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Aromatic compounds and soluble carbohydrate profiles of different varieties of Tunisian raisin (Vitis vinifera L.) a

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Mnari Bhouri Amira , Flamini Guido , Chraief Imed & Hammami Mohamed

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- Biochemistry Laboratory, Research Laboratory LR12ES05: Lab-NAFS ‘Nutrition - Functional Food & Vascular Health’. Faculty of Medicine - University of Monastir (Tunisia). b

- Dipartimento di Farmacia Via Bonanno 33, 56126 Pisa, Italy Accepted author version posted online: 29 May 2015.

To cite this article: Mnari Bhouri Amira, Flamini Guido, Chraief Imed & Hammami Mohamed (2015): Aromatic compounds and soluble carbohydrate profiles of different varieties of Tunisian raisin (Vitis vinifera L.), International Journal of Food Properties, DOI: 10.1080/10942912.2015.1027920 To link to this article: http://dx.doi.org/10.1080/10942912.2015.1027920

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Aromatic compounds and soluble carbohydrate profiles of different varieties of Tunisian raisin (Vitis vinifera L.)

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Mnari Bhouri Amira1,*; Flamini Guido2; Chraief Imed1 & Hammami Mohamed1.

1- Biochemistry Laboratory, Research Laboratory LR12ES05: Lab-NAFS ‘Nutrition Functional Food & Vascular Health’. Faculty of Medicine - University of Monastir (Tunisia).

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*Corresponding author:

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Dr Amira Mnari Bhouri PhD, Academic/Research Assistant Biochemistry Laboratory,

Research Laboratory LR12ES05: Lab-NAFS ‘Nutrition - Functional Food & Vascular Health’. Faculty of Medicine - University of Monastir (Tunisia).

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ABSTRACT

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Email: [email protected]

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This study analyzed the aromatic composition and established the soluble carbohydrate profiles of the Chriha, Razeki, Assli and Meski varieties of Tunisian raisin (Vitis vinifera L.). A total of 80 compounds obtained by headspace solid phase micro-extraction were detected by GC–MS.

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2- Dipartimento di Farmacia Via Bonanno 33, 56126 Pisa, Italy

Non-terpene hydrocarbon derivatives were the major compounds of the Chriha and Assli

varieties (35.8% and 26.3%, respectively). The Razeki variety accumulated 25.5%.

apocarotenoids. Oxygenated non-terpene derivatives, including esters, alcohols, aldehydes, acids, ketones and others were the most abundant (57.5%) in the Assli variety. The presence and

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amounts of volatiles were different among varieties and might be responsible, in part, for the aroma and taste of raisins. The concentration of total sugars was highest in the Razeki variety and lowest in the Chriha variety. The content of individual sugars differed quantitatively among

individual and total sugars compared to the other three varieties.

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the varieties in this study. The Razeki variety had the best fruit quality with higher contents of

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INTRODUCTION

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extraction, GC–MS, carbohydrate profiles

Raisins (dried grapes; Vitis vinifera L.) are produced in most regions of the world where grapes are grown, and consumption occurs in all cultures and demographic sectors. Grapes were

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probably dried for storage and travel in the Neolithic period, leading to the early production of raisins, and there is evidence of the early use of raisins as food and decorations. Raisins are a

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favored dried fruit throughout the world because of their high nutritional value and pleasant

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flavor. They are rich in several micronutrients, including carotenoids, polyphenols, tocopherols, vitamins and oligo elements, whose beneficial effects on human health are well known.[1,2] Drying methods have a significant impact on the sensory characteristics and consumer

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KEYWORDS: raisins, dried grapes, aromatic compounds, headspace solid phase micro-

preference for raisins. The main difference between grapes and raisins is the water content and

two main methods of drying grapes are used to produce raisins. One method is sun-drying for 2–

3 weeks and the other is a short (15–20 s) exposure to hot water (87ºC–93ºC) followed by dehydration at 71°C for 20–24 h.[2,3] Many new methods of dehydration have been developed,

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including microwave vacuum-drying,[2–4] dipping pretreatments to expedite the drying process or chamber-drying at a controlled temperature.[2–5] In Tunisia, sun-drying is the most ancient and most frequently used method, which consists of exposure to hot water (87°C–93°C) followed by

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drying for 2–3 weeks under direct sunlight.[6] Chriha, Razeki, Asli and Meski are the main varieties of raisin (Zbib) produced in Tunisia.

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use of these components in both the food and pharmaceutical industries. Moreover, phenolic and aromatic compounds as well as carbohydrates are concentrated during grape dehydration.[7–10]

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These are very important parameters for judging the market quality of fruit.[11] To evaluate the volatile compounds, various methods have been developed for their extraction, including hydrodistillation, supercritical fluid extraction and headspace solid phase micro-extraction (HS-

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SPME). HS-SPME is a simple, sensitive and solvent-free sampling and concentration technique that can be used in combination with GC–MS for analysis of the volatile components of natural

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products and foods.[12]

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Only the physicochemical compositions, including moisture, ash, protein, fat and some minerals, have been reported for the Chriha, Razeki, Assli and Meski varieties.[6] The objective of this study was to qualify and quantify the aromatic volatile composition and the carbohydrate profiles

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Analysis of the volatile compounds in plant extracts has attracted increasing interest due to the

of different varieties of raisin (Vitis vinifera L.) produced in Tunisia.

