Microgreens, also known as ‘vegetable confetti’, consist of tender immature greens of wild species, herbs, grains, or vegetables, harvested upon the emergence of the first pair of true leaves [1
]. Microgreens are analogous in size to sprouts but are eaten without the roots and require additional days to thrive and acquire larger, colored, and flavor-rich leaves [2
] under light conditions. Despite their immaturity, microgreens are stamped with sharp flavors, vivid colors, tender textures, and a great pack of phytonutrients [3
]. Such captivating sensory attributes have bestowed microgreens a distinguished spot among chef’s resources for adorning soups, sandwiches, and drinks [5
], and earned them a place in “organic farming” stores [2
]. Based on sensory and health criteria, countless species are used for the production of microgreens including commercial and local varieties, which belong to the following botanical families: Amarillydaceae
Microgreens are also regarded as fresh “super foods” [4
] due to their innate fortification with plant secondary metabolites [9
]. Additionally to carotenoids, ascorbic acid, phylloquinone, γ-tocopherols, and phenolic compounds, microgreens are also a source of macro and micro-minerals. Such nutritive and functional values enhance human diet and prevent a range of common diseases [4
]. Indeed, microgreens enclose a greater load of essential phytonutrients compared to their mature counterparts [3
]. Suchlike dense phytochemical composition has garnered the attention of nutrition researchers [6
] and gained them prevalence among food technologists, urban farmers, and consumers [15
]. As public concern about environmental and nutritional aspects of food production has recently arisen [16
], consumers are orienting their purchasing behavior toward healthier and environmentally friendlier food products [18
Major components aside from nutritional values dictate consumer acceptance of a food product, such as sensory attributes (i.e., appearance, texture, and flavor) [21
]. Appearance dominates consumer choice, while other attributes sustain future purchases [4
]. Microgreens offer a palette of colors (i.e., green, yellow, red, crimson, or multicolor), flavors (i.e., neutral, slightly sour, spicy, or bitter), and texture (i.e., juicy, crunchy, or regular) [4
]. Humans’ organoleptic system allows for the perception of taste and olfactory sensations, and hand over the knowledge about the sensory attributes [5
]. Sensory attributes are interconnected with the chemical composition of the product and its acceptability; for instance, the phenolic content is tightly associated with microgreens’ astringency, sourness, bitterness, and sweetness attributes [11
]. In fact, mixing microgreens with salads is a smart strategy to meliorate the quality and appearance of food without compromising the overall taste [23
To date, several studies have examined how sensory attributes and visual appearance influence consumer perception towards microgreens per se [5
] while others held comparative studies at different maturity stages [25
]. Altogether, numerous microgreens species are still not assessed for their sensory attributes and acceptance. This current paper aims to examine whether sensory attributes and visual appearance affect consumer preferences and modality for microgreens, and their “Willingness To Consume it” (WTC as product acceptability). Based on the aforementioned, the sensory attributes of 12 microgreens species were appraised through an untrained consumer test. Based on the collected information, a partial least squares structural equation model was developed to link sensorial attributes to consumer willingness to consume it, as consumer preferences will drive the future of the microgreens market [30
3.1. Sensory Attributes and Acceptability
reports for all microgreens species the mean value and its standard error for each sensory attribute. ANOVA and Tukey post-hoc test revealed that, except for the acceptability for texture, the mean value of sensory attributes considered in this study was significantly different among microgreens.
For the intensity attributes, “Sweetness” scored significantly higher (5.9 ± 1.1) for Swiss chard, while the “Aroma” was highly perceived in coriander and amaranth (13 ± 0.6 and 12.2 ± 0.7, respectively) without significant differences among tatsoi, green basil, Swiss chard, and purple basil species. The lowest value of “Aroma” (3.4 ± 0.8) was expressed for purple basil cultivar. The latter also showed the lowest mean value of “Astringency” (3.0 ± 0.9) that reached the highest value (7.5 ± 0.9) in mibuna and cress. Moreover, both mibuna and cress were perceived as the most bitter species (10.0 ± 0.8; 9.0 ± 0.9, respectively), thus showing the largest mean difference with respect to Swiss chard (3.8 ± 0.9). Regarding the “Grassy” intensity, green basil, and komatsuna species showed mean values significantly higher than the other microgreens (12.7 and 12.1, respectively). The intensity of “Heat” was highly perceived in cress (12.6 ± 0.6) as well as the “Sourness” attribute (8.7 ± 0.9). However, in the last case, the mean value was not statistically different from mibuna (8.3 ± 0.9) and amaranth (7.3 ± 1.1) species. Participants perceived the highest mean value of “Texture” intensity (9.5 ± 0.7) after tasting mibuna even if it was not statistically higher than coriander (9.1), green basil (8.9), tatsoi (8.7), and purslane (8.2).
