Aassalamu alikum how are you I hope you are all well. All the praise to Allah subhanahu oatala.I am Abu Saeid Studying MS in Food Processing and Preservation in Hajee Muhammad Danesh Science and Technology University, Dinajpur. Stay in Zia hall room no#226# 1st floor in HSTU campus, Basher hat, Dinajpur.

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Thursday, June 9, 2016

Microorganisms associated with food

Microorganisms associated with food
The most common microorganisms (MOs) associated with food are:
1.      Bacteria
2.      Yeast and
3.      Mold
The primary sources of MOs are
1.      Soil, water and air
2.      Plants and their products
3.      Animal and human beings
4.      Food handling equipments
The roles of MOs are:
1.      Spoilage
2.      Diseases
3.      Food fermentation
Bacteria: Bacteria are  unicellular organisms of aerobic or anaerobic nature an exhibit many morphological forms (mainly spherical, rod and spiral) having length in the range of 0.5 to 10.0 μm and width of about 0.5 to 2.5 μm
Three principles shapes have been well recognized namely
        i.            Spherical shape of cocci
     ii.            Rod shape of bacilli and
   iii.            Spiral form of spirilla
Important food spoilage bacteria:
Groups
Genus
Acetics
Acetobacter and Gluconobacter
Lactices
Lactobacillus,Leuconostoc, Pediococcus, Streptococcus
Butyrices
Clostridium
Propionics
Propionobacterium
Proteol Gytics
Bacillus, Pseudomonous, Clostridium, Proteus etc.

Some useful bacteria:
1.      Acetobacter sp. (A. Aceti, A. oreleansis, A. schutzenbachi): These bacteria also known as vinegar bacteria that oxidize ethyl alcohol to acetic acid. They are found on fruits, vegetables and alcoholic beverages.
2.      Lactobacillus sp. (L. plantarum): They ferment sugars with the products of lactic acid. So they are used at fermented plant and dairy products but they deteriorate some products i.e. wine, beer
other important species : Pediococcus cerevisiae, Leuconostoc mesenteroids, Streptococcus faecalis, Lactobacillus brevis
Yeast
Yeast are unicellular fungi of larger size compared tobacteria of oval, elongate, elliptical or spherical cell shape having length in the range of 10 to 20 μm and dia about 6 to 7 μm.
This organism produce pigments of many colors with red and black pigments producers being common. Optimum temperature of growth for most yeast is 25 to 30oC and maximum range is 40 to 47oC.
Most yeast used industrially is in the genus of Saccharomyces cerevisiae. Yeast are used in the manufacture of foods such as bread, beer, wine, vinegar and for surface ripening of cheese.
Yeast + Sugar          Alcohol +Carbon dioxide (gas)
Mold
Molds are multicelllular filamentous fungi growing as a network of hair like fibers called mycelia with a fuzzy or cottony appearance.
Optimum temperature of growing mold is 25 to 31oC some grows in 35 to 37oC. The mold thallus consists of a mass of branching, intertwined filaments called hyphae (singular hypha). The whole mass of these hyphae is known as mycellium. Molds are used in manufacturing of certain food such as: oriental food that includes soya sauce, jonti, miso etc.
The important molds are:
a)     Penicillium sp. (blue mold)
b)     Aspergillus sp. (black mold also known as laboratory fungi)
c)     Mucor sp. (gray mold)
d)     Byssochlamys fulva
Yeasts are grown well in sugar able condition. Bacteria cannot grow in minimum content of moisture but yeast and mold can grow.
Growth relation of MOs with aw
Microorganism
Minimum aw
Bacteria
0.91
Yeasts
0.88
Molds
0.80
Halophilic bacteria
0.75
Xerophilic fungi
0.65
Osmophilic yeasts
0.60

Factors affecting the growth and survival of microorganisms are:
·        Nutrient
·        Time
·        Temperature
·        pH
·        Water activity (aw)
·        Oxygen
·        Chemical factors
·        Radiation
Food Wastage
Food wastage mainly occurs through:
1.      Contamination
2.      Consumption by pest
3.      Inefficient utilization
4.      Spoilage
Food spoilage can be defined as any change in the nature of a fresh or processed food material whereby changes in chemical, physical or organoleptic properties of the food take place, leading to its rejection as acceptable food by the consumers.

 Types of food spoilage and causative organisms:
Food
Type of spoilage
Causative microorganism
Fresh fruits and vegetables
Gray mold rot
Botrytis cinerea
Rhizopus soft rot
Rhizopus nigricans
Blue mold rot
Penicillium italicum
Black mold rot
Aspergillus niger, Alternaria sp.
Sliminess or souring
Saprophytic bacteria
Bread
Moldy
Rhizopus sp., Aspergillus sp.
Ropy
Penicillium sp.

Red bread
Bacillus sp. Serratia marcescens
Fresh meat
Putrefaction
Cholstridium sp., Pseudomonas sp., Proteus sp., Alcaligenes sp. Chromobacterium sp.

Souring
Chromobacterium sp., Lactobacillus sp., Pseudomonas sp..
Fish
Discoloration
Pseudomonas sp.,
Putrefaction
Choromobacterium sp., Halobacterium sp.
Poultry
Odor, slimy
Pseudomonas sp., Alcaligenes sp.
Xanthomonous sp.
Eggs
Green rot
Pseudomonas flourescens
Colorless rot
Pseudomonu sp., Alcaligenes sp., Chromobacterium sp., Cloiformis sp.
Black rot
Proteus sp.
Fungal rot
Penicillium sp., Mucor sp.
Bacterial soft rot
Erwinia carotovera, Pseudomonas sp.


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