Subscriber access provided by UNIV AUTONOMA DE COAHUILA UADEC
Biofuels and Biomass
Interrelation of Volatile Organic Compounds and Sensory Properties of Alternative and Torrefied Wood Pellets Barbara Poellinger-Zierler, Irene Sedlmayer, Carina Reinisch, Hermann Hofbauer, Christoph Schmidl, Larissa Patricia Kolb, Elisabeth Wopienka, Erich Leitner, and Barbara Siegmund Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.9b00335 • Publication Date (Web): 08 May 2019 Downloaded from http://pubs.acs.org on May 9, 2019
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
1
Interrelation of Volatile Organic Compounds and
2
Sensory Properties of Alternative and Torrefied
3
Wood Pellets
4 5
Barbara Pöllinger-Zierler a,%, Irene Sedlmayer b,c, Carina Reinisch a,§, Hermann Hofbauer c,
6
Christoph Schmidl b, Larissa Kolb a, Elisabeth Wopienka b, Erich Leitner a,
7
Barbara Siegmund a *
8
a
Graz University of Technology, Institute of Analytical Chemistry and Food Chemistry, Stremayrgasse 9/II, 8010 Graz, Austria
9 10
b
BIOENERGY 2020+ GmbH, Gewerbepark Haag 3, 3250 Wieselburg-Land, Austria
11
c
Technische Universität Wien, Institute of Chemical, Environmental and Bioscience Engineering, Getreidemarkt 9/166, 1060 Vienna, Austria
12 13
* corresponding author: Tel.: +43 316 873 32506, mail to:
[email protected] 14
%
current address: Oberberg 120, 8151 Hitzendorf, Austria
15
§
current address: Muellegg 4, 8524 Bad Gams, Austria
1 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
16
KEYWORDS
17
Pellets from alternative material; torrefied wood pellets, volatile compounds, gas
18
chromatography-mass spectrometry; sensory evaluation; correlation
Page 2 of 43
19
2 ACS Paragon Plus Environment
Page 3 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
20
Energy & Fuels
TOC GRAPHICS
21
22 23
3 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 43
24
ABSTRACT
25
The increasing demand for wood pellets on the market, which is caused by their excellent
26
combustion properties, inspires the production as well as the utilization of alternative biomass
27
pellets as fuel. However, the emission of volatile organic compounds gives pellet materials a
28
distinct odor or off-odor, which is directly perceived by the end user. Thus, there is an urgent
29
need for knowledge about the emitted volatile organic compounds and their potential
30
formation pathways as well as their contributions to odor properties of the pellets. In this
31
study, pellets made of biomass energy crop (i.e. straw, miscanthus), by-products from food
32
industry (i.e. rapeseed, grapevine, DDGS ˗ dried distillers grains with solubles from beer
33
production), eucalyptus as well as of torrefied pinewood and torrefied sprucewood were
34
investigated with respect to the emitted volatile compounds and their possible impact on the
35
pellet odor. Headspace solid-phase microextraction in combination with gas chromatography–
36
mass spectrometry was used to enrich, separate and identify the compounds. Techniques used
37
in sensory science were applied to obtain information about the odor properties of the
38
samples. A total of 59 volatile compounds (acids, aldehydes and ketones, alcohols, terpenes,
39
heterocyclic and phenolic compounds) was identified with different compound ratios in the
40
investigated materials. The use of multivariate statistical data analysis provided deep insight
41
into product-compound interrelation. For pellets produced from bioenergy crop as well as
42
from by-products from food industry, the sensory properties of the pellets reflected the odor
43
properties of the raw material. With respect to the volatiles from torrefied pellets, those
44
volatiles that are formed during the torrefaction procedure, dominate the odor of the torrefied
45
pellets covering the genuine odor of the utilized wood. The results of this work serve as a
46
substantiated basis for future production of pellets from alternative raw materials.
4 ACS Paragon Plus Environment
Page 5 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
47
Energy & Fuels
1. Introduction
48
Wood pellets are widely used for residential and commercial heating purposes in Europe,
49
North America and Asia1. Due to the increasing demand for pellet material, the thermal
50
utilization of non-wood and pretreated biomass pellets as alternatives to wood pellets has been
51
topic of several recent investigations2,3 whereby attention has been paid on the fuel properties
52
and combustion behavior of pellets made of energy crop biomass4, straw as well as from
53
torrefied wood5. Moreover, the thermal utilization of by-products from food industry as for
54
example pellets made of dried distillers grains with solubles (DDGS) – a by-product from
55
beer production – has attracted attention as an additional, sustainable raw material for heating
56
purposes6.
57
Even though the combustion behavior of pellet material is well understood, there is a lack of
58
knowledge and understanding about the off-gassing behavior of different pellet materials. It is
59
well known that wood pellets emit gases during storage. Odorless gases like carbon monoxide
60
(CO), carbon dioxide (CO2), methane (CH4) and hydrogen (H2) are emitted with a
61
simultaneous oxygen reduction in the storage atmosphere7–14, which is most probably caused
62
by oxidation processes undergone by genuine wood extractives15,16. Besides CO, CO2, CH4
63
and H2 emissions, a range of other volatile organic compounds (VOCs) such as straight-chain
64
aldehydes and ketones, alcohols, short chain organic acids, as well as terpenes is emitted by
65
pellets7–9,17. It has been shown recently that pellets produced from different wood species can
66
be differentiated according to their wood origin on the basis of the emitted VOCs18. The
67
emission of VOCs is of special importance as many of these compounds are odor-active and
68
are responsible for the odor or potential off-odor perceived from these materials17.
69
Furthermore, the emission of VOCs is presumed to be the reason for eye and respiratory
70
irritation by people working in pelletizing companies or in pellet storage facilities9,19.
5 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 43
71
Several papers are available describing the release of volatile compounds from unpelletised
72
biomass other than wood and from torrefied material, respectively20–23. However, to the best
73
of our knowledge, little is known about the release of volatile and potentially odor-active
74
compounds from pellets produced from alternative biomass, by-products from food industry,
75
or torrefied wood. Due to the harsh conditions during the pelletising process, chemical
76
reactions such as oxidation or degradation reactions with potential impact on the VOC
77
composition are most likely to occur. Thus, we investigated the release of VOCs from
78
different promising pellet materials (i.e., pellets made of the food processing by-products
79
DDGS, rapeseed and grapevine, the energy crop biomass straw and miscanthus, eucalyptus,
80
as well as torrefied sprucewood and torrefied pinewood). To gain a comprehensive picture
81
about the investigated pellets, the combination of sensory evaluation conducted by
82
specifically trained panelists and gas chromatography–mass spectrometry (GC-MS) after
83
enrichment of the volatile compounds by headspace solid-phase microextraction (HS-SPME)
84
was applied24,25. Results from sensory evaluation were used to estimate the sensory impact of
85
the identified VOCs on the perceived odor of the products. Thus, the combination of the
86
results obtained from this scientific approach will contribute to a better the understanding of
87
the odor properties of pellets produced from alternate raw materials.
88 89
2. Materials and Methods
90
2.1 Sample materials
91
Raw material for the laboratory scale production of pellets made of rapeseed (Brassica napus;
92
derived from rape seed extraction), miscanthus, grapevine (Vitis vinifera) (i.e., vine pruning
93
and vine pomace in a ratio of 50:50), DDGS (dried distillers grains with solubles derived from
94
beer production), torrefied pinewood (Pinus sylvestris) and torrefied sprucewood (Picea 6 ACS Paragon Plus Environment
Page 7 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
95
abies) were received from different sources (Table 1). All pellets with the exception of straw
96
and eucalyptus were produced in pilot-scale using a laboratory-scale pelletizing press
97
(Amandus Kahl type 14-175, Amandus Kahl GmbH & Co KG, Reinbeck, Germany). Pellets
98
made of straw and eucalyptus (Eucalyptus) were kindly provided by industrial pelletizing
99
companies. The moisture content of the pellets was determined according to ISO 18134-326.
100
The pellets were dried at 105 ± 2ºC in a drying cabinet until a constant mass had been
101
achieved. The moisture contents as well as the perceived color of the investigated pellets are
102
given in Table 1. Sampling was performed according to ISO 1813527. The pellets were stored
103
in 1-L glass jars in the dark at 6°C until they were further used to maintain the original pellet
104
quality.
