The Application of Mulberry Elements into a Novel Form of Easy-to-Prepare Dried Smoothie

Featured Application

The proposed new form of smoothie can find an application among young, busy people worldwide who are interested in a nutritious and easy-to-prepare meal, as well as manufacturers of food supplements and food concentrates.

Abstract

The European market offers a variety of functional foods targeted at prediabetic and diabetic patients, with different approaches to reducing postprandial glucose levels. The utilization of white and black mulberry in new products could be an area of interest to many conscious consumers. The study aimed to design a novel form (dried) of easy-to-prepare product by applying nutritious mulberry in various proportions and creating an aesthetically appealing smoothie product with a distinctive taste profile. Such an easy-to-prepare form of smoothie was obtained by utilizing the freeze-drying process, while typical market smoothies are liquid. Sensory evaluations of the fresh, dried, and reconstructed smoothies and their basic characteristics were conducted. Moreover, antiradical tests (with ABTS+^• and DPPH^•), the phenolic compound profile (HPLC/PDA), and the L*a*b profile were analyzed. The results of the sensory evaluation tests were divided into two groups: Polish and foreign panelists. It was observed that mulberry-licorice drop-based smoothies were preferred fresh. Yet dried and reconstituted capsule-based smoothies were favored overall. Generally, both Polish and foreign panelists preferred lower concentrations of mulberry and licorice extracts (DB) in fresh smoothies, while in dried or reconstructed smoothie form, panelists scored higher (DC) and lower (DB) concentrations quite similarly (favored both concentrations). From the group of identified phenolic compounds, cinnamic acid derivates dominated all analyzed smoothies. Many analyzed types of flavonoids (quercetin, rutin, kaempferol) and naringenin were found in the smoothies. Some differences were noted in the antiradical tests but were only statistically significant for DPPH^• scavenging activity, which was higher for the DB1, DB2, and DC1 samples. Generally, even higher addition of licorice and mulberry did not negatively affect panelists’ ratings and the analyzed activities.

1. Introduction

Mulberry elements are known as important elements of the diabetic diet, in the form of dietary supplement or food. Regarding the European Consensus, a food that satisfactorily demonstrates the ability to affect beneficially one or more target functions in the body, beyond adequate nutritional effects, in a way that is relevant to either an improved stage of health and well-being and/or reduction of risk of disease, can be called functional [1]. Functional foods are created to act preventively and/or to support the treatment of lifestyle diseases [2]. Lifestyle diseases like obesity and type 2 diabetes mellitus (T2DM) are progressive with time, which gives the opportunity for patients who are prediabetic and first-stage diabetic to control the development of the disease by a commitment to healthy food choices and physical activity. There are many studies confirming that lifestyle changes along with a diabetes prevention program can delay diabetes complications and the onset of diabetes for 10 years and more [3]. Currently, available pharmaceutical treatments for diabetes can have serious side effects. On the other hand, centuries ago, people used plants to cure many diseases.

There are different ways of introducing such plants into the diet. The first way is to consume them in the primary or modified form or in a slightly changed state of matter. The second way to use raw plant materials with antidiabetic activity is to change the matrix bringing the given substance, i.e., designing a food containing a given raw material and giving it strictly defined characteristics [4].

In the literature, many medicinal plants have been found to possess antidiabetic properties due to their high levels of bioactive compounds, such as alkaloids, polyphenols, and flavonoids, which have been shown to improve insulin sensitivity and glucose metabolism [4,5,6]. Today, the use of antidiabetic plants as a complementary therapy to conventional medicine has gained popularity owing to their effectiveness, affordability, and low side effects compared to traditional medications, which may have adverse effects and high costs. White mulberry and licorice are such traditional medicinal plants. Mulberry’s antidiabetic and anti-obesity activities are based on enzyme (e.g., lipase, esterase, α-amylase, α-glucosidase) inhibition, adipocyte differentiation, and blood lipid profile regulation [4,7,8]. Moreover, licorice, known as Ramadan Street Juice, is traditionally planted in Arab countries and used by people especially during Ramadan time. However, the amount of it should be monitored when added to food products due to its activity [9].

Due to the high demand for antidiabetic food products appropriate for diabetics and prediabetics with simultaneously low side effects, in this study, the concept of a totally new product was developed, in the form of a dried smoothie. Typically, busy consumers are interested in using smoothies as a part of their diet [10], as well as preschoolers [11]. In the USA, the smoothie market was worth $4.8 billion in 2022 while in Europe, it was worth $5 billion in 2023, with an estimated future growth of 7.2% in the years 2024–2030 [12]. Scientists promote new variants of smoothies to be introduced to the industry [13,14,15,16]. Typically, market smoothies are available in liquid form; however, new techniques of their preparation and preservation have been also improved [17,18,19]. When analyzing the smoothie market, Spanish authors have observed difficulties in separating juices from smoothies in terms of labeling and promoted the ‘smoothie’ to exist as a separate type of product [20].

In the study, the application of mulberry elements together with other valuable components into a nutritious smoothie was made to be introduced to conscious consumers worldwide. For the first time, the dried form of smoothie was proposed, which could be in area of interest to busy people. The technological premise was to create a dry smoothie suitable for reproduction at any place and at any time by the future consumer. This required an efficient technique to ensure that the nutritional qualities of the product were maintained. The freeze-drying technique prevents the large loss of nutrients and helps to preserve the intense color of the components [21].

Bearing in mind that equal cultures have different culinary habits, extensive research was conducted into the taste acceptance of the smoothies produced among two groups of people: Polish and foreign panelists. For future producers, proposed labels were also prepared.

