Skip to main content

Advertisement

  • Research Article
  • Open Access

Classification of different pineapple varieties grown in Malaysia based on volatile fingerprinting and sensory analysis

Chemistry Central Journal201812:140

https://doi.org/10.1186/s13065-018-0505-3

  • Received: 17 October 2018
  • Accepted: 27 November 2018
  • Published:

Abstract

Background

Pineapple is highly relished for its attractive sweet flavour and it is widely consumed in both fresh and canned forms. Pineapple flavour is a blend of a number of volatile and non-volatile compounds that are present in small amounts and in complex mixtures. The aroma compounds composition may be used for purposes of quality control as well as for authentication and classification of pineapple varieties.

Results

The key volatile compounds and aroma profile of six pineapple varieties grown in Malaysia were investigated by gas chromatography–olfactometry (GC-O), gas-chromatography–mass spectrometry and qualitative descriptive sensory analysis. A total of 59 compounds were determined by GC-O and aroma extract dilution analysis. Among these compounds, methyl-2-methylbutanoate, methyl hexanoate, methyl-3-(methylthiol)-propanoate, methyl octanoate, 2,5-dimethyl-4-methoxy-3(2H)-furanone, δ-octalactone, 2-methoxy-4-vinyl phenol, and δ-undecalactone contributed greatly to the aroma quality of the pineapple varieties, due to their high flavour dilution factor. The aroma of the pineapples was described by seven sensory terms as sweet, floral, fruity, fresh, green, woody and apple-like.

Conclusion

Inter-relationship between the aroma-active compounds and the pineapples revealed that ‘Moris’ and ‘MD2’ covaried majorly with the fruity esters, and the other varieties correlated with lesser numbers of the fruity esters. Hierarchical cluster analysis (HCA) was used to establish similarities among the pineapples and the results revealed three main groups of pineapples.

Keywords

  • Pineapple varieties
  • Volatile fingerprinting
  • PCA
  • HCA
  • Sensory evaluation
  • GC-O

Background

Pineapple (Ananas comosus L. Merr) which is one of the most popular exotic fruits in the world trade is widely distributed in tropical regions such as the Philippines, Thailand, Malaysia and Indonesia. In 2016, the global pineapple production was estimated at 24.78 million metric tons with Costa Rica (2930.66 metric tons), Brazil (2694.56 metric tons), Philippines (2612.47 metric tons), India (1964 metric tons),Thailand (1811.59 metric tons, and Nigeria (1591.28 metric tons) as the top five pineapple producers in the world [1]. Other important producers are: Indonesia, China, India, Mexico, and Colombia [2]. Malaysia is part of a new group of pineapple-producing countries. Malaysia exported approximately 20,000 tons of fresh pineapples annually [2]. The main pineapple varieties grown in Malaysia are: ‘Moris’, ‘N36’, ‘Sarawak’, ‘Gandul’, ‘Yankee’, ‘Josapine’, ‘Maspine’, and most recently ‘MD2’. Some of these varieties such as N36 and Josapine were locally developed for the local fresh fruit market.

Pineapple is highly relished for its attractive sweet flavour and it is widely consumed in both fresh and canned forms [3]. Pineapple flavour is a blend of a number of volatile and non-volatile compounds that are present in small amounts and in complex mixtures [4]. The volatile constituents of pineapples have been studied extensively and more than 280 compounds have been reported [4, 5]. Aroma chemicals are organic compounds with defined chemical structures. They are generated by organic or bio-catalytic synthesis or isolated from microbial fermentations [4]. There are many pathways involved in volatile biosynthesis starting from lipids [6], amino acids [7], terpenoids [8] and carotenoids [9]. Once the basic skeletons are produced via these pathways, the diversity of volatiles is achieved via additional modification reactions such as acylation, methylation, oxidation/reduction and cyclic ring closure [6]. As the content of aroma compounds in pineapple depends on many factors such as the climatic and geographical origin [10], varieties [11], different stages of ripening [12], and postharvest storage conditions [13], the aroma compounds composition may be used for purposes of quality control as well as for authentication and classification of pineapple varieties.

Fingerprinting techniques, based on chemical composition and multivariate statistical analysis have been used in characterising or classifying wines according to origin, quality, variety and type [14, 15]. It was also used in the authentication of green-ripe sea-freighted and air-freighted pineapple fruits harvested at full maturity [16]. Application of untargeted fingerprinting techniques as a means of gaining insight into the reaction complexity of a food system has received tremendous interest among researchers [17]. Fingerprinting is defined as a more unbiased and hypothesis-free methodology that considers as many compounds as possible in a particular food fraction [18]. Fingerprinting doesn’t concentrate on a specifically known compound, rather it allows for an initial fast screening to detect differences among samples. Meanwhile, chemometric techniques such as principal component analysis (PCA) and hierarchical cluster analysis (HCA) are employed in the analysis of generated data. PCA is often complemented with HCA to explore data sets obtained by gas chromatography. This method has been used in the classification of wines based on their volatile profiles [19]. Multivariate techniques of data analysis represent a useful statistical tool to differentiate between different fruit varieties [20]. Also, this chemometric approach has been used to classify muskmelon [21], tomato fruit [22], and citrus juice [20].

Although much work has been done on volatile fingerprinting in apple fruits [23], and grape fruits [24], there has been no systematic study on volatile fingerprinting of fresh pineapple fruits grown in Malaysia. The purpose of this study were: (1) to identify and quantify the volatile compounds in six different varieties of pineapples grown in Malaysia (Moris, Maspine, MD2, N36, Josapine and Sarawak) and (2) apply fingerprinting technique to determine which volatile compounds may be potential markers for pineapple varieties grown in Malaysia.

