Original article

1 Dep. Postharvest Sci. FreshProd., ARO, Volcani Cent.,P.O. Box 6, Bet Dagan 50250,Israel,rporat@volcani.agri.gov.il

2 Dep. Fruit Tree Sci., ARO,Newe Ya'ar Res. Cent.,P.O. Box 1021,Ramat Yishay 30095,Israel

3 Currently Ph.D. studentat Fac. Agric. Food Environ.Qual. Sci. Hebr. Univ. Jerus.,Rehovot 76100,Israel

Genetic diversity and sensory preference in pomegranate fruitsLina MAYUONI-KIRSHENBAUM1,3, Irit BAR-YA’AKOV2, Kamel HATIB2, Doron HOLLAND 2, Ron PORAT1*

* Correspondence and reprints

Received 28 November 2012Accepted 22 February 2013

Fruits, 2013, vol. 68, p. 517–524© 2013 Cirad/EDP SciencesAll rights reservedDOI: 10.1051/fruits/2013090www.fruits-journal.org

RESUMEN ESPAÑOL, p. 524

Genetic diversity and sensory preference in pomegranate fruits.

Abstract – Introduction. The aims of our study were to evaluate the genetic diversity in flavorattributes of and preferences for fresh pomegranate arils. Materials and methods. Experimentswere conducted with fresh arils extracted from 18 distinct pomegranate varieties within theIsrael Pomegranate Breeding Collection of the ARO. Consumer flavor acceptance tests wereconducted at a commercial supermarket branch, and descriptive flavor analysis tests wereconducted by a trained sensory panel. Results and discussion. Consumer flavor acceptancetests revealed wide diversity in the flavor preferences for various pomegranate varieties. Furtherdescriptive flavor analysis tests revealed that arils from highly preferred varieties werecharacterized by high sweetness, moderate to low acidity levels, rich red wine and pomegranatefruity odors, low bitterness and astringency, and soft seeds. In contrast, arils from the leastpreferred varieties were either too sour or bitter, had low red wine and pomegranate fruityodors, or had very hard seeds. Furthermore, all “sour” varieties tested (acid content ≥ 1.8%)received low sensory preference scores, whereas “sweet-sour” and “sweet” varieties (acidcontents 0.7–1.8% and ≤ 0.7%, respectively) achieved variable flavor preference scores. Overall,it is suggested that pomegranate flavor preference derives mainly from high sweetness, low tomoderate acidity, rich red wine and pomegranate fruity odors, and soft seeds.

Israel / Punica granatum / fruits / organoleptic analysis / variety choice / flavor /sweetness / consumer surveys

Diversité génétique et préférences gustatives de grenades.Résumé – Introduction. Les objectifs de notre étude ont été d’évaluer la diversité génétiquedes composantes du goût et des préférences des arilles de grenades fraîches. Matériel etméthodes. Des expérimentations ont été menées avec des arilles frais extraits des fruits de18 variétés distinctes de grenadiers issus de la collection génétique israélienne de grenadiers del’ARO. Des tests d’acceptation de la saveur lors de la consommation des fruits ont été effectuésen supermarché, et des tests descriptifs de l’analyse de la perception gustative ont été menéspar un panel sensoriel expérimenté. Résultats et discussion. Les tests d’acceptation de lasaveur lors de la consommation des fruits ont révélé une grande diversité dans les préférencesgustatives des fruits des différentes variétés de grenadiers étudiées. Les analyses de la percep-tion gustative ont révélé que le goût des arilles des variétés préférées était caractérisé par unegrande douceur, un taux d’acidité modéré à faible, des sensations de vin rouge et de grenadesfruitées, une faible amertume et une faible astringence et des fruits contenant des grainestendres. En revanche, les arilles des fruits des variétés les moins appréciées étaient trop aigresou trop amers, avaient une faible odeur de vin rouge et de grenade fruitée, ou contenaient desgraines très dures. En outre, toutes les variétés « aigres » testées (teneur en acide ≥ 1,8 %) ontreçu de faibles scores de préférences sensorielles, tandis que les variétés « aigres-douces » et« douces » (teneurs en acide 0,7–1,8 % et ≥ 0,7 %, respectivement) atteignaient des scores depréférence variables. Dans l’ensemble, il apparaît que la préférence gustative des grenadesserait principalement liée à une grande douceur de l’arille, une acidité faible à modérée, desodeurs de vin rouge et de grenades fruitées et la présence de graines tendres.

