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1. Introduction
Mandarins are among the most consumed citrus worldwide, being a rich source of different antioxidant and health-promoting compounds1)(2)(3. An extraordinary genetic diversity regarding fruit-quality traits and harvest periods has been described within this citrus group4. Mandarin harvest season in the Southern Hemisphere starts in March with Satsumas and Clementines, and ends in October with Murcott and Ortanique cultivars, offering a great diversity of fruit quality and sensory experiences during the whole period. Mandarins stand out among citrus for their intense coloration and appreciated balance between soluble solids and acidity, showing a specially high accumulation of soluble sugars (compared to other citrus) ranging between 9 and 16 °Brix, while acidity at harvest usually oscillates between 0.6 and 2.0%1)(4)(5)(6. Soluble solids and acids concentration change as fruit ripens in the tree, increasing sugars content while reducing acids until reaching a desired balance that determines harvest time3)(7. If the fruit does not reach its desired external coloration, a degreening process is carried out after harvest in order to promote chlorophyll breakdown and orange peel color8. Genetic background, rootstock selection, harvest time during the season, commercial postharvest operation treatments such as degreening and waxing and storage time were described to impact on sensory quality of mandarins9)(10)(11.
Mandarin typical flavor is highly appreciated by citrus consumers12)(13. Additionally, mandarins’ easy peeling, absence of seeds and its whole market window are among the factors favoring a rise of mandarin consumption and its higher prices as fresh product compared to oranges2)(14. Development of different trademarks such as Cuties®, Halos® (Clementines, as an example of an early-season cultivar by Sun Pacific and Wonderful Citrus companies, respectively), Dimples® and Suki® (Gold Nugget mandarin, as an example of late-season cultivar by Cecelia and Suntreat companies, respectively) have notably improved mandarin success in the United States of America (USA). Both products exalt sensory, convenience-related aspects or external fruit characteristics such as ‘bumpy and sweet’ or ‘sweet, seedless, easy peel’ in their packages. This represent a new product segment with higher prices for new cultivars with valued sensory characteristics, most of them being easily recognizable by fruit external appearance14.
Sensory characteristics play a key role in consumer acceptance of mandarins6)(13)(14. In this sense, large differences among cultivars have been reported. A study including 46 different mandarin cultivars revealed large differences in consumer liking: cultivars ranged from high scores (7.5 on a 1-9 scale) for several common mandarin cultivars down to scores below 5.0 (indifference score) for satsumas4. Regarding the purchase intention, some authors reported that consumer purchase decision mainly rely on external appearance14)(15. In particular, rind color has been shown to be an important factor for early purchase intention8. However, repeated purchase decisions are more influenced by internal sensory characteristics of mandarins13)(16. Flavor has been identified as the most relevant factors underlying consumer willingness to try and purchase intention of mandarins12)(14)(16. A recent study with Spanish consumers has shown that the main drivers of mandarin liking in this market are aroma intensity, color intensity, flavor intensity, sweetness and juiciness6. Similarly, a sensory study carried out in Israel revealed that the most preferred mandarin cultivars show high sweetness, strong mandarin and fruity flavor, moderate or low acidity levels and high juiciness17.
Information about consumer sensory and hedonic perception of new mandarin cultivars provides valuable insights for breeders4)(16)(17, informing potential production and marketing strategies for increasing mandarin consumption6)(18. However, studies on consumer perception of mandarins are still scarce.
In this context, the objectives of this work were: a) to obtain a sensory characterization of novel hybrids from Uruguay compared to commercial cultivars based on consumers' perception; and b) to identify key sensory characteristics defining consumer liking of Uruguayan mandarins. This knowledge will feedback breeding decisions towards the sensory improvement of Uruguayan citrus and provide valuable information for the development of marketing strategies.
2. Materials and methods
2.1 Mandarin samples
Six promising mandarin hybrids (B475, A218, F3P8, F5P8, F2P3 and M19) registered by the National Institute of Agricultural Research (INIA) and the Faculty of Agronomy (Udelar), and four reference cultivars (Gold Nugget, Tango, Murcott and Ortanique) were included in the present study. Hybrids and commercial cultivars evaluated were grown under the same climatic conditions and agricultural practices in an experimental field located at INIA Salto Grande (Southern Hemisphere: 31º 16'S; 57º 41'W, 46 m height, Salto, Uruguay). All varieties were grafted in Trifolia, the most widespread rootstock in Uruguay.