Results and discussion

Sensory evaluation

The aroma qualities of the six different pineapple varieties were elucidated by ten trained panellists. The obtained relative standard deviation from the mean aroma quality intensities varied within the range of 1.2–5.9% depending on the pineapple variety and the aroma quality. The details of the aroma qualities of the pineapples are listed in Table 1. Results of the aroma qualities revealed significant differences (p < 0.05) among varieties for all attributes. For instance, while pineapple ‘MD2’ presented the highest intensities for sweetness (8.62), floral (6.88) and apple-like (8.31) attributes, ‘Moris’ produced the highest intensities for fruity (6.83) and fresh (7.31) attributes, respectively. On the other hand, ‘Sarawak’ had the strongest woody (7.46) and green (7.62) attributes. The other pineapple varieties (‘Josapine’, ‘N36’ and ‘Maspine’) produced varied aroma responses. ‘Josapine’ had strong sweet and woody attributes with relatively low floral aroma. ‘Maspine’ exhibited strong sweet and green aroma notes. ‘N36’ had strong sweet and woody aroma, respectively.
Table 1

The mean scores and relative standard deviation of the seven aroma-attributes for the six pineapple varieties grown in Malaysia

Fruit

Mean values

 

Sweet (RSD %)

Floral (RSD %)

Fruity (RSD %)

Fresh (RSD %)

Green (RSD %)

Woody (RSD %)

Apple-like (RSD %)

Moris

8.50b (2.8)

5.67b (4.0)

6.83a (2.2)

7.31a (4.5)

3.85e (4.8)

5.63d (5.9)

6.81b (5.7)

Maspine

6.81e (2.6)

2.56f (3.1)

4.40f (1.2)

6.75b (4.9)

6.00b (5.6)

4.00f (4.8)

6.15c (5.3)

MD2

8.62a (2.9)

6.88a (3.7)

6.40b (1.1)

6.05c (4.1)

2.57f (3.4)

5.15e (3.1)

8.31a (2.6)

N36

7.82d (3.3)

4.66c (4.1)

5.13e (4.3)

4.75e (4.6)

5.26c (4.7)

6.05c (3.0)

4.15e (3.4)

Josapine

8.01e (4.0)

3.58d (3.0)

5.05d (3.7)

5.35d (5.5)

4.50d (5.3)

6.91b (5.0)

5.34d (4.5)

Sarawak

6.45f (2.5)

3.05e (2.7)

5.52c (1.6)

4.54f (2.3)

7.62a (4.4)

7.46a (3.7)

3.56f (2.1)

Superscripts with different letters are significantly (p < 0.05) different

To have an insight into the reasons behind this observation, the different pineapple varieties were subjected to AEDA and GC-O.

Characterization of aroma-active compounds by GC-O analysis

A total of 59 volatile compounds were detected in the six different pineapple varieties grown in Malaysia (Table 2). The details are listed in Table 2. Pineapple ‘Moris’ had the highest number of compounds with a total of 31 compounds and this was followed by ‘MD2’ with 27 aroma-active compounds. The next were ‘N36’, ‘Maspine’, and ‘Sarawak’ which produced 24, 20 and 18 aroma-active compounds respectively. ‘Josapine had the least number (16) of aroma-active compounds. Some of the compounds detected were methyl-2-methylbutanoate, dimethyl malonate, methyl-2-methyl acetoacetate, methyl-2-hydroxy-2-methylbutanoate, methyl hexanoate, ethyl isohexanoate, methyl-2-methylhexanoate, methyl-3-(methylthiol)-propanoate, ethyl hexanoate, y-lactone, 2,5-dimethyl-4-hydroxy-3(2H)-furanone, methyl-3-hydroxyhexanoate, 2,5-dimethyl-4-methoxy-3(2H)-furanone, methyl octanoate, methyl-(4E)-octenoate, 2,4-dihydroxy-2,5-dimethyl-3(2H)-furanone. Among the aforementioned compounds, 12 aroma-active compounds with flavour dilution (FD) ≥ 16 were identified as key odorants through the application of the aroma extract dilution analysis (AEDA) (Table 2). For all the pineapple varieties, the highest FD factor was attributed to methyl-2-methylbutanoate (FD, 1024), methyl hexanoate (FD, 128) and 2,4-dihydroxy-2,5-dimethyl-3(2H)-furanone (DMHF) (FD, 128), respectively.
Table 2

Detected aroma compounds with retention index and mean concentration (µg/kg fresh fruit) found in each pineapple varieties grown in Malaysia

No

Compounda

Aroma-qualityb

Moris

Maspine

MD2

N36

Josapine

Sarawak

RI on TG-5 ms

C1

Methyl-2-methylbutanoate

Apple-like

103 ± 8.5

771 [770] [31]

C2

2-Hexanol

Winey

2.1 ± 0.0

1.0 ± 0.0

780 [786] [32]

C3

3-Methylbutanoic acid

Cheesy

21.0 ± 1.5

792

C4

Methyl butyl acetate

Banana

8.0 ± 1.0

812

C5

Methyl-2-methylpentanoate

Fruity

7.3 ± 1.2

6.7 ± 0.1

823 [nf]

C6

Gamma-butyrolactone

Milky

3.0 ± 0.1

837

C7

Dimethyl malonate

Fruity

48.2 ± 3.5

2.0 ± 0.0

2.0 ± 0.0

843 [nf]

C8

Ethyl-2,3-dimethylbutanoate

Fruity

1.5 ± 0.0

856 [856] [32]

C9

Methyl-2-methyl acetoacetate

Fruity

156.1 ± 12.0

13.0 ± 1.5

868 [nf]

C10

Methyl-2/3-hydroxy-2/3-methylbutanoate

Fruity

86.0 ± 6.5

7.0 ± 0.1

877

C11

Methyl hexanoate

Fruity

397 ± 15.0

tr

44.0 ± 2.1

19.0 ± 0.1

tr

32.0 ± 1.0

884

C12

Ethyl isohexanoate

Pineapple

13.0 ± 1.0

920

C13

Methyl-2-methylhexanoate

Fruity

8.0 ± 0.1

931

C14

Methyl-3-(methylthiol)-propanoate

Sulphurous

307 ± 9.7

28.7 ± 1.0

17.0 ± 0.1

936

C15

Hexanoic acid

Fatty

12.4 ± 0.1

974 [975] [32]

C16

(E)-β-Ocimene

Sweet/herbal

4.0 ± 0.0

1.0 ± 0.0

2.0 ± 0.0

1.0 ± 0.0

976

C17

Methyl-3-hydroxy-4-methylpentanoate

Fruity

65.0 ± 5.6

983

C18

Ethyl hexanoate

Fruity

13.0 ± 1.2

1.0 ± 0.0

984 [1002] [32]

C19

Gamma-lactone

Creamy

202.0 ± 9.7

11.0 ± 0.1

5.0 ± 0.1

986 [986] [32]

