Valorization of Melon (Cucumis melo L.) Peels as Flour for Vegan and Gluten-Free Muffins

Abstract

Losses resulting from food processing have encouraged the search for sustainable alternatives for the use of agro-industrial by-products. Melon is a fruit widely consumed in Brazil, but during its processing, by-products are generated, such as peels. This study utilized yellow melon peels to produce flour and incorporated it into the formulation of vegan and gluten-free muffins. Three muffin formulations were processed, with the partial replacement of rice flour by melon peel flour (MPF): Control (0%), F10 (10%), and F20 (20%). The flour and muffins were characterized according to their physicochemical properties. The muffins were evaluated based on color, texture, expansion factor, height, specific volume, and sensory acceptance. Considering the fiber and ash content (17.38 g/100 g and 10.14 g/100 g, respectively), MPF can be classified as a food with “high fiber and mineral content”. The specific volume of the muffins ranged from 1.403 to 1.756 cm³/g, with the lowest value found for the muffins made with the highest amount of MPF (F20). The muffins with 20% MPF had the lowest expansion factor (1.213 mm) due to the higher amount of fiber (4.45%). The most accepted sample was the F10 formulation (7.21), with an acceptance index of 88.88%.

1. Introduction

Melon belongs to the Cucurbitaceae family, originating from Asia, and comprises subtypes distinguished by their shape, size, and color. It is a prominent fruit in the food market and can be consumed fresh or in ready-to-eat salads [1,2]. In 2023, 862.387 tons of melons were produced in Brazil. In the state of Paraná, this represents an annual production of 2.613 tons [3].

Waste production during food processing is a growing concern. According to the Food and Agriculture Organization (FAO), 1/3 of the world’s food production (1.3 billion tons) is lost or wasted [2]. However, these food by-products are considered a source of essential ingredients for human nutrition due to their nutritional components, including proteins, minerals, bioactive compounds, and fiber. Therefore, many researchers have investigated the conversion of by-products into high-value-added products [2,4,5,6,7,8,9].

Among various agro-industrial by-products, melon processing generates significant residues, such as seeds, peels, and processing residues [10,11]. Sustainable technological alternatives can be utilized, such as the production of flour, which, because it is produced from fruits, makes its production cheaper than for other flour products [12,13]. This flour can be used to create new food products, such as bakery products. Thus, it improves the composition of foods, as the use of unconventional flours can offer a considerable amount of nutrients, including proteins, minerals, bioactive compounds, and fiber [6,7,8,14,15,16,17]. Furthermore, they can be used as an alternative to replace wheat flour or to compose create mixed flour in the preparation of new products, mainly serving people who have dietary restrictions, such as celiac disease and lactose intolerance, or who have chosen to exclude or reduce certain foods, such as vegans [5,18]

Celiac disease is an autoimmune disorder triggered by gluten proteins found in wheat, barley, rye, and malt, leading to intestinal damage in susceptible individuals [19]. Lactose intolerance results from the insufficient digestion of lactose, the primary sugar in milk, causing gastrointestinal symptoms [20].

This work aims to utilize the peel of yellow melons to produce flour and apply it to the preparation of various gluten-free vegan muffin formulations. Additionally, this study aims to provide an innovative solution to reduce food waste, thereby supporting the development of a circular economy.

2. Materials and Methods

2.1. Raw Material

Melon (Cucumis melo L.) peels from the yellow melon cultivar were kindly provided by a local vegetable agro-industry in Colombo, Paraná, Brazil. The samples were transported under refrigerated conditions (8 °C) to preserve their quality prior to analysis (Figure 1).

2.2. Melon Peel Flour (MPF) Preparation

The peels were washed in running water, fractionated, and treated with sodium hypochlorite (100 ppm) for 10 min. After rinsing, they were subjected to an enzyme inhibition treatment process with 5% citric acid for 3 min [21] and rinsed in running water. The sanitized peels were subjected to a drying process in a hot oven with forced air circulation (Luca-82/27, Lucadema) at 65 °C for 17 h. The dried peels were ground using an analytical grinder (A11 Base, Ika) and then sieved through 42-mesh stainless steel sieves (Bertel, Inox 304) to obtain the flour. The flour was then vacuum-packed and stored at −18 °C until the time of analysis (Figure 2).

