Consumer testing is crucial for the development of a product and proving that it has met presumed acceptance standards [117]. Sensory evaluation is a popular tool that could indicate consumers’ possible reactions to proffered cookies. In fact, the functionality of a product is not always a sufficient reason to buy shortbread cookies if the sensory quality is not satisfactory. In recently published papers, parameters such as taste, texture, aroma, aftertaste, and important overall acceptability are most often considered [45,106]. A nine-point hedonic scale is mainly used for consumers’ acceptance evaluation of different food products [38]. The quality, intensity, or type of sensory attributes are usually examined organoleptically by panels of trained testers on five- and ten-point scales [21,38]. Purchase intention for enriched cookies could be determined using a seven-point structured scale [117]. The physical and chemical characteristics of shortbread are related to sensory quality and consumer acceptability. Changes in these factors were demonstrated by the variability in sensory evaluations in recent years’ papers.

In a study by Borczak et al. [21], a trained group of panelists organoleptically evaluated (on a five-point scale) shortbread cookies enriched with fruit powders from elderberry, rosehip, chokeberry, sea buckthorn, hawthorn, and rowan. The following factors were considered quality parameters: taste (0.25), shape (0.2), aroma (0.2), surface (0.15), color (0.1), and consistency (0.1). It was found that the baked products enriched with rosehips received the total best score (4.40 points) when compared to the control sample (4.14 points). The cookies with the rowan additive received a high rating (4.19 points), which was not significantly different from those without the supplement. Although the other fortified products received a lower score than the control, they obtained a more-than-satisfactory rating. The panelists gave similar approval ratings to the tastiness and flavor of all tested cookies, except for the elderberry and hawthorn cookies, which were not as well-liked as other products, including the control. The appearance of the chokeberry, hawthorn, sea buckthorn, and elderberry cookies received lower ratings compared to the control. The color ratings of the enriched cookies, on the other hand, were not significantly different from those of unenriched products. However, this study did not establish the optimal addition of the analyzed by-products to the cookies, and the evaluation was conducted with the same percentage of each fruit powder to the dough.

Other authors [38] conducted a sensory panel evaluation of cookies supplemented with freeze-dried chokeberry using qualitative descriptive analysis. The intensity of the selected attributes was tested on a scale of 1 to 10. Furthermore, a hedonic consumer test was conducted based on a nine-point hedonic scale. Experts positively assessed the quality of the enriched shortbreads with 5%, 10%, and 15% of freeze-dried chokeberry, with scores of 7.4, 8.4, and 6.3, respectively. With increasing additive proportion, the cookies became gradually darker, which was related to the anthocyanin pigments present in the raw material. Moreover, a sweet taste was clearly perceptible at the 5% inclusion level. Increasing the chokeberry powder proportion improved the astringency, chokeberry flavor, and sour flavor intensity. The addition of 5 and 10% fruit resulted in crispness values remaining high, which was similar to the results for the control. Moreover, cookies with 15% of chokeberry powder showed lower crispness, possibly related to the reduced fat content of the final product. The authors found that the sample fortified with 10% powder balanced all the analyzed characteristics with a significant overall quality. Interestingly, the concentration of chokeberry had no significant effect on the overall consumer acceptability of the cookies. The authors’ meticulous examination of the sensory properties of the cookies in this study is noteworthy, but they did not carry out a consumer hedonic test of the control cookies (without the chokeberry powder).

