Volatile constituents of unripe and ripe kundang fruits (Bouea macrophylla Griffith)

ABSTRACT

Kundang, a seasonal, tropical fruit is consumed either as raw (unripe) or ripe in south-east Asia. Investigations performed by using gas chromatography-mass spectrometry revealed volatile constituent compounds in ripe fruits to be much higher than unripe fruits. Nearly 82 compounds (comprising 99.96% of the total volatiles) and 121 compounds (encompassing 97.33% of the total volatiles) were identified in unripe and ripe fruits, respectively. Results generated is envisaged to enhance the existing database on tropical fruits volatile profiles, as well as benefit local food industries (to exploit the unique fragrance character impact compounds for aroma essence production) for commercial usage.

KEYWORDS:

• Kundang
• Plum mango
• Tropical fruit
• Freeze drying
• Volatiles

Introduction

Of late, world over, consumption of fresh fruits is given high preference and is recommended as a part of human diet. This is mainly due to the rich nutraceuticals/functional values imparted by fruits. Besides, there are countless scientific and epidemiological reports available on health benefits incurred on regular consumption of fruits.^[1–4] Malaysia, being a tropical country of south-east Asia, has a wide diversity of underutilized and underexplored fruits, which are preferred by the local population for their acceptable organoleptic qualities.^[2,3] It is opined that a large amount of non-traditional fruits remains under-exploited (rather underutilized) world over, specifically being true in case of many tropical fruits, which has rather remained inaccessible in international markets.^[5] In south-east Asia, some of the most popular local fruits includes: durian, rambutan, longan, mangosteen, and many others. Majority of the underutilized/underexploited fruits are commonly encountered in the wild, specifically in the regions of Peninsular Malaysia, Sabah, and Sarawak.^[6] Among a wide array of seasonal tropical fruits of south-east Asia, kundang fruits (referred to as setar in Malaysia; English name: gandaria or plum mango; Botanical name: Bouea macrophylla Griffith, family Anacardiaceae), is popular among the local communities, which still remains underutilized. The trees bearing kundang fruit are widely cultivated in Malaysia for shade as well as for ornamental purpose in gardens. Apart from Malaysia, kundang tress are frequently encountered in regions of Indonesia (North Sumatra and West Java), Thailand, and in the Philippines.^[7,8]

Traditionally, almost all the parts of kundang plant (leaves, unripe and ripe fruits, and seeds) are edible, and have been used for various culinary purposes. The fruits attaining commercial maturity (unripe and ripe) are sub-globose drupes (4–5 cm and being 3.4–5 cm in size). The ripe fruit skin (peel) and pulp are orange colored, very juicy, and tastes a mixture of sweet to sour with a pleasant aroma. Traditionally, ripe fruits have been used in Malaysia to prepare refreshing drinks, or are processed into jam or syrup. Whereas, unripe fruits have green skin, neutral aroma, and are sour taste. In Malaysia, unripe fruits are used in salad preparation, such as that of “rojak” or “asinan” (pickles). In Thailand, unripe fruits are used as an added ingredient to prepare spicy food preparations, including those of pickles.^[8]

As in the case of any other aromatic fruits, such as mango, durian or pineapples, the flavors/aroma of kundang are also unique. The aroma/volatile compounds present in a fruit is an important criteria to govern their freshness attributes. Besides, research interests have been enhanced recently to identify volatile compounds in various fruits world over.^[9,10] Moreover, volatile compounds in a fruit can be produced during pre- or post-harvest stages (via metabolic pathways) or during storage and technological treatments imposed.^[10] Some of the naturally present volatile constituents in aromatic fruits include those of terpenes, alcohols, aldehydes, esters, and ketones.^[11] There is a single report available on the volatile constituents of ripe fruits of kundang,^[12] wherein nearly 40 components were identified (mainly of monoterpene and sesquiterpene hydrocarbons).

Based on this background, the main objective of this study was to identify the volatile constituents of both unripe and ripe kundang fruits. To the authors’ knowledge, this is the first detailed report comparing the volatile compounds in unripe and ripe kundang fruits. The results generated in this study is envisaged to not only enhance the existing database on this tropical fruits volatile profile, but is also expected to benefit the local food industries (to exploit the fragrance/character impact compounds for aromatic essence production) for commercial usage, as well as help in breeding programs related to kundang.

