Effects of Fluidized Bed Coating with Carboxymethyl Cellulose and Pectin on the Physicochemical Properties of Fermented Black Bean Dregs

Abstract

The changes in the physicochemical properties of fermented black bean dregs (FBBD) coated with carboxymethyl cellulose (CMC) solution (0–3%) and pectin solution (0–3%) on a fluidized bed were analyzed. The Carr index of the FBBD powder decreased from 55.4 ± 0.3% to 7.5 ± 0.4% after coating with CMC solution (3%) and to 11.3 ± 1.6% after coating with pectin solution (3%) for 120 min. After coating with CMC solution (3%) for 120 min, the proportion of medium-sized particles decreased significantly with the increased duration of the coating process, whereas the proportion of large-sized particles increased. Microstructural analysis by scanning electron microscopy showed that the particle size significantly increased and the surface changed from rough to smooth. The L* and b* values of the powder samples decreased from 45.5 ± 0.1 and 17.2 ± 0.1 to 32.9 ± 0.2 and 15.3 ± 0.1, respectively, whereas the a* value increased from 7.6 ± 0.1 to 8.9 ± 0.1; thus, the sample color changed from bright to dark and tended toward bluish and reddish colors. The wettability and solubility of the powder samples increased significantly with the increased duration of the coating process, but the water-holding capacity decreased. Moreover, FBBD coated with pectin solution (3%) and CMC solution (3%) on a fluidized bed for 120 min exhibited similar physicochemical properties. Thus, FBBD powder exhibited favorable flowability, wettability, and solubility after 120 min of coating with CMC solution (3%) or pectin solution (3%).

1. Introduction

Soybean dregs are a by-product of soybean product processing and are rich in fibers, proteins, and lipids. The fibers in soybean dregs have the potential to prevent metabolic diseases such as diabetes and obesity, and the proteins in soybean dregs can be added to animal feed to increase its protein content [1,2]. Soybean dregs can also be fermented and reused. Li et al. [3] demonstrated that Bacillus subtilis var. natto produces nattokinase and α-amylase, which can be used to ferment soybean dregs. After optimization of culture conditions through the response surface methodology, Li et al. [3] observed that the best enzymatic activity was obtained with 36 h of fermentation, a rotation speed of 170 rpm, and an inoculum volume of 9%. These conditions were predicted to reduce the production cost of the enzymes. Razavizadeh et al. [4] showed that fermentation of soybean dregs with the Lactobacillus plantarum P1 and Lactobacillus acidophilus 308 strains improved the physicochemical properties of fermented soybean dregs in plant-based meat, including significant increases in water- and oil-holding capacities and improved juiciness of the product. In addition, the carbonylation of amino acid side chains in proteins indicates protein oxidation. Analysis of the carbonyl content showed that protein oxidation levels in fermented soybean dregs were lower than in unfermented soybean dregs, indicating better antioxidant activity.

Gupta et al. [5] observed that the antioxidant activity of soybean dregs significantly increased after 48 h of fermentation with Rhizopus oligosporus at 30 °C. Vong et al. [6] showed that fermentation of soybean dregs with Yarrowia lipolytica increased the total ferulic acid content, antioxidant capacity, and amino acid content, as well as increasing bioavailability and bioactivity. In addition, Vong et al. [7] conducted single-culture fermentation using Rhizopus oligosporus and co-culture fermentation with Rhizopus oligosporus and Yarrowia lipolytica on soybean dregs. They observed that both fermentation methods facilitated the conversion of insoluble dietary fibers in soybean dregs into soluble dietary fibers. Additionally, the organic acid content and antioxidant activity increased. However, co-culture fermentation demonstrated greater efficiency in dietary fiber conversion, higher organic acid production, and enhanced antioxidant capacity compared to single-culture fermentation, indicating that co-culture fermentation led to a higher reutilization value of soybean dregs. Our previous study showed that the application of radiofrequency drying for 60 min could dry fermented soybean dregs efficiently, with water activity decreasing from 0.9–0.6, thereby accelerating drying by 10-fold compared to conventional hot-air drying [8]. Srivastava and Mishra [9] showed that fluidized bed treatment can increase the particle size of powders and improve their flowability, wettability, and product appearance. Thus, fluidized bed treatment of dried soybean dregs is beneficial for subsequent processing.

