Monitoring of volatile organic compounds

Monitoring of Volatile Organic Compounds for early detection of storage diseases in Onions

Introduction

During storage, onions spoil due to microbial growth and spread from infested but healthy-looking tissues. Early detection of volatile organic compounds for prediction of onion diseases can be a way to minimize the economic losses if methods allow for remedial actions in storage.

Objective

To determine if the volatile organic compound (VOC) profiles differ bet-ween healthy and different types of diseased onions.

Aimei Wang1*, Filippo Casadei2,3, Heleen Bukman4, Anders Johansen3, and Merete Edelenbos1

1Department of Food Science, Aarhus University, Kirstinebjergvej 10, DK-5792 Aarslev, Denmark, 2Department of Land Ecology and Terrestrial Environments, University of Pavia, Italy, 3Department of Environmental Science, Aarhus University, Frederiksborgvej 399, DK-4000 Roskilde, Denmark, 4 Bejo Zaden B.V., Trambaan 2a, NL-1749 CZ Warmenhuizen, The Netherlands.

AARHUS UNIVERSITY

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Material and Methods

Summary

The respiration rate for Penicillium infected onions was nearly 4 fold higher than that of healthy and soft rot infected onions. Healthy onions emitted less VOCs than soft rot and Penicillium

infected onions. Soft rot infected onions had high values for ethanol. 1-propanol,

1-propanethiol, acetic acid, 3-methyl-1-butanol, and methyl propyl disulfide..

Penicillium infected onions had high values for (E)-1-(methylthio)- 1-propene. The volatile organic compound profiles differed between the

different qualities of onions.

Volatile biomarkers can be a promising tool for early detection of onion diseases

Results

Fig. 1. Respiration rate of healthy and diseased onions.

8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 0

5000000

1e+07

1.5e+07

2e+07

2.5e+07

3e+07

3.5e+07

4e+07

4.5e+07

5e+07

Time

Abu

ndan

ce

Healthy onions

Penicillium infected onions Soft rot infected onions

1

4

2

3

9

8

7 6

5

10

Fig. 2. Chromatogram of VOCs from healthy and diseased onions.

Table1. Normalized abundance1 of VOCs from healthy and diseased onions.

Peak No. RT Compound name Healthy Soft Rot Penicillium

1 8.65 Ethanol 397 b2 40725 a 482 b

2 10.44 1-Propanol 2 b 5246 a 9 b

3 11.20 1-Propanethiol 13 c 6739 a 146 b

4 11.67 Acetic acid 91 b 9464 a 74 b

5 12.48 (E)-1-(Methylthio)-1-propene 1 c 111 b 1095 a

6 12.60 1-(Methylthio)-propane 6 b 7381a 6488 a

7 12.78 Dimethyl disulfide 65 b 6342 a 7291 a

8 13.20 3-Methyl-1-butanol nd b 3470 a nd b

9 15.95 Styrene nd c 2144 a 1684 b

10 17.30 Methyl propyl disulfide 60 c 10908 a 4693 b

Total volatiles 635 c 92530 a 21962 b

1Abundance of the peak divided by the abundance of external standard multiplied by 100.2Different letters within a row show significant differences at P≤0.05 between healthy, soft rot and Penicillium infected onions .

Healthy

Soft Rot

Penicillium

250 min

Room temp

Determination of Respiration Rate

O2 &

CO

2 ana

lyze

r

GC-MS

SPME for 5 min for sampling of VOCs