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EXPERIMENTAL

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Plant material

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Four varieties of dried raisins (Vitisvinifera L.) (Chriha, Raseki,Assli and Meski) were harvested in August-mid September 2013 season from different regions of Tunisia: Chriha and Meski from

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been deposited in the Herbarium of the Laboratory of Biochemistry, Faculty of Medicine of

carbohydrates profiles.

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Monastir (Tunisia). Samples were immediately used for analysis of aromatic composition and

HS-SPME and GC–MS analysis

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SPME analyses were performed using a Supelco SPME device coated with polydimethylsiloxane (PDMS, 100µm). The fiber was pre-conditioned according to the manufacturer instructions.

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After the equilibration time, the fiber was exposed to the headspace for 20 min at room

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temperature. When sampling finished, the fiber was withdrawn into the needle and transferred to the injection port of the GC or GC-MS system. GC analyses were accomplished with an HP5890 series II instrument equipped with a DB-5 and DB-WAX capillary columns (30 m × 0.25

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Rafraf (located in the region of bizerte), Raseki from Tunis and Assli from Sfax. Specimens have

mm, 0.25 µm film thickness), using the following temperature program: 60◦C for 10 min, ramp of 5◦C/minto 220◦C; injector and detector temperatures, 250◦C; carrier gas, helium (2 ml/min); detector, dual FID; split ratio, 1:30. The identification of the components was performed, for both columns, by comparison of their retention times with those of pure authentic samples and

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by means of their linear retention indices (LRI) relative to the series of n-hydrocarbons. Gas chromatography–electron impact mass spectrometry (GC–EIMS) analyses were performed with a Varian CP 3800 gas chromatograph (Varian, Inc. Palo Alto, CA) equipped with a DB-5

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capillary column (Agilent Technologies Hewlett-Packard, Waldbronn, Germany; 30 m × 0.25 mm, coating thickness 0.25 µm) and a Varian Saturn2000 ion trap mass detector. Analytical conditions were as follows: injector and transfer line temperature at 250 and 240◦C, respectively;

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ml/min; splitless. Identification of the constituents was based on comparison of the retention

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times with those of the authentic samples, comparing their LRI relative to the series of nhydrocarbons, and on computer matching against commercial NIST 98 (U.S. National Institute of Standards and Technology) and ADAMS and homemade library mass spectra built from pure substances and components of known samples and MS literature data.[13-18] Moreover, the

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molecular weights of all the identified substances were confirmed by gas chromatography– chemical ionization mass spectrometry (GC–CIMS), using methanol as chemical ionization gas.

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All the analyses were performed at least in triplicate.

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Carbohydrates analysis

Carbohydrates were extracted according to the method described by Bartolozzi et al.[19]Extracts

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oven temperature was programmed from 60 to 240◦C at 3◦C/min; carrier gas, helium at 1

were dried and converted into trimethylsilyl ethers with a silylation mixture made up of pyridine, hexamethyldisilazane and trimethylchlorosilane. An aliquot of 1 µl of each silylated total extract of the raisins samples was analyzed using a Hewlett-Packard 5890 series II gas chromatograph equipped with a flame ionization detection (FID) system and a HP-5MS capillary column (30 m

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× 0.25 mm) as described by Bartolozzi et al.[19]Using this program, 23.6 min were required to elute the trimethylsilyl derivatives. Identification of individual carbohydrates was achieved by the use of the relative retention times, i.e., in comparison with the standard used. These were

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compared to those identified earlier by gas chromatography-mass spectrometry.

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All parameters analyzed were carried out in triplicate. The results were reported as mean values of three repetitions and standard deviation.The significance of differences between mean values

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was determined by one-way analysis of variance. A post hoc analysis using Tukey’s test was carried out to compare the means, using the SPSS program, release 11.0 for Windows (SPSS, Chicago, IL, USA). Differences were considered to be significant when p Assli (26.3%) > Razeki (25.5%) and

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Meski (2.9%). Among this group of volatiles, which impart the characteristic intense fruity aromas to raisins, the most abundant were n-pentadecane (Chriha, 11.9%), n-hexadecane

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(Razeki, 8.2%) and n-tetradecane (Assli, 7.8%). Oxygenated non-terpene derivatives were accumulated in Meski (57.7%) > Razeki (24.7%) > Chriha (24.3%) > Assli (22.7%). This group

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of compounds includes alcohols, esters, aldehydes, ketones and acids, which are responsible for citrus, floral and fruity aromas.[20] Alcohols were the most abundant group of volatiles identified in the order Meski (28.9%) > Chriha (11.9%) > Razeki (8%) (Fig.1). Aldehydes were present in