Material and methods

Samples collection

Freshly harvested, matured unripe and ripe fruits (fruits that have attained physiological and commercial maturity) of kundang fruits (B. macrophylla) were collected from a local farm in Kampung Jelai, Perak region in Malaysia (see Fig. 1a and 1b). Further, maturity indices were based on horticultural maturity, which is considered to be a stage when a plant part such as those of fruits are rendered edible or ready to be used by consumers for a particular purpose. As kundang fruiting is seasonal, the ripe fruits were harvested from the same ‘marked’ or the ‘identified trees’ as those of unripe fruits in the same selected farm. For the analysis, utmost care was taken to see that both unripe and ripe fruits do not have any physical injuries, and are devoid of insects or microbial damages. After transporting to the laboratory (within 2 h after harvest), fruits were washed thoroughly under running tap water (to remove dust or soil particles, if present), and were individually wiped using a clean, dry cloth. Further, the pulp and peel portions (seeds were removed) were cut into small portions/cubes of equal sizes (2 × 2 cm). Followed by this, fruits were freeze-dried (in dark by covering with an aluminium foil), until they were devoid of any appreciable amount of water contents (or moisture). The final moisture level was approximately 7 and 6% in unripe and ripe fruits, respectively. For freeze drying, the temperature set at: –46°C with a vacuum pressure maintained at 0.030 mBar (freeze drier Model 7754511, Labconco Corporation, Kansas City, USA). We adopted freeze drying process, as normally fruits undergoing this process do not lead to loss of any micro-nutrients and are capable of retaining their original flavor and overall sensory attributes.^[13]

Figure 1. A: Unripe; and B: ripe kundang fruits.

Using freeze-dried fruit samples for analysis assumes much importance as it can offer a better consistency in results, compared to fresh fruit extracts. It is a universally accepted fact that freeze-dried samples can retain better nutritional and sensory qualities, as well as those compounds responsible for inducing aroma and flavor (essential oils). During freeze drying, low temperature is maintained in a product that tends to avoid deterioration in the quality. Also, low water activity in freeze-dried samples can enhance the products stability against microbial contamination. Further, freeze-dried fruits does not deteriorate during extended storage period (especially during the study time period). Later on, the freeze dried fruit were grinded in a kitchen blender and sieved with a 250 µm sieve to obtain the fruit powder.

Determination of volatile compounds

Fifty grams of unripe and ripe freeze-dried fruit powder samples was subjected to continuous hydro-distillation process by using a Likens-Nickerson distillation unit (for 2–3 h).^[14] The distillate obtained was trapped in dichloromethane, followed by drying of the extracted volatiles over anhydrous sodium sulphate, which was later flushed using nitrogen gas to obtain pure oil extract.^[15] Gas chromatography–mass spectrometry (GC-MS) analysis was carried out to analyze the volatile compounds (GC system coupled to a mass selective detector, Model: Clarus 600, Perkin Elmer, MA, USA; column equipped with HP-5 of 30 m x 0.25 mm id × film thickness 0.25 µm). The temperature programming for operating conditions (starting temperature 40–60°C [2°C/min] and later ramped up to 220°C [4°C/min] with injecting temperature set at 220°C) was based on the method reported earlier.^[16]

All the chemical compounds were identified by comparing the retention time (RT) and mass with the standards after injecting into the GC-MS. Wherever applicable, clarifications were also done by matching with the instruments inbuilt mass library (based on the National Institute of Standards and Technology-Electron Impact mass spectral library, GC data library, NIST MS search software, automated mass spectral deconvolution and identification system for complex chromatograms, and Wiley 8th Mass Spectral Library). The run time was approximately 60 min, and we considered 96% of the match as the minimum for a positive identification.

Statistical analysis

Results of all the analysis carried out in the present study are based on means of three individuals (n = 3) ± standard deviation (SD). We used SPSS VERSION 16.0 to analyze the data, and one way analysis of variance (ANOVA) was undertaken to determine the significant difference between the mean values by using Duncan’s new multiple range test (level of significance of p < 0.05).

