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). Bacteria are one-celled, or unicellular, microorganisms. 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. Or, you can press a variety of common objects like coins, combs, etc. Another factor that could’ve influenced the outcome was the different expiry dates for the types of milk. 6 . The lactobacillus bacteria existent in milk fermented the carbohydrates such as glucose and lactose in milk into lactic acid. For thousands of years, fermented foods have been present in traditional diets around the world and continue to be widely consumed. 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. It could be concluded that several factors influenced the bacterial growth rate in milk. 2 . Take the lid off of the Petri dish (the lid is larger than the dish) and carefully cover the bottom-half of … Whereas, the milk samples in the fridge had less amount of lactic acid present and produced a faint or no sour odour (Chua, 2008). The most common bacteria found in milk were the lactobacilli. The colour of milk was due to the ability of these protein molecules to refract light. h�b```f``�d`a``�� ̀ �@1V �8l(Ƞ�*����;V+ϝ�{\� �����c�,�R�'��}8��[�`�Ig���FqG�mIsT$}��3�Vtt4( ���F a��h0qL�{�@�A�� H�� X� �Va1�_ �Xz���'E3�^u,7���b��8M�Ab�= ��]@�� ��gd0 °Dk Hyperthermophilic bacteria will grow extreme heat, 70 to 110 degrees C (158 to 230 degrees F). The test tube with the methylene blue is your test sample. 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). Generation time is the time required for a bacterium to give rise to two daughter cells under optimum conditions. For example, the production of sour cream, yogurt, and cheese were all results of the fermentation of milk where the lactobacilli broke down lactose in milk into lactic acid. From simple essay plans, through to full dissertations, you can guarantee we have a service perfectly matched to your needs. influence of mastitis on the total bacteria count of bulk milk depends on type of bacteria, the stage of infection and the percent of the herd infected. Pour 9 ml milk into each test tube. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. The generation time for most of the pathogenic bacteria, such as … You can test the effectiveness of different soaps by treating different petri dishes with "dirty" hands before washing and "clean" hands after washing. Study for free with our range of university lectures! Furthermore, the lactobacilli bacteria existent in milk produced lactic acid by fermenting the sugars in milk. In unfavourable conditions, a few bacteria were able to reproduce sexually by a process called conjugation with the intention of increasing the survival probability. The purpose of this experiment was to understand the conditions which encouraged and inhibited bacterial growth by observing the rate of bacterial reproduction in milk samples stored at different temperatures. All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. of incubation is indicated (Figure 1). VAT Registration No: 842417633. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). However, milk is unique with respect to its sugar. Many micronutrients such as vitamins and micro-minerals are also available. They could be photoautotrophic, photoheterotrophic, chemoautotrophic, or chemo- heterotrophic. Furthermore, the results could’ve been different depending on how each individual perceived the changes that had occurred to the milk samples. Mastitis organisms Warmer temperatures provoked bacteria to reproduce quicker as opposed to cold temperatures which restricted bacterial growth. Do you have a 2:1 degree or higher? Data representative of the results obtained in manyexperiments are presented in tables 1 and 2. As bacteria grow and reproduce in milk, the pH level of milk drops. Various bacteria could grow in an environment with the pH level close to 7; hence in a close to neutral environment, bacteria reproduce rapidly. 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�(. A preliminary experiment showed that two of the powders and one of the syrups had high bacterial counts, and the others had low counts. *You can also browse our support articles here >, To understand the favourable and unfavourable conditions for bacterial reproduction, To monitor and compare the rate of bacterial growth in milk stored at warm and cool temperatures. Our academic experts are ready and waiting to assist with any writing project you may have. Lastly, the sharp sour odour of the cupboard samples after a few days were produced by the lactic acid present in the milk. The final stage of bacterial growth byBacillus The most significant factor proven in this experiment was temperature. Individual bacteria can only be seen with a microscope, but they reproduce so rapidly that they often form colonies that we can see. Bacteria count correlated highly with CO 2 but not with pH. No plagiarism, guaranteed! and growth. 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. 0 The chocolate milk in both the fridge and the cupboard seemed to have undergone the greatest amount of change after the six days compared to the other three types of milk left in the corresponding conditions. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream Hence, the bacteria in the milk samples kept in the cupboards were multiplying at a much faster rate than the milk samples in the fridge. In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. Coccus had protection against drying out, bacillus bacteria had great surface area for nutrients absorption and spirilla bacteria were able to travel through fluids with ease. Milk contained various compounds, the main ones being fat, protein, and sugar. In general, a higher count was obtained in those samples containing 25% and/or 50% of … Procedure: Registered office: Venture House, Cross Street, Arnold, Nottingham, Nottinghamshire, NG5 7PJ. 353. Experimental Procedure #2:Repeat Experiment #1, using raw milk and pasteurized milk. These errors affected the analysis greatly since the information wasn’t specific and accurate. During conjugation, two bacterial cells with slightly different genetic make-ups were connected to each other through protein tube structures called pili. Instead, their DNA floats in a tangle inside the cell. The pH values were another factor that affected the bacterial reproduction in the milk samples. During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. Using the kitchen tongs remove the test tube caps from the pot, and cap the test tubes. However in milk, as the lactobacilli population grew rapidly, the amount of lactic acid increased greatly also, considering that these bacteria broke down the lactose in milk