Laboratory‎ > ‎Fruit juice

PURPOSE:

The purpose of this experiment was to investigate microbiological properties of orange fruit juice

THEORY:

In non-acid, moist foods, yeasts and moulds grow more slowly than bacteria and therefore seldom cause problems in such foods. However, in acid foods and foods of low water activity, they outgrow bacteria and thus cause spoilage losses especially if the products (e.g., fresh fruit and vegetables, frozen or dried foods) are improperly stored. Additionally, there is also the potential hazard form production of mycotoxins by moulds.

Humans should not consumer foods that are visibly mouldy. This excludes cheeses such as Roquefort or Camembert and certain salamis, which owe their special flavours to mould. Their presence is of little significance in fresh and frozen foods. One can expect to find small numbers of spores and yeast cells present in these foodstuffs. Consumers will recognise spoilage when very high numbers of yeast or visible moulds are present. It must be noted that yeast spoilage is not a hazard to health.

MATERIALS:

  • Tubes

  • Fruit juice in can

  • PCA (plate count agar)

  • PDA (potato dextrose agar)

  • Bunsen burner

  • Spreader

  • Sterile water

  • Alcohol

  • Etuv

  • Pipette

  • Test tube rack

PROCEDURES:

Firstly; the surface of can was sterilized with alcohol then fruit juice was shaken for homogenization then can was opened and 1 ml sample was taken with a sterile pipette. 1 ml sample was put on the 9 ml of sterile water and 10-1 dilution was prepared from 10-1 dilution. Then; 10-2, 10-3, 10-4, 10-5 dilutions were prepared from 10-1 dilution. Then; 0,2 ml dilution was taken and inoculated to PCA with spread plate method and incubated at 37 oC for 24 hours. Finally; number of microorganisms was calculated.

Secondly; after opening the can, lid was put into 20 ml of sterile waster and shaken then 0,2 ml sample was taken and inoculated separately both PCA and PDA and incubated PCA at 37 oC for 24 hours, PDA at 25 oC for 2 – 5 days then number of microorganisms was calculated.

Thirdly; after opening the can, empty can was filled with 10 ml of sterile waster and shaken then 0,2 ml sample was taken and inoculated separately both PCA and PDA and incubated PCA at 37 oC for 24 hours, PDA at 25 oC for 2 – 5 days then number of microorganisms was calculated.

Fourthly; mold and yeast were examined. For this from dilution, 0,2 ml sample was taken and inoculated with sterile pipette to PDA at 25 oC for 2 – 5 days then number of microorganisms was calculated.

RESULTS and CALCULATIONS: 

PCA

non

10-1

10-2

10-3

10-4

10-5

Peach juice

2

5

12

1

3

1

Orange juice

40

28

50

34

28

19

Apricot juice

5

6

10

6

6

PDA

non

10-1

10-2

10-3

10-4

10-5

Peach juice

1

0

1

2

6

3

Orange juice

3

2

7

4

3

2

Apricot juice

1

2

3

2

3

2

For orange;      #
of m/o’ s = (50*102) / 0,2ml = 25000

# of m/o’ s = (34*103)
/ 0,2ml = 170000

DISCUSSION:

In this experiment; we examined microbiological properties of fruit juices. In fruit juices number of microorganisms was calculated with total count method and mold and yeast were investigated on potato dextrose agar.

Secondly; number of microorganisms was determined with total count method. In each fruit juices dilution, number of microorganisms was calculated with accordance to between 30 – 300 microorganisms and as a result; we observed that orange juice was to contain more number of microorganisms than other fruit juices.

Next; mold and yeast test was applied the fruit juices and in here number of microorganisms was calculated but microorganisms number was low. And we decided to not include mold and yeast.

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