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Article

Characterization of a New Powdered, Milk-Based Medicinal Plant (Alcea rosea) Drink Product

by
Mustafa Mortas
Food Engineering Department, Faculty of Engineering, Ondokuz Mayıs University, Samsun 55139, Turkey
Sustainability 2023, 15(12), 9320; https://doi.org/10.3390/su15129320
Submission received: 26 April 2023 / Revised: 30 May 2023 / Accepted: 30 May 2023 / Published: 9 June 2023
(This article belongs to the Special Issue Food Science and Engineering for Sustainability)
Browse Figures
Versions Notes

Abstract

:
Alcea rosea, known as hollyhock, is an ornamental dicot flower in the Malvaceae family, and it has been used for different purposes, ranging from traditional medicine to food applications, through the use of its leaves, roots, and seeds. The hollyhock flowers possess several properties, including a diuretic, cooling, demulcent, emollient, febrifuge, and astringent effects. Hollyhock flowers were commonly included in a traditional medicine formulation for hypoglycemic or hypolipidemic treatments. Along with its use in traditional medicine, it has also been considered a valuable ingredient in some traditional food preparations; however, the processing of hollyhock into a new food product has not been studied. Accordingly, this study aimed to evaluate the production of a new product, a milk-based Hollyhock (Alcea rosea) powder, and its powder product characterization via particle size, water activity, density, flowability, etc., in addition to the determination of its chemical composition (with 5.73% ash and 29.12% protein). In this paper, we report the application of spray-dried milk-based hollyhock flower extract to produce a new ready-to-drink product of this medicinal plant for food sustainability.

1. Introduction

Hollyhock (Alcea rosea) belongs to the Althaea genus and Malvaceae (Mallow) family. It is commonly known as marshmallow plant but can be called different names depending on the location. It is called hollyhock in English; malva rosa and rosoni in Italian; shi kui in Chinese; passe rose and rose paple in French; khatmae in Arabic; jeop-si-kkot in Russian; and rishak hatmi, khatmi, and khaira in Japanese [1]. The reason why it is so well known is that it has been used in traditional treatment processes from the past to the present. Traditional medicine is the oldest method of curing diseases and infections, a practice that uses various plants, and hollyhock is one of them [2]. Although hollyhock was reported to have originated from China or tropical areas [3], similarly to other common medicinal plants, its different parts, including the leaves, roots, and seeds, have be used in various applications all over the globe [4].
The health-promoting attributes of different parts of the hollyhock plant have been investigated; its roots are used against a wide range of health problems, such as diarrhea, constipation, inflammation, bronchitis, severe cough, and angina [5]. The whole plant has favorable effects on asthma, coughing, throat pain, jaundice, swelling, stomach irritation, kidney pain, and urinary irritation [6]. Furthermore, its flowers, ranging from white to dark red [7], present some significant properties, such as diuretic, cooling, demulcent, emollient, febrifuge, and astringent effects [8]. Lastly, the anti-influenza properties of hollyhock were investigated in mice, and the data suggested promising results for its use as an anti-influenza drug [9].
In addition to its health benefits, the hollyhock flower can also be consumed in different ways [10]. It can be one of the agents in herbal tea mixtures for brightening [2] and can be used as a cooking material for different purposes [10]. Moreover, a novel product that has been developed [11] is an edible film made of hollyhock flower gum. The flower petals, flower buds, and hollyhock leaves are also used in salads [10] and can be used with milk to obtain a milky extract for health benefits. Although hollyhock flowers were usually prepared with milk for use in traditional medicinal formulas for hypoglycemic or hypolipidemic treatment, there are currently no similar industrial products, such as a milky drink or powdered formulas. For this purpose, a new possible product was produced from hollyhock flower (Figure 1) mixed with milk by using a spray dryer, and the quality parameters of the product, in terms of chemical composition and physical properties, were investigated.

2. Materials and Methods

2.1. Materials

For producing the traditional milky hollyhock extract, the milk (M) with 1.5% fat (Birsah, Selçuklu/Konya, Turkey) and dried hollyhock flowers (Alcea rosea) (Toroslar Naturel Aktar Organik, Toroslar/Mersin, Turkey) used in the study were obtained from local markets in Samsun, Turkey. The chemicals used for all the listed methods were Sigma-Aldrich and Merck brands.

