The incorporation of CT in the scone dough was effective, readily integrating with the other ingredients to produce a dough with suitable properties. Consistent with this observation, Gu et al. (2020) reported that CT exhibits high water retention capacity (7.9 g g^-1), water solubility (18%), oil retention capacity (4.5 g g^-1), and swelling capacity (12.4 mL g^-1), due to its dietary fiber content, which likely facilitated its convenient addition and homogeneous mixing with the other components.

As shown in Table 2, the protein and ash content do not exhibit statistically significant differences between the analyzed samples. In contrast, the fat content was significantly higher (P<0.05) in the control sample and demonstrated a reduction with increasing CT incorporation. The carbohydrate content was significantly higher (P<0.05) in sample M1. Statistically significant differences (P<0.05) were observed in the total dietary fiber (TDF) content, with M1 displaying the lowest value and M4 the highest. A similar trend was observed for soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). The caloric intake is significantly higher in M1 and significantly lower in M4 (P<0.05).

Table 2

Eliminating milk from formulations and substituting part of the margarine with tomato peels resulted in a significant decrease in fat content of 32, 38, and 40% in M1, M2, and M3, respectively, compared to M1. The incorporation of CT also led to a reduction in caloric intake in M2, M3, and M4 by 11, 12, and 14%, respectively. Furthermore, a significant increase in dietary fiber, primarily in IDF, was observed. A negative correlation was found between the CT content in scones and both fat and energy (R²=0.994, 0.960, and 0.780, respectively). From a nutritional perspective, scone formulations incorporating CT appear healthier due to their lower fat, carbohydrate, and caloric content, coupled with a higher DF contribution. These findings align with other studies demonstrating that the addition of vegetable peels can reduce caloric intake while enhancing dietary fiber content (Martins et al. 2017; Quitral et al. 2022).

The carotenoid content in CT was measured at 15.5 mg 100 g^-1, and its concentration in the scone samples increased with higher CT concentrations in the formulations. No statistically significant differences in carotenoid content were observed among the scone samples containing CT. Notably, the total carotenoid concentration in CT is higher than that reported by Beltrán et al. (2012) for common raw tomato (2.66 mg 100 g^-1) and by Pataro et al. (2018) for tomato skin (10 mg 100 g^-1). It is important to note that the carotenoid content in tomatoes is generally higher in the peel than in the pulp (Meléndez-Martínez et al. 2023).

Carotenoids are susceptible to degradation by heat; the baking temperature of 175 °C is relatively high, likely to affect the carotenoid concentration in the scone samples. Burešová et al. (2021) reported a 26% loss of carotenoids in bread baked al 220 °C. Elevated temperatures can induce degradation, isomerization, and oxidation of carotenoids (Shen et al. 2015). Conversely, thermal processing of food can lead to interaction with other lipophilic constituents, potentially modifying the quantity of carotenoids released from the food matrix (Kotíková et al. 2016).

The incorporation of tomato peels into flour-based products increases the carotenoid concentration, offering potential health benefits due to their antioxidant properties and provitamin A activity. Furthermore, they impart reddish hues to foods, which can be a desirable attribute (Salanţă and Fărcaş 2024). The addition of peels or other fruit and vegetable by-products to baked goods introduces bioactive compounds, such as polyphenols and carotenoids, thereby enhancing the antioxidant capacity of the products (Santos et al. 2022).

Table 3 presents the luminosity (L*), which shows no significant differences between the samples. However, the a* (redness) and b* (yellowness) values increased noticeably with CT incorporation. Chroma (C*) and hue angle (H*) were also higher in samples containing CT. The color difference (ΔE*) compared to the control sample did not show significant differences between among the CT-containing samples.

Table 3

The instrumental color analysis results are consistent with a study on bread incorporating tomato pomace, which also reported an increase in a* and b* values (Martins et al. 2017). The intense red color of tomatoes and their peels contributes to this coloration in the final products. The observed increase in a* and b* aligns with the findings of Bhat and Ahsan (2015) in cookies containing tomato pomace powder (OTP). However, their study reported a decrease in L* with OTP addition, which the authors attributed to the reduced flour concentrations as OTP concentration increased.

By incorporating CT in scones, the specific volume decreases proportionally, as seen in Table 3 and Figure 1. Tomato peel contains dietary fiber, which weakens the structure of gluten, causing less CO₂ retention in the scones (Bora et al. 2019).

Figure 1

Figure 1 presents the differences in color and shape of the samples. The color differences in the crumb are more noticeable than in the crust. The specific volume of the samples is lower than the values reported by other researchers for bread, which typically exceed 3 cc g^-1 (Mudgil et al. 2016; Ding et al. 2019). However, the results of this study are comparable to those observed in gluten-free bread and muffins by Gostin (2019) and Bora et al. (2019). According to Burton and Lightowler (2006), this reduction in specific volume could be advantageous as it is associated with a lower glycemic index and increased satiety.

