Modeling the growth of Byssochlamys fulva and Neosartorya fischeri on solidified apple juice by measuring colony diameter and ergosterol content

• The growth of B. fulva and N. fischeri was assessed at 10, 15, 20, 25 and 30 °C.
• Colony diameter and ergosterol content data were used to quantify the fungal growth.
• The Baranyi and Roberts model described well the growth data for both methods.
• Correlations between the parameters of both methods were established.

Byssochlamys fulva and Neosartorya fischeri are heat-resistant fungi which are a concern to food industries (e.g. apple juice industry) since their growth represents significant economic liabilities. Although the most common method used to assess fungal growth in solid substrates is by measuring the colony's diameter, it is difficult to apply this method to food substrates. Alternatively, ergosterol contents have been used to quantify fungal contamination in some types of food. The current study aimed at modeling the growth of the heat-resistant fungi B. fulva and N. fischeri by measuring the colony diameter and ergosterol content, fitting the Baranyi and Roberts model to the results, and finally establishing a correlation between the parameters of the two analytical methods. Whereas the colony diameter was measured daily, the quantification of ergosterol was performed when the colonies reached diameters of 30, 60, 90, 120 and 150 mm. Results showed that B. fulva and N. fischeri were able to grow successfully on solidified apple juice at 10, 15, 20, 25 and 30 °C, and the Baranyi and Roberts model showed good ability to describe growth data. The correlation curves between the parameters of colony diameter and ergosterol content were obtained with satisfactory statistical indexes.