There are two common methods of fluidized bed processing, namely fluid bed agglomeration and fluid bed coating. Fluid bed agglomeration has been widely used, primarily in the food and pharmaceutical industries to form agglomerates through interaction between particles in the fluidized state. In the food industry, fluid bed agglomeration is chiefly applied to instant food products such as milk powder, cocoa powder, starch products, and food thickeners, as it can aggregate small-sized particles into larger-sized particles and improve their physical properties, such as bulk density, particle size distribution, shape, fluidity, dispersion, and stability [10]. Generally, agglomerated powders exhibit better mobility due to reduced cohesion and better solubility due to increased powder porosity. During fluid bed agglomeration, the surface of fluidized particles is surrounded by a sprayed adhesive solution, which binds the particles together. The adhesive solution is subsequently evaporated, forming bridges between the particles and leading to the formation of a composite with larger particle sizes and a more porous structure [11]. Fluid bed coating is essential in the pharmaceutical, chemical, and food industries. In the food industry, the major purposes of coating are appearance modification, nutritional supplementation, functionalization, and extension of shelf life. Fluid bed coating is the application of a coating solution to the surface of fluidized particles, which is dried by the heat from the fluidizing gas. The thickness of the coating results in a particle size of 0.1 to several millimeters [12]. Palamanit et al. [13] used this technique to apply turmeric extract solution to white rice to increase its total phenolic content and total antioxidant capacity.

As black soybean dregs are a by-product of the soybean product manufacturing process, they can be converted through microbial fermentation into a functional fermented product with high bioavailability that is rich in physiologically active ingredients. Carboxymethyl cellulose (CMC) and pectin have been selected as coating agents due to their well-documented film-forming abilities and functional properties in food applications. CMC, a hydrophilic polymer, enhances moisture retention and structural stability in coatings [14]. Pectin, a biodegradable polysaccharide, has been extensively studied for its role in improving food coatings and promoting sustainable packaging [15]. Their combined properties make them suitable for enhancing the physical characteristics of FBBD powder. However, the powder characteristics of FBBD may affect their processing and application performance. Therefore, in this study, the fluidized bed coating of FBBD with CMC and pectin was performed to improve the flow and physicochemical properties of the fermented product. CMC and pectin were used as the coating materials, and the effects of different concentrations and durations and the coating process on the physicochemical properties of FBBD powder were evaluated. By analyzing these physicochemical properties, we aim to establish optimal coating conditions to improve the processing characteristics and application value of FBBD.

2. Materials and Methods

2.1. Preparation and Fermentation of Black Bean Dregs (BBD)

Black soybeans (Glycine max (L.) Merr.) (purchased from Hongyu Food Enterprise Co., Ltd., Taipei City, Taiwan) were used as the raw material. The black soybeans were washed and soaked in water at a bean-to-water ratio of 1:5 in a refrigerator for 7 h. After soaking, a grinder (CH-102, Cheng Huei Machinery Co., Ltd., Taichung City, Taiwan) was used to grind the black soybeans. Then, an automatic filter (Chang Sheng Machinery Industry Co., Ltd., Taoyuan City, Taiwan) was used to separate the soybean milk and BBD. A water spray retort sterilizer (CY-3000H-RD-770-1P, Chang Yu Machinery, Changhua, Taiwan) was used to heat the BBD at 121 °C for 20 min. After cooling, the BBD were prepared as described by Huang et al. [8] into FBBD. BBD (7.2 kg) were mixed with a Rhizopus oligosporus spore suspension (10⁵ spores/mL) at a ratio of 16:1 and homogenized for 3 min. The homogenized black soybean dregs were incubated at 30 °C for 24 h. Afterward, the black soybean dregs were mixed with a suspension of Yarrowia lipolytica (10⁶ CFU/mL) at a ratio of 16:1 and homogenized for 3 min. After homogenization, the black soybean dregs were incubated at 30 °C for 60 h to obtain the FBBD, and the samples were then freeze-dried. The freeze-dried FBBD were ground using a grinder (CK-JY, CK Chin Kang Industry Co., Ltd., New Taipei City, Taiwan) and then sieved using a high-efficiency vibrating sieving machine (CK-450-A, CK Chin Kang) (150 μm mesh). One thousand grams of sieved FBBD was placed in a fluid air backwash spray granulator (ST-5, Shia Machinery Industrial Co., Ltd., Taichung City, Taiwan) with a top-spraying chamber fluidized bed for the granulation of the FBBD. The granulation conditions were a coating solution of 15% maltodextrin, a granulation temperature of 80 °C, an air inlet speed of 1500 rpm, and a pump flow rate of 10 mL/min. After 10 min of granulation, the samples were dried at 80 °C for 10 min and then cooled to 40 °C to obtain the FBBD samples, which were used to investigate the effect of fluidized bed coating with CMC and pectin on the physicochemical properties of FBBD.