C20

Delta-lactone

ND

221 ± 11.0

15.1 ± 1.2

9.0 ± 0.1

5.6 ± 0.1

1006

C21

2,5-Dimethyl-4-hydroxy-3(2H)-furanone

Strawberry

55.0 ± 3.4

9.0 ± 1.0

1.5 ± 0.0

1.2 ± 0.0

54.2 ± 2.0

6.0 ± 0.1

1022

C22

Methyl-3-hydroxyhexanoate

Fruity

11.2 ± 0.1

1047

C23

2,5-Dimethyl-4-methoxy-3(2H)-furanone

Roasty/sweet

7.4 ± 0.1

1055

C24

Methyl octanoate

Fruity

101.0 ± 8.0

3.0 ± 0.0

4.0 ± 0.1

1083

C25

Methyl (4E)-4-octenoate

Fruity

30.0 ± 3.0

1091

C26

3-Octyl acetate*

Herbal/green

2.0 ± 0.0

1118 [1119] [32]

C27

2,4-Dihydroxy-2,5-dimethyl-3(2H)-furanone

Fruity

2.0 ± 0.0

3.2 ± 0.1

4.3 ± 0.1

1173

C28

Octanoic acid

Rancid

5.0 ± 0.1

2.0 ± 0.0

2.1 ± 0.0

1174

C29

Gamma-octalactone

Coconut-like

86.2 ± 4.0

1184

C30

Delta-octalactone

Creamy

11.0 ± 1.5

3.5 ± 0.0

3.0 ± 0.1

11.0 ± 0.1

7.0 ± 0.1

1205

C31

Copaene

Woody

40.1 ± 3.9

12.0 ± 1.2

3.0 ± 0.1

1221

C32

Methyl decanoate

Floral

4.0 ± 0.1

1282

C33

2-Methoxy-4-vinyl phenol

Smoky

4.0 ± 0.1

2.0 ± 0.0

18.0 ± 1.0

1293

C34

Decanoic acid

Sweaty

2.0 ± 0.0

2.0 ± 0.0

2.0 ± 0.0

1372

C35

Methyl-5-acetoxy octanoate

Wine-like

5.0 ± 0.1

1385

C36

gamma-Farnesene

ND

2.7 ± 0.0

1453

C37

Delta-undecalactone*

Coconut-like

2.0 ± 0.1

4.1 ± 0.1

1483 [1488] [33]

C38

Germacrene

Woody

1.0 ± 0.0

1515 [1502] [33]

C39

Globulol

Floral

2.0 ± 0.1

1530

C40

(-)-Spathulenol

Earthy

19.0 ± 1.0

8.0 ± 1.5

1536

C41

Dodecanoic acid

Sweaty/soapy

7.0 ± 0.1

3.0 ± 0.1

1570

C42

Gamma-dodecalactone

Fruity

1.0 ± 0.0

1582 [1587] [32]

C43

(Z)-7-Tetradecenal

ND

1139 ± 34.0

1609

C44

Pentadecanal*

Fresh/waxy

18.1 ± 1.0

4.0 ± 0.1

1701 [1712] [36]

C45

3,5-Dimethoxy-4-hydroxycinnamaldehyde

Cocoa-like

3.0 ± 0.1

1788

C46

Pentadecanoic acid

Waxy

3.0 ± 0.1

2.0 ± 0.0

1.0 ± 0.0

1869

C47

Methylhexadecanoate*

Waxy

2.6 ± 0.0

1.0 ± 0.0

1878[1878] [32]

C48

Methyl-(2E)-2-hexadecenoate

ND

8.0 ± 0.1

1886

C49

Ethyl hexadecanoate

Waxy

4.0 ± 0.1

1.0 ± 0.0

1928

C50

Hexadecanoic acid*

Waxy

51.7 ± 3.2

255.0 ± 9.0

5.0 ± 0.1

393.0 ± 11.2

2.0 ± 0.0

1968 [1970] [32]

C51

9-Hexadecenoic acid

Waxy

2.0 ± 0.0

1976

C52

Octadecanal

Fatty/greasy

21.0 ± 1.5

1999 [2002] [32]

C53

Eicosane

ND

105.1 ± 9.0

2.0 ± 0.0

14.0 ± 2.0

2.0 ± 0.0

16.0 ± 1.0

2009

C54

Heptadecanoic acid*

Waxy

4.0 ± 0.1

3.0 ± 0.1

2067 [2067] [32]

C55

Octadecanoic acid*

Pungent

149.0 ± 9.0

1.0 ± 0.0

69.0 ± 5.1

89.0 ± 7.0

2167 [2167] [32]

C56

Ethyl octadecanoate*

Waxy

46.0 ± 3.0

2.0 ± 0.0

2177 [2174] [33]

C57

(Z,Z)-9,12-Octadecadienoic acid*

Waxy

37.0 ± 2.1

37.0 ± 4.0

16.0 ± 1.5

2183 [2183] [36]

C58

Ethyl oleate*

Fatty

89.0 ± 6.5

57.0 ± 2.0

2185 [2180] [32]

C59

Geranyl geraniol

Floral

11.0 ± 0.1

2192

– Odorant not detected

ND not detectable

tr Trace (< 1.0 µg/kg), [RIlit]35; Scheidig et al. [31], [RIlit]36; NIST [32], [RIlit]37; El-Sayad [33]

aCompounds were identified by comparing their retention indices on the TG-5 ms column, their mass spectra, and odour nuances with the respective data of the reference odorants

bAroma-quality perceived by panellists during olfactometry

* Compounds tentatively identified with the MS database and retention index

Meanwhile, methyl-2-methylbutanoate which exhibited the highest FD factor had a bigger influence on the aroma profile of pineapple ‘Moris’. It was however, not detected in the other varieties. On the other hand, methyl hexanoate and DMHF contributed significantly to the aroma profiles of the different pineapple varieties. This observation was similar to those of Zheng et al. [3]. For instance, the FD factors of methyl hexanoate in the different pineapple varieties were 64, 128, 64, 32 and 16 corresponding to ‘Moris’, ‘MD2’, ‘N36’, ‘Josapine’ and ‘Sarawak’. 2,4-Dihydroxy-2,5-dimethyl-3(2H)-furanone had greater influence on the aroma profiles of “Moris’ ‘Maspine’ and ‘MD2’ with a corresponding FD factors of 16, 64 and 128, respectively. In addition, aroma-active compounds with relatively high FD factors such as δ-octalactone, 2-methoxy-4-vinyl phenol, methyl octanoate and hexadecanoic acid had appreciable influence on the aroma profile of the pineapple varieties (Table 2).