2.3. Elaboration of the Muffins

Three muffin formulations were prepared with the partial replacement of rice flour and corn starch by MPF: Control (0% MPF), F10 (10% MPF), and F20 (20% MPF). The muffins were produced at the Food Processing Laboratory of the Instituto Federal do Paraná, Colombo Campus, following the methodology of Saraç et al. [22], with the modifications shown in

Table 1. Formulations for gluten-free and vegan muffin production.

Ingredients	Formulations
	Control	F10	F20
Rice flour (g)	95.00	85.50	76.00
Corn starch (g)	47.50	42.75	38.00
Melon peel flour (g)	0.00	14.25	28.50
Sugar (g)	90.00	90.00	90.00
Xanthan gum (g)	0.50	0.50	0.50
Sunflower oil (mL)	30.00	30.00	30.00
Melon peel juice (mL)	140.00	160.00	180.00
Baking powder (g)	4.85	4.85	4.85

Control: formulation without MPF; F10: formulation with 10% MPF; F20: formulation with 20% MPF.

.

Initially, the dry ingredients, except for the baking powder, were mixed. Melon juice was prepared by homogenizing 500 g of melon peels with 100 mL of water for 5 min. The resulting filtrate was then used for muffin preparation. Then, the liquid ingredients were added and homogenized. The homogeneous mixture was left to rest for 20 min at room temperature. After this process, the baking powder was added and lightly homogenized. Finally, the dough was divided into 43 g portions, placed in disposable paper molds, and baked at 175 °C for 17 min. Each formulation yielded eight muffins (Figure 3).

2.4. Physicochemical Characterization of Flour and Muffins

Proximate analyses of the flour and muffins were performed in triplicate using the following standard methods [23]. The moisture content was determined by the oven-drying method at 105 °C to constant mass (method 925.09), the ash content was determined after incineration of the sample in a muffle furnace at 550 °C (method 923.03), the crude protein was determined by the Kjeldahl method using a nitrogen-to-protein conversion factor of 6.25 (method 954.01), and the total lipid content was determined by the Soxhlet extraction method (method 920.39). The crude fiber was determined by the acid-based digestion method (method 962.09), and the available carbohydrates were calculated (100%—all other components). The water activity (Aw) value was determined using an electronic meter (Pre Aqualab, Decagon) at a constant temperature (25.0 ± 0.30 °C).

2.5. Technological Parameters of Muffins

2.5.1. Color

The color of the muffins (crumb and crust) was determined by a portable colorimeter (Check II plus, Datacolor), using the CIEL*a*b* system, in which the luminosity values (L*) vary between zero (black) and one hundred (white) and the values of the chromaticity coordinates a* and b* vary from −a* (green) to +a* (red) and from −b* (blue) to +b* (yellow).

2.5.2. Texture

The texture of the muffins was analyzed using a texture analyzer (TA.XT2, Stable Micro Systems, UK) equipped with an SMS P/36R probe. The parameters used were pre-test speed = 1.0 mm/s, test speed = 2.0 mm/s, post-test speed = 10.0 mm/s, and distance = 8 mm, in accordance with the AACC modified method [24]. The results were expressed in grams.

2.5.3. Diameter and Height Before and After Baking

The diameters and heights of the muffins were determined using a digital caliper (R 500-171-30B, Mitutoyo), and the results were used to calculate the expansion factor.

2.5.4. Apparent Volume

The muffin volume was determined according to the AACC-approved method 10.05.01 (rapeseed displacement test) [24], and its value was used only to determine the density and specific volume.

2.5.5. Expansion Factor

The calculation of expansion factor (EF) values was conducted using the equation below [25]:

$$Expansion factor \left(EF\right)={\displaystyle \frac{\left(D_{after} +H_{after}\right)/2 }{\left(D_{before}+H_{before}\right)/2 }}$$

(1)

where

• D_after = diameter of the muffin after baking (mm);
• H_after = height of the muffin after baking (mm);
• D_before = diameter of the muffin before baking (mm);
• H_before = height of the muffin before baking (mm).