2.2. Preparation Methods

Traditional milky hollyhock extract was produced with milk and hollyhock flower; a spray dryer (Bushi, B-290) was used to create the powdered product after the extract was obtained. In addition, reconstitution was applied to the powdered product to compare it to the traditional extract. The traditional milky hollyhock drink was produced from milk and dried hollyhock flowers by adding about 25 g of the flowers into 500 mL of milk according to the traditional preparation ratio. The mixture was stirred and heated (50 °C) on a hot plate for 30 min; then, the mixture was filtered using filter paper. The dried milky hollyhock drink was produced from the milky hollyhock drink using a spray dryer with a 150 °C inlet temperature. The milk powder was produced from milk under the same spray dryer conditions in order to compare the effect of hollyhock in the milk. After spray drying was complete, the reconstituted hollyhock drink was produced from the dried milky hollyhock drink by dissolving the powder in water at the same Brix as the milky hollyhock drink. Through this process, the differences between the milk powder and dried new products, and between traditional milky drinks and reconstituted samples from the new product with 1–9% ratio were able to be compared.

2.2.1. Process Yield

The production process yield from milky hollyhock drink to dried milky hollyhock drink was calculated as the ratio of the total powder weight after spray drying to the initial amount of solid-liquid feed

2.2.2. Proximate Analysis

Proximate analysis as moisture contents, ash contents, pH levels, and protein contents were measured in both the milk powder and dried milky hollyhock drinks according to the Association of Office Analytical Chemists [12]. For water activity measurements, samples were filled in the special containers at 2/3 and measured at 25 °C (Aqualab Dewpoint Water Activity Meter 4TE, Pullman, WA, USA).

2.2.3. Total Phenolic Content

Total phenolic content (TPC) was determined according to Singleton and Rossi (1965). The extract (0.5 mL) was mixed with 2.5 mL Folin Ciocalteau’s phenol reagent (0.2 N) and 2 mL Na2CO3 (7.5%) and incubated at room temperature. After thirty-minute incubation, absorbance was measured at 760 nm using a UV/VIS spectrophotometer (Shimadzu UV-1800, Kyoto, Japan). TPC was expressed as gallic acid equivalent [13] and calculated according to Equation (1) as below;
TPC (mg/L) = [Absorbance − 0.0166)/0.0102] × Dilution Factor

2.2.4. Antioxidants Capacity

The antioxidant capacity analysis was conducted to determine the free DPPH radical scavenging capacity [14]. A total of 0.1 mL extract was mixed with 4.9 mL of DPPH solution (0.1 mM) in ethanol. After being incubated at room temperature for half an hour, the absorbance was measured at 517 nm. The antiradical activity (ARA, %) can be calculated using the following equation:
ARA(%) = ((Ac − As)/Ac) ×100
Ac represents the absorbance of the control (ethanol and DPPH), while As represents the absorbance of the sample. The results were expressed as Trolox equivalent and calculated using the following equation:
Trolox equivalent (mM) = [(ARA% + 0.5998)/56.608] × Dilution Factor

2.2.5. Measurement of Color Properties

The color properties were assessed using a Minolta colorimeter, which utilizes the CIELAB scale (L*, a*, and b*). The color parameters range from L* =  0 (representing dark) to L*  =  100 (representing light), −a* (representing greenness) to  + a* (representing redness), and −b* (representing blueness) to +b* (representing yellowness).

2.2.6. Viscosity Measurement

The rheological measurements of the samples were conducted using a rheometer (HAAKE Mars III; Thermo Scientific, Karlsruhe, Germany) equipped with a cone and plate system (diameter: 25 mm; cone angle: 2°; gap between cone; and plate: 0.106 mm). The samples were allowed to equilibrate for 5 min at the desired temperature (25 °C), and the measurements were performed at this temperature. The shear rate was increased linearly from 0.1 to 100 s −1 over a period of 3 min.

2.2.7. FTIR

The molecular differentiation of the milk powder and dried milky hollyhock drink samples was determined using an MN 115 Bruker Tensor 27 FTIR (Rheinstetten, Germany) with a wavelength range of 4000–400 cm−1. Prior to measuring the samples, background spectra of the medium were collected and recorded using OPUS software 6.5 (Bruker Corporation, Ettlingen, Germany).

2.2.8. Sensory Evaluation

The samples were evaluated by a panel of 15 individuals consisting of semi-trained staff and graduated students. The evaluation criteria included color, taste aroma, viscosity and mouthfeel, which were assessed using a numerical scale ranging from 1 to 9. The samples were enumerated with different three-digit numbers.

