended and dispersed within a water-based solution. Pour 9 ml milk into each test tube. However, due to the low temperature that the samples in the fridge were kept in, the bacterial growth was restricted, hence less lactic acid was produced maintaining the pH levels of the milks close to 7, while the samples kept in the cupboards all dropped in pH levels significantly; became more acidic after the six days. The most significant factor proven in this experiment was temperature. Methylene blue is a dye that is normally blue but turns colorless when it acted upon by bacteria (it is reduced, or it gains electrons, through the aerobic electron transport system). The low^count milk gives the greatest increase in bacterial count in … 6 . experiment, there was a floating substance of lumps and bubbles at the top, and a clear liquid underneath. For that reason, after about two days, the subject would be able to notice distinctive changes in the odour and appearance of the milk samples from the cupboards (“Danger zone,” 2014). 57 0 obj <> endobj Experimental Procedure #2:Repeat Experiment #1, using raw milk and pasteurized milk. Looking for a flexible role? %PDF-1.3 %���� Study for free with our range of university lectures! The most significant factor proven in this experiment was temperature. 100 0 obj <>stream Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. For thousands of years, fermented foods have been present in traditional diets around the world and continue to be widely consumed. 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