Effect of water activity, modified atmosphere packaging and storage temperature on spore germination of moulds isolated from prunes

Abstract

The combined effect of medium water activity (a(w)) modified atmosphere packaging (MAP) on the conidial germination of Aspergillus niger, Eurotium amstelodami, Penicillium chrysogenum and Fusarium oxysporum was studied by applying response surface methodology (RSM) for 45 days incubation at 20, 30 and 40°C. Oxytetracycline glucose yeast extract (OGYE) agar media were prepared over a wide range of a(w) (0.80-0.95), controlled by glucose. The headspace atmosphere composition varied from 0-20% for O2 and from 0-80% for CO2 with N2 as balance in the ratio medium/gas mixture of 1/3 (v/v). The results of this experiment were confirmed by repeating some combinations (a(w)-MAP) in the zone where the inhibition was effective. In contrast to A. niger which germinated and grew better at 30 and 40°C, P. chrysogenum and F. oxysporum were capable of germinating and growing at 20°C but not at 40°C. E. amstelodami was less influenced by the incubation temperature than were the other species. Under anaerobic atmospheres, germination and growth of all tested species were completely inhibited at low a(w), while at high a(w) because of residual O2, conidia germinated but failed to grow. At any a(w) value between 0.88 and 0.92, conidia failed to germinate when 100% CO2 was applied. Similar results were obtained for E. amstelodami and F. oxysporum in 80% CO2-20% N2, and 60% CO2-40% N2. Under aerobic conditions, at 5% O2 germination and growth occurred only at high a(w), while 10 or 20% O2, combined with either 80 or 60% CO2 conidial germination and mould growth were only delayed comparing to the control (air).