Therefore, the main objective of this study was to design and create an innovative, nutritious mulberry-based smoothie in new formula that was dried and easy-to-prepare. An additional aim was to evaluate the sensory acceptability of the final food product among consumers from different cultures, together with its biological activity.

2. Materials and Methods

2.1. Materials

Bananas were purchased from a Polish market in fresh form (more green than yellow, not matured). Strawberries were purchased in frozen form from a Polish market (Mroźna Kraina, Poland). The licorice extract was used in the form of drops purchased from Alcea Natural (Zielona, Poland). White mulberry leaf extract was used in two forms: capsules with dried extract inside (OstroVit, Poland) and drops of white mulberry leaf extract in liquid form (Alcea Natural, Zielona, Poland). Black mulberry fruit were purchased from BioPlanet (Leszno, Poland) in dried form. Dragon fruit was purchased from GymBeam (Berlin, Germany) in lyophilized form (cubes), also as a color enhancer. The water used instead of milk as the base of the smoothie was in the form of tap water and dragon fruit soaking water (ratio 1.35:100). Chia seeds were purchased from Bio Planet (Leszno, Poland). Lucuma powder was purchased from Bio Planet (Leszno, Poland).

2.2. Methods

2.2.1. Designing Process

Designing the smoothie composition started with vast research about special, interesting medicinal plants from European and Asian cultures for developing a fusion that would be aesthetically appealing and provide a distinctive taste profile. Licorice and white mulberry leaves were mainly considered for the richness of phenolic compounds and antioxidant activity. The research model is shown on Figure 1. Then, many trials were conducted with numerous variants, considering factors such as color intensity and sweetness levels, and verified by the investigator. Each variant underwent preliminary sensory evaluation to assess its appeal and balance of flavors. After that, the main variants were chosen according to the preliminary sensory profile. Certain variables were established for further variants:

• The ratio between licorice and mulberry leaf extract amounts;
• The color of the smoothie (presence of dragon fruit or beetroot);
• Consistency (presence or absence of chia seeds).

2.2.2. Preparation of Four Variants of Fresh Smoothies

The preparation process started with cleaning and peeling the bananas, followed by dragon fruit solution (ratio 1.35:100) preparation. Next, other components were weighed according to the designed recipes (

Table 1. Recipes of the four variants of fresh smoothies.

	DB1	DB2	DC1	DC2
Bananas [g]	90.0	90.0	90.0	90.0
Strawberries [g]	40.5	40.5	40.0	40.0
Licorice root extract (LE) [mL]	0.125	0.125	0.225	0.225
White mulberry leaf extract (capsule) (ME) [g]	0.125	0.125	0.700	0.700
Black mulberry [g]	7.0	7.0	7.0	7.0
Dragon fruit powder [g]	3.0	3.0	3.0	3.0
Liquid-DW [mL]	150.0	150.0	150.0	150.0
Chia seeds (CS) [g]	8.0	0.0	8.0	0.0
Lucuma [g]	5.0	5.0	5.0	5.0

DW—Dragon fruit soaking water.

), and all components were mixed to obtain one homogeneous smoothie using a blender (Braun Multiquick 5 Pro, Neu-Isenburg, Germany).

2.2.3. Sensory Evaluation for Fresh, Dried, and Reconstructed Smoothies

Sensory analysis was conducted on four different variations of the novel food product by 36 panelists representing diverse cultural backgrounds, including Asian, African, and Polish, at the Sensory Laboratory of the Department of Gastronomy Science and Functional Foods, Poznan University of Life Sciences. No ethical approval was required for this study. Participants were informed about the study’s aim and that their participation was entirely voluntary. Volunteers could stop the analysis at any point, and the responses were anonymous. The authors did not ask for sensitive data or personal information.

The evaluation took place under controlled and consistent environmental conditions. During the assessment, panelists were presented with fresh smoothies (ca. 30 mL), dried powdered smoothies (ca. 2 g), and reconstructed smoothies (ca. 3 mL), as aimed to be utilized by consumers. A dissolving ratio of 1:1 was used for the dried smoothie powders to obtain reconstructed smoothies. Panelists were tasked with assessing their sensory attributes. Each panelist utilized a scorecard to rate the product based on various characteristics, such as flavor, texture, overall appearance, and aroma (Figure S1). The card was designed according to the order (ranking) method, with broad scores: 1 point for the least liked and 4 points for the most liked. The paired comparison test, a commonly employed statistical analysis method in food product sensory evaluation, was used to compare the performance or preferences for the different smoothie variants. The results of the paired comparison tests provided meaningful insights. The test results were evaluated statistically according to referenced Kramer’s Tables for the four variants of smoothies [22].

2.2.4. Basic Composition, Basic Characteristics of Fresh, Dried Smoothies

The dry matter content and ash content were determined by obtaining four samples of each variant (ca. 5 g), in accordance with the AOAC method [23].

The pH was measured using a pH meter (CP-411, Elmetron, Toruń, Poland). The procedure started with calibration of the pH meter using distilled water. After calibration, the sample was placed in a clean, dry beaker, and the pH meter’s electrode was immersed in the sample for measurement. The pH reading was then directly obtained from the pH meter’s display. The measurement was conducted 3 times for every sample in order to ensure accuracy and reliability. The results were shown as the average and standard deviation. In the determination of pectin content, the modified Morris method [24] was used. The sample (ca. 2 g) was dissolved in a mixture of acetone and water (1:2). The solution was agitated, filtered through a previously dried filter, and dried in an oven at 75 °C/30 min (Heratherm OMH60, Thermo Scientific, Langenselbold, Germany). Dried samples were weighed to calculate the % of pectin included in each sample. The results were determined in triplicate and are shown as the average and standard deviation.