105 106
2.2 Sample preparation for the analysis of the volatile compounds
107
The pellets were ground using a laboratory mill (IKA® A11 basic Analysenmühle, IKA
108
Werke GmbH & Co KG, Staufen, Germany). The pellets were milled for a total of 15 sec-
109
onds, applying 5 seconds per milling cycle with a break of 10 seconds between each cycle to
110
prevent the samples from being excessively warmed.
111 112
2.3 Sensory evaluation
113
2.3.1
Training of the panelists
114
To perform the sensory evaluation of the pellets, a sensory panel made up of 15 well-trained
115
panelists was used. All panelists were trained and selected according to EN ISO 858632. Due
116
to their collaboration on previous research work, the panelists had vast experience in the
117
evaluation of non-food and wood-based materials. Before the sensory evaluation of the pellets
118
in this study was performed, the panelists were trained on odors that were expected to occur in 7 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 8 of 43
119
the investigated non-wood pellets. All compounds used (i.e., -terpineol, verbenone, -
120
pinene, 1,8-cineol, camphor, borneol, fenchyl alcohol, pentanal, hexanal, heptanal, 2-hep-
121
tanone, octanal, nonanal, benzaldehyde, 8-mercapto menthone, phenol, 2-methoxyphenol) are
122
registered in the European Union as flavoring compounds and are authorized to be used in
123
flavored foods according to regulation (EU) No 872/2012. All compounds used for the train-
124
ing were purchased from Sigma-Aldrich (Vienna, Austria). The compounds had purities of
125
≥ 96%. For evaluation purposes, ethanolic solutions of the relevant compounds were prepared
126
in adequate concentrations (i.e., 0.5–2% depending on the odor threshold of the compound
127
which is the concentration of the compound that is necessary for human perception). Filter
128
strips were dipped into the solutions. After evaporation of ethanol, the panelists were asked to
129
sniff the filter strips and describe the perceived odor. To improve the training effect, per-
130
ceived odors and corresponding descriptors were discussed among members of the panel.
131 132
2.3.2
Sensory description of pellets
133
The sensory evaluation was carried out in a sensory laboratory under standardized conditions.
134
Crushed pellet samples (2 g per sample) were presented in blue tasting glasses (0.11-L ca-
135
pacity) that had originally been designed for the sensory evaluation of olive oil. The cups
136
were covered with lids that had to be removed by the panelists immediately before they
137
sniffed the samples. To avoid biasing, all samples were blind tasted. The samples were coded
138
with three-digit random numbers. To avoid effects based on the order of presentation, samples
139
were presented in a random order to each panelist. The panelists were asked to open the lid,
140
sniff the samples and note adequate descriptors for each sample.
141 142 8 ACS Paragon Plus Environment
Page 9 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
143
Energy & Fuels
2.4 Sampling of the volatile compounds
144
To extract and enrich the volatile compounds that were released from the pellets, headspace
145
solid-phase microextraction (HS-SPME) was used. 300 mg of each ground pellet sample was
146
transferred into a 20-mL headspace vial. 50/30-μm DVB/Carboxen/PDMS fibers (2-cm stable
147
flex, Supelco, Bellfonte, USA) were used to enrich the volatiles. Prior to fiber exposure, the
148
samples were equilibrated for 5 min at 40°C while stirring thoroughly. To enrich the volatile
149
compounds, the fiber was exposed to the headspace of the samples for 20 min at 40°C. After
150
enrichment, the SPME fiber was transferred directly into the GC injection port, where ther-
151
modesorption and the direct transfer of the analytes onto the head of the GC column were
152
carried out. Each sample was extracted and analyzed in four-fold repetition.
153 154
2.5 Analysis of the volatile compounds by gas chromatography–mass spectrometry
155
Separation and identification of the volatile compounds were performed by means of gas
156
chromatography–mass spectrometry (GC-MS). After thermodesorption of the volatile com-
157
pounds from the SPME fiber in the liner of the injection system (injector temperature 270°C,
158
splitless injection mode; glass liner geometry with a constant inner diameter of 0.75 mm), the
159
gas chromatographic analyses were performed on an Agilent system (GC 7890, MS 5975c VL
160
MSD, Santa Clara, CA, USA) using an analytical column of medium polarity (HP5MS,
161
30 m × 0.25 mm × 1 µm, Agilent Technologies) and the following temperature program:
162
10°C for 1 min with a temperature ramp of 12°C min-1 up to 280°C (3 minutes) at a constant
163
flow rate of 31 cm sec-1. Low temperatures were achieved by blowing liquid nitrogen into the
164
GC oven. Helium was used as carrier gas for the GC separation. The mass selective detection
165
(single quadruple MS) was performed in the scan mode (35-300 amu) using electron impact
166
ionization (EI at 70 eV). The detection temperature was 280°C. The identification of the com9 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 10 of 43
167
pounds was based on the comparison of the obtained mass spectra to those from MS databases
168
(i.e. NIST 14 Mass Spectral Library; Adams MS Library on Essential Oils; FFNSC-Flavor
169
and Fragrance Natural and Synthetic Compounds Library). In addition, the linear temperature
170
programmed retention indices were calculated according to Van den Dool & Kratz as well as
171
Farkaš et al.28,29. The retention times of the n-alkanes required for the calculation of the RI
172
where obtained by analyzing a solution containing the homologous series of n-alkanes (C5 to
173
C24 diluted in methanol, 10 ng absolute per compound) under the same chromatographic
174
conditions. The experimentally obtained retention indices were compared to those from an in-
175
house RI database (RI in this database had been determined with the use of authentic
176
reference compounds) as well as with RI from RI databases30,31. To survey the performance of
177
the HS-SPME-GC-MS procedure, the compound mixture described by Farkaš et al.29 was
178
analyzed after every 10th GC run.
179
To calculate correlations of the relative amounts of the released volatiles and the investigated
180
pellet materials, multivariate statistical data analysis (i.e., principal component analysis
181
(PCA)) was carried out. For this purpose, the average peak areas of the volatile compounds
182
from GC-MS analysis were statistically processed using the Pearson correlation method.
183
Cluster analysis of the data was also carried out using the average VOC peak areas and
184
applying the agglomerative hierarchical clustering (AHC) regarding the Euclidean distance
185
between the samples using Ward’s procedure as an agglomeration method. The multivariate
186
data analysis was performed by using XLSTAT (AddinSoft (2019) XLSTAT statistical and
187
data analysis solutions. Long Island, NY, USA. https://xlstat.com).
188 189 190 10 ACS Paragon Plus Environment
Page 11 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
191
3. Results and Discussion
192
3.1 Sensory evaluation
193
The odor that is emitted from pellet material during storage is regarded to be an important
194
property, as the emitted odor or off-odor has a significant impact on the product acceptance
195
by the end user. In this context, not only the intensity, but also the quality of the product odor
196
is highly relevant. Thus, sensory evaluation of the investigated pellets was performed to char-
197
acterize the odor properties. The sensory evaluation was carried out by well-trained members
198
of a sensory panel and using state-of-the art techniques applied in sensory science. Results of
199
the sensory evaluation are given in terms of descriptors for each type of material (Table 2).
200
The results corresponded well with our expectations. For all alternative products – with the
201
exception of the torrefied pellets – the sensory properties of the pellets reflected the odor
202
properties of the raw material. Pellets from miscanthus and straw were described as straw- or
203
hay-like, with more green, herbal odor assigned to the straw pellets. Pellets from eucalyptus
204
were described as being dominated by fresh, minty, eucalyptus/camphor-like notes that were
205
perceived as medicinal by some panelists. Pellets from rapeseed were perceived as fatty and
206
oily with nutty notes – sensory notes that were expected from a raw material that is rich in
207
lipids. The odor of DDGS, as a side product of a brewing process, reflected the roasted, malty
208
and slightly fruity odor of the materials from the proceeding workup. Interestingly, the odor
209
of the torrefied sprucewood and pinewood pellets was described as highly similar to one
210
another. Both torrefied materials were described by the panel as having smoky, phenolic and
211
burnt notes – flavor characteristics that are associated with burning or coking processes.