2.2.9. Mineral Contents

Approximately 1 g of powder sample was weighed. It was turned into ashes at 500 °C in the furnace (Nuve MF 120). Then, the ash was dissolved in 3N HCl by stirring in a heater for 10 min. Subsequently, the ash was filtered through filter paper (Whatman no.1). Sodium (Na), potassium (K), and calcium (Ca) contents were determined using the BWB-1 Flame Photometer. Phosphorus (P) was determined using the vanadomolybdophosphoric acid colorimetric method [15]. The measurement of phosphorus was performed at 420 nm using a UV/Vis spectrophotometer (Agilent Technologies, Cary 60, Victoria, Australia). The phosphorus contents of the samples were calculated based on a calibration curve (y = 0.0397x + 0.014, R2: 0.9997) constructed using KH2PO4.

2.2.10. Powder Characterization

The loose density (ρL) of the milk-based Alcea powder was determined by pouring it into a 25 mL graduated cylinder and measuring the corresponding weight. Tapped density (ρT) was determined after completing the tapping process 125 times. Apparent density (ρP) was measured using a gas steropycnometer (Quantachrome Instruments, Boynton Beach, FL). The samples were placed into sample cells and degassed by purging with helium gas. The porosity (Ɛ) was calculated based on the relationship between the tapped bulk density (ρT) and apparent density (ρP) as follows:
Ɛ = ((ρP − ρT)/ρP) × 100
Cohesiveness (Hausner ratio, HR) properties of powders were characterized by a ratio of the two density types.
HR = ρT/ρL
where ρT is tapped density, and ρL is loose density.
The flowability properties of the powders were evaluated using Carr’s index (Cl) and angle of repose (AOR) approach.
Cl = (ρT − ρL)/ρT × 100
where ρT is tapped density, and ρL is loose density.
The AOR value was measured using a powder AOR device (Torontech, ON, Canada). The angle of repose (AOR) (θ) was calculated using the following formula:
AOR(θ) = arc tan  h/r
where h is the height of powder after dropping;, and r is the average radius of powder after dropping.
The physical properties of the powder are presented in Table 1.

2.2.11. Solubility

The total solubility of the powder was assessed by determining the total solids remaining after dissolution and centrifugation [16]. A total of 0.1 g of the powder was dispersed in 24.9 g of distilled water and stirred for 30 min to ensure proper dispersion. The dispersions were then transferred to 50 mL conical tubes and centrifuged (Hettich 320R, Germany) at 5000 rpm for 20 min. The supernatant was carefully transferred to a preweighed moisture dish and dried overnight at 105 °C. The solubility was calculated using the following the equation:
Solubility (%) = (Weight of the dry supernatant)/(Weight of the supernatant × 0.4%) × 100

2.2.12. Particle Size Distribution (PSD)

The particle size distribution (PSD) levels of the samples were determined using a static laser light (Malvern Mastersizer 2000 with Hydro 2000S (A), Malvern Instruments Ltd., Worcestershire, UK). The powder samples were dispersed into ultrapure water at a ratio of 1:100 for measurement. The refractive index used for the powders was 1.57, while that for water was 1.33 [17]. The mean diameter of the powdered sample was evaluated using Equation (9) for volume-weighted mean diameter (d4,3) and Equation (10) for particle surface area (d3,2). This approach is useful when the particles are not ideal spheres, as the (d4,3) value is more influenced by the larger particles, while the d3,2 value is more influenced by the smaller particles [18]. The values of d0.1, d0.5 and d0.9 represent the cumulative percentiles and indicate that 10%, 50% and 90% of the particles, respectively, fell below the specified diameter [19],
d4,3 = (∑inidi4)/(∑ inidi3)
d3,2 = (∑inidi3)/(∑ inidi2)

2.2.13. Scanning Electron Microscopy (SEM) Analysis

For SEM analysis, the morphological properties of the powder samples were examined using a scanning electron microscope (JEOL JSM-7001FTTLS LV, Peabody, MA, USA). The images of the samples were captured at 5 kV with magnifications of ×100 and ×2000.

2.2.14. Statistical Analysis

All the measurements occurred triplicated and statistical analysis, comparison of Tukey’s test results, was analyzed with Statistical Package for Social Sciences (SPSS), v23.0 (IBM SPSS Statistics, Armonk, NY, USA).

3. Results and Discussion

3.1. Process Yield

Process yield is an important factor for production cost as it is closely related to the morphologies of the particles and is critical for powder flowability, redispersibility, and density. All the mentioned morphological properties are affected by the operating conditions of the spray dryer spray, such as drying air temperature, feed rate, and viscosity [20]. Additionally, the presence of sugars in the extract is closely related to process yield [19], and phenolic content is another factor that affects the stickiness of powders [21]. In this situation, the stickiness of herbal extract on the dryer walls was similar to the spray drying process of herbal medicinal powders (P. boldus and C.asiatica), and the process yield of the mentioned process was found to be 46% by Gallo et al. [19]. Our process yield percentage for dried hollyhock drink was found to be 53%, which is within the mentioned range, and the main reason for the lower process yield is closely related to the presence of high-chain carbohydrates in the sample.