Two studies were carried out in different moments of the harvest season: mid-season and late season. Due to the wide ripening window of mandarins, the hybrids and cultivars that were fully ripe for consumption were included in each study (Figure 1). F2P3 was included in both studies (mid-season and late-season harvests) due to its extended harvest period (from June to October). In the late season harvest, F2P3 was included in two different rootstocks (Trifolia-T and Flying Dragon-FD) to obtain insights on the potential impact of agronomical decisions on the sensory characteristics and consumer liking of this hybrid.
All cultivars were harvested at commercial maturity, the day before the study grouping. A ten-fruit sample was taken to the laboratory for physicochemical analyses. The rest of the fruit were stored in a cold chamber (5ºC) until the sensory evaluation.
2.2 Physicochemical characterization
Peel and pulp color were determined with a colorimeter (CR-400, D65 illuminant, Konika Minolta, Tokyo, Japan), taking three measures per fruit. L, a and b means from Hunter space color were calculated and expressed as a color index (CI=1000 a / L b). Juice was extracted with a commercial juice squeezer (APOL.N.M., Sirman, Marsango, Italy), and expressed as a percentage of the sample weight. Total soluble solids were measured with a refractometer (DBX-55, Atago Co. Ltd., Tokyo, Japan) at 20°C and expressed as °Brix. Titratable acidity was determined by titration with 0.1 N NaOH solution, using phenolphthalein as an indicator. Results were expressed as g of citric acid in 100 mL of juice (%).
2.3 Consumer studies
Two consumer studies were carried out in a supermarket in Montevideo (Uruguay). Consumers were intercepted by researchers while doing their purchases at the fruit and vegetables section and invited to participate in the study. All participants consumed mandarins, at least occasionally. A total of 106 consumers participated in the first study (mid-season): 58% female, aged 18-75 years old (M=47.0 years old, SD=14.1). The second study (late-season) involved 102 consumers: 57% female, aged 18-78 years old (M=48.0 years old, SD=15.9).
Participants completed the study in a quiet and well illuminated area of the supermarket. After seating, they were presented with one fruit from each hybrid/cultivar on a white plastic tray, coded with random 3-digit number, following a Williams' Latin square experimental design. Participants were asked to rate their liking of the mandarin appearance using a 9-point hedonic scale (1 = ‘dislike very much’, 9 = ‘like very much’). They were also asked to describe external appearance using a check-all-that-apply (CATA) question composed of 8 terms: small, regular shape, smooth, big, orange color, green color, rough and irregular shape.
Then, participants were presented with one mandarin segment per hybrid/cultivar on white plastic plates, coded with 3-digit random numbers. They could ask for more sample if needed, but almost none did. Samples were presented following a Williams' Latin square experimental design. Consumers were asked to taste each of the samples and to score their overall liking using a 9-point hedonic scale (1= ‘dislike very much’, 9 = ‘like very much’). They also had to describe their sensory characteristics using a CATA comprised of 18 terms related color, texture and flavor: sweet, typical mandarin flavor, juicy, intense flavor, firm, intense color, orange flavor, soft, barely sour, gummy, pale color, not much typical mandarin flavor, sour, barely sweet, dry, off-flavor, tasteless, bitter.
2.4 Data analysis
All statistical analyses were performed using R software19. Analysis of variance (ANOVA) was performed on overall liking scores considering sample as fixed effect and consumer as random effect. Mean ratings were calculated and Tukey’s test was used for post-hoc comparisons (p ≤ 0.05).
Frequency of mention for each term of the CATA question was determined by counting the number of consumers who used that word to describe each cultivar. Cochran's Q test was used to evaluate the existence of significant differences among samples. When differences were significant, the sign test was used for post-hoc comparisons. Correspondence analysis was used to obtain a graphical representation of samples and terms based on the frequency table.
