Fungal growth rates and volatile organic compound (VOC) production depend on temperature and growth medium. Three fungal species - Penicillium polonicum, Aspergillus niger, and Botrytis allii - grew faster and produced unique VOCs on onion medium (OM) compared to potato dextrose agar (PDA) at temperatures of 15°C and 25°C. VOC profiling may provide early detection of fungal spoilage of stored onions.

1. Department of Environmental Science – Section of Environmental
Microbiology and Biotechnology- Aarhus University – Denmark
Filippo Casadei1,2, Aimei Wang3*, Merete Edelenbos3, Heleen Bukman4 and Anders Johansen2
CONCLUSIONS/SUMMARY
Fungal growth rate was strictly dependent on temperature and medium. For all the three fungal species, different growth rates
were observed when growing on the two media, with faster growth on OM medium than on PDA. Volatile analysis showed that B.
allii, as well as P. polonicum and A. niger (data not shown), produced VOCs that were not present in the OM medium background.
VOC profiling may be a suitable method for early warning detection of storage diseases,
Filippo Casadei
filippo.casadei01@
gmail.com
7th June 2015 – III International Symposium on Postharvest Pathology 2015 Bari, Italy
MATERIAL AND METHODS
Mycelial radial distribution on solid PDA and OM medium was
used as a measure of growth. To evaluate the influence of
temperature and medium on the production of VOCs, 35 μl of
fungi spore suspension was inoculated on PDA and OM in 20 ml
vials. Vials were placed at 4°C, 15°C and 25°C and VOC profiles
recorded after 9 days by SPME/GC-FID and GC-MS analyses.
The sporification of Penicillium polonicum is greatly influenced by
growth medium, here after 7 day of cultivation on PDA and OM medium.
OBJECTIVES
The aim of this study was to evaluate the effects of medium (PDA:
potato dextrose agar; OM: onion medium) and temperature (4°C,
15°C, 25°C) on growth and production of VOCs from Penicillium
polonicum, Aspergillus niger and Botrytis allii, which are common
spoilage organisms on onions.
1Department of Territorial Ecology and Environment, Faculty of Sciences, Pavia University, via S. Epifanio 14, 27100 Pavia, Italy
2Department of Environmental Science, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
3Department of Food Science, Aarhus University, Kirstinebjergvej 10, DK-5792 Aarslev, Denmark
4Bejo Zaden B.V., Trambaan 2a, NL-1749 CZ Warmenhuizen, The Netherlands
INTRODUCTION
Onions are lost during post-harvest storage due to water loss, sprouting and microbial spoilage. Detection of fungal infection is a
difficult task often leading to heavy economical losses due to improper detection technology and timely action. The use of
volatile organic compounds (VOCs) as an early-warning tool to detect deterioration of onion produce, related to proliferation of
fungal spoilage organisms, may be a solution for spoilage monitoring during storage.
Radial growth (mm) of A.niger on PDA and OM. Values are mean ± standard deviations (n=4)
The project: 'Strategies and
technologies to reduce postharvest
losses of potatoes and vegetables’
is funded by the Innovation Fund.
OMPDA
RESULTS – MYCELIAL GROWTH
Mycelial radial distribution was strongly influenced by
temperature and to some extend growth medium as shown here
for A. niger. In contrast to A. niger, P. polonicum and B. allii grew
well at 4°C (data now shown), which is close to the temperature
conditions at commercial storage facilities.
Propanoic acid ethyl-ester
Methyl propyl sulfide
(1Z)-1-(Methylsulfanyl)-1-propene
Dimethyl disulfide
OM background
RESULTS – VOC PROFILES
All the fungal isolates produced volatiles. Below is
shown overlayed chromatograms of VOC profiles
obtained by SPME/GC-FID from three replicates of B.
allii cultures grown on OM at 15°C for 9 days. Non-
inoculated OM background is also shown. The
individual compounds was tentatively identified by
comparing with respective GC-MS data.
Days of
Incubation
4°C 15°C 25°C
PDA OM PDA OM PDA OM
3 -¹ - - - 7.83 ± 1.16 8.50 ± 1.95
5 - - 1.34 ± 0.51 1.34 ± 0.12 20.58 ± 0.42 24.34 ± 1.53
7 - - 9.50 ± 2.07 6.42 ± 1.53 23.50 ± 1.47 30.92 ± 2.72
10 - - 15.34 ± 1.05 13.75 ± 2.81 29.25 ± 0.82 n.d.
13 - - 21.83 ± 3.23 28.08 ± 6.07 38.08 ± 1.83 n.d.
16 - - 26.50 ± 0.00 36.08 ± 4.84 n.d. n.d.
20 - - 31.75 ± 1.47 39.18 ± 3.32 n.d. n.d.
24 - - 34.34 ± 1.23 41.58 ± 0.59 n.d. n.d.
24 - - 37.07 ± 0.82 n.d.² n.d. n.d.
¹no visibile growth; ²the fungal mycelium reached the entire petri plate.
PDA OM