In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. This was because of the difference in the amounts of lactic acid present in the two groups of samples. Moreover, bacteria commonly grew in distinguishing arrangements. Furthermore, the results could’ve been different depending on how each individual perceived the changes that had occurred to the milk samples. 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. 2 . 57 0 obj <> endobj Bacteria count correlated highly with CO 2 but not with pH. 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. In this type of experiment, bacteria is transferred directly to the prepared petri plate via direct contact. Study for free with our range of university lectures! 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. 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. If turmeric is applied to foods, then the growth of bacteria and fungi will be suppressed. Our academic experts are ready and waiting to assist with any writing project you may have. 6 . Many micronutrients such as vitamins and micro-minerals are also available. If it takes less than 20 minutes, then there are over 20 million organisms/ml. 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 Furthermore, the lactobacilli bacteria existent in milk produced lactic acid by fermenting the sugars in milk. When the chemical indicator, methylene blue, is added to the milk, the milk is turned blue. 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). 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). These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). The pH levels of all the milk samples excluding the buttermilk, were very close the neutral, therefore they encouraged bacterial growth. There were also other types of reproduction that bacteria go through such as transformation, transduction, and spore formation (Galbraith et al., 2001). The temperature was taken for each sample of milk and recorded in the appropriate observation table. The low^count milk gives the greatest increase in bacterial count in … The growth rate of a bacterium is measured by measuring the change in bacterial number per unit time. *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. 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. A few factors were temperature, pH levels, water content, and available food sources. The generation time for most of the pathogenic bacteria, such as … 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. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. 4 glass cups were labeled with the different types of milk: whole, skim, butter, and chocolate. Warm temperature provided bacteria a favourable environment for reproduction which caused them to multiply quickly as opposed to cooler temperatures. Looking for a flexible role? 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. %PDF-1.3 %���� Furthermore, foods should be kept refrigerated in order to inhibit bacterial growth. and growth. The greenish yellow liquid residue surrounding the floating clump was a solution of translucent whey. Company Registration No: 4964706. Hence, the clumps of a cheese-like substance that was formed at the end of the experiment in the cupboard samples were protein (casein) molecules. Also, different individuals might interpret the colours differently and for the buttermilk and whole milk, the values of the exact pH levels weren’t recorded. Mastitis organisms Procedure: These errors would’ve altered the observations that were made significantly. Milk contains a significant amount of protein, a nutrient made of nitrogen-rich amino acids. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. 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. Also, the substances in milk such as sugar (lactose, glucose), milk fat, protein, and other compounds provided the bacteria with a great amount of food supply for energy. 8 observation tables were created; 2 tables for each type of milk; fridge vs. cupboard. Fission occurs rapidly in as little as 20 minu… As the increasing bacteria population in the cupboard milk samples continued to produce lactic acid, they were creating an unfavourable condition for themselves. experiment, there was a floating substance of lumps and bubbles at the top, and a clear liquid underneath. Warmer temperatures provoked bacteria to reproduce quicker as opposed to cold temperatures which restricted bacterial growth. The bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. Bacteria are one-celled, or unicellular, microorganisms. Do you have a 2:1 degree or higher? Therefore, the greater amount of available food supply, the faster the bacteria multiply in the milk (“What is lactobacillus?,” 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. Milk provides the newborn (neonate) with nutrients and an array of antimicrobial factors. However, milk is unique with respect to its sugar. During conjugation, two bacterial cells with slightly different genetic make-ups were connected to each other through protein tube structures called pili. No plagiarism, guaranteed! Instead, their DNA floats in a tangle inside the cell. 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. 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. 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. 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. A preliminary experiment showed that two of the powders and one of the syrups had high bacterial counts, and the others had low counts. This process allowed new gene combinations to be introduced which may provide the daughter cells a better chance of adapting to the changing conditions. Errors which occurred during this experiment included inaccurate measurements of the pH values considering that the colours of the red litmus paper strip were difficult to differentiate. 