2.5.6. Density

From the apparent volume analysis, the density was calculated by the ratio of the weight of the muffins and their displaced volume, expressed in g/mL:

$$\mathrm{Density}\left(\mathrm{g}/{\mathrm{cm}}^3\right)={\displaystyle \frac{W }{V }}$$

(2)

where

• W = weight of the muffin after baking (g);
• V = apparent volume of the muffin (cm³).

2.5.7. Specific Volume

The specific volume was obtained by the ratio between the apparent volume and the weight of the dough after baking, expressed in cm³/g, in accordance with AACC-approved method 55.50.01 [24], using the following equation:

$$Specific volume \left({\mathrm{cm}}^3/\mathrm{g}\right)= {\displaystyle \frac{V_{apparent} }{W }}$$

(3)

where

• V_apparent = apparent volume of the muffin (cm³);
• W = weight of the muffin after baking (g).

2.6. Microbiological Analysis

Microbiological analyses were defined based on Normative Instruction 161/2022 [26] and RDC 724/2022 [27]. Analyses of presumptive Bacillus cereus, Salmonella, Escherichia coli, and molds and yeasts were performed according to the manual of methods for microbiological analysis of food and water [28]. Total coliform and thermotolerant coliform analyses were also performed to assess whether all Good Manufacturing Practices for Food Handling (GMP) standards were followed correctly [28].

2.7. Sensory Analysis

Sensory analyses were performed after the project had been evaluated and approved by the Research Ethics Committee of the Federal Institute of Paraná (CAAE: 80117324.0.0000.0177). The acceptance test was applied to 103 untrained panelists (34 men and 69 women), the majority (69.90%) of whom were young people aged up to 25 years, with 18.45% aged between 26 and 50 years, and 11.65% aged over 50 years. The sensory attributes (appearance, color, flavor, texture, and overall acceptance) were evaluated using a structured 9-point hedonic scale, in which 9 represented “I liked it very much” and 1 represented “I disliked it very much”. Additionally, the intention to purchase the muffins was assessed. The sensory analysis was conducted in the Sensory Analysis Laboratory of the Federal Institute of Paraná, Colombo Campus. The samples were presented to the panelists randomly, at room temperature, on disposable plates coded with a randomly chosen three-digit number. Room-temperature water was served so that the panelists could clean their palates between samples. The panelists were instructed to observe the product’s characteristics and complete the response sheets. The acceptance index (AI) was calculated by taking the average score obtained in overall acceptance, dividing it by the highest score, and multiplying by 100 [29].

2.8. Statistical Analysis

All analyses were conducted in triplicate. The data were subjected to analysis of variance (ANOVA), with comparisons of means using the Tukey test at a significance level of 5% via the Statistica 10.0 program [30].

3. Results and Discussions

3.1. Physicochemical Characterization of Flour and Muffins

The results regarding the nutritional composition of the melon peel flour and muffins are presented in

Table 2. Physicochemical characterization of melon peel flour and muffins.

Analysis	Melon Peel Flour	Control Muffin	F10 Muffin	F20 Muffin
Water activity	0.411 ± 0.004	0.914 b ± 0.001	0.925 a ± 0.002	0.930 a ± 0.012
Moisture (g/100 g)	11.947 ± 0.227	29.142 b ± 0.179	30.834 b ± 1.568	35.611 a ± 0.074
Ash (g/100 g)	10.141 ± 0.154	0.891 c ± 0.029	1.224 b ± 0.026	1.533 a ± 0.015
Lipids (g/100 g)	1.738 ± 0.019	0.865 c ± 0.048	5.800 a ± 0.418	4.789 b ± 0.165
Proteins (g/100 g)	12.278 $\pm$ 0.169	3.052 a ± 0.700	3.016 a ± 0.636	3.221 a ± 0.076
Crude fiber (g/100 g)	17.389 $\pm$ 0.011	1.708 b ± 0.052	3.884 a ± 0.321	4.447 a ± 0.097
Carbohydrates * (g/100 g)	63.896	66.050	59.126	54.846

All data represented as mean ± standard deviation (n = 3). A different superscript letter in the same line indicates a statistical difference (p < 0.05). * Carbohydrate results obtained by difference.