The osmolality was measured using an Osmometer OS 3000 (Marcel, Gonotec, Berlin, Germany), following the manufacturer’s guidelines. The process began with calibrating the device using distilled water, then placing the sample in the osmometer chamber. The osmolality reading was obtained directly from the device’s display, with triplicates for each sample. The results were shown as average and standard deviation.

The soluble solids content was measured using a refractometer (MyBrix, Mettler Toledo, Giessen, Germany) to determine the Brix value (°Bx), which indicates the % of sugar in the sample. The method involved the calibration of the refractometer with distilled water, then applying a small amount of the sample onto the device’s prism and reading the Brix value directly from the scale provided by the refractometer. This process was repeated 3 times for each sample. The results were shown as the average and standard deviation.

To analyze the glucose, sucrose, fructose, glycerol, and citric acid contents, the Agilent (Santa Clara, CA, USA) 1260 Infinity II liquid chromatograph with a spectrum review (190–400 nm) at 210 nm wavelength was used. A Rezex ROA 300 × 7.80 mm column from Phenomenex (Torrance, CA, USA) was utilized for the analysis. The eluent, 0.005 N H₂SO₄, was run isocratically at a flow rate of 0.6 mL/min, with the temperature set at 40 °C. Samples of 10 mL were applied to the column, and qualitative and quantitative identification was performed using the external standard method through measurement and computer integration with OpenLab CDS ChemStation Edition from Agilent.

Color analysis was conducted using a Konica Minolta digital colorimeter (Chroma meter CR-5, Konica Minolta, Tokyo, Japan). The device was initially calibrated in accordance with the manufacturer’s guidelines, then the sample was positioned within the measurement area. The color metrics, including L* (lightness), a* (red-green), and b* (yellow-blue) coordinates, were directly recorded from the colorimeter’s display. This process was repeated with each sample 3 times before and after the lyophilization process. The results were shown as the average and standard deviation.

Nutritional information was prepared according to European Union rules and Regulation (EU) No 1169/2011 [25] and shown in graphical form.

2.2.5. Freeze-Drying (Lyophilization) of the Fresh Smoothie to Obtain the Final Convenient Smoothie in Dried Form

Lyophilization of the fresh samples was conducted by initially freezing the four variants at the temperature of −80 °C for 24 h using a freezer. Subsequently, the variants were transferred to a lyophilizer (freeze-dryer) (Christ Alpha 1-4 LSC, Osterode am Harz, Germany), where the vacuum was adjusted to sufficiently reduce the pressure, and the initial temperature was set at −50 °C. It took 96 h to achieve complete drying for all samples. In the final stage, the temperature was gradually increased to reach 25 °C to ensure the complete removal of water. Afterward, the smoothie powders were obtained, which were then ground and stored in airtight containers in a cool and dry place.

2.2.6. Antioxidant Activity and Bioactive Compound Content

To extract components for analyses, 20 g of sample was dissolved in 80 mL of methanol (C = 80%) and shaken in an ultrasound bath for 15 min, followed by centrifugation (3000 rpm/5 min) and filtration (syringe filter, 0.45 µm) to obtain the final supernatant. The total phenolic compounds (TPC) content in the extracts was determined by spectrophotometric analysis using a SP-830 plus (Metertech, Taipei, Taiwan) with Folin–Ciocalteu reagent. Absorbance measurements were taken at 765 nm against a methanol blank. Each solvent solution of the extract served as a control [26]. The results were expressed as mg gallic acid equivalents (GAE) per g of dry matter. Phenolic compounds in the smoothie samples were assessed following alkaline and acidic hydrolysis as described by other authors [27,28]. Then, analysis was conducted utilizing an Acquity H class UPLC system featuring a Waters Acquity PDA detector (Waters, Milford, MA, USA). Separation of compounds was achieved using an Acquity UPLC BEH C18 column (100 mm length × 2.1 mm width, particle size 1.7 μm) (Waters, Dublin, Ireland). The elution process involved a gradient utilizing the following mobile phase composition: A: acetonitrile with 0.1% formic acid, B: 1% aqueous formic acid mixture, until pH = 2 was reached. The concentrations of phenolic compounds were quantified employing an internal standard at wavelengths λ = 320 nm and 280 nm. Compound identification was based on comparing the retention time of the analyzed peak with that of the standard and by introducing a specific quantity of the standard to the samples for repeated analysis. The detection limit was set at 1 μg/g.

The DPPH^• scavenging activity assay was based on spectrophotometric assessment (SP-830 plus, Metertech) of absorbance variation at a wavelength of 517 nm [29]. The results were expressed as mM Trolox equivalents per g of dry matter. The ABTS^+• scavenging activity assay was based on analysis of the change in absorbance at λ = 734 nm using spectrophotometry (SP-830 plus, Metertech). The ABTS^+• solution was prepared one day before the analysis, according to [29], in triplicate, and the results were expressed as mM Trolox equivalents per g of dry matter.

2.2.7. Statistical Analysis

Each variant of the product was replicated twice to create primary samples, while the laboratory sample was a composite of equal proportions. Three analytical samples were analyzed for each variant. One-way analysis of variance (ANOVA) was conducted on the experiment results followed by Tukey’s multiple range test to compare the means. Significant differences are indicated by distinct letters in the tables at a significance level of p < 0.05. Statistical analysis was performed using Statistica software version (14.0.1.25).

2.3. Reagents

All of the chemicals that were used in the analytical tests were purchased from POCH (Gliwice, Poland) or Merck (Darmstadt, Germany).