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. In this lab everything went as originally planned. 0 If the factors were considered, one would be able to control the growth of bacteria. The receiving cell would then undergo binary fission with the new gene content to produce more cells with this new gene combination. Whereas, the milk samples in the fridge had less amount of lactic acid present and produced a faint or no sour odour (Chua, 2008). Using your calibrated eye dropper or pipette, measure 1 ml methylene blue. The final stage of bacterial growth byBacillus 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). All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. As bacteria grow and reproduce in milk, the pH level of milk drops. Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. 353. Classification of the Bacteria Kingdom was based on the shape, structure/thickness of cell walls, sources of food and energy, and the analysis of RNA sequences. The other 4 glass cups filled with different types of milk samples were placed in a cupboard/cabinet. The pH values were another factor that affected the bacterial reproduction in the milk samples. Experimental Procedure #2:Repeat Experiment #1, using raw milk and pasteurized milk. In this experiment, you will qualitatively assess the presence of bacteria in milk using the methylene blue reductase test. Hyperthermophilic bacteria will grow extreme heat, 70 to 110 degrees C (158 to 230 degrees F). The protein in milk also provides a source of carbon the bacteria can use, in addition to lactose, as a fuel source. The most common bacteria found in milk were the lactobacilli. at 55C on the growth of microorganisms in the 0.1 m MF systems used for milk protein fractionation. 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. Subsequently, the model was extended with the average competition coefficients (E-BR–GD model) that represented quantitative relations among the populations. There was no significant relationship between growth phenotypes and bacterial diversity in the fecal microbiota of recipient animals (table S6A). 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). on different plates and compare the bacteria growth that results. 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). 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). 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 presence of Listeria in Nataliya’s blood suggests that her symptoms are due to listeriosis, an infection caused by L. monocytogenes.Listeriosis is a serious infection with a 20% mortality rate and is a particular risk to … 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. Milk contained various compounds, the main ones being fat, protein, and sugar. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream First, the prediction ability was performed only with parameters estimated from individual growth curves of E. coli, S. aureus and the lactic acid bacteria in milk (Dataset 1, 21 experiments). This lowered the pH level greatly which caused the death of bacteria. This is not an example of the work produced by our Essay Writing Service. You can test the effectiveness of different soaps by treating different petri dishes with "dirty" hands before washing and "clean" hands after washing. Some grew in pair (diplo), some in clusters (staphylo), and others grew in a chain (strepto) (“Bacterial shapes and,” 2014). This was what happened at the molecular level when milk developed curd. %%EOF Registered office: Venture House, Cross Street, Arnold, Nottingham, Nottinghamshire, NG5 7PJ. We're here to answer any questions you have about our services. The colour of the milk samples were identified and noted in the corresponding observation table. VAT Registration No: 842417633. of incubation is indicated (Figure 1). 8th May 2018 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. MILK 5 MILK 1 MILK 2 MILK 3 MILK 4 MILK 64 MILK 7 0 . The effect of water dilution on bac- terial growth as measured by logarithms of bacterial counts made after 6 hr. 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). endstream endobj startxref 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). The main one was temperature. Furthermore, research showed that food bacteria reproduce the quickest at temperatures ranging between 21 and 47°C. Using the kitchen tongs remove the test tube caps from the pot, and cap the test tubes. As the cell continued to grow, it would elongate and begin to form a septum between the two DNA molecules. V2 = volume of the inoculums (in this experiment, 50 ml) Substitute the values in the equation and V1 was calculated. 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. The most significant factor proven in this experiment was temperature. h�bbd``b`�� � Hp5 � �b���灄� !+$�|��p5�� The lactobacillus bacteria existent in milk fermented the carbohydrates such as glucose and lactose in milk into lactic acid. The results collected after the six day period of observation revealed that factors which influenced the rate of bacterial growth were temperature, pH level, moisture and the amount of food sources available. 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. Various bacteria could grow in an environment with the pH level close to 7; hence in a close to neutral environment, bacteria reproduce rapidly. 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