Characterization of Potent Aroma Compounds of Cape Gooseberry (Physalis Peruviana L.) Fruits Grown in Antalya Through the Determination of Odor Activity Values

Abstract

This article presents the investigation of the aroma profile of cape gooseberry (Physalis peruviana L.) grown in Antalya, Turkey. The analyses were carried out by means of liquid-liquid extraction followed by gas chromatography-flame ionization detection and gas chromatography-mass spectrometry for quantification and identification, respectively. Sensory analysis confirmed that the organic extract obtained by liquid–liquid extraction was representative of cape gooseberry odor. A total of 83 volatile compounds were identified and quantified in fruit pulp, including 23 esters, 21 alcohols, 11 terpenes, 8 ketones, 8 acids, 6 lactones, 4 aldehydes, and 2 miscellaneous. The main aroma components of the cape gooseberry (concentration >3%) were γ-hexalactone (17.66%), benzyl alcohol (17.22%), dimethylvinylcarbinol (6.54%), 1-butanol (5.71%), 2-methyl-1-butanol (5.22%), cuminol (3.98%), γ-octalactone (3.64%), and 1-hexanol (3.25%). The calculated odor activity values suggest that γ-octalactone, γ-hexalactone, ethyl octanoate, 2-heptanone, nonanal, hexanal, citronellol, 2-methyl-1-butanol, benzyl alcohol, phenethyl alcohol, 1-heptanol, ethyl decanoate, and 1-butanol were the potent aroma compounds of cape gooseberry. Within these, γ-octalactone (OAV: 46.9) was the most powerful contributor to the aroma of the fruit. It was concluded that cape gooseberry has characteristic indicator odorants that contribute to the overall aroma, which also can be used as quality-freshness markers of this fruit.

Keywords:

• Physalis peruviana L.
• Aroma compounds
• Representativeness
• Odor activity value
• GC-MS

INTRODUCTION

Cape gooseberry (Physalis peruviana L.) is an exotic fruit that belongs to the Solanaceae family from the Amazon and Andes. This golden-colored spherical fruit is commercially produced in Ecuador, South Africa, Kenya, Zimbabwe, Australia, New Zealand, Hawaii, India, Malaysia, Colombia, and China. Currently, the production of cape gooseberry has expanded to tropical and subtropical countries, such as the Caribbean and Colombia, the major producer.[1] It has achieved increasing economic importance in the last two decades and has been introduced as a specialized culture in warm regions worldwide.[2] There is also an attempt for the production of this exotic fruit in Antalya, the southern coastal region of Turkey.

The fruit, with an approximate weight of 4–5 g, is protected by an accrescent calyx and is covered by a brilliant yellow peel. It is somewhat tomato-like in flavor and appearance, though the taste (sweet and sour) is much richer with a hint of tropical luxuriance.[3] In addition to having a future as fresh fruit, the exotic fruit can be enjoyed in many ways as an interesting ingredient in salads, cooked dishes, desserts, jams, natural snacks, and preserves.[2, 4] Aroma and flavor are one of the most important attributes and quality criteria that affect the consumption of fruits, and both qualitative and quantitative information is desired for characterizing aroma producing compounds.[5] This information is important for the flavor industry, which use different aroma compounds for the formulation of fragrances and flavorings to be used in foods.[6] Different analytical methods have been developed to determine the concentration of flavor components in fruits.[7] The most frequently used methods for the isolation of flavor constituents from fruits involve extraction with organic solvent, dynamic headspace analysis, or headspace solid phase microextraction. The last two are quick methods, but they do not enable quantification unless an adequate methodology is developed. On the contrary, the quantification through solvent extraction technique is quite easy through an internal standard technique. Furthermore, solvent extraction often yields an extract with an odor that is representative of the original product.[8] If the representativeness of an aroma extract has not been confirmed before analysis, the validity of the volatile analysis must therefore be questioned.

