Effect of heat exposure on the colour intensity of red pigments produced by Penicillium purpurogenum GH2

• Thermal stability of a fungal red pigment studied in the 30–80 °C range and pH 4–8.
• The pigment extract is sufficiently stable for minimal losses with HTST processing.
• pH had a significant effect on the stability, with lower stability the lower the pH.
• Process provides a potentially economically viable natural alternative for colorants.

Natural pigments are alternatives to synthetic colorants with growing industrial interest for food and non-food uses (e.g. textiles). However, they are generally thermally labile and therefore their practical interest depends on the loss under typical processing conditions being acceptable. Penicillium strains are producers of natural red pigments of potential interest. The loss of colour of these pigments was studied at relevant conditions for food and beverage pasteurisation. Thermal liability of colour was well described by a first order model (with a constant off-set) at pH 6 up to 80 °C, and at 80 °C for pH 4–8, with a z-value of 48.7 ± 0.9 °C and a D80C,pH6 of 981 ± 5 min. The stability was significantly affected by pH, with an approximately linear increase of 173 ± 3 min in D80 per pH unit. The high z-value, which is 5 times the z of typical target micro-organisms in thermal processing, suggests a good scope for process optimisation to minimise losses. At the middle point of pH 6 these kinetic parameters would suggest that losses of red colour intensity (OD at 500 nm) of less than 1% in pasteurisation are feasible. Losses will be higher in matrices of lower pH, where process optimisation will therefore be more relevant. It was concluded that these red pigments are of industrial interest, as with further optimisation of industrial production yields to minimise costs, and then going through the process of acceptance as new food ingredients, they are potentially economically competitive.