Israël / Punica granatum / fruits / analyse organoleptique / choix des variétés /flaveur / douceur / enquête auprès des consommateurs

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1. Introduction

Pomegranates (Punica granatum L.) origi-nated in Central Asia (Iran, Turkmenistanand northern India) from where, thousandsof years ago, they were probably dispersedthroughout the Mediterranean Basin to therest of the world, including Asia, NorthAfrica, Europe and, later, to North and SouthAmerica [1]. Overall, there are more than500 known pomegranate varieties world-wide, of which several dozens are com-monly cultivated [2, 3]. Obviously, geneti-cally different varieties exhibit differinggrowth characteristics and fruit quality at-tributes, including size, color, shape, seedhardness, taste and flavor [1, 2]. Recentscientific studies demonstrated that pome-granates provide a rich and unique sourceof bioactive phytochemicals, and that con-sumption of pomegranate fruit or juice con-fers proven medicinal benefits in preventionof serious chronic diseases, such as cardio-vascular diseases, diabetes and cancer [4–6].These findings, together with increasingproduction and sales by major pomegran-ate-juice manufacturers such as the Califor-nian ‘POM Wonderful’ and the European‘Pomegreat’, have led to dramatic increasesin world trading and consumption of pome-granate fruit and juice [7]. Nevertheless, de-spite the increasing commercial importanceof pomegranates, relatively little is knownregarding the genetic diversity related topomegranate flavor traits, or about con-sumer preferences regarding pomegranateflavor.

In previous studies, pomegranate varie-ties were generally categorized into threemajor groups according to their averageacidity levels: “sweet”, “sweet-sour” and“sour” varieties, which contain mean aciditylevels of 0.32%, 0.79% and 2.72%, respec-tively [8]. However, despite detailed chem-ical analyses of sugar and acid contents,consumer flavor preferences among theproposed pomegranate classes were notevaluated [8, 9]. Recent sensory evaluationstudies suggested that the flavor of pome-granate juices could be characterized bysweet, sour, musty/earthy, fruity aromaticnotes and astringent mouth-feel [10]. Fur-thermore, recent gas chromatography-mass

spectrometry (GC-MS) analysis of aromavolatiles of various Spanish and Californianpomegranate varieties revealed that freshpomegranate juice contained between 18and 23 aroma volatiles, comprising mainlyaldehydes, alcohols and terpenes [11–14].By characterizing the juice of ‘Wonderful’pomegranate fruit, we recently identified12 aroma-active compounds, which providea mixture of ‘green’, ‘woody’, ‘earthy’,‘fruity’, ‘floral’, ‘sweet’ and ‘musty’ notes [15].

In the present study, consumer flavoracceptance tests and descriptive sensoryanalysis tests were conducted in order tocharacterize the flavor of fresh pomegranatearils from 18 distinct varieties. Overall, largegenetic diversity in pomegranate flavor pref-erences was observed, and accordingly,preferred flavor attributes were defined.

2. Material and methods

2.1. Plant material

Flavor preferences for 18 distinct pome-granate varieties from the Israel Pomegran-ate Breeding Collection at the Newe Ya’arResearch Center of Israel's AgriculturalResearch Organization (ARO) were defined.All tested pomegranate varieties are regis-tered in the Israeli Gene Bank for Agricul-tural Crops (IGB)1 (figure 1). The variouspomegranate varieties were harvested fromSeptember until November throughout the2011 and 2012 growth seasons. Each varietywas harvested at full maturity, as deter-mined by a combination of maturity indices,including fruit size, color, shape and taste(i.e., loss of astringency), as well as thebreeding team's personal experience.

2.2. Chemical analysis

For chemical analysis, fruits were cut witha knife, the arils were separated manuallyand placed within four layers of Miracloth,and the juice was extracted by squeezingand collected into beakers.