3. Results and Discussion

3.1. Smoothie Characteristics

In the study, a comprehensive exploration of the properties, composition, and sensory appeal of various new types of smoothie, with a particular focus on a mulberry-licorice-based formulation, is presented. Through the utilization of blending techniques and freeze-drying technology, a new form of food product was developed, combining banana, strawberries, white mulberry leaf extract, licorice extract, lucuma powder, and chia seeds (Figure 2). This quite new approach not only ensures ease of preparation and extended shelf-life but also preserves the nutritional integrity of the ingredients.

Table 2. Basic chemical characteristics of the smoothies.

	DB1	DB2	DC1	DC2
Ratio ME:LE:CS [g]	0.125:0.125:8	0.125:0.125:0	0.7:0.225:8	0.7:0.225:0
FRESH smoothies
Dry matter [%]	4.358 cd ± 0.016	4.472 a ± 0.006	4.323 c ± 0.033	4.404 bd ± 0.021
Ash [%]	4.933 a ± 0.155	5.349 a ± 0.604	4.273 a ± 0.056	4.447 b ± 0.005
pH	4.550 a ± 0.026	4.563 a ± 0.005	4.457 b ± 0.005	4.447 b ± 0.005
Osmolality [Osmo/kg]	−12.040 c ± 0.559	−11.396 c ± 1.327	−5.433 a ± 1.406	−9.790 bc ± 0.232
Soluble solid [°Bx]	9.500 d ± 0.082	9.500 d ± 0.100	11.167 b ± 0.125	10.500 c ± 0.020
DRIED smoothies
Dry matter [%]	86.387 a ± 2.935	87.852 a ± 0.568	87.046 a ± 1.845	86.711 a ± 1.888
Pectin [%]	2.540 c ± 0.100	3.357 d ± 0.296	1.865 b ± 0.028	0.455 a ± 0.161
Sacarose [%]	0.140 a ± 0.003	0.235 c ± 0.009	0.160 b ± 0.002	0.132 a ± 0.012
Glucose [%]	0.170 d ± 0.003	0.138 a ± 0.003	0.165 c ± 0.001	0.145 b ± 0.001
Fructose [%]	0.166 b ± 0.002	0.127 a ± 0.002	0.161 b ± 0.003	0.141 a ± 0.009
Glycerol [%]	0.003 b ± 0.000	0.002 a ± 0.000	0.002 a ± 0.000	0.002 a ± 0.000
Citric Acid [%]	0.017 b ± 0.000	0.017 b ± 0.000	0.018 b ± 0.000	0.015 a ± 0.000

^a,b,c,d—different letters show statistically significant differences (p ≤ 0.05).

summarizes the main chemical characteristics of the formulated fresh smoothies, including dry matter content, pH, soluble solids, ash content, and osmolality, and shows the chemical characteristics of the dried smoothies. There was significant variation among the results of dry matter content between the fresh and lyophilized samples. It was obvious that the highest dry matter content for the fresh product was 4.472% but the lowest was 4.196%; on the other hand, the dry matter content for the lyophilized product was high, with a minimum value of 86.125% and a maximum value of 88.118%. The wide variation was due to the lyophilization process, so there was an inverse relationship between the percentage of dry matter and moisture content.

Interestingly, analysis of the soluble solids content revealed significant variability, ranging between 9.500 °Bx and 11.167 °Bx, with statistically significant differences between the fresh DB and DC samples (p = 0.05). Samples with higher dry matter content (those formulated without chia seeds) exhibited a greater concentration of saccharose (DB2), likely due to consistent initial water content employed during production. The amounts of fructose and glucose were found to be higher in samples with chia seeds included.

The ash content ranged from 4.273% to 5.617%, with the type of semi-processed ingredient exerting a more pronounced influence compared to the ratios used in the fresh smoothies. It was found that there was no statistically significant difference among the samples, meaning that the total minerals contents of the four samples of smoothie after incineration were relatively similar and constant.

The pH values of the four fresh smoothies were quite close to each other—ca. 4.5 for DB samples and 4.4 for DC.

The osmolality value refers to the concentration of the solute in the solution that contributes to the osmotic pressure. In the analyzed fresh smoothies, the osmolality ranged from −5.433 to −12.040 Osmo/kg, indicating low osmolality. This could be due to factors such as dilution or variability of ingredients and interference in measurement due to the fiber and sugar contents.

The dry matter and pectin contents of the dried smoothie samples (after lyophilization) were found to be at levels of ca. 86–87%. Notably, the DB samples exhibited the highest pectin amounts, with black mulberry and bananas identified as the primary contributors, respectively, to the observed pectin content, compared with the DC samples. This significant variation underscored the influence of the smoothie’s composition on its pectin content, with black mulberry serving as a notable gelling agent for achieving the desired consistency. Understanding the contributions of the individual ingredients to the pectin content was essential for optimizing the texture and consistency of the smoothie formulation.

The nutritional value of the final product in the form of a dried smoothie was underscored by its composition, being rich in fiber and micronutrients inherent in fruits, making it ideal for conscious consumers, including those with hyperglycemia problems. The synergistic effect of licorice and mulberry leaf extract further enhanced its potential as a possibly antidiabetic agent (or preventive agent), judging by the ingredients used in the designed formulations [30,31,32,33]. This made the developed dried smoothie a promising easy-to-prepare food product available not only for individuals managing type 2 diabetes mellitus but also for those seeking preventive measures against the onset of the condition. To achieve such an effect in the final form, the freeze-drying process was included.

Table 3. Color analysis of the fresh (before lyophilization) and dried (after lyophilization) smoothies.