Quantitation of aroma-active compounds

The detected aroma-active compounds and their mean concentrations were listed in Table 3. Most of the aroma-active compounds were branched esters. Recently, Steingrass et al. [12, 21] also reported that esters were the main volatile compounds in fresh pineapple, which is in agreement with our findings. In addition, several other groups of compounds such as ketones, alcohols, terpenes, lactones and acids were detected in the different pineapple varieties. Branched esters such as methyl-2-methyl butanoate, methyl-2-methyl pentanoate, ethyl-2,3-dimethylbutanoate, methyl-2-methyl acetoacetate, methyl-2-hydroxy-2-methylbutanoate, methyl-3-(methylthiol)-propanoate, methyl-3-hydroxy-4-methylpentanoate, methyl hexanoate, and methyl-3-hydroxyhexanoate were the most abundant compounds. Among these compounds, methyl-3-(methylthiol)-propanoate (307 ± 9.7 µg/kg) methyl-2-methylbutanoate (103 ± 8.5 µg/kg), methyl-2-hydroxy-methylbutanoate (86.0 ± 6.5 µg/kg), methyl-3-hydroxy-4-methyl pentanoate (65.0 ± 5.6 µg/kg), methyl hexanoate (397 ± 15 µg/kg) and methyl-2-methyl acetoacetate (156.1 ± 12.0 µg/kg) produced higher concentrations than other esters in the pineapple varieties (Table 3). However, research to determine the mechanism by which these esters are generated has been limited. The primary enzyme believed to be responsible for ester production is the alcohol acyltransferase (AAT), which was first isolated from ‘Chandler’ fruit [25].
Table 3

Detected aroma compounds with their flavour dilution (FD) factors in each pineapple varieties (Moris, Maspine, MD2, N36, Josapine and Sarawak) grown in Malaysia

No

Compounda

Aroma-qualityb

Moris

Maspine

MD2

N36

Josapine

Sarawak

RI on TG-5 ms

1

Methyl-2-methylbutanoate

Fruity

1024

771

2

2-Hexanol

Winey

2

2

780

3

3-Methylbutanoic acid

Cheesy

2

792

4

Methyl butyl acetate

Banana

2

812

5

Methyl-2-methylpentanoate

Fruity

4

2

823

6

Gamma-butyrolactone

Weak, milky

2

837

7

Dimethyl malonate

Fruity

8

2

2

843

8

Ethyl-2,3-dimethylbutanoate

Fruity

8

856

9

Methyl-2-methyl acetoacetate

Fruity

8

8

868

10

Methyl-2/3-hydroxy-2/3-methylbutanoate

Fruity

8

4

877

11

Methyl hexanoate

Fruity

64

128

64

32

16

884

12

Ethyl isohexanoate

Pineapple

8

920

13

Methyl-2-methylhexanoate

Sulfurous

8

4

2

931

15

Hexanoic acid

Fatty

2

974

16

(E)-β-Ocimene

Sweet, herbal

2

2

2

2

976

17

Methyl-3-hydroxy-4-methylpentanoate

Fruity

8

983

18

Ethyl hexanoate

Fruity

16

16

984

19

Gamma-lactone

Creamy

16

16

8

986

20

Delta-lactone

ND

1006

21

2,5-Dimethyl-4-hydroxy-3(2H)-furanone

Strawberry

16

16

32

16

1022

22

Methyl-3-hydroxyhexanoate

Fruity

8

1047

23

2,5-Dimethyl-4-methoxy-3(2H)-furanone

Caramel, sweet

32

1055

24

Methyl octanoate

Fruity

32

16

16

1083

25

Methyl (4E)-4-octenoate

Fruity

8

1091

26

3-Octyl acetate

Herbal/green

2

1118

27

2,4-Dihydroxy-2,5-dimethyl-3(2H)-furanone

Fruity

16

64

128

1173

28

Octanoic acid

Rancid

2

2

2

1174

29

Gamma-octalactone

Coconut

4

1184

30

Delta-octalactone

Creamy

16

32

16

16

16

1205

31

Copaene

Woody

8

8

2

1221

32

Methyl decanoate

Floral

2

1282

33

2-Methoxy-4-vinyl phenol

Smoky

16

4

32

1293

34

Decanoic acid

Sweaty

2

2

2

 

1372

35

Methyl-5-acetoxy octanoate

Winey

8

1385

36

gamma-Farnesene

ND

1453

37

Delta-undecalactone

Coconut

32

16

1483

38

Germacrene

Woody

2

1515

39

Globulol

Floral

4

1530

40

(-)-Spathulenol

Earthy

8

8

1536

41

Dodecanoic acid

Soapy/sweaty

2

4

1570

42

y-Dodecalactone

Fruity

2

1582

43

(Z)-7-Tetradecenal

ND

=

1609

44

Pentadecanal

Waxy/fresh

4

4

1701

45

3,5-Dimethoxy-4-hydroxycinnamaldehyde

Cocoa-like

2

1788

46

Pentadecanoic acid

Waxy

2

2

2

1869

47

Methylhexadecanoate

Waxy

4

4

4

1878

48

Methyl-(2E)-2-hexadecenoate

ND

1886

49

Ethyl hexadecanoate

Waxy

2

2

1928

50

Hexadecanoic acid

Waxy/sweaty

4

64

4

32

2

1968

51

9-Hexadecenoic acid

Waxy

2

1976

52

Octadecanal

Greasy

4

1999

53

Eicosane

ND

2009

54

Heptadecanoic acid

Waxy

2

2

2067

55

Octadecanoic acid

Pungent/sweaty

8

2

4

8

2167

56

Ethyl octadecanoate

Waxy

8

2

2177

57

(Z,Z)-9,12-Octadecadienoic acid

Waxy/sweaty

8

8

4

2183

58

Ethyl oleate

Fatty

8

8

2185

59

Geranyl geraniol

Floral

8

2192

ND not detectable, FD Flavour dilution factor determined in extract containing the juice volatiles