212
However, the burnt, coked notes were predominant for the torrefied sprucewood, whereas
213
typical descriptors such as resinous and woody were given as well for the torrefied pinewood
214
pellets.
215 11 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
216
Page 12 of 43
3.2 Analysis of the volatile organic compounds (VOCs)
217
The analyses of volatile organic compounds as well as their potential formation pathways are
218
important to understand the odor properties of the investigated alternate pellet materials. To
219
investigate the volatiles, analytical techniques that are generally acknowledged for the analy-
220
sis of flavor compounds were applied33. Headspace solid-phase microextraction (HS-SPME)
221
was used to enrich the volatiles, which were subsequently analyzed by gas chromatography-
222
mass spectrometry (GC-MS). Results obtained from this study demonstrate the suitability of
223
these techniques for the analysis of VOCs from pellets.
224
Table 3 shows the relative amounts of VOCs that were identified in the investigated pellet
225
materials. A total of 59 VOCs was identified, which belong to the chemical classes of acids,
226
esters, alcohols, aldehydes and ketones, terpenes, heterocyclic compounds and aromatic
227
compounds such as phenols. For better visibility, Figure 1a and Figure 1b demonstrate the
228
distributions of the different compound classes per investigated pellet material. This way of
229
presentation clearly shows the large differences in the distribution of the volatile compounds
230
depending on the raw material and on the torrefaction process, respectively. We took a more
231
detailed look at the different compound classes to better understand the sources and formation
232
pathways of the compounds and their potential influences on the perceived sensory properties
233
of the products.
234
The identified short-chain fatty acids belong to the homologous series ranging from C2 to C6.
235
Acetic acid was identified in all investigated pellet materials in varying, but large amounts.
236
The source for the high relative concentrations of acetic acid is not clear. However, these
237
findings correspond well with the previously reported occurrence of acetic acid in wood
238
pellets18. Significant differences were detected between the investigated pellet materials with
239
respect to the other straight-chain acids. Whereas acetic acid was identified in varying
240
amounts in all investigated pellet materials, significant differences were detected between the 12 ACS Paragon Plus Environment
Page 13 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
241
investigated pellet materials with respect to the other straight-chain acids which are most
242
likely degradation products from cell membrane lipids and/or lipids derived from the plant
243
material/seeds. Pellets produced from rape – a crop with a high fat content in the seeds –
244
possessed the highest diversity of straight-chain fatty acids. In straw, however, only acetic
245
acid was identified. The methyl-branched fatty acid 3-methyl butanoic acid is most likely
246
derived from the precursor amino acid leucine and is, thus, found in pellets made of protein-
247
rich raw material like DDGS, grapevine and miscanthus. The presence of these fatty acids in
248
wood pellets has been described in the results of our own previous research17. In this previous
249
study, we showed that high concentrations of free fatty acids – and especially the presence of
250
3-methyl butanoic acid with a low odor threshold – were strongly correlated with off-flavor
251
formation in wood pellets. Hence, attention should be paid to the formation/the presence of
252
short-chain free fatty acids which might contribute to off-odor formation. However, the
253
formation and/or degradation pathways, respectively, of the free short chain fatty acids are not
254
completely clear and would need further investigations. Two esters were identified in this
255
study: methyl acetate is most likely a reaction product of acetic acid and methanol and was
256
identified in all types of pellets. Methanol emission from wood pellets during storage has been
257
shown before34. Methyl pentanoate, however, was only detected in pellets made of rape,
258
which correlates with the presence of the corresponding free acid that was also only detected
259
in this pellet type.
260
Eight different alcohols were identified which are supposed to be degradation products of (i)
261
membrane lipids, (ii) fat derived from the lipids of the seeds, or (iii) amino acids, especially in
262
pellets made of protein-rich raw material, with respect to the methyl-branched alcohols as
263
well as phenyl alcohol. The alcohol 2,3-butanediol was identified in large relative amounts in
264
pellets produced from DDGS and grapevine. The fermentative formation of 2,3-butanediol is
265
well described in literature35. Both raw materials DDGS and grapevine are derived from 13 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 43
266
biotechnological processes during which the 2,3-butanediol formation is most likely to occur.
267
A broad range of carbonyl compounds (11 aldehydes and 6 ketones) was identified, although
268
the amounts varied greatly between the investigated materials. As with the other compound
269
classes, different precursors can be made responsible for the aldehyde and ketone formation;
270
however, lipid oxidation is supposed to be the main reaction pathway7,36. The straight-chain
271
C6 aldehyde hexanal, for example, like other straight chain aldehydes, is well-known to be a
272
reaction product of lipid oxidation from either membrane lipids or lipids derived from seeds.
273
The formation of straight-chain aldehydes in sawdust and pellets produced from coniferous
274
wood has been shown previously 7,9,37–39. With green, soapy, fatty flavor characteristics in
275
dependence on chain lengths and concentrations, we suspect that these carbonyls influence the
276
odor of the investigated material, especially as many of these compounds show low odor
277
thresholdsi. The presence of 2- and 3-methyl butanal, which have sweet, malty odor
278
properties, again strongly correlates with the presence of other methyl-branched metabolites
279
in miscanthus and grapevine40. These compounds are believed to be responsible for the malty,
280
beer-like odor in the latter. 6-Methyl-5-hepten-2-one is a known degradation product of
281
carotenoids41. It was only identified in the grapevine pellets. Carotenoids from wine are
282
thought to be the precursor compounds for this ketone in pellets derived from grapevine.
283
Thousands of different terpenoid compounds are found in nature as secondary metabolites in
284
plant material, all of which have different physiological roles42. Many of these also possess
285
distinct odor properties that may have a significant impact on the aroma of the respective
286
plant material. As the investigated alternative pellet materials were produced from different
287
plant sources, the presence of a broad range of terpenes was to be expected. Eight different
288
terpenes were identified in the investigated pellet materials, reflecting their occurrence in the
289
respective raw material. For example, eucalyptus is well-known for its typical smell – and this
290
was reflected in the presence of 1,8-cineol (i.e., eucalyptol) that was found in high relative 14 ACS Paragon Plus Environment
Page 15 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
291
concentrations in eucalyptus pellets only, as well as other terpenes that had previously been
292
identified in eucalyptus oil43 as well as in eucalyptus wood from Portuguese forests22. Wine
293
flavor is described as being highly influenced by the presence of terpenes, some of which, like
294
limonene and -cyclocitral, have also been identified in grapevine pellets. -Copaene is the
295
only terpene that could be found in DDGS pellets. We believe that this compound was not
296
derived from barley, but from hops, another essential ingredient in beer production44. The
297
resins and essential oils derived from coniferous trees are well-known to contain high terpene
298
concentrations. All terpenoids that we identified in torrefied sprucewood and pinewood
299
pellets had been described before from these plant sources45,46.
300
Among the heterocyclic compounds, the group of alkylated furans is the most important com-
301
pound group detected in the investigated pellets. The formation of alkylated furans in ther-
302
mally processed foods has been thoroughly described, and carbohydrates are known to act as
303
precursors for 2-furancarboxaldehyde, 2-acetylfuran and 2-methylfuran. Alkylated furans
304
with longer alkyl chains such as 2-pentylfuran result from lipid degradation, whereby -
305
unsaturated aldehydes represent precursor compounds in thermally processed foods47,48. In the
306
raw material used for the production of the investigated pellet materials, excess amounts of
307
complex carbohydrates were present; furthermore, unsaturated aldehydes were detected, re-
308
sulting from lipid oxidation. Thus, the large number of alkylated furans is explained by the
309
presence of these compounds in combination with the thermal treatment during pellet produc-
310
tion. Interestingly, 2-methylpyrazine was found in pellets made of rape, DDGS but also in
311
pellets from torrefied sprucewood. 2-Methylpyzarine is a characteristic product of the Mail-
312
lard reaction, one of the most important reactions in thermally processed foods that contain
313
reducing sugars and amino acids. Many Maillard reaction products have roasted, nutty, burnt
314
odor properties and a strong odor impact on the related food material49.