Although the cape gooseberry finds acceptance by consumers, knowledge about its flavor is ambiguous. However, there are only a few studies regarding volatile composition and aroma precursors of cape gooseberry. Berger et al.[9] characterized the volatile constituents of cape gooseberry using liquid/liquid extraction and they showed that methyl 2-methylbutyrate, 2,5-dimethyl-4-hydroxy-3(2H)-furanone and its 4-methoxy derivative, 4- and 5-octanolide, β-ionone, and β-damascenone are the impact volatile components of the fruit. Later, 1-O-trans-cinnamoyl-β-d-glucopyranosyl-(1→6)-β-d-glucopyranose, a carbohydrate ester of cinnamic acid, was isolated from fruits of cape gooseberry by Latza et al.[10] Finally, the glycosidically bound volatile component of cape gooseberry (Physalis peruviana L.) fruit has been examined by high resolution gas chromatography (HRGC) and HRGC-mass spectrometry (HRGC-MS) after enzymatic hydrolysis using pectinase, and two glycosides, (1S,2S)-1-phenylpropane-1,2-diol 2-O-β-D-glucopyranoside and p-menth-4(8)-ene-1,2-diol 1-O-α-L-arabinopyranosyl-(1-6)-β-D-glucopyranoside, were identified for the first time in nature.[11] The aim of the study was to determine the aroma compounds in cape gooseberry grown in Turkey, as well as to provide useful information about the most important potent odorants that significantly contribute to the aroma of this fruit thanks to determination of the odor activity values of volatile compounds. This is the first study on distinction of the more potent odorants from volatiles having low or no aroma activity in cape gooseberry (Physalis peruviana L.) fruit.

MATERIALS AND METHODS

Fruit Samples

Full ripe cape gooseberry fruits were hand harvested from plants growing in Antalya, located in the southern coastal region of Turkey, in September 2010. The berries were transferred to the laboratory and individually quick frozen (IQF) and stored at −18°C until analysis. Intact fruits were carefully selected according to the degree of ripeness measured by the fruit color (L: 58.5 ± 1.25, a: 21.1 ± 2.09, b: 54.5 ± 3.55; brilliant orange), the pH value of the pulp (pH: 3.8 ± 0.01), the total soluble solids (°Brix: 21.3 ± 0.35), the total titratable acidity (1.2 ± 0.05% as citric acid), as well as the value of the soluble solids/total titratable acidity ratio (SS/TTA: 17.8 ± 1.23), which was proposed as a maturity indice for flavor quality of fruits by Kader.[12]

Chemicals

2-Methyl-1-propanol, 1-butanol, methyl octanoate, ethyl octanoate, isobutyl octanoate, butyl octanoate, γ-octalactone, γ-undecalactone, γ-valerolactone, 4-terpineol, α-terpineol, acetic acid, isobutanoic acid, hexanoic acid, 3-heptanone, 2-heptanone, 2-methyl-1-butanol, 1-pentanol, 3-heptanol, 4-methyl-2-pentanol, 2-heptanol, 1-heptanol, 1-octanol, benzyl alcohol, 2-phenyl ethanol, γ-pentalactone, γ-hexalactone, butyl acetate, 2-methylbutyl acetate, butyl butanoate, hexyl acetate, ethyl decanoate, ethyl 3-hydroxyhexanoate, benzyl ethanoate, isobutyl decanoate, prenyl alcohol, and 1-hexanol were obtained from Sigma-Aldrich (St. Louis, MO, USA). 3-Pentanol, 4-nonanol, butyl decanoate, ethyl dodecanoate, butyl dodecanoate, butyl hexadecanoate, β-myrcene, α-terpinolene, cyclohexyl butanoate, citronellol, cuminol, 2-hydroxy cineol, octanoic acid, nonanoic acid, decanoic acid, benzoic acid, hexanal, nonanal, benzaldehyde, 6-methyl-5 -hepten-2-one, 5-hydroxy-4-octanone, and 2,5-dimethyl-4-methoxy-3(2h)-furanone were purchased from Merck (Darmstadt, Germany). Dichloromethane and sodium sulphate anhydrous, both analytical grade, were purchased from Merck. The dichloromethane was redistilled in a Vigreux column and then used. The water used in the study was purified by a Millipore-Q system (Millipore Corp., Saint-Quentin, France). A C₈–C₄₀ n-alkane mixture, used for determination of Kovats’ retention indices, was obtained from Sigma-Aldrich.

