Microorganisms
Microorganisms are any substances which causes food spoilage and are responsible for many diseases. Generally they are too small to see in naked eyes.
Microorganisms Associated with Food
The most common microorganisms (MOs) which are associated with foods are:
I. Bacteria
II. Yeast and
III. Mold
Bacteria
Bacteria are unicellular spherical, rod or spiral shaped prokaryotic microscopic organisms. They may be aerobic or anaerobic. The length of bacteria varies from 0.5 um to 10.0 um and width of about 0.5 to 2.5 um.
Electron microscopic features of bacteria:
I. Cell wall
II. Cell membrane
III. Cytoplasm
Light microscopic features:
I. Capsule
II. Spore
On the basis of cell wall composition: Two types
I. Gram positive: The bacteria which retain the basic dye crystal violet are called gram positive bacteria.
II. Gram negative: The bacteria which retain red stain by safranin treatment is known as gram-negative bacteria.
Yeast
Yeasts are non filamentous unicellular fungi having oval or spherical shape. Yeasts reproduce by budding or fission or by producing ascospores.
True yeast: The yeasts which produce ascospore is called true yeast.
False yeast: The yeasts which produce no ascospores or other sexual spores is called false yeasts.
Yeasts of Industrial Importance
i) Saccharomyces cerevisiae: Used for leavening of bread and for the production of alcohol.
ii) Zygosaccharomyces: Spoilage of honey, syrup and molasses, fermentation of soyasauce.
iii) Schizosaccharomyces: Generally found in tropical fruits, molasses, soil, honey and elsewhere. They causes spoilage of these foods.
iv) Pichia: Normally grows on beers or wines.
v) Debryomyces: Grows on cheese and sausage..
Molds
Molds are multicellular filamentous fungi which are readily recognized by its fuzzy or cottony appearance. Normally it is white in color but may be coloured, dark or smoky. Molds can be reproduced by sexual or asexual spores or sometimes by both.
On the basis of cellular structure molds are two types:
i) Septate: Hyphae are divided into cells by cross wall and in some by divisions by the tip cells.
ii) Non-septate: Hyphae apparently consisting of cylinders without cross walls.
Molds of Industrial Importance
i) Mucor: Causes spoilage of food, helps in cheese ripening and also used in amylo process
ii) Saprolegnia: Causes fungal growth on fish called saprolegniasis.
iii) Rhizopus: It is known as bread mold, some of them are involved in the spoilage of many foods, berries, vegetables, bread, sweet potato, tomato etc.
iv) Aspergillus: Involved in the spoilage of foods and some are useful in the preparation of some foods.
v) Penicillium: Used in producing penicillin, causes soft rots of fruits.