In another study [41], a team of experienced panelists tested the intensity of sensory attributes of Japanese quince-powder-enriched cookies using an unstructured 10 cm linear scale from “no intensity” to “very high intensity.” Additionally, consumer acceptability of the fortified products was assessed on a nine-point hedonic scale. Both analyses were conducted 24 h after baking and after 16 weeks of storage. Sour and lemon flavor intensity ratings improved with increasing lyophilized quince, which is related to the richness of the volatile compounds of the raw material. Citrus and sour flavor intensity scores also increased with the additive, whereas buttery and sweet flavors decreased. The addition of Japanese quince also resulted in a decrease in the cookies’ fracturability, possibly due to the high concentration of fiber, including pectin and cellulose-like polysaccharides. Generally, cookies containing 1 and 1.5% Japanese quince were more acceptable to consumers than control products and those containing 6 and 9% [41]. The storage period generally affected the evaluation of the many sensory attributes’ intensity, mainly reducing their value. The sensory panel identified a decrease in the intensity of citrus, sour, and buttery flavors, as well as buttery and aromatic flavors, although not in all samples. The cookies also became less crumbly, slightly gummy, and softer under storage, mainly those enriched with a high powder concentration (6 and 9%). The authors pointed out this might be linked to the enhancement of hydration properties caused by the presence of fiber, which consequently leads to more interactions with water through hydrogen bonds. However, in the presented study, the authors stored the cookies in cardboard boxes without indicating the relative humidity during storage, which could have caused an increase in their moisture content and consequently changes in their physicochemical properties, negatively affecting the sensory acceptability of the cookies. The sensory evaluation of the cookies containing jujube (Zizyphus lotus) confirmed the colorimetric measurements and the instrumental data related to hardness and crispness. Sensory acceptability expressed by color and taste parameters increased by jujube fruit enrichment. On the other hand, texture and aftertaste evaluation were reduced after the powder introduction. Most importantly, the overall acceptability of the cookies did not change significantly after enrichment, except for a reduction in the value of this parameter in products containing 15% of jujube powder [45]. The sensory evaluation (using a nine-point hedonic scale by semi-trained judges) showed that the texture and color parameters of the dragon-fruit-enriched cookies had lower scores if compared to the control [50]. The differences may be linked to the high water absorption and the dark brown color of the powdered dragon fruit. The panelists did not tolerate it. The taste of the cookies improved slightly, due to the mild Kiwi-ish taste. In another study [54], under the influence of papaya powder fortification, the cookies were similarly rated by consumers in crispness and general acceptability when compared to the product without the additive. On the other hand, taste ratings decreased slightly from a score of 8 to 7 (on a nine-point hedonic scale). Furthermore, the overall acceptability of cookies containing date palm fruit powder in the sensory test was not significantly affected by date palm fruit, except for 50% supplementation, compared to the control (refined flour cookie with no additive) or cookies made with whole flour alone [56].

In summary of the above works, it can be concluded that enriching cookies with powdered fruits has a significant effect on their sensory characteristics. Therefore, a nine-point hedonic test is most often applied to evaluate consumer preferences for cookies enriched with these additives, as it allows for more nuanced and differentiated ratings. This test enables participants to express subtle differences in their preferences, providing more precise information for researchers and producers.

Many studies in recent years have also focused on the sensory properties evaluation of cookies enriched with FBP. In the work conducted by Rocha Parra et al. [118], a group of untrained consumers participated in the sensory assessment of the 15% apple pomace cookies, using a nine-point hedonic scale. There were no significant differences in appearance, aroma, texture, or overall appreciation scores. However, the additive effect was positive on taste, regardless of the size of the particles used. Zlatanović et al. [60] assessed the sensory properties of apple pomace powder cookies using a point method on a scale from 0 to 5, where parameters regarding appearance, texture, and taste were analyzed. In general, cookies enriched with coarse flour received higher ratings from consumers than those enriched with fine flour. The differences in particle size distribution and processing of the apple pomace in these two studies may have led to a noticeable difference in the effect of particle size on the sensory evaluations of the cookies. Baked products enriched with 25% apple pomace coarse flour were rated the highest in overall sensory quality [60]. They scored highest in all tested parameters, and their values were greater or not significantly different from the results of the control sample. The cookies with 25% powder additive showed a standard appearance, adequate aroma, and optimal texture. Interestingly, the product supplemented with 50% coarse apple pomace flour also was within “excellent quality”. The other samples and the control were of “very good quality”. The products containing 25 and 50% pomace additives showed the slightest change in sensory properties over the 12-month storage period. Following the sensory quality assessment, cookies containing 50% of coarse powder were finally selected and used for acceptance testing on a nine-point hedonic scale. During the consumer acceptance test, the respondents liked these products, with average hedonic scores above 6 (6.2 ± 1.8). Moreover, the authors identified two significant consumer groups, the first of which felt that the cookies had “too little apple aroma” (41.7% of respondents), while the second admitted that the final product was “not sweet enough” (32.2% of respondents). In another study, ratings for flavor, mouthfeel, texture, and overall acceptability decreased with increasing apple pomace levels [119]. The highest notes for color and flavor were found for 10% powdered cookies, and ultimately, this quantity of additive was deemed optimal. Based on the studies mentioned, it can be concluded that incorporating apple by-products in cookies generally has a positive effect on sensory properties, but this can vary depending on the type and amount of addition. The studies [60,118] revealed that adding 15–50% of apple pomace powder to cookies did not significantly affect aroma, texture, and overall evaluation, and even improved taste. However, another study [119] found that supplementation levels greater than 10% were unacceptable from the consumer’s point of view. The aforementioned differences may be due to variations in apple pomace processing (different temperatures, drying time, and degree of grinding), cookie composition and preparation, heat treatment and exposure time, as well as the individual taste preferences of each group of panelists participating in the study. Therefore, further investigation is needed to determine the optimal amount and form of apple pomace for use in cookies to achieve the best sensory attributes without compromising the texture or other characteristics of the final product.