1 Web site: http://igb.agri.gov.il.

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Total soluble solids (TSS) content in thejuice was determined with a PAL-1 digitalrefractometer (Atago, Tokyo, Japan), and

acidity percentages were measured bytitration to pH 8.3 with 0.1 M NaOH in a CH-9101 automatic titrator (Metrohm, Herisau,

Figure 1.Fruits of 18 distinct pomegranate varieties from the pomegranate collection of Israel's Agricultural Revaluated to study their genetic diversity and sensory preference.

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esearch Organization (ARO),

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Switzerland). Each measurement includedfive replications, each using juice collectedfrom two fruits, i.e., a total of 10 fruits permeasurement.

2.3. Sensory evaluations

The sensory quality of separated arils wasevaluated by acceptance and descriptivetests [16]. In all cases, separated arils wereextracted from at least five different fruitsand placed in plastic cups identified by ran-domly assigned three-digit codes. Con-sumer sensory acceptance tests wereevaluated according to a 9-point hedonicscale ranging from “very strong dislike” to“very strong like”. The consumer flavoracceptance tests were conducted at Shufer-sal Deal Supermarket, Rishon Lezion, Israel,and included between 80–90 consumerevaluations per variety.

Descriptive flavor analysis tests wereconducted by a trained sensory panel of10 members – five males and five females,aged 25 to 62. Each panelist assessed thevarious attributes of the samples accordingto an unstructured 100-mm scale for each at-tribute, with the anchor points “very weak”and “very strong”, and sensory data were re-corded as distances (mm) from the origin.The trained sensory panel gathered threetimes prior to the experiments in order todefine the provided sensory attributes, andpracticed by performing open discussionpanels, in order to normalize perceived fla-vor attribute intensities among all members.All sensory panel members were techni-cians or students working in the Departmentof Postharvest Science at the ARO, theVolcani Center (Israel), already familiar withsensory analysis and evaluation [17, 18]. Thesensory attributes chosen by the trainedpanel were: taste (sweet, sour and bitter),odor (red wine, and pomegranate fruitynotes), and mouth-feel sensations (astrin-gency, juiciness and seed hardness). The at-tribute of “red wine” odor corresponds tothe “wine-like” definition provided byKoppel and Chambers [10], describing thesharp fruity alcohol-like aroma associatedwith red wine.

2.4. Statistical analysis

One-way analysis of variance (ANOVA) andTukey’s HSD pairwise comparison testswere applied by means of the JMP statisticalsoftware program, version 7 (SAS InstituteInc., Cary, NC, USA).

3. Results

The flavor preferences for 18 distinct pome-granate varieties selected from the IsraeliPomegranate Breeding Collection at theNewe Ya’ar Research Center were exam-ined. These pomegranate varieties had dis-tinct shapes, and a range of external peeland aril colors including red, pink andwhite/yellowish (figure 1).

The selected pomegranate varietiesexhibited remarkable differences amongtheir juice TSS and acidity levels. Overall,juice TSS levels ranged from 14.2% to 17.5%,and juice acidity levels from just 0.3% to3.2% (figure 2). These observed differencesin total TSS and acidity levels resulted inremarkable differences in juice [TSS/acidity]ratios (fruit ripening ratios) from just5 through 74 (figure 2). Furthermore, theobserved differences in juice [TSS/acidity]ratios were primarily governed by theobserved differences in acidity levels ratherthan by differences in TSS levels (figure 2).