Results and discussion

In this study, we employed steam hydro-distillation method for isolation of the volatile compounds (essential oils) from unripe and ripe kundang fruits. Hydro-distillation is one of the popular, cost-effective and a routinely adopted method world over used to isolate volatile compounds. The distillation of freeze-dried unripe and ripe kundang fruits yielded 0.05 and 0.16% (dry weight) of essential oils, respectively. In total, nearly 82 compounds (comprising 99.96% of the total volatiles) were identified in unripe kundang fruits, whereas, 121 compounds (encompassing 97.33% of the total volatiles) were identified in the ripe kundang fruits by GC-MS (Table 1). In general, we categorized the composition of unripe and ripe kundang fruits as terpene hydrocarbons and oxygenated compounds (acids, alcohols, aldehydes, esters, and ketones). The percentage of oxygenated compounds was higher in ripe kundang fruits in comparison to the unripe fruits by 0.67, 5.42, 10.42, and 3.41%, respectively. Among the compounds, in unripe kundang fruit, terpene hydrocarbons (32.89%), acids (29.72%), esters (17.32%), and ketones (16.85%) were the major components. On the contrary, compounds in ripe fruit comprised mainly of terpene hydrocarbons (29.28%), ketones (27.27%), and esters (20.73%; Table 1).

Table 1. The major chemical compounds identified in unripe and ripe kundang fruits oil.

Compounds	Unripe		Ripe
	amount (%)	Number of compounds	amount (%)	Number of compounds
Terpene hydrocarbons	32.89	37	29.28	57
Aldehydes	0.35	1	1.02	5
Alcohols	2.83	11	9.35	19
Ketones	16.85	4	27.27	10
Esters	17.32	21	20.73	24
Acids	29.72	9	9.68	6
Total	99.96	82	97.33	121

In Tables 2 and 3, volatile compositions of essential oil from unripe and ripe kundang fruits are depicted. Some of the major essential components of terpenes (based on percentage) identified in unripe kundang fruits were alpha-cadinol (4.94%), delta-cadinene (4.80%), tumerone (3.65%), and alpha-muurolene (1.14%). Further in ripe fruits, alpha-terpineol (4.41%), candin-4-en-10-ol (3.46%), 1,10-di-epi-cubenol (2.84%), (e,e)-alpha-farnesene (2.34%), alpha-muurolol (1.44%), (E)-beta-ionone (1.17%), and delta-cadinene (1.32%) were the major terepene based compounds identified (on percentage). Among the ketones, 5,6-decanedione (13.99%) and acetophenone (2.59%) were the major compounds in unripe fruits while in ripe, acetophenone (12.31%) acetyl valeryl were the major compounds (10.99%) identified.

Table 2. Chemical composition of the essential oil from unripe kundang fruits.

