The effect of water dilution on bac- terial growth as measured by logarithms of bacterial counts made after 6 hr. A small sample of the different types of milk (~50mL) was poured in the corresponding labeled glass cups. The other 4 glass cups were labeled as; whole, skim, butter, and chocolate as well. endstream endobj startxref This example concludes Nataliya’s story that started in How Microbes Grow and Oxygen Requirements for Microbial Growth.. Company Registration No: 4964706. These errors would’ve altered the observations that were made significantly. Subsequently, the model was extended with the average competition coefficients (E-BR–GD model) that represented quantitative relations among the populations. The temperature was taken for each sample of milk and recorded in the appropriate observation table. Furthermore, foods should be kept refrigerated in order to inhibit bacterial growth. If the factors were considered, one would be able to control the growth of bacteria. 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. 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 pH levels of all the milk samples excluding the buttermilk, were very close the neutral, therefore they encouraged bacterial growth. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). If you need assistance with writing your essay, our professional essay writing service is here to help! 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). 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. 4 glass cups each with a different type of milk sample were placed in the fridge. Furthermore, bacteria existed everywhere; in the deserts and the oceans, in glaciers and hot springs, in the bodies of other living organisms and even in the Earth’s atmosphere (“Bacteria,” 2014). These errors affected the analysis greatly since the information wasn’t specific and accurate. Bacteria reproduce when one cell splits into two cells through a process called binary fission. Generation time is the time required for a bacterium to give rise to two daughter cells under optimum conditions. 100 0 obj <>stream The rate of the curdling of milk is caused by both the warm temperature and acidic conditions in the cupboard milk samples. of incubation is indicated (Figure 1). In unfavourable conditions, a few bacteria were able to reproduce sexually by a process called conjugation with the intention of increasing the survival probability. 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 colour of the milk samples were identified and noted in the corresponding observation table. There were also other types of reproduction that bacteria go through such as transformation, transduction, and spore formation (Galbraith et al., 2001). experiment, there was a floating substance of lumps and bubbles at the top, and a clear liquid underneath. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). It could be concluded that several factors influenced the bacterial growth rate in milk. Bacteria require nitrogen to synthesize new proteins as they increase their population during growth. Hyperthermophilic bacteria will grow extreme heat, 70 to 110 degrees C (158 to 230 degrees F). 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 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 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. The OD was checked at every 30 minutes interval and recorded. The pH level was taken for each milk sample and recorded in the appropriate observation table. Therefore, the greater amount of available food supply, the faster the bacteria multiply in the milk (“What is lactobacillus?,” 2014). Some grew in pair (diplo), some in clusters (staphylo), and others grew in a chain (strepto) (“Bacterial shapes and,” 2014). The colour of milk was due to the ability of these protein molecules to refract light. The Kingdom Bacteria consisted of anaerobic unicellular microorganisms with exceptional abilities of adapting to wide ranges of environment conditions. %PDF-1.3 %���� Milk was an emulsified colloid where the protein molecules are suspended and dispersed within a water-based solution. They are different from plant and animal cells because they dont have a distinct, membrane-enclosed nucleus containing genetic material. of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. 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 Clinical Focus: Nataliya, Resolution. 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 There was no significant relationship between growth phenotypes and bacterial diversity in the fecal microbiota of recipient animals (table S6A). The low^count milk gives the greatest increase in bacterial count in … Bacteria count correlated highly with CO 2 but not with pH. 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. Take the lid off of the Petri dish (the lid is larger than the dish) and carefully cover the bottom-half of … Most bacteria preferred to live in a pH value of 7; neutral. However, milk is unique with respect to its sugar. 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. Milk provides the newborn (neonate) with nutrients and an array of antimicrobial factors. Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. 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. All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. Quarters from infected cows have the potential to shed in excess of 10,000,000 bacterial cfu/ml of milk produced. Using the kitchen tongs remove the test tube caps from the pot, and cap the test tubes. Moreover, bacteria commonly grew in distinguishing arrangements. at 55C on the growth of microorganisms in the 0.1 m MF systems used for milk protein fractionation. 0 Furthermore, research showed that food bacteria reproduce the quickest at temperatures ranging between 21 and 47°C. 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. 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. 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). Materials: Two pieces of white bread; Four pieces of strawberry; One cup of milk; Ten grams of turmeric powder; Methylene Blue; 4 test tubes; Liquid Dropper Control: The control group in this experiment are the bread, strawberries, and milk without turmeric. As the increasing bacteria population in the cupboard milk samples continued to produce lactic acid, they were creating an unfavourable condition for themselves. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. The bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. Study for free with our range of university lectures! on different plates and compare the bacteria growth that results. %%EOF An experiment can be preformed to monitor the rate of bacterial growth in milk by testing the acidity of the milk liquid. Place the methylene blue in one of the test tubes. This indicates the succession of bacteria in the liquid. 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. 4 glass cups were labeled with the different types of milk: whole, skim, butter, and chocolate. 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. Growth of the bacterial flora of the milk itself was inhibited when powder or syrup was added, except with one syrup (S) which … Instead, their DNA floats in a tangle inside the cell. However, most bacteria cannot survive in very acidic environments; a low pH level. Do you have a 2:1 degree or higher? Among the samples left in the cupboard, the skim milk and chocolate milk showed the greatest amount of difference in appearance from day 0; the beginning, to day 6; the end of the experiment. You can view samples of our professional work here. 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. Furthermore, the lactobacilli bacteria existent in milk produced lactic acid by fermenting the sugars in milk. 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. Milk is a good source of all principal nutrients, including carbon, nitrogen and macro-minerals. Reference this. Procedure: Here: α-hemolysis (S. mitis, L); β-hemolysis (S. pyogenes, M); γ-hemolysis (also called non-hemolytic, S. salivarius, R). During conjugation, two bacterial cells with slightly different genetic make-ups were connected to each other through protein tube structures called pili. The protein in milk also provides a source of carbon the bacteria can use, in addition to lactose, as a fuel source. Warm temperature provided bacteria a favourable environment for reproduction which caused them to multiply quickly as opposed to cooler temperatures. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream V2 = volume of the inoculums (in this experiment, 50 ml) Substitute the values in the equation and V1 was calculated. 8 observation tables were created; 2 tables for each type of milk; fridge vs. cupboard. Another factor that could’ve influenced the outcome was the different expiry dates for the types of milk. 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. 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. 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 most common bacteria found in milk were the lactobacilli. No plagiarism, guaranteed! Many micronutrients such as vitamins and micro-minerals are also available. There were several factors that affect the rate of bacterial growth. Bacteria are one-celled, or unicellular, microorganisms. We're here to answer any questions you have about our services. 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. There were several factors that affect the rate of bacterial growth. Registered office: Venture House, Cross Street, Arnold, Nottingham, Nottinghamshire, NG5 7PJ. 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. In this lab everything went as originally planned. 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. In this experiment, you will qualitatively assess the presence of bacteria in milk using the methylene blue reductase test. Our academic experts are ready and waiting to assist with any writing project you may have. Various bacteria could grow in an environment with the pH level close to 7; hence in a close to neutral environment, bacteria reproduce rapidly. 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. During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. 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. Lastly, the sharp sour odour of the cupboard samples after a few days were produced by the lactic acid present in the milk. In general, a higher count was obtained in those samples containing 25% and/or 50% of … As the cell continued to grow, it would elongate and begin to form a septum between the two DNA molecules. If turmeric is applied to foods, then the growth of bacteria and fungi will be suppressed. Experimental Procedure #2:Repeat Experiment #1, using raw milk and pasteurized milk. All work is written to order. For thousands of years, fermented foods have been present in traditional diets around the world and continue to be widely consumed. Data representative of the results obtained in manyexperiments are presented in tables 1 and 2. The test tube with the methylene blue is your test sample. 57 0 obj <> endobj 6 . These protein molecules repelled each other, however when the pH level decreases, the molecules suddenly became attracted to each other forming chunks. Looking for a flexible role? Milk contains a significant amount of protein, a nutrient made of nitrogen-rich amino acids. The pH values were another factor that affected the bacterial reproduction in the milk samples. In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. 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. This process allowed new gene combinations to be introduced which may provide the daughter cells a better chance of adapting to the changing conditions. 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. Fission occurs rapidly in as little as 20 minu… 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. 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). Historically, communities produced fermented foods within the home, a practice that continues to this day in many settings. and growth. As bacteria grow and reproduce in milk, the pH level of milk drops. The donor bacterium would transfer all or part of its chromosome to the receiving bacterium. 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 Biology 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). Pour 9 ml milk into each test tube. 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). 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. A few factors were temperature, pH levels, water content, and available food sources. The main one was temperature. Free resources to assist you with your university studies! The most significant factor proven in this experiment was temperature. The factors that control the rate of bacterial growth discovered in this experiment could be applied to everyday life. 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. Growth over the course of the 5-week experiment in the 19 different groups of recipient mice ranged from 107 to 156% of the starting weight (averaged per group; table S6A). 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. Disclaimer: This work has been submitted by a university student. 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. The other 4 glass cups filled with different types of milk samples were placed in a cupboard/cabinet. From -30 degrees C (-22 degrees F) and below, bacteria growth slows rapidly. This suggests that non- refrigerated milk increases the growth of bacteria in milk, compared to refrigerated milk. 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. This was what happened at the molecular level when milk developed curd. 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. Furthermore, the results could’ve been different depending on how each individual perceived the changes that had occurred to the milk samples. Milk contained various compounds, the main ones being fat, protein, and sugar. 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… This is not an example of the work produced by our Essay Writing Service. Registered Data Controller No: Z1821391. 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). 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. Individual bacteria can only be seen with a microscope, but they reproduce so rapidly that they often form colonies that we can see. A preliminary experiment showed that two of the powders and one of the syrups had high bacterial counts, and the others had low counts. The greenish yellow liquid residue surrounding the floating clump was a solution of translucent whey. RESULTS Experiments with raw milk as inoculum. Extreme freezing. 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. h�bbd``b`�� � Hp5 � �b���灄� !+$�|��p5�� 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 growth rate of a bacterium is measured by measuring the change in bacterial number per unit time. VAT Registration No: 842417633. Warmer temperatures provoked bacteria to reproduce quicker as opposed to cold temperatures which restricted bacterial growth. 353. 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 then please: Our academic writing and marking services can help you! Or, you can press a variety of common objects like coins, combs, etc. They could be photoautotrophic, photoheterotrophic, chemoautotrophic, or chemo- heterotrophic. Bacteria count correlated highly with CO 2 but not with pH. This was because of the difference in the amounts of lactic acid present in the two groups of samples. In this type of experiment, bacteria is transferred directly to the prepared petri plate via direct contact. 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 … 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. The most common bacteria found in milk were the lactobacilli. A description of the appearance of the milk samples were made and noted in the appropriate observation table. When the chemical indicator, methylene blue, is added to the milk, the milk is turned blue. 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 lactobacillus bacteria existent in milk fermented the carbohydrates such as glucose and lactose in milk into lactic acid. 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.

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