3.2. Proximate Analysis

In this study, proximate analysis of milk powder and dried milky hollyhock drink samples were conducted to compare differences at the same process conditions in terms of adding hollyhock into the milk. The dry matter of the dried milky hollyhock drink sample was found to be 98.40 ± 0.29, while the milk powder had a dry matter of 99.42 ± 0.43. The dry matter value of the dried milky hollyhock drink was higher than that of the MP because the soluble dry matter of the dry hollyhock flowers in the milk contributed to an increase in the dry weight of the dried milky hollyhock drink. The situation was similar for the ash content as the value of the dried milky hollyhock drink (5.73 ± 0.28) was higher than the milk powder value (4.67 ± 0.21) because the mineral content of the dried milky hollyhock drink was more than the milk powder sample. The pH value of the milk powder (6.693 ± 0.006) was found to be a higher value than the dried milky hollyhock drink one (6.340 ± 0.053). In addition to this, the pH value of the reconstituted hollyhock drink was determined as 6.347 ± 0.006. It was statistically different but closer to each other, and changes in pH and acidity can affect the stability of the structural network of the drink [22]. There was no statistical importance between the protein content of the milk powder (29.92 ± 2.40) and dried milky hollyhock drink (29.12 ± 1.26) samples. Water activity (aw) results of the samples milk powder (0.1463 aw) and dried milky hollyhock drink (0.0931 aw) are given in Table 2, and the result is similar to other research (aw 0.20) [23].

3.3. Total Phenolic Content (TPC)

The spray drying process can decrease the total phenolic content. It has been reported that using an inlet temperature of 150 °C (air outlet temperature: 80 °C) for the spray drying process can recover approximately 94% of bioactive antioxidant components, such as phenolic content and total anthocyanins in bayberry juice [24]. Prior to the spray drying process, the milky hollyhock drink had a TPC value of 681.44 ± 9.88 mg GAE/kg, whereas the dried milky hollyhock drink had a TPC value of 603.56 ± 10.52 mg GAE/kg after the process. The spray-dried process yield of the TPC recovery was calculated as 88%, which was acceptable for this kind of heat-based process. In a study involving 56 medicinal plants, the total phenolic content ranged from 0.12 ± 0.01 to 59.43 ± 1.03 mg GAE/g, and our finding for phenolic content of the hollyhock were consistent with the literature [25].

3.4. Antioxidant Capacity

One of the factors contributing to diseases, such as atherosclerosis, cancer, aging, and coronary heart diseases, is oxidative stress [26,27,28]. Minimizing oxidative stress is crucial for promoting our physical condition and preventing degenerative diseases. The total antioxidant capacity of the milky hollyhock drink was calculated to be 1.49 ± 0.07 mmol Trolox/g, while the dried milky hollyhock drink had a total antioxidant capacity of 1.32 ± 0.04 mmol Trolox/g. The recovery ratio of antioxidant capacity value for the spray drying process was calculated as 89%. Similarly, the antioxidant capacity values of some medical plants ranged from 0.61 ± 0.05 to 326.87 ± 7.17 μmol Trolox/g [25]. Furthermore, the results for the other medicinal plants were consistent with our results [29,30].

3.5. Color Measurements

Color is a crucial quality attribute for food products because the appearance can significantly impact consumer acceptability as it is the first thing consumers judge. Dried hollyhock flower can impart color to the milk. The L*, a*, and b* values for milk powder were found to be 91.80 ± 0.01, 0.41 ± 0.00, and 10.98 ± 0.00, respectively. For the milky hollyhock drink, the values were 66.79 ± 0.03, 67.17 ± 0.08, and 0.02 ± 0.00, respectively. Kalusevic et al. [31] observed the highest L* and a* values in their spray-dried black soybean coat extract, indicating that this sample had the darkest color with the highest proportion of red. Hollyhock flowers contain carbohydrates, cyanides, tannins and alcea mucilage, and kaempferol, which is present in all flower varieties. Additionally, different flower colors such as pink and orange, mauve and red, white and yellow contain herbacetin, quercetin, and undefined pigments, respectively [8]. After extracting hollyhock flowers into milk, the spray drying process affects color values of the milky hollyhock drink and dried hollyhock drink samples, resulting in L*, a*, and b* values of 77.75 ± 1.37, 1.22 ± 0.03, and 3.03 ± 0.06, respectively, for the dried hollyhock drink. The observed color differences between the samples were primarily due to variations in the b* values, which is typical for the spray-dried product in terms of increased yellowness. This could be attributed to the presence of sugars [32], mucilage and pigment degradation. After preparing the dried hollyhock drink sample, it was reconstituted in the same ratio to prepare the reconstituted hollyhock drink, and the L*, a*, and b* values were measured as 67.17 ± 0.08, 0.26 ± 0.01, and 2.37 ± 0.02, respectively. Furthermore, there were statistical differences in the L* value between dried milky hollyhock and reconstituted hollyhock drink samples, but there were none in the a* and b* values.

