Introduction

Temulawak (Curcuma xanthorrhiza Roxb.), also known as Java turmeric, is a native plant in Indonesia. In addition, temulawak is cultivated in other Southeast Asian countries such as the Philippines, Malaysia, and Vietnam.¹  It is reported that temulawak cultivation in Indonesia has been carried out massively, with a production area reaching 13.05 million m² and a harvest of around 24.33 million kg.² In Indonesia, temulawak is commonly used as a food supplement and herbal medicine to treat and control various diseases. This is inseparable from the health effects of temulawak, which have been confirmed to have pharmacological properties such as anti-oxidative, anti-inflammatory, antitumor, antibacterial, nephroprotective, and neuroprotective to hepatoprotective activities.³

Curcuminoids are the most abundant phytochemicals reported in temulawak. Therefore, the health effects of temulawak mostly come from this compound.⁴ Curcuminoids in temulawak consist of curcumin, demethoxycurcumin, and bisdemethoxycurcumin,⁵ of which are abundant in the temulawak rhizome.³ Specifically, curcumin from temulawak rhizome has been reported to be obtained through liquid-liquid extraction using ethanol and n-hexane solvents. The resulting extract showed intense antioxidant activity, with an IC₅₀ value of 87.01 ppm.⁶ Despite its various health effects, curcumin has drawbacks such as low solubility in water, short shelf life due to poor chemical stability, low bioavailability due to suboptimal absorption, rapid metabolism that is easily eliminated, and most molecules produce a bitter taste.^3,7

Microencapsulation of curcumin compounds by spray drying is a new approach that has been recommended.⁸ This method is known to be more competitive on an industrial scale and allows the production of commercially profitable powders.^9-10 The method produces curcumin microcapsules applied to dairy products and their derivatives.^11-13 Spray drying has been shown to increase curcumin’s stability significantly.¹⁴ The resulting microcapsules contain bioactive components in the core surrounded by a layer of coating material. Coatings provide a physical barrier that prevents molecular diffusion and chemical reactions, thereby increasing the stability of the encapsulated compound. Therefore, selecting coating materials is an essential step in the microencapsulation process of curcumin.¹⁵ Amount studies have summarized various types of coating materials that can be used in curcumin microencapsulation, such as the use of Maltodextrin (MDE) in microencapsulation of curcumin from Curcuma longa,¹⁶ whey protein isolate (WPI) in microencapsulation of commercial curcumin powder^17-18 and gum arabic (GAR) in microencapsulation of curcumin from Zingerol officinale.¹⁹

Microcapsules with a single coating material generally have lower performance, while combining two structurally different polymers may provide better results, especially regarding stability and solubility in water.²⁰ using composite coating materials has been proposed to prepare curcumin microcapsules. This is associated with the ability of the composite coating material, which has a role as an emulsifier, film former, matrix former, and filler.²¹ Based on previous studies, it was concluded that the addition of β-cyclodextrin (βCD) as a composite coating material significantly increased the efficiency of curcumin microencapsulation, followed by increased stability to high temperatures and acidic conditions.¹⁵ In addition, the addition of βCD as a coating material has been confirmed to cover the bitter taste of catechin,²² prevent hygroscopicity, and maintain bioactive compounds from the core material.²³ These results are also expected in the microencapsulation of curcumin from temulawak.

Based on the description above, various studies have reported the superior efficacy of curcumin microencapsulation from various coating materials. However, no study has used MDE, WPI, and GAR composite coating materials combined with βCD to microencapsulate curcumin from temulawak extract. Therefore, this study was conducted to prepare curcumin microcapsules from temulawak using composite coating materials MDE, WPI, and GAR combined with βCD produced by spray drying. This study provides a precious reference for selecting the best coating material in preparing curcumin microcapsules from temulawak using spray drying.

Materials and Methods 

Materials and Chemicals

Temulawak rhizome powder was obtained from local farmers in Semarang, Indonesia. MDE with DE 10-12 from Lihua Starch (China), WPI with 90% protein content from Beyon Nutrisi (Indonesia), GAR from Ingredion (Thailand), and βCD from Landor Trading Company (Thailand). Chemicals such as ethanol, n-hexane, methanol, curcumin, quercetin, gallic acid, folin-ciocalteu and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) from Sigma Chemical Company (Sigma-Aldrich, St. Louis, Missouri, USA).

