of bacterial growth while experiment 2 had the least amount of bacterial growth. Company Registration No: 4964706. As the cell continued to grow, it would elongate and begin to form a septum between the two DNA molecules. 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. *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. The pH level was taken for each milk sample and recorded in the appropriate observation table. 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. 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 Kingdom Bacteria consisted of anaerobic unicellular microorganisms with exceptional abilities of adapting to wide ranges of environment conditions. 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. 57 0 obj <> endobj The donor bacterium would transfer all or part of its chromosome to the receiving bacterium. Experimental Procedure #2:Repeat Experiment #1, using raw milk and pasteurized milk. The greenish yellow liquid residue surrounding the floating clump was a solution of translucent whey. Milk contained various compounds, the main ones being fat, protein, and sugar. 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 Copyright © 2003 - 2020 - UKEssays is a trading name of All Answers Ltd, a company registered in England and Wales. 4 glass cups each with a different type of milk sample were placed in the fridge. In this type of experiment, bacteria is transferred directly to the prepared petri plate via direct contact. 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. From simple essay plans, through to full dissertations, you can guarantee we have a service perfectly matched to your needs. Procedure: 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. You can view samples of our professional work here. 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). All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. Subsequently, the model was extended with the average competition coefficients (E-BR–GD model) that represented quantitative relations among the populations. This was what happened at the molecular level when milk developed curd. A preliminary experiment showed that two of the powders and one of the syrups had high bacterial counts, and the others had low counts. If it takes 20 minutes to 2 hours, then there are 4 to 20 million organisms/ml of milk. If the factors were considered, one would be able to control the growth of bacteria. Our academic experts are ready and waiting to assist with any writing project you may have. 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! Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. Here: α-hemolysis (S. mitis, L); β-hemolysis (S. pyogenes, M); γ-hemolysis (also called non-hemolytic, S. salivarius, R). 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. 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. 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. 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. In general, a higher count was obtained in those samples containing 25% and/or 50% of … Clinical Focus: Nataliya, Resolution. 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. %PDF-1.3 %���� However, milk is unique with respect to its sugar. No plagiarism, guaranteed! Quarters from infected cows have the potential to shed in excess of 10,000,000 bacterial cfu/ml of milk produced. Pour 9 ml milk into each test tube. Furthermore, research showed that food bacteria reproduce the quickest at temperatures ranging between 21 and 47°C. V2 = volume of the inoculums (in this experiment, 50 ml) Substitute the values in the equation and V1 was calculated. 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. A population of bacteria could increase greatly in a fairly little amount of time considering that they reproduce exponentially. Instead, their DNA floats in a tangle inside the cell. Hyperthermophilic bacteria will grow extreme heat, 70 to 110 degrees C (158 to 230 degrees F). Using your calibrated eye dropper or pipette, measure 1 ml methylene blue. A small sample of the different types of milk (~50mL) was poured in the corresponding labeled glass cups. of growth of the bacteria in differently pretreated milks were carried out on the basis of these data. Bacteria are one-celled, or unicellular, microorganisms. 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. 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. Most bacteria preferred to live in a pH value of 7; neutral. During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. 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). Place the methylene blue in one of the test tubes. There was no significant relationship between growth phenotypes and bacterial diversity in the fecal microbiota of recipient animals (table S6A). This process allowed new gene combinations to be introduced which may provide the daughter cells a better chance of adapting to the changing conditions. 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. Milk provides the newborn (neonate) with nutrients and an array of antimicrobial factors. 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. When the chemical indicator, methylene blue, is added to the milk, the milk is turned blue. This is not an example of the work produced by our Essay Writing Service. Therefore, the greater amount of available food supply, the faster the bacteria multiply in the milk (“What is lactobacillus?,” 2014). 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. These errors affected the analysis greatly since the information wasn’t specific and accurate. 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. As the increasing bacteria population in the cupboard milk samples continued to produce lactic acid, they were creating an unfavourable condition for themselves. Historically, communities produced fermented foods within the home, a practice that continues to this day in many settings. 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 bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. "B����`��_�@���ϸ�@� ,S However, most bacteria cannot survive in very acidic environments; a low pH level. Various bacteria could grow in an environment with the pH level close to 7; hence in a close to neutral environment, bacteria reproduce rapidly. 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). There were several factors that affect the rate of bacterial growth. A description of the appearance of the milk samples were made and noted in the appropriate observation table. This suggests that non- refrigerated milk increases the growth of bacteria in milk, compared to refrigerated milk. %%EOF 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. on different plates and compare the bacteria growth that results. 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 test tube with the methylene blue is your test sample. 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. The other 4 glass cups were labeled as; whole, skim, butter, and chocolate as well. The most common bacteria found in milk were the lactobacilli. Or, you can press a variety of common objects like coins, combs, etc. The effect of water dilution on bac- terial growth as measured by logarithms of bacterial counts made after 6 hr. These errors would’ve altered the observations that were made significantly. 353. This was because of the difference in the amounts of lactic acid present in the two groups of samples. The factors that control the rate of bacterial growth discovered in this experiment could be applied to everyday life. 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 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. If you need assistance with writing your essay, our professional essay writing service is here to help! Mastitis organisms The most significant factor proven in this experiment was temperature. This lowered the pH level greatly which caused the death of bacteria. 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). The final stage of bacterial growth byBacillus 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). 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. This indicates the succession of bacteria in the liquid. 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). It could be concluded that several factors influenced the bacterial growth rate in milk. The pH values also affected the bacterial growth rate. Individual bacteria can only be seen with a microscope, but they reproduce so rapidly that they often form colonies that we can see. Milk contains a significant amount of protein, a nutrient made of nitrogen-rich amino acids. RESULTS Experiments with raw milk as inoculum. of incubation is indicated (Figure 1). An experiment can be preformed to monitor the rate of bacterial growth in milk by testing the acidity of the milk liquid. 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. 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. 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. If it takes less than 20 minutes, then there are over 20 million organisms/ml. 6 . 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. In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. Generation time is the time required for a bacterium to give rise to two daughter cells under optimum conditions. endstream endobj startxref 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. Moreover, bacteria commonly grew in distinguishing arrangements. Looking for a flexible role? The growth rate of a bacterium is measured by measuring the change in bacterial number per unit time. 0 The pH levels of all the milk samples excluding the buttermilk, were very close the neutral, therefore they encouraged bacterial growth. 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. 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). We've received widespread press coverage since 2003, Your UKEssays purchase is secure and we're rated 4.4/5 on reviews.co.uk. These protein molecules repelled each other, however when the pH level decreases, the molecules suddenly became attracted to each other forming chunks. Many micronutrients such as vitamins and micro-minerals are also available. VAT Registration No: 842417633. Milk is a good source of all principal nutrients, including carbon, nitrogen and macro-minerals. Furthermore, the lactobacilli bacteria existent in milk produced lactic acid by fermenting the sugars in milk. Milk was an emulsified colloid where the protein molecules are suspended and dispersed within a water-based solution. 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. 4 glass cups were labeled with the different types of milk: whole, skim, butter, and chocolate. 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. endstream endobj 58 0 obj <> endobj 59 0 obj <> endobj 60 0 obj <>stream Bacteria could obtain energy from various sources. 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… 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. 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. 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). 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). Fission occurs rapidly in as little as 20 minu… The nutrients in the four different types of milk were also a big factor that influenced the rate of bacterial growth. 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. The most significant factor proven in this experiment was temperature. 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. Extreme freezing can stop bacterial growth and/or kill bacteria altogether. 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