3.6. Viscosity

The viscosity range for milky hollyhock drink was measured as 1.916–9.597 mPas, while for the reconstituted hollyhock drink samples, it was 0.848–2.269 mPas (Table 3). Generally, the viscosity values of the milky hollyhock drink samples were higher than those of the reconstituted hollyhock drink samples. The viscosity values of all reconstituted hollyhock drink samples, with different concentrations (1–9%), were higher than the viscosity value of the milk used as a control. This can be attributed to the direct effect of the polysaccharide structure of alcea mucilage on viscosity; however, after applying the reconstitution step using different concentration scale (1–9%) for the reconstituted hollyhock drink, the viscosity values of some samples (1, 3, 5%) were found to be lower than that of the milk sample (1.556 mPas). The main reason for the lower viscosity in these cases is the heat treatment during the spray drying process, which leads to the breakdown of the polysaccharide chains in the alcea mucilage.

3.7. FTIR

The FTIR spectra of the milk powder and powdered hollyhock in the 4000–400 cm−1 spectroscopic region are shown in Figure 2. The figure indicates that the O-H groups, which belong to bound water, and N-H streches of proteins were observed in the 3000–3700 cm−1 and 2800–3000 cm−1 regions, respectively. The vibrational modes of CH groups were represented by the centered peaks at 2917.61–2988.22 cm−1. The protein amide groups (-CONH-) appeared as a peak at 1640 cm−1 [33], and the C=O stretch assigned to acetyl groups was centered at 1646 cm−1 [33]. Furthermore, the peaks centered between 1300 and 1450 cm−1 correspond to CH2 or C=O-H groups, and OH in plane bending [34]. The peaks between 800 and 1200 cm−1 were attributed to the stretching of CO, CC, COC and to the skeletal modes of vibration of sugar residues [35,36]. In a study related to Alcea rosea flower extract encapsulated with nanoparticles, the main peaks in the FTIR spectrum were attributed to oxygen-bearing functional groups [37].

3.8. Sensory Evaluation

Adding hollyhock extract up to 3–5% to milky hollyhock drink and hollyhock powder to reconstituted hollyhock drink samples has a negative effect on sensory scores. The color values of low concentration samples, both milky hollyhock drink and reconstituted hollyhock drink, were acceptable to sensory analysts. As the concentration increased, the sensory scores decreased, which was consistent with the changes in L* and b*, while the a* values. The overall acceptability scores were higher for samples with concentration between 1 and 5% compared to the other samples. It was observed that as the concentration increased, the acceptability of the samples improved due to the presence of polysaccharides and mouthfeel, but the sensory scores decreased as the color deviated from the color of milk (Table 3). The situation is similar to the browning observed in watermelon powder due to presence sugar [32]. Alcea rosea contains mucilage, which is a high molecular weight acidic polysaccharides ranging from 1.3 to 1.6 million Dalton and is abundant in flowers. The mucilage is composed of glucoronic acid, galacturonic acid, rhamnose, and galactose. Some of the acidic polysaccharides also contain carboxyl groups and/or sulfuric ester groups; therefore, the sulfuric ester groups can be a major factor contributing to the aroma acceptability of the product [38].

3.9. Mineral Contents

Mineral contents (Na, K, Ca, and P) of the milk powder and dried milky hollyhock drink samples are given in Table 2. The mineral contents of the milk powder were found to be consistent with the values reported in the literature [39]; however, for the dried milky hollyhock drink, the addition of hollyhock resulted in increased mineral contents in the product. The dried milky hollyhock drink exhibited higher levels of P, Ca, and Na, with values of 747 mg/100 g, 724 mg/100 g and 502 mg/100 g, respectively, compared to regular milk powder. Hollyhock can be utilized to enhance the mineral contents in milk due to its natural mineral composition, which includes calcium, sodium, potassium, and phosphorus [1].

