Cheddar citrate

Members of three genera are used as cheese starters. For cheeses that are cooked to a temperature below about 39°C, species of Lactococcus, usually Lc. lactis ssp. cremoris, are used, i.e. for Cheddar, Dutch, Blue, surface mould and surface-smear families. For high-cooked varieties, a thermophilic Lactobacillus culture is used, either alone (e.g. Parmesan) or with Streptococcus salivarius ssp. thermophilus (e.g. most Swiss varieties and Mozzarella). Leuconostoc spp. are included in the starter for some cheese varieties, e.g. Dutch types the function is to produce diacetyl and C02 from citrate rather than acid production. 

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. 

Approximately 90% of the citrate in milk is soluble and is lost in the whey however, the concentration of citrate in the aqueous phase of cheese is approximately three times that in whey (Fryer et al., 1970), reflecting the concentration of colloidal citrate. Cheddar cheese contains 0.2 to 0.5% (w/ w) citrate which decreases to 0.1% at 6 months (Fryer et al., 1970 Thomas, 1987). Inoculation of cheesemilk with Lb. plantarum accelerated the depletion of citrate pediococci did not appear to utilize citrate (Thomas, 1987). 

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. 

Fig. 10.29. RP-HPLC of the pH 4.6-soluble fraction of a citrate extract of Cheddar cheese after 3 (a) and 24 (b) weeks ripening at 10 °C (according to Kaiser et ah, 1992)...

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