Penalty-lift analysis was used to estimate the effect of each term of the CATA question on consumers' liking of mandarins. The penalty lift was calculated as the average liking score (across consumers and samples) when a term was selected minus the average liking score (across consumers and samples) when the term was not selected20.
Figure 1: Graphic representation of the ripening period of the novel hybrids and commercial cultivars included in the present work. Month and weeks (1-4) are presented to limit the beginning and the end of the harvest period for each cultivar. Dark grey bars represent the harvest period of the novel hybrids. Light grey bars represent the harvest period of commercial cultivars. Arrows indicate the harvest time for each of the two studies
3. Results
3.1 Physicochemical characteristics
External coloration varied between 9.8 for Gold Nugget to 19.1 in A218 for midseason harvest. Among late-season cultivars, M19, F2P3-FD and Ortanique showed the highest external coloration values, whereas Murcott, B475 and F2P3-T showed the lowest (Table 1). Regarding juice content, A218 showed the lowest value (36%), F5P8 and F3P8 showed the highest values (55.7% and 52.3%, respectively) in mid-season, whereas in the late season harvest, Murcott and Ortanique showed the highest values (53.6% and 50.5%, respectively). Regarding soluble solids, F2P3 stood out with the highest values in both harvests, registering 13.8 °Brix in the mid-season harvest and 14.7 and 16.5 °Brix for F2P3-T and F2P3-FD, respectively, in the late season harvest (Table 1). The acidity was higher for A218 and B475 in the mid and late-season harvest, respectively, while the lowest values were found for Gold Nugget, M19 and F2P3-T.
3.2 Sensory characterization
In the mid-season study, significant differences in the frequency of use of all the terms of the CATA question for describing the external appearance of the mandarin samples were found. As shown in Figure 2, in the mid-season study Gold Nugget was characterized by its roughness, irregular shape and green color, whereas A218 was characterized by its large size and external roughness. Tango was characterized by external smoothness and small size. F3P8 and P5P8 were characterized by their regular shape, smoothness and orange color. F2P3 was described as having a smooth skin.
Regarding the evaluation of mandarin segments, significant differences among samples were found for all terms except for tasteless (p=0.916), gummy (p=0.170), barely sour (p=0.445) and not much typical mandarin flavor (p=0.848). Samples were sorted into three main groups in the first two dimensions of the correspondence analysis. As shown in Figure 2, hybrid A218 was characterized by bitterness, sourness and off-flavor. Pale color, dryness and orange flavor differentiated Gold Nugget and F2P3 from the rest of the samples. Finally, Tango and hybrids F3P8 and F5P8 were located at positive values of the first dimension of the correspondence analysis, and were characterized by softness, sweetness, intense color, typical mandarin flavor and juiciness (Figure 2).
Figure 2: Representation of mandarin samples and terms in the first two dimensions of the correspondence analysis performed on the frequency table obtained from consumer responses to the check-all-that-apply (CATA) question for the evaluation of external appearance (top) and tasting (bottom) in the studies conducted in the mid-season (left) and late season (right)
In the late season study samples largely differed in their appearance: significant differences among samples were found for all the terms of the CATA question. As shown in Figure 2, B475 was described using the terms small, green color and irregular shape. Murcott was clearly differentiated from the rest of the materials by its smoothness and regular shape. Ortanique was more frequently described as big than the rest of the materials. Finally, F2P3-F, F2P3-T and M19 were mainly described by the terms orange color and regular shape. Cultivation of F2P3 on two rootstocks led to significant differences in size and smoothness: F2P3-FD was more frequently described as bigger and rougher than F2P3-T (62% vs. 45%, and 49% vs. 22%, respectively).
Regarding the characteristics of the segments, significant differences among samples were found for all terms except for gummy (p=0.066) and barely sour (p=0.387). The first two dimensions of the correspondence analysis showed that samples were sorted into four main groups. F2P3-FD was clearly differentiated from the rest and was characterized by its intense flavor, typical mandarin flavor, sweetness, intense color and juiciness. F2P3-T showed lower juiciness, sweetness, total flavor intensity and typical mandarin flavor, and higher dryness and firmness than F2P3-FD. Meanwhile, Murcott, B475 and Ortanique were characterized by the terms sourness, orange flavor and softness. In particular, hybrid B475 received the highest frequency of use of the term sour. Finally, Hybrid M19 was characterized by its firmness and low sweetness intensity, being described as tasteless, bitter, barely sweet, and having off-flavor.