Preparation of Curcumin Extract

Temulawak rhizome powder was macerated using 70% ethanol at room temperature for 24 hours, filtered (200 mesh), and concentrated using an evaporator at 50 °C. The extract obtained was then purified using the liquid-liquid extraction method, n-hexane 1:3, for 30 minutes, using a separating funnel. The temulawak extract was in the ethanol phase (bottom layer). The ethanol solvent was then separated using an evaporator until a thick temulawak extract was obtained.^6,24

Preparation of Curcumin Microcapsules

Curcumin microcapsules of Javanese ginger were formed using various composite coating materials consisting of structure-forming materials (MDE, WPI, and GAR) and auxiliary materials (βCD). First, at room temperature, each structure-forming material (19 g) was dissolved in 100 ml of distilled water using a homogenizer for 10 minutes (10,000 rpm). Then, βCD (1 g) was added and homogenized using a homogenizer for 10 minutes at 10,000 rpm at 50 °C, until completely dissolved. Curcumin extract (1 g) was then added to the composite coating material solution and homogenized for 30 minutes at 10,000 rpm. Microencapsulation of Javanese ginger curcumin with a single coating material (MDE/WPI/GAR) was also prepared as a comparison using the same steps. All prepared solutions were then dried using spray drying under the following conditions: inlet temperature, outlet temperature, air flow rate, and air pressure were set at 150 ± 1°C, 80 ± 2°C, 4 ml/min at 25 ± 2°C, and 5 bar, respectively.^8,15,18

Spray-Drying Yield, Curcumin Content and Curcumin Recovery

The yield (%) of the spray drying process was studied and expressed as the ratio of the recovered powder compared to the amount of solid raw material used. Curcumin content was determined based on the previous method.²⁴ Standard solutions of curcumin in ethanol were prepared at concentrations of 0, 2, 4, 6, 8, 10, and 12 ppm. The absorbance was measured at a wavelength of 425 nm using a UV-Vis spectrophotometer (UV-1800, Shimadzu Scientific Instrument, Japan) and used to obtain a standard curve equation. Each sample weighed 1 g, dissolved in 10 ml of ethanol, and centrifuged at 5000 rpm for 5 minutes. Then, the absorbance was measured at a wavelength of 425 nm using a UV-Vis spectrophotometer (UV-1800, Shimadzu Scientific Instrument, Japan). A calibration curve of the standard solution was developed to evaluate the concentration of curcumin and expressed in mg/100g. Curcumin recovery from temulawak extract with various coating materials was calculated as follows: (Total curcumin content in the obtained microcapsules – Curcumin content on the surface of the obtained microcapsules)/ Total curcumin content in the obtained microcapsules.¹⁷

Total Phenolic Content 

Total phenolic content (TPC) in the microcapsules was quantified using the Folin-Ciocalteu method.²⁷ A 0.5 g microcapsule sample was homogenized with 5 ml of 10% (v/v) Folin-Ciocalteu reagent for 5 minutes in the dark. Subsequently, 4 ml of 7.5% (w/v) Na₂CO₃ solution was added, followed by a 60-minute incubation at room temperature. A gallic acid standard curve (100-500 ppm in ethanol) was used to determine TPC, measured at 765 nm via UV-Vis spectrophotometry and expressed as mg gallic acid equivalents per gram of temulawak extract microcapsules (mg GAE/g).

Total Flavonoid Content

Determination of total flavonoid content (TFC) was carried out using a modified previous research method.²⁵ A 0.5 g microcapsule sample was prepared with ethanol (1.5 ml), 10% AlCl₃ (0.1 ml), 1 M CH₃COOK (0.1 ml), and distilled water (2.8 ml) in a dark test tube.  After homogenization and 30-minute incubation at 25 ± 1 °C, absorbance was measured at 415 nm using a UV-Vis spectrophotometer against a distilled water blank.  A quercetin standard curve (20-100 ppm) was employed, and TFC was expressed as mg quercetin equivalents per gram of temulawak extract microcapsules (mg QE/g).

