Relationships between Fruit Acceptability and Health-Case of Seven Pomegranate (Punica granatum L.) Juices


The objective of this study was to evaluate acceptability and instrumental measurements (titratable acidity, total soluble sugar, total phenolic, flavonoids, anthocyanins, and condensed tannin contents as well as antioxidant capacity) of seven Tunisian pomegranate cultivars to relate fruit acceptability and beneficial health. Seventy one participants were asked to complete a questionnaire and to indicate their level of acceptance, on a nine point-hedonic scale, for fruit size, sweetness, bitterness, juice color and juice overall acceptability. Taste and aril color were the main criteria to select Pomegranate. Significant differences occurred for all the acceptability tests. Titratable acidity determines the taste and important inter-specific variability in the phenolic contents as well as for the antioxidant capacities was noticed. Anthocyanin and condensed tannin were contributing to the organoleptic properties while bitterness acceptability was negatively correlated to the antioxidant capacity. Also, a relationship was found between the fruit size acceptability and the antioxidant capacity.

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C. Kar, N. Mtimet, A. Ferchichi and J. Bouajila, "Relationships between Fruit Acceptability and Health-Case of Seven Pomegranate (Punica granatum L.) Juices," Food and Nutrition Sciences, Vol. 4 No. 8A, 2013, pp. 119-130. doi: 10.4236/fns.2013.48A015.

1. Introduction

“The eyes are the gatekeeper to the mouth”. Color was suggested to be the most influential quality factor, as consumers have expectations of overall quality based on color [1]. Most of the yellow, red and blue colors in fruit are related to the flavonoids [2]. Flavonoids are a group of polyphenolic compounds naturally present in a wide variety of fruit and vegetables. Fruit and vegetable consumption decreases the risks of coronary heart disease and lung cancer probably to their phenolic compounds [3].

Phenolics are secondary metabolites synthesized by plants, both during normal development and in response to stress conditions such as infection, wounding and UV radiation, among others [4]. In plants, phenolics may act as phytoalexins, antifeedants, attractants for pollinators, contributors to plant pigmentation, antioxidants and protective agents against UV light, among others. In food, phenolics may contribute to their organoleptic properties, such as, bitterness, astringency, color, flavor, odor and oxidative stability [5].

Among colored fruits, containing phenolics there is the Pomegranate [6,7]. The Pomegranate (Punica granatum L. Punicaceae) is a fruit becoming more popular because of its healthy properties [8]. These healthy properties come from the high antioxidant activity of the phenolic compounds content of the Pomegranate fruit [8,9]. However, it is surprising that the literature focused on the antioxidant properties of the phenolics but little is yet known about their contribution to the organoleptic properties of the Pomegranates.

Thus, the present study aims at relating the phenolic contents to the organoleptic properties of the Pomegranate juices as perceived by a panel of participants. To achieve this objective, a collection of seven Tunisian pomegranate cultivars differing in fruit internal color (from light pink to deep pink), taste (from sour-sweet to sweet) and fruit size (from small to large) was examined. The results were used to test for correlations between acceptability tests, physicochemical properties, phenolic contents and antioxidant capacity. This study allows identifying a possible link between the acceptability of Pomegranates and the protective effect of their phenolic compounds.

2. Materials and Methods

2.1. Participants

Seventy one adults, eligible and volunteers (40 men and 31 women) were recruited through ad wall in the Institute of Arid Regions of Medenin in Tunisia during the two last weeks of October 2008. Criteria for participation were: age from 18 to 55 years, regular consumer of pomegranate, no experience in sensory analysis, not being allergic to any food and availability for the test. Students and staff of the Institute of Arid Regions who work-ed on pomegranate were excluded in this study as it was thought they may affect the outcomes with their advanced skills on pomegranate taste. Participants reported their answers on individual ballots.

