Starter cultures dairy fermentations

EPSs produced by starter cultures in fermented dairy products represent a complex matrix of polymers that provide a protective function to the fermenting strains against phages and toxins. After ingestion, these EPSs will ultimately come into contact with the host intestinal microbial population the question is therefore raised is there a relationship that emerges between this EPS and the microbiome ... 

Apart from public health impacts, residual antimicrobials in animal products can bring about technoeconomic losses in the food processing industry. It has long been known that the presence of some antimicrobial compounds in milk can dramatically affect the production of fermented dairy products such as yogurt, cheese, buttermilk and sour cream (72, 73). As shown in Table 10.2, even minute concentrations of antibiotics in milk can cause inhibition of the growth of commonly used dairy starter cultures (74). 

The most important fermentative reaction used in dairy processing is the homofermentative conversion of lactose to lactic acid. The efficient manufacture of high-quality cultured products, including most cheese varieties, yogurt, and cultured buttermilk, requires a rapid and consistent rate of lactic acid production. Lactic acid helps to preserve, contributes to the flavor, and modifies the texture of these products. Nearly all starter cultures used to produce acidified dairy products contain one or more strains of lactic streptococci, because these organisms can produce the desired acidity without causing detrimental changes in flavor or texture. Strains of lactic streptococci can be classified as... 

Small amounts of hydrogen peroxide in raw milk can activate the lactoperoxidase-catalyzed oxidation of thiocyanate to produce a bacterial inhibitor (Hogg and Jago 1970). Inhibitory compounds resulting from oxygen metabolism can produce initially slow starter culture growth in industrial dairy fermentations if the milk has been excessively agitated. 

Cultured dairy foods seldom cause foodborne illness in the consumer. If an active starter culture is used, common foodborne pathogens, even if present in the milk, do not grow well and often are inactivated during the fermentation or early during the storage life of the product. Even if some cultured products are recontaminated after manufacture, pathogens generally do not survive well. Several examples will illustrate these points. 

Leuconostoc Starter culture in dairy fermentation Antimicrobial activity by producing various bacteriocins... 

Lactic acid bacteria and bifidobacteria are preferred as protective and probiotic cultures, and have been used since the beginning of history as starter cultures. They have a long history of being safely used and consumed. LAB are widely used for fermentation of milk, meat, and vegetable foods. In fermentation of dairy products, lactose is metabolized to lactic acid. Other metabolic products, hydrogen peroxide, diacetyl, and bacteriocins may also play inhibitory roles and contribute to improving the organoleptic attributes of these foods, as well as their preservation (Messens and De Vuyst, 2002). 

LAB are industrially used as starter cultures and as probiotics to perform controlled fermentations for the production of dairy, meat, vegetable, and bakery-fermented foods. L7U1 with specific characteristics have been isolated from a variety of traditional fermented products or from diverse raw materials used as starter cultures to obtain controlled and uniform fermented foods [14-16]. 

In fermented probiotic dairy products, probiotics are usually accompanied by starter cultures such as Lactobacillus delbrueckii subsp. bulgaricus and/or Staphylococcus thermophilus. There are two main reasons for the inclusion of starter cultures in a probiotic product. The first is technological starter cultures provide sttucture and flavour to the product. In addition, starter cultures support functionality some probiotics do not grow well as a pure culture in mUk and grow better in symbiosis with a starter culture. 

Hubert, E. M., Raya, R. R., TaUUez, R, De Giori, G. S. (2000). Characterization of natural isolates of Lactobacillus strains to be used as starter cultures in dairy fermentation. International Journal of Food Microbiology, 59,19—27. 

In the production of fermented food, starter cultures are used to prevent fermentation failure and to ensure high-product quality. Starter cultures are cultures with well-defined properties that ensure a fast, safe, and defined fermentation and lead to fermented food products with high and constant product quality. The use of defined starter cultures is state-of-the-art in the dairy industry, and replaces traditional procedures in the production of meat and bakery products and other fermented commodities. Starter cultures are mostly produced by specialized companies that distribute the cultures worldwide, and are being used increasingly in concentrated forms for direct inoculation into the food matrix (direct-to-vat-set cultures, DVS Hansen, 2002). 

Some species of the LAB group such as Leuconostoc mesenteroides subsp. cremoris, Leuconostoc mesenteroides subsp. dextranicum, and Lactococcus lactis subsp. lactis biovar diacetylactis, are known for their capability to produce diacetyl (2,3-butanedione) from citrate, and this metabolism appears especially relevant in the field of dairy products (Figure 13.4). Actually, selected strains belonging to the above species are currently added as starter cultures to those products, e.g., butter, in which diacetyl imparts the distinctive and peculiar aroma. Nevertheless, in particular conditions where there is a pyruvate surplus in the medium (e.g., in the presence of an alternative source of pyruvate than the fermented carbohydrate, such as citrate in milk or in the presence of an alternative electron acceptor available for NAD+ regeneration) (Axelsson, 2(X)9, pp. 1-72), even other LAB such as lactobacilli and pediococci can produce diacetyl by the scanted pyruvate (Figure 13.5). Thus, in addition to butter and dairy products, diacetyl can be present in other fermented foods and feeds, such as wine and ensilage (Jay, 1982). 

Microorganisms in food production have been associated mainly with fermented dairy products, wine and beer. They are of equal importance, however, in fermented meat, bread and vegetables, and it is only recently that the potential of using starter cultures in such products has been fully recognised. 

Nowadays most fermented milks are manufactured under controlled and sanitary conditions. As in the past, the main purpose of using starter cultures is to preserve the milk, but other reasons for using starter cultures in modern dairy industry are diverse and may be summarised as follows ... 

The use of fermentation to preserve and improve the properties of food has a long history. For example, milk has been preserved by fermentation for at least seven millennia (Dunne et ah, 2012). Initially, fermentation was a spontaneous process, probably with mixed results, and it was quickly learned that inoculation of the material to be fermented with a suitable inoculum would increase the likelihood of success. Traditionally, this was done by using part of a previous fermentation as an inoculum, but as microbiological knowledge increased, inoculation with specifically prepared fermentation starter cultures developed (Hpier et al., 2010). This in turn gave a better control of the fermentation process and allowed for the development of new products with novel properties. This is well illustrated in the dairy industry, where a diversity of bacterial species is used to manufacture a large variety of fermented dairy products (Table 10.1). 

Dairy starter cultures have been used traditionally in the production of a variety of fermented milk products. These cultures consist mainly of several members of the LAB and have been involved in the production of numerous fermented foods, such as yogurts, sour cream, buttermilk, acidophilus milk, kumiss, kefir, and approximately 2,000 different cheeses (O Sullivan 2005). LAB are the backbone of the dairy industry and the main dairy industry starters are contained in five genera Lac-tococcus lactis. Enterococcus faecalis and faeciunr, Lactobacillus bul-garicus, L. casei, L. brevis, L. helveticus, L. rhamnosus, L. fermentum, L. curvatus, L. johnsonii, and L. gasseri (O Sullivan 2005). 

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