PIG-HOUSE ODOURS – A REVIEW USING ODOUR ACTIVITY VALUES
Linda J Farmer, James T. Kennedy and Elizabeth Magowan
Agri-Food and Biosciences Institute, Newforge Lane, Belfast, UK
Abstract – This paper reviews the literature on pighouse odours using odour activity values to
determine the main compound classes contributing
to pig-house odour. These are short chain acids,
sulphur compounds, phenols, indoles and amines.
These compounds have the highest odour activity
values and pungent and offensive odours.
The contribution to the offensive odour by these
compounds is affected by location, timing and
method of analysis. Mitigation factors related to
slurry management or pig diets have differential
effects on these classes of odorous compounds.
Key Words –animal house, pig odour, slurry odour.
I.
INTRODUCTION
The odour downwind from pig-houses can be
offensive to nearby residents. Researchers have
reported up to five hundred different volatile
organic compounds emitted from pig production
facilities (1). However, it is often unclear which of
these many compounds make the most important
contribution to the noxious odour. Furthermore,
the composition of the odour from the waste itself
may differ depending on the location sampled and
the methods used (2).
Quantification of volatile compounds from pighouses has been used to estimate the effectiveness
of any mitigation factors employed to reduce them.
However, few have attempted to determine which
of these many compounds makes the greatest
contribution to the offensive odour.
Calculation of an odour activity value (OAV) is a
method widely used in flavour chemistry to
identify those odours with the potential to
contribute most to an odorant mixture and is
defined as the concentration of a single compound
divided by the odour threshold concentration for
that compound (3). Compounds with an OAV
greater than 1.0 are likely to contribute to the
overall odour of a sample mix and compounds
with large OAV would contribute substantially.
The odour thresholds reported in the literature can
vary considerably, with sometimes a range of
several orders of magnitude for a particular
chemical compound. In order to minimise the
impact of this variability on the odour activity
values derived, a consistent set of odour thresholds
is required for the compounds determined in pighouse odour.
Two research groups have used odour activity
values (OAVs) for studies on pig-house and have
assessed the impact of a limited list of compounds
(<20) for their own analyses only (4, 5).
The aim of this work was to evaluate the relative
importance for pig-house odour of a
comprehensive list of volatile compounds reported
by a number of authors from pig house emissions.
This was achieved through a reanalysis of the
extensive published data using a consistent set of
odour thresholds to calculate OAVs.
II.
MATERIALS AND METHODS
The odour detection threshold (ODT) is usually
determined as the concentration at which 50% of
assessors can detect an odour.
No one research group has determined odour
detection thresholds for all the odour compounds
of interest. Nagata et al. (6) measured the odour
thresholds of 223 chemicals by the Japanese
triangular bag method. For some compounds,
Nagata et al (6) did not report an ODT; then one
was estimated from another source. The methods
used and the resulting set of odour threshold data,
denoted “Nagata+”, is presented elsewhere (7).
A second set of odour thresholds (“Devos+”) was
based on the list published by Devos et al. (8),
taken from over a hundred references for over six
hundred chemical compounds. OAVs were also
calculated using the “Devos+” list and are
presented elsewhere (7).
Out of 89 papers on pig-house odours, 22 were
identified which presented quantitative data of the
air or slurry headspace concentration of volatile
compounds released from piggery facilities. Some
of these had collected volatile odour compounds
using Tedlar odour bags and others using thermal
61st International Congress of Meat Science and Technology, 23-28th August 2015, Clermont-Ferrand, France
desorption from adsorption tubes. Furthermore,
the location and type of sample varied.
The concentrations of volatile compounds released
from pig-houses have been collated from the
literature and the OAV values presented in this
paper were calculated by using the ODTs from the
“Nagata+ list”.
OAV = [compound in air (mg m-3)]
ODT in air (mg m-3)
III.
RESULTS AND DISCUSSION
Figure 1 presents the mean OAV, calculated using
the “Nagata+ list”, from those publications which
reported quantitative data using adsorption tubes
for these compounds. A simple mean of variable
data can only provide a very approximate picture
of the relative OAVs of the compounds shown and
the data is examined in more detail elsewhere (7).
However, an examination of the results from the
individual authors showed good agreement on the
identity of the compounds with the highest OAVs.