15 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 16 of 43
315
Volatile compounds with aromatic rings in the structures represent a compound class, mem-
316
bers of which were identified in the torrefied pellet materials. Chen et al.50 previously de-
317
scribed the formation of alkylated methoxyphenols in the course of the torrefaction process.
318
The sensory potency of compounds from this compound class was recently described by
319
Schranz and colleagues51. In contrast to the phenolic compounds derived from torrefaction,
320
the large amount of phenolic compounds in pellets produced from eucalyptus is mainly based
321
on the presence of cymol a compound that has been described previously as constituent of
322
Eucalyptus essential oil52. With its fresh, terpeny odor properties this compound most likely
323
also contributes to the fresh odor of eucalyptus pellets.
324 325
3.3 Correlations among results
326
To obtain a clearer insight into product-compound interrelations, multivariate statistical data
327
analysis was performed, taking all relative concentrations of the identified volatile compounds
328
into consideration. Cluster analysis as a mathematical procedure to condense heterogeneous
329
objects (i.e., the investigated pellets) with a high number of characteristics (i.e., relative
330
concentrations of the volatiles) into homogenous groups was conducted on the volatile
331
compounds. The result is presented in terms of a dendrogram (Figure 2), showing the
332
similarities of the products under investigation. Three distinct clusters were identified:
333
cluster 1 contained pellets produced from DDGS and torrefied sprucewood, cluster 2 had
334
only one member (pellets from grapevine) and cluster 3 contained pellets from torrefied
335
pinewood and eucalyptus, on the one hand, and the pellets of the herbaceous plants rape,
336
straw and miscanthus, on the other hand. To obtain deeper understanding of the formed
337
clusters, principal component analysis based on the relative concentrations of volatile
338
compounds was performed. Thereby, it was possible to further structure the data set and to
339
identify compound-pellet interrelations. Results are given in Figure 3a (observations plot) and 16 ACS Paragon Plus Environment
Page 17 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
340
Figure 3b (corresponding biplot with factor loadings), whereas the first two, most informative
341
principal components were selected for the graphic presentation. The cluster labelings in
342
Figure 3b were taken from the dendrogram (Figure 2).
343
Expressed correlations among certain compound groups are found for the torrefied spruce-
344
wood pellets as well as for pellets made of grapevine. With reference to torrefied sprucewood,
345
the importance of the alkylated methoxyphenols as well as of the alkylated furan derivatives
346
can be seen clearly. These compounds are highly correlated to each other and are located in
347
quadrant II. The sensory thresholds for furan derivatives are generally highi; consequently,
348
their sensory impact on the product flavor is considered to be negligible. However, various
349
furan derivatives had been reported as volatile compounds emitted by steam exploded and
350
torriefied wood before20. In contrast, the odor thresholds of the identified methoxyphenol
351
derivatives are in general significantly lower than those of alkylated furans51. In the sensory
352
evaluation, the torrefied sprucewood pellets were described as smoky, phenolic and woody,
353
which can be explained by the presence of the phenolic compounds. Pellets made of
354
grapevine were described as dried fruit-like, green and sweet. A high correlation was found
355
with products from amino acid degradation, the corresponding free acids, methyl acetate,
356
aldehydes and alcohols from lipid degradation, as well as the two terpenes limonene and -
357
cyclocitral, all of which are located in quadrant I. These compounds have more or less
358
pronounced sweet, fruity odor properties with different odor thresholds, which influence the
359
perceived odors of the pellets. The grapevine used was a 50:50 mixture of wine pruning and
360
pomace and, thus, contained a high proportion of grape seeds. Grape seeds are known for
361
their high amounts of mono- and polyunsaturated acids, which are precursors of the straight-
362
chain aldehydes or alcohols, as well as leucine and isoleucine, which are precursor
363
compounds for 2/3-methyl-branched aldehydes and alcohols53. Clear correlations can also be i
For a survey of odor thresholds for selected compounds, please see the database „Odor & Flavor Detection Thresholds in Water,“ www.leffingwell.com, last access Dec. 19, 2018
17 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 18 of 43
364
seen between the VOCs of torrefied pinewood and eucalyptus pellets. In contrast to torrefied
365
sprucewood pellets, torrefied pinewood pellets were not correlated with methoxyphenols, but
366
with the monoterpenes camphene, cumol and 1,8-cineol. These findings are also reflected by
367
the sensory descriptors of resinous, dried wood. Burnt notes derived from methoxyphenols
368
were perceived as well, but obviously did not dominate the odor of the torrefied pinewood
369
pellets. The eucalyptus pellets were also highly correlated with the same terpenes as the
370
torrefied pinewood pellets which is as well reflected in the sensory properties. Pellets
371
produced from rape, straw and miscanthus showed no clear correlations with any specific
372
compound group that could explain the odor of the products.
373 374
4. Conclusions and Future Perspectives
375
In this study, gas chromatographic and sensory techniques, which are usually applied in flavor
376
chemistry, have been used for the investigation of the odor properties and VOCs emitted from
377
pellets produced from alternative raw materials such as energy biomass crop, eucalyptus, by-
378
products from food industry as well as from torrefied sprucewood and pinewood. To the best
379
of our knowledge, this is the first time that pellets made of miscanthus and straw on the one
380
hand and DDGS, grapevine and rapeseed on the other hand were investigated with respect to
381
the released volatiles, their sensory properties and the interrelation with possible sources and
382
formation pathways. The results of this investigation deliver new insights into the VOC
383
composition and the sensory properties of these pellet types and will serve as a basis for
384
future investigations.
385
With the general increasing demand for pellets, the odor of the products will gain increasing
386
importance as the odor is perceived directly by people working in pellet production and
387
storage sites as well as by the end users. Thus, the odor properties have to be considered an
388
important quality criterion. Future investigations are required regarding the identification of 18 ACS Paragon Plus Environment
Page 19 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
389
those compounds with the highest impact on the odor formation as well as on the impact of
390
external parameters such as storage on a possible alteration of the VOC composition and
391
possible off-odor formation.
392 393 394
Acknowledgements
395
The authors thank the members of the sensory test panel for evaluating the samples.
396
This study was financially supported by the Provincial Government´s office from Lower
397
Austria, Department for Economy, Tourism and Technology as well as by the Austrian Re-
398
search Promotion Agency (FFG) in the frame of General Programme – Collective Research
399
within the projects ‘Smell - Study on malodorous emissions from wood pellets’ (FFG project
400
No. 839962 and 847138). Financial support obtained from ProPellets Austria ppA as well as
401
industry partners (Hasslacher Norica Timber GmbH, Binderholz GmbH, DEPV e.V., German
402
Pellets GmbH, Andritz AG, Agrana Stärke GmbH) is gratefully acknowledged.
403 404
Conflict of interest disclosure
405
The authors declare no competing financial interest.
19 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 20 of 43
406
Abbreviations
407
AHC, agglomerative hierarchical clustering; amu, atomic mass units; DDGS, dried distillers
408
grains with solubles; DVB, divinyl benzene; GC, gas chromatography; HS, headspace; MS,
409
mass spectrometry; PCA, principal component analysis; PDMS, polydimethylsiloxane; RI,
410
retention index; SPME, solid phase microextraction; VOCs, volatile organic compounds
20 ACS Paragon Plus Environment
Page 21 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
411
References
412
(1)
413 414
Bioenergy Outlook, Full Report; 2017. (2)
415 416
Döring, S. Pellets Als Energieträger; Springer Berlin Heidelberg, 2011. https://doi.org/10.1007/978-3-642-01624-0.
(3)
417 418
European Biomass Association (AEBIOM). Aebiom Statistical Report 2017, European
Oberberger, I., Thek, G. The Pellet Handbook. The Production and Thermal Utilization of Pellets; Earthscan: London, 2010.
(4)
Carroll, J. P.; Finnan, J. Physical and Chemical Properties of Pellets from Energy Crops and
419
Cereal Straws. Biosyst. Eng. 2012, 112 (2), 151–159.
420
https://doi.org/10.1016/j.biosystemseng.2012.03.012.