Liquid-Liquid Extraction of Aroma Compounds

Liquid-liquid extraction of aroma compounds was performed using the method of Serot et al.[8] with some modifications. Briefly, 100 g of IQF fruits were thawed in a refrigerator (1°C). The sample was then pureed in a blender (Moulinex, France). The homogenized fruit and 50 ml of freshly distilled dichloromethane were transferred in a 500-ml Erlenmeyer flask and cooled quickly to 4°C in an ice bath. Then, 5 μl of a mixture of 4-nonanol (2.46 mg/ml in ethanol), γ-valerolactone (3.98 mg/ml in ethanol), and cyclohexyl butanoate (2.78 mg/ml in ethanol) was added as internal standards before extraction. The mixture was agitated at 750 rpm during 30 min under a gaseous nitrogen saturated atmosphere. Later, the mixture was centrifuged at 10,000× g at 4°C during 15 min. The aqueous phase was removed and the organic phase was dehydrated with Na₂SO₄ and filtrated through glass fiber, collecting the filtrate in a flask of conical bottom of 250 ml. The sample filtrated was distilled in a Vigreux column followed by a Dufton column at 40°C, to concentrate the volume of the sample approximately to 0.5 ml. The organic extract was stored at −20°C in a 1.5-ml vial, until the moment of analysis by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The extraction was performed in triplicate.

Sensory Analysis/Representativeness of the Extract

Representativeness of the cape gooseberry extract obtained by liquid–liquid extraction was performed according to Serot et al.[8] The panel was composed of 10 assessors (6 females and 4 males between 25 and 45 years old) previously trained in odor recognition and sensory evaluation techniques. The fruit samples were thawed overnight at 4°C in a refrigerator. Five grams of homogenized sample was placed in 15-ml black coded flasks, and then the temperature was raised to 20°C just before the samples were presented to the panel. An aliquot of extract was adsorbed onto a cardboard smelling strip (reference 7140 B.P.S.I., Granger-Veyron, Lyas, France), and after 30 s (the time necessary for solvent evaporation), the ends of the strips were cut and placed in dark coded flasks. These flasks were hermetically closed and presented to the panel after 30 min to check the representativeness of the aromatic extract of cape gooseberry obtained by the liquid–liquid extraction with dichloromethane.

Similarity of cape gooseberry and extract evaluation

A similarity test was performed to compare the odor of the extract with the odor of the cape gooseberry. The cape gooseberry and its extract were presented simultaneously to the panel, and assessors evaluated the similarity of the odor. A 100-mm unstructured scale was used, anchored with “very different from the fruit odor” on the left and “identical to the fruit odor” on the right. The position of the extract on the scale was read as distance in centimeters from the left anchor.

Odor intensity evaluation

The odor intensity of the extract was evaluated by using an unstructured scale anchored with “no odor” on the left and “very strong odor” on the right. The position of the extract was read as distance in centimeters from the left anchor. All of the samples were assessed at 20°C.

GC-FID and GC-MS Analysis

All analyses were performed on a Shimadzu QP 2010 Plus (Shimadzu, Kyoto, Japan) GC equipped with an AOC-20i/20s autosampler, a flame ionization detector, and a MS-QP 2010 series mass selective detector. The GC was fitted with a TRB-Wax (Teknokroma, Barcelona, Spain) fused silica capillary column (60 m × 0.25 mm i.d. and 0.25 μm film thickness). Helium was used as the carrier gas at a flow rate of 1 ml/min. The column was maintained at 40°C for 5 min after injection, then programmed at 3°C/min to 240°C, which was maintained for 15 min. The total run time including oven cooling was 86 min. The same oven temperature program was used for both the flame ionization and the mass selective detector analysis. Injector, transfer line temperature, and ion-source temperatures were 250°C. All mass spectra were acquired in electron-impact (EI) mode; the ionization voltage was 70 eV; the mass range was 35–450 m/z; and scanning rate was 1 scan/s. A mixture of n-alkanes was injected under the above temperature program to calculate the retention indices (as Kovats’ indice, I) of each compound.