The OAVs calculated using the “Devos+ list” (not
shown) showed similar relative trends. Figure 1
therefore provides a reasonable illustration of the
relative importance of the compounds shown.
Short chain acids were important for pig-house
odour whether collected from slurry or adjacent to
the pig-house itself. They were more prevalent
when collected using thermal desorption rather
than odour bags (7). These acids result from
intestinal microbial activity in the large intestine
and cause rancid, cheese, faecal odours. OAVs
only show the relative importance of individual
odour compounds and different compounds,
especially from the same compound class, can
have a cumulative effect. The large number of
acids detected at above their ODT suggests that
these may have a greater combined effect.
Ammonia is frequently associated with pig-house
odour within the industry. However, these results
confirm previous work (2), showing that amines
are only one of many odorous compound classes.
Indoles, including the compounds 3-methylindole
or skatole, and alkylphenols are well known for
their faeces-like and pungent odours. They were
consistently present at high odour activity values.
Indoles are formed in the gut by microbial
metabolism of tryptophan and the alkyphenols
are formed by microbial fermentation of tyrosine
and phenylalanine.
Figure 1. Compounds contributing to pig-house odour, determined by thermal desorption
ACIDS
10000
ALIPHATICS
AMINES
INDOLES
PHENOLS
BENZENES
KETONES
SULPHUR
1000
100
10
OAV
1
0.1
0.01
0.001
2-MethylButanoic Acid
2-MethylPropanoic Acid
3-MethylButanoic Acid
4-MethylPentanoic Acid
Acetic Acid
Butanoic Acid
Dodecanoic Acid
Heptanoic Acid
Hexanoic Acid
Nonanoic Acid
Octanoic Acid
Pentanoic Acid
Propanoic Acid
1-Butanol
1-Decanol
1-Dodecanol
1-Pentanol
2-Butanol
3-Octanol
3-Methylbutanal
Acetaldehyde
Butanal
Hexanal
Pentanal
Hexane
Tetradecane
Dimethylacetamide
2-Amino acetophenone
Ammonia
Trimethylamine
Acetophenone
Benzaldehyde
Benzene
Benzyl alcohol
Butylated hydroxytoluene
Toluene
2-Furanmethanol
3-methylindole
Indole
2-Butanone
3-Hydroxy-2-butanone
3-Methyl-2-butanone
Acetone
2-Methoxyphenol
4-Ethylphenol
4-Methylphenol
4-propylphenol
Phenol
Dimethyl disulphide
Dimethyl sulphide
Dimethyl trisulphide
Hydrogen sulphide
0.0001
0.00001
61st International Congress of Meat Science and Technology, 23-28th August 2015, Clermont-Ferrand, France
Some aliphatic and aromatic compounds
(‘aliphatics’, ‘ketones’, ‘benzenes’) are reported
occasionally at sufficient concentrations to give an
OAV>1, and may sometimes contribute to pighouse odour. However, their odour is not generally
unpleasant and their OAV is generally
considerably lower than that of other compound
classes and it is unlikely that they will make a
large contribution to pig-house odour.
These data (illustrated in Figure 1) show that the
most important compound classes for pig-house
odour are short chain acids, sulphur compounds,
phenols, indoles and amines.
Where suitable quantitative data was published, it
has been possible to use the same approach to reevaluate data on potential mitigation factors.
Figures 2 and 3 shows the results for two of these:
covering the slurry tank (9) and increasing the
liquid content of the diet (10).
Figure 2 shows that the most important odour
compounds change during 9 weeks storage and
that covering the slurry reduces the impact of
ammonia, indoles and phenols but has little effect
on the impact of acids or sulphur compounds (9).
In contrast, increasing the liquid component of the
diet (Figure 3) decreases the contribution to the
odour of acids and sulphur compounds, but has
little effect on other compounds (10). Thus,
different mitigation factors influence different
compound classes. This suggests that there is no
single method for reducing pig-house odour. This
has implications for the selection of abatement
strategies.