– odorant not detected

aCompounds were identified by comparing their retention indices on the TG-5 ms column, their mass spectra, and odour nuances with the respective data of the reference odorants

bAroma-quality perceived by panellists during olfactometry

Whilst methyl-branched esters such as methyl-2-methyl butanoate, methyl-2-methylpentanoate, etc. are assumed to be derived from branched-chain amino acid catabolism [25], Methyl-3-(methylthiol)-propanoate which exhibited high concentrations in ‘Moris’, ‘MD2’ and ‘Sarawak’ has been attributed to the Stickland reactions of methionine [26]. It is worthy of note that the ethyl derivatives of odd numbered carboxylic acids or branched carboxylic acids such as ethyl-2,3-dimethylbutanoate, ethyl isohexanoate and ethyl hexanoate were more specific and appeared in appreciable amount in pineapple ‘Moris’ only (Table 3). Furthermore, ‘Moris’ was also characterized by several acetates and acetoxy esters such as methyl-2-methyl acetoacetate, methyl butyl acetate, methyl-5-acetoxy octanoate and 3-octyl acetate. The acetates probably resulted from the condensation of acetyl-CoA with alcohols and hydroxyl-fatty acids [25]. Earlier on Steingass et al. [25] postulated that accumulation of acetyl-CoA under anaerobic condition can facilitate the production of both acetates and acetoxylated esters. To corroborate this position, alcohol acetyl transferase (AATs) enzymes’ involvement in the genesis of acetates have been reported in different fruits such as; apples, bananas, pineapples and melon [16]. In addition, there was a marked dominance of the furanones (i.e. 2,5-dimethyl-4-hydroxy-3(2H)furanone; 2,4-dihydroxy-2,5-dimethyl-3(2H)-furanone) and lactones (i.e. y-lactone, δ-lactone, y-octalactone, and δ-octalactone) in ‘Moris’ as compared to the other pineapple varieties. Surprisingly, δ-undecalactone was mainly detected in ‘MD2’ and ‘Josapine’. Lactones which exhibited creamy and coconut-like aroma notes in the pineapple varieties have been identified as most potent odorants in pineapples [27]. The formation of lactones in fruits has been documented. There are two proposed pathways for the formation of lactones [28]. The first pathway is from unsaturated fatty acids to lactones via hydroperoxy fatty acids and monohydroxy fatty acids under the actions of lipoxygenase (LOX) and peroxygenase (PGX). The second pathway is from unsaturated fatty acids to lactones via epoxy fatty acids and dihydroxy fatty acids under the actions of PGX and epoxide hydrolase. 4-Hydroxy-2,5-dimethyl-3(2H)-furanone and its methyl ether 2,5-dimethyl-4-methoxy-3(2H)-furanone are important odorants of many fruits [29]. Whereas, 4-hydroxy-2,5-dimethyl-3(2H)-furanone and its derivatives are synthesized by a series of enzymatic steps in fruits, they are also products of Maillard reaction [30].

Relationship between pineapple varieties and odour-active compounds

In order to differentiate between the six different pineapples in terms of the aroma-active compounds associated with each variety, principal component analysis (PCA) was used. PCA provides a visual relationship between the pineapple varieties and their aroma-active compounds. This method makes the interpretation of the multivariate analysis easy. A first PCA was performed on the concentration of the 59 volatile compounds (Table 2) analysed in the pineapple varieties. Based on the samples grouping from PCA, a partial least square discriminant analysis (PLS-DA) was established (Fig. 1a). The scatter plot of scores of the first two components (in PLS-DA which explained 95% of the total variance in the data) showed the differences among the six pineapple varieties. The corresponding PLS weight plot (Fig. 1b) revealed the inter-relationship between the aroma compounds and the pineapple varieties.
Fig. 1
Fig. 1

Score scatter PLS-DA and PLS weight plots (a, b) of the pineapple varieties grown in Malaysia, The PLS-DA plot shows similarities and differences in pineapple varieties while PLS-weight plot reveals the inter-relatedness between the fruits and 97 aroma-active compounds (P1–P97) shown in Table 2

Fig. 2
Fig. 2

Visualization of PLS weight plot of Fig. 1b. 1, 2 and 3 are aroma compounds correlating with Moris, (yellow), Sarawak, Josapine, N36 and Maspine respectively

Malaysian pineapples were separated according to their varieties (Fig. 1a). Low negative component 1 and high positive component 2 corresponded to pineapple ‘MD2’. The pineapple variety ‘Maspine’ was situated within low negative components 1 and 2, respectively. While pineapple ‘Moris’ was within the area of high positive component 1 and low negative component 2, other varieties such as ‘Sarawak’, Josapine and N36, were all situated at the region of low negative component 1 and low positive component 2.

In addition, the inter-relationship between the aroma-active compounds and the pineapple varieties were carried out by the partial least square (PLS)-weight plot (Fig. 1b). The results revealed that ‘Moris’ covaried with 31 aroma-active compounds, majority of which were the fruity esters with FD ≥ 8 such as methyl-2-methylbutanoate (C1), methyl butyl acetate (C4), ethyl-2,3-dimethylbutanoate (C8), ethyl iso hexanoate (C12), methyl-3-hydroxy-4-methylpentanoate (C17), 2,5-dimethyl-4-hydroxy-3(2H) furanone (C21), methyl octanoate (C25), methyl-5-acetoxy octanoate (C35) and geranyl geraniol (C59) (Table 3) and (Fig. 2). Similarly, ‘Moris’ also covaried with other compounds such as y-octalactone (C29), δ-octalactone (C30), and (-)-spathulenol (C40). On the other hand, ‘Maspine’ was correlated with 2-methoxy-4-vinyl-phenol (C33), (Z)-7-tetradecenal (C43), 3,5-dimethoxy-4-hydroxycinnamaldehyde (C45), pentadecanoic acid (C46), methyl hexadecanoate (C47) and octadecanoic acid (C55) (Fig. 2). In the case of ‘Sarawak’, ‘Josapine’ and ‘N36’, they covaried with ethyl hexanoate (C18)), y-lactone (C42)), methyl octanoate (C24), δ-octalactone (C20), and 2-methoxy-4-viny phenol (C33). However, ‘MD2’ covered with methyl-3(methylthiol)-propanoate (C14), methyl-3-hydroxyhexanoate (C22), 2,4-dihydroxy-2,5-dimethyl-3 (2H)-furanone (C27), δ-undecalactone (C37), (Z)-7-tetradecenal (C43), 3,5-dimetoxy-4-hydroxycinnamaldehyde (C45), methyl hexadecanoate (C47) and decanoic acid (C34).