and released a by-product of lactic acid. As time passed by, this lowered the pH level of the milk samples, which caused the milk to curdle and produce a pungent sour smell. The odour of the samples of milk was described and recorded in the correct observation table. When the chemical indicator, methylene blue, is added to the milk, the milk is turned blue. In this experiment, you will qualitatively assess the presence of bacteria in milk using the methylene blue reductase test. The main one was temperature. The temperature was taken for each sample of milk and recorded in the appropriate observation table. There was no significant relationship between growth phenotypes and bacterial diversity in the fecal microbiota of recipient animals (table S6A). There were several factors that affect the rate of bacterial growth. Disclaimer: This work has been submitted by a university student. Furthermore, foods should be kept refrigerated in order to inhibit bacterial growth. Membranes2020, 10, 326 3 of 11 The purpose was to identify at which filtration temperature the hygiene conditions could be kept under control in the range of 10 to 20C, and therefore, to define how the production time between Milk is a good source of all principal nutrients, including carbon, nitrogen and macro-minerals. 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. 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. of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. The OD was checked at every 30 minutes interval and recorded. A small sample of the different types of milk (~50mL) was poured in the corresponding labeled glass cups. Bacteria reproduce when one cell splits into two cells through a process called binary fission. Lightened agar around bacterial growth = complete blood cell lysis (S. pyogenes) The amount of blood cell lysis by the bacteria results in a different color in the media. The protein in milk also provides a source of carbon the bacteria can use, in addition to lactose, as a fuel source. If it takes less than 20 minutes, then there are over 20 million organisms/ml. This is not an example of the work produced by our Essay Writing Service. All work is written to order. Registered Data Controller No: Z1821391. An experiment can be preformed to monitor the rate of bacterial growth in milk by testing the acidity of the milk liquid. Free resources to assist you with your university studies! 4 glass cups were labeled with the different types of milk: whole, skim, butter, and chocolate. The pH values also affected the bacterial growth rate. Bacteria could obtain energy from various sources. 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). 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 effect of water dilution on bac- terial growth as measured by logarithms of bacterial counts made after 6 hr. A description of the appearance of the milk samples were made and noted in the appropriate observation table. 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. There were also other types of reproduction that bacteria go through such as transformation, transduction, and spore formation (Galbraith et al., 2001). The majority of the milk samples, 79.2% (228/288 samples), had no bacterial growth after 48 hours, 20 samples (6.9%) had sparse growth, 34 samples (11.8%) had moderate growth and six samples (2.1%) had abundant growth of bacteria after 48 hours (Table 1). 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. MILK 5 MILK 1 MILK 2 MILK 3 MILK 4 MILK 64 MILK 7 0 . 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. Fission occurs rapidly in as little as 20 minu… 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). We've received widespread press coverage since 2003, Your UKEssays purchase is secure and we're rated 4.4/5 on reviews.co.uk. Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. %PDF-1.3 %���� Foods which were kept in warmer temperatures such as in the oven for at least a day or two should not be consumed; they might be hazardous to one’s health considering that warm temperatures encourage bacterial reproduction. The chocolate milk with the most amount of sugar content, which provided the bacteria more food supply, spoiled the quickest compared to the other types of milk. 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 has ideal conditions for bacterial growth having high water content, plentiful nutrients, and a pH level that’s very close to neutral (6.4-6.8). In this lab everything went as originally planned. This was because of the difference in the amounts of lactic acid present in the two groups of samples. The growth rate of a bacterium is measured by measuring the change in bacterial number per unit time. 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 … This example concludes Nataliya’s story that started in How Microbes Grow and Oxygen Requirements for Microbial Growth.. Extreme freezing. We're here to answer any questions you have about our services. Bacteria require nitrogen to synthesize new proteins as they increase their population during growth. The bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. As the increasing bacteria population in the cupboard milk samples continued to produce lactic acid, they were creating an unfavourable condition for themselves. These protein molecules repelled each other, however when the pH level decreases, the molecules suddenly became attracted to each other forming chunks. The low^count milk gives the greatest increase in bacterial count in … This was what happened at the molecular level when milk developed curd. As the cell continued to grow, it would elongate and begin to form a septum between the two DNA molecules. Subsequently, the model was extended with the average competition coefficients (E-BR–GD model) that represented quantitative relations among the populations. 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. Extreme freezing can stop bacterial growth and/or kill bacteria altogether. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). Additionally, these organisms came in several different shapes; the most common being cocci (round), bacilli (rod-shaped), and spirilli (spiral shaped) (“Classification of bacteria,” 2012).Each shape offered distinctive advantages. In this experiment, milk, which has ‘lactose’ as the sugar, will be broken down into lactic acid by the bacteria present, which will lower the pH-level to make it acid. However, most bacteria cannot survive in very acidic environments; a low pH level. 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). , NG5 7PJ spoilage bacteria most common bacteria found in milk fermented the carbohydrates such vitamins! 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