Antioxidant Activity 

The antioxidant activity (AA) of the microcapsules (0.2 g) was assessed using the DPPH method.²⁰ After adding 1.5 ml of 0.2 mm DPPH ethanol solution and 3.5 ml of ethanol to the microcapsules in a sealed test tube, the mixture was homogenized and incubated in the dark at room temperature for 60 minutes.  UV-Vis spectrophotometry at 517 nm determined absorbance, with the percentage radical scavenging activity (RSA) calculated from the difference between sample and blank absorbances.

Color Profile 

The color profile of curcumin microcapsules of temulawak was determined using the Minolta CR-310 Chroma Meter instrument (Konica Minolta, Japan), with CIELab scale parameters (L*, a* and b*), where L* indicates brightness, a* red and green, and b* yellow and blue.²¹

Moisture Content and water activity (a_w) 

A moisture analyzer instrument (Shimadzu MOC63u, Japan) was used to determine the moisture content of microcapsules. In contrast, a water activity analyzer instrument (Rotonic Hygropalm-HP23-Aw-A, Switzerland) was used to determine the law of microcapsules operated at 25 °C.

Hygroscopicity

The hygroscopicity of microcapsules was obtained by placing 1 g of sample in an airtight jar containing saturated NaCl solution (relative humidity ± 75%) and storing for 7 days at a controlled temperature (± 25 °C). The hygroscopicity value was expressed in g of water vapor adsorbed per 100 g dry sample (g/100g).²⁶

Solubility

The solubility of microcapsules was obtained by preparing 1 g of sample added to 100 ml of distilled water with magnetic stirring for 10 minutes. The suspension was filtered, and the filtrate was dried at 105 °C until a constant residual weight was obtained.²⁷ The solubility of microcapsules is expressed in percent.

Foaming Capacity and Foaming Stability

The samples’ foaming capacity (FC) and foaming stability (FS) were evaluated using a previously reported method.²⁸ Microcapsules were prepared in as much as 1 g, dissolved in distilled water, and the pH was adjusted to 7.0. The samples were then homogenized using a homogenizer for 5 minutes at a speed of 4000 rpm, and the results were then transferred into a 250 ml measuring cylinder. The volume of foam formed after whipping was recorded at 0 and 30 minutes. The increase in volume percentage represents the FC value, and the FS Value is calculated based on the stability of foam volume after whipping.

Wettability

The wettability of microcapsules was assessed using earlier research methods, in which 1 g of sample was added to 100 ml of distilled water in a 250 ml beaker at room temperature. The time required for the powder particles to sink and disappear from the water surface was recorded as wettability.²⁸

Dispersibility

The dispersibility of microcapsules was obtained by preparing 1 g of microcapsules in a 50 ml beaker and adding 10 ml of distilled water. Constant stirring was carried out for 30 minutes until the microcapsules were dispersed entirely and did not form lumps at the bottom of the beaker. The sample was filtered using a 200-mesh sieve, and the filtrate obtained was dried to constant weight.²⁸

where, ‘a’ is the amount of powder sample being used, ‘b’ is the moisture content of the powder, and TS are the total solids of the filtrate.

Particle Size Distribution and Morphology Structure

The laser instrument particle size analyzer LLPA-C10 (Labron Equipment Ltd., United Kingdom) was used to measure microcapsules’ particle size using the laser light scattering principle. Meanwhile, the morphology structure of the samples was evaluated using scanning electron microscopy (SEM) type JSM-6510LA (Jeol Ltd., Japan). The prepared microcapsules were then coated with gold with an ion layer and observed at an acceleration voltage of 12 kV.

Statistical Analysis

All experiments were performed in triplicate and presented as mean ± standard deviation. ANOVA test was used to see significant differences between treatment. When a significant difference (p < 0.05) was identified, further testing was conducted using Duncan’s test at a 95 % confidence level with SPSS software version 22.0.

