They could be photoautotrophic, photoheterotrophic, chemoautotrophic, or chemo- heterotrophic. 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 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. 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… 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). 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. 8th May 2018 During conjugation, two bacterial cells with slightly different genetic make-ups were connected to each other through protein tube structures called pili. V2 = volume of the inoculums (in this experiment, 50 ml) Substitute the values in the equation and V1 was calculated. These bacteria converted the sugar in milk (lactose) into lactic acid (“Biochemical changes in,” 2014). These errors affected the analysis greatly since the information wasn’t specific and accurate. Bacteria count correlated highly with CO 2 but not with pH. 2 . Pour 9 ml milk into each test tube. Our academic experts are ready and waiting to assist with any writing project you may have. The greenish yellow liquid residue surrounding the floating clump was a solution of translucent whey. 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 … A small sample of the different types of milk (~50mL) was poured in the corresponding labeled glass cups. Milk contained various compounds, the main ones being fat, protein, and sugar. Bacteria reproduce when one cell splits into two cells through a process called binary fission. A description of the appearance of the milk samples were made and noted in the appropriate observation table. VAT Registration No: 842417633. In favourable conditions, bacteria would reproduce asexually through a type of cell division process called binary fission. Looking for a flexible role? 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 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 was an emulsified colloid where the protein molecules are suspended and dispersed within a water-based solution. 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. This lowered the pH level greatly which caused the death of bacteria. Extreme freezing. The low^count milk gives the greatest increase in bacterial count in … The odour of the samples of milk was described and recorded in the correct observation table. Extreme freezing can stop bacterial growth and/or kill bacteria altogether. Using your calibrated eye dropper or pipette, measure 1 ml methylene blue. Therefore, the greater amount of available food supply, the faster the bacteria multiply in the milk (“What is lactobacillus?,” 2014). RESULTS Experiments with raw milk as inoculum. 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). The temperature was taken for each sample of milk and recorded in the appropriate observation table. Milk is a good source of all principal nutrients, including carbon, nitrogen and macro-minerals. There were several factors that affect the rate of bacterial 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. 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. The nutrients in the four different types of milk were also a big factor that influenced the rate of bacterial growth. Here: α-hemolysis (S. mitis, L); β-hemolysis (S. pyogenes, M); γ-hemolysis (also called non-hemolytic, S. salivarius, R). 4 glass cups were labeled with the different types of milk: whole, skim, butter, and chocolate. During this method of asexual reproduction, the single DNA molecule would replicate to create a copy of its original single chromosome. 6 . All the milk samples kept in the cupboard developed curd after the six day observations; this was because of the ingredients in milk. Bacteria are one-celled, or unicellular, microorganisms. 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. Data representative of the results obtained in manyexperiments are presented in tables 1 and 2. The other 4 glass cups were labeled as; whole, skim, butter, and chocolate as well. If it takes less than 20 minutes, then there are over 20 million organisms/ml. The bacteria present in milk could be arranged into two main groups; pathogenic, and spoilage bacteria. 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. In this type of experiment, bacteria is transferred directly to the prepared petri plate via direct contact. 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. Quarters from infected cows have the potential to shed in excess of 10,000,000 bacterial cfu/ml of milk produced. Therefore, after a few days the pH values of buttermilk sample in the cupboards increased as more bacteria died and stopped producing lactic acid. Instead, their DNA floats in a tangle inside the cell. 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). 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. 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). endstream endobj startxref Take the lid off of the Petri dish (the lid is larger than the dish) and carefully cover the bottom-half of … 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. Company Registration No: 4964706. 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). 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