As concerns the WTC (acceptability), values for acceptability of “Appearance” were extremely high and always greater (except for purslane) than those concerning “Texture” and “Flavor”. The highest mean score for the “Appearance” was assessed for coriander (11.4 ± 0.6) that was 5.2 points higher than the lowest value (6.2 ± 0.8) expressed for cress. As for the “Flavor”, the most preferred microgreens were Swiss chard (8.5 ± 0.9), coriander (7.9 ± 1.0), and purslane (7.0 ± 0.9) while the less preferred were cress (3.9 ± 0.8), mibuna (3.6 ± 0.8), and amaranth (2.5 ± 0.8). Finally, as concerns the overall eating quality, wide heterogeneity existed among microgreens, with both Swiss chard and coriander benefitting a very high score (8.1 ± 0.9) while on the opposite, amaranth showed the lowest score (3.0 ± 0.7).
3.2. Exploratory Factor Analysis (EFA) and PLS-SEM Measurement Model
The analysis in this sub-section aimed to identify a possible relation between sensory attributes and consumer WTC (acceptability). In order to pursue this objective, an explanatory factor analysis (EFA) was carried out on the sensory attributes in order to identify the main latent sensory dimensions characterizing microgreens tasting. EFA identified two main latent constructs: factor loadings are shown in the second and third columns of Table 3
, while the last column summarizes the fraction of the information of each sensory attribute not taken into account by the two factors (uniqueness). The first latent construct (Factor 1) was positively correlated with the Intensity of Astringency, Heat, and Sourness. These three sensory attributes were strictly associated with each-other in a unique dimension that was termed as “Sourness and Heat”. Similarly, the second dimension was positively associated to the intensity of “Bitterness and Grassy”, and (coherently) negatively with sweetness. Accordingly, this second dimension can be named as “Bitterness and Grassy”.
The identified relationships among sensory attributes, however, need to be confirmed through the measurement model of the PLS-SEM in which “Sourness and Heat” and “Bitterness and Grassy” constructs are ex-ante structured according to the EFA results. Moreover, the acceptability constructs will be developed on the basis of the information on the acceptability scores given by consumers for the four separate attributes: appearance, flavor, texture, and overall eating quality.
The PLS-SEM model, and its main results, are summarized in Figure 2
. Measurement model output is shown in Table 4
, presenting the standardized loadings interpretable as correlation between the latent constructs with each related sensory attribute. The results confirmed that “Sourness and Heat” dimension is indeed well associated with three sensory attributes, astringency (0.653), heat (0.511), and sourness (0.833), while the texture and aroma sensory attributes play a very limited role. On the other side, “Bitterness and Grassy” is mainly characterized by bitterness (0.725) and sweetness (−0853) sensory attributes rather than grassy (0.425). Similarly, the WTC construct is mainly characterized by flavor (0.936), texture (0.867), and the overall eating quality attributes (0.952) while the role of the “appearance” in affecting the WTC seems relatively marginal (0.477).
plots for each of the 12 microgreens the mean and the 95% confidence intervals of the three latent constructs as calculated by PLS-SEM. A preliminary examination of the figure indicates that Swiss chard and coriander scored the higher level of acceptability while for almost all the considered microgreens, a higher (lower) value of acceptability is associated to a lower (higher) value of “Sourness and Heat”. The relation between “Bitterness and Grassy” and acceptability seems a little bit less direct and deserve a specific examination through the estimated PLS-SEM standardized path coefficients. Indeed, they indicate the existing statistical relations between sensory attributes and consumer acceptability. The results in Figure 2
showed that both the sensorial dimensions negatively affected the consumers WTC of microgreens (path coefficient of sourness and heat equal to −0.312; path coefficient of bitterness and grassy equal to −0.278). In other words, the acceptability (WTC) of microgreens decreased when the perceived sensorial intensity of bitterness and sourness increased.
represents graphically the estimated relations between the two main sensory dimensions experienced by our consumer sample group with the acceptability of microgreens species. In particular, Swiss chard (indicated with number 12 in Figure 4
) is the most appreciated by participants followed by coriander (indicated with number 10). Both species are characterized by low score of intensity in the two main sensorial dimensions. Conversely, mibuna, cress, and amaranth (numbers 5, 6, and 7 in Figure 2
) are the less appreciated ones, being characterized by the highest intensity of “Bitterness and Grassy” and “Sourness and Heat”.
The sensory attributes of 12 microgreens species were analyzed through a consumer test, and based on the experimental data, a specific PLS-SEM model was developed to link sensorial attributes to consumer acceptability.
Our findings showed that consumer acceptability of the 12 considered microgreens was largely influenced by their sensory characteristics as well as by their visual appearance. It is well documented in the literature that the appearance of food products massively influences consumer choices, providing in the case of vegetables, direct quality signals to the consumer on their naturalness and freshness [31
]. In our study, appearance scores of the assessed microgreens were consistently greater (except for purslane) than those concerning texture and flavor. This outcome is not completely unexpected, since recent studies attributed high scores of microgreens’ acceptability to appearance [8
]. Additionally, our results provide substantial evidence of the high potential for microgreens to be used as garnishes in enhancing the overall visual appearance of prepared meals. Nonetheless, Michell et al. [8
] stressed the importance of using microgreens in a balanced way, considering their impact on the overall taste of the meal. Indeed, once tasted, the overall acceptability of the analyzed microgreens mainly depends on some specific sensory attributes. This result is in line with the findings of Tan et al. [6
], who indicated that broccoli microgreens grown in diverse methods, had different taste, smell, and appearance, which contributed to consumer perception of microgreens. Indeed, flavor-related characteristics predict the best the consumer preferences for overall eating quality.