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Each volatile compound is characterized by an odor threshold and even if different fruits have

higher proportions (Fig. 2). The Assli variety was quantitatively the richest (13.1%) because of a considerable amount of benzaldehyde, followed by the Razeki (10.9%) and Meski (6.9%)

varieties (Fig. 2). The other volatile compounds of this group were distributed in different proportions among the four varieties. Aldehydes are known to be derived from thermal oxidative

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degradation of amino acids and fatty acids; also, SPME extracted hexanal, which is present naturally in plants and fruits.[22] Using HS-SPME, esters were detected only in the Meski variety (12.4%). This group was

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represented mainly by fatty acid ethyl and methyl esters related to lipid metabolism, including ethylacetate present only in the Meski extract (11.2%). Finally, ketones were present in the order

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Terpenes constitute another important group of volatiles that cover a wide range of herbaceous,

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fruity, citrus, floral and fungal odors.[20] In this study, the terpenoids could be placed into three classes: monoterpene hydrocarbons, oxygenated monoterpenes and sesquiterpene hydrocarbons. The Assli variety had qualitatively and quantitatively the richest content of monoterpene hydrocarbons. It was the only variety containing appreciable proportions of two of the five

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monoterpene hydrocarbons identified, including γ-terpinene (12.5%) and δ-3carene (3%). By contrast, only γ-terpinene was detected in the Chriha and Meski varieties (2.1% and 2%,

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respectively).

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Oxygenated monoterpenes were present in greater proportions in the Meski and Assli extracts with total contents of 26.4% and 16.7%, respectively. Meski was the only variety containing appreciable amounts of seven of the 15 monoterpene hydrocarbons identified, including mostly

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Assli (9.6%) > Razeki (5.8%) > Meski (4.6%) but were absent from the Chriha variety (Fig. 2).

pyranoid (8.7%) and furanoid (7.3%). Linalool and carvone were the major compounds of this group in the Assli variety (7.8% and 6%, respectively). The sesquiterpene class was represented by a single component, β-caryophyllene, which was present only in the Assli and Meski varieties (3.6% and 0.7%, respectively).

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Apocarotenoids, known also as carotenoid cleavage products (CCPs), have become exciting molecules with excellent prospects for novel functions.[23,24] In this study, the apocarotenoid components were qualitatively and quantitatively different among the four varieties of raisin in

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the order Razeki (25.5%) > Chriha (23.4%) > Assli (7.2%) > Meski (6.1%). (E)-Geranylacetone, detected in all varieties, was the most abundant compound of this chemical class in the Assli (7.2%) and Meski (6.1%) varieties, whereas allyl ionone 2 was the most abundant compound in

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the flavor and/or aroma of flowers and a variety of fruits and vegetables.[25–27]

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Phenylpropanoids, a diverse group of compounds derived from the carbon skeleton of phenylalanine, are involved in the defense, structural support and survival of plants.[28] This group, which was present mostly in the Razeki (15%), Assli (3.6%) and Chriha (3.2%) varieties,

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was represented mainly by (E)-anethole (9.5%) and methyl chavicol (5.5%) in the Razeki variety. The phenylpropanoids pathway, an important source of metabolites in plants, is required

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for the biosynthesis of lignin and serves as a starting point for the production of many other important compounds, including flavonoids, coumarins and lignans.[28] Furthermore, diverse

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physiological and pharmacological properties of these natural compounds, including antioxidant,[7–32] anti-inflammatory and antinociceptive,[33] hypoglycemic[7–34] and antidepressant effects[35] and antitumor activity[36] have been reported.

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the Razeki (16.6%) and Chriha (14%) varieties. This group of volatile compounds contributes to

The four varieties of raisin, which were collected on the same date and dried under the same conditions, could be distinguished on the basis of the qualitative and quantitative difference in the contents of volatile components. The accumulation of metabolites depends on the genetically

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determined enzyme composition of the fruit.[7–37] By contrast, the method of analysis chosen can affect the aromatic composition. HS-SPME was used in this study to evaluate aroma compounds because it is a non-destructive technique,[38] which has become the method of choice in aroma

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analysis. HS-SPME offers rapid solvent-free sampling with facility of operation and low cost;

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moreover, it is sensitive, selective and compatible with low detection limits.[39] Because of these advantages, HS-SPME is used frequently to extract volatile and semi-volatile compounds from

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Carbohydrate profile

The concentrations of monosaccharides (mannose, glucose, fructose, galactose, arabinose, rhamnose, xylose), sugar alcohols (mannitol, sorbitol, inositol and adonitol) and polysaccharides (sucrose, trehalose and raffinose) detected in the Chriha, Razeki, Assli and Meski varieties of

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raisin expressed as mg/kg dry weight (DW) are given in Table 2. The total sugars content in the raisins ranged from 3501.4 to 9017.6 mg kg-1 DW. The highest and lowest values were found for

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the Razeki and Chriha varieties, respectively, and there was no significant difference between the

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Assli and Meski varieties (Table 2).

The total monosaccharides content followed the same trend as the total sugars content and all

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biological, environmental, food and drink samples.[22,40,41]

differences between the varieties were statistically significant (p