3.3. Consumer overall liking
Table 2 shows the mean liking scores for external appearance and segment tasting of the hybrids and commercial cultivars in the studies conducted in the mid-season and late-season harvest. Most samples showed an external acceptance liking close to or higher than 6, the first score of the scale denoting a positive hedonic reaction. The only exception was Gold Nugget, which received an external appearance score in the disliking region of the scale (4.4). In the mid-season harvest, three hybrids and one commercial cultivar showed the highest external appearance scores: F2P3, F3P8, P5P8 and Tango (Table 2). In the late-season harvest, all the hybrids and the commercial cultivar Murcott showed the highest liking scores (close to 6).
Liking scores after segment tasting showed a different ranking of samples. In the mid-season harvest two novel hybrids (F3P8 and F5P8) and the reference cultivar Gold Nugget showed high liking scores, achieving mean values close to 7 in the 9-point hedonic score. On the contrary, hybrid A218 showed the lowest score (4.4), denoting disliking. Interestingly, Gold Nugget was better appreciated by consumers in segment tasting than in the external appearance evaluation (increasing its liking score from 4.4. to 6.7), whereas the opposite trend was observed for A218 (decreasing its liking score from 6.1 to 4.4).
In the late-season harvest, liking scores tended to be lower than in the mid-season harvest. F2P3-FD showed the highest liking score (7.7) and Murcott the lowest (5.3), whereas all other hybrids and cultivars did not largely differ in their liking score, which ranged between 5.3 to 6.3 (Table 2). It is worth highlighting that F2P3 cultivated on different rootstocks during the late season study showed different liking scores after tasting and obtained higher liking scores compared to Murcott reference cultivar. Besides, F2P3-FD showed a higher liking score than F2P3-T (Table 2). In this study differences between the evaluation of external appearance and segment tasting were not large.
Table 2: Mean consumer overall liking scores of different mandarin hybrids (codes) and commercial cultivars (Gold-Nugget, Tango, Murcott, Ortanique) in two studies conducted in different moments of the harvest season
Mean values with different letters within a column and season are significantly different according to Tukey's test (p<0.05).
3.4. Penalty-lift analysis
Penalty lift analysis was used to estimate the relative impact of the sensory characteristics included in the CATA question on consumer liking. As shown in Figure 3, orange color, regular shape and smoothness positively influenced consumer liking of the external appearance of mandarins, regardless of the harvest season. On the contrary, green color and irregular shape negatively influenced consumer appearance liking.
After tasting, sweetness, typical mandarin flavor, total flavor intensity and juiciness were the main attributes driving consumer liking, whereas bitterness, off-flavor, dryness and low flavor intensity were negative attributes for consumer liking when tasting the segments (Figure 3).
4. Discussion
The present study evaluated consumer sensory and hedonic perception of different hybrids and commercial cultivars of mandarins in two moments of the harvest season. The hybrids and reference cultivars largely differ in their internal fruit quality according to physicochemical measurements of external coloration, soluble solids and juice content. Results also revealed large differences in the sensory characteristics of the different genotypes, in agreement with previous studies2)(4)(6)(21. Cultivars largely differed in their external appearance, internal color, flavor and texture. Interestingly, several novel hybrids showed similar sensory characteristics compared to international reference cultivars. In particular, consumers perceived the sensory characteristics of segments from F3P8 and F5P8 similar to those from Tango in the mid-season study, whereas segments of B475 were perceived similarly to Murcott and Ortanique. Consumers described as juicy genotypes with higher juice content (Tango, F3P8 and F5P8) and as sour the hybrids with lower soluble solids and higher acidity (A218). Similarly, F2P3-FD, the genotype with the highest soluble solid content (16.5°Brix), was described as sweeter by consumers than F2P3-T, despite its higher acidity.