Results

Spray-Drying Yield, Curcumin Content and Curcumin Recovery

The product yield was calculated as the ratio of the mass of solids obtained from the drying process to the mass of solids in the feed solution. The yield of all microcapsules ranged from 62.34 to 72.72% (Figure 1A). In general, the yield of WPI-based microcapsules (70.54-72.21%) was better than that of MDE-based microcapsules (65.34-68.10%), while the lowest yield was GAR-based coating material (63.24-63.41%). Using composite coating materials significantly increased the yield of microcapsules for all treatments. The curcumin content of the microcapsules from temulawak extract ranged from 284.94 to 404.67 mg/100 g (Figure 1B). Based on the type of coating material, MDE (361.97-404.67 mg/100 g) significantly produced the highest curcumin content of microcapsules, followed by WPI (349.94-359.38 mg/100 g) and GAR (284.93-302.21 mg/100 g). Meanwhile, the microencapsulation efficiency of curcumin varies from 64.76 to 91.97% (Figure 1C). MDE-based coating material resulted in the highest microencapsulation efficiency, while the presence of βCD as a composite coating material had a statistically positive impact.

Figure 1: Spray-drying yield (A), curcumin content (B), and curcumin recovery (C) of microcapsule curcumin from temulawak extract. Click here to view Figure

Table 1: Chemical properties and AA of microcapsule curcumin from temulawak extract

Note: The data are representation of the mean values ±standard deviation. Different superscript letters in each column indicate significant differences at P <0.05.

Total Phenolic Content, Total Flavonoids Content, and Antioxidant Activity

Temulawak extract microcapsules produced with WPI (40.35 mg GAE/g) coating material had higher TPC than those made with MDE (38.32 mg GAE/g) and GAR (37.48 mg/ GAE/g) coating materials. In contrast, composite coating material significantly increased the TPC for all microcapsules, ranging from 43.76 to 45.23 mg GAE/g (Table 1). The average TFC of microcapsules from temulawak extract ranged from 29.68 to 97.49 mg QE/g (Table 1). Each coating material produced significantly different TFC, while the presence of βCD as a composite coating material significantly increased the TFC trapped in the microcapsules. Based on the data in Table 1, the microcapsules of temulawak extract have AA values of 67.70 to 77.56 %RSA. Each coating material produces microcapsules with significantly different AA values. The WPI-βCD composite coating material significantly produced microcapsules with the highest AA value, while the lowest was observed in microcapsules prepared with GAR coating material.

Color Profile

The color profile reflects curcumin microcapsule particles’ brightness and saturation levels from the temulawak extract. All microcapsules showed a very high brightness level with L* values ranging from 70.44 to 82.34 (Figure 2A). The a* value was in the range of 5.56-20.98 (Figure 2B), which indicated a slight reddish tendency. While the b* value is relatively high, around 53.82-67.77 (Figure 2C), indicating that the microcapsules have a significant yellow color.

Figure 2: Color properties of microcapsule curcumin from temulawak extract. Different superscripts in (a-e) each figure indicate statistically significant differences (P< 0.05), as determined by Duncan’s test. Click here to view Figure

Moisture content and a_w

The moisture content of the microcapsules from temulawak extract was 2.13 to 3.71% (Table 2), and all coating materials produced particles with moisture content below 5%. Significant differences were observed for all microcapsule water contents; the composite coating materials produced statistically higher microcapsule water contents than the single coating materials. In contrast to moisture content, the a_w value of microcapsules from temulawak extract did not differ between treatments, ranging from 0.31-0.33 (Table 2).

Table 2: Physical properties of microcapsule curcumin from temulawak extract

Note: The data are representation of the mean values ± standard deviation. Different superscript letters in each column indicate significant differences at P <0.05.

Hygroscopicity and Solubility

The hygroscopicity of temulawak extract microcapsules varies, ranging from 8.11 to 9.90%, which is highly dependent on the type and composition of the coating material. It can be observed that microcapsules prepared with MDE have a lower hygroscopicity value compared to GAR. At the same time, WPI coating material produces the most hygroscopic product. The solubility of microcapsules from temulawak extract ranged from 89.52-97.23% (Table 2). Based on the type of coating material, microcapsules prepared with MDE had the highest solubility, followed by GAR and the lowest WPI. Meanwhile, the presence of βCD in the composite coating material significantly reduces the solubility of microcapsules.

Foaming Capacity and Foaming Stability

The average FC and FS values of temulawak extract microcapsules were 12.36-58.66% and 33.29-81.02%, respectively (Table 3). This study obtained significantly higher FC and FS values in microcapsules with WPI-based coating materials.

Table 3: Functional properties of microcapsule curcumin from temulawak extract

Note: The data are representation of the mean values ± standard deviation. Different superscript letters in each column indicate significant differences at P <0.05.

