EM Diisterhoft and G van den Berg

The soapy off-flavour is caused by the combination of different free fatty acids (FFA) derived from hydrolytic degradation (lipolysis) of milk fat [90]. Lipolysis during ripening in normal Gouda-type cheese (made from pasteurised milk) is rather low (ca. 400 mg FFA/kg at 8 weeks). It is principally the short chain fatty acids (C4-C6) which - in low levels - contribute positively to the Gouda flavour profile. In contrast to some other (semi) hard cheeses, even a low level of longer chain FFA (e.g. C14 to C18) is considered undesirable and will lead to a 'soapy' off-flavour. This level corresponds to an acidity of the milk fat of 1.5mmol/ 100 g or higher in young cheese. Depending on the cause of this soapiness, it may continue to increase with prolonged ripening or may remain relatively stable after about 8-12 weeks of ripening. In general, soapiness will be perceived most in young to medium aged Gouda cheeses, as with increasing maturation, the soapy off-flavour may be increasingly hidden by a higher overall flavour intensity.

The hydrolysis of the triglycerides present in cheesemilk into mono-, diglycerides and FFA is catalysed by lipases. Lipases are found in milk (although their activity is greatly reduced by pasteurisation), they are present (at very low activities) in starter cultures used for Gouda-type cheese production [23] and may derive from adventituous microbial flora (e.g. from psychrotrophic bacteria, yeasts and moulds). Lipases of different origins have different specificities. As a consequence, they release different mixtures of free fatty acids (short, medium, long chain) and the corresponding off-flavours may vary.

Lipases act rapidly on triglycerides when they are released from the natural fat globule in which they are normally protected by the fat globule membrane. Thus, any treatment of raw milk, in particular destroying (part) of the milk fat globule membrane, may lead to enhanced lipolysis. Homogenisation, membrane filtration processes and pumping through the equipment at the cheese factory lead to different extents of damage to the fat globules, causing the release of triglycerides. Pasteurisation of cheese milk (72 0C x 15 s) largely inactivates the indigenous milk lipase [11] and residual activity is considered irrelevant for Gouda-type cheese made from milk of normal quality. Lipases of the adventitious psychrotrophic microflora [7] are, however, more heat resistant and pose a significant risk, if these bacteria have been able to grow to high numbers in the cheesemilk prior to heat treatment or if post-pasteurisation contamination occurs. The lipolytic activity of the usual starter cultures used in Gouda-type cheesemaking, however, is normally very low and probably does not contribute to soapiness, if the quality of cheesemilk is normal.

Although mould growth on naturally ripened Gouda-type cheeses is largely controlled and inhibited by good hygienic conditions and by inclusion of natamycin in the coating, the cheese surface cannot be regarded as sterile. Growth of bacteria and moulds on the surface during ripening may contribute to 'soapy' off-flavours, as many have considerable lipolytic activity.

Further reading

DEETH, H.C. and FITZ-GERALD, c.H. (2006). Lipolytic enzymes and hydrolytic rancidity, in Advanced Dairy Chemistry Volume 2 Lipids, 2nd edn, P.F. Fox (ed.), Springer, New York, pp. 481-556. DRIESSEN, F.M. (1983). Lipases and proteinases in milk. Occurrence, heat inactivation and their importance for the keeping quality of milk products. PhD thesis, Wageningen University, The Netherlands VAN DEN BERG, M.G. (1984). The thermization of milk. Bull. IDF 182, 3-11.

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