Effect of modified atmosphere packaging and water activity on growth of Eurotium amstelodami, E-chevalieri and E-herbariorum on a sponge cake analogue

The combined effects of water activity (a(w)), oxygen (O-2) and carbon diox ide (CO2) levels on growth variables of three species of Eurotium (two isol ates of each) on a sponge cake analogue were studied. The use of a multivar iate statistical method (PLS) for the analysis of data showed that in gener al, the fungi had the same behaviour, according to their growth responses, to changes in the three tested factors. However, the maximal growth of E. h erbariorum was somewhat more affected by the O-2 level at lower CO2 levels. On the other hand, CO2, a(w) and the interaction between CO2 and O-2 were found to be the most significant factors describing growth variables. In ad dition, the model found in this study had a good predictive power. There wa s a positive correlation between the CO2 concentration in the bags and the lag phase, and a negative correlation between the growth rate and maximum m ycelial growth. In general, no isolates were able to growth when CO2 concen trations were higher than 60% under anaerobic conditions. At lower values o f CO2, a(w) and O-2 influenced growth variables. Low levels of O-2 (0.02-0. 5%) did not affect the growth variables studied when levels of CO2 in the b ags were high. However, when the CO2 concentration decreased, the different O-2 levels had an influence on the growth variables, i.e., a small differe nce in the concentration of O-2 can allow fungi to grow.