Wettability and Dispersibility

The effect of coating type and composition on the wettability and dispersibility of microcapsules is shown in Table 3. Significant differences were observed in these properties and were greatly influenced by the coating material used, including the presence of βCD as a composite coating material. The lowest wettability of microcapsules (65.36 seconds) was provided by MDE coating material, while the highest wettability (278.86 seconds) was observed in microcapsules with WPI-βCD coating material. On the contrary, the lowest dispersibility value of microcapsules was produced by WPI-βCD coating material (71.84%), while the highest was produced by MDE coating material (80.78%). It can be concluded that microcapsules with short wettability tend to have higher dispersibility.

Particle Size

Figure 3 presents the particle size distribution pattern of temulawak extract microcapsules. The average particle size of the resulting microcapsules ranged from 1.13 to 2.43 mm, with an unimodal distribution pattern.

Figure 3: Particle size distribution of microcapsule curcumin from temulawak extract by different coating materials (MDE; MDE-βCD; WPI; WPI-βCD; GAR and GAR-βCD). Click here to view Figure

Figure 4: SEM micrograph of microcapsule curcumin from temulawak extract by different coating materials (MDE; MDE-βCD; WPI; WPI-βCD; GAR and GAR-βCD). Click here to view Figure

Morphology Structure

The morphological structure of temulawak extract microcapsules examined by SEM is presented in Figure 4. In addition to differences in particle size, microcapsules prepared with various types of coating materials produce very different characteristics. In general, temulawak extract microcapsules have very diverse shapes. Specifically, microcapsules prepared with GAR coating materials have irregular surfaces, are very rough, and have cracks and many wrinkles.

Discussion

The yield of WPI-based microcapsules is the highest. WPI is a promising coating material for curcumin encapsulation. At the same time, GAR is less than optimal due to the hydrophilic nature of the short-chain branch structure of GAR, which causes many components not to be atomized perfectly and stick to the spray dryer wall.²⁹ Using composite coating materials significantly resulted in higher microcapsule yields than single coating materials, except for GAR-based microcapsules. The inclusion process and loading of more curcumin with the presence of βCD have been reported.³⁰ The presence of βCD in composite coatings significantly increased the glass transition temperature of the particles.³¹ When the glass transition temperature is above the drying temperature, there is a decrease in the rate of physicochemical changes in the product, such as stickiness, breakdown, and agglomeration, which is inhibited so that the availability of coating materials is greater to form microcapsules and the product yield increases.^32-33 This result is higher than the previous report, reaching only 46.1% to 57.3%.⁸ High yield in production is essential and related to the efficiency and effectiveness of the process.

The curcumin content of the microcapsules from temulawak extract is similar to microcapsules from turmeric extract, which are 324-425 mg/100 g,³⁴ and 432-569 mg/100 g.³⁵ These results are higher than the curcumin content of microencapsulated fermented turmeric extract, which is only 86.6 mg/100 g.³⁶ These results are quite interesting. Generally, curcumin binding activity becomes more effective with the presence of protein fractions.³⁷ Also, the presence of proteins that can form a protective layer around the core material can maintain curcumin’s stability.²¹ This provides information that curcumin from temulawak extract is coated more optimally using MDE. MDE is known to have high solubility in water and can form a very stable film layer and a hollow structure that is effective in trapping curcumin during the microencapsulation process.³⁸ While using GAR produces microcapsules with the lowest curcumin content, it is less effective in the microencapsulation process of curcumin from temulawak extract. On the other hand, composite coating materials significantly increase the curcumin content of microcapsules, both those prepared from MDE-βCD, WPI-βCD, and GAR-βCD. This confirms that curcumin can be encapsulated into the βCD cavity through the inclusion complexation process between curcumin and βCD. This process occurs through Van der Waal interactions, hydrogen bonds, and hydrophilic interactions.³¹

Microencapsulation efficiency describes the coating material’s effectiveness in protecting the encapsulated core compound from loss or oxidation. Thus, the microencapsulation efficiency value aligns with the curcumin content produced. The microencapsulation efficiency obtained in this study is slightly better than that of previous studies, namely 31-70%,²⁷ and 41.36-82.50%.¹⁵ However, this value is still lower than reported, namely 95.0-97.5%.13 The use of composite coating materials significantly increases microencapsulation efficiency. The curcumin inclusion complex and the increase in the glass transition temperature of the particles have been able to explain the mechanism of increasing the microencapsulation efficiency of curcumin from temulawak extract with the presence of βCD in the composite coating.