		DB1	DB2	DC1	DC2
Fresh smoothies	L*	32.612 b ± 0.056	33.480 c ± 0.025	30.666 a ± 0.032	32.713 b ± 0.030
	a*	23.570 b ± 0.044	25.863 d ± 0.032	21.510 a ± 0.045	24.333 c ± 0.011
	b*	5.140 a ± 0.030	6.643 a ± 0.450	9.546 b ± 0.152	9.526 b ± 0.015
Dried smoothies	L*	45.090 b ± 0.137	54.603 c ± 0.286	44.523 a ± 0.332	46.850 b ± 0.000
	a*	21.216 b ± 0.061	19.963 a ± 0.035	19.916 a ± 0.089	20.110 a ± 0.103
	b*	10.416 b ± 0.056	6.946 a ± 0.058	12.053 d ± 0.040	11.606 c ± 0.092

^a,b,c,d—different letters show statistically significant differences (p ≤ 0.05).

represents the color characteristics of fresh and freeze-dried samples using the CIELAB color metric system, which closely aligns with human vision perception. This system comprises three key attributes: ‘L*’ representing lightness, ‘a*’ indicating the position between green and red tone, and ‘b*’ delineating the position between blue and yellow tone. Evidently, significant differences existed between the L*a*b* values before and after the lyophilization process.

For instance, examining sample DB1 revealed a substantial increase in L* value after lyophilization compared to its pre-lyophilization (fresh) state. Moreover, a slight decrease in a* value suggested a tendency toward green hues. Notably, a significant increase in b* value indicated a shift away from blue toward yellow hues in the dried sample. Conversely, DB2 exhibited the highest L* value in the post-lyophilization state. Notably, statistical analyses indicated significant differences between all samples based on dragon fruit (DB1, DB2, DC1, DC2). The lyophilization process induced notable alterations in color attributes across the samples, manifesting predominantly in changes in the lightness and shifts in color toward green and yellow hues.

Lyophilization was used as the most important step in the proposed production process and is the most appropriate for such products, including preservation of nutritional value, color quality, long shelf-life without pasteurization, and safety due to low water activity [34]. Lyophilization was used to obtain a new form of smoothie to be introduced to the market as ready-to-dissolve, probably in small pockets, and easy-to-prepare for consumers. The drying process impacts many active components in the raw material. Their bioavailability can be significantly improved after freeze-drying by their release from destroyed cell structures [21], resulting in changes in antioxidant activity. When compared with sun drying, the freeze-drying process caused significant increases in free and bound polyphenol contents and 3–4-fold higher amounts of flavonoids [35]. When considering very nutritional products, it is essential to select the appropriate method for dehydration.

The nutritional analysis conducted using USDA (U.S. Department of Agriculture) software revealed insightful findings regarding the dragon fruit-based smoothie’s composition in terms of macronutrients and micronutrients (Figure 3). Notably, the smoothie emerged as a noteworthy source of dietary fiber, boasting a content of 2–4 g per 100 mL, thereby contributing to its potential health benefits for digestive health and satiety. Furthermore, the absence of added sugars underscored its appeal as a health-conscious option within the beverage category.

Interestingly, variants of the smoothie incorporating chia seeds (DB1 and DC1) exhibited higher energy content per 100 mL, while DB2 and DC2 maintained a fat-free profile due to the absence of chia seeds. This indicated a potential source of sustained energy without the addition of dietary fats. The food labels, as depicted in Figure 3, elucidate the nutritional attributes of the dragon fruit-based smoothie with chia seeds (DB1 and DC1), positioning it as a nutrient-dense snack option enriched with phytonutrients. These findings underscored the importance of considering both nutritional composition and sensory characteristics in product development and consumer acceptance.

3.2. Antioxidant Activity of Smoothies

The authors chose to use raw materials with high nutritional value, known, among other things, for the presence of polyphenols, for the smoothie. The quantification of the phenolics content of each extract was achieved through the utilization of the Folin–Ciocalteu reagent with methanolic extracts of the dried smoothies. The quantification relied on a calibration curve generated from gallic acid standards ranging from 0 to 250 µg/mL, with a regression equation of y = 4.1323x − 0.0041 and a coefficient of determination (R²) of 0.999. The analysis revealed that the total phenolics content ranged from 1.095 to 3.434 mg GAE/g d.m., indicating an approximate 3-fold variation. Notably, the DC2 and DB1 samples exhibited the highest phenolic compounds content: 3.434 ± 0.200 mg GAE/g and 3.227 ± 0.115 mg GAE/g, respectively. Conversely, the lowest TPC concentrations were observed in the DC1 sample (1.095 ± 0.181 mg GAE/g). When comparing the results of the designed smoothies with other authors’ medicinal plant-based smoothies [36], the TPC was quite close to other designed mulberry-licorice-based smoothies, and in honeysuckled berry-based smoothies, it ranged from 3.469 to 4.268 mg GAE/g (

Table 4. Phenolic compounds content [mg/g d.m.] of the smoothies.