Chemical compound		RT	%
Terpene hydrocarbons			32.89
1	delta-Cadinene	-	4.80
2	α-Terpineol	24.11	1.25
3	β-Terpineol	24.26	0.22
4	Neral	27.52	0.26
5	Rose oxide	28.05	0.54
6	Santolinatriene	28.20	0.24
7	Eugenol	29.80	0.50
8	α-Copaene	30.30	0.48
9	Isogermacrene D	33.61	0.53
10	α-amorphene	33.68	0.40
11	β-Maaliene	33.99	0.16
12	Zingiberene	34.16	0.51
13	α-Muurolene	34.56	1.14
14	β-Bisabolene	34.57	0.09
15	γ-Muurolene	34.86	0.37
16	γ-Cadinene	34.86	0.53
17	Zonarene	35.13	0.24
18	α-Cadinene	35.57	0.17
19	Valencene	35.64	0.24
20	Selina-3,7(11)-diene	35.67	0.27
21	Cadina-1(6),4-diene	35.80	0.44
22	γ-Gurjunene	36.78	0.51
23	Caryophyllene alcohol	36.96	0.96
24	Viridiflorol	37.22	0.26
25	Globulol	37.23	0.48
26	Cubeban-11-ol	37.54	0.34
27	1,10-di-epi-Cubenol	37.82	0.90
28	Spathulenol	37.83	0.83
29	Copaborneol	37.96	0.24
30	Cubenol	38.22	3.45
31	γ-Eudesmol	38.56	0.97
32	α-Muurolol	38.98	1.38
33	α-Cadinol	39.05	4.94
34	Tumerone	39.52	3.65
35	Aristolone	40.33	0.15
36	Curlone	40.54	0.39
37	Andrographolide	42.58	0.06
Oxygenated compounds		RT	%
Aldehydes (Total)			0.35
38 2-Isopropylidene-3-methylhexa-3,5-dienal		30.90	0.35
Alcohols (Total)			2.83
39	Linalool oxide	19.54	0.52
40	1-(2-Methylenecyclohexyl)-1-phenylethanol	19.76	0.15
41	2,6-dimethyl-5,7-Octadien-2-ol	22.85	0.35
42	Artemisia alcohol	23.21	0.24
43	3,3,6-trimethyl-4,5-Heptadien-2-ol	23.91	0.16
44	(E,E)-2,6-Dimethyl-3,5,7-octatriene-2-ol	27.37	0.28
45	cis-p-Mentha-2,8-dien-1-ol	27.51	0.25
46	3-(5’,5’-Dimethyltetrahydrofuran-2’-yl)-cis-2-buten-1-ol	28.09	0.38
47	1,4,4-trimethyl-tricyclo[6.3.1.02,5]dodecan-8-ol	36.95	0.34
48	1-Hexadecanol	45.02	0.16
Ketones (Total)			16.85
49	5,6-Decanedione	2.56	13.99
50	Bicyclo[3.3.1]nonane-2,7-dione	18.50	0.16
51	Acetophenone	18.96	2.59
52	2,2,7,7-Tetramethyltricyclo[6.2.1.0(1,6)]undec-4-en-3-one	40.34	0.11
Esters (Total)			17.32
53	Butanoic acid, 3-hexenyl ester, (Z)-	24.01	0.09
54	cis-3-Hexenyl iso-butyrate	24.02	0.06
55	cis-8,11,14-Eicosatrienoic acid methyl ester	30.03	0.41
56	Geranyl acetate	30.41	0.21
57	Propanoic acid, 2-methyl-, 1-(1,1-dimethylethyl)-2-methyl-	36.88	0.11
	1,3-propanediyl ester
58	Sulfurous acid, 2-propyl undecyl ester	37.10	0.17
59	Diethyl Phthalate	37.31	0.54
60	Ergostane-3,5,6,12,25-pentol, 25-acetate, (3.beta.,5.alpha.,6	39.13	0.14
61	1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester	44.67	0.19
62	Hexadecanoic acid, methyl ester (methyl hexadecanoate)	46.08	0.37
63	Dibutyl phthalate	46.78	1.96
64	Docosanoic acid, ethyl ester	47.72	0.65
65	Isopropyl Palmitate	48.38	0.10
66	1-Propene-1,2,3-tricarboxylic acid, tributyl ester	51.69	0.30
67	Acetyl tributyl citrate	53.63	0.48
68	Hexanedioic acid, bis(2-ethylhexyl) ester	56.52	6.96
69	Hexanoic acid, 2-ethyl-, octadecyl ester	58.06	0.15
70	5-Bromopentanoic acid, 2-methylphenyl ester	58.65	0.13
71	Oxalic acid, 2-methylphenyl tetradecyl ester	58.94	0.96
72	Decanedioic acid, bis(2-ethylhexyl) ester	59.08	2.82
73	1,2-Benzenedicarboxylic acid, bis(2-ethylhexyl	59.45	0.52
Acids (Total)			29.72
74	Trimethylacetic anhydride	2.12	22.16
75	Caprylic acid	23.07	0.18
76	Octanoic acid	23.11	0.23
77	Nonanoic acid	26.75	0.29
78	Decanoic acid	30.10	0.25
79	Dodecanoic acid	36.29	0.49
80	Myristic acid	41.88	0.12
81	Heptadecanoic acid (Margaric acid)	47.08	2.69
82	Hexadecanoic acid (Palmitic acid)	47.08	3.31

Results are average mean of three independent replicates with standard error detected < ± 0.01.

Table 3. Chemical composition of the essential oil from ripe kundang fruits.

