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 microbial volatile organic compounds (MVOCs) 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.

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 OEM medium than on PDA. Volatile analysis showed that
B. allii sp., as well as B. cinerea sp., P. polonicum sp. and A. niger sp. (data not shown), produced VOCs that were not present in
the OEM medium background. VOCs 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 OEM 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 OEM in 20 ml
vials. Vials were placed at 4 °C, 15 °C and 25 °C and VOCs profiles
recorded after 3, 7 and 10 days by SPME/GC-FID and GC-MS
analyses.
The sporification of Penicillium polonicum sp. is greatly influenced by growth
medium, here after 7 day of cultivation on PDA medium (left) and OEM (right).
1Department of Department of Earth Science and Environment, Mycology Laboratory, University of Pavia, 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 microbial volatile organic compounds (MVOCs) 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 mycelial growth (mm) of A. niger on PDA and OEM.
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
Denmark.
RESULTS - MYCELIAL GROWTH
Mycelial radial distribution was strongly influenced by
temperature and growth medium as shown here for A. niger sp.
In contrast to A. niger sp., the other species, P. polonicum sp., B.
allii sp. and B. cinerea sp., grew well at 4 °C (data not shown),
which is close to the temperature conditions at commercial
storage facilities.
Methanethiol
RESULTS - VOC PROFILES
All the fungal isolates produced volatiles.
Below is shown overlayed chromatograms of VOCs
profiles obtained by SPME/GC-FID from selected
species cultures grown on OEM at 25 °C for 7 days.
Non-inoculated OEM 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 OEM PDA OEM PDA OEM
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 OEM
8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00
5000000
1e+07
1.5e+07
2e+07
2.5e+07
3e+07
3.5e+07
4e+07
4.5e+07
5e+07
5.5e+07
6e+07
6.5e+07
7e+07
7.5e+07
Time
Abundance
OEM Blank
B. cinerea
B. allii
A. niger
P. polonicum
Ethanol
Dimethyl sulfide
1- Propanethiol
Dimethyl disulfide
Mercaptoacetone
Methyl propil disulfide
2- Heptanone
Styrene
OBJECTIVES
The aim of this study was to evaluate the effects of medium (PDA:
potato dextrose agar; OEM: onion extract medium) and
temperature (4 °C, 15 °C, 25 °C) on growth and production of VOCs
from Penicillium polonicum sp., Aspergillus niger sp., Botrytis allii
sp. and Botrytis cinerea sp., which are common spoilage
organisms on onion bulbs.