Concentrations of volatile compounds were calculated as internal standards equivalents and expressed by average of three repeated analytical assays in μg/kg of pulp. The peaks were identified by comparison of the obtained mass spectra of the relevant chromatographic peaks with spectra of the NIST (National Institute of Standards and Technology, Gaithersburg, MD, USA) and Wiley libraries. In addition, the compounds were tentatively identified by comparing the experimental retention indices with the theoretical ones, which were obtained from the NIST Standard Reference Database.[13] Peak enrichment on co-injection with authentic reference compounds was also carried out. The comparison of the MS fragmentation pattern with those of pure compounds and mass spectrum database search was performed using the MS spectral databases.

Odor Activity Value (OAV) Determination

OAVs were calculated[14] according to OAV_i = C_i /OT_i , where C_i is the concentration of the compound i in the sample and OT_i is its odor detection threshold concentration measured in water found in the literature.[15, 16] Compounds with OAV equal to or greater than 1 may contribute to aroma as they are above their odor threshold concentration, whereas those with OAV smaller than 1 may not.

RESULTS AND DISCUSSION

Similarity and Intensity Evaluation of the Extract

The representativeness of the odor of aromatic extract with cape gooseberry was checked by the similarity and intensity evaluation tests. The similarity score of the extract obtained by dichloromethane extraction was found as 61.2 ± 3.6 mm on a 100-mm unstructured scale. The between-assessor coefficient of variance was 5.8% for similarity test. Mehinagic et al.[17] found that similarity scores of the apple extracts were between 49.1 and 53.4 mm, which were regarded as satisfactory. With regard to intensity evaluation, the intensity score of aromatic extract was 59.0 ± 5.7 mm on a 100-mm unstructured scale, with a coefficient of variance of 9.6% between assessors. The intensity score of the extract was also high. The results obtained by similarity and intensity evaluation tests demonstrated that liquid–liquid extraction was convenient for the extraction of volatile compounds from cape gooseberry and provided an extract that was representative of original fruit.

Aroma Compounds Identified in Cape Gooseberry

The volatile compounds identified in cape gooseberry are presented in Table 1. In all, 83 different volatile compounds were identified representing a total concentration of 9012.2 μg/kg of pulp and were grouped in classes of substances, including 23 esters, 21 alcohols, 11 terpenes, 8 ketones, 8 acids, 6 lactones, 4 aldehydes, and 2 miscellaneous. Various types of fresh fruits were reported to produce distinct volatile profiles. The produced compounds are mainly comprised of diverse classes of chemicals, including esters, alcohols, aldehydes, ketones, lactones, and terpenoids. Although an overwhelming number of chemical compounds have been identified as volatile compounds in fresh fruits, only a fraction of these compounds have been identified as impact compounds of fruit flavor based on their quantitative abundance and olfactory thresholds.[18]

The aroma impacts of volatile compounds in cape gooseberry are discussed in terms of their odor activity values (OAV).[14] Indeed, determination of OAVs enables to evaluate the contribution of the identified compounds to the aroma of foods. For this purpose, the aroma potential of each compound was assessed by calculating the OAV. The odor thresholds may depend on the sample matrix and the methodologies of determination. Therefore, comparisons of aroma contribution on OAVs are very difficult when odor thresholds from different sources are used. In this study, odor thresholds in water were used for all the compounds since these values were not calculated yet in cape gooseberry matrix. In considering the estimates of OAV for the volatile compounds present in cape gooseberry (Table 2), 13 compounds out of 83 were distinguished with OAV greater than 1, thus suggesting their contribution to cape gooseberry's flavor.

Table 1 Volatile compounds of cape gooseberry (Physalis peruviana L.)