.

The results show that the main constituents of melon peel flour are crude fiber (17.389 g/100 g) and available carbohydrates (63.896 g/100 g). Melon peel flour can be considered a good source of dietary fiber [11]. The total dietary fiber contents of melon peel flour ranged from 34.62 to 50.00 g/100 g [11,31,32]. It is possible to observe that MPF presents high fiber values, thus indicating that MPF is rich in fiber.

In studies on melon peel flour, water activity (Aw) values ranged from 0.20 to 0.26 [33], which are notably lower than the 0.41 observed in the present study. This difference may be attributed to variations in processing methods or moisture content between the samples. It is common for flour to present an Aw level lower than 0.6, guaranteeing the product a longer shelf life since Aw is one of the factors that determine the growth of microorganisms, most of which cannot develop in Aw conditions lower than 0.6 [33].

In studies to verify the moisture content of melon peel flour, the maximum moisture content for the flour was 9.86 ± 0.04 [33]. According to the Brazilian National Health Surveillance Agency, the maximum moisture content in starches, cereals, bran, and flour is 15% [34]. Based on these values, we can assume that the moisture content of the flour determined in this study falls within the standards established in literature and legislation.

According to Trojahn [32], MPF was performed in a forced air circulation oven at 70 °C for 24 h, yielding protein and lipid results of 14.78 ± 0.86 and 11.83 ± 1.09, respectively. The results obtained in the analysis of proteins and lipids in the present study were lower than those reported in the literature [32].

In other studies, approximate values of proteins (10.84 g/100 g) and lipids (1.65 g/100 g) were found [31], which are similar to those found in this study (12.278 and 1.738 g/100 g, respectively). In addition, Pereira et al. [33] showed similar results for lipid content (1.10 g/100 g) to those in this study.

The ash content reported in some literature was similar to that found in the present work (9.40 g/100 g [32] and 9.35 g/100 g [33]). Therefore, the obtained ash content is consistent with the data available in the literature.

Regarding the physicochemical parameters of the muffins, a significant difference was observed between the formulations (p < 0.05), except for protein and crude fiber contents.

Water activity values were higher than 0.90. This is a crucial quality parameter, as it significantly influences the appearance and flavor of the final product. In the literature, it was observed that the Aw of muffins made with flaxseed and yam mucilage varied from 0.798 to 0.856 [35], which is lower than that observed in the Control samples, F10 and F20, which had values for water activity ranging from 0.914 to 0.930. In muffins enriched with dietary fiber from kimchi by-products, the determined Aw values varied between 0.93 and 0.94 [36], thus demonstrating values closer to those of the analyzed samples. Higher Aw values generally indicate a greater availability of free water, which can accelerate microbial growth and biochemical reactions, potentially leading to a shorter shelf-life. Therefore, to ensure safety and prolong shelf life, appropriate packaging and storage conditions should be considered to limit microbial proliferation and quality deterioration [37].

Comparing the results obtained with the addition of melon peel flour in cupcakes by Heo et al. [31], lower results were obtained for moisture (26.77%) and carbohydrates (45.53%) and higher for ash (2.52%), proteins (7.04%), lipids (18.14%), and fiber (8.63%), considering that the formulations used by the author contain gluten and are not vegan. It is possible to observe that the higher the percentage of MPF, the higher the fiber and ash content is (Table 2). The Control formulation had a higher carbohydrate content than F10 and F20 (66.05%), as rice flour is rich in carbohydrates (78%) [31]. In comparison with the values obtained, as shown in Table 2, it was determined that the MPF developed for application to muffins in this study has a high ash content, indicating that it is considered a flour with a high amount of minerals, protein, and crude fiber.

3.2. Technological Properties of Muffins

Table 3. Crumb and crust color values of muffins.