2.2. Effect of CMC and Pectin Coating Concentrations on the Flowability of FBBD

A 200 g sample of FBBD was placed in a pilot-type fluid bed spray granulator dryer/coater (HT-02S-7, Hong Dau Industrial Co., Ltd., Taichung, Taiwan), and the FBBD granulated with a side-rotating spray fluidized bed were coated with different concentrations of CMC (0, 1, 2, and 3%, w/v) or pectin (0, 1, 2, and 3%, w/v). The coating conditions were CMC (0, 1, 2, and 3%) or pectin (0, 1, 2, and 3%) as the coating solution, a coating temperature of 50 °C, an inlet air velocity of 30 m³/h, a pump flow rate of 2.4 mL/min, and a nebulization pressure of 1.0 kg/cm². The coated FBBD powder was obtained after coating for 120 min. Afterward, the effects of the CMC and pectin coating process on the flowability of these powder samples were analyzed.

2.3. Effect of Coating Duration on the Physicochemical Properties of FBBD

A 200 g sample of FBBD was placed in a pilot-type fluid bed spray granulator dryer/coater (HT-02S-7, Hong Dau), and the FBBD granulated with a side-rotating spray fluidized bed were coated with CMC or pectin solution. The coating conditions were 3% CMC or 3% pectin as the coating solution, a coating temperature of 50 °C, an inlet air velocity of 30 m³/h, a pump flow rate of 2.4 mL/min, and a nebulization pressure of 1.0 kg/cm². The coated FBBD powder was obtained after coating for 0, 30, 60, 90, and 120 min, and its physicochemical properties were analyzed, including particle size distribution, flowability, microstructure, color, appearance, wettability, water-holding capacity, solubility, moisture content, and water activity.

2.4. Measurement of Particle Size Distribution, Flowability, and Cohesion of Coated FBBD Powder

The particle size distribution of the coated FBBD powder was determined as described by Moraga et al. [16]. A vibrating sieving machine was used with two different types of standard sieves with pore sizes of 425 and 106 μm. The sieves were arranged from largest to smallest pore size, and the samples were sieved sequentially. Ten grams of coated FBBD powder was weighed and placed in a sieve and shaken for 4 min to separate the samples into sieves of different pore sizes based on particle size, after which the weights of the samples were recorded. The flowability and cohesion of the coated FBBD powder were determined as described by Geldart et al. [17]. The flowability of the coated FBBD powder was determined by calculating the Carr index (CI) of the samples, where CI% < 15% indicates good flowability and CI% > 35% indicates poor flowability. The cohesion of the coated FBBD powder was determined by using the Hausner ratio (HR) as a parameter and calculated from the tap density and bulk density of the powder. HR was used to determine the cohesion of the powder, where HR < 1.25 indicates low cohesion and HR > 1.4 indicates high cohesion.

2.5. Determination of Wettability of Coated FBBD Powder

The wettability of the coated FBBD powder was determined as described by Ji et al. [18]. An optical tensiometer (Attension Theta, Biolin Scientific Ltd., Espoo, Finland) was used to measure the change in contact angle upon spread wetting of the coated FBBD powder at the three-phase contact point. Using a ruler with circular holes fixed on a glass slide, the powder was placed in a circle and its surface was scraped flat such that it formed a diffuse block with a fixed radius of 70 mm and a height of 0.75 mm. A syringe was used to gently drop 5 μL of distilled water from a fixed height to the central flat surface of the powder for dynamic real-time measurements. The change in contact angle at the surface was recorded every 0.03 s during the first second (0–1 s).

