14th April, 2011.
Objectives/Aims
1) The aim of the experiment was to scrutinize food samples for the presence of microorganisms using the Australian Standard (AS) techniques to establish quality and safety of food produce for consumption.
2) The experiment is also aimed at comparing standard and new techniques of food sampling. This will assist in establishing the most efficient, convenient, cheap, reliable, sensitive and easy to use technique in analyzing food samples for the presence of microbial organisms.
Introduction
Microbial organisms in food can either be useful or poisonous if consumed. For years now, microorganisms have been used in the food processing industries. They have been used in the preservation process especially in the production of cheese, butter and fermented or minced meat. On the contrary, microorganisms like Salmonella typhi, Escherichia coli, Staphylococcus aureus, Clostridium perfrigens, Yersinia pestis and Cryptosporidium species and other coliforms have been debated to cause food poisoning, gas gangrene and other diseases. Australian Standard (AS) techniques among the modern methods of food analysis are essentially applied in examining the suitability of food samples for consumption. Therefore this paper basically evaluates and examines modern techniques of analyzing food samples and compares them with the traditional methods. These rapids tests are examined and evaluated for consistency, efficiency, ease, expediency, sensitivity and specificity. Some of these techniques are AS while some are not AS but both of them are critically scrutinized to establish the best techniques to embrace.
Apparatus/Equipments/Materials
-Buffered Peptone Water -Aerobic Count Plate -Vortex Mixers
-Stomacher
-Sterile test tubes
-Wide-bore pipettes - Spatulas
-Sterile Stomacher bags
-Plate Count Ager (PCA) - Salmonella-shigella LTB -RV Broth
-MKTTn broth
-Petri dishes
-Baird Parker Ager Plates (BPA) -Scalpels -Food sample
-Tryptose Broth
-Salmonella enrichment broth -PH Paper -Petrifilm spreader
-Pasteur Pipettes
-Water balance
-Paraffin Oil
-Oxidase strips
-Kovac’s Indole reagent
-Microbact I.D reagent
-Salmonella polyvalent O agglutination antiserum
Procedure (AS)
Multiple Tube Technique (MPN)
10 g of the food sample was weighed ascetically into a sterilized stomacher bag, obtaining five different samples from various parts of the food sample. 90 ml of 0.1 % peptone water was then added to yield a 1 in 10 dilution factor after which the mixture was blended for about 2 minutes using a stomacher. A 10-1 dilution was prepared by transferring 10 ml of the solution ascetically into a sterile test tube. Double strength Lauryl Tryptose Broth was incubated with 10 ml of 10-1 dilution while 12 tubes of single strength tubes of LTB was incubated with 1 ml of 10-1, 10-2, 10-3 and 10-4 dilutions. The tubes were incubated at 37° for 48 hours after which they were placed at 4° until the next practical session.
Aerobic Plate Count (Petrifilm TM Technique)
The cover of a Petrifilm TM Aerobic Count Plate was ascetically lifted for incubation. 1 ml of the innoculum of 10-6 dilution factor was then pipetted into the Petrifilm TM plate. Using the same pipette, the process was repeated using 10-5, 10-4, 10-3, 10-2 and 10-1 dilution factors after which, a Petrifilm TM spreader was used to spread the inoculums evenly. The plates were then incubated at 30° for a period of 48 hours after which the plates were replaced at temperatures of 4° until the next practical session.
Results
Microorganisms can either be beneficial or destructive when exposed to food (Microbiological Criteria, 2006). Microorganisms like Salmonella, E. coli, Shigella, Campylobacter and Serratia species when exposed to food may cause food spoilage and gas gangrene (Pico, 2008). From the experiment conducted, it can be deducted that AS methods of food analysis are efficient in analyzing and scrutinizing coliforms and other microorganisms. Pour Plate, Spread Plate and ParrafinTM methods employed all gave closely related results in relation to the number of MPN counts. This demonstrates the efficiency of AS methods of microbiological food analysis. From the above experiment, the Australian Standard method of MPN analysis gave 3 positive tubes for both 10-2 and 10-3 dilutions. For a dilution of 10-4, one positive tube was obtained while the final MPN count was 46. The final calculation of MPN per gram food gave 4, 600 bacteria. For the Petrifilm technique of food analysis, 10-1 and 10-2 dilutions gave MPN counts of more than 300 while dilutions of 10-3 and 10-4 gave MPN counts of 237 and 26 respectively. On the other hand, chromogenic agar method yielded 46 and 9 counts for 10-1 and 10-2 dilutions respectively (Hui & Khachatourians, 1995).