Samples	Crumb			Crust
	L*	a*	b*	L*	a*	b*
Control	${75.849}^{\mathrm{a}}\pm$ 2.106	${-3.722}^{\mathrm{c}}\pm$0.315	${23.083}^{\mathrm{c}}\pm$ 1.644	${70.878}^{\mathrm{a}}\pm$ 3.734	${8.297}^{\mathrm{a}}\pm$ 2.073	${31.625}^{\mathrm{b}}\pm$ 1.234
F10	${69.957}^{\mathrm{b}}\pm$2.753	${-1.213}^{\mathrm{b}} \pm$0.268	${24.655}^{\mathrm{b}}\pm$ 0.566	${70.620}^{\mathrm{b}}\pm$ 3.015	${8.857}^{\mathrm{a}}\pm$ 2.908	${35.757}^{\mathrm{a}}\pm$1.229
F20	${66.061}^{\mathrm{c}}\pm$ 1.148	${0.114}^{\mathrm{a}} \pm$ 0.242	${27.588}^{\mathrm{a}}\pm$ 0.740	${65.877}^{\mathrm{a}}\pm$ 2.210	${3.727}^{\mathrm{b}}\pm$ 1.798	${33.143}^{\mathrm{b}}\pm$ 1.714

All data represented as mean ± standard deviation (n = 6). A different superscript letter in the same column indicates a statistical difference (p < 0.05).

shows the colorimetric parameters of the muffins. The color of the samples can be influenced by the ingredients used, one of which is flour, which, when added, can significantly increase chromaticity levels and decrease luminosity [22]. Thus, the luminosity (L*), chromaticity a* (green–red), and b* (blue–yellow) of both the muffin crumb and its crust were measured (Figure 4). It is possible to observe that the luminosity of the crumb of the samples differed from each other (p < 0.05), while in the crust sample, F10 differed from the others (p < 0.05). The values obtained from the measurement of chromaticity a* of the crumb varied between −3.722 and 0.114 (p < 0.05). For the crust, the values ranged from 3.727 to 8.857. Sample F20 differed from the others (p < 0.05). Regarding b* chromaticity, the crumb values ranged from 23.083 to 27.588. All samples showed differences between each other. For the crust, the values ranged from 31.625 to 35.757, with only sample F10 differing from the others (p < 0.05).

The addition of MPF contributed to a decrease in the luminosity of the muffins, that is, to their darkening. Regarding the a* parameter, the addition of MPF increased the reddish coloration. The same occurred with the b* chromaticity values, in which the yellow color increased. These reactions may be related to the intense coloration of the carotenoids present in the melon peel that remained in the flour [22].

In bakery products, specific volume (SV) is a quality parameter that indicates whether problems occurred during the fermentation process. If SV values are high, the fermentation was excessive; however, if there were problems in the formation of the dough structure, the result is a low SV [38]. In this study, the values obtained for the Control, F10, and F20 samples were 1.756, 1.515, and 1.403, respectively. It is possible to observe that the values decreased according to the addition of MPF. These results align with those of another study, which found that the addition of wheat substitute flour also decreased the respective SV values of the product [39]. The decrease in specific volume may be related to the high fiber content present in melon peel flour. According to Li et al. (2022), fiber contains numerous hydroxyl groups that compete with starch for water, preventing water from associating with the amorphous regions of starch granules. This reduces the swelling properties of the granules and, consequently, their specific volume [40,41].

The expansion factor assesses the dough’s ability to expand vertically and horizontally, that is, how much the product grows during baking [33]. The addition of MPF decreased the expansion factor values (

Table 4. Technological properties of muffins.

Samples	Hardness (g)	Elasticity (g)	Specific Volume (cm3/g)	Density (g/cm3)	Expansion Factor	Height (mm)
Control	1903.682 b ± 378.990	52.536 a ± 6.252	1.756 a ± 0.328	0.584 b ± 0.103	1.263 a ± 0.010	34.587 a ± 0.937
F10	2807.544 a ± 236.967	50.219 a ± 1.339	1.515 ab ± 0.143	0.665 ab ± 0.067	1.261 a ± 0.005	31.501 b ± 0.463
F20	3052.473 a ± 381.888	53.191 a ± 1.511	1.403 b ± 0.068	0.714 a ± 0.035	1.213 b ± 0.010	29.526 c ± 0.651

All data represented as mean ± standard deviation (n = 6). A different superscript letter in the same column indicates a statistical difference (p < 0.05).

