Characteristics and Production of Microbial Cultures

Juliano De Dea Lindner[1] [2]

Abstract

The successful manufacture of all fermented products relies on the presence, growth, and metabolism of specific microorganisms. Non fermented products generally lack the desired organoleptic qualities that are present, and that consumers expect, in the fermented products. This is because microorganisms are responsible for producing an array of metabolic end-products and textural modifications, and replicating those effects by other means is simply not possible. Starter cultures are defined as a preparation containing large numbers of variable microorganisms, which may be added to accelerate and/or improve a fermentation process. Microorganisms selected to be used as starter cultures are expected to have some characteristics such as adapting easily to raw food matrix and process, developing nutritional value and digestibility, improve safety by preservative effect and sometimes add functionality. The use of starter cultures in the food fermentation industry is widely known, such as cheese, yogurt, bread, beer and wine. In many cases, the technology has evolved from a traditional, spontaneous fermentation to a controlled industrialized process based on the use of well defined microbial strains as cultures to conduct the fermentation. Starter manufacture is one of the most important and also one of the most difficult processes in the food biotechnology. Production failures can result in heavy financial loss, as modern industries process large quantities of raw materials. Very careful attention must therefore be paid to the manufacturing technology and choice of process equipment.

Introduction

During past decades, specialists in different areas have experimented and developed methods to isolate, select, investigate, improve and produce different natural microorganism strains to apply in food fermentation with different purposes. The availability of microorganisms with highly specific activity (technological and/ or functional characteristic) is the basic element for the development of fermented products. Nowadays, selected strains of bacteria, yeasts and moulds are widely applied in the food industry for preparation, improvement and preservation of food.

Fermentation is a biological process conducted by microorganisms. The successful manufacture of fermented products relies on the presence, growth and metabolism of specific microorganisms. What the consumers expect in a fermented product generally lacks in an unfermented one. They desire organoleptic qualities that are present only in a fermented product, because microorganisms are responsible for producing metabolic end-products and textural modifications.

Food microbiology began with the study of the natural fermentation process that occurs when the raw food matrix are held for a time. These products had long been used as inocula to produce dairy products, but the resulting fermentations were of uneven quality. For example, in the 1880s, Conn in the United States, Starch in Denmark and Weigmann in Germany demonstrated the advantages of using lactic acid bacteria (LAB) to culture cream for butter manufacture. Also, in the United States, the brothers Fleischmann, in the 1860s, began a yeast factory (first culture industry devoted to baker’s yeast) producing a compressed yeast cake for commercial as well as home-baking markets use. Bread produced using this yeast culture was far superior to breads made using brewing yeasts, which was the common form at the time.

There are essentially three ways to induce food fermentation. The oldest method simply relies on the autochthonous microorganisms present in the raw material. Raw milk, for example, usually harbors the very LAB necessary to convert the matrix into cheese. Grapes contain likewise the yeasts responsible for fermenting sugars into ethanol, transforming juice into wine. Suitable conditions for microorganism growth are necessary and, in terms, select the microflora. Even if these requirements are satisfied, however, there is no guarantee that the product will meet the quality expectations, be safe to consume, or even be successfully produced. Once a successful fermentation has been achieved, a portion of that product could be transferred to use as fresh raw material to initiate a new fermentation. This method works for almost any fermented food and is still commonly used for beer, sour dough bread and vinegar. This ancient method based on natural fermentation is called back-slopping and is still practiced for small-scale production facilities in artisanal/ethnical type products. Due to limitations in infrastructure and technologies, rural areas in most countries have not been able to keep informed of global developments toward industrialization. At the same time, fermented foods play a major role in the diet of numerous regions in Latin America, Africa and Asia.

Experience has also shown that back-slopping, or the inoculation of raw materials with a residue from a previous batch, accelerates the initial phase of fermentation and, consequently, the risk of fermentation failure is reduced. This practice results in the promotion of desirable changes during the fermentation process and selects well-acclimated and predominant microorganisms with many of the desired traits necessary for successful production. Thus, an organism isolated from the back-slope could be purified, studied and characterized to be introduced as a culture for fermentation. The implication of this method that pure cultures could be obtained and used to start fermentations resulted in a modern way to produce fermented foods. The technology has evolved from a traditional, spontaneous fermentation to a controlled industrialized process based on the use of well-defined microbial strains as cultures to conduct the fermentation.

European Food and Feed Cultures Association (EFFCA) defined microbial food cultures (MFC) as live microorganisms used in food production. MFC are preparations that consist of one or more microbial strains, including components that are used to give support for survival, storage and application in the food matrix. These microbial preparations can consist of LAB, propionibacteria, surface-ripening bacteria, yeasts and moulds. Equivalently by definition, starter cultures (SC) consist in a preparation containing large numbers of variable selected microorganisms, which may be added to accelerate and improve a fermentation process. The term “starter” in this context is appropriate because the SC initiates and carries through the necessary changes in the raw material to yield the cultured product. The entire cultured products manufacture is dependent upon the activity of the starter.