In order to validate the results obtained by PCA analysis, a hierarchical cluster analysis (HCA) was carried out using Ward’s method of agglomeration and Euclidean distances to evaluate similarity between varieties. The test was performed on the complete dataset, thus obtaining the dendrogram in Fig. 3. Three main groups of pineapple varieties were identified by HCA. The first group comprised pineapple ‘Moris’ and ‘MD2’ Fig. 3. This group was characterized by high numbers of aroma-compounds most especially the fruity esters. They contained some of the highly intense aroma-active compounds (FD ≥ 64) such as methyl-2-methyl butanoate, methyl hexanoate, methyl-3-(methylthiol)-propanoate and 2,4-dihydroxy-2,5-dimethyl-3 (2H)-furanone. The second group contained pineapple ‘Maspine’. This group contained the least quantity of fruity esters. The third group included ‘Sarawak’, ‘Josapine’ and ‘N36’. This group contained more of the fatty acid methyl esters.
Fig. 3
Fig. 3

Dendrogram of hierarchical cluster analysis of six pineapple varieties grown in Malaysia

Conclusion

Sensory evaluation, GC-O and GC–MS analysis were employed to elucidate the characteristic aroma of six pineapples varieties grown in Malaysia. Application of qualitative descriptive sensory analysis on the six pineapple varieties revealed seven quality terms such as sweet, floral, fruity, fresh, green, woody and apple-like. In addition, 97 aroma-active compounds were identified by GC-O and AEDA in the pineapple varieties. Of this, pineapple ‘Moris’ had the highest numbers of aroma-active compounds with a total of 31 compounds and this was followed by ‘MD2’ with 27 compounds. The next were the ‘N36’, ‘Maspine’, and ‘Sarawak’ which produced 24, 20 and 18 aroma-active compounds, respectively. ‘Josapine’ had the least number of aroma-active compounds (16). In order to address the inter-relationship between the sensory attributes and the aroma compounds, the PLSR analysis was employed. Results of the analysis showed that ‘Moris’ and ‘MD2’ covaried majorly with the fruity esters with higher FD factors. ‘Sarawak’, ‘Josapine’ and ‘N36’ were correlated with fewer fruity esters; they covaried majorly with the lactones. However, the variety ‘Maspine’ was correlated with 2-methoxy-4-vinyl-phenol (C33), (Z)-7-tetradecenal (C43), 3,5-dimethoxy-4-hydroxycinnamaldehyde (C45), pentadecanoic acid (C46), methyl hexadecanoate (C47) and octadecanoic acid (C55), respectively. In addition, hierarchical cluster analysis was used to establish similarities among the pineapples and the results revealed three main groups of pineapples.

Experimental

Pineapple fruits

Fresh, fully-ripe pineapples of six different varieties (‘Moris’, ‘Maspine’, ‘MD2’, ‘N36’, ‘Josapine’, and ‘Sarawak’) grown in Johor, Malaysia were obtained from an established farmer. Three fruits of each variety were stored at 8 ± 1 °C and 80–90% relative humidity until analysed. Fruits were selected with similar characteristics of ripening (i.e. pale-yellow skin colour; flat eyes; and degree of Brix), hand-peeled, cored, sliced and cut into small pieces before blending with a Panasonic Food Processor (model PSN-MKF300, Panasonic, Malaysia). One fruit weighed 927–1201 g apart from the crown. The pH and Brix values were 3.49, 3.50, 3.52, 3.54, 3.60, 10.33 o Brix, 11.45 o Brix, 12.48 o Brix, 13.25 o Brix, 14.01 o Brix, and 16.50 o Brix for Sarawak, Maspine, N36, Josapine, Moris and MD2, respectively. At least three separate measurements were carried out for each analysis.

Chemicals

Pure reference standards of methyl-2-methylbutanoate (98.0%), 2-hexanol (97.0%), 3-methylbutanoic acid (97.5%), methyl butyl acetate (98.0%), methyl-2-methylpentanoate (99.5%), gamma-butyrolactone (98.0%), dimethyl malonate (97.0%), ethyl-2,3-dimethylbutanoate (99.5%), methyl-2-methyl acetoacetate (99.5%), methyl-2-hydroxy-2-methylbutanoate (98.0%), methyl hexanoate (99.5%), methyl-3-(methylthiol)-propanoate (99.5%), hexanoic acid (97.0%), trans-β-ocimene (98.0%), methyl-2-methylhexanoate (99.5%), ethyl hexanoate (98.0%), δ-lactone (98.0%), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (99.5%), methyl-3-hydroxyhexanoate (99.5%), 2,5-dimethyl-4-methoxy-3(2H)-furanone (98.0%), methyl octanoate (99.5%), octanoic acid (97.0%), y-octalactone (98.5%), δ-octalactone (98.0%), copaene (97.0%), methyl decanoate (99.5%), 2-methyl-4-vinyl phenol (99.5%), decanoic acid (97.0%), y-farnesene (98.0%), germacrene (98.0%), globulol (98.0%), spathulenol (98.0 5), (Z)-7-tetradecenal (97.0%), and octadecanal (99.5%) were purchased from Aldrich, Steinheim, Germany. Gamma-lactone (98.0%) and methyl dodecane (99.5%) were obtained from Parchem, New Rochelle, NY and Achemica Corp. Aigle, Switzerland, respectively. The n-alkane standard (C7–C30) was obtained from Sigma-Aldrich Chemicals Co. (St. Louis, MO). Other chemicals were of analytical grade.

Isolation of pineapple volatile compounds

The isolation of the pineapple volatile compounds was performed by extracting 300 mL of juice with dichloromethane (300 mL), followed by distillation in vacuum [34]. A similar workup procedure reported earlier [35] was carried out on juice to produce 400 µL extract.

GC–MS and GC-FID analyses

The extracts were injected into a QP-5050A (Shimadzu, Kyoto, Japan) gas chromatograph equipped with a GC-17A Ver.3, and a flame ionization detector (FID). Two microliters of the extract was vaporized in the injector port maintained at 220 °C in split less mode (1 min). The oven temperature was varied from 50 °C to 250 °C at 15 °C/min, and holding times of 3 and 10 min respectively [36]. A 30–300 m/z mass range was recorded in full-scan mode. The quadrupole ion source and transfer line temperatures were maintained at 150 and 250 °C. respectively and the ionisation energy was set at 70 eV. The column (30 m × 0.25 mm i.d., and 0.25 µm film thickness; 5% diphenyl/95% dimethylpolysiloxane phase; Thermo Scientific, Milan Italy) was a TG-5 ms [36]. The carrier gas was helium at 1.5 mL/min (column-head pressure of 13 psi).

GC-O analysis

A Trace Ultra 1300 gas chromatograph (Thermos Scientific, Waltham, MA, USA) fitted with a TG-5 ms column (30 m × 0.25 mm i.d., film thickness, 0.25 µm, Thermo Scientific, Milan Italy) and an ODP 3 olfactory Detector Port (Gerstel, Mulheim, Germany), with additional supply of humidified purge air, was operated as earlier reported by Lasekan [35]. The split ratio between the sniffing port and the FID detector was 1:1. Two replicate samples were sniffed by three trained panellists who presented normalized responses, with strong agreement with one another.