A strong negative correlation (-0.946) was observed between the specific volume of the scones and increasing CT concentration. This phenomenon can be attributed to the incorporation of dietary fiber from CT. Specific volume is a critical characteristic of baked products, influencing the perception of a light and spongy texture. It is primarily determined by gas production and retention during baking, a process largely dependent on gluten development. The samples containing CT exhibited significantly higher DF content, and increasing its concentration in the dough has been shown to reduce the rate of hydration and gluten development (Xu et al. 2021), consequently affecting the specific volume. Furthermore, the reduction in fat content, which plays a crucial role in air bubble incorporation and contributes to increased volume and a porous structure, also likely influenced this result. Fat also aids in moisture retention, leading to a moist and tender crumb, and interacts with starch to form lipid-amylose complexes, thereby inhibiting retrogradation (Garvey et al. 2020).

Overall, the samples demonstrated high sensory acceptability, as illustrated in Figure 2. Appearance was rated significantly higher (P<0.05) in M1 and M4. No significant differences were found in the color of the samples. Regarding aroma, significant differences (P<0.05) were observed, with M4 receiving the highest acceptability score and M2 the lowest. Flavor acceptability was significantly higher (P<0.05) in M1, M2, and M4. Texture was also rated significantly higher (P<0.05) in M1 and M4.

Figure 2

Despite the variations in individual attributes, all samples exhibited high overall sensory acceptability. No significant correlation was found between the amount of CT incorporated into the samples and the ratings of the sensory attributes evaluated using a 9-point hedonic scale. Based on the overall evaluation, sample M4 was the preferred formulation.

In contrast to the results obtained in this study, Bhat et al. (2015) reported that the incorporation of tomato pomace powder negatively impacted the sensory parameters of appearance, color, texture, and flavor in cookies, recommending a maximum addition of 5%. In this study, the addition of fresh tomato peel, without dehydration, as a substitute for milk and part of margarine, yielded more favorable sensory outcomes.

Based on the results presented in Table 4, sample M4 exhibits a higher proportion of saturated fatty acids compared to M1. The amount of monounsaturated fatty acids is similar between the samples, while polyunsaturated fatty acids are present at a slightly higher concentration in M1. Notably, sample M4 contains linolenic acid, whereas trans fatty acid content is below 0.1% in both samples.

Table 4

The fatty acid profile reveals that in M4, saturated fatty acids increased by 18% compared to the control sample, while monounsaturated and polyunsaturated fatty acids decreased by 6.4 and 14.4%, respectively. Different results might have been anticipated, given that M4 is formulated without milk, a significant source of saturated fatty acids, and relatively low in polyunsaturated fatty acids. However, margarine, an ingredient in M4, does contribute saturated fatty acids. Consequently, while the concentration of SFAs in M4 is lower compared to milk-containing formulations, their presence is still attributable to the inclusion of margarine. Linolenic acid was detected in sample M4 but not in M1. Sample M4 had a lower margarine content and did not contain milk; the primary lipid source in this formulation was eggs. Among individual fatty acids, palmitic acid and oleic acid concentrations were 75 and 11% higher in M4 compared to M1, respectively. These fatty acids are constituents of eggs, an ingredient present at a higher ratio to margarine in M4 (1.1:1) than in M1 (0.5:1). The concentration of palmitic acid, oleic acid, and linolenic acid were significantly elevated in M4. According to Elbadrawy and Sello (2016), tomato peel contains 15.2% palmitic acid, 19.1% oleic acid, and 4.3% linolenic acid. The latter two are particularly beneficial for health: oleic acid is associated with a reduced incidence of cardiovascular disease, and linolenic acid is an essential fatty acid and a precursor to EPA and DHA. Tomato peel also contains linoleic acid, another essential fatty acid.

A key strength of this study is its demonstration that vegetable peels can be utilized at the consumer level with minimal processing (simply washing) and still yield positive nutritional and sensory outcomes. Common baked goods like scones often have a high fat content, which can be effectively reduced through the incorporation of vegetable peels, leading to healthier products.

Incorporating fresh tomato peels as an ingredient in scones, substituting part of the margarine and all the milk, yielded favorable outcomes. From a nutritional standpoint, this approach effectively reduced total fat content and caloric intake while increasing dietary fiber. Furthermore, carotenoids were successfully incorporated into the scones. The addition of CT influenced the color, resulting in predominantly red tones and a decrease in luminosity. However, the specific volume was negatively affected, indicating a need to explore alternative strategies to mitigate this issue. Scone samples containing CT demonstrated high sensory acceptability, with sample M4 (containing 30% CT and 50% margarine reduction) identified as the most promising formulation. This sample exhibited significantly high levels of TDF, SDF, and IDF, along with a lower caloric content and a distinct fatty acid profile compared to the control sample M1, notably including linolenic acid. This study contributes to the growing body of knowledge regarding the utilization of vegetable peels, specifically fresh tomato peels, in this case, as functional ingredients in flour-based foods. Future research should focus on investigating methods to enhance the specific volume of scones incorporating CT, determining their shelf life, and evaluating their potential for industrial-scale applications.

The authors have no conflict of interest.