More importantly, consumer liking of local hybrids was similar or even higher to international reference standards. In the mid-season study, F3P8 and F5P8 were similarly perceived to Tango and Gold Nugget, whereas in the late season study F2P3-FD showed a higher overall liking score than Murcott and Ortanique, typical late-season options. Overall liking scores of the most liked hybrids and cultivars ranged between 6.5 to 7.7 in the 9-point hedonic scale, evidencing a positive hedonic reaction. These values are similar or even higher than those reported by other studies4)(6.
The results discussed above confirm the potential of local hybrids and provide key information for breeding decisions. A similar approach has been recently applied to study Spanish local cultivars from a breeding program and compare them with commercial cultivars6. It is important to highlight that F2P3 an F3P8 local hybrids reached high overall liking scores and were described similarly compared to commercial reference cultivars. In the late-season, F2P3 appeared as a unique and novel option that is commercially available at the same time as Murcott and Ortanique. Results showed that the sensory characteristics of F2P3 were influenced by its harvest date and rootstock (FD vs. T). Late season is a preferred harvest time for this hybrid due to its higher soluble solid accumulation and lower acidity. Scion/rootstock combination has been reported to influence the sensory characteristics of mandarins; however, its effect seems to be dependent on the mandarin cultivar10)(11. For example, three different rootstocks (SO, Volkameriana and US-812) exerted an effect on the sensory characteristics of Odem but not the characteristics of Orri10. Similarly, in Tango fruit, sugars and acids concentration were reported to be influenced by the rootstock although these differences did not affect consumer liking scores nor purchase intention11. In the present study fruit from plants grafted in FD were described as sweeter and juicier with more typical mandarin flavor and intense flavor, less firm and softer compared to fruit from T rootstock, leading to higher consumer liking.
The existence of differences in sensory characteristics as well as internal fruit composition associated with harvest date or scion-rootstock combinations, especially in extended-harvest cultivars such as F2P3, should be considered when planning to build up a consistent brand image, which must offer a similar sensory experience of consumption14. The identification of the main agronomic, ambient or storage-conditions factors that differentially affect sensory experience when consuming a new mandarin is among future challenges for further research, which will help to select the most sensory stable genotypes in a breeding context.
Results from the present study enable the identification of the main sensory characteristics that drive Uruguayan consumer liking of mandarins. Orange color, regular shape and smoothness were the main drivers of consumer liking of external appearance, whereas sweetness, flavor intensity, typical mandarin flavor and juiciness were consistently identified as the main drivers of liking when tasting the segments. These results are similar to those reported by other authors in different countries2)(14)(16, highlighting the relevance of sensory studies in breeding process.
Results revealed that external appearance is not a good predictor of the sensory characteristics of the segments. The magnitude of the difference between liking scores for appearance and the tasted segments largely depended on the cultivar. This indicates that the sensory characteristics perceived after tasting would change consumer preliminary opinion (based merely on fruit appearance). In the same line, studies with consumers in USA revealed that after peeling the fruit, ease of peeling became more important than appearance to consumers. However, after tasting, consumers attached more importance to acidity and seeds compared to ease of peeling or appearance14. In this sense, tasting trials inside local marketing stores might be a successful strategy to introduce new mandarin cultivars, especially if they do not exhibit the most desired external characteristics (orange color, regular shape and smooth skin). In the present study, this was the case of Gold Nugget.
5. Conclusions
The present study explored Uruguayan consumers' sensory and hedonic perception of local hybrids and reference cultivars of mandarins. Orange color, regular shape, smoothness, sweetness, intense flavor, typical mandarin and juiciness are the key drivers of consumer liking of mandarins. External appearance was not a good predictor of consumer liking after tasting. Hybrids F3P8, F5P8 and F2P3 (specially in FD rootstock and late season harvest) were described using terms related to positive sensory characteristics and received liking scores similar or higher to reference cultivars, such as Tango. It is important to highlight that most new international varieties are limited and subjected to royalties, while national varieties are available. In this line, having a new Uruguayan variety with good sensory characteristics (as good as Tango) is a big advantage for all Uruguayan growers. These results stress the importance of sensory and consumer science as an integral part of the breeding process in order to understand consumer preferences and underpin marketing strategies.