2.2. Samples

Seven Tunisian pomegranate cultivars differing in fruit size, juice color and juice taste were examined (Table 1). The fruits were classified as large when their diameter was superior to 95 mm, they were medium if their diameter was from 75 to 95 mm and they were small when their diameter was inferior to 75 mm. The juice color was determined visually while the juice taste was defined according to their sugar to acidity ratio [10]. A sugar to acidity ratio between 8 and 24 indicated sour-sweet cultivars, while a ratio from 25 to 98 referred to sweet cultivars. The cultivars included in the present study were chosen according to customary consumer purchasing practices and the answers to the questionnaire on perceptions and consumption of pomegranate. The denominations of the cultivars refer, in Tunisian, to the population where they belong or to the taste of the fruit [11]. The cultivars were selected from mature fruits grown in the collection of the Tunisian National Germplasm of pomegranate located at Zerkin (3345'N, 1016'E) [11]. They were cultivated under homogenous conditions, without any special management (no fertilizers, no irrigation except natural rainfall). Approximately, fifteen kg of each cultivar were picked at harvesting maturity in the last week of September 2008 and in the last week of October 2008. According to Mirdehghan and Rahemi [12], the harvest maturity for pomegranate is achieved, when the arils’ weight is greater than that of the peel. Fruits were transported by ventilated car to the laboratory, and trans-

Table 1. Codes, cultivars, main characteristics, mean value and standard deviations of instrumental analyses of the seven Tunisian Pomegranate (Punica granatum) studied.

ferred to a 4˚C store room on the same day as they were harvested. To avoid possible contamination of the juices with the metabolites produced by microorganisms, fruits with cracks, cuts, sunburn and other defects in husk were disposed of and only healthy fruits of uniform size and appearance were arranged in one row in wooden boxes containing packing material during the experiments. Whole fruits were preserved for the fruit size acceptability while others were squeezed to juices for further analysis. For thus, fruits for each cultivar were manually peeled, ground in a commercial turmix blender (Moulinex) for 30 s, and filtered through muslin cloth (0.5 mm). The homogenate juices obtained were freshly utilized for physico-chemical analyses and acceptability tests.

2.3. Sensory Analyses

2.3.1. Questionnaire

Participants were asked to complete a one-page questionnaire (Table 2) developed and administered by the author, on their consumption of Pomegranate. The questionnaire included three types of questions: 1) eat, 2) purchase and 3) medicinal effects. For each question, participants indicated their responses by a cross in front of the answer(s) corresponding to their choice. Each participant indicated his answer(s) on an individual questionnaire.

2.3.2. Acceptability Tests

Prior to the acceptability tests, participants were given a presentation outlining the methodology and the procedure of the sensory methods.

Participants evaluated the samples in one session (30 minutes). They were asked to assess, in a first time, the acceptability of the fruit size and the juice color, and, in a second time, to assess the acceptability of sweetness, bitterness and juice overall acceptability. The assessments were done by using a nine-point hedonic scale, where 1 = dislike extremely, 2 = dislike very much, 3 = dislike moderately, 4 = dislike slightly, 5 = neither like nor dislike, 6 = like slightly, 7 = like moderately, 8 = like very much and 9 = like extremely [13]. The samples were presented with 3-digit codes in a balanced order to account for first order and carry-over effects [14]. The whole washed fruits were placed on white plates and the juices were presented in transparent glasses at room temperature. The assessments were done in a well ventilated and at

Table 2. Questionnaire on perceptions and consumption of pomegranate (N = 71).

ambient temperature room of the Institute of Arid Regions. Participants were provided with mineral water, unsalted crackers, and expectorant cups to cleanse the palate between sample evaluations. They were instructed to pause for one min between samples.

2.4. Instrumental Analyses

All chemicals used were of analytical reagent grade. All reagents were purchased from Sigma-Aldrich-Fluka (SaintQuentin France).