2.6. Determination of Moisture Content, Water Activity, Appearance, and Color of Coated FBBD Powder

The moisture content of the coated FBBD powder was determined as described by Pompe et al. [19] with modifications. A two-gram portion of FBBD was placed in a constant-weight glass weighing bottle, dried in an oven at 103 °C for 3 h, and weighed. Moisture content was calculated as follows: moisture content (%) = (weight of sample − weight of sample after drying/weight of sample) × 100. The water activity of the coated FBBD powder was determined as described by Wang et al. [20]. One hundred grams of coated FBBD was weighed into a round plastic container (4.5 cm diameter × 1.5 cm height), and its relative humidity was determined using a water activity meter (AQUA LAB, Model CX-2, Decagon Devices Inc., Pullman, WA, USA). Water activity was calculated as follows: water activity = relative humidity/100. The color change in the coated FBBD powder was determined as described by Dias et al. [21]. Color parameters (L*, a*, b*) were measured using a color quality spectrophotometer (Ci60, X-Rite Color Technology Co., Ltd., Grand Rapids, MI, USA). L* values ranged from 0 to 100, with 0 representing black and 100 representing white. Negative values of a* indicate colors tending toward green, whereas positive values of a* indicate colors tending toward red. Negative values of b* indicate colors tending toward blue, whereas positive values of b* indicate colors tending toward yellow. ΔE indicates the degree of difference between two colors and is calculated as follows: ΔE = (ΔL*² + Δa*² + Δb*²)^1/2.

2.7. Analysis of Solubility, Swelling Capacity, and Water-Holding Capacity of Coated FBBD Powder

The solubility, swelling capacity, and water-holding capacity of the coated FBBD powder were determined as described by Chang et al. [22]. Here, 40 mL of water and 0.4 g of sample (m₀) were placed in a 50 mL centrifuge tube (m₁) and mixed by shaking for 30 min, allowed to stand for 30 min at 4 °C, and then centrifuged (MX-307, Tomy Seiko, Tokyo, Japan) at 6000× g for 10 min at 4 °C. After centrifugation, the supernatant was collected, dried in an oven at 120 °C, and weighed (m₂). Finally, the precipitate and centrifuge tubes were weighed (m₃). To calculate the solubility and swelling capacity of the powder, another 0.4 g sample was collected for moisture content analysis, and the weight of the sample after drying was calculated (m₄): m₄ = (100 − % moisture content of the sample)/100 × m₀.

m₀: 0.4 g sample weight; m₁: centrifuge tube weight; m₂: weight of supernatant after drying; m₃: weight of precipitate plus centrifuge tube; m₄: 0.4 g sample weight after drying.

• Solubility (%) = (m₂/m₄) × 100;
• Swelling capacity (g/g) = (m₃ − m₁)/m₄;
• Water-holding capacity (g/g) = (m₃ − m₁)/m₀.

2.8. Microstructural Analysis of Coated FBBD Powder

The coated FBBD powder was fixed on a stainless-steel stage with carbon tape and coated with a gold sputtering device (MSP-1S, Vacuum Device Inc., Osaka, Japan) for 30 s. The microstructure of the coated FBBD powder was analyzed using a tabletop scanning electron microscope (TM4000PLUS, Hitachi, Tokyo, Japan) at an accelerating voltage of 10 kV in high vacuum with a backscattered electron detector at a magnification of 500×.

2.9. Statistics

All experiments were performed in triplicate. Data are expressed as the mean ± standard deviation. Statistical Analysis System software (Version 9.4, SAS Institute Inc., Cary, NC, USA) was used for statistical analysis of experimental data, including one-way ANOVA and Duncan’s multiple range test for comparing significant differences between the groups. Differences with p < 0.05 were considered statistically significant.

