HE Spinnler and MN Leclercq Perlat

The main microorganisms able to raise the pH of Camembert type cheeses are yeasts and Penicillium camemberti. Normally, owing to the low buffering capacity of the curd [22], consumption of lactate changes the pH at the surface very easily, during the first phase of ripening. Yeasts and G. candidum develop quickly immediately after moulding, consuming residual lactose and starting to consume the lactate produced by lactic acid bacteria. The main yeasts found in these cheeses are Debaryomyces hansenii, Kluyveromyces lactis and Kluyvero-myces marxianus. G. candidum grows somewhat later than the yeasts. Other species such as Saccharomyces cerevisiae, Yarrowia lipolytica and Candida spp. are also sometimes present. These organisms may have different metabolisms; for example Kluyveromyces spp. will consume residual lactose first and, only after its exhaustion, lactate will be metabolised though Debaryomyces will consume both simultaneously. In mould-ripened cheese it is not uncommon that the pH will increase slowly during the first 5 days, but the growth of P. camemberti will cause a very fast increase in pH at the surface (Fig. 1). The pH increases from less than 5 to 7.5 in less than 2 days. However, the increase in pH inside the cheese is due to a migration of lactate from the core to the cheese

Fig. 1 Change in pH at the surface (A) and in the core (A) during the ripening of Camembert cheese (Leclercq-Perlat et al., 2004).

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Fig. 2 Transfer of solutes inside Camembert-type cheese from regions of high (+) to low (—) concentration (Leclerq-Perlat et al, 2000).

surface and diffusion of ammonia from the surface to the core (Fig. 2). This mass transfer is quite slow and so, the curd pH rises quite slowly in the core of the cheese (Fig. 1).

Consequently if the pH of a Camembert-like cheese does not increase as quickly as it should, it could be for any of three main reasons:

1. The buffering capacity of the curd is too high. This can be due to too high a pH at the end of moulding, leading to an excessive concentration of minerals present in the curd after draining. Thus, even if a part of the lactate is consumed, the pH stays quite low. It is very important to control pH at the different steps of cheesemaking, particularly at renneting, cutting and moulding, at the end of draining (up to 24 h) and just before salting.

2. Poor development of deacidifying flora. The acid-tolerant and acid-consuming microflora may not grow well and so the lactate consumption will not be adequate. Spraying Penicillium or Geotrichum spores onto the surface of the cheese may help to start the deacidification process.

3. Poor solute transfer. Poor solute transfer (mainly lactate transfer) is due mainly to limited water transfer. Several reasons can be considered. For example, if there is too much fat or if the curd is too dry, the water mobility is limited. An increase in fat content has a general impact on the solute behaviour inside the cheese.

In conclusion, it is noticeable that an excessively high pH (over 4.8) at the end of moulding will cause a whole series of problems that starts with more difficult drainage of the curd and a more moist cheese. This problem will consequently change the mobility of water and the lactate transfer in the curd. The buffering capacity will also be changed because a high concentration of minerals will still be present, which will cause pH buffering.

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