3.10. Powder Characterization and Particle Size Distribution

While powder characterization is important for assessing a new spray-dried product, the shape of the particles generally tends to be spherical with a size range of 10–250 microns, which is primarily influenced by the properties of the spray dryer nozzle [40]; however, the overall properties of the food samples are equally significant. The D [4,3] (the volume-weighted mean) and D [3,2] (the surface weighted mean) diameters values of the milk powder were determined as 55.35 and 25.00 microns, respectively. For the dried milky hollyhock drink samples, the corresponding values were calculated as 29.1 and 21.3 microns, respectively (Table 4). Fitzpatrick et al. [41] also reported values of 53 and 99 microns for skim milk and whole milk, respectively. Additionally, the D [4,3] value for infant milk formula was found to be 155.4 microns by Murphy et al. [42]. Powder flowability is directly influenced by the drying process and is affected by both the size distribution and interparticle relationships [43]. Narrower size distributions tend to result in better flow properties [44]. Carr’s index, also known as the compressibility index, measures a powder’s ability to reduce in volume when tapped [43]. According to the classification in Table 1 based on Carr’s index (CI) and the Hausner ratio (HR), the CI value for milk powder was determined to be 40.60, indicating very poor flowability. Similarly, the dried milky hollyhock drink exhibited a CI value of 36.93, also indicating very poor flowability. The poor flowability can be attributed to the increased contact surface area between powder particles, which enhances frictional and cohesive forces impeding powder flow [45]. While, both samples demonstrated similar flow tendencies, there were statistical differences between them.
Another parameter that can affect the powder flowability is the Hausner ratio (HR), for which the values were calculated as 1.68 and 1.56 for milk powder and dried milky hollyhock drink, respectively. Similar results were observed for HR values as for Carr’s index (CI). Ilari and Mekkoui [46] calculated HR values of 1.59 for skim milk and 1.26 for whole milk, which align with the findings in the present study. The presence of large agglomerates and minimal fines can contribute to improved flow properties of powders [46]. Lower cohesion due to weaker Van der Waals forces and reduced friction is one of the main reasons for larger particle size [46]. The density of the powder is also associated with the economic factors, such as packaging, transportation and storage cost in the dairy industry [47]; therefore, bulk density, also known as apparent or packing density, is used as a measure of powder mass. It depends on particle density, internal porosity of particles, their porosity of particles, and their arrangement within the container. In addition to that, another factor can be listed as the volume of solids/liquids and open/closed pores [48]. In this study, the bulk density (ρT) was determined as 0.22 kg/m3 for milk powder and 0.31 kg/m3 for dried milky hollyhock drink. Literature reports various bulk density values for milk powders ranging from 0.30 to 0.62 kg/m3 [44]. Bulk density can be categorized in four ways [48], and the tapped density, one of the density groups, is particularly useful in describing the powder behavior during compaction [44].
Powder density is also linked to economic challenges in the dairy industry, such as packaging, transportation and storage costs. In this study, the bulk density values were 0.37 for MP and 0.49 kg/m3 for DMHFEP samples. While the presence of milk fat decreased the bulk density and the flowability of cow milk powder [9], the inclusion of starch in powder form can increase the tapped density [15]. Another important physical property, known as the angle of repose, is used to characterize the bulk behavior of particulate foods characterization and design processing, storage, and conveying systems. A high angle of repose is indicative of very fine and sticky food, while a low angle of repose suggest highly flowable food [49]. In this study, the angle of repose values was calculated as 35° for MP and 42° for DMFEP, with the hollyhock-based milk powder having a higher value than the milk powder. The addition of an extra component, such as Alcea rosea, can increase the apparent density, which is consistent with findings from previous research [50].
For dairy powders, the solubility is based on the remaining amount of total solids in the supernatant after the stirring and centrifugation process [16]. This technique can be applied to different dairy powder products, such as cheese powder [51]. The solubility values of the milk powder and dried milky hollyhock drink samples were calculated as 90 and 84%, respectively. The lower solubility of the dried milky hollyhock drink sample compared to the milk powder can be attributed to the fact that small hydrophilic molecules promote dissolution [52]. Achieving high solubility in milk powder production is important for its future applications, as solubility is a key factor on the solubility of milk powder [53]; however, milk fat content can be as a significant influencing factor on the solubility of milk powder [47]. Additionally, the presence of mucilage has a negative effect on solubility due to its long-chain molecular structure.