3. Results and Discussion

3.1. Effect of CMC and Pectin Coating Exposure on the Flowability of Coated FBBD Powder

Samples were coated with different concentrations of CMC solution (0%, 1%, 2%, and 3%) or pectin solution (0%, 1%, 2%, and 3%) in a fluidized bed granulator. After coating for 120 min, the flowability of the samples was determined. The results showed that the CI and HR of the coated FBBD powder decreased with increasing concentration of CMC (Figure 1A,B). The CI and HR were 7.5 ± 0.4% and 1.08 ± 0.01, respectively, with the addition of 3% CMC solution, which were significantly lower (p < 0.05) than the CI (55.4 ± 0.3%) and HR (2.24 ± 0.01) without the addition of CMC solution. Jeong et al. [23] stated that the CI is an indicator of the flowability of a powder, with values greater than 35% indicating poor flowability and values less than 15% indicating good flowability. The HR is an indicator of the cohesion of a powder, with values greater than 1.4 indicating high cohesion and values less than 1.25 indicating low cohesion. Therefore, our results show that coating FBBD powder with 3% CMC solution for 120 min significantly improved the flowability and cohesion of the powder. The results of the flowability testing of the FBBD powder coated with 3% pectin solution for 120 min were similar to those of the FBBD powder coated with CMC, and the CI and HR of the FBBD powder coated with 3% pectin solution significantly decreased (p < 0.05) with the addition of 3% pectin solution, with 11.3 ± 1.6% and 1.13 ± 0.02, respectively. Our results showed that coating with either a 3% CMC cellulose solution or a 3% pectin solution can improve the flowability and reduce the cohesion of coated FBBD powder. Therefore, the effects of the coating duration on the physicochemical properties of the coated FBBD powder were investigated by coating with 3% CMC solution and 3% pectin solution in subsequent experiments.

3.2. Effect of Coating with Pectin or Carboxymethyl Cellulose on Particle Size, Microstructure, and Flowability of Coated FBBD

In this study, the effect of the coating duration on the particle size of coated FBBD powder was investigated (Figure 2). FBBD samples were processed in a fluidized bed granulator for 120 min under three different conditions: without a coating solution, with 3% CMC solution, or with 3% pectin solution. The resulting particle size distributions were then analyzed. As shown in Figure 2A, the FBBD powder without a coating solution contained small-sized particles (diameter < 106 μm), medium-sized particles (106 μm < diameter < 425 μm), and large-sized particles (diameter > 425 μm), with the proportion of medium-sized particles being the largest. There were no significant changes in these proportions with the increased coating duration, indicating that the particle size of the powders did not increase. However, the percentage of medium-sized particles in the FBBD powder coated with 3% CMC solution decreased significantly with increasing coating duration, whereas the percentage of large-sized particles significantly increased (p < 0.05), suggesting that the particle size of the powders had become larger (Figure 2B). The effect of coating FBBD powder with 3% pectin solution on the particle size was similar to that of coating with 3% CMC solution, with a slight decrease in the percentage of medium-sized particles with the increased coating duration (Figure 2C). These results demonstrate that the coating of the surface of FBBD with CMC and pectin solution resulted in the adhesion of pectin particles to each other and the formation of larger particle sizes with increasing duration of the coating process. Lee and Yoo [24] prepared xanthan gum powder with maltodextrin as a coating solution and demonstrated that the particle size of the maltodextrin-coated samples was significantly larger than that of the original samples, with the proportion increasing with increasing coating duration.

