Bacterial Contamination Of Defrosted Food In Different Conditions Biology Essay

This experiment was carried out to look into and demo the effects of different dissolving methods of nutrient on the growing of bacteriums. Corn suspension was prepared utilizing consecutive dilution and introduced onto the agar home base by spread home base method. The grade of bacterial taint of the defrosted nutrient was represented by the figure of bacterial settlements formed on the agar.

After 48 hours of incubation, the figure of bacterial settlements found on the agar was measured and recorded. Aseptic technique was used throughout the experiment to better truth of the consequences as it could forestall taint. The information collected was analyzed by utilizing Kruskal-Wallis trial. The void hypothesis was rejected. The consequences supported the experimental hypothesis ; there are important differences in the growing of bacterial settlement on the agar by utilizing different dissolving methods. The best method to deice the nutrient is utilizing icebox.

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Freezing is a modern convenience for hive awaying and continuing food.

1 When nutrient is brought to a temperature of -18A°C ( 0A°F ) , the growing of the micro-organism is halted and the activity of the enzyme is greatly reduced. Besides, stop deading turns the H2O of course present in nutrients to frost crystals. Since liquids expand when they freeze, these crystals can interrupt the nutrient ‘s fragile cell construction. The more rapidly nutrient is frozen, the smaller the ice crystals will be and the less harm they will make to the nutrient construction.Defrosting the nutrient which is besides known as melt is a process to take the nutrient from hoar or ice. 2 The nutrient is warmed so that it can be prepared and served. Frozen nutrient should be defrosted in either really hot or cold conditions, where micro-organisms will non boom. Extreme heat will perforate and deice veggies really rapidly whereas at low temperature, the activity of the bacterium is slowed down and finally stopped.

The experiment is aimed to rede people based on probe consequences on the safest manner to deice nutrient by comparing the consequence of different methods of deicing the nutrient on the growing of the bacteriums.In this experiment, frozen maizes were used as it was safer than to utilize meat. Bacteria nowadays in the uncooked meat might incorporate pathogens that were harmful to the individual transporting out the experiment. 5 However, the frozen maizes could non to the full and absolutely represent the different categories of nutrient as a whole. Therefore, the consequences might differ for other categories of nutrient and farther plants could be done by transporting out on the experiment with other categories of nutrient.( 438 words )

Experimental HYPOTHESIS:

There is a important sum of bacterial growing in the defrosted nutrient matching to the different methods of defrosting.


There is no important difference in bacterial growing on the agar home base corresponding to the different methods of defrosting.


Manipulated: Different methods of deicing the frozen maizesReacting: The figure of bacterial settlements formed on agarChangeless: Temperature of incubation, continuance of incubation, thickness and composing of agar, volume and concentration of solution.


Petri dishes, label spines, 20uL micropipette, braces of sterilised forceps, stamp and howitzer, weighing balance, Bunsen burner, trial tubings, trial tubing rack, unfertile glass rod, vortex machine, brooder, autoclave.


70 % ethyl alcohol, unfertile distilled H2O, molten alimentary agar, antiseptic solution ( Dettol ) , frozen maizes, unfertile 1cm3 syringe, unfertile 10cm3 syringe. ( 565 words )



A test experiment was carried out to find the volume and dilution of the solution required for the experiment and the suitableness of the methods and processs.

In this test, two volumes were chosen, 10 AµL and 20AµL. A micropipette was used to mensurate the maize suspension to be introduced to the agar. Spread home base method was used to distribute the dilution equally over the agar by utilizing the unfertile glass rod. Besides, a consecutive dilution was carried out to find the most appropriate dilution for all the 8 samples.

5cm3 of unfertile H2O was added to 5g of the maize sample. The maizes were crushed by utilizing pestle and howitzer. The stock solution was vortexed utilizing a vortex machine. The samples were diluted to different concentrations to bring forth a little figure of settlements on each agar home base. Each 10AµL and 20AµL of the dilutions was spread on the agar home bases.

