Effects of microorganisms on food

Foods undergo deterioration to varying degrees in organoleptic properties, nutritional value, safety and esthetical appeal.  The term food deteriorations, is often associated with advanced spoilage.

Bacteria, molds and yeasts are the main causes of the spoilages of unpreserved foods, with bacteria playing the major role in the spoilage of meats, poultry, dairy, and fish products.

Mold and yeast play the major role in the spoilage of fruits and vegetables. The changes in foods due to microbial action can be classified into two types: undesirable changes and desirable changes.

These microorganisms do not cause disease but they spoil food by growing in the food and producing substances which alter the color, texture and odor of the food, making it unfit for human consumption.

All bacteria associated with foods are small. Most are of the order of one to a few micrometers in length and somewhat smaller than this in diameter. All bacteria can penetrate the smallest openings; many can pass through the natural pores of an egg shell once the natural bloom of the shell is worn.

Yeasts are somewhat larger, of the order of 20 um or so in individual cell length and about a third this size in diameter.

Typically, the effects of temperature, pH, and the acidulants, water activity and the humectants, oxygen availability, redox potential and identity and concentration of inhibitory agents are among the variables that must be considered when assessing whether microorganisms will pose a problem in particular food system.
Effects of microorganisms on food

What is so special about blue cheese?

Blue cheese may be made from raw, heated or pasteurized whole milk or from skim. 

The earliest makers of blue cheese used bread to begin production of the distinctive mold and then waited patiently for the veins of mold to grow and spread naturally between the curds. 

Consumers need to ask for a taste before buying moldy chees. A good always is flavorful but never is sour or harsh. 

Penicillium roquefortii is primarily responsible for ripening blue cheese. Proteolytic enzymes from the mold act to soften the curd and thus to produce the desired body in the cheese. 

This cheese is a heterogeneous microenvironment comprising different habitats for microorganisms in the core with its fissures and piercing channels and on the surfaces of the cheese. 

Most blue cheese are pierced at specific times during aging to allow the molds access to more oxygen once they have used up the supply inside the cheese. 

A complex microflora develops ripening and adapts to the pronounce pH and NaCl gradients and the large variation in content of O2 and CO2. 

The best known varieties today, worldwide are considered to be Gorgonzola, Roquefort, Stilton and Danablu, all which have been granted the status of Protected Designation of Origin. 

Roquefort is the original blue cheese. The designation ‘Roquefort’ is applicable only to cheeses made from ewe’s milk in the area of France. 

Gorgonzola is the principal blue mold cheese of Italy where it is claimed to have been made in the Po Valley since 879 AD. 

What is so special about blue cheese?