2.4.1. Physico-Chemical Properties

Titratable Acidity (TA) was determined by potentiometry, using a pH meter, with a 0,1N NaOH solution to a pH of 8.1. The results were expressed as percentage of Malic Acid (%MA). A hand refractometer type OPTECH K7 1319 (Optical Technology, Munich, Germany) graduate of 0˚ - 32˚ Brix was used to determine the Total Soluble Solids (TSS). Results were expressed in degrees Brix (˚Brix). The sugar to acidity ratio (TSS/TA) was calculated using the relation between Total Soluble Solids by Acidity. Color Density (CD) was determined by measuring the absorbance at 420, 520 and 620 nm in a cell of 1 mm using a spectrophotometer Shimadzu (Shimadzu Corporation, Kyoto, Japan) UV-1201.

2.4.2. Phenolics Content

The phenolics of each fruit extract were determined by the method of Georgé et al. [15]. The diluted aqueous solution of each extract (0.5 mL) was mixed with Folin Ciocalteu reagent (0.2 N, 2.5 mL). The mixture was allowed to stand at room temperature for 5 min before adding sodium carbonate solution (75 g/L in water, 2 mL). An hour later, the absorbances were measured at 765 nm against a water blank. A standard calibration curve was plotted using gallic acid (0 - 300 mg/L). The results were expressed as mg of gallic acid equivalents (GAE)/L of juice.

1) Flavonoids Content The flavonoids were estimated according to the Dowd method as adapted by Arvouet-Grand, et al. [16]. A diluted methanolic solution (4 mL) of each plant extract was mixed with a solution (4 mL) of aluminium trichloride (AlCl3) in methanol (2%). The absorbance was read at 415 nm after 15 min against a blank sample consisting of methanol (4 mL) and plant extract (4 mL) without AlCl3. Quercetin was used as reference compound to produce the standard curve. The results were expressed as mg of quercetin equivalents (QE)/L of juice.

2) Anthocyanins Content Total anthocyanin contents were measured with the pH differential absorbance method, as described by Cheng and Breen [17]. Briefly, absorbance of the extract was measured at 510 and 700 nm in buffers at pH 1.0 (hydrochloric acid-potassium chloride, 0.2 M) and 4.5 (acetic acid-sodium acetate, 1 M). The wavelength reading was performed after 15 min of incubation. Anthocyanin contents were calculated using a molar extinction coefficient (ε) of 29600 (cyanidin-3-glucoside) and absorbance of A = [(A510 – A700)pH 1.0 – (A510 – A700)pH 4.5]. Results were expressed as mg cyanidin-3-glucoside equivalents/ L of juice.

3) Tannins Content Proanthocyanidins reactive to vanillin were analyzed by the vanillin method [18]. One milliliter of extract solution was placed in a test tube together with 2 mL of vanillin (1% in 7 M H2SO4) in an ice bath and then incubated at 25˚C. After 15 min, the absorbance of the solution was read at 500 nm. Concentrations were calculated as (+)-catechin (mg/L of juice) from a calibration curve.

2.4.3. Antioxidant Capacity

Antioxidant capacity was measured using the improved ABTS method. The radical scavenging capacity of antioxidants for the ABTS (2, 2’-azinobis-3-ethylbenzothiazoline-6-sulphonate) radical cation was determined as described by Re et al. [19]. ABTS radical was generated by mixing a 7 mM of ABTS at pH 7.4 (5 mM NaH2PO4, 5 mM Na2HPO4 and 154 mM NaCl) with 2.5 mM potassium persulfate (final concentration) followed by storage in the dark at room temperature for 16 h before use. The mixture was diluted with ethanol to give an absorbance of 0.70 ± 0.02 units at 734 nm using Helios Alpha spectrophotometer (Thermospectronic, USA). For each sample, the diluted methanol solution of the extract (100 μL) was allowed to react with fresh ABTS solution (900 μL), and then the absorbance was measured 6 minutes after initial mixing. Ascorbic acid was used as a standard and the capacity of free radical scavenging was expressed by IC50 (mg/L). Values calculated denote the concentration required to scavenge 50% of ABTS radical.