Component	Group	DB1	DB2	DC1	DC2
Apigenin		0.174 a ± 0.002	0.753 c ± 0.013	0.422 b ± 0.021	0.172 a ± 0.008
Luteolin		0.028 a ± 0.009	0.078 b ± 0.009	0.062 b ± 0.010	0.036 a ± 0.012
Vitexin		0.002 a ± 0.000	0.010 b ± 0.002	0.010 b ± 0.001	0.002 a ± 0.000
Total flavones		0.204	0.841	0.494	0.210
Quercetin		0.891 a ± 0.031	1.840 b ± 0.102	1.945 b ± 0.080	0.856 a ± 0.029
Rutin		3.373 a ± 0.053	3.823 b ± 0.034	3.832 b ± 0.014	3.698 b ± 0.016
Total flavanols		4.264	5.663	5.777	4.554
Kaempferol	Flavonols	0.001 a ± 0.000	0.004 b ± 0.001	0.008 c ± 0.001	0.004 a ± 0.001
Naringenin	Flavanones	0.077 a ± 0.006	0.161 b ± 0.011	0.169 b ± 0.009	0.074 a ± 0.006
Total flavonoids		4.546	6.669	6.448	4.842
Gallic acid		0.003 a ± 0.001	0.004 a ± 0.001	0.004 a ± 0.001	0.003 a ± 0.000
4-Hydroxybenzoic acid		0.002 b ± 0.000	0.004 c ± 0.001	0.001 a ± 0.000	0.000 a ± 0.000
Vanillic acid		0.000 a ± 0.000	0.000 a ± 0.000	0.000 a ± 0.000	0.000 a ± 0.000
Protocatechuic acid		0.000 a ± 0.000	0.001 a ± 0.000	0.002 b ± 0.000	0.001 a ± 0.000
Salicylic acid		0.002 a ± 0.000	0.004 b ± 0.000	0.004 b ± 0.001	0.002 a ± 0.000
Total benzoic acid derivates		0.007	0.013	0.011	0.006
Caffeic acid		0.001 a ± 0.000	0.001 a ± 0.000	0.002 b ± 0.000	0.001 a ± 0.000
Syringic acid		0.001 a ± 0.000	0.002 b ± 0.000	0.003 b ± 0.000	0.001 a ± 0.000
Ferulic acid		0.025 a ± 0.002	0.050 b ± 0.008	0.057 b ± 0.010	0.026 a ± 0.003
Sinapic acid		0.040 a ± 0.011	0.100 b ± 0.008	0.107 b ± 0.007	0.051 a ± 0.004
t-Cinnamic acid		0.031 a ± 0.007	0.070 b ± 0.009	0.090 c ± 0.005	0.027 a ± 0.002
Chlorogenic acid		0.103 a ± 0.008	0.235 c ± 0.012	0.162 b ± 0.007	0.080 a ± 0.009
Rosmaric acid		0.000 a ± 0.000	0.001 a ± 0.000	0.001 a ± 0.000	0.001 a ± 0.000
Total cinnamic acid derivates		0.201	0.459	0.422	0.187
Total phenolics with HPLC		4.754	2.141	6.881	5.035

^a,b,c—different letters show statistically significant differences (p ≤ 0.05).

, Figure 4).

Such results suggested that the smoothie product serves as a rich source of phenolic compounds, which have the potential to alleviate oxidative stress within the body. The reducing compounds present in the smoothies were classified into phenolic compounds and flavonoids based on their chemical structure.

The contents of phenolic acids across the four types of smoothies elucidated notable variations between benzoic acid derivatives and cinnamic acid derivatives. Product DB2 exhibited the highest concentration of cinnamic acid derivative phenolics (0.459 mg/g d.m.), followed by DC1 (0.422 mg/g d.m.). Additionally, the concentration of analyzed selected benzoic acid derivatives appeared to surpass that of analyzed cinnamic acid derivatives.

Flavonoids, which are phytonutrients found in plants with antioxidant properties, play a pivotal role in reducing oxidative stress and imparting color. The contents of flavonoids varied among the four variants of smoothie, with the highest subgroup being flavanols (mainly rutin), followed by flavones, while flavanones exhibited the lowest levels, from those analyzed in studies. Samples DB2 and DC1 demonstrated the highest levels of flavanols, flavones, and flavanones. The elevated levels of flavanols and flavonols in the samples based on capsules were attributed to the higher concentration of licorice-mulberry leaf extract at a ratio of 0.7:0.225. According to the results, the rutin levels surpassed those of other flavonoids.

In the assessment of DPPH^• scavenging activity for the four distinct dried smoothies, it was evident that DB1 exhibited the most pronounced scavenging activity, registering at a level of 0.699 mM TE, together with DC2 (0.972 mM TE).

The ABTS^+• assay measure the ability of sample to scavenge ABTS^+• radicals. The higher the amount of ABTS^+• scavenged from the sample, the higher the antioxidant activity of the sample. The results indicated there were no differences between the analyzed variants of smoothie.

When comparing the smoothies’ antiradical activity with that of other fruit-based smoothies, it was observed that licorice-mulberry-based smoothies had 3-times higher antiradical activity compared with other authors’ findings [36]. This revealed that the innovative product had potent antioxidant activity and it could be used to prevent oxidative stress-related diseases.

Phenolic compounds are essential compounds in plant-based products and exhibit redox properties that work as antioxidant agents. The hydroxyl groups present within plant extracts are responsible for scavenging free radicals [37]. From the polyphenols group, rutin was found to be the main flavonoid in such compositions. In some samples, high levels of quercetin were also identified (2-fold lower amount than rutin). Samples with the highest rutin levels could be associated with anti-inflammatory and antioxidant activities according to the literature [38]. Rutin was found by other authors in mulberry leaves [29,39,40] and licorice [41]. Notably, two important phenolic acids (chlorogenic and sinapic) were identified, similarly to other samples of mulberry leaves [4,42] and fruits [43]. Chlorogenic acid is credited with the ability to attenuate glycogenolysis and reduce glucose absorption, having strong antioxidant properties [44,45]. In the mulberry leaves industry, chlorogenic acid together with rutin are considered to be indicators of their quality [42]. On the other hand, other interesting biological components occurring in mulberry [4] (not analyzed in this study), such as morin and DNJ, would have important inputs into the final preventive activity of the dried smoothies. Scientists found the combination of morin (25 mg/kg) and DNJ (5 mg/kg) as preventive against T2DM. These chemical compounds inhibited SOCS3 and SOCS2 and promoted PPARγ, together with combating adipogenesis and dyslipidemia via CD36/Serbp1/Fas signaling suppression [46].

