Microorganism Detection in Foods: Approaches and Strategies with Types

The most effective method to identify microorganisms in food ?

Different methods can be utilized for assurance of microorganisms in food.

Some of them give complete count (viable+ non-suitable) while others give just feasible count.

1. Standard plate count (SPC):

Standard plate count gives suitable include of organic entity present in food.

System of performing standard plate include is given above in figure.

The quantity of living beings in unique food is controlled by counting the settlement on agar plate.

Two significant suppositions of SPC are:

Microorganisms in suspension are isolated as single cell so every state is created from single cell.

All suitable cells set on medium will duplicate and deliver a settlement

Brooding time and temperature for various microorganisms:

Psychrophilesà 7oC, 7 days

Mesophilesà 35oC, 24-48hrs

Thermophilesà 55oC, 48hrs


It gives feasible count.

It is incredibly delicate for example incredibly low and high microbial populace can be counted.


In the event that the suspension isn't homogenous and contain total of cells, the state count will be lower than the real number of microorganisms.

Assuming that the suspension contains various kinds of microorganisms, every one of them can't fill in a similar medium and under a similar condition.

Sorts of Standard plate count (SPC) strategy:

Pour plate strategy:

In this strategy, food is first and foremost sequentially weakened in proper diluent.

Then, at that point, estimated volume of test from weakened cylinder is put in petriplate.

Dissolved agar at 44-45oC is blended in with it.

Later homogenous blending of test with liquefied agar, it is saved for cementing.

Then, at that point, the petri plates are brooded at proper time and temperature.

Plate containing states between 30-300 is chosen and number of settlements are counted.

Presently, number of creatures in unique food test is determined by the accompanying equation:

Province shaping units (CFU/ml) = (Number of states/volume of test ) x weakening component

Since psychrophiles can't endure temperature of softened agar, this method isn't appropriate for them.

In this technique, both surface and subsurface states are created.

Subsurface settlements are hard to be secluded.

Spread plate procedure:

In this technique, suitably weakened example is put on the outer layer of hardened agar.

Then, at that point, the drop of test is spread over agar surface utilizing bowed glass pole.

Plate is hatched for adequate time and temperature, then, at that point, number of provinces are counted.

Computation of number or creatures is done in much the same way as in pour plate strategy.

This technique is appropriate for psychrophile likewise and just surface provinces are created.

Streak plate method:

In this method, an exchange circle is utilized to spread the particular volume of example over a surface of hardened agar.

The exchange is finished by aligned circle of explicit volume.

Once in a while, particular and differential media can be utilized to choose development of explicit living being.

2. Film channel strategy:

This procedure is especially essential to break down microorganisms in fluid food in which microbial substance is excessively low.

In this techniques, major estimated volume of fluid separated through layer channel of explicit porosity.

Then, at that point, channel cushion is taken out and set on the outer layer of agar plate and afterward brooded.

Microorganisms develop on surface of film channel to shape province.

Then, at that point, all out number of creatures in unique example is determined.

Supplement or particular agar media can be utilized for microbial development.

3. Most likely number (MPB) technique:

It is measurable procedure to decide number of creatures in example.

It gives most likely number however not the genuine number.

Turbidity, gas creation and corrosive creation are seen to decide microorganisms.

This strategy depends on 3 stages:

Possible test

Affirmed or corroborative test

Finished test

4. Direct infinitesimal count (DMC):

In this strategy, there is no contrast among dead and suitable cells.

Complete cells are counted.

In this strategy, the outcome is gotten quicker than most different techniques since brooding period isn't needed.

Methodology of Direct Microscopic Count is given in above diagram.

If there should arise an occurrence of fluid food, direct smear is made.

For strong food, it should be first split to 10-1.

Greasy food varieties should be defatted in xylene or CH3)2CO for arrangement of smear.

The xylene/CH3)2CO is then eliminated by plunging it in ethanol.

In this technique, number of microorganisms in tiny field are counted straightforwardly.

This procedure is broadly used to survey the nature of crude milk and other dairy item.

Breed count strategy:

It is an illustration of Direct Microscopic Count.

This strategy was at first evolved by R.S Breed.

In this technique, 0.01ml example is spread over 1cm square region on slide.

Assuming that example is greasy, it ought to be defatted with xylene or CH3)2CO.

Overabundance xylene or CH3)2CO is then taken out by plunging it into ethanol.

Then, at that point, slide is dried, fixed and stained with fitting color and saw under magnifying instrument.

Normal number of microorganisms per field is counted.

Then, at that point, space of infinitesimal not set in stone from which number of microorganisms in unique example is determined.

It isn't down to earth to count whole field.

Along these lines, just not many infinitesimal fields are built up to decide normal number of life forms in example.

Normal number of microorganisms Number of fields to be counted

0-3                                                                                  64

4-6                                                                                   32

7-12                                                                                   16

13-25                                                                             8

26-50                                                                            4

51-100                                                                            2

>100                                                                             1

Fig: Wilson's Chat

Benefits of DMC:

It is basic and quick strategy.

Morphology just as gram response of microorganism spore creation and so forth can be seen in magnifying instrument.

Tiny measure of test is required.

The pre-arranged slides can be put away and kept up with as long-lasting record.

Weaknesses of DMC:

DMC can't recognize feasible and non-practical cells.

Food particles are not generally discernable from microorganism's cell.

A few microorganisms don't take stain and may not be counted.

It is undeniably challenging to count microorganisms when the underlying burden is exceptionally high.

5. Electronic counter:

In this technique, standard volume of appropriate weakening of suspension is set in electronic counter.

The machine has little opening through which microorganisms can pass.

The entry of microorganisms through gap causes modification in electric opposition across it which is recorded as on motivations.

These driving forces are included by reasonable circuit in the counter.

Number of driving forces from fixed volume of test is utilized to ascertain number of organic entities in unique food test.

6. Color decrease test:

Two colors are generally utilized in color decrease test to assess reasonable number of life forms.

Methylene blue decrease test:

Methylene blue decrease test is generally used to decide number of reasonable living beings in crude milk.

In this technique, methylene blue is blended in with crude milk or hatched.

Microorganisms present in milk diminish methylene blue to shape leucomethylene blue so that milk becomes blue to boring.

The hour of decolorization of milk is characteristic of number of suitable living beings.

On the off chance that number of creatures are higher it is decolorized in more limited time as well as the other way around.

In this technique microbial nature of milk surveyed by decrease time.

Resazurin decrease test (fast test):

It is an illustration of fast color decrease test use to decide number of feasible organic entity in food like crude milk.

In this test, resazurin color is blended in with crude milk. Microorganism present in milk diminish resazurin to such an extent that its tone changed from flat blue to pink or lackluster.

Assuming that the quantity of microorganism is higher, color is diminished in more limited time and vieversa

Subsequently, microbial heap of milk can be anticipated by decrease season of resazurin. In this technique, result is gotten inside 10 mins.

Benefits of color decrease test:

It is basic, more straightforward, and modest test.

Just suitable cells effectively lessen the color. In this way, that number of feasible creature can be anticipated.

Hindrances of color decrease test:

Not all microorganisms lessen the color similarly.

They are not material for food that contain decreasing substances, for example, diminishing proteins except if exceptional advances are utilized.

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