Peak number	I ^a	Compounds	Concentration^b(mean ± SD)	Identification^c
		Alcohols *
1	1041	Dimethylvinylcarbinol	589.1 ± 21.3	A, B
4	1092	2-Methyl-1-propanol	182.4 ± 17.5	A, B, C
6	1144	1-Butanol	514.3 ± 5.09	A, B, C
11	1206	2-Methyl-1-butanol	470.4 ± 13.54	A, B, C
14	1249	1-Pentanol	8.0 ± 0.62	A, B, C
19	1293	3-Heptanol	2.1 ± 0.25	A, B, C
20	1310	4-Methyl-2-pentanol	2.4 ± 0.19	A, B, C
21	1317	2-Heptanol	10.7 ± 1.03	A, B, C
22	1320	Prenyl alcohol	5.0 ± 1.01	A, B, C
24	1352	1-Hexanol	292.9 ± 15.32	A, B, C
26	1384	Z-3-Hexenol	10.4 ± 0.99	A, B
29	1403	1-Cyclohexanol	9.8 ± 0.85	A, B
30	1406	3-Pentanol	4.7 ± 0.33	A, B, C
34	1454	1-Heptanol	4.2 ± 0.25	A, B, C
37	1489	2-Ethyl hexanol	8.4 ± 1.10	A, B
41	1557	1-Octanol	11.3 ± 0.91	A, B, C
51	1664	2-Furfuryl alcohol	17.6 ± 1.23	A, B
66	1884	Benzyl alcohol	1551.9 ± 54.34	A, B, C
67	1919	2-Phenyl ethanol	88.4 ± 7.04	A, B, C
70	1967	2,3-Dimethyl-1-butanol	72.3 ± 5.24	A, B
73	2054	3-Phenyl-1-propanol	92.3 ± 3.87	A, B
		Subtotal (μg/kg)	3948.7
		Subtotal (%)	43.81
		Lactones **
46	1619	γ-Pentalactone	24.7 ± 1.98	A, B, C
47	1624	ß-Methyl-γ-butyrolactone	5.7 ± 0.44	A, B
55	1714	γ-Hexalactone	1591.2 ± 77.5	A, B, C
68	1928	γ-Octalactone	328.3 ± 17.2	A, B, C
75	2158	γ-Undecalactone	49.3 ± 3.10	A, B, C
81	2368	Actinidiolide	168.8 ± 11.43	A, B
		Subtotal (μg/kg)	2168.1
		Subtotal (%)	24.06
		Esters ***
2	1076	Butyl acetate	19.4 ± 1.12	A, B, C
5	1124	2-Methylbutyl acetate	7.1 ± 0.72	A, B, C
12	1220	Butyl butanoate	8.6 ± 0.88	A, B, C
16	1273	Hexyl acetate	5.7 ± 0.43	A, B, C
27	1390	Methyl octanoate	8.7 ± 0.72	A, B, C
32	1436	Ethyl octanoate	28.8 ± 1.89	A, B, C
36	1484	Methyl 3-hydroxybutanoate	14.1 ± 1.13	A, B
38	1521	Ethyl 3-hydroxybutanoate	60.0 ± 3.45	A, B
40	1554	Isobutyl octanoate	10.1 ± 0.97	A, B, C
45	1616	Butyl octanoate	27.0 ± 1.80	A, B, C
48	1629	Methyl benzoate	20.9 ± 2.01	A, B
49	1640	Ethyl decanoate	130.2 ± 3.42	A, B, C
50	1645	Isobutyl 3-hydroxybutanoate	11.0 ± 0.95	A, B
52	1683	Ethyl 3-hydroxyhexanoate	23.6 ± 2.11	A, B, C
54	1709	Butyl 3-hydroxybutanoate	104.3 ± 7.34	A, B
57	1736	Benzyl ethanoate	9.3 ± 0.66	A, B, C
58	1758	Isobutyl decanoate	39.3 ± 2.98	A, B, C
60	1805	Methyl dodecanoate	78.5 ± 6.43	A, B
61	1820	Butyl decanoate	58.6 ± 4.44	A, B, C
62	1846	Ethyl dodecanoate	177.0 ± 10.98	A, B, C