Another interesting addition to consider is apple peel. In a study by Nakov et al. [62], during the sensory analytical tests (on a five-point scale), the apple peel powder had a positive impact on the aroma and flavor scores of the cookies, while not damaging the smell, appearance, or internal structure ratings. The control sample obtained better grades than the other shortbreads only with regard to texture, except for the cookies with 24% supplementation. The products enriched with 24% apple peel demonstrated the best ratings for flavor, appearance, internal structure, texture, and taste, compared to other supplemented cookies and the control. Substituting wheat flour with 16% and 32% fruit additives also yielded a positive impact on flavor evaluations. In general, it can be inferred that substituting wheat flour with 24% apple peel powder in shortbread pastries may present a trade-off between their chemical and physical properties and sensory evaluation. As the contribution (5, 10, 15, and 20%) of orange peel powder to the cookies increased, the sensory parameter values for color, appearance, aroma, texture, taste, and overall acceptability decreased, but the differences were not significant [72]. Enriched products’ ratings for overall acceptability ranged from 7.30 to 8.30, demonstrating that the semi-educated judges ‘moderately liked’ to ‘very much liked’ the cookies with the additive. The findings suggest that the substitution of wheat flour with powdered orange peel at levels up to 20% can confer functional benefits to cookies while maintaining their sensory attributes. Interestingly, cookies with the addition of 2.5% bergamot pulp powder were most favored by the panelists in overall acceptance when compared to the control and other levels of fortification products [79]. Samples supplemented with 10 and 15% bergamot pulp flour were significantly less acceptable, related to their bitter taste. During the sensory analysis conducted by trained panelists (on a nine-point hedonic scale), the increase in pomace and kinnow peel led to a significant reduction in the flavor and texture notes [120]. Ratings observed for color showed no substantial difference among products enriched with pomace, peels, and the control. The cookies with 10% peel and 5% pomace showed the best overall acceptability, with scores of 8.33 and 8.33, respectively. The outcomes of the aforementioned studies demonstrate that bergamot pulp, as well as kinnow peel and pomace powders, may serve as beneficial supplements for cookies with good sensory acceptance.

Tarasevičienė et al. [65] used a nine-point hedonic scale in the sensory evaluation. The shortbread cookies with the addition of 20% strawberry pomace scored highest in color (7.83 points), aroma (7.83 points), and texture (7.33 points). However, products with 10% raspberry pomace flour were the tastiest (7.33 points). On the contrary, cookies that were enriched with 15% red currant pomace flour received lower ratings in terms of color, aroma, texture, and flavor, as compared to other enriched cookies and the control group. Consequently, it can be deduced that strawberry and raspberry pomace flours would make more suitable functional additives for shortbreads with regard to consumer acceptance, which is a crucial factor that affects purchase decisions. In other studies [29], the extra addition of passion fruit epicarp flour did not significantly modify the flavor ratings of the cookies assigned by the trained panelists on a nine-point hedonic scale. In addition, the flavor, texture, and overall acceptability scores of the products with 3 and 6% admixture were not considerably different from those of the control. Only the supplement at the level of 9% significantly reduced the value of these parameters. The aroma of enriched cookies was judged worse than the control due to astringency. The results of the appearance evaluation of the cookies did not vary significantly between the baked product without the additive and the one containing 3% of epicarp. The 6 and 9% addition of fruit flour caused a reduction in this parameter, which correlates with the markedly darker color of the cookies. Passion fruit epicarp powder can serve as a suitable functional additive for shortbread pastries at levels of 3% and 6%, providing added nutritional and health-promoting benefits while maintaining most sensory attributes at acceptable levels. Based on the results of the preference ranking test in other studies [121], it was determined that there were no discernible differences between the control cookies and those that were fortified with by-products derived from pineapple, apple, and melon [121]. Consequently, cookies that contained the highest concentration of the supplement (15%) were chosen for the acceptance test. The addition of fruit powder did not have any impact on the ratings of the appearance and flavor of the samples. However, pineapple and apple powder improved the flavor of the cookies, whereas the addition of melon rind had an adverse effect, which may have been attributable to the acidity and bitterness of the additive. Ratings for texture and overall acceptability were comparable for all additives, with the exception of melon by-product powder, which had a negative impact on the scores. Moreover, the cookies with a 15% pineapple substitution achieved the highest scores in sensory evaluation among the tested samples. To summarize, based on the findings of this study, it can be concluded that pineapple and apple by-product powders are suitable for fortifying shortbread cookies at a concentration of 15%. However, further research is necessary to determine the optimal amount of melon peel additive to enhance the sensory characteristics of the product.

