Factors affecting penicillium roquefortii (penicillium glaucum) in internally mould ripened cheeses: implications for pre-packed blue cheeses

The amount and vivid colour of blue veins of internally mould ripened cheeses are desirable quality characteristics. It is therefore important that there is a sufficient amount of veining and that it maintains its blue appearance to be appealing to consumers therefore leading to maximised sales potential and profit for the manufacturing company. Optimum in vitro growth mimicking the conditions typically found in prepacked blue cheeses, and using lactose as the sole carbon source, was facilitated by a gas mixture of 5% oxygen ⁄0% carbon dioxide ⁄ balance nitrogen). The work undertaken in this study determined that the factors for optimum in vitro growth of Penicillium roquefortii (strain PRB6) were: a temperature of 20 ± 1 �C, pH of 6.0 ± 0.1, and a relative humidity of 70 ± 0.1%. Further in vitro studies have also shown that the increasing ‘in-pack’ carbon dioxide concentration not only depresses the growth of P. roquefortii but also affects immature conidiospore pigmentation (no effect has been seen on mature conidiospore pigmentation). The implications of this study suggest that the majority of pre-packed internally mould ripened blue cheeses on sale in supermarkets are packaged in inappropriate materials. For some cheeses (e.g. the Roquefort-type cheeses) this is not an issue since these are packed in a much more mature state and some loss of veining colour is not appreciably noticeable.