Therefore, sensory characteristics play a crucial role in affecting consumer preferences. Previous literature indicated how the latter strongly depends on the biochemical composition of microgreens which, in turn, is ruled by the genotype, developmental stage, or maturity level of the plant, pre-harvest conditions and finally by the post-harvest treatments. For instance, Talavera-Bianchi [25
] concluded that by analyzing the sensory characteristics of pak choi, that many attributes such as crispness, texture, green-grassy/leafy, and bitterness had lower intensities in earlier stages than in older plants. Similarly, Oruna-Concha et al. [27
] showed that coriander as microgreens contained significantly higher concentrations of phenolic compounds and terpenes and a more intense bitter/sweet taste compared to the mature stage. Finally, Dalal et al. [47
] demonstrated that sensory characteristics of microgreens are heavily influenced by post-harvest and packaging treatments showing a progressive decrease of acceptability due to change in sensory attributes during storage.
In order to consider the above-mentioned framework, all the 12 microgreens species were tasted by consumers at the same stage of development (emergence of the first two true leaves), thereby our analyses focused on analyzing explicitly the influence of genotype. Of the 12 assessed microgreens species, five showed a satisfactory (equal or greater than 7.5) overall acceptability (Swiss chard, coriander, komatsuna, pak choi, tatsoi), while only three (amaranth, mibuna, and cress) recorded a score completely unsatisfactory (lower than 5). Based on the work of Kyriacou et al. [9
], amaranth, mibuna, and cress are rich in polyphenols that confer the heat intensity and the astringency level. According the same the authors, amaranth is rich in Mg and cress is rich in vitamin C, which is behind the metallic taste in the mouth. Moreover, mibuna and cress are rich in sulphate that is responsible of the bitterness. These attributes are the cause of the low overall acceptability of these three species (score < 5). Our statistical analysis indicated that the observed differences in microgreens acceptability depended on two main sensory dimensions experienced through the consumer test: (i) astringency/sourness and (ii) bitterness. Particularly, the lower the astringency, sourness, and bitterness, the higher the consumer acceptability of microgreens.
Although there are only a few studies about consumer acceptability of microgreens, these results are consistent with previous studies in which the bitterness and astringency attributes represent important factors for consumers to reject vegetables [11
]. Appreciating the nutritive attributes of quality, necessitates that consumers familiarize their perception of palatability to encompass fruits and vegetables of conventionally less agreeable, more astringent, bitter, and sour sensory profile [48
]. High concentrations of chemopreventive phytonutrients tend to characterize foods less pleasant or familiar in taste, which constitutes a barrier to more diversifying the genetic basis of resources utilized for food production [49
]. For instance, Senevirathne et al. [28
] evaluated the sensory characteristics of 10 microgreens species and while lettuce and carrot received the highest preference, radish that is particularly bitter and astringent due to the glucosinolates and polyphenols compounds, received the lowest preference. Similarly, in our consumer test, mibuna and cress showed the lowest acceptance and the highest level of astringency and bitterness. Conversely, Swiss chard, as well as coriander, which showed low levels of bitterness and astringency, were the most appreciated by consumers. These results can be compared with those reported by Xiao et al. [11
] that identified the same negative relation between the overall eating quality of microgreens with some sensory characteristics connected to the high phenolic content, that are the same to what we identified: sourness, astringency, and bitterness. In particular, authors identified the bull’s blood beet (characterized by the lowest intensity in sourness, astringency, and bitterness) as the most appreciated microgreens by the consumer test while peppercress (characterized by the highest intensity in sourness, astringency, and bitterness) had the lowest acceptability.
Moreover, several studies have demonstrated that consumers in Western countries have a generalized aversion to food with a bitter taste [21
]. The main explanations behind this aversion seem to be associated to the human evolution process, since bitterness in nature indicates possibly dangerous ingredients to health [50
]. However, bitterness as well as astringency are also associated, to various biochemicals that are beneficial to human health, contemporarily with consumer demand for healthy products increasing over time [51
]. Consumer interest in healthy food can be mostly explained by the exponential growth of lifestyle related diseases (e.g., obesity, diabetes) specifically dietary related [20
]. To this extent, microgreens can be considered as ideal candidates for meeting consumer request for healthier eating beyond their biochemical compounds content, and rather their perceived naturalness. The latter is explained by the fact that microgreens are grown and marketed without the use of synthetic substances that are considered by consumers to pose health risks. Microgreens perceived naturalness depends also on their minimal processing requirements, while human interventions, contact, and intense processing stages may reduce the perceived naturalness, and consequently healthiness of food [52
]. These attributes, if well communicated to consumers, may contribute significantly to the market success of microgreens.