Preincubation of Penicillium commune conidia under modified atmosphere conditions: Influence on growth potential as determined by an impedimetric method.

The combined effect of preincubation time, relative humidity (r.h.), headspace carbon dioxide (CO2) and oxygen (O2) on subsequent growth potential of conidia from Penicillium commune was studied using Response Surface Modelling (RSM). Native conidia were preincubated under modified atmosphere conditions in sealed vials for 14, 35 and 56 d. Lag time and growth rates were determined using impedance microbiology on a Bactometer. Conidia survived and some swelling was observed during all experimental preincubation conditions. Regression analysis of the subsequent growth responses showed that relative humidity in the vials was the most significant factor affecting lag time of the conidia after preincubation for 14 and 35 d. Storage for 35 d extended lag times by 15 h when the level of r.h. was increased from 41% to 80%. After prolonged storage (56 d) r.h. and CO2 levels elicited a significant effect on the growth potential of the conidia. Increasing CO2 levels (7% to 20%) in the storage atmosphere, reduced lag times from 65 to 25 h. By the same increase in CO2 levels, at 70% r.h., growth rates were doubled. Oxygen in the range 2-18%, did not produce any significant effect on either lag time or growth rate during the time of preincubation. This paper describes the first investigation of the combined effect of two significant environmental factors on the growth potential of conidia from P. commune. It is demonstrated that storage for more than 56 d in levels of CO2 below 20% results in sublethal injury of the conidia from P. commune, retarding growth by increasing lag times and decelerating growth rates.