HE Spinnler and MN Leclercq Perlat

In general, the accumulation of short hydrophobic peptides in cheese is the major source of bitterness [89], and mould-ripened varieties are not an exception. The very strong proteolytic activity of Penicillium camemberti, especially its acid protease, as compared to its ability to break down peptides, causes the accumulation of bitter peptides. It has been shown using a trained panel [79] that the increase in peptide concentration is correlated to the bitter taste descriptor. On the other hand, Geotrichum candidum has high peptidase activity (carboxypeptidase and aminopeptidase) and it has been shown that when Geotrichum is used in association with Penicillium, the cheeses are significantly less bitter. The use of lactic acid bacteria with low or medium proteolytic activity [23] may also prevent the formation of bitter peptides.

A few other flavour defects in this Camembert-type cheeses have been reported. Some years ago, in summer, quite often mould-ripened cheeses made using stabilised curd technology had a celluloid taste. It has been shown that P. camemberti can be responsible for the production of styrene. When easily usable substrates such as lactose or lactate are exhausted, Penicillium attacks proteins and fat. The oxidation of certain amino acids such as phenylalanine is catalysed through action of phenylalanine ammonia lyase. Phenylalanine can be degraded to styrene probably with cinnamic acid as a metabolic intermediate. The addition of phenylalanine labelled with 13C on its benzene ring in a culture medium for P. camemberti, together with low concentrations of glucose, leads to the accumulation of styrene with the label on its benzene ring. All conditions resulting in the quick exhaustion of the easily usable substrates (lactose and lactate) lead to the production of styrene. The substrate uptake is more intense at the cheese surface, where Penicillium grows, than within the cheese. The concentration gradient causes lactate to migrate from inside the cheese to the surface. If lactate uptake at the surface is quicker than the diffusion of the lactate from within the cheese to the rind, as it is the case for ripening temperatures >15 0C, the starving Penicillium starts to break down the other substrates of the medium such as fat or proteins. This also occurs if curd is washed to remove a part of the lactose and lactate in order to speed up the ripening reactions, or when the enrichment of the curd in fat limits diffusion of lactate. It has been reported that styrene is produced mainly in case of starvation but only by certain strains of P. camemberti (Spinnler et al., 1992).

Penicillium camemberti has also been reported to produce geranium-like, musty, potato-like or earthy mushroom flavours. Most of the compounds involved in these defects are related to the catabolism of unsaturated fatty acids. The mushroom-like odour, which can be a desirable note in some mould-ripened cheeses, becomes a defect when the level of this olfactive note is too high. Compounds such as 1-octen-3-ol or 3-octanone are produced by Penicillium and have this olfactive property. Geranium odour is related to the production of 1,5-octadien-3-one and 1,5-octadien-3-ol, while the earthy note is related to 2-methyl isoborneol. Finally, the potato-like odour was attributed to 2-methoxy, 3-isopropyl pyrazine produced by certain strains of Penicillium.

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