Starter cultures contaminants

Milk Substrates Cheese is perhaps the oldest of the fermented foods. (Fig. 1) The basic underlying microbial transformation in all cheese manufacture is the conversion of lactose of milk into lactic acid. The microorganisms in the starter culture contribute significantly to the flavor of the cheese. The secondary microbial flora of the cheese also elaborate taste and odor active substances. These organisms may be present as chance contaminants or introduced intentionally(8), and result in distinctive types of cheeses such as Cheddar, blue veined and Swiss. 

Contamination by all relevant Saccharomyces sensu stricto species can be detected directly in Saccharomyces pastorianus ssp. carlsbergensis brewing yeast containing beer or starter cultures with the exception of Saccharomyces bayanus/eubayanus/ pastorianus contaminations. For this specific problem, an additional quantitative approach, which is shown in Figure 5.6, can be implemented. 

White beer (weissbier) is a special beer that is very pale in color. A lactic fermentation is carried out following the addition of a starter culture resulting in a very low pH 3.2-3.4. Lactobacillus brevis, a top fermenting yeast, and Brettanomyces bruxellensis are used in fermentation resulting in pure lactic acid flavor (Anderson et al., 2000 Back, 2005 Vriesekoop et al., 2012). Sensory panels would need to ensure the quality of the pure lactic acid flavor and lack of any contaminant-generated off-flavors in such highly acidic/tart beers. 

The ability to transfer microorganisms from one container to another without contamination is crucial to success in the microbiology laboratory. These techniques serve as the basis for subsequent work such as starter culture preparation or maintaining viable cultures in long-term storage. Transfer loops are normally used to transfer to the surface of agar (Petri plates and slants), whereas transfer needles are used to prepare stab cultures. Both implements are sterilized by heating in an open flame until red hot (Fig. 13.1). 

LAB are the most important bacteria used in food fermentations and many LAB species are involved. Their presence results from either a natural, spontaneous contamination derived from the raw materials themselves or the environment, the inoculation by foods from a previous batch (a practice referred to as back slopping), a dehberate addition of cultures (starters), or a combination of these different sources (Table 19.2). Most fermented foods consumed in developing countries are manufactured from spontaneous fermentation, without addition of any starters (Tamang and Delwen 2010). However, food fermentations have evolved towards a systematic use of starters to control fermentation, and nowadays starter cultures are widely used in the manufacture of many fermented products, such as dairy products, sourdough, and fermented dry sausages (Leroy et al. 2006). 

Koji starter, also known as seed koji, koji seeds, or tane-koji, provides spores of microorganisms to make koji. Preparation of koji starter is essentially the same as making regular koji for soy paste and soy sauce except that in making koji starter, pure culture and different raw materials are used and longer fermentation is needed to produce abundant spores. In addition, a sterile condition is needed to avoid contamination. 

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