Criteria for Selecting and Developing Starter Cultures

When SC technology first developed, the actual microorganisms contained within most MFC were generally not well established in terms of strain or even species identity. Rather, a culture was used simply because it worked, meaning that it produced a good product with consistent properties. Such undefined cultures, however, are now less frequently used. Instead, the organisms present in modern commercial SC preparations are usually very well defined strains. They are also carefully selected based on the precise phenotypic criteria relevant for the particular product. For example, any potential new SC for cheese must produce at least acid, lack off-flavour development in milk and be phage-resistant (Carminati et al. 2010).

Pure culture fermentations also have disadvantages. Selecting one single strain with all beneficial characteristics necessary for an efficient and high-quality fermentation might prove difficult, since the diversity of wild, contaminating yeasts and bacterial species create a distinct fermentation and flavour profile and a lot of the complexity or subtle aromatic notes might be eliminated in pure culture fermentations.

Selection of strains for use in food fermentation is a highly complex and challenging task that requires a solid understanding of microorganism growth and manipulation, as well as microbial interactions with other organisms. The use of microorganisms follows a logical sequence. First, it is necessary to determine matrices to isolate microorganisms that carry out the desired process in the most efficient manner that potentially exhibit technological properties. Next, phenotypic traits and technological suitability evaluation have to be taken into consideration. After that, the taxonomic affiliation is determined using DNA-DNA hybridization and the analysis of 16S rDNA gene sequence. The name of the identified strain needs to be consistent with the list of “history of safe use”. This microorganism then is used, in a controlled environment such as a fermenter to achieve specific goals.

Basically, the criteria for the selection and development of SC for the food fermentation industry can be considered under three common categories: (1) properties that affect the performance and efficiency of the fermentation process; (2) properties that

Characteristics and Production of Microbial Cultures

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determine food quality and character; (3) properties associated with the commercial production of MFC. Buchenhuskes (1993) and Champagne and Mollgaard (2008) (Table 14.2) summarized the selection criteria for LAB to be used for food fermentations (desired properties for industrial use): lack of pathogenic or toxic activity (e.g. production of biogenic amines); ability to accelerate metabolic activities (acidification or alcohol production); production of desired changes in the matrix (structural and sensorial); improvement in safety and reduce hygienic and toxicological risks; ability to dominate microbial consortium; ease of propagation; ease of preservation; stability of desirable properties during culturing and storage. Specific properties desired in a MFC depend on the product being produced.

TABLE 14.2 Main selection criteria of lactic acid cultures (not exhaustive). Adapted from Buchenhuskes (1993) and Champagne and M0llgaard (2008)

Technological properties

Other properties

Dominate microbial consortium

Be easy for propagation and preservation

Assimilate other non-conventional carbon fonts

Improve safety and reduce hygienic and toxicological risks

Produce desired changes in the matrix

Be absent of pathogenic or toxic activity

Produce flavour and polysaccharides metabolites

Produce antimicrobial substances (bacteriocins)

Induce proteolysis

Resist to bacteriophages

Resist to process pressure (acidity, NaCl concentration, oxygen)

Have desirable properties stability during culturing and storage

 
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