FBBD samples were coated in a fluidized bed granulator for 0 and 120 min without a coating solution, with 3% CMC solution, or with 3% pectin solution, and the samples were analyzed by scanning electron microscopy (Figure 3). No significant changes in the microstructure of the FBBD powder were observed when no coating solution was added (Figure 3A,B). However, the microstructures of the fermented black soybean dregs coated with 3% CMC solution (Figure 3C,D) or 3% pectin solution (Figure 3E,F) exhibited significantly enlarged particle sizes and surfaces that changed from rough to smooth. FBBD samples were coated with 3% CMC solution in a fluidized bed granulator for 120 min, and their flowability was analyzed (Figure 4). The CI and HR of the coated FBBD powder decreased with increasing coating duration (Figure 4A,B). The CI and HR of the coated FBBD powder were 11.29 ± 1.50% and 1.13 ± 0.02, respectively, after 120 min of coating, which were lower than the CI (31.72 ± 0.44%) and HR (1.46 ± 0.02) of the uncoated FBBD powder. Sakai et al. [25] indicated that rougher limestone powder particles have a greater contact area between particles and thus exhibit poorer flowability. In contrast, samples with particles that are smoother and more spherical have less contact area and better flowability. In addition, the CI and HR of the coated FBBD powder decreased with increasing coating duration. After 120 min of coating with 3% pectin solution, the CI and HR were 14.48 ± 1.18% and 1.17 ± 0.02, respectively. Because the CI and HR of the uncoated FBBD powder were higher than those of the powders coated with 3% CMC solution and 3% pectin solution, the uncoated samples had poorer flowability and higher cohesion. Our results demonstrate that the FBBD powders with 3% CMC solution and 3% pectin solution exhibited favorable flowability and low cohesion after coating for 120 min. Our findings are consistent with those of Ferreira et al. [26], who demonstrated that curcumin-loaded liposomes coated with corn starch solution exhibited better flowability and lower cohesion. Therefore, our results demonstrate that the FBBD samples increased in particle size after coating, resulting in a reduced contact area between the particles in the sample, leading to reduced cohesion and increased flowability. These properties are useful for storage, as powders with high cohesion may experience problems such as difficult flow and severe agglomeration, which can affect the transport, mixing, and packaging of powder products. The coated FBBD have potential applications in functional foods and nutraceuticals, where improved stability and processability are essential. CMC enhances structural integrity and modulates the release of bioactive compounds [27], while pectin provides effective encapsulation, protecting sensitive ingredients and extending shelf life [28]. Additionally, fluidized bed coating improves the flowability and dispersibility of powdered materials, facilitating their incorporation into various formulations [29].

3.3. Effect of Coating Duration on Color, Appearance, Moisture Content, and Water Activity of Coated FBBD Powder

FBBD samples were either not coated or coated with 3% CMC solution or 3% pectin solution in a fluidized bed granulator for 120 min, and their color and appearance were analyzed (

Table 1. Effect of coating duration on color of coated FBBD powder.

	Duration of Coating (min)	L*	a*	b*	ΔE
Without CMC and pectin	0	45.5 ± 0.1 a	7.6 ± 0.1 a	17.2 ± 0.1 a	0 a
	60	39.9 ± 0.3 b	8.0 ± 0.1 b	15.8 ± 0.1 b	5.7 ± 0.35 b
	120	41.1 ± 0.2 b	7.9 ± 0.1 b	15.9 ± 0.1 b	4.5 ± 0.30 c
With 3% CMC	0	45.5 ± 0.1 a	7.6 ± 0.1 a	17.2 ± 0.1 a	0 a
	60	34.7 ± 0.4 b	8.7 ± 0.1 b	15.7 ± 0.1 b	10.9 ± 0.4 b
	120	32.9 ± 0.2 b	8.9 ± 0.1 b	15.3 ± 0.1 c	12.7 ± 0.2 c
With 3% pectin	0	45.5 ± 0.1 a	7.6 ± 0.1 a	17.2 ± 0.1 a	0 a
	60	33.9 ± 0.2 b	9.2 ± 0.1 b	16.3 ± 0.1 b	11.6 ± 0.2 b
	120	32.6 ± 0.2 c	9.2 ± 0.1 b	16.1 ± 0.1 b	13.0 ± 0.1 c

Carboxymethyl cellulose: CMC. Values are presented as mean ± standard deviation (n = 3). Different superscript lowercase letters within the same column indicate significant differences (p < 0.05).