Figure 2. Effect of covering and ageing slurry on odour activity of compound classes (9)
(b) Covered slurry at start of expt
10000
1000
1000
100
100
10
10
1
1
OAV
0.1
0.1
0.01
0.01
OAV
1
0.1
1
0.1
Carbon disulphide
Dimethyl sulphide
Dimethyl disulphide
Phenol
4-Methylphenol
Indole
3-Methylindole
Benzaldehyde
1-Butanol
Benzyl alcohol
Ammonia
Trimethylamine
Pentanoic acid
Butanoic acid
(d) Slurry covered with dry straw at 9 weeks
Hydrogen sulphide
10
Compound
3-Methylbutanoic Acid
100
2-Methylpropanoic acid
1000
Acetic acid
Carbon disulphide
Dimethyl sulphide
Dimethyl disulphide
Hydrogen sulphide
Phenol
4-Methylphenol
Indole
3-Methylindole
Benzaldehyde
1-Butanol
Benzyl alcohol
Ammonia
10
Compound
0.01
0.01
Compound
Carbon disulphide
Dimethyl disulphide
Dimethyl sulphide
Hydrogen sulphide
Phenol
4-Methylphenol
3-Methylindole
Indole
Benzaldehyde
1-Butanol
Benzyl alcohol
Trimethylamine
Ammonia
Pentanoic acid
3-Methylbutanoic Acid
Butanoic acid
2-Methylpropanoic acid
0.001
0.0001
Acetic acid
0.001
0.0001
propanoic acid
OAV
Trimethylamine
Pentanoic acid
Butanoic acid
(c) Uncovered slurry at 9 weeks
0.00001
0.000001
propanoic acid
100
3-Methylbutanoic Acid
1000
2-Methylpropanoic acid
Acetic acid
0.001
0.0001
propanoic acid
0.001
0.0001
Acetic acid
propanoic acid
2-Methylpropanoic acid
Butanoic acid
3-Methylbutanoic Acid
Pentanoic acid
Ammonia
Trimethylamine
1-Butanol
Benzyl alcohol
Benzaldehyde
Indole
3-Methylindole
Phenol
4-Methylphenol
Hydrogen sulphide
Dimethyl sulphide
Dimethyl disulphide
Carbon disulphide
OAV
(a) Uncovered slurry at start of expt
10000
Compound
61st International Congress of Meat Science and Technology, 23-28th August 2015, Clermont-Ferrand, France
Figure 3. Effect of liquid diet on odour activity of pighouse odours (10)
(a) Dry feed
1000000
100000
OAV
10000
1000
100
methyl mercaptan
Hydrogen sulphide
Dimethyl sulphide
Dimethyl disulphide
Dimethyl disulphide
Dimethyl trisulphide
Phenol
Phenol
Phenol
(b) 3:1 water/feed
Dimethyl disulphide
4-Methylphenol
4-Methylphenol
4-Methylphenol
Indole
4-Ethylphenol
4-Ethylphenol
4-Ethylphenol
Indole
Indole
3-Methylindole
3-Methylindole
3-Methylindole
propanoic acid
propanoic acid
propanoic acid
Pentanoic acid
Pentanoic acid
Pentanoic acid
Acetic acid
Butanoic acid
Butanoic acid
Butanoic acid
3-Methylbutanoic …
1000
2-Methylpropanoic…
OAV
10000
3-Methylbutanoic…
100000
2-Methylpropanoic …
1000000
3-Methylbutanoic Acid
1
2-Methylpropanoic acid
10
100
Hydrogen sulphide
methyl mercaptan
Hydrogen sulphide
methyl mercaptan
1000
Dimethyl sulphide
OAV
10000
Dimethyl trisulphide
100000
(c) 4:1 water/feed
Dimethyl sulphide
1000000
Dimethyl trisulphide
1
Acetic acid
10
100
10
IV.
Acetic acid
1
CONCLUSION
The most important odour compounds contributing
to pig-house odour are short chain acids, sulphur
compounds, phenols, indoles and amines. These
compounds have the highest odour activity values
and often have pungent and offensive odours.
The odour activity of these compounds is affected
by a number of factors, including method of
analysis. Potential mitigation factors related to
slurry management or pig diets have differential
effects on these classes of odorous compounds,
suggesting that there is no single solution to the
problem of pig-house odour and that an analysis of
the compounds responsible is essential before
considering mitigation strategies.
ACKNOWLEDGEMENTS
The authors would like to thank the Department of
Agriculture and Rural Development, Northern Ireland,
for funding this research and Ms Barbara Alaejos for her
assistance with the collation of the published data.
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61st International Congress of Meat Science and Technology, 23-28th August 2015, Clermont-Ferrand, France