). Sample F20 differed from the others (p < 0.05), presenting the lowest expansion factor (1.213) due to the higher fiber content present.

In a study on the influence of adding green banana flour to bread, it was demonstrated that its addition contributed to a decrease in the specific volume and expansion factor [33]. However, these results are directly related to the water absorption capacity of bakery products. Since the relationship between the physical factor and the increase in ingredients causes competition with the free water in the food, the expansion rate of the food is limited. In the case of fiber, it can absorb up to one-third of the total water in the food. In addition to these factors, the results obtained are also due to the absence of gluten. Gluten is a crucial protein in bakery products during dough formation, as its exclusion can cause technological problems in certain products, resulting in limited sensory aspects [39]. Therefore, the total exclusion of gluten from the formulations, combined with the high fiber and protein content present in the flour, limited the water absorption rate, which in turn favored a decrease in the expansion factor values and the specific volume of the muffins. These factors influenced all technological properties, as can be seen in Table 4.

The results obtained for the height parameter of Control, F10, and F20 samples were 34.587 mm, 31.501 mm, and 29.526 mm, respectively, where all the samples differed from each other (p < 0.05). In another study, muffins made from pine nut flour were found to have values of 47.68 mm, 45.80 mm, and 50.23 mm [41]. These results differ from those previously reported, which may be attributed to the presence of MPF. Due to its high water absorption capacity, MPF promoted the retrogradation of amylose and amylopectin chains in the muffins, especially at higher levels of addition (20%). Retrogradation is a process in which gelatinized starch molecules—mainly amylose and amylopectin—realign and recrystallize over time during cooling. This molecular reorganization reduces the swelling capacity of starch and leads to a harder, more compact structure. As a result, a decrease in both the specific volume and height of the muffins was observed [42].

Adding new ingredients to existing formulations makes them heavier, thus increasing their density [25]. This sentence proves to be true because the results for the density analysis were 0.584 g, 0.665 g, and 0.714 g for the Control, F10, and F20 formulations, respectively, with the F10 sample being equal to the Control sample and the F20 sample showing an increase in values proportional to the increase in MPF.

Density values between 0.456 and 0.839 g/cm³ are expected in muffin-type cakes that contain gluten, indicating that the muffins developed in this work did not suffer any interference due to the exclusion of this parameter, thus demonstrating that the difference between the volumes is not noticeable by consumers [41].

Texture analysis determines the deformation of a food when subjected to a force, including biting and pressing. From this, the parameters of hardness, also called firmness, and elasticity can be determined. Hardness is the maximum force applied in the first cycle of compression of the sample. Elasticity, on the other hand, is the ability of the material to return to its original shape when subjected to a force [43].

In products such as cakes and muffins, the texture depends on the formulation, dough moisture, fat, and sugar content, and high texture values are unfavorable [35]. The greater the specific volume of a product, the softer it is; consequently, its hardness values are lower [35]. Therefore, when observing the hardness results obtained, it was determined that the addition of MPF to muffins makes them harder. Thus, through statistical data, the Control sample proved to be softer, and the least soft was sample F20; their respective results were 1903.682 g and 3052.473 g. In muffins fortified with apple pomace, the firmness values vary from 754 g to 1980 g [44]. Thus, it is possible to observe that the values obtained in this study were higher; however, gluten-free cakes present large variations in texture due to the starch source used [35]. However, the incorporation of MPF did not alter the results obtained for elasticity (50.219–53.191). Therefore, there was no difference in this parameter (p < 0.05).

3.3. Microbiological Analysis

Although melon peel flour is rich in dietary fiber and may contain bioactive compounds with potential antimicrobial effects, its impact on microbial stability requires careful evaluation, especially given its high water absorption capacity.

Table 5. Microbiological analysis of muffins.

