Starter culture

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. 

There are many reasons for using starter cultures in food production. In fact, recent research has turned the use of starter cultures into high technology by which it is possible to govern flavour development, texture and viscosity as well as the keeping quality of foods. Research in starter cultures has been increasingly focused on the further added value that may be achieved by using these bacteria. This includes improvement of the dietetic and health-benefit properties of foods. 

From the beginning, the natural occurrence of lactic acid bacteria and yeast has reduced our need for using additives. The natural presence of these organisms in foods has directed research to exploit further the possibilities in utilising biotechnology instead of chemistry. 

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Commercially available yeast extracts are made from brewers yeast, from bakers yeast, from alcohol-grown yeast (C. utilis) and from whey grown yeast (K fragilis). Extracts are used ia fermentation media for productioa of antibiotics, ia cheese starter cultures, and ia the productioa of viaegar. They are also exteasively used ia the food iadustry as condiments to provide savory flavors for soups, gravies and bouillon cubes, and as flavor intensifiers ia cheese products. 

To ensure the safety of food products, representative samples must be inspected so that foodborne bacteria can be identified.15,18,19 Bacteria producing heat-stable enterotoxins, such as Staphylococcus aureus, may be identified by biochemical and serological techniques.20,21 Molecular methods are now widely used for the identification of many pathogenic foodborne bacteria,15,22,23 In addition bacteria used as starter cultures for cheese, yogurt, other fermented foods and beverages, and probiotic dietary supplements may be identified for quality assurance.22,24,25... 

If the culture is to provide both the yeast and the flavour of sour dough then either it must acquire a wild yeast or a starter culture that includes yeast must be added. In some cases the sour dough culture is only used to give the sour dough taste while conventional yeast is added. 

The upstream processing element of the manufacture of a batch of biopharmaceutical product begins with the removal of a single ampoule of the working cell bank. This vial is used to inoculate a small volume of sterile media, with subsequent incubation under appropriate conditions. This describes the growth of laboratory-scale starter cultures of the producer cell line. This starter culture is, in turn, used to inoculate a production-scale starter culture that is used to inoculate the production-scale bioreactor (Figure 5.7). The media composition and fermentation conditions required to... 

Figure 5.7 Outline of the upstream processing stages involved in the production of a single batch of product. Initially, the contents of a single ampoule of the working cell bank (a) are used to inoculate a few hundred millilitres of media (b). After growth, this laboratory-scale starter culture is used to inoculate several litres/tens of litres of media present in a small bioreactor (c). This production-scale starter culture is used to inoculate the production-scale bioreactor (d), which often contains several thousands/tens of thousands litres of media. This process is equally applicable to prokaryotic or eukaryotic-based producer cell lines, although the bioreactor design, conditions of growth, etc., will differ in these two instances...

Fermentation follows for several days subsequent to inoculation with the production-scale starter culture (Figure 5.7). During this process, biomass (i.e. cell mass) accumulates. In most cases, product accumulates intracellularly and cells are harvested when maximum biomass yields are achieved. This feed batch approach is the one normally taken during biopharmaceutical manufacture, although reactors can also be operated on a continuous basis, where fresh nutrient media is continually added and a fraction of the media/biomass continually removed and processed. During... 

A single colony was used to inoculate a 5 mL starter culture in LB medium with 30 jig mL kanamycin, which was grown overnight at 37 °C. 

Batch cultivation of P. mendocina KRl was carried out in 2 x 2 L centre column Erlenmeyer flasks. Each flask contained stock solution 1 (8 mL) and deionized water (390 mL). This solution was autoclaved and cooled before adding 400 /iL stock solution 2,400 uL stock solution 3 and 400 pL stock solution 4. Toluene (600 /iL) was added to the centre column. Overnight starter cultures were used to inoculate (2% v/v) the growth medium. Cultures were incubated at 30 °C shaking at 200 rpm. 