Microorganisms selected to be used as SC are expected to have some characteristics such as: adapting easily to raw food matrix and process; carrying through every change to attain the desired body, texture and flavour in the final product; developing nutritional value and digestibility; improving safety by preservative effect retarding or inhibiting pathogenic and spoilage flora and thereby increasing shelf life; sometimes adding functionality, for example, in probiotic products the added cultures impart health-promoting properties to the consumer.

In fermented dairy products, SC have a multifunctional role. Their fundamental ability to produce acid aids in separation of curd from whey during cheese manufacture, modifies texture by proteolytic activity during ripening, enhances preservation by competition with microbial consorcium, produces low molecular weight compounds that contribute to flavour and aroma, etc. Some LAB and yeast strains are capable of degrading antinutritional factors, such as phytic acid and phenolic compounds. Incorporation of these microorganisms as SC in fermented matrices, therefore, upgrades the nutritional value of food (De Dea Lindner et al. 2013). Selected strains may improve protein digestibility and micronutrient bioavailability and contribute more specifically to nutritional enrichment through the biosynthesis of vitamins and aminoacids (Holzapfel 2002).

Bourdichon et al. (2012) revised and updated the taxonomy and the inventory of microorganisms used in food fermentations covering a wide range of food matrices (dairy, meat, fish, vegetables, legumes, cereals, beverages and vinegar), and reviewed the US and European regulatory frameworks for use of microorganisms in food fermentations. Those regulatory frameworks emphasised on “the history of use”, “traditional food”, or “general recognition of safety”.

Today, defined (single- and multiple-strains) and undefined (mixed-strain and back-slopping) cultures are extensively used around the world to produce fermented food (Table 14.1). Food processors in most cases do not propagate the SC at the industrial plant and prefer the simpler approach of carrying out a direct vat inoculation (DVI) with commercial products (frozen and freeze-dried culture concentrates). Although this appears simple to carry out, there are critical manipulations to ensure adequate storage and inoculation of the cultures. Furthermore, the use of commercial SC has reduced the diversity of fermented products because the available new and interesting cultures are limited.

TABLE 14.1 Defined (single- and multiple-strains) and undefined (mixed-strains and back- slopping) cultures used to produce fermented food. - not used; + applied. Source: Holzapfel (2002) and De Dea Lindner et al. (2013)

Food

Single culture

Multiple cultures

Mixed cultures

back-slopping

Beer

+

+

-

-

Bread

+

+

+

+

Cacao

-

+

+

-

Cheese

+

+

+

-

Coffee

-

+

+

-

Miso

+

-

-

-

Olive

+

-

+

-

Pickled cucumber

+

-

+

-

Sauerkraut

+

-

-

+

Sausage

+

+

-

+

Soy sauce

+

-

-

-

Spirits

+

+

-

-

Tea

-

+

+

-

Vinegar

+

+

-

-

Wine

+

+

-

-

Because of the fundamental functions of cultures in fermented products, the selection, propagation and handling of SC are of paramount importance in successful product manufacture and merchandizing. This holds true in the industrial production of SC, which would entail an additional burden in using the most optimum harvesting and preservative techniques that would ensure optimum functionality of the culture during application. Selection and use of MFC in food industry are challenging tasks that require a solid understanding of manipulation and factors that affect microbial interaction. The first task is to find a suitable microorganism for use in the desired process, isolating from the environment or modifying using molecular techniques.

Commercial production of SC grew rapidly and was widespread at the beginning of the 20th century. The advantages of using SC to initiate fermentation were convincing as before their use, fermentations were long in hours and much of the product was too poor in terms of quality. Slow fermentation was also a public health threat, because raw materials were not thermal treated. Production failures can result in heavy financial loss, as modern industries process large quantities of raw materials. SC manufacture is one of the most important and also one of the most difficult processes in the food biotechnology. Very careful attention must therefore be paid to the manufacturing technology and choice of process equipment.

As consumers increasingly look for fermented products to improve their health, food and beverage companies can leverage the natural wholesomeness of cultured products to provide flavourful, innovative solutions that support their organoleptic requirements or meet their needs for convenience. Growing consumer interest in healthy, portable, convenient food and beverages has played an important role in the growth of cultured products which in turn has created a wide-open field of opportunity for product developers to formulate innovations to meet the needs of today’s consumers. Advances in technology, processes and packaging, as well as investments in research and development, can benefit food and beverage companies as they continue to identify opportunities for product development.

Innovation is one of the main strategies of the food industry to generate growth and economic vitality. Latin America is a dynamic market, as well as mature and expressive in the fermented food production sector. However, the industries that use biotechnological processes have a barrier to expansion: there is a shortage in mainland production of inputs such as cultures for fermented products.

The intent of this chapter is to describe our current understanding of what constitutes MFC, microorganisms involved and functions, the criteria for selecting and developing SC, as well as evaluating performance, the use and production of SC, manufacturing parameters to consider in the use of cultures and future prospects.

  • [1] Food Science and Technology Department, Federal University of Santa Catarina, Rod. AdmarGonzaga, 1346. Itacorubi. 88034-001, Florianopolis, SC, Brazil.
  • [2] Corresponding Author: This email address is being protected from spam bots, you need Javascript enabled to view it
 
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