When focusing on antioxidant activity, the smoothies were also found have valuable products. The DPPH (2,2-diphenyl-1-picrylhydrazyl) molecule is a stable organic free radical characterized by its absorption spectrum alteration at 517 nm upon electron acceptance [47]. Utilizing the DPPH^• assay, one can evaluate the capacity of a smoothie extract to scavenge DPPH^• radicals, evidenced by a color shift from purple to yellow. The efficacy of this scavenging process is inversely correlated with the amount of DPPH^• radicals required to neutralize a given sample; thus, higher scavenging activity is indicated by lower DPPH^• concentrations. The antiradical activity, assessed by assays with DPPH^• cations and ABTS^+• cation radicals, underscored the potency of the select smoothie formulations, with DB1 and DB2 exhibiting the highest efficiency in scavenging these free radicals. In the composition of these smoothies, strawberries were proposed as one of the ingredients creating its consistency. However, their antioxidant activity was proven by other authors [48]. Prymont-Przymińska et al. found that even 500 g of strawberries consumed daily resulted in higher antioxidant status, measured with the DPPH^• test, in the blood plasma of a group of healthy volunteers [48].

3.3. Sensory Analysis of Smoothies

Sensory evaluation is a critical factor that affects consumer purchasing and acceptance decisions. Figure 5 depicts the sensory profile results for the fresh, dried, and reconstructed smoothies, evaluating taste, aroma, consistency, color, and overall acceptability on a 6-point scale ranging from the least to the highest favorability: 1: for scores from 20–29, 2: for scores from 30–39, 3: for scores from 40–49, 4: for scores from 50–59, 5: for scores from 60–69, and 6: for scores from 50–59. Keeping in mind the goal of this research was to produce an easy-to-prepare form of smoothie, sensory analysis of all three smoothie forms was performed. The results for the fresh smoothies were relevant to the development of the smoothie recipe. The results for the dried smoothies showed whether the product the authors intended to package and sell in the future would satisfy the consumer organoleptically. Finally, the results for the reconstructed smoothies showed whether the consumer would be sensorially interested in a smoothie after reconstruction from powder form before consumption.

The data revealed that Polish participants rated the taste most favorably for formulation DB1 in the fresh smoothies. Interestingly, formulations DB1 and DC2 achieved the highest scores for aroma, and DB2 received the highest score for color attractiveness. By contrast, the sensory profile results for foreign participants showed that the taste preference leaned toward formulations DB1 and DB2. Interestingly, in the group of foreigners panelists, aroma received the highest scores for DB1 samples. Similarly to Polish panelists, DB2 smoothies achieved the top score for color attractiveness in the group of foreign panelists. The results highlighted a preference among foreign panelists to fresh formulations DB2 and DB1 (ca. 3 points) when considering the overall sensory attributes of the fresh smoothies, while in the Polish panelist group, the DB1 samples achieved even higher scores (ca. 5 points). This suggested that the combination of dragon fruit (‘light smoothies’) with licorice/mulberry leaf drops (1:1) (DB2) was rated as the most appealing, followed by the formulation containing dragon fruit with licorice/mulberry leaf drops (1:1) with chia seeds (DB1). Both Polish and foreign panelists rated fresh formulation DC1, containing dragon fruit with a licorice and mulberry leaf capsule, as the least favorable overall (points: 2 and 1, respectively).

On the other hand, when comparing dragon fruit-based smoothies (‘light’) DB1 and DB2, it was observed that there were no statistically significant differences in aroma, color, consistency, and overall appearance, except taste, among Polish panelists (p = 0.05). In the group of the foreign panelists, there was only a significant difference in consistency of the analyzed smoothies. For the formulation containing dragon fruit and white mulberry extract capsule, no statistical differences (p = 0.05) were shown between DC1 and DC2 in taste and color among Polish panelists and in taste, color, and consistency among foreign panelists.

After drying, the smoothies changed to powder form. Panelist were also asked to analyze this new form of smoothie. Polish panelists favored the dried form of DC1 and DC2 (in descending order), while foreign panelists preferred DC2 and DB2 (dried smoothies). When comparing these results with the sensory test results obtained for smoothies before lyophilization, the preferred types of smoothie were totally different. Moreover, it was clear that the preferred dried form of smoothie was the one without chia seeds.

Paired comparison tests within each group yielded further insights. Dragon fruit-based smoothies (DB1 vs. DB2) showed no significant taste or aroma differences but significant variations in color and consistency. The inclusion of chia seeds and capsules in DC1 resulted in significant taste and color differences compared to DC2. Foreign panelists exhibited a wider range of variations. Dried DB1 samples displayed significant variations (p = 0.05) across all sensory features compared to the control with drops (DB2). Finally, DC1 and DC2 differed significantly in taste, color, and overall appearance. These findings suggested that the addition of chia seeds and mulberry extract capsules could significantly impact the sensory profile of the dried smoothies, particularly in the foreign panelists group.

The last part of the experiment focused on reconstruction of the smoothie into liquid-like form. During the study, the reconstructed form was also analyzed by panelists, which revealed distinct preferences between Polish and foreign panelists. Polish panelists favored reconstructed DC1 and DB1 smoothies, while foreign panelists preferred DC1. This suggested that DC1 (dragon fruit with mulberry leaf capsule and chia seeds) was the most attractive for all panelists in the final proposed new form of smoothie, according to the aim of the study.

