Microbiology Vi sinh trong sữa

Microbial LoadsLocality CFU/hour and 100cm 2 Mibi Picture In-doors: Dry environment Office far from people Office close to people Corridor people passing 16 240 40 Gram pos.. Bacteria :

Microbiology

1 µm = 0,001 mm

Microbiology is the study

of organisms which are

so small that they can

only be seen with the aid

of a microscope Size is

measured in micrometer.

5 µm

Micro-organisms in the Laboratory

cfu,

colony

forming

unit

Microbial Loads

Locality CFU/hour and 100cm 2

Mibi Picture In-doors: Dry environment

Office far from people

Office close to people

Corridor people passing

16 240 40

Gram pos.

bacteria dominate In-doors: Wet environment

Toilets

Cleaning room

280 320

A lot of gram neg.

bacteria Out-doors environment

Lawn far from people 150

Moulds dominate

d ) b)

The Bacterial Cell - Basic Structures

Cell wall(1) Cell membrane(2) Chromosome(3) Cytoplasm(4)

1 2 3 4

Bacterial Cell - Structures

Capsule Cell wall

Granule

Bacteria :

Function of Cell Structures

CELL WALL ◊ giving the cell its specific shape

◊ protects the cell against high pressure and mechanical forces

CELL MEMBRANE ◊ acts as osmotic barrier

◊ active transport of nutrients and metabolites

CYTOPLASM ◊ place of production

CHROMOSOME ◊ carrier of genetic information

s

Gram+ and Gram- Bacteria

t = incubation time, i.e the time for growth

N 0 = number of bacteria at time zero

N t = number of bacteria at time t

Generation Time

Bacterium medium temp.( o C) g(min)

The Bacterial Growth Curve

a s e

Time

Reproduction of Moulds

Reproduction of Yeast

Important Growth Factors

Oxygen Nutrients

Growth factor - Oxygen

Bacteria all types of relationships

Moulds are strictly aerobic organisms

with a few exceptions…

Yeasts are facultative anaerobic organisms

Growth factor - Oxygen

oxygen at lower pressure than

Growth factor - Oxygen

Aerobe MO that use O 2 for growth and can tolerate

O 2 at atmospheric level or higher i.e 21%.

Microaerophile MO is capable of using O2 for growth but only

at lower O2 levels than in the atmosphere Some can respire without O2.

Anaerobe MO that is incapable of O2 -dependent growth

and can not grow in oxygen of atmospheric level.

Some are fermentative and some have anaerobic respiration.

Facultative anaerobe MO that can grow well both in the absence and

presence of oxygen of atmospheric level

Some can grow aerobically with oxygen and anaerobically with fermentation Others can only grow with fermentation.

Growth factor - Water

Water activity, a w , is a measure of the

water available for growth

a w = p p

0

p = actual water vapor pressure

p 0 = pure water vapor pressure

0 < a w < 1

Growth factor - Water

a w = p p

Milk Beverage Evaporated milk Tomato paste

Sweet Condensed milk

Growth factor - Water

Minimum a w for Growth

Growth factor - pH

High Acid Food 4,6

Low Acid Food 4,6

Fruit juices

Growth factor - Temperature

Influence of Temperature on Growth

Rate

minimum optimum maximum

Growth factor - Temperature

Examples of Genera with

Streptomyces Vibrio

Yersinia Listeria

Yeast

Candida Crytococcus Rhodotorula Torulopsis

Mould

Aspergillus Cladiosporium Penicillium Trichothecium

Growth factor - Nutrients

Large amounts of: C, O, H, N, P, S

Small amounts of: Na , K , Mg, Ca

Quantitative composition of milk

Mean Value,

%

87,5 3,9

4,3 4,8 0,8

Mean Value,

%

Minerals Lactose Protein Fat Water

Structure of fat

Protein Structure

A given enzyme will only split certain

molecules, and only at certain bonds.

Lactose and sucrose are split

to galactose, glucose and fructose.

Microbial Degradation Products

Sugar Protein Lipid

Waste Products ENZYMES

Several

incl oxidase

Drop in pH and Blown packs

Blown packs

Unpleasant odour

Microbial Degradation Products

Microbial Degradation Products

Microbial Degradation Products

CARBOHYDRATES

I Prescence of oxygen: CO 2 + Water + Energy

II Absence of oxygen

a) Alcoholic fermentation: Ethanol + CO 2

b) Butyric acid fermentation: Butyric acid + etc.

c) Lactic acid fermentation

- Homofermentative: Lactic acid

- Heterofermentative: Lactic acid + Ethanol

Microbial Degradation Products

Breakdown of lactose by enzymatic action

and formation of lactic acid.