Identification and quantification

Kovats method which employs a mixture of normal paraffin C7-C30 as external references was used to calculate the linear retention indices [36]. The identification of compounds was as described by Lasekan and Ng [34]. When it was not possible to find appropriate reference standard, a tentative identification was obtained by matching retention index with mass spectral libraries data (WILEY 275, NBS75K). Semi-quantitative data were obtained by relating the peak area of each compound to that of the corresponding standard and were expressed as µg/kg. For compounds tentatively identified, their semi-quantitative data were obtained by relating their peak area to that of octadecane and were expressed as µg/kg octadecane.

Aroma extracts dilution analysis (AEDA)

The flavor dilution (FD) factors of the aroma-active compounds were evaluated by GC-O using the AEDA approach earlier reported by Lasekan [35]. Each of the obtained dilution was injected into the GC-O. The highest dilution in which an aroma compound was observed is referred to as the flavor dilution (FD) factor of that compound [37].

Sensory analysis

Sensory analysis was carried out by ten trained panelists (6 females and 4 males) in a sensory laboratory according to the International Standard ISO 8589: [29]. All panelists who have passed screening test as described earlier [34] were recruited from the University Putra Malaysia. Prior to the test, the panelist were taken through 1 h training session with selected aroma compounds such as: ethyl hexanoate (fruity), 2,5-dimethyl-4-hydroxy-3(2H)-furanone (Strawberry), β-damascenone (floral), ethyl isohexanote (pineapple-like), etc. Descriptors used by panelists were determined after three preliminary sensory experiments. Finally, the panelists were asked to evaluate ortho-nasally fresh pineapple juice placed inside glass containers (7 cm × 3.5 cm). Seven aroma attributes (sweet, floral, fruity, fresh, green, woody and apple-like) were obtained. Panelists were asked to score each attribute on a 10-point interval scale with 9 = strong intensity, and 0 = weak with no perception. To aid the sensory analysis, the following reference compounds: ethyl hexanote (fruity), β-damascenone (floral), methyl-3(methylthiol)-propanoate (apple-like), hexanal (green), germacrene (woody), p-anisaldehyde (sweet) and (E,Z)-3,5-undecatriene (fresh, pineapple-like) were dissolved in water at a concentration of 100 × above their respective threshold values. The fresh pineapple varieties were evaluated in triplicate and the results obtained were averaged.

Statistical analysis

Analysis of variance (ANOVA) and Duncan’s multiple comparison tests were carried out to establish if statistical differences existed among individual pineapple variety for each sensory attribute at (p < 0.05). Partial least square discriminate analysis (PLS-DA) and PLS-regression coefficient were employed as an exploratory tool to describe and summarise the data by grouping variables that are correlated. The mean concentrations of the 59 aroma-active compounds and the six different pineapple varieties (Table 3) were the data set. The multivariate statistical analyses were performed using the SIMCA-P software (V. 10.0, Umetricus, Umea, Sweden). Principal Components Analysis (PCA) and Hierarchical Cluster Analysis (HCA) using the Software package SPSS Statistics 17.0 (SPSS Inc., Chicago, IL) were also employed.

Abbreviations

ANOVA: 

analysis of variance

PCA: 

principal component analysis

HCA: 

hierarchical cluster analysis

FD: 

flavour dilution

Declarations

Authors’ contributions

OL conceptualized this study and critically review the content of the manuscript. FKH carried out the experiments, data analysis and interpretations. OL has made intellectual contributions. All authors read and approved the final manuscript.

Acknowledgements

The authors are grateful for the extensive financial support received from the University Putra Malaysia research scheme Grant (9478500).

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

Authors’ Affiliations

(1)
Department of Food Technology, University Putra Malaysia, 43400 UPM Serdang, Malaysia