2.5. Statistical Analysis

All measurements were expressed as mean ± standard deviation of triplicate measurements. Standard deviations (SD) did not exceed 5% for the majority of the values obtained. Acceptability data was collected manually on a MS Excel spreadsheet and was recorded with “dislike extremely” equal to one, “like extremely” equal to nine, and intermediate points numbered appropriately. Analysis of Variance (ANOVA) was performed on the qualitative data obtained from the acceptability tests with α set at 0.05. Friedman’s test [20], employing a significance level of α < 0.05, was applied to the results of the hedonic test, to separate the means of the acceptability tests. Standardized Principal Component Analysis (PCA) was performed on the mean ratings among the participants for all acceptability tests. Hierarchical cluster analysis (HCA) with the Ward criteria was applied on the first two principal components of the PCA [21]. To compare the variability in quantitative physico-chemical composition of the samples having different averages and expressing in different units, the coefficient of variation (CV) was used. It expresses the standard deviation as a percentage of the mean. The data will be considered homogeneous if the CV is less than 15%, and conversely, the data will be considered heterogeneous if the CV is greater than 15%.

A Pearson correlation analysis was carried out between the instrumental measurements with a 95% significance level. A Partial Least Square (PLS) regression analysis was performed to relate the acceptability data (Y-variables) to the instrumental data (X-variables). Regression coefficients for the relations between variables revealed by the PLS regression were estimated by jack-knifing, and significance levels were determined. All the data were collected in spread sheets and the statistical analyses were done using MS Excel Xlstat 2009 (Addinsoft, New York).

3. Results and Discussion

3.1. Questionnaire

The participants were asked to complete a questionnaire (Table 2) about their perceptions and consumptions of pomegranate. The external sensory attributes, such as appearance, color, size and hand-evaluated texture, which are evaluated by the consumer prior to consumption, are intrinsic quality cues. Taste and oral texture evaluated at the time of consumption are experience-quality attributes.

Among intrinsic quality cues, appearance (fruit size and fruit color) was the major factor (one of two) in the purchase of pomegranate fruits for the participants. Of all appearance factors, fruit color (one of three) was suggested to be the most influential quality factor, as participants have expectations of overall quality based on color, while fruit size (one of five) was considered to have minor influence on the consumer evaluation of Pomegranate quality. To our knowledge, no study was conducted on the intrinsic quality cues of pomegranates. Nevertheless, according to Kays [1], color was suggested to be the most influential quality factor, as participants have expectations of overall quality based on color, such as color cues for banana ripeness. The same author notes that at times, color expectations of quality may not be valid because, for example, some orange (Citrus spp.) cultivars are at their optimum when they are green, not orange as most participants perceive.

When experience-quality attributes, participants may be intending to consume pomegranate because of its beneficial health consequences (one of ten), but taste (two of three) and aril color (two of seven) were the fundamental quality that must be satisfied for continued consumption. According to Kays [1], taste is ranked more highly than texture and appearance as a contributor to overall liking for food products; however, color and texture of horticultural products are more frequently cited as consumer quality attributes. Also, pomegranates were preferred as fresh fruit (three of seven) and juice (one of four). These results confirm those of Marlette [22], who found that apple sauce was preferred to whole apples. Thus, fruits would be preferred if they required no preparation, were ready-to-eat or not too difficult to eat.

Results from this study show that the size of the fruit, the taste, the color of the arils and the consumption of the Pomegranate as fresh fruit were the main criteria for participants to select and consummate pomegranate. Thus, these criteria were considered to select the plant material. In order to homogeneity experimental conditions, pomegranate juices were used also for the acceptability tests and the instrumental analyses.

3.2. Acceptability Tests

As seen in Table 3, significant differences (p < 0.05) existed among pomegranate juices for all the acceptability tests. The participants liked most of the pomegranate juices (as indicated by mean scores > 5) and the average scores for the pomegranate juices were particularly high. Also, participants preferred the juices from the cultivars CH 2 and NB 1 and the cultivar JB 1 received the highest score for juice color acceptability.

