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Microbial food cultures - Probiotics and starter cultures
Friday, 31 July, 2020, 14 : 00 PM [IST]
Annette Gowda, Rita Yadav
Humans have been storing food at least since the beginning of the Neolithic period, around 10,000 years ago. The availability of storable and hygienically safe food was a decisive prerequisite for the development of mankind and society. Traditional methods for preserving food, such as drying, smoking, salting and fermentation are still in use today.

The active principles of fermentation were unknown until modern times; Louis Pasteur was the first to recognise its nature, describing it as a (microbial) “life without air”. The causers of the process were called ferments and classified into ‘formed’ and ‘unformed’ variants. Hans Buchner showed that they correspond to microorganisms and enzymes, respectively.

Subsequently, food fermentation processes underwent a process of continuous improvement, and microbial cultures became essential components of food production. They form a continuum, encompassing the historically ancient use of fermenting food substrates up to pure cultures that are characterised taxonomically, physiologically, biochemically and genetically.

From cultures traditionally used in food fermentations, new fields of application have arisen on the basis of extensive scientific studies, which allowed utilising specific features of the culture organisms for specific applications. An understanding of the historical relationships as well as the scientific and practical background for the use of cultures is not common knowledge.

Food Cultures (FC) are safe live bacteria, yeasts or moulds used in food production which are in themselves a characteristic food ingredient. FC preparations are formulations, consisting of concentrates (> 108 CFU/g or ml) of one or more live and active microbial species and/or strains, including unavoidable metabolites and media components carried over from the fermentation and components (e.g. carbohydrates, organic acids, minerals, vitamins) which are necessary for their survival, storage and to facilitate their application in the food.

Fermentation is one of the oldest food processing technologies and food cultures have traditionally been used to ferment raw materials such as milk, meat, fish, flour, grapes and vegetables to produce safe foods with distinctive organoleptic properties at the same time improving the shelf life and reducing food waste.

Food cultures preparations are traditionally used as food ingredients at one or more stages in the food manufacturing process to develop their desired metabolic activity. They contribute to one or more unique properties of the food stuff especially in regard to flavour, colour, texture, wholesomeness, health and nutritional benefits and food safety through protection and conservation.

These unique properties of the fermented food stuff are the results of the presence of FC in food and of their metabolism.
Through metabolism, food cultures
•    Consume nutrients, setting up a complex system of competition for nutrients and binding sites
•    Produce metabolites like organic acids, hydrogen peroxide, volatile or low molecular weight compounds (such as ketones and aldehydes) or peptides (e.g., some bacteriocins) some of which exert inhibitory effect towards other micro-organisms.

The application of FC constitutes among other functions an additional measure to improve food hygiene by outcompeting unwanted microorganisms and is therefore complementary to Good Manufacturing Practices. In conclusion, inhibition along with other properties of FC is a natural consequence of FC metabolism in food which has been used traditionally worldwide.

About one-third of all food currently being consumed is fermented. These fermented foods feature a number of advantages: - They offer a high degree of hygienic safety.1 - They have an increased shelf life compared to the raw product. - Raw materials are refined by improving quality-determining properties. - Toxic or harmful substances derived from the raw material, such as cyanides, hemagglutinines, goitrogens, proteinase inhibitors, phytic acid, oxalic acid, glucosinolates and indigestible carbohydrates, are partly degraded. - Manufacture requires only basic technology and low energy consumption. - They meet a demand for natural and organic food.

Starter cultures are preparations of live microorganisms or their resting forms, whose metabolic activity has desired effects in the fermentation substrate, the food. The preparations may contain unavoidable residues from the culture substrate and additives that support the vitality and technological functionality of the microorganisms (such as antifreeze or antioxidant compounds). This definition includes a multitude of preparations, which is based on the history of starter cultures. The development of fermented foods was determined by the fact that originally a special microbial association developed under the influence of ecological factors prevailing in the respective substrate. Such spontaneous processes in the fermentation of sauerkraut (pickled cabbage), olives or pickles are still state-of-the-art.

In other areas, fermenting substrate was used to inoculate new fermentation methods. Still standard practice today is for instance ‘old-new inoculation’ with cheeses, ‘back-slopping’ or ‘back shuffling’ with sourdough. Vinegar is also produced in this way.

The inoculum obtained in this way (having been propagated many times) undergoes a high level of organism selection and is practically synonymous with starter cultures. Such ‘undefined cultures’ are still in use today, for example, ‘Flora Danica’, used as a milk starter culture from more than 100 Leuconostoc and Lactococcus strains or ‘Reinzuchtsauer’ used as a sourdough starter.

These cultures are subject to a continuous change in composition, as strains may disappear or mutate, or may change their properties after phage attacks. The use of ‘defined cultures’ allows for a greater degree of control over the fermentation process. Mäyrä-Mäkinen and Bigret, (1998) made a distinction between: - Single-strain cultures: contain one strain of a species; - Multi-strain cultures: contain more than one strain of a single species; - Multi-strain mixed cultures: contain different strains from different species. These different cultures are used in the fermentation of milk, meat, wine, fruit, vegetables and cereals.``

To maintain their stability, effectiveness and applicability, they are prepared, packaged, chilled, frozen or freeze-dried. Using such starter cultures offers a number of benefits, such as: - Food production at a uniform level of high quality; - Control of fermentation time; - Economic process management through reductions in process time and/or improvement of the substrate turnover; - Reduction of hygienic risks; - Access to new products that cannot be produced by spontaneous fermentation.

Probiotics are live microorganisms which when consumed in adequate amounts confer a health effect on the host” (FAO/WHO, 2001) Probiotic microorganisms are normally not involved in the microbial fermentation process in food. It cannot be excluded that organisms used in classical food fermentation may also be metabolically active and probiotic in the gastrointestinal tract. In addition, it should also be considered that probiotic effects ascribed to living microorganisms can often be triggered by cell (wall) fractions of these organisms.

Food must not endanger the health of the consumer. Responsibility for consumer safety lies with the distributor. One of the factors in determining microbiological safety is long-term experience (‘history of safe use ’). Experience going back a long way can be called upon for a variety of spontaneously fermented foods.

In such foods, a microbial association will always develop, the composition of which depends on the ecological factors acting on the microorganisms that are characteristic to the specific food. With the aid of the refined testing methods of today, it is possible to isolate and identify from such microbial associations previously unknown microorganisms.
As long as the history of use shows that foods contain no microorganisms that are hazardous to health, the content of microorganisms in food will generally be tolerated up to the spoilage limit.

For the introduction of novel microorganisms (including GMOs), a safety assessment is mandatory. A safety assessment should also be carried out for undefined cultures. It should be noted, however, that the strain composition therein cannot be kept constant and therefore is also not suited for the adequate characterisation of such cultures.

(Gowda is manager, molecular biology, Yadav is trainee molecular biology analyst at Envirocare Labs Pvt. Ltd, Mumbai. They can be contacted at annettemartin24@gmail.com)
 
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