References

  1. Jaji K, Man N, Nawi NM (2018) Factors affecting pineapple market supply in Johor, Malaysia. Int Food Res J 25:366–375Google Scholar
  2. Food and Agriculture Organization (FAO). Pineapple fresh production. http://faostat3.fao.org/home/index.html. Accessed 20 Mar 2018
  3. Zheng LY, Sun GM, Liu YG, Lv LL, Yang WX, Zhao WF, Wei CB (2012) Aroma volatile compounds from two fresh pineapple varieties in China. Int J Mol Sci 13:7383–7392View ArticleGoogle Scholar
  4. Zemlicka L, Fodran P, Kolek E, Pronayova N (2013) Analysis of natural aroma and flavour of MD2 pineapple variety (A. comosus L. Merr). Acta Chim Slovaca 6:123–128View ArticleGoogle Scholar
  5. Steingass CB, Langen J, Carle R, Schmarr HG (2015) Authentication of pineapple (A. comosus L. Merr.) fruit maturity stages by quantitative analysis of gamma- and delta-lactones using headspace solid-phase micro extraction and chirospecific gas chromatography- selected ion monitoring mass spectrometry. Food Chem 168:496–503View ArticleGoogle Scholar
  6. Schwab W, Schreier P (2002) Enzymic formation of flavour volatiles from lipid. In: Kuo TM, Gardner HW (eds) Lipid biotechnology. Marcel Dekker, New York, pp 293–318Google Scholar
  7. Baldwin IT, Kessler A, Halitschko R (2002) Volatile signalling in plant-herbivore interactions: what is real. J Curr Opin Plant Biol 5:351–354View ArticleGoogle Scholar
  8. Newman JD, Chappell J (1999) Isoprenoid biosynthesis in plants: carbon partitioning within the cytoplasmic pathway. Crit Rev Biochem Mol Biol 34:95–106View ArticleGoogle Scholar
  9. Rosati C, Diretto G, Giuliano G (2009) Biosynthesis and engineering of carotenoids and apocarotenoids in plants: state of the art and future prospects. Biotech Genet Eng Rev 26:151–174View ArticleGoogle Scholar
  10. Teai T, Claude-Lafontaine A, Schippa C, Cozzdino F (2001) Volatile compounds in fresh pulp of pineapple (A. comosus L. Merr) from French Polynesia. J Essent Oil 13:314–318View ArticleGoogle Scholar
  11. Liu SH, Wei CB, Sun GM, Zang XP (2008) Analysis of aroma components in 3 pineapple cultivars. Food Sci 29:614–617Google Scholar
  12. Zhang XM, Du LQ, Sun GM, Liu SH, Wei CB, Liu ZH, Xie JH (2009) Analysis of aromatic components in pineapple varieties. Food Sci 30:275–279Google Scholar
  13. Wei CB, Liu SH, Liu YG, Zhang XP, Lu LL, Sun GM (2011) Changes and distribution of aroma volatile compounds from pineapple fruit during postharvest storage. Acta Hortic 902:431–436View ArticleGoogle Scholar
  14. Robinson AL, Boss PK, Heymann H, Solomon PS, Trengrove RD (2011) Development of a sensitive non-targeted method for characterizing the wine volatile profile using head space solid-phase microextraction comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry. J Chromotogr A 1218:504–517View ArticleGoogle Scholar
  15. Saurina J (2010) Characterization of wines using compositional profiles and chemometrics. Trends Anal Chem 29:234–245View ArticleGoogle Scholar
  16. Steingass CB, Jutzi M, Muller J, Carle R, Schmarr HG (2015) Ripening-dependent metabolic changes in the volatiles of pineapple (A. comosus L. Merr.) fruit: II. Multivariate statistical profiling of pineapple aroma compounds based on comprehensive two- dimensional gas chromatography mass spectrometry. Anal Bio Chem 407:2609–2624View ArticleGoogle Scholar
  17. Picariello G, Mamone G, Addeo F, Ferranti P (2012) Novel mass spectrometry-based applications of the ‘Omic’ sciences in food technology and biotechnology. Food Technol Biotechnol 50:286–305Google Scholar
  18. Wibowo S, Grauwet T, Kebede BT, Hendrickx M, Loey AV (2015) Study of chemical in pasteurised orange juice during shelf-life: a finger printing-kinetics evaluation of the volatile changes fraction. Food Res Int 75:295–304View ArticleGoogle Scholar
  19. Dall’Asta C, Cirlini M, Morini E, Galaverna G (2011) Brand dependent volatile fingerprinting of Italian wines from Valpolicella. J Chrom A1218:7557–7565View ArticleGoogle Scholar
  20. Hirri A, DeLuca M, Ioele G, Balonki A, Bassbasi EM, Kzaiber F, Oussama A, Ragno G (2015) Chemometric classification of citrus juices of Moroccan cultivars by infrared spectroscopy. Czech J Food Sci 33:137–142View ArticleGoogle Scholar
  21. Jordan MJ, Shaw PE, Goodner KL (2001) Volatile components in aqueous essence and fruit of Cucumis melo cv. fresh Athena (Muskmelon) by GC-MS and GC-O. J Agric Food Chem 49:5929–5933View ArticleGoogle Scholar
  22. Tikunov Y, Lommen A, Ric de Vos CH, Verhoeven HA, Bino RJ, Hall BR, Bovy AG (2005) A novel approach for non-targeted data analysis for metabolomics, large-scale profiling of tomato fruit volatiles. Plant Physiol 139:1125–1137View ArticleGoogle Scholar
  23. Farneti B, Khomenko I, Cappellin L, Ting V, Costa G, Biasioli F, Costa F (2015) Dynamic volatile organic compound finger printing of apple fruit during processing. LWT-Food Sci Technol 63:21–28View ArticleGoogle Scholar
  24. Farrell RR, Fahrentrapp J, Garcia-Gomez D, Sinues PML, Zenobi R (2017) Rapid finger-printing of grape volatile composition using secondary electrospray ionization orbitrap mass spectrometry: a preliminary study of grape ripening. Food Control 81:107–112View ArticleGoogle Scholar
  25. Steingass CB, Grauwet T, Carle R (2014) Influence of harvest maturity and fruit logistics on Pineapple (A. comosus L. Merr) volatiles assessed by headspace solid phase Micro extraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS). Food Chem 150:382–391View ArticleGoogle Scholar
  26. Takeoka GR, Buttery RG, Teranishi R, Flath RA, Guentert M (1991) Identification of additional pineapple volatiles. J Agric Food Chem 39:1848–1851View ArticleGoogle Scholar
  27. Tokitomo Y, Steinhaus M, Buttner A, Schieberle P (2005) Odor-active constituents in fresh pineapple (Ananas comosus L. Merr) by quantitative and sensory evaluation. Biosci Biotechnol Biochem 69:1323–1330View ArticleGoogle Scholar
  28. Deshpanda AB, Chidley HG, Oak PS, Pujari KH, Giri AP, Gupta VS (2017) Isolation and characterization of 9-lipoxgenase and epoxide hydrolase 2 genes: Insight into lactone biosynthesis in mango fruit (Mangifera indica L.). Phytochem 138:65–75View ArticleGoogle Scholar
  29. ISO (2007) Sensory analysis. General guidance for the design of test room. HIS, GenevaGoogle Scholar
  30. Schwab W (2013) Natural-4-hydroxy-2,5-dimethyl-3(2H)-furanone-A review. Molecules 18:6936–6951View ArticleGoogle Scholar
  31. Scheidig C, Czerny M, Schieberle P (2007) Changes in key odorants of raw coffee beans during storage under define conditions. J Agric Food Chem 55:5768–5775View ArticleGoogle Scholar
  32. NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg MD, 20899. http://doi.org/10.18434/T4M88Q, Accessed 22 Nov 2018
  33. El-Sayed A (2005). Pherobase. HortResearch, Lincoln, New Zealand. http://www.pherobase.com. http://www.pherobase.com/database/kovats/kovats-index.php
  34. Lasekan O, Ng SS (2015) Key volatile aroma compounds of three black velvet tamarind (Dialium) fruit species. Food Chem 168:561–565View ArticleGoogle Scholar
  35. Lasekan O (2017) Identification of the aroma compounds in Vitex doniana sweet: free nand bound odorants. Chem Cent J 11:19–25View ArticleGoogle Scholar
  36. Lasekan O, Khatib A, Juhari H, Patiram P, Lasekan S (2013) Headspace solid-phase micro extraction gas chromatography-mass spectrometry determination of volatile compounds in different varieties of African star apple fruit (Chrysophillum albidum). Food Chem 141:2089–2097View ArticleGoogle Scholar
  37. Schieberle P (1995) Recent developments in methods for analysis of flavour compounds and their precursors. In: Gaonkar A (ed) Characterization of food: emerging methods. Elsevier, Amsterdam, pp 403–431View ArticleGoogle Scholar

Copyright

© The Author(s) 2018

Advertisement