421
(5)
Lasek, J. A.; Kopczyński, M.; Janusz, M.; Iluk, A.; Zuwała, J. Combustion Properties of
422
Torrefied Biomass Obtained from Flue Gas-Enhanced Reactor. Energy 2017, 119, 362–368.
423
https://doi.org/10.1016/j.energy.2016.12.079.
424
(6)
Eriksson, G.; Grimm, A.; Skoglund, N.; Boström, D.; Öhman, M. Combustion and Fuel
425
Characterisation of Wheat Distillers Dried Grain with Solubles (DDGS) and Possible
426
Combustion Applications. Fuel 2012, 102, 208–220.
427
https://doi.org/10.1016/j.fuel.2012.05.019.
428
(7)
Arshadi, M.; Geladi, P.; Gref, R.; Fjällström, P. Emission of Volatile Aldehydes and Ketones
429
from Wood Pellets under Controlled Conditions. Ann. Occup. Hyg. 2009, 53 (8), 797–805.
430
https://doi.org/10.1093/annhyg/mep058.
431
(8)
Sedlmayer, I.; Arshadi, M.; Haslinger, W.; Hofbauer, H.; Larsson, I.; Lönnermark, A.; Nilsson,
432
C.; Pollex, A.; Schmidl, C.; Stelte, W.; et al. Determination of Off-Gassing and Self-Heating
433
Potential of Wood Pellets – Method Comparison and Correlation Analysis. Fuel 2018, 234
434
(July), 894–903. https://doi.org/10.1016/j.fuel.2018.07.117.
435
(9)
Svedberg, U. R. A.; Högberg, H. E.; Högberg, J.; Galle, B. Emission of Hexanal and Carbon
436
Monoxide from Storage of Wood Pellets, a Potential Occupational and Domestic Health
437
Hazard. Ann. Occup. Hyg. 2004, 48 (4), 339–349. https://doi.org/10.1093/annhyg/meh015.
438
(10)
Meier, F.; Sedlmayer, I.; Emhofer, W.; Wopienka, E.; Schmidl, C.; Haslinger, W.; Hofbauer, 21 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
439
H. Influence of Oxygen Availability on Off-Gassing Rates of Emissions from Stored Wood
440
Pellets. Energy and Fuels 2016, 30 (2), 1006–1012.
441
https://doi.org/10.1021/acs.energyfuels.5b02130.
442
(11)
Kuang, X.; Shankar, T. J.; Sokhansanj, S.; Lim, C. J.; Bi, X. T.; Melin, S. Effects of Headspace
443
and Oxygen Level on Off-Gas Emissions from Wood Pellets in Storage. Ann. Occup. Hyg.
444
2009, 53 (8), 807–813. https://doi.org/10.1093/annhyg/mep071.
445
(12)
Kuang, X.; Shankar, T. J.; Bi, X. T.; Lim, C. J.; Sokhansanj, S.; Melin, S. Rate and Peak
446
Concentrations of Off-Gas Emissions in Stored Wood Pellets - Sensitivities to Temperature,
447
Relative Humidity, and Headspace Volume. Ann. Occup. Hyg. 2009, 53 (8), 789–796.
448
https://doi.org/10.1093/annhyg/mep049.
449
(13)
Page 22 of 43
Kuang, X.; Shankar, T. J.; Bi, X. T.; Sokhansanj, S.; Jim Lim, C.; Melin, S. Characterization
450
and Kinetics Study of Off-Gas Emissions from Stored Wood Pellets. Ann. Occup. Hyg. 2008,
451
52 (8), 675–683. https://doi.org/10.1093/annhyg/men053.
452
(14)
Yazdanpanah, F.; Sokhansanj, S.; Lim, C. J.; Lau, A.; Bi, X.; Melin, S. Stratification of Off-
453
Gases in Stored Wood Pellets. Biomass and Bioenergy 2014, 71, 1–11.
454
https://doi.org/10.1016/j.biombioe.2014.04.019.
455
(15)
Svedberg, U.; Samuelsson, J.; Melin, S. Hazardous Off-Gassing of Carbon Monoxide and
456
Oxygen Depletion during Ocean Transportation of Wood Pellets. Ann. Occup. Hyg. 2008, 52
457
(4), 259–266. https://doi.org/10.1093/annhyg/men013.
458
(16)
Rahman, M. A.; Hopke, P. K. Mechanistic Pathway of Carbon Monoxide Off-Gassing from
459
Wood Pellets. Energy and Fuels 2016, 30 (7), 5809–5815.
460
https://doi.org/10.1021/acs.energyfuels.6b00874.
461
(17)
Pöllinger-Zierler, B.; Sedlmayer, I.; Hofbauer, H.; Wopienka, E.; Siegmund, B. Identification
462
of Malodourous Emissions of Wood Pellets during Storage. In Flavour Science - Proceedings
463
of the XV Weurman Flavour Research Symposium; B. Siegmund, E. Leitner, Eds.; Verlag der
464
TU Graz, Austria, 2018; pp 403–406. https://doi.org/10.3217/978-3-85125-593-5-84.
465 466
(18)
Costa, C.; Taiti, C.; Zanetti, M.; Proto, A.; D’Andrea, S.; Greco, R.; Demattè, L.; Mancuso, S.; Cavalli, R. Assessing VOC Emission by Wood Pellets Using the PTRToF-MS Technology. 22 ACS Paragon Plus Environment
Page 23 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
467 468
Chem. Eng. Trans. 2017, 58 (November), 445–450. https://doi.org/10.3303/CET1758075. (19)
469 470
Svedberg, U.; Galle, B. Assessment of Terpene Levels and Workers’ Exposure in Sawmills with Long Path FTIR. Appl. Occup. Environ. Hyg. 2000, 15 (9), 686–694.
(20)
Borén, E.; Yazdanpanah, F.; Lindahl, R.; Schilling, C.; Chandra, R. P.; Ghiasi, B.; Tang, Y.;
471
Sokhansanj, S.; Broström, M.; Larsson, S. H. Off-Gassing of VOCs and Permanent Gases
472
during Storage of Torrefied and Steam Exploded Wood. Energy and Fuels 2017, 31 (10),
473
10954–10965. https://doi.org/10.1021/acs.energyfuels.7b01959.
474
(21)
Tumuluru, J. S.; Jim Lim, C.; Bi, X. T.; Kuang, X.; Melin, S.; Yazdanpanah, F.; Sokhansanj, S.
475
Analysis on Storage Off-Gas Emissions from Woody, Herbaceous, and Torrefied Biomass.
476
Energies 2015, 8 (3), 1745–1759. https://doi.org/10.3390/en8031745.
477
(22)
478 479
Nunes, T. V; Pio, C. A. Emission of Volatile Organic Compounds from Portuguese Eucalyptus Forests; 2001.
(23)
Copeland, N.; Cape, J. N.; Heal, M. R. Volatile Organic Compound Emissions from
480
Miscanthus and Short Rotation Coppice Willow Bioenergy Crops. Atmos. Environ. 2012, 60,
481
327–335. https://doi.org/10.1016/j.atmosenv.2012.06.065.
482
(24)
Methven, L. Techniques in Sensory Analysis of Flavour. In Flavour Development, Analysis
483
and Perception in Food and Beverages; 2014; pp 353–368. https://doi.org/10.1016/b978-1-
484
78242-103-0.00016-3.
485
(25)
Elmore, J. S. Extraction Techniques for Analysis of Aroma Compounds. In Flavour
486
Development, Analysis and Perception in Food and Beverages; 2015; pp 31–46.
487
https://doi.org/10.1016/B978-1-78242-103-0.00002-3.
488
(26)
489
ÖNORM EN ISO 18134-3:2015. Solid Biofuels - Determination of Moisture Content - Oven Dry Method - Part 3: Moisture in General Analysis Sample, 2015.
490
(27)
ÖNORM EN 18135:2017 08 01. Solid Biofuels - Sampling (ISO 18135:2017), 2017.
491
(28)
Van Den Dool, H.; Kratz, P. D. A Generalization of the Retention Index System Including
492
Linear Temperature Programmed Gas—liquid Partition Chromatography. J. Chromatogr. A
493
1963, 11 (3), 463–471. https://doi.org/10.1016/S0021-9673(01)80947-X.
