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DAIRY STARTER CULTURES -- GENERAL CHARACTERISTICS
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DAIRY STARTER CULTURES -- GENERAL CHARACTERISTICS

 

BASIC DEFINITION

 

Dairy starter cultures are microorganisms that are intentionally added to produce a desired outcome in the final product, most often through their growth and “fermentation” of the dairy food. The most common use of starter organisms is for the production of lactic acid from lactose (milk sugar), which in most cases causes or assists in the coagulation of milk protein. Certain starter organisms are added specifically for the production of flavor compounds such as diacetyl though the production of lactic acid and other compounds also contributes to flavor. Starter organisms can also influence flavor and texture of cultured and/or aged products through the breakdown of proteins, fat and other milk constituents in addition to the pH effect. The lower pH of cultured products can be inhibitory to certain spoilage organisms. Inhibition is also associated with other by-products of growth with some starters. More recently, probiotic cultures are finding their way into cultured milk products. These are cultures that have some claimed health benefit for those that consume them, i.e. better digestion, anti-cancer compounds, and prevention of heart disease. Probiotic cultures may be added as adjuncts or they may be directly involved in the fermentation process.

 

CULTURE SELECTION

 

The type of starter culture used depends on the desired product. Culture supply companies can provide processors with a variety of cultures tailored for their operation. It is very important to follow the supplier’s advice on the handling, storage, rotation, use rate, and incubation temperature for their cultures. Generally, dairy cultures are classified as Mesophilic cultures with optimum growth at 70 - 90oF or Thermophilic cultures with optimum growth at 100 - 115oF. Varying the incubation temperature of certain cultures can influence the flavor profile and other attributes of the final product. A summary of common dairy cultures and their uses is on the following page.

 

FACTORS AFFECTING CULTURE ACTIVITY

 

Slow acid development by starter cultures can result in an inferior product or the discarding of a vat full of milk. Starter activity can be influenced by a number of factors including the age of the culture, handling and storage practices, incubation temperature, the quality of the raw milk, bacteriophage, and the presence of inhibitors such as drug or sanitizer residues. Penicillin and related antibiotics can inhibit cultures at levels as low as 1-2 parts per billion (ppb). Sanitizers can cause inhibition, especially those that leave residual activity, such as quaternary ammonia compounds. Natural inhibitors associated with high SCC or late lactation can also slow culture growth.

 

BACTERIOPHAGE

 

Bacteriophage (phage) are viruses that attack and destroy bacteria. They are very small and cannot be seen with an ordinary microscope. Phage require a host cell to reproduce; one phage per bacterial infection can result in up to 200 phage being released, each of which can infect a new bacterial cell. Phage are very strain specific which is why culture rotation and resistance are used as control mechanisms. Phage can enter the dairy plant through the raw milk supply though some culture strains are “carriers.” Problems with “dead vats” due to phage can often be linked to phage in the plant environment (i.e. poor plant hygiene). Key to preventing phage contamination is a stringent culture handling and plant sanitation program.