69	1962	Isobutyl dodecanoate	32.4 ± 3.10	A, B
72	2026	Butyl dodecanoate	65.2 ± 4.33	A, B, C
82	2439	Butyl hexadecanoate	116.9 ± 9.25	A, B, C
		Subtotal (μg/kg)	1056.3
		Subtotal (%)	11.72
		Terpenes *
8	1165	β-Myrcene	7.9 ± 4.65	A, B, C
15	1253	β-(Z)-Ocimene	2.8 ± 0.12	A, B
17	1284	α-Terpinolene	13.2 ± 0.97	A, B, C
44	1605	4-Terpineol	128.5 ± 5.67	A, B, C
53	1699	α-Terpineol	160.7 ± 12.34	A, B, C
56	1731	2-Hydroxy-1,8-cineol	63.7 ± 5.87	A, B
59	1767	Citronellol	26.0 ± 1.90	A, B, C
63	1853	Cuminol	358.8 ± 16.7	A, B, C
65	1865	2-Hydroxy cineol	162.5 ± 10.09	A, B, C
71	2000	ß-Ionone epoxide	31.3 ± 2.87	A, B
78	2278	8-ρ-Menthen-1,2-diol	86.0 ± 7.90	A, B
		Subtotal (μg/kg)	1041.3
		Subtotal (%)	11.55
		Acids *
35	1466	Acetic acid	20.2 ± 1.99	A, B, C
42	1580	Isobutanoic acid	7.9 ± 0.67	A, B, C
64	1857	Hexanoic acid	21.8 ± 1.87	A, B, C
74	2072	Octanoic acid	172.0 ± 12.97	A, B, C
76	2177	Nonanoic acid	37.3 ± 2.99	A, B, C
79	2285	Decanoic acid	70.5 ± 4.73	A, B, C
80	2351	Neric acid	45.9 ± 2.69	A, B
83	2491	Benzoic acid	80.0 ± 4.33	A, B, C
		Subtotal (μg/kg)	455.5
		Subtotal (%)	5.05
		Aldehydes *
3	1086	Hexanal	11.9 ± 0.78	A, B, C
10	1188	2-Ethyl hexanal	9.8 ± 0.87	A, B
28	1395	Nonanal	14.9 ± 1.23	A, B, C
39	1530	Benzaldehyde	110.4 ± 8.99	A, B, C
		Subtotal (μg/kg)	147.1
		Subtotal (%)	1.63
		Ketones *
7	1155	3-Heptanone	1.5 ± 0.09	A, B, C
9	1183	2-Heptanone	5.2 ± 0.50	A, B, C
13	1244	3-Hydroxy-3-methyl-2-butanone	2.5 ± 0.11	A, B
18	1288	3-Hydroxy-2-butanone	26.3 ± 1.87	A, B
23	1339	6-Methyl-5-hepten-2-one	4.0 ± 0.31	A, B, C
25	1364	4-Hydroxy-4-methyl-2-pentanone	26.8 ± 1.93	A, B
33	1439	5-Hydroxy-4-octanone	8.1 ± 0.77	A, B, C
43	1597	2,5-Dimethyl-4-methoxy-3(2h)-furanone	72.5 ± 5.69	A, B, C
		Subtotal (μg/kg)	147.0
		Subtotal (%)	1.63
		Miscellaneous *
31	1413	Isooctane	16.7 ± 0.95	A, B
77	2192	3-Ethylphenol	31.6 ± 1.87	A, B
		Subtotal (μg/kg)	48.3
		Subtotal (%)	0.53
		Total (μg/kg)	9012.2
^aRetention index on TRB-Wax column.
^bConcentration in μg/kg of pulp.
^cA: Confirmed by mass spectral data fitting NIST and Wiley libraries; B: identified by retention index and compared with those reported in the literature; C: peak enrichment on co-injection with authentic reference compounds.
*Quantified with 4-nonanol.
**Quantified with γ-valerolactone.
***Quantified with cyclohexyl butanoate.