Chemical compound		RT	%
Terpene hydrocarbons (Total)			29.28
1	Delta-Cadinene	-	1.32
2	4-Diene -Cadina-1(6)	-	0.68
3	Dill Ether	19.89	0.12
4	β-Terpineol	22.29	0.09
5	Cis-Ocimenol	22.84	0.60
6	α-Terpineol	24.10	4.41
7	Trans-Verbenol	24.56	0.08
8	γ-Terpinene	24.70	0.06
9	Trans-(+)-Carveol	25.02	0.44
10	Phellandral	25.03	0.42
11	Neral	27.51	0.21
12	Thymol	27.64	0.55
13	Santolinatriene	28.21	0.25
14	Eugenol	29.80	0.12
15	α-Copaene	30.30	0.57
16	Trans-Caryophyllene	30.41	0.04
17	α-Cis-Bergamotene	31.51	0.25
18	β-Caryophyllene	31.84	0.28
19	Isocaryophyllen	31.84	0.30
20	(Z)-Trans-Alpha-Bergamotene	32.13	0.13
21	α-Caryophyllene	33.04	0.05
22	Alloaromadendrene	33.19	0.09
23	Isogermacrene D	33.61	0.32
24	Ethyl-(E)-Cinnamate	33.71	0.28
25	(E)-Beta-Ionone	33.85	1.17
26	(Z,E)-Alpha-Farnesene	33.94	0.22
27	Valencene	34.16	0.19
28	Cadina-3,5-Diene	34.29	0.07
29	E,E-Alpha-Farnesene	34.38	2.34
30	β-Bisabolene	34.57	0.27
31	γ-Cadinene	34.87	0.19
32	Zonarene	35.15	0.14
33	7(11)-Diene-Selina-4(15)	35.65	0.28
34	γ-Maaliene	35.65	0.22
35	α-Maaliene	35.76	0.14
36	Selina-3,7(11)-Diene	35.76	0.11
37	Globulol	37.23	0.33
38	Cubeban-11-ol	37.54	0.42
39	Caryophyllene Oxide	37.72	0.07
40	Copaborneol	37.95	0.20
41	1,10-di-epi-Cubenol	38.22	2.84
42	γ-Eudesmol	38.56	0.59
43	Carotol	38.65	0.08
44	α-Muurolol	38.99	1.44
45	Cadin-4-En-10-ol	39.09	3.46
46	α-Bisabolol Oxide B	39.14	0.11
47	Ar-Tumerone	39.46	0.51
48	β-Bisabolol	39.58	0.35
49	Longicyclene	39.79	0.16
50	α-Bisabolol	40.06	0.33
51	Aristolone	40.33	0.06
52	Ledol	40.55	0.08
53	β-Copaen-4 .Alpha.-Ol	40.80	0.11
54	Farnesene	45.17	0.85
55	Farnesol	46.93	0.09
56	D-Nerolidol	46.93	0.10
57	Squalene	59.35	0.10
Oxygenated compounds		RT	%
Aldehydes (Total)			1.02
58	Octanal	7.92	0.10
59	Phenylacetaldehyde	18.05	0.13
60	Nonanal	20.36	0.16
61	Para-menth-3-en-7-al	27.37	0.55
62	2,4-Decadienal	28.66	0.08
Alcohols (Total)			9.35
63	Linalool Oxide	18.79	0.69
64	α,α-Dimethyl-Benzenemethanol	19.74	0.70
65	1-Methylcycloheptanol	20.69	0.12
66	2,6-Dimethylcyclohexanol	20.69	0.12
67	Artemisia Alcohol	23.21	1.10
68	2,2-Diethyl-1,3-Propanediol	23.69	0.05
69	2-Methyl-5-(1-Methylethenyl)-Cyclohexanol	24.26	0.44
82	3,5-Dimethyl-Benzenemethanol	24.70	0.06
70	Cis-p-mentha-1(7),8-dien-2-ol	26.09	0.29
71	2-Pentadecyn-1-ol	26.54	0.25
72	Cumin Alcohol	27.78	0.31
73	4-(1-Methylethenyl)-1-cyclohexene-1-methanol	28.03	0.45