494
(29)
Farkas, P.; Le Quere, J.-L.; Maarse, H.; Kovac, M. The Standard GC Retention Index Library. 23 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
495
In Trends in Flavour Research - Proceedings of the 7th Weurman Flavour Research
496
Symposium; 1994; Vol. 35, pp 145–149.
Page 24 of 43
497
(30)
Flavornet http://www.flavornet.org/flavornet.html (accessed Dec 8, 2018).
498
(31)
Pherobase http://www.pherobase.com/ (accessed Dec 8, 2018).
499
(32)
DIN EN ISO 8586:2014-05. Sensory Analysis—General Guidelines for the Selection, Training
500 501
and Monitoring of Selected Assessors and Expert Sensory Assessors. 2014. (33)
Gamero, A.; Wesselink, W.; de Jong, C. Comparison of the Sensitivity of Different Aroma
502
Extraction Techniques in Combination with Gas Chromatography-Mass Spectrometry to
503
Detect Minor Aroma Compounds in Wine. J. Chromatogr. A 2013, 1272, 1–7.
504
https://doi.org/10.1016/j.chroma.2012.11.032.
505
(34)
Soto-Garcia, L.; Ashley, W. J.; Bregg, S.; Walier, D.; Lebouf, R.; Hopke, P. K.; Rossner, A.
506
VOCs Emissions from Multiple Wood Pellet Types and Concentrations in Indoor Air. Energy
507
and Fuels 2015, 29 (10), 6485–6493. https://doi.org/10.1021/acs.energyfuels.5b01398.
508
(35)
509 510
Technology. 1995, pp 103–109. https://doi.org/10.1016/0960-8524(94)00136-O. (36)
511 512
Frérot, E. Fats and Oils. In Springer Handbook of Odor; Springer International Publishing: Cham, 2017; pp 31–32. https://doi.org/10.1007/978-3-319-26932-0_11.
(37)
513 514
Garg, S. K.; Jain, A. Fermentative Production of 2,3-Butanediol: A Review. Bioresource
Granström, K. M. Sawdust Age Affect Aldehyde Emissions in Wood Pellets. Fuel 2014, 126, 219–223. https://doi.org/10.1016/j.fuel.2014.02.008.
(38)
Rahman, M. A.; Rossner, A.; Hopke, P. K. Occupational Exposure of Aldehydes Resulting
515
from the Storage of Wood Pellets. J. Occup. Environ. Hyg. 2017, 14 (6), 417–426.
516
https://doi.org/10.1080/15459624.2017.1285491.
517
(39)
Wang, S.; Yuan, X.; Li, C.; Huang, Z.; Leng, L.; Zeng, G.; Li, H. Variation in the Physical
518
Properties of Wood Pellets and Emission of Aldehyde/Ketone under Different Storage
519
Conditions. Fuel 2016, 183, 314–321. https://doi.org/10.1016/J.FUEL.2016.06.083.
520
(40)
Smit, B. A.; Engels, W. J. M.; Smit, G. Branched Chain Aldehydes: Production and
521
Breakdown Pathways and Relevance for Flavour in Foods. Applied Microbiology and
522
Biotechnology. 2009, pp 987–999. https://doi.org/10.1007/s00253-008-1758-x. 24 ACS Paragon Plus Environment
Page 25 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
523
Energy & Fuels
(41)
Lewinsohn, E.; Sitrit, Y.; Bar, E.; Azulay, Y.; Meir, A.; Zamir, D.; Tadmor, Y. Carotenoid
524
Pigmentation Affects the Volatile Composition of Tomato and Watermelon Fruits, as Revealed
525
by Comparative Genetic Analyses. J. Agric. Food Chem. 2005, 53 (8), 3142–3148.
526
https://doi.org/10.1021/jf047927t.
527
(42)
528 529
Pichersky, E.; Raguso, R. A. Why Do Plants Produce so Many Terpenoid Compounds? New Phytol. 2018, 220 (3), 692–702. https://doi.org/10.1111/nph.14178.
(43)
Barbosa, L. C. A.; Filomeno, C. A.; Teixeira, R. R. Chemical Variability and Biological
530
Activities of Eucalyptus Spp. Essential Oils. Molecules 2016, 21 (12), 1–33.
531
https://doi.org/10.3390/molecules21121671.
532
(44)
Yan, D. D.; Wong, Y. F.; Shellie, R. A.; Marriott, P. J.; Whittock, S. P.; Koutoulis, A.
533
Assessment of the Phytochemical Profiles of Novel Hop (Humulus Lupulus L.) Cultivars: A
534
Potential Route to Beer Crafting. Food Chem. 2019, 275 (June 2018), 15–23.
535
https://doi.org/10.1016/j.foodchem.2018.09.082.
536
(45)
Mardarowicz, M.; Wianowska, D.; Dawidowicz, A. L.; Sawicki, R. Comparison of Terpene
537
Composition in Engelmann Spruce (Picea Engelmanii) Using Hydrodistillation, SPME and
538
PLE. Ann Univ Mariae Curie Sklodowska, Sect. AA Chem. 2004, 59, 641–648.
539
https://doi.org/10.1515/znc-2004-9-1006.
540
(46)
Fahed, L.; Khoury, M.; Stien, D.; Ouaini, N.; Eparvier, V.; El Beyrouthy, M. Essential Oils
541
Composition and Antimicrobial Activity of Six Conifers Harvested in Lebanon. Chem.
542
Biodivers. 2017, 14 (2), 1–7. https://doi.org/10.1002/cbdv.201600235.
543
(47)
Fromberg, A.; Mariotti, M. S.; Pedreschi, F.; Fagt, S.; Granby, K. Furan and Alkylated Furans
544
in Heat Processed Food, Including Home Cooked Products. Czech J. Food Sci. 2014, 32 (5),
545
443–448. https://doi.org/10.17221/341/2013-CJFS.
546
(48)
Adams, A.; Bouckaert, C.; Van Lancker, F.; De Meulenaer, B.; De Kimpe, N. Amino Acid
547
Catalysis of 2-Alkylfuran Formation from Lipid Oxidation-Derived α,β-Unsaturated
548
Aldehydes. J. Agric. Food Chem. 2011, 59 (20), 11058–11062.
549
https://doi.org/10.1021/jf202448v.
550
(49)
Parker, J. K. Thermal Generation or Aroma. In Flavour Development, Analysis and Perception 25 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
551
in Food and Beverages; 2015; pp 151–185. https://doi.org/10.1016/B978-1-78242-103-
552
0.00008-4.
553
(50)
Chen, W. H.; Hsu, H. C.; Lu, K. M.; Lee, W. J.; Lin, T. C. Thermal Pretreatment of Wood
554
(Lauan) Block by Torrefaction and Its Influence on the Properties of the Biomass. Energy
555
2011, 36 (5), 3012–3021. https://doi.org/10.1016/j.energy.2011.02.045.
556
(51)
Schranz, M.; Lorber, K.; Klos, K.; Kerschbaumer, J.; Buettner, A. Influence of the Chemical
557
Structure on the Odor Qualities and Odor Thresholds of Guaiacol-Derived Odorants, Part 1:
558
Alkylated, Alkenylated and Methoxylated Derivatives. Food Chem. 2017, 232, 808–819.
559
https://doi.org/10.1016/j.foodchem.2017.04.070.
560
(52)
Page 26 of 43
Tapondjou, A. L.; Adler, C.; Fontem, D. A.; Bouda, H.; Reichmuth, C. Bioactivities of Cymol
561
and Essential Oils of Cupressus Sempervirens and Eucalyptus Saligna against Sitophilus
562
Zeamais Motschulsky and Tribolium Confusum Du Val. J. Stored Prod. Res. 2005, 41 (1), 91–
563
102. https://doi.org/10.1016/j.jspr.2004.01.004.
564
(53)
Kamel, B. S.; Dawson, H.; Kakuda, Y. Characteristics and Composition of Melon and Grape
565
Seed Oils and Cakes. J. Am. Oil Chem. Soc. 1985, 62 (5), 881–883.
566
https://doi.org/10.1007/BF02541750.