This study’s TPC of temulawak extract microcapsules was higher than that of temulawak extract microcapsules from Malaysia, which was only 9.99 mg GAE/g.³⁹ However, this value was still lower than that of turmeric extract microcapsules, which reached 81.69-86.89 mg GAE/g.⁴⁰ Interesting results were observed in microcapsules with GAR coating material; the resulting TPC value was not different from MDE. The branched structure of GAR can bind to the phenolic groups of temulawak extract.⁴¹ On the other hand, phenolic compounds have been confirmed to interact positively with milk proteins, so the recovery of phenolic compounds increases.¹⁸ The use of βCD as a composite coating material significantly increased the TPC of microcapsules. This was associated with the ability of βCD to form inclusion complexes with phenolic compounds from temulawak extract. The interaction between polyphenols and cyclodextrins has been confirmed to increase the stability of phenolic compounds so that the TPC of microcapsules increases.⁴² The phenolic compounds, which are antioxidants, play a role in preventing and treating various degenerative diseases, including cancer, diabetes mellitus, premature aging, and immune system disorders. Therefore, microcapsules with high levels of phenolic compounds offer significant potential health benefits.

Previous researchers have reported that microcapsules from temulawak extract prepared with sodium tripolyphosphate and chitosan have TFC values of 6.30-33.58 mg QE/g.⁴³ This means that MDE, WPI, and GAR coating materials more effectively protect flavonoid compounds from temulawak extract. The TFC value of microcapsules tends to have the same pattern as the curcumin content. High TFC values do not always indicate high flavonoid content in a product. However, high TFC values can be caused by other compounds that are also measured because they react with aluminium chloride.⁴⁴ Curcuminoid compounds have ortho hydroxyl groups, which will be read as flavonoids when reacted with aluminium chloride. Therefore, the TFC value will have the same pattern as the curcumin content.^45-46 This phenomenon was also observed in the microencapsulation process of curcumin extract from turmeric.

This AA comes from the curcumin compound.¹⁸ Although the curcumin in microcapsules with WPI coating material is lower than that of the MDE coating material, the curcumin-WPI microcapsules show higher AA. Similar results have also been reported previously.¹⁷ The free radical scavenging activity of the curcumin compound is not affected after being encapsulated with sodium caseinate, a protein from milk. Even the antioxidant capacity of curcumin produced increased significantly.⁴⁷ This phenomenon is acceptable because WPI has been confirmed to show AA from protein components.⁴⁸ The increase in AA in microcapsules with WPI coating materials shows curcumin’s effectiveness in donating its hydrogen atoms to radicals.⁴⁹ In addition, the AA value of microcapsules was significantly higher when encapsulated with composite coating materials. In addition to increasing the glass transition temperature of particles, the presence of βCD effectively forms inclusion complexation with curcumin.^31,50  This complexation has good stability against light exposure, pH changes, and storage.⁵¹ A study has concluded that increased AA of curcumin microcapsules can be obtained with WPI coating materials complex with βCD.⁵² This has confirmed why curcumin microcapsules from temulawak extract have the highest AA after being encapsulated with WPI-βCD. Consuming a diet rich in antioxidants through natural foods is key to maintaining health and preventing future disease.⁵³

Curcumin microcapsules with a high b* value indicate a higher availability of curcumin in the microcapsules, which can be confirmed in Figure 1B that the microcapsules prepared with the MDE-βCD composite coating material contain higher levels of curcumin. In contrast, the lowest is prepared with the GAR coating material. The microcapsules prepared with the composite coating material showed a lower brightness level (L*) than the single coating material. This finding is consistent with previous studies showing that the brightness value of microcapsules decreases with the presence of βCD.⁵⁴ This decrease can be attributed to the TPC value of microcapsules. Microcapsules with higher TPC values will be more susceptible to oxidation and impact decreasing particle brightness.⁵⁵ Interestingly, the presence of βCD significantly increases the b* value of microcapsules. This means that there is a good inclusion complex between curcumin and βCD. Previous findings support these results; the color of microcapsules resulting from curcumin-βCD complexation has excellent yellow color stability, even stable against sunlight, pH, storage, and isothermal heating compared to natural dyes without complexation with βCD.⁵¹