To determine the relationships between the juice over-

Table 3. Mean scores (n = 71) for acceptability tests of the seven Tunisian Pomegranate (Punica granatum) cultivars studiedA.

all acceptability of the seven cultivars and the acceptability of the sweetness, the bitterness, the juice color and the fruit size, a PCA was performed. Principal Components 1 (PC1) and 2 (PC2) accounted for 55% and 30% of the total variance, respectively. As shown in Figure 1, it seems that participants have clearly distinguished cultivars from each other, since the products were dispersed in the space of the representation. To improve the interpretation of the PCA map, a HCA on the PC1 and PC2 was performed. Three classes of cultivars were revealed (Figure 2). A first class, named liked, includes the cultivars CH 2 and NB 1. A second class corresponds to the neither liked nor disliked cultivars, such as, CH 4 and KL 11 and a third class, namely, disliked, was composed of the cultivars GR 2, JB 1 and ZG 11. By representing the three classes of cultivars on the PCA biplot, the liked class was closest to the juice overall acceptability and the acceptability of the sweetness. The neither liked nor disliked and the disliked classes seem to be grouped with the bitterness and diametrically opposed to the juice overall acceptability.

Figure 1. PCA map of consumer acceptability of the seven Tunisian Pomegranate (Punica granatum) cultivars studied. Forms dashed represent the three classes of cultivars defined by the HCA.

Figure 2. Dendrogram obtained by HCA on the first two principal components of the PCA.

Although, the significant negative correlation (R = −0.82, p < 0.05) found between the sweetness and the bitterness acceptability explains the natural opposition between the two attributes. Also, the significant correlations found between the juice overall acceptability and the bitterness acceptability on one side (R = −0.83, p < 0.05), and the sweetness acceptability (R = 0.82, p < 0.05), on the other, confirmed that heightened perception of bitterness was the principal reason for food rejection [23]. Other significant differences, less expected, were found. In fact, Friedman’s test indicated highly significant differences (p < 0.05) between fruit size and juice color acceptability, in a hand, and fruit size and bitterness acceptability, in another hand. There is no report, to our knowledge, on the consumer acceptability of Pomegranate.

Thus, it can be concluded that the sweetness accounted for most of the variation in overall acceptability and the consumer rejection of the pomegranate juices was mainly related to the bitterness rather than to the color of juice or the fruit size.

3.3. Physico-Chemical Properties

Table 1 shows the average value and the standard deviations for the physico-chemical properties of the seven pomegranate juices analyzed. As seen, the pomegranate juices differed little in TSS (CV = 6%) with values ranging from 14.0 ˚Brix for the cultivar CH 4 to 16.5 ˚Brix for the cultivar GR 2. However, great differences (CV = 90%) were observed in TA with values ranging from 0.2% MA for the cultivar CH 2% to 1.8% MA for the cultivar GR 2. The TSS/TA ratio gives an indication of the sweetness of fruits. The higher the TSS/TA ratio, the sweeter is the fruit. With the highest values for TA and TSS, GR 2 was the sourness cultivar (TSS/TA = 9.2) while with lowest values for TA and TSS, CH 2 was the sweetness cultivar (TSS/TA = 59.2). The TSS of the studied cultivars was close to 15.1 ˚Brix, both sweet and sour-sweet, thus, the TA was the factor which determines the taste of the Pomegranate. This result was confirmed by the significant negative correlation (R = −0.85, p < 0.05) found between the TSS/TA ratio and the TA. So, it can be concluded that the taste of the pomegranate juices is inversely related to their TA. Similar conclusion was advanced for orange [24]. Table 1 shows also that there were great differences (CV = 57%) with respect to the instrumental measurement of color of the pomegranate juices. Juice from the cultivar CH 2 was differentiated as the lighter sample (CD = 0.3) while juice from the cultivar GR 2 was the darkest (CD = 1.7) one; NB 1 cultivar presented intermediate values of lightness (CD = 1.0). The higher CD of the pomegranate juices could be explained by the heat units accumulated (difference between the daily average temperature and 25˚C) prior to harvest. Indeed, the intensity of the red color of fresh Israeli pomegranate arils was found to be inversely related to the sum of heat units accumulated during fruit development and ripening [25].

Conflicts of Interest

The authors declare no conflicts of interest.


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