). In the FBBD powder samples coated with 3% CMC solution for 120 min, the L* and b* color values decreased from 45.5 ± 0.1 to 17.2 ± 0.1 and from 32.9 ± 0.2 to 15.3 ± 0.1, respectively, whereas a* increased from 7.6 ± 0.1 to 8.9 ± 0.1. In the FBBD powder samples without a coating or coated with 3% pectin solution for 120 min, the L* and b* values decreased and the a* values increased with increasing coating duration. Bhavya and Prakash [30] stated that the L* value of a sample indicates the color brightness, with higher values indicating greater brightness; the a* value indicates the color intensity in the blue-red direction; and increased b* values indicate increased yellow color intensity. The results of this study show that the L* and b* values decreased and the a* value increased after 120 min of coating, indicating that the color of the samples changed from bright to dark and tended to be blue and red. We also observed that the ∆E value of the FBBD increased with increasing coating duration, with the ∆E value of the fermented black bean dregs being greater than 5 after drying for 60 min. Mokrzycki and Tatol [31] suggested that an observer cannot notice a difference in color between two samples when 1 > ΔE > 0, but an observer can notice a difference when ΔE > 5. Thus, ΔE can be used as a reference for color changes, with ΔE > 5 indicating that a color difference can be perceived clearly with the naked eye. The ΔE of the FBBD powder was greater than 5 after coating, indicating that the color change in the FBBD powder could be observed. Figure 5 shows the effect of the coating duration on the appearance of FBBD powder. FBBD samples were either not coated with a coating solution (Figure 5A,B) or coated with 3% CMC solution (Figure 5C,D) or 3% pectin solution (Figure 5E,F) for 0 or 120 min, and the samples were imaged at 120 min. After coating for 120 min, the color of the three groups of FBBD powder samples differed significantly from that of the group coated for 0 min, becoming deeper and darker.

This study investigated the effects of the coating duration on the moisture content and water activity (a_w) of coated FBBD powder. FBBD samples were either not coated with a coating solution or coated with 3% CMC solution or with 3% pectin solution in a fluidized bed granulator for 120 min, and their moisture content and water activity were analyzed. In FBBD powder samples coated with/without 3% CMC and 3% pectin solution for 120 min (

Table 2. Effect of coating duration on moisture content and activity of coated FBBD powder.

	Duration of Coating (min)	Water Content (%)	Water Activity
Without CMC and pectin	0	5.0 ± 0.1 a	0.39 ± 0.01 a
	60	4.6 ± 0.1 b	0.33 ± 0.01 b
	120	4.6 ± 0.1 b	0.32 ± 0.01 b
With 3% CMC	0	5.0 ± 0.1 a	0.39 ± 0.01 a
	60	5.4 ± 0.1 b	0.37 ± 0.01 b
	120	6.6 ± 0.1 c	0.46 ± 0.01 c
With 3% pectin	0	5.0 ± 0.1 a	0.39 ± 0.01 a
	60	5.9 ± 0.1 b	0.40 ± 0.01 a
	120	6.5 ± 0.1 c	0.42 ± 0.01 b

Carboxymethyl cellulose: CMC. Values are presented as mean ± standard deviation (n = 3). Different superscript lowercase letters within the same column indicate significant differences (p < 0.05).

), the moisture contents of these three groups of FBBD powder samples were 4.6 ± 0.1%, 6.6 ± 0.1%, and 6.5 ± 0.1%, whereas the water activities were 0.32 ± 0.01, 0.46 ± 0.01, and 0.42 ± 0.01, respectively. Moisture content can be used as an indicator of food preservation. Kong and Chang [32] observed that a moisture content of soybean products exceeding 12% and a temperature exceeding 25 °C during storage can alter the functional properties of soybean proteins and affect product quality. Thus, low moisture content is more likely to ensure food quality, prolong shelf life, and improve food safety. In addition, López-Malo and Alzamora [33] observed that most microbial growth is inhibited in food products with water activity (a_w) less than 0.6 because less water is available for utilization by microorganisms, which can extend the shelf life of the food product under proper storage conditions. Peleg [34] also indicated that a_w < 0.9 is not conducive to the growth of most bacteria, yeasts, and molds. In this study, the water activity of all three groups of FBBD powder samples was less than 0.46, so the growth of most microorganisms is inhibited and the shelf life of the products is extended.