3.11. Particle Appearance

The morphological characteristics of the particles in the samples are described in Figure 3. As observed in the micrographs, milk particles with hollyhock extract exhibit larger particles and have smaller materials surrounding them. The presence of agglomerates in samples, as confirmed by scanning electron microscopy (SEM) and light microscopy, aligns with the specifications for powder physical properties. The morphological changes observed in the samples produced by spray dryer are consistent with previous findings [54].

4. Conclusions

Although the hollyhock (Alcea rosea) plant and its various parts have been used in traditional medicine for hypoglycemic or hypolipidemic treatment, there is currently no processed industrial product available in the literature or markets. Based on the results of the aforementioned study, it is possible to develop a new powdered product from the traditional milky hollyhock drink. This new powdered product possesses distinct nutritional and morphological properties when compared to milk powder, including differences in terms of particle size, water activity, density, and flowability. Additionally, the inclusion of hollyhock can contribute to increased mineral content, such as sodium (Na) and potassium (K). Through sensory evaluation, it was determined that the optimal concentrations of hollyhock flower and the new powder were 5% for both the traditional milky drink and reconstituted drink.
This paper presents the application of spray-dried milk-based hollyhock flower extract for the production of a new ready-to-drink product derived from this medicinal plant. The resulting ready-to-drink powdered product can be used for general consumption due to its health benefits.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data developed in this study will be made available upon request to the corresponding authors.

Conflicts of Interest

The author declares no conflict of interest.