These were repeated with the different samples. The agar home bases were incubated for 48 hours. The figure of bacterial settlements formed on the agar was counted.The agar home bases were labeled with alphabets for easiness of work.A – Defrosted by utilizing the microwaveB – Defrosted under the sunshineC – Defrosted by utilizing the conventional ovenD – Defrosted at room temperatureE – Defrosted in a bucket of cold H2OF – Defrosted in the iceboxG – Frozen maizes ( positive control )H – Sterile distilled H2O ( negative control )( 803 words )

Tests result

10AµL of maize suspensionDilutionNumber of Bacterial ColonyABacillusCCalciferolTocopherolFGram10-11351251068342513710-2128112977431422510-31161047263TFTC34TFTC10-495796851TFTCTFTCTFTC10-583645645TFTCTFTCTFTCTable 120AµL of maize suspensionDilutionNumber of Bacterial ColonyABacillusCCalciferolTocopherolFGram10-1TNTCTNTC228189831035710-222520417914768894210-32001851651325564TFTC10-41761631411114056TFTC10-515414812891TFTC37TFTCTable 2( 934 words )From the consequences obtained from the tests, 20AµL of the dilutions and the concentration of the dilution ( 10-2 ) were selected. 20AµL was chosen as some of the stock solution may stay on the glass rod and resulted in less bacterial settlements formed on the agar home base.

Concentration of the dilution ( 10-2 ) was appropriate as agar home bases that had 30 to 300 settlements were statistically valid 3 and suited for numbering. It was because a home base with less than 30 settlements was less accurate and dependable and would ensue in higher per centum mistake. However, a home base with more than 300 settlements would be excessively hard to be seen clearly and counted. For the agar home base with less than 30 settlements, the information was recorded as excessively few to number ( TFTC ) and for the home base with more than 300 settlements, the information was indicated as excessively legion to number ( TNTC ) .

3( 1083 words )


Fixing Agar Home plates

The oral cavity of the conelike flask incorporating the unfertile molten agar was flamed by utilizing a Bunsen burner.In the laminar flow chamber, the palpebra of the Petri dish was lifted every bit small as possible when pouring the agar to the home base.The agar was poured until half of the Petri dish and no air bubbles were trapped in the agar.

The agar was set aside to solidify at room temperature.Stairss 1 to 4 were repeated for the staying 23 Petri dishes.The Petri dishes were labeled and the replicates were differentiated by 1, 2 and 3 severally.

Fixing Inoculum Using Serial Dilution

5g of the maizes were weighed by utilizing the electronic deliberation balance.5ml of sterile distilled H2O was added to the maizes.The maizes were crushed every bit finely as possible by utilizing pestle and howitzer.

The maize suspension was vortexed by utilizing a vortex machine.9cm3 of sterile distilled H2O was added to each of the two trial tubings by utilizing a 10cm3 syringe.1cm3 of the maize suspension was transferred by utilizing a 1cm3 syringe to the first trial tubing labeled A ( I ) . This was the 10-1 solution. The solution was assorted good.1cm3 of the solution from the 10-1 solution was transferred to the 2nd trial tubing labeled A ( two ) . This was the 10-2 solution that would be used in the experiment.

Stairss 1 to 7 were repeated for the maize samples defrosted in different status and sterile distilled H2O.( 1349 words )

Introducing Inoculum to the Agar Plate

20AµL of the solution from trial tubing labeled A ( two ) was transferred to the agar home base by utilizing a micropipette.The palpebra of the Petri dish was lifted every bit small as possible to forestall entry of other bacteriums from milieus.The solution was spread equally onto the surface of agar by utilizing a unfertile glass rod.

This was known as the spread home base method.Stairss 1 to 3 were repeated with different replicates and the maize samples of different method of deicing.The Petri dishes were placed inverted in the brooder at 30A°C for 48 hours.

The figure of bacterial settlement formed on the agar was counted and tabulated.( 1470 words )


Laminar flow chamber was used in the experiment to forestall taint of the agar. Aseptic technique was used throughout the experiment to forestall bacterial taint in the agar and the topographic point carry oning the experiment. 70 % ethyl alcohol was used to pass over the tabular array top before and after carry oning the experiment. Handss were cleaned by utilizing Dettol before managing the sterilized setup to avoid the setup from being contaminated.

These steps were taken to better the truth of the consequences. Baseball gloves were worn throughout the experiment. Glass wares such as trial tubings and glass rod were handled with attention. Sterile setup and distilled H2O were used to end any other bacteriums that might be present. Petri dish palpebras were lifted every bit little as possible when pouring the agar and presenting the inoculants.

