Cheddar cheese NSLAB

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. 

Several studies, especially in Australia, have shown that provided cheese of good composition and with a low count of NSLAB is used, the ripening of Cheddar cheese can be accelerated and its flavor intensified by using higher than normal ripening temperatures. Optimum results have been reported at 13-15°C at which the ripening time required for the production of mature cheese can be reduced by 50% (Folkertsma et al, 1996). Such practices are in fact reverting to traditional methods. 

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). 

The number of NSLAB in Cheddar decreases with fat content (Figure 11.6b), with the count in LFC (5%, w/w) being significantly lower than that in FFC (33%, w/w) (Haque et al., 1997 Fenelon et al., 2000a). The decrease in NSLAB as the fat content of cheese is reduced may be due to a number of factors including ... 

Typical levels of lactate in Camembert, Swiss, and Cheddar are 1.0,1.4, and 0.5%, respectively (Karahadian and Lindsay, 1987 Turner et al, 1983 Turner and Thomas, 1980). The fate of lactic acid in cheese depends on the variety. Initially, Cheddar contains only l(+) lactic acid but as the cheese matures, the concentration of o-lactate increases. The latter could be formed from residual lactose by lactobacilli (Turner and Thomas, 1980 Thomas and Pearce, 1981 Tinson et al, 1982) or by racemization of l-lactate by NSLAB. Except in cases where the post-milling activity of the starter is suppressed (e.g., by S/M > 6%), racemization is likely to be the principal mechanism (Thomas and Crow, 1983). Racemization of L-lactate, which appears to occur in several cheese varieties (Thomas and Crow, 1983), is probably not significant from the flavor viewpoint. However, calcium D-lactate may crystallize on the surface of cheese, causing undesirable white specks (Pearce et al, 1973 Severn et al, 1986 Dybing et al, 1988). 

Despite the findings by a number of authors that the NSLAB can dominate the microflora of Cheddar-type cheese during much of its ripening. 

The predominant NSLAB in Cheddar and Dutch-type cheeses are meso-philic Lactobacillus, which possess a cell wall-associated and intracellular proteinases. A range of intracellular peptidases, including dipeptidases, aminopeptidases, and endopeptidases, have been identified in Lactobacillus (see reviews by Khalid and Marth 1990a Peterson and Marshall, 1990). Interestingly, carboxypeptidase activity, which has not been found in lacto-cocci, has been reported in Lactobacillus casei (El Soda et al., 1978). 

Since the numbers and strains of lactobacilli in cheese are uncontrolled, it is likely that they contribute to variability in cheese quality. Since it is impossible to eliminate NSLAB completely, even under experimental conditions, it appears worthwhile to determine what factors affect their growth. The number of NSLAB in Cheddar is strongly influenced by the rate at which the curd in cooled and subsequently ripened (Folkertsma et al., 1996). The growth of NSLAB does not appear to be influenced by the concentration of NaCl in the cheese (Turner and Thomas, 1980). It is likely that the moisture content of cheese affects the growth of NSLAB but we are not aware of studies in which this effect has been studied. 

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