Why does processed cheese sometimes have a soapy flavour

Soapiness is a flavour defect that occurs infrequently in processed cheese products [189]. The presence of this defect is probably due to the formation of soaps such as sodium palmitate or potassium oleate as a result of the interaction of the cations of emulsifying salts (e.g. Na+, K+) and medium to long chain fatty acids. The formation of these compounds is favoured by the high pH and high temperature during cheese processing. Their perception will depend on the pH of the processed cheese, the concentration present and the ability of other flavour/odour compounds present (e.g. natural cheese flavours, sodium chloride) to mask or accentuate them.

Soapiness in processed cheese is most frequently associated with the use of sodium or potassium phosphates, especially orthophosphates, as emulsifying salts. The soapy flavour associated with orthophosphates is probably due in part to their strong buffering capacity and ability to increase the pH of the processed cheese blend to relatively high values (>6) compared with salts with lower buffering capacity (e.g. sodium salts of polyphosphoric acids or citric acid). The higher pH with sodium orthophosphates favours the formation of soap compounds. The dissociation constants, pKa, for phosphoric acid (H3P04) are 2.14, 6.86 and 12.4 at 25 0C. From the Henderson-Hasselbalch equation:

the pKa values correspond to the pH values at which the concentrations of the acid and salt forms of the compound are present at equal concentrations. The acid-salt (sodium) forms of H3PO4 are H3PO4 and NaH2PO4 (pKa 2.14), NaH2PO4 and Na2HPO4 (pKa 6.86), and Na2HPO4 and Na3PO4 (pKa 12.4). The corresponding pKa values for citric acid are 3.0, 4.5 and 4.9, respectively. Owing to its ability to buffer the processed cheese blend to high pH values, the use of a high level of trisodium orthophosphate (Na3PO4) as an emulsifying salt increases the risk of soapy flavour, especially if high levels of free fatty acids are present in the natural cheese being processed [90]. In contrast to phosphates, citrates impart a clean flavour to processed cheese products. This may be expected because of their inability to increase the pH to values as high as that obtained with orthophosphates; the pKa values for citric acid are much lower than those of phosphoric acid. Soapiness in processed cheese may be also due the carry-over of soapy flavours from the natural cheese.

Soapy flavour has been reported in several cheese types including Blue-type [137], Camembert [128] and Cheddar [100]. Its incidence is associated with high levels of free fatty acids, especially capric (C10:0) and lauric (C12:0) acids. The prevalence of soapy flavours in cheese is increased by the addition of lipolytic agents such as moulds (e.g. Aspergillus species) and/or lipolytic enzymes to the cheese milk and/or by homogenisation of cheesemilk or cream [31, 32].

Homogenisation increases the susceptibility of milk fat to break down into free fatty acids by the lipolytic agents in the milk or cream. Soapiness in processed cheeses may be reduced by:

• avoiding the use of natural cheese with soapy off-flavour;

• avoiding the use of cheese or other materials (e.g. hydrolysed butter oil, cheese flavours) with high levels of free fatty acids;

• reducing the pH of the processed cheese;

• reducing the level of orthophosphate emulsifying salts, especially trisodium orthophosphate (ideally use a blend of sodium phosphates and trisodium citrate);

• reducing the processing temperature;

• avoiding the use of 're-worked' processed cheese with soapy off-flavour; and/or

• reducing the levels of fat and/or moisture of the product Further reading

COLLINS, Y.F., MCSWEENEY, P.L.H. and WILKINSON, M.G. (2004). Lipolysis and catabolism of fatty acids in cheese, in Cheese: Chemistry, Physies and Mierobiology Volume 1 General Aspeets, 3rd edn, P. F. Fox, P.L.H. McSweeney, T. M. Cogan and T.P. Guinee (eds.), Elsevier Academic Press, Amsterdam, pp. 373-389. GUINEE, T.P., CARiC, M. and KALAB, M. (2004). Pasteurized processed cheese and substitute/ imitation cheese products, in Cheese: Chemistry, Physies and Mierobiology Volume 2 Major Cheese Groups, 3rd edn, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds.), Elsevier Academic Press, Amsterdam, pp. 349-394. WOO, A.H.Y. (1983). Characterization of the relationships between free fatty acids and dairy flavors. Dissertation Abstraets International, B 44, 742 (Abstract).

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