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Sustainability 15 09320 g001 550
Figure 1. Hollyhock flower (Alcea rosea).
Figure 1. Hollyhock flower (Alcea rosea).
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Figure 2. FTIR spectra of the milk powder and hollyhock extract powder.
Figure 2. FTIR spectra of the milk powder and hollyhock extract powder.
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Figure 3. Scanning electron micrographs of hollyhock extract powder (A,B) and milk powder (C,D).
Figure 3. Scanning electron micrographs of hollyhock extract powder (A,B) and milk powder (C,D).
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Table
Table 1. Specification for powder physical properties.
Table 1. Specification for powder physical properties.
FlowabilityCarr’s Index (%)Hausner RatioAngle of Repose (°)
Excellent0–101.00–1.1125–30
Good11–151.12–1.1831–35
Fair16–201.19–1.2536–40
Passable21–251.26–1.3441–45
Poor26–311.35–1.4546–55
Very poor32–371.46–1.5956–65
Very, very poor>38>1.60>66
Table
Table 2. Analysis results of milk powder and dried hollyhock extract.
Table 2. Analysis results of milk powder and dried hollyhock extract.
AnalysisMilk PowderDried Hollyhock Extract
Dry Matter (%)98.40 ± 0.29 b99.42 ± 0.43 a
Ash Content (%)4.67 ± 0.21 b5.73 ±0.28 a
Water Activity (aw)0.1463 ± 0.0033 a0.0931 ± 0.0009 b
Protein content29.92 ± 2.40 a29.12 ± 1.26 a
pH6.693 ± 0.006 a6.340 ± 0.053 b
Mineral ContentsNa (mg/100 g)429.52 ± 22.14 b502.71 ± 17.37 a
K (mg/100 g) 1652.18 ± 41.51 a1346.91 ± 41.44 b
Ca (mg/100 g)724.02 ± 13.84 a704.31 ± 15.92 a
P (mg/100 g)418.96 ± 3.48 b747.45 ± 1.78 a
Values are means ± standard deviation. (a,b) Different letters on the same line show the significant differences (p < 0.05) between samples.
Table
Table 3. Sensory and appearance of the milky hollyhock extract and reconstituted milky hollyhock drink.
Table 3. Sensory and appearance of the milky hollyhock extract and reconstituted milky hollyhock drink.
SamplesHollyhock Amount %ViscosityColor ValuesSensory Evaluation
L*a*b*ColorConsistencyAromaSandinessOverall Accep.
Milk01.556 ± 0.073 efg81.84 ± 0.03 a−2.80 ± 0.01 h5.41 ± 0.00 a9.22 ± 1.71 a9.00 ± 1.58 a4.66 ± 1.53 a9.55 ± 0.72 a8.88 ± 1.27 a
Milky hollyhock extract11.916 ± 0.195 ef75.25 ± 0.03 b−0.33 ± 0.00 g4.62 ± 0.01 b7.11 ± 2.31 ab6.00 ± 2.44 a6.22 ± 1.43 a9.33 ± 1.11 a5.77 ± 2.05 a
33.417 ± 0.282 d68.71 ± 0.01 c1.64 ± 0.03 e3.55 ± 0.00 c5.44 ± 1.08 ab6.44 ± 1.94 a6.55 ± 1.81 a9.11 ± 1.53 a5.44 ± 1.87 a
54.899 ± 0.359 c64.98 ± 0.01 d2.55 ± 0.00 c2.67 ± 0.01 d4.33 ± 1.06 b5.22 ± 2.68 a6.55 ± 1.81 a8.88 ± 1.45 a5.11 ± 1.52 a
76.641 ± 0.541 b62.18 ± 0.24 e3.09 ± 0.02 b2.03 ± 0.01 g4.45 ± 1.12 b6.33 ± 1.23 a7.11 ± 2.14 a9.22 ± 1.45 a4.33 ± 2.34 a
99.597 ± 0.741 a59.43 ± 0.48 f3.55 ± 0.03 a1.37 ± 0.04 h4.66 ± 1.80 b7.33 ± 1.65 a7.55 ± 1.74 a9.22 ± 1.39 a3.88 ± 2.47 a
Reconstituted hollyhock drink10.848 ± 0.086 fg45.87 ± 0.02 h−1.28 ± 0.01 h−2.29 ± 0.01 j5.66 ± 1.57 ab4.55 ± 1.69 a5.11 ± 1.16 a8.88 ± 2.31 a3.88 ± 1.96 a
31.025 ± 0.069 fg58.89 ± 0.02 g−0.37 ± 0.00 g1.02 ± 0.01 i6.11 ± 1.31 ab5.44 ± 1.96 a6.22 ± 2.98 a9.00 ± 1.80 a5.00 ± 1.39 a
51.431 ± 0.036 efg64.50 ± 0.01 d1.15 ± 0.00 f2.21 ± 0.01 f4.78 ± 1.27 b5.33 ± 1.95 a6.00 ± 1.41 a9.22 ± 1.30 a5.55 ± 2.06 a
71.861 ± 0.066 ef64.65 ± 0.01 d2.21 ± 0.01 d2.23 ± 0.00 f5.11 ± 1.31 ab5.66 ± 2.69 a6.33 ± 1.93 a9.11 ± 1.69 a4.66 ± 1.54 a
92.269 ± 0.071 e64.91 ± 0.01 d2.23 ± 0.02 d2.55 ± 0.00 e4.77 ± 1.22 b6.22 ± 1.11 a6.33 ± 1.65 a8.66 ± 2.00 a5.00 ± 1.87 a
Values are means ± standard deviation. Different letters on the same column show the significant differences (p < 0.05) between samples.
Table
Table 4. Powder properties of the milk powder and dried hollyhock extract.
Table 4. Powder properties of the milk powder and dried hollyhock extract.
Milk PowderDried Milky Hollyhock Extract
Particle PropertiesBulk Density (ρT) (kg/m3)0.222 ± 0.003 b0.315 ± 0.003 a
Tapped Density (ρT) (kg/m3)0.378 ± 0.003 b0.490 ± 0.001 a
Carr’s Index (Cl) (%)40.606 ± 0.525 a36.932 ± 0.964 b
Powder Cohesiveness Hausner Ratio (HR)1.684 ± 0.015 a1.569 ± 0.023 b
Angle of Repose (AOR) (°)35.725 ± 2.043 b42.325 ± 2.489 a
Apparent density1.481 ± 0.050 b3.073 ± 0.039 a
Porosity (epsilon)64.123 ± 0.141 b84.360 ± 0.631 a
Particle SizeD10 µm0.091 ± 0.001 a0.068 ± 0.001 b
D50 µm0.532 ± 0.005 b3.315 ± 0.049 a
D90 µm249.5 ± 3.535 a27.35 ± 0.212 b
D [4,3] µMm55.35 ± 1.484 a29.1 ± 0.84 b
D [3,2] µm0.25 ± 0.001 a0.213 ± 0.008 b
a,b Means within a row with different superscripts differ (p < 0.05).
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Mortas, M. Characterization of a New Powdered, Milk-Based Medicinal Plant (Alcea rosea) Drink Product. Sustainability 2023, 15, 9320. https://doi.org/10.3390/su15129320

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Mortas M. Characterization of a New Powdered, Milk-Based Medicinal Plant (Alcea rosea) Drink Product. Sustainability. 2023; 15(12):9320. https://doi.org/10.3390/su15129320

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Mortas, Mustafa. 2023. "Characterization of a New Powdered, Milk-Based Medicinal Plant (Alcea rosea) Drink Product" Sustainability 15, no. 12: 9320. https://doi.org/10.3390/su15129320

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