Food Safety

Table of Contents

1.0 Abstract

2.0 Introduction

3.0 Materials and Methods

4.0 Results

5.0 Discussion

6.0 Conclusion

References

1.0 Abstract on Enumeration of Microbes from Food

The research study focuses on the microbial growth in food samples collected from various sources. Also this experiment is used to count the microbial colonies. This microbial growth is inherent property of the food’s natural micro biota and thus microbes were used in preparation of such foods. Then the microbial colonies were enumerated from the collected food samples. Products used for sample preparation were converted into homogenized mixture and it was are representative of the whole sample. Also the direct concentrated samples were not used and serial dilutions were prepared for the samples for analyzing microbial growth on spread plates.

2.0 Introduction to Enumeration of Microbes from Food

The microbes being unicellular in nature reproduce and increase their count, to produce an entire microorganism by replicating. Microbe enumeration is an important process to check microbe growth patterns and also apoptosis. The enumeration methods(Kramer 1978) are a direct measure for analyzing the number of microbial cells in form of colonies for analyzing cell mass and cell constituents.

But this microbial growth is hazardous and proper safety measures need to be established to avoid contamination in the samples. Also the spread of such microbial spores can disturb the ecological balance and cause widespread devastation. Therefore it is important to do the enumeration and microbial growth under controlled conditions , so that there is no disease outbreak. Use of a stomacher enables homogenous mixing of the samples with a suitable solution, for release of microbes present in the food. The food samples used were Coleslaw and Salami to check for microbial load.

Also it is important to use serial dilutions, rather than concentrated samples. This is done to reduce the bacterial load in the food to certain permissible levels as per set standards.

The bacterial serial dilutions were used for inoculation and further growth of microbial cells using agar media in either pourplate technique or spread plate technique. Neo films (Hsih and Tsen 2001) were developed for checking microbial growth and enumeration. The objective is to check the microbial growth and thus enumeration from food samples by reducing the microbial growths to certain permissible levels and also to avoid overgrowth and crowding , that makes enumeration difficult.

3.0 Materials and Methods of Enumeration of Microbes from Food

HSN204 Food Safety Practical Manual-Part 2, Trimester 2, 2020 ,page number-13.

4.0 Results of Enumeration of Microbes from Food

Table 1: Microbial load of food samples using different methods of enumeration

Food item	Technique	Dilution used for counting	Colony count	Dilution factor	Volume of inoculum	Total plate count cfu/g
e.g. Sushi	Pour plate	10^-3	276	10⁴	0.1	2.76E+06
	Spread plate	10^-1	136	10²	0.1	1.36E+05
	NeoFilm (Aerobic Count)	10^-3	184	10⁴	0.1	1.84E+06
	NeoFilm (Yeast and mould)	10^-1	3	10²	0.1	Not countable

As given in the table, for calculating the total plate cfu:

Total plate count cfu/g =(no. colonies x total dilution factor) / volume of inoculums.

Determination of the total dilution factor in this case will be as follows; Dilution factor 1 will be recorded from the observation table as used in the procedure.

Dilution factor 2=10 (10 g of food sample was diluted with 90 mL of BPW in the stomacher bag)

Total dilution factor = Dilution factor 1 X Dilution factor 2

5.0 Discussion on Enumeration of Microbes from Food

The results generated after incubating the plates , revealed a significant microbial growth in different serial dilution used for the 3 methods i.e. spread plate, pour plate and neofilm method to count the microbial colonies. The microbial load in the sushi samples were high. But it is difficult to enumerate (Sharpe 1997) the colonies on NeoFilm (Yeast and mould) due to less microbial count. Also as interpreted from the results as the dilution increases, the number of colonies decrease. In addition to this the plate that were chosen for enumeration had 30-300 colonies growing on it. Colony Forming Units (CFUs) for each method differed as in case of spread plate the colonies grew on the surface of agar , in pour plate the colonies grew into and on the agar making it difficult to visualize as it was easy in spread plate method. Also in case of neo films two different growths were observed i.e. aerobic growth to check bacterial growth colonies and other other anaerobic yeasts and moulds. So it was observed that yeasts and moulds grew in very small numbers and were difficult to count whereas the aerobic neo film growth was still less than enumerated in spread plate method.

6.0 Conclusion on Enumeration of Microbes from Food

The enumeration is possible only when the food sample is made into a homogenous mixture that was made by stomacher. Also it is recommended to wear proper personal protective equipment so that microbial spores donot enter the respiratory tract and also to avoid any contamination on culture plates containing agar and also on neo films. The additional plates were made in each case so as to be precautious about the accuracy of results and to avoid any errors due to contamination in the plates due to environmental conditions .

The bacterial and fungal counts including the yeast and moulds were found in the pour plates, spread plates and neo films. The enumeration was best done in spread plate method as the colonies grew on surface of the solidified agar plates. Also the microbial loads in samples were too high even after diluting with Buffered peptone water.

The neo films also help in enumeration and recording bacterial growth but show microbial colonies less than growth in spread plate method.

References for Enumeration of Microbes from Food

Kramer, J. M., & Gilbert, R. J. . Enumeration of micro-organisms in food: a comparative study of five methods. The Journal of hygiene, 1978,81(1), 151–159.

Mossel D.A.A., Van Netten P., Van der Zee H. , Essentials of Enumeration and Identification Methods for Microorganisms Which Interfere with the Safety of Foods with Particular Reference to Simplification Avoiding the Use of Nonconventional Instrumentation., In: Habermehl KO. (eds) Rapid Methods and Automation in Microbiology and Immunology. 1985,Springer, Berlin, Heidelberg.

Gracias K. and. McKillip J.L ,A review of conventional detection and enumeration methods for pathogenic bacteria in food , Can. J. Microbiol. 2004,Vol. 50.

Blackburn, C., and McCarthy, J.D.. Modifications to methods for the enumeration and detection of injured Escherichia coli O157:H7 in foods. Int. J. Food Microbiol. 2000,55 ,pp. 285–290.

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