Curcumin microcapsules with water content below 5% are made from the right coating material.⁵⁶ Microcapsules prepared with WPI coating materials produced the lowest moisture content significantly. Higher moisture content was observed in microcapsules prepared with composite coating materials. Similar findings include microcapsules from seaweed extract,²³ Elshotltzia ciliata Herb extracts,⁵⁷ and grape cane extract.⁴² βCD can form hydrophobic cavities that can trap core materials, and some trapped water molecules are difficult to evaporate when the feed liquid is dried.⁵⁸ Powder products with moisture content below 5% have been confirmed to have good long-term storage stability.⁵⁹ In addition, aw values below 0.4 can be considered ideal conditions to prevent the growth of microorganisms and overcome coagulation problems during storage.⁶⁰

Hygroscopicity is closely related to the capacity of microcapsules to absorb moisture in the environment and can also affect physical-chemical stability, product shelf life, and product fluidity.⁶¹ An observation is related to the fact that GAR has a higher glass transition temperature than MDE, thus increasing the hygroscopicity of the product.⁶² Also, using protein-based coating materials produces microcapsules with high hygroscopicity values. The resulting microcapsules tend to have a more porous morphological structure, making them more likely to absorb water from the environment.⁶³ This study observed that the increase in hygroscopicity was inversely proportional to the moisture content, so microcapsules with lower moisture content tended to be hygroscopic. This can be attributed to the more significant water concentration gradient between the particles and the surrounding air, leading to a greater capacity to absorb water at room temperature.²⁹ The presence of βCD tends to increase the hygroscopicity value of the microcapsules. This result is not surprising; βCD is known to have a solid capacity to attract water molecules from the surrounding air.³¹ The hygroscopicity of a product is a challenge in the food and pharmaceutical industries. Understanding the hygroscopicity of a product allows for proper handling, especially for products with low hygroscopicity that are easier for consumers to store.

The solubility of curcumin microcapsules in this study was slightly better than that of microcapsules from turmeric extract, which was 86.71-89.52%.²¹ However, the solubility trend of curcumin extract microcapsules is similar to that of microcapsules from grape skin extract and black rice prepared with MDE coating materials, high-protein skim milk powder, and GAR.^63-64 The high hydroxyl groups (-OH) in MDE can be the reason for the high solubility of microcapsules.⁶⁵ Meanwhile, GAR-based microcapsules have better solubility than WPI. A study observed the effect of the GAR to soy lecithin ratio on curcumin’s solubility, concluding that a more dominant GAR ratio produced microcapsules with higher solubility.²⁷ The solubility of GAR is reported to be around 90%,⁶⁶ like the solubility of GAR-based microcapsules in this study (Table 2). The decrease in solubility in microcapsules prepared with WPI is due to the formation of cross-links between protein fragments by disulfide bridges, which then reduce the solubility of the particles.⁶⁷ Meanwhile, microcapsules prepared with composite coating materials tend to have lower solubility. βCD has a hydrophobic structure, where hydrogen bonds between hydroxyl groups can cause the structure to become rigid, making it difficult to dissolve.^68-69 This is also confirmed by a study reporting that spray-dried microcapsules prepared with βCD have a solubility of around 40-60%.⁵⁷

The increase in FC values in WPI-based microcapsules can be associated with partial protein folding, resulting in increased flexibility of the protein chain if aggregates are not formed.⁷⁰ In addition, WPI protein molecules decompose when heated and reveal their reactive side so that the FS value of the particles increases.⁷¹ The presence of βCD in the composite coating material does not affect the FC value of the microcapsules. This is because FC is related to the amount of air trapped in the foaming system. In contrast, the addition of βCD significantly increased the FS of microcapsules for all coating materials, meaning that the interfacial layer formed was stronger.⁷² MDE is hydrophilic. Thus, the hydrophilicity of the particle wall system increases and helps in the accessibility and penetration of microcapsules into water.⁷³ In addition, particles with fast wettability are generally produced from coating materials with high solubility,²⁶ making them easier to disperse maximally.²¹ The faster the wettability of a particle and the higher its dispersibility, the better its physical properties in food processing.^73-74

