Starter bacteria

Novella-Rodriguez et al. (2002) tested in vitro the starter bacteria Lactococcus lactis subspecies lactis combined with Lactococcus lactis subspecies cremoris, and Lactococcus lactis subspecies lactis, and found that they did not decarboxylate amino acids or produce amines. The conclusion was that the biogenic amine content found in cheese should be attributed to the presence of non-starter bacteria. Some researchers believe that biogenic amines are produced through the interaction of adventitious microorganisms (Joosten and... 

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... 

Figure 10.20 Formation of water-soluble nitrogen (WSN) in (A) Cheddar cheese with a controlled microflora (free of non-starter bacteria) (B) controlled microflora chemically-acidified (starter-free) cheese (C) controlled microflora, rennet-free cheese (D) controlled microflora, rennet-free, starter-free cheese.

O Keeffe et al. (1977) reported that some porcine pepsin survives Cheddar cheesemaking and contributes to casein breakdown during cheese curing. However, it has been shown that the breakdown they attributed to pepsin occurs in curd containing neither coagulant nor starter bacteria (Majeed 1984). More recent studies have shown that porcine pepsin does not survive in Cheddar cheese when the milk is set at pH 6.6 (Yiadom-Farkye 1986). This supports earlier reports of Green (1972) and Wang (1969). 

Combined or single effects of heating and acid production by the starter bacteria increase whey syneresis and establish moisture levels for a given variety of cheese. Almost 96% of the moisture lost in Cheddar cheese during cooking occurs in the first 30 min (Lawrence 1959). A comprehensive review of syneresis has been written by Walstra et al. (1985). 

Rash, K. E. and Kosikowski, F. V. 1982. Influence of lactic acid starter bacteria on enteropathogenic Escherichia coli in ultrafiltration prepared Camembert cheese. J. Dairy Sci. 65, 537-543. 

Thomas, T. D. and Mills, O. E. 1981. Proteolytic enzymes of starter bacteria. Neth. Milk Dairy J. 35, 255-273. 

The starter and non-starter bacteria appear to attach, via filaments from their cell walls, to the casein matrix (Kimber et al., 1974) and are concentrated near the fat-casein interface (Laloy et al., 1996 Haque et al.,... 

A more heterogeneous distribution of starter bacteria in cheese at the microstructural scale, as the level of fat is reduced owing to the concomitant reduction in fat/casein surface area, and... 

Hence, the location of bacteria in cheese at the fat-casein interface may be important in relation to the growth dynamics of starter and non-starter bacteria in cheese and their effects on cheese maturation (cf. Sections 11.5, 11.7-11.8). 

During cheese ripening, the population of starter bacteria generally decreases while the number of non-starter lactic acid bacteria (NSLAB) generally increases these changes are well documented for many full-fat rennet-curd cheese varieties, (e.g., Cheddar) (Cromie et al., 1987 Jordan and Cogan, 1993 McSweeney et al., 1993 Lane et al., 1997 Haque et al., 1997 Beresford and Williams, 2004). 

Figure 11.6. Age-related changes in the populations of starter (A) and non-starter bacteria (B) in full-fat (30.4%, w/w ( ) reduced-fat (21.9%, w/w (O) half-fat (17.2%, w/w A) and low-fat (7.2%, w/w A) Cheddar cheese. The values presented are the means of three replicate trials (drawn from data of Fenelon el al., 2000a).

Collins, Y.F., McSweeney, P.L.H., Wilkinson, M.G. 2003b. Evidence for a relationship between autolysis of starter bacteria and lipolysis in Cheddar cheese. J. Dairy Res. 70, 105-113. 

Oxidized flavor is of minor importance in fermented dairy products such as cheese or yogurt (Wong et al., 1973 Czulak et al., 1974 Korycka-Dahl et al., 1983). Several factors may be involved, including depletion of oxygen by the growth of starter bacteria, the acidic pH of the products, peptides produced by proteolysis, and the formation of antioxidants by microorganisms (Eriksson, 1982). 

Although the safety of traditional lactic starter bacteria has never been in question, the more recent use of intestinal isolates of bacteria (bifidobacteria, intestinal lac-tobacilli, and enterococci), to be delivered as probiotics in high numbers to consumers with potentially compromised health, has raised the question of safety. These intestinal isolates do not share the centuries-old tradition of being consumed as components of fermented dairy products. However, their presence in commercial products over the past few decades has not given any indication of a safety concern. 

Daryaei, H., Coventry, M.J., Versteeg, C., and Sherkat, E. 2008. Effect of high pressure treatment on starter bacteria and spoilage yeasts in fresh lactic curd cheese of bovine milk. Innovative Eood Science and Emerging Technologies 9 201-205. 

Lactate in cheese may be oxidized to acetate. Pediococci produce 1 mol of acetate and 1 mol of CO2 and consume 1 mol of O2 per mole of lactate utilized (Thomas et al, 1985). The concentration of lactate in cheese far exceeds that required for optimal oxidation, and lactate is not oxidized until all sugars have been exhausted. The oxidation of lactate to acetate in cheese depends on the NSLAB population and on the availability of O2, which is determined by the size of the block and the oxygen permeability of the packaging material (Thomas, 1987). Acetate, which may also be produced by starter bacteria from lactose (Thomas et al., 1979) or citrate or from amino acids by starter bacteria and lactobacilli (Nakae and Elliott, 1965), is usually present at fairly high concentrations in Cheddar cheese and is considered to contribute to cheese flavor, although high concentrations may cause off-flavors (see Aston and Dulley, 1982). Thus, the oxidation of lactate to acetate probably contributes to Cheddar cheese flavor. 

Most of the lactose in milk is lost in the whey during cheese manufacture and hence most cheese contain only trace amounts of carbohydrate (Table XIII). Furthermore, the residual lactose in cheese curd is usually fermented to lactic acid by starter bacteria. Thus, cheeses are suitable dairy foods for lactose-malabsorbing individuals who are deficient in the intestinal enzyme, lactase. 

At present, many of the techniques used to genetically engineer starter bacteria are not food-grade but it is almost certain that food-grade techniques will be developed which will enable super tailor-made strains to be developed. Very exciting developments can be expected in this area. 

Thomas, T. D. (1987). Acetate production from lactate and citrate by non-starter bacteria in Cheddar cheese. N.Z. J. Dairy Sci. TechnoL 22, 25-38. 

Visser, F. M. W. (1977a). Contribution of enzymes from rennet, starter bacteria and milk to proteolysis and flavour development in Gouda cheese. 1. Description of cheese and aseptic cheesemaking techniques. Neth. Milk Dairy J. 31, 120-133. 

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