Table 2 Odor descriptors, odor thresholds, and odor activity values of aroma active compounds in cape gooseberry (Physalis peruviana L.)

Peak number	Compound	Odor descriptors^a	OT^b	OAV^c
68	γ-Octalactone	Fruity, peach, apricot	7	46.9
55	γ-Hexalactone	Sweet, creamy, coconut-like	260	6.1
32	Ethyl octanoate	Ripe fruit, sweet, pear	5	5.8
9	2-Heptanone	Cheese, fruity, ketonic	1	5.2
28	Nonanal	Waxy, aldehydic, citrus	4	4.3
3	Hexanal	Green, fatty, leafy	5	2.7
59	Citronellol	Floral, rosey, citrusy	11	2.4
11	2-Methyl-1-butanol	Sweet, floral, fruity	300	1.6
66	Benzyl alcohol	Sweet, floral, fruity	1000	1.6
67	2-Phenyl ethanol	Sweet, floral, rosey	60	1.5
34	1-Heptanol	Musty, herbal, woody	3	1.4
49	Ethyl decanoate	Sweet, waxy, fruity	122	1.1
6	1-Butanol	Sweet, floral, fruity	500	1.0
^aOdor descriptors from the Leffingwell web page (http://www.leffingwell.com).
^bOdor thresholds in water (ppb) from the literature.[15, 16]
^cOdor activity values (OAV) were calculated by dividing the concentration by the odor thresholds. Note that only compounds with OAV greater than 1 are reported here.

Alcohols

Alcohols were found to be the most abundant volatile constituents, as they accounted for the largest proportion of the total aroma (43.8%). Benzyl alcohol, followed by dimethylvinylcarbinol, 1-butanol, and 2-methyl-1-butanol were the alcohols present in highest concentration. Among the alcohols, 1-butanol, 2-methyl-1-butanol, 1-heptanol, benzyl alcohol, and 2-phenyl ethanol were found to have OAVs slightly greater than 1 (Table 2). 1-Butanol and 2-methyl-1-butanol have sweet, floral, and fruity notes, while 1-heptanol is described as having a musty, herbal, and woody odor. 2-Phenyl ethanol and benzyl alcohol have an aromatic description of floral and rose.[19] Because of their high threshold values they are regarded as not contributing significantly to the flavor of cape gooseberry. Volatile alcohols have been generally identified as aroma compounds of many fruits.[18] Quantitatively, alcohols, such as l-butanol, 3-methyl-l-butanol, and l-hexanol, were reported to be the major part of the volatiles in Annona cherimolia. It was also observed that among 46 compounds identified in the volatile fraction of acerola fruit, the majority of flavor compounds were alcohols, such as 3-methyl-1-butanol and 2-methyl-1-butanol.[6]

Lactones

The next most abundant compounds were lactones comprising 24.1% of the total volatile components identified; γ-hexalactone as the major one, followed by γ-octalactone. The odor of γ-hexalactone is described as being sweet, creamy, lactonic, tobacco, and coumarin-like with green coconut nuances, while γ-octalactone has fruity, peach, and apricot notes.[19] γ-Octalactone had the highest OAV of all volatiles. It contributes more than all the other lactones combined. γ-Hexalactone is the second most odor active compound behind γ-octalactone. It is likely that they play a key role in the characteristic flavor of cape gooseberry. Lactones are important flavor substances for pineapples, papayas, and passion fruits. Due to their low odor threshold, they have a high flavor value in the fruits. The coconut-like aroma often found in pineapple has been attributed to lactones, namely, γ-octalactone, δ-octalactone, and γ-nonalactone.[20] MacLeod and Ames[21] reported that lactones are significant components of the starfruit aroma. Furthermore, Gómez-Plaza and Ledbetter[22] identified a large number of lactones including γ-octalactone, decalactone, and γ-dodecalactone in plums.

Esters

The next most abundant compounds were esters comprising 11.72% of the total volatile components identified. Among these esters, ethyl dodecanoate, ethyl decanoate, butyl hexadecanoate, and butyl 3-hydroxybutanoate were the esters found in greatest concentration. Based on OAV, ethyl octanoate and ethyl decanoate are considered to be important contributors to the fruity character in cape gooseberry. Aliphatic esters contribute to the aroma of nearly all fruits and many other foods. Some are also responsible for the smell of a particular flower; however, many of these esters possess a nonspecific fruity odor.[23] Methyl hexanoate; ethyl octanoate; methyl and ethyl benzoate; methyl salicylate; and butyl, isobutyl, hexyl, cis-3-, and trans-2-hexenyl acetates were identified in tomatillo, which also belongs to the Solanaceae family, by McGorrin and Gimelfarb.[24] Werkhoff et al.[25] also reported that the major part of volatiles identified as constituents of yellow passion fruit flavor consisted of esters. Similarly, Boylston[26] indicated that esters, especially methyl and ethyl esters of butanoic and hexanoic acids, are major contributors to the volatile flavor compounds present in fresh strawberry.