By conducting consumer acceptancetests, remarkable differences in the overallflavor preference ratings for the variouspomegranate varieties were found, rangingfrom very high scores (7.9; variety P.G.100-1)through low scores (4.1; variety P.G.162-63),thus demonstrating the wide genetic diver-sity associated with pomegranate fruit flavoracceptability (figure 3). In the past, pome-granate varieties were divided according totheir acidity levels into “sweet”, “sweet-sour” and “sour” varieties [8]. Therefore, inorder to determine the importance of thesweetness and sourness traits for pomegran-ate flavor preference, we classified the pres-ently tested varieties as “sweet” (aciditylevels below 0.7%), “sweet-sour” (aciditylevels of 0.7–1.8%) and “sour” varieties(acidity levels above 1.8%). Sorting accord-ing to this classification revealed that all

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three tested “sour” varieties (P.G.162-63,P.G.165-66 and P.G.112-13) received thelowest flavor preference scores, whereas the“sweet” and “sweet-sour” varieties receiveddivergent flavor preference scores (fig-ure 3). These results suggest that “sour”varieties are not preferred, and that other fla-vor attributes, in addition to just sweetnessand acidity, are also involved in determiningpomegranate flavor acceptance. Anotherfactor that putatively might affect flavorpreference is aril color, but we did not detectany meaningful correlations among the var-ious aril colors, such as “dark red”, “red”,“pink” or “white”, and observed flavor pref-erences (figure 4). Thus, aril color does notsignificantly influence its perceived flavor.

To better elucidate which flavor attributesare important in defining pomegranate fla-vor preferences, we examined the flavorprofiles of the tested varieties with the aidof a trained sensory panel. The five mostpreferred varieties (consumer flavor prefer-ence scores above 7.0) shared more or lesssimilar flavor profiles, including relativelyhigh sweetness, moderate to low sournessscores, high red wine and pomegranatefruity flavor notes, low bitterness and astrin-gency scores, and medium to soft seeds(figure 5A). According to these findings, anaverage preferred pomegranate flavor pro-file was composed (figure 5B).

In contrast to the preferred pomegranateflavor profile, the six least preferred varie-ties, which achieved flavor preferencescores below 6.0, could be distinguishedfrom the preferred flavor profiles accordingto various parameters (figure 6). For exam-ple, the varieties P.G.162-63, P.G.165-66and P.G.112-13 were very sour; P.G.219-230was very bitter; P.G.119-20, P.G.213-224,P.G.165-66 and P.G.162-63 had low redwine and pomegranate fruity odors; andP.G.119-20 and P.G.112-13 had extremelyhard seeds (figure 6).

4. Discussion

Despite the increasing importance of pome-granates in global trading and juice con-sumption, and their important nutritionalcontributions to the human diet, very little

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igure 2.otal soluble solids, acidontents and [TSS/acid] ratios

n fruit juices of 18 distinctomegranate varieties. Datare means ± standard errors ofive replications, each usinguice collected from two fruitsi.e., total of 10 fruits per

easurement).

igure 3.onsumer flavor preferencecores of pomegranate arilsxtracted from 18 distinctomegranate varieties. Datare means ± standard error of0 testers. In the upper panel,he pomegranate varieties areresented in order from high to

ow flavor preference scores;n the lower panel they arelassified according to theircidity levels (“sweet”arieties, acid levels < 0.7%,sweet-sour” varieties, acidevels 0.7–1.8%, and “sour”arieties, acid levels > 1.8%).

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is known regarding the genetic diversity ofpomegranate flavor traits, or about con-sumer sensory preferences for pomegranatefruits. In our present study, wide geneticdiversity associated with flavor traits andsensory preferences among 18 distinctpomegranate varieties were explored.

According to sensory analysis evaluationswith the aid of a trained panel, it was sug-gested that the main flavor attributesrequired to characterize the flavor of freshlyextracted pomegranate arils include taste(sweet, sour, bitter), odor (red wine andpomegranate fruity notes) and mouth-feelsensations (astringency, juiciness and seedhardness). Pomegranate varieties thatachieved overall high consumer flavor pref-erence scores were characterized by highsweetness, moderate to low acidity levels,rich red wine and pomegranate fruity odors,low bitterness and astringency, and, prefer-ably, soft seeds. In contrast, varieties withlow flavor preference scores were either toosour or bitter, had low red wine and pome-granate fruity odors, or had very hard seeds.This information regarding the sensory pref-erence ratings of pomegranates is obviouslyvery important to pomegranate breeders,growers, exporters, buyers and juice manu-facturers, as it might assist in future selectionof new desired pomegranate varieties withhigh consumer sensory preference scores.Nevertheless, it is worth noting that thedesired pomegranate flavor preference maydiffer among distinct cultures and countries.For example, in the Far East andNorthAfrica,consumers often prefer sweet fruit, whereasin Russia and other Northern countries, con-sumers may prefer more sour fruit [9].

