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Starter Cultures; Definition, Classification and Characteristics

History of Starter Cultures

By the 19th century, discovering microorganisms and clarifying fermentation chemistry enabled us to understand fermented products. With the developing technology, the possibilities have expanded; the journey to reach a healthier and standard fermented product production method by controlling spontaneous production has begun.

Today, fermented foods such as dairy products, meat products, cereal products, fruit and vegetable products, alcoholic beverages and soy-based products are produced by large commercial enterprises globally using the fermentation technique.

In this context, the studies of Louis Pasteur (1822-1895) about 150 years ago are considered a milestone in fermented food technology. Pasteur, who gave his name to the “pasteurization” process, which is a fundamental process in the dairy industry, explained that this change in fermented foods occurs due to the activities of microorganisms and laid the foundations of the starter culture and fermented food production technique.

In light of these studies, in the 1860s, researchers such as Storch, Weigman, and Cohn used sour whey and buttermilk to make new butter and cheese; and they obtained better quality products.

In 1873, about ten years after Pasteur’s fermentation studies, Lister produced the first pure culture of lactic acid bacteria. In 1890, in Denmark, The first commercial company with starter cultures for dairy products was established (Chr. Hansen).

In the 1950s, due to the development of the lyophilization technique, the use of starter culture spread to broad geographies.

Definition, Characteristics and Classification of Stater Cultures

A starter culture is “a microbial preparation containing a very high number of cells (such as 1012 g-1) of one or more microorganism species to be added to the raw material to produce a fermented food by accelerating and directing the fermentation process”.

The traditional production of fermented foods is based on spontaneous fermentation due to naturally occurring microflora in the raw material. The quality of the final product thus depends on the raw material’s initial microbial load and spectrum.

The direct addition of selected starter cultures to the raw materials was a milestone in processing the food served, resulting in a high degree of control over the fermentation process and standardization of the end product. Strains with suitable physiological and metabolic properties have been isolated from their natural habitats or successfully fermented products.

It is estimated that the starter culture market used in the dairy industry in the world is at the level of $1,124 billion and will reach the level of $1,670 billion in 2027, mainly depending on the development of Asia Pacific.

When we look at the world in general, it is seen that the production with starter culture in the dairy industry is mainly carried out in Europe, North America and the Asia Pacific. In relatively developing and underdeveloped countries, starter culture has remained limited in parallel with the industry level.

However, to ensure the continuity of local flavors, especially in Europe, many types of cheese produced by traditional methods without using starter culture are protected by law.

Starter cultures are subject to different classifications according to various criteria. This classification is given in the table below. According to their commercial forms, cultures are divided into liquid, powder and frozen cultures.

Starter cultures were first produced in liquid form. Liquid cultures, which can maintain their viability for about one week at 5oC, are now being replaced by powdered and frozen cultures due to their low strength, high risk of contamination, rapid deterioration of the ratio between strains in mixed cultures and complex preparation for use.

However, the ease of direct use of powdered and frozen cultures produced in high concentration, known as DVS (Direct Vat Set) or DVI (Direct Vat Inoculation), has been an important reason for preference.

Powdered cultures are forms obtained by drying liquid cultures by spraying or lyophilization technique. Powder cultures contain a much higher number of microorganism cells on a unit mass basis than liquid cultures and can be stored for up to 6 months at 5oC and up to 1 year at -20oC.

On the other hand, frozen cultures are produced by freezing liquid cultures at -20 to -40oC or in liquid nitrogen at -196oC and can be stored for up to 3 months at -45oC and up to one year at -196oC.

Classification of starter cultures
Classification of starter cultures

If it is necessary to mention other criteria briefly, mesophilic cultures refer to cultures containing microorganisms that can grow optimally at 20-30oC and thermophilic cultures at 37-45oC.

In classification according to the microorganism strains they have, cultures consisting of a single strain of a species are single-strain cultures; cultures containing different strains of the same species are called multi-strain cultures and cultures composed of the combinations of different strains of more than one species are called mixed cultures.

It should be noted here that single-strain cultures are highly susceptible to phages. Multi-strain and mixed cultures are more resistant to phage attacks because other strains can continue to work even if one strain they contain becomes inactive due to the phage.

Classification according to types can be a subclassification of mesophilic cultures. Accordingly, type L contains Leuconostoc, type D contains Lactococcus diacetylactis strain, DL type contains Leuconostoc and Lactococcus diacetylactis strains, and type O; is expressed as mesophilic starter cultures that do not contain aroma-producing strains.

Although most of them are bacteria, microorganisms such as yeast and mold can also be used as starter cultures in the dairy industry. For example, Penicillium roqueforti molds are used to produce roquefort cheese, Lactobacillus bulgaricus and Streptococcus thermophilus bacteria are used as starter cultures in yogurt production.

In the kefir sample, yeasts are Kluyveromyces lactis, Kluyveromyces marxianus, Torula kefir, Saccharomyces cerevisiae and bacterias are Lactobacillus brevis, Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus helveticus, Lactobacillus delbruecki, Streptococcus salivarus, Lactococcus lactis ssp. thermophilus, Lactococcus cremoris and Leuconostoc mesenteroides are used as a mixed starter culture.

Undoubtedly, microorganisms used as starter cultures are selected according to the product and its characteristics.

Generally speaking, the industry’s most critical feature expected from a starter culture is producing lactic acid from lactose. In addition, it is among the desired properties to provide the aroma and texture specific to the product, inhibit unwanted microorganisms in the product due to increased acidity and produce components such as H2O2, nisin, diacetyl, and acetaldehyde.

At the same time, a very different and wide range of properties, such as exopolysaccharides, can improve the product’s structure and are very beneficial to human health. Their sensitivity to antibiotics is effective in the selection of starter cultures.

On the other hand, nowadays, scientists have focused on probiotic starter culture studies, and probiotic products have become very popular.

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Lactic acid bacteria; definition, classification and characteristics

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