Sensory evaluation (on a nine-point hedonic scale) revealed that cookies containing 4 and 6% of grape pomace were best accepted by the partially trained panelists (also compared to the control) [96]. The fortified products with 2% powder showed an indifferent taste compared to the control (pomace was not perceptible). In contrast, cookies containing 8% powder demonstrated a bitter taste and worse texture. In other studies [97], the acceptance test on a nine-point hedonic scale was applied. The purchase intention of the cookies manufactured with grape pomace, on the other hand, was determined using a seven-point structured scale, ranging from 7 (I would definitely buy) to 1 (I would definitely not buy). There were positive responses from panelists regarding the enriched products, highlighting the excellent acceptance of cookies containing 19.8% pomace flour from three grape varieties. The authors revealed a high frequency of responses on the “I liked it a lot” scale for odor (31.2%), texture (30.4%), taste (25%), and overall impression (28%). The positive response frequency was highest for the purchase intention attribute and was 55.2%. The most common reply was ‘buy’ (six points on a structured scale) and the negative response rate was very low (15.2%) [97]. Grape seeds could be incorporated into the cookies at a level of 5% without significantly impacting their overall acceptability, based on the sensory evaluation conducted by Kuchtová et al. [23]. In contrast, the ratings for this parameter decreased with increasing grape peel levels. It can be inferred that consumers may generally show interest in purchasing cookies enriched with grape by-products. Moreover, if added at optimal concentrations, pomace and seeds may have a neutral or positive impact on the sensory properties of shortbreads. The aforementioned studies propose that substituting wheat flour with pomace up to a maximum level of 6% and incorporating seeds at a concentration of 5% could yield a final product with a high level of consumer acceptance.

Sensory evaluation of shortbread cookies enriched with sea buckthorn by-product powder was performed using a scale of 1.0 to 10 [122]. Panelists found the cookies containing 20% of the additive to have the most pleasing sea buckthorn and sour flavors. Moreover, the control cookies were rated as the hardest and crumbly. In the sensory evaluation of structural properties, hardness decreased with increasing sea buckthorn biomass content, as confirmed by the results obtained with the texture analyzer. Most importantly, the highest overall acceptability was achieved by cookies that consisted of 15% powder compared to products without the additive. In other studies [101], semi-trained judges, during the organoleptic evaluation (using a nine-point hedonic scale), generally rated the unfortified cookies higher in flavor, aroma, color, and overall acceptability attributes, compared to the chiku pomace products, especially at higher levels of supplementation. The authors observed the opposite effect with the texture of the products, but the differences between all samples were not significant. The results of this study showed that the incorporation of chiku fruit pomace into cookies at concentrations of up to 7% resulted in the same outcomes in terms of taste, aroma, and texture when compared to the control. The cake fortified with 7% powder demonstrated the highest overall acceptability in organoleptic tests, indicating an optimal level of supplementation that can reconcile the health-promoting effects of the additive with the consumer acceptability of the end product.