3.4. Effect of Coating Duration on the Wettability, Solubility, and Water-Holding Capacity of Coated FBBD Powder

Ji et al. [18] indicated that wetting is the first step when the sample particles make contact with the liquid during sample dissolution. Next, dispersion and dissolution are key stages when the sample particles begin to be released from the surface of the particles into the liquid. The contact angle is a major indicator that is widely used to evaluate wettability. FBBD samples were either not coated with a coating solution or coated with 3% CMC solution or 3% pectin solution in a fluidized bed granulator for 120 min, and their contact angles were analyzed (Figure 6). There was no significant change in the contact angle of the FBBD powder with no coating solution added (Figure 6A). However, after coating with 3% CMC solution (Figure 6B) or 3% pectin solution (Figure 6C) for 120 min, the contact angle of the samples decreased significantly, with the decrease in the samples coated for 120 min with 3% pectin solution being particularly pronounced. This indicates that the 3% pectin solution group had the best wettability. At 0.15 s of contact between the water droplet and the surface of the granule, the contact angle was already 0°, indicating that the water had completely penetrated the granule. Ji et al. [18] reported that greater porosity allows for a higher rate of water diffusion to the interior and therefore better wettability. Our results are consistent with those of Cardona et al. [35], who performed fluid bed granulation of pineapple powder. They utilized a binder solution comprising ginger extract and vitamin C to enhance the properties of pineapple powder. In our research, we focused on coating FBBD with CMC and pectin, aiming to enhance the physicochemical properties of FBBD powder. After nebulization, the samples were wet with a binding solution, and the powder particle structure re-formed into a larger porous structure, thus facilitating the flow of water through the gaps between the particles and resulting in better wettability.

In this study, the effect of the coating duration on the solubility and water-holding capacity of coated FBBD powder was also investigated. FBBD samples were either not coated with a coating solution or coated with 3% CMC solution or 3% pectin solution in a fluidized bed granulator for 120 min, and their solubility and water-holding capacity were analyzed (

Table 3. Effect of coating duration on solubility and water-holding capacity of coated FBBD powder.

	Duration of Coating (min)	Solubility (%)	Water-Holding Capacity (g/g)
Without CMC and pectin	0	29.4 ± 0.3 a	4.9 ± 0.2 a
	60	33.1 ± 0.4 b	4.8 ± 0.3 a
	120	34.8 ± 0.1 c	4.4 ± 0.1 a
With 3% CMC	0	29.4 ± 0.3 a	4.9 ± 0.3 a
	60	34.2 ± 1.9 b	4.2 ± 0.1 b
	120	35.5 ± 0.9 c	4.3 ± 0.1 b
With 3% pectin	0	29.4 ± 0.3 a	4.9 ± 0.3 a
	60	34.8 ± 0.7 b	4.1 ± 0.1 b
	120	31.6 ± 0.8 c	4.0 ± 0.1 b

Carboxymethyl cellulose: CMC. Values are presented as mean ± standard deviation (n = 3). Different superscript lowercase letters within the same column indicate significant differences (p < 0.05).

). The solubility of all three groups of samples increased after coating for 120 min, but the water-holding capacity decreased. After coating for 120 min, the solubilities of the three groups of FBBD powder samples were 34.8 ± 0.1%, 35.5 ± 0.9%, and 31.6 ± 0.8%, respectively, while the water-holding capacities were 4.4 ± 0.1, 4.3 ± 0.1, and 4.0 ± 0.1, respectively. Bhattachar et al. [36] defined solubility as the amount of solute per unit of saturated solution. In addition, Elleuch et al. [37] defined water-holding capacity as the amount of water that can be absorbed or retained in a unit sample. Thus, the wettability, solubility, and water-holding capacity results show that the wettability of the FBBD powder increased with increasing coating duration, which in turn increased the solubility and decreased the water-holding capacity of the samples.

4. Conclusions

After coating FBBD with 3% CMC solution or 3% pectin solution for 120 min, the proportion of medium-sized particles in the FBBD powder decreased with increasing coating duration. These particles agglomerated into large-sized particles, which reduced the contact area between the particles, thereby reducing cohesion and improving flowability. After coating FBBD with 3% CMC solution or 3% pectin solution for 120 min, the L* and b^* values of the samples decreased, whereas the a* and ΔE values increased, indicating that the color of the samples changed from bright to dark and the colors tended toward blue and red. The moisture content of the coated FBBD powder ranged between 4.6 and 6.5%, whereas the water activity ranged from 0.32 to 0.46. These values indicate low moisture content and water activity, which inhibit microbial growth and are favorable conditions for storage. In addition, FBBD powders coated with CMC solution or pectin solution have good wettability and solubility. The enhanced solubility, flowability, and stability achieved through CMC and pectin coating support the application of FBBD powder in food manufacturing. This study highlights its industrial potential in functional food formulations.