For S. aureus, the black and circular colonies observed were indicative of coagulase positive staphylococcus. The coagulase confirmatory test gave a positive result while presumptive counts gave MPN values of 2 and 13 for dilutions of 10-1 and 10-2 respectively. Also, presumptive tests for Salmonella species gave similar colony characteristics; pinkish circular colonies with dark centers. Confirmatory tests like Ortho-Nitrophenyl-β-D-Galactopyranoside (ONPG) test was negative while Kligler’s Iron Ager (KIA) test gave negative results for glucose and lactose. Additionally, Indole, Urea and Oxidase tests all were negative.
Conclusion
In conclusion, it can be deducted that AS techniques of food analysis are efficient in analyzing food for safety (ICMSF, 1996). Specifically, the Petrifilm technique of food analysis gave the best results hence the most sensitive method for analyzing food; more than 300 counts were obtained in 10-1 and 10-2 dilutions. In relation to Salmonella and S. aureus test results obtained, it can be concluded that raw food contains microorganisms. Therefore, it is very essential to maintain high quality in terms of food preservation to eliminate bacteria and other microorganisms (Marriot & Gravani, 2006).
References
Microbiological Criteria. (2006). MIG Part Three 2. Retrieved from < http://www.ukmeat.org/pdf/MIG3Final.pdf>
Pico, Y. (2008). Food Contaminants and Residue Analysis. Oxford: Elsevier. Retrieved from < http://books.google.co.ke/books?id=NdI74loMXDkC&printsec=copyright#v=onepage&q&f=false>
Raugel, P. J. (1999). Rapid Food Analysis and Hygiene Monitoring: Kits, Instruments, and Systems. New York: Springer-Verlag Berlin Heidelberg. Retrieved from < http://books.google.co.ke/books?id=upFdCm0uo_8C&printsec=copyright#v=onepage&q&f=false>
Australian New Zealand Food Standard Code (ANZFSC). Retrieved on April 16, 2011. From < http://www.foodstandards.gov.au/foodstandards/foodstandardscode.cfm>
International Commission on Microbiological Specifications for Food. (1996). Microorganisms in Food: Microbiological Specifications of Food Pathogens. New York, NY: ICMSF. Retrieved from < http://books.google.co.ke/books?id=lxycHnaPfCYC&printsec=frontcover&dq=FOOD+MICROORGANISMS&hl=en&ei=9pGpTbKmGMSdgQfluOHzBQ&sa=X&oi=book_result&ct=book-thumbnail&resnum=1&ved=0CC0Q6wEwAA#v=onepage&q&f=false>
Hui, Y. H., & Khachatourians, G. G. (1995). Food Biotechnology: Microorganisms. Hoboken: Wiley-VCH, Inc. Retrieved from < http://books.google.co.ke/books?id=TxCQlmasQh8C&printsec=frontcover&dq=FOOD+MICROORGANISMS&hl=en&ei=9pGpTbKmGMSdgQfluOHzBQ&sa=X&oi=book_result&ct=book-thumbnail&resnum=4&ved=0CDsQ6wEwAw#v=onepage&q&f=false>
Marriot, N. G., & Gravani, R. B. (2006). Principles of Food Sanitation. New York, NY: Springer Science+ Business Media, Inc. Retrieved from < http://books.google.co.ke/books?id=lCRxcp3gfhUC&printsec=copyright#v=onepage&q&f=false>