Based on a preliminary sensory evaluation on a nine-point hedonic scale, the authors of another study [106] found that taste and texture scores decreased with increasing goji pomace content. Incorporation at a level of 10% did not significantly change the acceptability of the appearance of the cookies to consumers, while the others were less liked. The aftertaste and the type of aftertaste were measured on a three-point scale. Cookies with the highest level of incorporation (40%) had the lowest ratings of taste and texture, which were associated with a strong, unpleasant, bitter, and astringent aftertaste, soft texture, and fibrous/grainy taste. In general, cookies can be enriched with goji berry by-product powder up to a concentration of 10% without a significant impact on consumer perception of the products. However, if a higher level of supplementation is desired, further experiments are necessary to improve the organoleptic characteristics of the final cookies. The sensory properties of shortbread pastries were evaluated by other researchers who examined the impact of kiwi powder and its by-products [109]. The 5% and 10% content of both edible portions and kiwi fruit peels did not significantly reduce the notes (on a nine-point hedonic scale) regarding appearance, compared to the control. The cookies with the 15% kiwi fruit edible portion also obtained the highest scores for odor (8.81) among the samples, which is related to the presence of volatile constituents in the fruit. The additions of 5, 10, and 15% of edible portion powder and 5 and 10% of peel caused no significant differences in the flavor acceptability of the cookies. Texture ratings were also similar to those of the control, except for the highest levels of supplementation (20% of edible portion and 15 and 20% of peels). The overall acceptability of cookies containing 5, 10, and 15% edible portion and 5 and 10% of peels was not significantly different compared to the control. Replacing wheat flour with kiwi fruit powder (including the edible part and peel) at levels of 10% and 15% resulted in an improvement in the antioxidant activity and nutritional quality of the cookies while maintaining acceptable sensory properties. The ratings of the cookies enriched with 7.5% cactus pear peel showed no significant difference in comparison to the control sample, as confirmed by the sensory evaluation (on a nine-point hedonic scale) [110]. Ratings of these cookies in appearance, color, taste, flavor, and, most importantly, overall acceptability indicated that the panelists liked them very much, with values of 8.1, 8.15, 8.15, 8.1, and 8.1, respectively. In addition, the researchers demonstrated that a product containing 10% cactus pear peel powder was not acceptable. The aforementioned findings suggest that the incorporation of cactus pear peel powder into cakes at a concentration of 7.5% may strike a balance between the concentration of bioactive compounds and the consumer acceptability of the final product.

For sensory evaluation of cookies enriched with fresh lemon peel, extract from lemon pomace, and a mix of them, a preference test was performed by judges experienced in this type of analysis [74]. The cookies acquired a bitter taste under the influence of the enrichment. In addition, the lemon aroma was more strongly perceptible in the supplemented products, indicating good retention of the aromatic components during baking. The replacement of skimmed milk with lemon pomace extract in the cookies resulted in lower scores for the superficial brown color attribute. It may be related to the less intense Maillard reaction and caramelization caused by the proteins and lactose reduction in the dough. Cookies with added extract were also the crispiest compared to other enriched products, relating to the lowest water activity (0.23) of the mentioned cookies. Incorporating lemon peel and lemon pomace extract into cookie formulations can increase their bioactive compound content without significantly impacting their overall appearance or texture, with the exception of color. This results in acceptable products with improved functional properties. Further research could explore the use of lemon by-products at varying levels of incorporation to determine the optimal concentration.

Considering the reports above, the enrichment of shortbread cookies with powdered and dried fruits and FBP almost always affects their sensory attributes. Fruit additives usually change the flavor and taste, and consequently decides the overall acceptability of cookies.

Table 1 summarizes the effect of the supplementation of shortbread cookies with fruits and FBP on their chemical composition, antioxidant properties, and sensory characteristics of the cookies. In most of the studies cited, the authors determined the optimal addition of fruits to cookies based on sensory evaluation results. However, in studies [21,22,65,74,82], it was not specified, which diminishes the practical value of these works. Furthermore, in the study [61], cookies made with the addition of blueberry powder were not acceptable to consumers. However, the authors only used a single level of addition. Moreover, baking conditions for the cookies are also significant, especially considering the content of bioactive compounds and the antioxidant activity of the obtained cookies. The majority of authors included the temperature and baking time in their studies. However, in studies [61,65,96], the baking conditions were not described. The main benefit of enriching cookies with fruits and FBP, as indicated by the authors mentioned in Table 1, is the increase in phenolic compound content and the accompanying enhanced antioxidant activity, along with an increase in fiber content in the cookies.