26 ACS Paragon Plus Environment
Page 27 of 43 1 2 3 568 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Energy & Fuels
Table 1: Detailed information on the investigated pellet materials Pellets made of
moisture content Raw material and source
production
(color of the pellets)
[mass fraction in % ]
Miscanthus
crushed miscanthus 100 %,
(medium-brown)
obtained from a German research institute
Rapeseed
extracted rape seed 100 %,
(light-brown, tan)
obtained from a German oil producing company
Straw
straw pellets 100 %
(light brown, yellowish)
obtained from a Danish pelletizing company
DDGS
Dried Distillers Grains with Solubles
(medium-brown)
obtained from a German brewery
Eucalyptus
eucalyptus pellets 100 %
(medium brown)
obtained from a Spanish pelletizing company
laboratory pelletizing press
8.2
laboratory pelletizing press
11.2
industrial pelletizing press
7.3
laboratory pelletizing press
12.6
industrial pelletizing press
5.3
27 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 569 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Grapevine
crushed vine pruning 50% and vine pomace 50%
(light to medium brown)
obtained from a German research institute
torrefied Sprucewood
torrefied spruce sawdust 100%
(black-brown)
obtained from a Dutch pelletizing company 1
torrefied Pinewood
torrefied pine sawdust 100%
(black brown)
obtained from a Dutch pelletizing company 2
Page 28 of 43
laboratory pelletizing press
10.1
laboratory pelletizing press
3.2
laboratory pelletizing press
6.4
28 ACS Paragon Plus Environment
Page 29 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
570
Energy & Fuels
Table 2: Results from the sensory evaluation – summary of the descriptors given by the sensory experts
571
Pellet type
Description
miscanthus
dried grain, straw/hay-like, ‘dusty’
rapeseed
oily, nutty, rancid, like feed for fattening animals
straw
greenish, herbage, resinous, aromatic, hay-like
eucalyptus
camphor-like, minty, refreshing, medicinal, essential
DDGS
roasted, malty, cereal-like, sweetish, mature/ripe fruits
grapevine
dried fruits, green, herbage, sweet
torrefied sprucewood
smoky, phenolic, woody, aromatic. smoked ham-like
torrefied pinewood
resinous, burnt notes, dried wood, pungent
572
29 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Page 30 of 43
Table 3: Relative amounts of VOCs determined in the investigated pellets samples (rape, miscanthus, straw, eucalyptus, DDGS, grapevine, torrefied sprucewood, torrefied pinewood) expressed as average peak areas obtained from HS-SPME-GC-MS (n = 4); n.d. not detected. Volatiles/samples
RIexp.
RIDB
torr.
torr.
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
Acetic acid1 STD [%]
612
600f
345 824 2
1 651 432 1
36 867 1
141 125 1
889 291 1
1 113 540 4
5 027 266 2
26 925 3
Propanoic acid2 STD [%]
709
668f
38 127 3
n.d.
n.d.
n.d.
27 956 1
n.d.
2 737 641 3
30 338 5
Butanoic acid1 STD [%]
780
821p
254 254 2
n.d.
n.d.
n.d.
n.d.
98 830 16
125 532 5
28 270 5
3-Methyl butanoic acid2 STD [%]
829
877p
n.d.
68 205 2
n.d.
n.d.
40 051 2
68 205 18
n.d.
30 415 3
Pentanoic acid2 STD [%]
870
911f
114 747 10
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
Hexanoic acid2 STD [%]
962
1019f
37 112 13
87 833 2
n.d.
8 850 11
22 296 6
87 833 13
n.d.
n.d.
Acids
Esters
30 ACS Paragon Plus Environment
Page 31 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Energy & Fuels
Volatiles/samples
RIexp.
RIDB
torr.
torr.
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
Methyl acetate STD [%]
516
515p
80 949 19
182 596 16
511 484 19
39 117 4
110 439 13
1 015 351 11
248 741 15
44 806 18
Methyl pentanoate STD [%]
810
821p
25 888 5
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3-Methyl-1-butanol STD [%]
745
737p
n.d.
24 844 6
n.d.
n.d.
n.d.
342 898 9
n.d.
n.d.
2-Methyl-1-butanol STD [%]
749
744p
n.d.
n.d.
n.d.
n.d.
n.d.
120 114 8
n.d.
n.d.
Pentanol STD [%]
772
766f
n.d.
71 882 7
162 846 4
n.d.
n.d.
148 182 9
n.d.
29 194 4
2,3-Butanediol STD [%]
782
769p
n.d.
n.d.
n.d.
n.d.
14 171 232 1
441 090 5
n.d.
n.d.
1-Hexanol STD [%]
869
869p
n.d.
107 012 12
n.d.
n.d.
n.d.
1 178 963 14
n.d.
n.d.
2-Ethyl-1-hexanol STD [%]
1031
1032f
n.d.
n.d.
n.d.
n.d.
93 846 11
n.d.
n.d.
n.d.
1-Octanol STD [%]
1071
1070p
n.d.
21 608 1
59 815 4
n.d.
n.d.
n.d.
n.d.
n.d.
Alcohols
31 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Page 32 of 43
Volatiles/samples
RIexp.
RIDB
torr.
torr.
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
1134
1122p
n.d.
n.d.
n.d.
n.d.
6 208 439 2
456 597 9
n.d.
n.d.
2-Butenal STD [%]
666
648f
n.d.
n.d.
n.d.
n.d.
n.d.
91 460 11
176 612 2
n.d.
3-Methylbutanal STD [%]
671
656p
n.d.
128 389 3
n.d.
n.d.
n.d.
103 737 14
n.d.
n.d.
2-Methylbutanal STD [%]
683
664p
n.d.
116 613 3
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
Pentanal STD [%]
715
699p
n.d.
101 378 1
128 478 4
76 619 5
n.d.
185 530 6
n.d.
88 400 19
3-Hydroxy-2-butanone STD [%]
727
718f
n.d.
n.d.
n.d.
n.d.
60 325 4
532 807 6
86 618 2
n.d.
Hexanal STD [%]
802
800p
377 194 2
576 816 3
2 375 951 2
643 113 2
224 695 12
1 845 498 13
386 584 10
1 239 120 5
2-Heptanone STD [%]
893
889p
50 502 5
33 169 1
276 414 5
102 013 3
n.d.
142 073 18
n.d.
n.d.
Heptanal STD [%]
905
900p
101 947 4
n.d.
279 316 1
92 557 1
n.d.
248 162 19
307 290 17
301 828 14
2-Phenylethanol STD [%] Aldehydes, ketones
32 ACS Paragon Plus Environment
Page 33 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Energy & Fuels
Volatiles/samples
RIexp.
RIDB
torr.
torr.
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
2-Heptenal STD [%]
963
957p
n.d.
n.d.
n.d.
n.d.
n.d.
643 246 7
n.d.
76 948 9
Benzaldehyde STD [%]
979
961p
155 441 7
45 697 7
104 332 1
89 727 4
153 654 7
418 479 6
387 699 6
169 345 3
6-Methyl-5-hepten-2-one STD [%]
990
958p
n.d.
n.d.
n.d.
n.d.
n.d.
232 904 18
n.d.
n.d.
2-Octanone STD [%]
993
999p
23 356 2
n.d.
34 362 5
n.d.
n.d.
n.d.
n.d.
n.d.
Octanal STD [%]
1007
1004p
61 178 7
30 826 2
149 571 3
89 543 7
n.d.
133 501 8
n.d.
114 531 18
2,4-Heptadienal STD [%]
1018
996p
n.d.
n.d.
54 774 5
n.d.
n.d.
n.d.
n.d.
n.d.
3,5-Octadien-2-one STD [%]
1077
1068p
n.d.
n.d.
109 988 6
n.d.
n.d.
n.d.
n.d.
n.d.
Nonanone STD [%]
1095
1093f
n.d.
n.d.
32 923 9
n.d.
n.d.
n.d.
n.d.
n.d.
Nonanal STD [%]
1110
1104p
90 288 6
55 062 2
302 679 4
175 002 8
70 102 4
405 155 7
n.d.
147 213 14
Terpenes
33 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Page 34 of 43
Volatiles/samples
RIexp.
RIDB
torr.
torr.