75	Z3,Z6,E8-Dodecatrien-1-ol	28.21	0.18
83	p-mentha-1(7),8(10)-dien-9-ol	28.21	0.17
74	1,4-Cyclohexadiene-1-Methanol	29.04	0.24
76	Perillyl Alcohol	30.03	1.19
84	(Z,Z,Z)-8,11,14-Eicosatrienoic Acid	30.04	1.23
77	1-Naphthalenol, 1,2,3,4,4a,7,8,8a-Octahydro	37.82	0.46
78	Naphth-1-ol <1,2,3,4,4a,7,8,8a-Octahydro-, 4-Isopropyl-, 1,6-	38.85	0.54
79	Decahydro-1,4a-Dimethyl-7-(1-Methylvinyl)-1-Naphthalenol	39.70	0.19
85	1-Naphthalenol, Decahydro-1,4a-Dimethyl	39.70	0.14
80	1-Hexadecanol	45.03	0.27
81	n-Heptadecanol-1	49.97	0.16
Ketones (Total)			27.27
82	Acetyl Valeryl	2.16	10.99
83	1,3-cyclohexanedione	15.76	0.12
84	Acetophenone	18.95	12.31
85	(E)-beta-damascenone	30.60	0.14
86	2,7,7-Trimethyl-Bicyclo[3.1.1]hept-2-en-6-one	30.91	0.37
87	6,10-dimethyl-, (z)-5,9-undecadien-2-one	32.73	0.25
88	(E)-beta-Ionone	33.85	1.13
89	2(4H)-Benzofuranone, 5,6,7,7a-Tetrahydro-4,4,7a	35.85	0.64
90	5,6,7,7a-Tetrahydro-4,4,7a-Trimethyl-2(4H)-Benzofuranone	35.86	0.66
91	5,6,7,7a-Tetrahydro-4,4,7a-Trimethyl-2(4h)-Benzofuranone	35.86	0.66
Esters (Total)			20.73
92	Pentanoic acid, 2-propenyl ester	2.56	8.25
93	(Z)-Butanoic acid, 3-hexenyl ester	24.01	0.10
94	Ethyl cinnamate	33.70	0.28
95	Benzeneacetic acid, α,3,4-tris[(trimethylsilyl)oxy]-, trimethylsilyl ester	37.10	1.83
96	diethyl-Phthalate	37.31	0.25
97	Cis-Sesquisabinene hydrate	39.58	0.20
98	2-ethylhexyl-Salicylate	43.15	0.14
99	isopropyl-Tetradecanoate	43.43	0.09
100	1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester	44.67	0.12
101	Tetramethyl-2,6,10,14-hexadecatetraenoic acid	45.81	0.16
102	Methyl hexadecanoate	46.08	0.25
103	Ethyl-Palmitate	47.72	1.14
104	(Z,Z)-9,12-octadecadienoic acid	51.15	0.67
105	Ethyl-linoleate	51.65	0.40
106	9-octadecenoic acid (z)-, ethyl ester	51.77	0.39
107	Tributyl acetylcitrate	53.64	0.22
108	Hexanedioic acid, bis(2-ethylhexyl) ester	56.52	2.62
109	Decanedioic acid, bis(2-ethylhexyl) ester	59.09	1.30
110	Dioctyl phthalate,(dop)	59.46	0.17
111	Guaiac acetate	37.82	0.39
112	2,6,10,14-hexadecatetraenoic acid, 3,7,11,15-tetramethyl-, methyl	45.80	0.17
113	Hexadecanoic acid, methyl ester	46.08	0.24
114	Ethyl iso-allocholate	30.04	1.29
115	Benzyl benzoate	42.58	0.06
Acids (Total)			9.68
116	Caprylic acid	23.09	0.47
117	Nonanoic acid	26.67	0.19
118	Dodecanoic acid	36.33	2.01
119	Myristic acid	41.89	0.34
120	N-hexadecanoic acid	47.11	5.60
121	Oleic acid	51.27	1.07