Terpenes

Terpenes are the next more abundant compounds comprising 11.55% of the volatile components determined. Among these, cuminol, α-terpineol, and 4-terpineol were detected at the highest levels. According to OAVs, the main contributor to cape gooseberry aroma from this group would be citronellol with an OAV of 2.36. Monoterpenes and sesquiterpenes have been identified at varying levels in most of the soft fruits,[27] and they are responsible to the varietal character of the fruits, being present, at least in part, as glycosides.[28] They were reported as volatile components responsible for a wide spectrum of aromas (woody, piney, turpentine-like, herbaceous, and terpy), mostly perceived as very pleasant.[28, 29] Carotenoid related volatiles, such as α-terpinolene and terpinen-4-ol, were also identified in the tomatillo.[24]

Aldehydes

Aldehydes represent 1.63% of the total volatile compounds. Benzaldehyde was the predominant aldehyde. Benzaldehyde is the volatile compound responsible for a typical cherry aroma.[30] Based on OAVs, the main contributors to cape gooseberry aroma of aldehydes would be nonanal and hexanal (Table 2). They are generally characterized by waxy, aldehydic, and green aromas.[19] In general, aldehydes are common to fruit flavors and are believed to play an important role in many fruits.[25] Guler et al.[31] detected hexanal in Inodorus melons, which are responsible for green (like grass) and herbaceous aromas. McGorrin and Gimelfarb[24] also reported hexanal and nonanal, which were considered to be significant to tomatillo flavor. Buttery et al.[32] reported that aldehydes, such as cis-3-hexenal, hexanal, 3-methylbutanal, and trans-2-hexenal, had a log odor unit higher than 1, which indicated a contribution to aroma of fresh tomato, a member of the Solanaceae family.

Ketones

Mesifuran or 2,5-dimethyl-4-methoxy-3(2h)-furanone was the major constituent among the ketones, which, altogether, accounted for the 1.63% of the identified volatile constituents. Mesifuran was previously mentioned as a cape gooseberry volatile component[9] and was described as having strong, sweet, and pleasant aromas.[19] It has also been shown to be an important contributor to strawberry aroma.[33] 2-Heptanone could be an aroma contributor based on its OAV compared to other ketones, and has been reported to exhibit a cheese, fruity, and ketonic odor.[19] In general, ketones are less abundant in the profile of volatile compounds in fruits. They can be formed by condensation of activated fatty acids.[34]

Acids

Free acids accounted for the 5.05% of the volatiles, with octanoic acid as the major one. Acids identified in this study do not seem to contribute to the overall aroma of cape gooseberry because of their high odor detection thresholds. The other volatiles identified in cape gooseberry were isooctane and 3-ethylphenol, which are a hydrocarbon and a volatile phenol, respectively.

CONCLUSIONS

Despite its importance, literature data about the flavor compounds of volatiles of cape gooseberry (Physalis peruviana L.) is scarce. Volatiles belonging to several classes, alcohols, lactones, esters, terpenes, aldehydes, ketones, and acids were detected in cape gooseberry. A tentative study to estimate the contribution of aroma active compounds to the overall aroma of fruit, on the basis of their odor activity values, has shown that γ-octalactone followed by γ-hexalactone, ethyl octanoate, 2-heptanone, and nonanal were the most potent odor-active compounds. The provided information about cape gooseberry flavor can be used in the food industry as quality-freshness markers of cape gooseberry and developing new products from this fruit.

ACKNOWLEDGMENTS

The author wishes to thank Mr. Mustafa Uysal for supplying the samples used in this study and to all of the members of the sensory panel for sensory assessment of cape gooseberry extract.