When comparing the reconstructed smoothies with the fresh smoothies, surprisingly it was found that the least preferred sample before lyophilization (DC1) was the most preferred in lyophilized form by both Polish and foreign panelists. When comparing the dragon fruit-based reconstructed smoothies (DB1 and DB2), there were significant differences found in taste, aroma, and color when p = 0.05; however, between DC1 and DC2 samples, there were significant differences in all sensory attributes except consistency. Regarding the dragon fruit-based smoothies, it was clearly found there were no significant differences between DB1 and DB2 in all sensory profiles at α = 0.05, but when comparing DC1 with DC2 samples, significant differences in all sensory profile attributes like taste, aroma, consistency, color, and overall appearance were found.

In brief, the smoothies made with small amounts of mulberry and licorice drop extracts were generally preferred in the fresh form. However, among the panelists, capsules containing mulberry-based smoothie were found to be most appealing after undergoing drying and reconstitution, even though they were least favored in their fresh form. It can be concluded that the lyophilization process was helpful in introducing the new final form of smoothie with higher amounts of proposed extracts to the panelists without lowering the sensory evaluation scores.

Generally, variants without chia seeds were preferred by the Polish group more than foreigners in reconstructed form, in contrast to fresh or dried smoothies. Polish panelists scored all fresh variants higher than foreigners, who preferred dried smoothies (higher scores). Mostly, dried or reconstructed smoothies with higher licorice and mulberry extract addition were scored higher than DB samples (lower licorice and mulberry addition) in both groups.

The sensory evaluation revealed nuanced preferences among Polish and international consumers (panelists), with varying preferences observed for dried versus reconstructed smoothies. DC2 (with lower concentration of ME and LE, without CS) and DB1 (with higher concentration of ME and LE, with CS) samples in dried and reconstructed form garnered widespread acceptance, highlighting their potential appeal across diverse demographic segments. On the other hand, the mulberry-licorice drop-based smoothies were preferred as fresh. Yet dried and reconstructed mulberry capsule-based smoothies were favored overall. Smoothies, as products, seem to be interesting to food-conscious staff and can change dietary habits into pro-healthy ones. Bates et al. [49] found that serving smoothies to children for breakfast at school led to an increase in the fraction of middle or high school students eating whole fruit during the day (from 4.3% to 45.1%). McCartney et al. [10] observed that Australian people decided to consume smoothies due to their ‘nutritious’ character (84%), willingness to increase the amount of fruits/vegetables in their diet (57%), or nutrients (50%). The presence of licorice in smoothies can shape the sensory analysis results to a large extent. Saponins from licorice are responsible for its specific sweet taste. However, the spatial arrangement of functional groups in the triterpenoid E-ring results in the well-known bitter/sweet taste of licorice products [50]. Therefore, its application in food product should always be considered according to consumers’ sensory perceptions.

Together with licorice, mulberry elements were used as components of the smoothie. In the literature, mulberry leaves and/or fruits were proposed as important functional components (in different amounts) of many other food products, including–yogurt, bread (fruits 3.7–6.4%, leaves 2.0%), flat bread (leaves 2.0%), snacks (leaves 1.0–5.0%), muesli (fruits 16.7%), cookies (leaves 4.0–12.0%), and meat alternatives (leaves 0.5–25.0%) [26,51,52,53,54,55]. In the dried smoothie, it was found that the proposed mulberry leaf extract addition (150–750 mg per portion) did not significantly affect the sensory evaluation results in taste and overall appearance of the smoothies, regardless of the form of extract (powder/capsules or liquid/drops). Mostly, mulberry fruits are proposed to be added in dried form (whole or grinded) and rarely in fresh form (limited availability). Mulberry leaves are introduced in dried (grinded) form or dried or liquid extracts (mainly in dietary supplements) into food products, or separately as mulberry teas. Notably, the possibility of using white mulberry leaves as a food ingredient is still unregulated within EFSA law. While the use of mulberry leaves directly may be an obstacle for manufacturers, the proposed smoothie used a liquid extract already labeled as a dietary supplement.

To sum up, the findings of this study not only validate the nutritional and functional attributes of the mulberry-licorice-based smoothies but also position them as reliable candidates for market introduction and as a compelling alternative to conventional pasteurization techniques, together with their easy-to-prepare form. The designed smoothies with their potential benefits, especially antioxidant and possible antidiabetic effects, as well as broad consumer appeal, stand poised to make significant contributions to both dietary management and preventive healthcare practices.

4. Conclusions

During the experiments, the aim of the study was achieved by designing a novel form (dried) of easy-to-prepare product. Nutritious natural components with proven activity were applied to create a tasty, dried smoothie for conscious consumers. The meticulous selection of ingredients ensured a low-calorie, low-fat, and sugar-free formulation while prioritizing palatability and aesthetic appeal. Moreover, a technologically valuable production process, freeze-drying, was proposed for future manufacturers. Lyophilization emerged as a promising technique for such dried smoothie production, preserving important phytochemicals and significantly extending the shelf-life. The application of the chosen extracts led to heightened levels of bioactive compounds and significantly enhanced antioxidant activity across various smoothie formulations, particularly notable in combinations featuring mulberry leaf extract capsules. For verification of the results obtained, the next step could be the introduction of the smoothies into volunteers’ diets and identifying health effects, e.g., antioxidant status of blood plasma. Moreover, another antidiabetic parameter related to the presence of mulberry (DNJ content) could be measured and labeled for conscious consumers. From an industry point of view, the stability of the fresh smoothies should also be verified.