RT: retention time.

Results are average mean of three independent replicates with standard error detected < ± 0.01.

Among the esters, this was dominated by hexanedioic acid, bis(2-ethyl) ester (6.96%) in unripe fruits, while in ripe fruits pentanoic acid, 2-propenyl ester (8.25%) was the dominant compound. For acids, the major compound in unripe fruits was trimethylacetic anhydride (22.16%), while in ripe fruits, the major compounds identified was N-hexadecanoic acid (5.60%), dodecanoic acid (2.01%), and oleic acid (1.07%). The presence of well-established aroma inducing compounds in threshold levels such as those of α and β-Terpineol (4.41 and 0.09%), thymol (0.55%), myristic acid (0.34%), eugenol (0.12%), octanal (0.10%), and non-anal (0.55%) can also have high impact on induction of unique aroma in ripe kundang fruits. However, further studies are warranted to characterize the main character impact compound in unripe and ripened kundang fruit.

A comparison between the composition (%) of similar principal components of essential oils present in both unripe and ripe kundang fruit is provided in Table 4. Majority of the identified compounds in unripe and ripe kundang fruits such as those of alcohols, aldehydes, terpene hydrocarbons, and ketones are aroma inducing components. Some of the identical compounds such as cadinene, alpha-terpineol, eugenol, linalool, and myristic acid, apart from being aroma inducing compounds, are also well-established for their broad spectrum of antimicrobial activities. In one of the studies in ripe kundang fruit by Wong and Loi,^[12] a total of 40 compounds were identified following vacuum distillation (capillary GC and GC-MS used to isolate the volatile constituents), which represented 98.4% of the total volatiles. However, in the present study, more compounds were isolated (121 compounds). It is worth to state here that the volatile composition/presence of various aroma inducing compounds can be influenced by cultivar, fruits maturity, and environmental conditions prevailing in the cultivation area. The volatile compound produced in fruits is reported to mainly comprise of terpenoids, sulphur compounds, aldehydes, esters, and ketones, which are all responsible for their aroma. Additionally, unique aroma or flavor of a specific fruit is often used as a recognition tool by consumers to classify the ripeness, freshness, as well as the superiority.^[17,18]

Table 4. Comparison between the composition (%) of similar components of essential oil identified in unripe and ripe kundang fruits.

	Composition (%)
Chemical compound	Unripe	Ripe
1) Terpene hydrocarbons
Delta-Cadinene	4.80	1.32
Beta-Terpineol	0.22	0.09
Alpha-Terpineol	1.25	4.41
Neral	0.26	0.21
Santolinatriene	0.24	0.25
Eugenol	0.5	0.12
Alpha-Copaene	0.48	0.57
Isogermacrene D	0.53	0.32
Valencene	0.24	0.19
Gamma-Cadinene	0.53	0.19
Seline-3,7(11)-Diene	0.27	0.11
Globulol	0.48	0.33
Cubeban-11-ol	0.34	0.42
Copaborneol	0.24	0.2
Gamma-Eudesmol	0.97	0.59
Alpha-Muurolol	1.38	1.44
Aristolone	0.15	0.06
2) Alcohols
Linalool Oxide	0.52	0.69
Artemisia Alcohol	0.24	4.41
1-Hexadecanol	0.16	0.27
3) Esters
(Z)-Butanoic acid, 3-hexenyl ester	0.09	0.1
4) Acids
Caprylic acid	0.18	0.47
Nonanoic acid	0.29	0.19
Dodecanoic acid	0.49	2.01
Myristic acid	0.12	0.34

Conclusion

Volatile profiles of unripe and ripe kundang fruits are reported in this study. Overall, results showed total volatile compounds (in percent) in ripe fruits to be much higher than the unripe fruits. Further, oxygenated compounds were also high in ripe kundang fruits in comparison to the unripe fruits. The unripe fruits had high levels of terpenoids hydrocarbons and acids compared to the ripe fruits. In general, ripe fruits usually have a pleasant aroma, which can now be attributed to the presence of higher number (and percentage) of compounds, as recorded in this study. Future studies are required to evaluate the influence of various physiological, biochemical, and environmental features that can influence volatile components, identify the key character impact compound that imparts the unique aroma, and identify the levels of various character imparting compounds occurring during various stages of ripening of kundang fruit. Besides, as essential oils are well known for their in vitro antimicrobial activities, this also merits investigations.

Acknowledgments

The authors thank the relevant authorities at Universiti Sains Malaysia for laboratory and other essential facilities provided.