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
α-Pinene STD [%]
952
939p
134 919 5
n.d.
201 907 8
496 637 13
n.d.
199 104 5
n.d.
85 994 6
Camphene STD [%]
971
953p
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
131 932 10
δ-3-Carene STD [%]
1029
1011p
111 078 2
n.d.
136 608 3
65 149 7
n.d.
128 993 14
n.d.
233 448 7
Limonene STD [%]
1046
1039p
33 811 4
n.d.
138 036 2
1 126 116 9
n.d.
1 146 124 17
337 344 3
97 006 5
1,8-Cineol STD [%]
1054
1039p
n.d.
n.d.
n.d.
49 83 857 6
n.d.
n.d.
n.d.
n.d.
trans-Pinocarveol STD [%]
1172
1169p
n.d.
n.d.
68 836 8
66 777 6
n.d.
n.d.
n.d.
n.d.
Camphor STD [%]
1180
1192p
n.d.
n.d.
20 900 4
n.d.
n.d.
n.d.
n.d.
n.d.
β-Cyclocitral STD [%]
1252
1224p
n.d.
n.d.
n.d.
n.d.
n.d.
21 399 11
n.d.
n.d.
α-Copaene STD [%]
1418
1391p
n.d.
n.d.
21 346 4
26 506 15
40 442 571 18
14 390 682 5
37 637 094 4
5 597 783 9
Caryophyllene
1474
1467p
n.d.
n.d.
137 489
n.d.
n.d.
n.d.
n.d.
n.d.
34 ACS Paragon Plus Environment
Page 35 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Energy & Fuels
Volatiles/samples
RIexp.
RIDB
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
STD [%]
Straw
torr.
torr.
Eucalyptus
DDGS
Grapevine
Sprucewood
Pinewood
4
heterocyclic compounds 2-Ethylfuran STD [%]
719
728p
n.d.
n.d.
102 432 4
n.d.
n.d.
n.d.
n.d.
n.d.
2-Methyl pyrazine STD [%]
831
827p
231 275 8
n.d.
n.d.
n.d.
65 405 4
n.d.
179 323 11
n.d.
2-furancarboxaldehyde STD [%]
839
830p
69 261 7
129 033 3
n.d.
n.d.
14 462 421 1
412 855 19
16 341 146 2
810 668 7
2-(Hydroxymethyl)furan STD [%]
858
866p
n.d.
n.d.
n.d.
n.d.
871 717 2
448 155 9
1 707 580 11
n.d.
Acetylfuran STD [%]
921
910p
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
689 713 4
25 567 8
Dihydro-2(3H)-furanone STD [%]
923
915p
166 201 6
n.d.
n.d.
n.d.
1 712 475 2
1 001 430 18
991 985 3
n.d.
2-Methyl-5-formylfuran STD [%]
928
945p
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
153 562 5
n.d.
974
978p
n.d.
n.d.
n.d.
n.d.
209 394
n.d.
1 923 005
58 152
5
12
5-methylfurancarboxaldhyde STD [%]
11
35 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Page 36 of 43
Volatiles/samples
RIexp.
RIDB
[peak area counts]
[HP5]
[HP5]
Rape
Miscanthus
Straw
Eucalyptus
DDGS
997
1001p
79 508 8
216 968 7
589 530 4
417 158 8
Ethylbenzene STD [%]
875
878p
n.d.
n.d.
n.d.
Cumol STD [%]
939
941p
n.d.
n.d.
p-Cymol STD [%]
1041
1033p
109 684 2
2-Methoxyphenol STD [%]
1107
1091p
2-Methoxy-4-methylphenol STD [%]
1213
4-Allyl-2-methoxyphenol STD [%] 2-Methoxy-4-propylphenol STD [%]
2-Pentylfuran STD [%]
torr.
torr.
Grapevine
Sprucewood
Pinewood
121 840 5
402 383 18
128 707 9
181 177 10
39 748 6
n.d.
n.d.
n.d.
34 835 5
n.d.
n.d.
n.d.
n.d.
n.d.
135 412 16
n.d.
72 029 6
118 2107 7
n.d.
257 163 13
682 208 5
1 032 529 2
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
2 545 025 5
124 118 14
1190p
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
684 074 6
66 366 15
1382
1364f
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
65 594 11
n.d.
1392
1365p
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
54 499 11
n.d.
aromatic compounds
-
Results are expressed as average values of four replicates in terms of area counts.
-
RI
retention index.
36 ACS Paragon Plus Environment
Page 37 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
Energy & Fuels
-
RIexp.
RI as determined in the experiments.
-
RIDB
reference-RI obtained from databases
-
STD
relative standard deviation in %
-
1
Areas were determined from the selected ion chromatograms, m/z =60
-
2
Areas were determined from the selected ion chromatograms, m/z = 73
-
f
RI obtained from www.flavornet.org
-
p
RI obtained from http://www.pherobase.com
37 ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 38 of 43
Figure Captions
Figure 1a. Relative distribution of the compound classes (acids, esters, alcohols, aldehydes and ketones, terpenes, heterocyclic compounds, aromatic compounds and phenols) determined in pellets from alternative biomass Figure 1b. Relative distribution of the compound classes (acids, esters, alcohols, aldehydes and ketones, terpenes, heterocyclic compounds, aromatic compounds and phenols) determined in pellets from torrefied sprucewood and torrefied pinewood Figure 2: Dendrogram resulting from cluster analysis of VOCs; three clusters were detected (cluster 1: DDGS and torrefied sprucewood; cluster 2: torrefied pinewood, eucalyptus, straw, rape and miscanthus; cluster 3: grapevine), cluster analysis was carried out using the Ward procedure Figure 3a. Correlations among the investigated pellet materials based on the average areas of VOCs analysed by HS-SPME-GC-MS. PCA based on Pearson correlation. Indicated clusters were derived from the cluster analysis conducted using the Ward procedure (Figure 2) Figure 3b: Biplot score and factor loadings obtained by PCA based on the average areas of VOCs obtained from HS-SPME-GC-MS analyses
38 ACS Paragon Plus Environment
Page 39 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Energy & Fuels
Figure 1a. Relative distribution of the compound classes (acids, esters, alcohols, aldehydes and ketones, terpenes, heterocyclic compounds, aromatic compounds and phenols) determined in pellets from alternative biomass
ACS Paragon Plus Environment
Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Page 40 of 43
Figure 1b. Relative distribution of the compound classes (acids, esters, alcohols, aldehydes and ketones, terpenes, heterocyclic compounds, aromatic compounds and phenols) determined in pellets from torrefied sprucewood and torrefied pinewood
ACS Paragon Plus Environment
Page 41 of 43
Dendrogram 2,5E+15
2E+15
1,5E+15
similarity 1E+15
Miscanthus
Rape
Straw
Eucalyptus
torr. Pine
grape-vine
0
torr. Spruce
5E+14
DDGS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Energy & Fuels
Figure 2: Dendrogram resulting from cluster analysis of VOCs; three clusters were detected (cluster 1: DDGS and torrefied sprucewood; cluster 2: torrefied pinewood, eucalyptus, straw, rape and miscanthus; cluster 3: grapevine), cluster analysis was carried out using the Ward procedure
1
ACS Paragon Plus Environment
Energy & Fuels
Observations (Axis F1 and F2: 51,02 %) 10
grapevine
Cluster 2
8
6
F2 (20,73 %)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Page 42 of 43
4
2
Cluster 1
torr. sprucewood
0
DDGS
Miscanthus torr.pinewood
rape
-2
Cluster 3
eucalyptus
straw
-4 -10
-8
-6
-4
-2
0
2
4
6
8
F1 (30,29 %)
Figure 3a. Correlations among the investigated pellet materials based on the average areas of VOCs analysed by HS-SPME-GC-MS. PCA based on Pearson correlation. Indicated clusters were derived from the cluster analysis conducted using the Ward procedure (Figure 2)
ACS Paragon Plus Environment
Page 43 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47
Energy & Fuels
Figure 3b: Biplot score and factor loadings obtained by PCA based on the average areas of VOCs obtained from HS-SPME-GC-MS analyses 1
ACS Paragon Plus Environment