Abstract
Penicillium roqueforti is a major cause of fungal food spoilage. Its conidia are the main dispersal structures of this fungus and therefore the main cause of food contamination. These stress resistant asexual spores can be killed by preservation methods such as heat treatment. Here, the effects of cultivation time and temperature on thermal resistance of P. roqueforti conidia were studied. To this end, cultures were grown for 3, 5, 7 and 10 days at 25 °C or for 7 days at 15, 25 and 30 °C. Conidia of 3- and 10-day-old cultures that had been grown at 25 °C had D56-values of 1.99 ± 0.15 min and 5.31 ± 1.04 min, respectively. The effect of cultivation temperature was most pronounced between P. roqueforti conidia cultured for 7 days at 15 °C and 30 °C, where D56-values of 1.12 ± 0.05 min and 4.19 ± 0.11 min were found, respectively. Notably, D56-values were not higher when increasing both cultivation time and temperature by growing for 10 days at 30 °C. A correlation was found between heat resistance of conidia and levels of trehalose and arabitol, while this was not found for glycerol, mannitol and erythritol. RNA-sequencing showed that the expression profiles of conidia of 3- to 10-day-old cultures that had been grown at 25 °C were distinct from conidia that had been formed at 15 °C and 30 °C for 7 days. Only 33 genes were upregulated at both prolonged incubation time and increased growth temperature. Their encoded proteins as well as trehalose and arabitol may form the core of heat resistance of P. roqueforti conidia.
Highlights
Food deterioration can have chemical, physical or microbiological causes
No further increase in thermal resistance was found when conidia were tested of cultures grown at 30 °C for 10 days (D56-value 3.97 ± 0.11 min) (Fig. 2B). This demonstrates that thermal resistance of the conidia was maximal after 7-days of cultivation at 30 °C. These results show that D56-values of P. roqueforti conidia differ 4-fold within the tested cultivation time and temperature range
P. roqueforti conidia that are present in air at a certain location and time will not all have matured for the same time on the conidiophores before they had been released and will not have been formed under the same environmental conditions
Summary
Food deterioration can have chemical, physical or microbiological causes. It results in a product with changed sensory properties such as visible appearance and the presence of off-odors and off-flavors. Food spoilage can be associated with the introduction of toxic compounds. The impact of spoilage on food security is significant. Fungal conidia are ubiquitously present in the environment. These asexual spores are produced in overwhelming quantities and are effectively dispersed by wind, water, or animals like insects (Dijksterhuis, 2019). As a single spore can cause spoilage, inactivating the most resistant spore is crucial from a food preservation perspective
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