The oral cavity of the flask incorporating agar was flamed to guarantee that there was no taint due to any other bacteriums. The micropipette was used with attention. When sucking up the solution, the boss should non be released excessively fast as air bubbles could organize in the tip. This would cut down the existent solution needed for the experiment and lead to inaccuracy of the consequences. The used nipples of the micropipette were discarded into the biohazard disposal container incorporating bactericidal solution. The Petri dishes were sent for autoclaving before disposal at the terminal of the experiment.( 1701 words )


Wayss of Defrosting CornsNumber of bacterial settlement units formedReplicate 1Replicate 2Replicate 3A233217228Bacillus200203205C180189181Calciferol153147129Tocopherol647375F879989Gram413849Hydrogen000Table 3( 1761 words )( 1761 words )

Statistical Analysis:

I chose Kruskal-Wallis trial as a mean to analyse the information. It was the nonparametric analysis of discrepancy by ranks.

4 It was because this trial was used to compare more than three samples to find if they came from equal populations.Wayss of Defrosting CornsNumber of Bacterial Colony FormedRankSum of DatasMean of DatasSum of RankMean of RankMedian of DatasDefrosted in the microwave23324.0678.0226.069.023.

0217.021722.022823.0Defrosted under sunshine20019.0608.


020521.0Defrosted in the oven18016.0550.0183.


018918.018117.0Defrosted at room temperature15315.0429.


0147.014714.012913.0Defrosted in the icebox647.


0Defrosted in a bucket of cold H2O8710.0275.091.733.011.089.09912.

08911.0Frozen maizes415.0128.


0Sterile distilled H2O02.00.00. 4( 1950 words )I± = 0.

05Degree of Freedom, df:df = k-1, where k= figure of groupsdf = 8-1 = 7Kruskal-Wallis trial value / Chi Square value, H:Degree centigrades: UsersUserDesktopUNIT 6formula.gifWhere H = Kruskal-Wallis trial value/ Chi Square valueN = Total figure of observations in all samplesTi2 = Square of the amount of rank of each groupn = entire figure of observations in each groupThe significance degree, I± = 0.05. The H value calculated harmonizing to the expression is 22.68. The grade of freedom calculated utilizing the expression is 7.

Therefore, critical value, I‡2 was obtained from the Chi-square tabular array. It was found out that the when the grade of freedom is 7, the I‡2 is 14.0671 at 5 % significance degree. ( Refer to appendix 1 for the Chi-square tabular array. )The H value that was calculated was 22.

68 which was greater than I‡2 = 14.0671. Therefore, void hypothesis was rejected.( 2107 words )

DATA Analysis:

A saloon chart of figure of bacterial settlements against ways of deicing maizes was plotted. Mistake bars were displayed on the saloon chart to demo the overall distribution of the information. The mistake bars did non overlap each other indicating that the agencies are statistically different.From the consequences that were obtained from the Kruskal-Wallis trial, it clearly showed that different methods of deicing the nutrient had different effects on the growing of the bacterium as the void hypothesis was rejected and there was adequate groundss to back up that the different methods of deicing would ensue in at least one set of differences in the growing of bacteriums.

From table 3, it was clearly shown that the best method to deice the frosted nutrient was to deice it in the icebox. It was because this method merely recorded 71 bacterial settlements when compared to the remainder. It was because at low temperature, the micro-organisms would non boom and therefore would non take to nutrient spoilage. Although it was the slowest method but it was the safest method to deice the nutrient. It was because the nutrient was still in good status and remained safe to be consumed.

This was followed by deicing in a bucket of cold H2O that recorded with a mean of 92 bacterial settlements with a difference of 21. This method was faster than icebox dissolving but required more attending. The defrosted nutrient must be stored in a plastic bag and placed in cold H2O, altering the H2O every 30 proceedingss so it would go on to dissolve.

It was because cold H2O would keep the encompassing temperature at a comparatively low temperature as compared to room temperature. It could assist to decelerate down the bacterial growing and therefore decreased the bacterial taint of the nutrient.( 2407 words )However, the least preferred method of deicing nutrient would be to deice it in the microwave which was the most convenient and common manner used by the people today. This method recorded the largest sum of bacterial settlement formed on the agar, with a mean of 226. While in the procedure of defrosting, outer bed might go warm and get down to cook.

