Food Micro S2 III

8/3/2019 Food Micro S2 III

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MIKROBIOLOGI PANGAN LANJUT(Advanced Food Microbiology)

Kuliah III

POST GRADUATE PROGRAM OF FOOD SCIENCE AND TECHNOLOGYPOST GRADUATE PROGRAM OF FOOD SCIENCE AND TECHNOLOGY

FACULTY OF AGRICULTURAL TECHNOLOGYFACULTY OF AGRICULTURAL TECHNOLOGY

UNIVERSITYUNIVERSITY OF BRAWIJAYA , MALANG -BRAWIJAYA , MALANG - EAST JAVA - INDONESIAEAST JAVA - INDONESIA


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Determining M.O.Determining M.O.

And/or Their ProductsAnd/or Their Productsin Foodsin Foods


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Culture, Microscopic, andCulture, Microscopic, and

Sampling MethodsSampling Methods

BBasic to food microbiologyasic to food microbiology :E:Examination ofxamination offoods for the presence, types, and numbersfoods for the presence, types, and numbers

of mof m.o..o. and/or theirand/or theirproductsproducts

None of the methodsNone of the methods in common use permitsin common use permitsthe determination of exact numbers of mthe determination of exact numbers of m.o..o. inin

a food producta food product..

SSome methods of analysis are better thanome methods of analysis are better thanothers, every method has certain inherentothers, every method has certain inherent

limitationslimitations associated with its useassociated with its use


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The four basic methods employed forThe four basic methods employed for

total numbers are as follows:total numbers are as follows:

1. Standard plate counts (SPC) or aerobic plate1. Standard plate counts (SPC) or aerobic plate

counts (APC) for viable cells or colony formingcounts (APC) for viable cells or colony forming unitsunits

(cfu).(cfu).

2. The most probable numbers (MPN) method as a2. The most probable numbers (MPN) method as astatistical determination of viable cells.statistical determination of viable cells.

3. Dye reduction techniques to estimate numbers of3. Dye reduction techniques to estimate numbers of

viable cells that possess reducing capacities.viable cells that possess reducing capacities.

4. Direct microscopic counts (DMC) for both viable4. Direct microscopic counts (DMC) for both viable

and nonviable cells.and nonviable cells.


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1.CONVENTIONAL STANDARD PLATE COUN1.CONVENTIONAL STANDARD PLATE COUNT

By the conventional SPC methodBy the conventional SPC method::

PPortions of food samples are blended orortions of food samples are blended or

homogenizedhomogenized

SeriallySerially diluted in an appropriate diluentdiluted in an appropriate diluent

PPlated in or onto a suitable agar medium, andlated in or onto a suitable agar medium, andincubated at anincubated at an appropriate temperature for a givenappropriate temperature for a given

timetime..

AAll visible colonies are counted by use of all visible colonies are counted by use of a QuebecQuebecor electronic counter.or electronic counter.


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The SPC is by far the most widely usedThe SPC is by far the most widely used

method for determining themethod for determining the numbers ofnumbers of

viable cells or colony-forming units (cfu)viable cells or colony-forming units (cfu)

in a food product.in a food product.

Among the disadvantages ofAmong the disadvantages ofSPCSPC areare

the problem of spreaders (especiallythe problem of spreaders (especially

when the agar surface is notwhen the agar surface is not

adequately dry prior to plating) andadequately dry prior to plating) and thethe

crowding of colonies, which makescrowding of colonies, which makes

enumeration more difficultenumeration more difficult


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Total viable countsTotal viable counts reported for a product shouldreported for a product should

be viewed as function ofbe viewed as function ofthethe following factors:following factors:

1. Sampling methods employed1. Sampling methods employed2. Distribution of the organisms in the food sample2. Distribution of the organisms in the food sample

3.3. Nature of the food biotaNature of the food biota

4. Nature of the food material4. Nature of the food material

5. The preexamination history of the food product5. The preexamination history of the food product

6. Nutritional adequacy of the plating medium employed6. Nutritional adequacy of the plating medium employed

7. Incubation temperature and time used7. Incubation temperature and time used

8. pH, water activity (8. pH, water activity (aw ), and oxidationreduction potentialaw ), and oxidationreduction potential

(Eh) of the plating medium(Eh) of the plating medium

9. Type of diluent used9. Type of diluent used

10. Relative number of organisms in food sample10. Relative number of organisms in food sample

11. Existence of other competing or antagonistic organisms.11. Existence of other competing or antagonistic organisms.


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2. MOST PROBABLE NUMBERS2. MOST PROBABLE NUMBERS

1. It is relatively simple.1. It is relatively simple.

2. Results from one laboratory are more likely than2. Results from one laboratory are more likely than

SPC results to agree with those from anotherSPC results to agree with those from another

laboratory.laboratory.

3. Specific groups of organisms can be determined by3. Specific groups of organisms can be determined by

use of appropriate selective and differentialuse of appropriate selective and differential media.media.

4. It is the method of choice for determining fecal4. It is the method of choice for determining fecalcoliform densitiescoliform densities


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3.3. DYE REDUCTIONDYE REDUCTION

Two dyes are commonly employed in this procedureTwo dyes are commonly employed in this procedure

to estimate the number of viable organisms into estimate the number of viable organisms in

suitable products: methylene blue and resazurin.suitable products: methylene blue and resazurin.

CConductonductinging a dye-reduction testa dye-reduction test::

PProperly prepared supernatants of foods are added toroperly prepared supernatants of foods are added to

standard solutions of either dye for reduction from blue tostandard solutions of either dye for reduction from blue to

whitewhite for methylene blue; and from slate blue to pink orfor methylene blue; and from slate blue to pink or

white for resazurin.white for resazurin.

The time for dye reduction toThe time for dye reduction to occur is inverselyoccur is inversely

proportional to the number of organisms in the sample.proportional to the number of organisms in the sample.


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4.4. DIRECT MICROSCOPIC COUNTDIRECT MICROSCOPIC COUNT

(DMC)(DMC)

In its simplest form, the DMC consists ofIn its simplest form, the DMC consists of::

MMaking smears of food specimens oraking smears of food specimens or

cultures onto acultures onto a

microscope slidemicroscope slide

.

.

SStaining with an appropriate dye,taining with an appropriate dye,

VViewing and counting cells with the aid ofiewing and counting cells with the aid of

aa microscope (oil immersion objective).microscope (oil immersion objective).

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Food Micro S2 III