Analysis	Control	F10	F20	Microbiological Standard
Bacillus cereus	<1.0 × 102 (est.) UFC/g	<1.0 × 102 (est.) UFC/g	<1.0 × 102 (est.) UFC/g	* 103
Salmonella	Absence	Absence	Absence	* Absence
Escherichia coli	<3.0 NMP/g	<3.0 NMP/g	<3.0 NMP/g	* 102
Molds and Yeasts	<1.0 × 102 (est.) UFC/g	<1.0 × 102 (est.) UFC/g	4.6 × 102 (est.) UFC/g	* 104
Total coliforms	<3.0 NMP/g	<3.0 NMP/g	<3.0 NMP/g	** 10
Thermotolerant coliforms	<3.0 NMP/g	<3.0 NMP/g	<3.0 NMP/g	*** 10

* IN 313/2024; ** CNNPA 12/1978; *** RDC 12/2001.

shows the results of the microbiological analyses of the Control, F10, and F20 muffin samples. The analyses of presumptive Bacillus cereus, Salmonella, Escherichia coli, and molds and yeasts revealed that the muffin samples presented values that meet the specifications required by legislation [26,27]. The analyses of total and thermotolerant coliforms presented values that meet established levels of tolerance [45]. The results indicate that the use of MPF did not negatively affect the microbial safety of the muffins. In addition, the production process, supported by good manufacturing practices, was effective in ensuring microbiological quality, even with the inclusion of MPF.

3.4. Sensory Evaluation

The scores for product attributes and overall acceptance (

Table 6. Sensory acceptance of muffins.

Samples	Appearance	Color	Flavor	Texture	Overall Acceptance
Control	7.990 a ± 1.107	7.941 a ± 1.194	6.990 a ± 1.774	6.864 a ± 1.738	7.242 a ± 1.568
F10	7.524 a ± 1.327	7.602 a ± 1.491	7.097 a ± 1.666	6.553 ab ± 1.898	7.213 a ± 1.582
F20	5.854 b ± 2.233	6.660 b ± 1.983	5.844 b ± 2.204	6.029 b ± 2.167	6.019 b ± 2.067

Different letters in the same column indicate a 5% significance difference (p < 0.05) using the Tukey test.

) indicated no significant differences between the Control and F10 samples (p > 0.05). As MSF was added and muffin hardness increased, the texture acceptance score decreased. The acceptance index of Control and F10 is 88.88%, whereas for F20, it is 66.66%. Samples that presented an acceptance index lower than 70% cannot be taken to the market due to their low acceptance [29]. In this case, the F20 sample does not require the other analyses because it presented a result equal to or lower than 70%. Similar results were reported by Heo et al. [36]; as the proportion of the kimchi by-product increased, muffin hardness also increased, leading to a decrease in texture acceptance scores. Additionally, flavor acceptance scores declined significantly with higher KBP levels.

Regarding the survey on purchase intention, a percentage of 47.62% of responses in favor of purchasing the muffins was obtained, with 19.47% choosing the option of “definitely would buy”, 28.15% choosing “probably would buy”, and a percentage of 37.86% selecting the intermediate option of “maybe would buy/maybe would not buy”; a percentage of 10.67% of responses were not in favor of purchasing the muffins, with 5.82% opting for “probably would not buy” and 4.85% for “definitely would not buy”. A percentage of 3.88% of people who did not respond to the purchase intention was also obtained. Therefore, it is possible to observe that although the highest value obtained was for the intermediate option, the positive values for the purchase are greater than the negative values, making it a product with a high purchase intention.

4. Conclusions

Melon peel flour has high ash, protein, and fiber content and can be used to enrich food products. It was observed that the higher the concentration of melon peel flour in the muffins, the more the technological parameters are impacted due to the absence of gluten and the high fiber, protein, and mineral content, as well as the high water absorption capacity. The muffins enriched with 10% melon peel flour (F10) represent the optimal formulation, as they exhibited no significant difference in sensory acceptance compared to the Control sample, thereby maintaining consumer acceptability. Furthermore, the F10 formulation offers enhanced dietary fiber content, contributing to improved nutritional quality without adversely affecting sensory attributes. Therefore, the use of agro-industrial by-products can be considered a sustainable alternative in the development of new functional food products, generating large-scale positive impacts on diversity, acceptance, and impulses for the creation of new ideas that aim to include different audiences. Future research could explore how agro-industrial by-products like melon peel can be further utilized in the food industry, investigating their technological, nutritional, and sensory effects across various food types and assessing their potential for large-scale applications.