Microbes would boom on defrosted nutrient as danger zone of temperature was reached and the nutrient was non cooked instantly after deicing.Frozen maizes were used as the positive control to demo that there were even bacteria nowadays in the frozen nutrient ab initio and the bacterial growing was due to the presence of the bacteriums in the nutrient. Sterile distilled H2O was used as the negative control to demo that debut of sterile distilled H2O would non do any bacteriums growing. This showed that agar itself will non advance the bacteriums growing and the sterile techniques were carried out suitably to guarantee that there was no taint from the milieus.( 2579 words )


Justifications of the usage of the stuffs and setup:

In this experiment, the volume of the dilution needed is 20AµL. Micropipette was used to mensurate accurately and distribute the dilution on the agar. Petri dishes were chosen to put the agar and let the growing of bacteriums.

Petri dishes were crystalline and we could detect the advancement of the experiment and record the figure of bacterial settlement formed on the agar easy.

Potential mistakes during the experiment

Mistakes may hold occurred due to bacterial infection because the oral cavity of the agar bottle was non flamed plenty. Besides, the maizes might non be crushed finely adequate and the suspension were non concentrated plenty for the bacteriums to turn.

Wayss to guarantee the dependability and preciseness of the consequences

A few stairss were taken to do certain that the consequences obtained from the experiment were accurate and dependable. First, the agar was poured at around 50A°C. It was because at this temperature, the agar was non excessively hot to be handled and would do less condensation in the Petri dishes doing the computation of the bacterial settlement less accurate.Second, the Petri dishes were placed upside-down inside the brooder to forestall H2O vapor from dripping onto the agar. If the H2O dropped on the turning bacteriums, it would be contaminated and lead to inaccuracy of the consequences.Third, none of the setup that were to be kept unfertile were removed or brought out of the laminar flow chamber throughout the experiment. It was to forestall bacterial taint from the surrounding.( 2838 words )


There was still some inevitable taint although safeguards had been taken and sterile techniques were carried out.

It may be due to the gap of the palpebra of the Petri dish during debut of dilution to the agar. Microorganisms in the surrounding might come in and take to taint. Furthermore, the different parts of maize might hold different degrees of susceptibleness to bacterial growing, taking to differences in the sum of bacterial growing.( 2911 words )

Further Work:

Further work could be carried out by utilizing different types of nutrient that was defrosted, non merely veggies but besides meat safely in a more advanced research lab.

This could demo that which type of nutrient is more prone to taint by bacteriums. Furthermore, nutrient taint was caused by many factors. Merely one factor was studied in this experiment. Other factors, for illustration, the relationship between method of dissolving and the method of cookery can be studied excessively.


Based on the consequences obtained and the statistical analysis, it can be concluded that different ways of deicing the nutrient have different consequence on the growing of bacteriums. Null hypothesis was rejected. Statistical analysis showed that there were important differences in figure of bacterial settlement formed on the agar at 5 % significance degree. The best method was chosen, that was to deice the frozen nutrient in the icebox.

( 3059 words )

Evaluation OF Beginnings:

Beginning 1, 4 and 9 are published books by the well-known writers that have been reviewed and up to day of the month. Thus the information is dependable and accurate.Beginning 2 is an on-line lexicon from Cambridge University imperativeness. It is the most popular online lexicon and synonym finder for scholars of English. So, the definition of defrosting is right and acceptable.Beginning 3 is a website created by the Northern Illinois University ( NIU ) .

The information is written and provided by the NIU Department of Biological Sciences therefore I t is trustable and acceptable.Beginning 5 and 7 is a website specifically designed for supplying illustrations of biological science practical by The Nuffield Foundation & A ; Society of Biology. The information provided had been reviewed before published.Beginning 6 is a website that provides 100s of free text and video-based talks on statistics. There are professionals that published the lectors online so the information should be factual.

Beginning 8 is a diary that obtained from the library database available in the college. The diary article used was written by the bookmans. It had gone through legion alterations before it is published.( 3248 words )


Appendix 1: Chi-Square Table





















885245.641754.0522740.113346.963055.4762841.337248.278256.8922942.556949.587958.3023043.772950.892259.7034055.758563.690773.4025067.504876.153986.6616079.081988.379499.6077090.5312100.425112.31780101.879112.329124.83990113.145124.116137.208100124.342135.807149.449Table from hypertext transfer protocol: // 3408 words )

Appendix 2: Degree centigrade: UsersUserDocumentscindycrop ori.jpg

Degree centigrades: UsersUserDocumentscindycrop result.jpgDiagrams demoing one set of the consequences from the existent experiment on methods of deicing in the icebox. Diagram at the top was taken before the experiment and diagram at the underside was taken after 48 hours incubation. ( 3448 words )


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