In the past, pomegranate varieties wereclassified into three major groups accordingto their acidity levels, i.e., “sweet”, “sweet-sour” and “sour” varieties [8]. Nevertheless,despite detailed biochemical analyses ofsugar and acid contents in these fruits, it stillremained unclear which of these diverse“sweet”, “sweet-sour” and “sour” varietieswere more preferred. In our present study,it was found that all three tested “sour” vari-eties achieved low sensory preferencescores, whereas “sweet” and “sweet-sour”varieties achieved divergent scores. Thesefindings present two major implications:1) “sweet” and “sweet-sour” pomegranatevarieties are favored and more preferred ascompared with “sour” varieties; and 2) otherfactors besides sweetness and sournesshave crucial importance in determiningpomegranate flavor preference. Our resultssuggest that these other factors of sensory

.

.

Figure 4.Consumer flavor preferencescores of pomegranate arilsextracted from 18 distinctpomegranate varieties. Dataare means ± standard error of70 testers. The pomegranatevarieties were classifiedaccording to their aril colors(see figure 1).

Figure 5.Evaluation of sensory quality ofpomegranate arils. A) flavorprofiles of arils from the fivemost highly preferred varietiesB) average flavor profile of high-ly preferred pomegranate fruitsFruit flavors were evaluated bya trained taste panel. Data aremeans of 10 replications.

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attributes are mainly rich red wine andpomegranate fruity odors, low bitternessand astringency, and soft seeds.

Acknowledgments

This manuscript is contribution no. 631/12from the Agricultural Research Organization,the Volcani Center, P.O. Box 6, Bet Dagan50250, Israel.

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igure 6.valuation of sensory quality ofomegranate arils extracted

rom the six least preferredarieties. Fruit flavors werevaluated by a trained tasteanel. Data are means of0 replications.

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Diversidad genética y preferencias gustativas de las granadas.

Resumen – Introducción. Los objetivos de nuestro estudio fueron evaluar la diversidadgenética de los componentes del gusto y las preferencias de arilos de granadas frescas.Material y métodos. Se llevaron a cabo experimentos con arilos frescos de 18 variedadesdistintas de granados extraídos de la colección genética de granados de la organización deinvestigación agrícola israelí (ARO). Se realizaron pruebas de aceptación del sabor en super-mercados, así como experimentos descriptivos del análisis de la percepción gustativa porparte de un grupo de expertos sensoriales. Resultados y discusión. Las pruebas de acepta-ción del sabor tras el consumo de frutas revelaron una gran variedad en las preferencias gus-tativas según los distintos tipos de granados estudiados. Los análisis de la percepcióngustativa revelaron que el sabor preferido de los arilos de las variedades estudiadas se carac-terizaba por un gran dulzor, un índice de acidez de moderado a débil sensaciones de vinotinto y de granadas afrutadas, una ligera amargura, una ligera astringencia, y frutas de granostiernos. Por el contrario, los arilos de las frutas de las variedades menos apreciadas erandemasiado agrios o demasiado amargos, tenían poco olor a vino tinto o a granada afrutada, ocontenían granos muy duros. Asimismo, todas las variedades “agrias” del experimento (conte-nido en ácido ≥ 1,8%) recibieron bajas puntuaciones de preferencias sensoriales, mientrasque las variedades “agridulces” y “dulces " (contenido en ácido 0,7–1,8% y ≤ 0,7%, respectiva-mente) alcanzaron puntuaciones de preferencia variables. En conjunto, parece que la prefe-rencia gustativa de las granadas está ligada, sobre todo, a un gran dulzor del arilo, una acidezde débil a moderada, olor a vino tinto y a granadas afrutadas y la presencia de granos tiernos.

Israel / Punica granatum / frutas / análisis organoléptico / elección devariedades / sabor / dulzura / encuestas al consumidor

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