The predominant amines found in cheese are tyramine, cadaverine, putrescine and histamine (Table 6.6) (Stratton et ah, 1991 Silla Santos, 1996 Novella-Rodriguez et ah, 2002 Novella-Rodriguez et al., 2003). Biogenic amine levels may vary between types of cheese as well as within the varieties themselves. The differences within a variety of cheese may be due to a number of factors, including manufacturing processes, bacterial counts in the milk, heat treatments used, use of starter cultures, and the duration and conditions of the ripening process (Stratton et al., 1991 Pinho et al., 2001 Novella-Rodriguez et al., 2003). 

Ansorena et al. (2002) also found that this change in pH leads to a decrease in the amounts of histamine and putrescine produced. Use of acidulants, such as glucono 8-lactone, may influence amine production by ensuring a drop in pH (Santos et al., 1986 Buncic et al., 1993 Maijala et al., 1993). A gradual increase in pH throughout the ripening process is related to the proteolytic activity of the starter culture as it forms peptides and amino acids (Bover-Cid et al., 1999). 

The hygienic quality of the raw material used for the manufacture of sausage is an important factor relating to the production of biogenic amines. High-quality meats with low initial bacterial counts help keep the biogenic amines well below the toxic level (Shalaby 1995 Bover-Cid et al., 2000) and should be used with the addition of a non-amine-producing starter culture. 

Fernandez-Garcia, E., Tomillo, J. and Nunez, M. (1999). Eflhct of added proteinases and level of starter culture on the formation of biogenic amines in raw milk Manchego cheese, Int. J. Food Microbiol., 52, 189. 

Hernandez-Jover, M., Izquierdo-Pulido, M., Veciana-Nogues, M.T., Marine-Font, A. and Vidal-Carou, M.C. (1997). Effect of starter cultures on biogenic amine formation during fermented sausage production, J. Food Prot., 60, 825. 

Komprda, T., Neznalova, J., Satndara, S. and Bover-Cid, S. (2001). Effect of starter culture and storage temperature on the content of biogenic amines in dry fermented sausage polican. Meat Sci., 59, 267. 

Residues in milk oeeur primarily as the result of the treatment of laetating eows for mastitis and post partum prevention of infeetion. Antibiotie and antimierobial residues in milk can pose significant problems in the making of milk products and cheeses. In the U.S., the primary drugs of concern are those of the p-lactam family, the sulfonamides and tetracyclines the p-lactams because of their ability to inhibit the starter cultures used in cheese and cultured milk products the tetracyclines and sulfonamides because of their... 

Many of the organisms employed are extremely sensitive to antibiotic residuals in the milk. As shown in Table III, as little as 0.05 to 1.0 lU/ml of penicillin and 0.05 to 10.0 microgram/ml of aureomycin inhibited the growth of 19 cheese starter cultures (18). Lower levels are capable of affecting the flavor and texture properties of the product (14, 19) as well as promoting the growth of undesirable antibiotic resistant coliforms (14, 20). 

Table III. Minimum Inhibitory Levels of Penicillin and Aureomycin for Common Dairy Starter Cultures ...

The primary function of cheese starter cultures is to produce lactic acid at a predictable and dependable rate. The metabolism of lactose is summarized in Figure 10.12. Most cheese starters are homofermentative, i.e. produce only lactic acid, usually the L-isomer Leuconostoc species are heterofermentative. The products of lactic acid bacteria are summarized in Table 10.4. 

Table 10.4 Salient features of lactose metabolism in starter culture organisms (from Cogan and Hill, 1993)...

Starter bacteria. The starter culture reaches maximum numbers at the end of the manufacturing phase. Their numbers then decline at a rate depending on the strain, typically by 2 log cycles within 1 month. At least some of the non-viable cells lyse at a rate dependent on the strain. As far as is known, the only extracellular enzyme in Lactococcus, Lactobacillus... 

Table 10.12 Some typical examples of starter cultures employed in the manufacture of fermented milks (from Robinson and Tamime, 1993)...

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