Previous researchers reported that the average particle size of curcumin prepared by spray drying was 3.31 mm.²⁰ Generally, curcumin microcapsules prepared by spray drying have a size of 10 mm.¹⁵ The smaller particle size of the microcapsules in this study was due to the extraction of curcumin using ethanol-aquadest. It has been confirmed that curcumin’s particle size from turmeric extract tends to be smaller when extracted using ethanol-aquadest compared to ethanol alone.²⁵ WPI as a coating material produces microcapsules with smaller particle sizes than GAR and MDE. In comparison, composite coating materials produce microcapsules with larger sizes. Similar results were also observed in the microencapsulation of seaweed extract using MDE and GAR combined with βCD.²³ Microcapsules with larger sizes are preferred for releasing bioactive compounds because they tend to have a porous structure, while microcapsules with smaller sizes generally provide better techno-functional properties.⁷⁵

GAR has been confirmed to produce microcapsules with slightly cracked surfaces, shrinkage, and many wrinkles as a curcumin coating material.²⁹ Microcapsules prepared with MDE tend to be more regular and have smooth surfaces; some particles are round and oval, and some have depressions without cracks. These results strengthen previous findings that MDE produces much smoother curcumin microcapsules with few wrinkles.¹⁸ WPI coating materials also produce particle morphology with the same characteristics as MDE, but there are many cracks on the surface. The presence of βCD in the composition of the composite coating material generally does not change the shape of the particles. However, what is interesting is that the resulting particles have a smooth surface without cracks. This can be attributed to the increase in the glass transition temperature of the particles by βCD.³¹ It is recognized that the encapsulation agent is the leading cause of the morphological characteristics of the formed microcapsules.¹⁶ The regular or irregular nature of the particle surface provides a first insight into the stability of the formed microcapsules. Generally, particles with smooth surfaces encourage less interaction with other particles, which may be useful in certain applications.⁷⁶ On the other hand, some researchers reported that microcapsules with rough surfaces had a slower release process.^77-78

Conclusion

In conclusion, the results of this study indicate that each coating material significantly affects the yield, curcumin content, microencapsulation efficiency, and physicochemical properties of curcumin microcapsules from temulawak extract, except for the a_w value. Composite coating materials produce microcapsules with better physicochemical characteristics than single-coating materials. Based on the curcumin content, microencapsulation efficiency, hygroscopicity, color profile, and morphological structure of the microcapsules, MDE-βCD coating material is highly recommended. Meanwhile, microcapsules prepared with WPI-βCD coating material produced better yield, chemical properties, and foaming profile. These results provide valuable information on the effectiveness of adding βCD in the composite coating material formula in preparing curcumin microcapsules from temulawak extract that can be applied in the food and pharmaceutical industries. It is interesting to study the application of the obtained microcapsules in functional products such as health drinks, instant milk, and yogurt. However, before that, further research is needed on the stability of the products produced on a pilot plant scale before being commercialized.

Acknowledgement

The authors gratefully acknowledge the Ministry of Education, Culture, Research and Technology, the Republic of Indonesia, for financial support through the Fundamental Research Grant program on behalf of Dr. Ali Rosidi.

Funding Sources

Fundamental Research Grant [grant numbers 022/LL6/PB/AL.04/2024 and 001/061026/PB/SP2H/AK,04/2024] from Ministry of Education, Culture, Research and Technology, the Republic of Indonesia.

Conflict of Interest

The authors declare no conflict of interest.

Data Availability Statement

The manuscript incorporates all datasets produced or examined throughout this research study.

Ethics Statement

This research did not involve human participants, animal subjects, or any material that requires ethical approval.

Informed Consent Statement

This study did not involve human participants, so informed consent was not required.

Permission to Reproduce Material from Other

This statement does not apply to this article.

Clinical Trial Registration

This research does not involve any clinical trials.

Author Contributions

• Ali Rosidi: Funding, Conceptualization, Methodology, Writing Original Draft.
• Edy Soesanto: Visualization, Project Administration, Writing Review
• Enik Sulistyowati: Supervision, Technical and Material Support
• Diode Yonata: Data Collection, Analysis, Writing Review and Editing.

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