Effect of Ultrafine Grinding on the Physicochemical Properties of Tremella fuciformis Powder and Its Aqueous Extracts

TL;DR

Ultrafine grinding improves the quality and extraction efficiency of Tremella fuciformis, making it more suitable for functional food and bioactive component production.

Contribution

The study demonstrates that ultrafine grinding significantly enhances the physicochemical properties and extraction yield of Tremella fuciformis.

Findings

Ultrafine grinding reduced particle size by 91.8% and increased specific surface area.

UFG powder showed higher extraction yields (60.98–66.48%) and improved solubility and color brightness.

Aqueous extracts from UFG powder exhibited more fluid-like rheological behavior.

Abstract

The grinding of Tremella fuciformis is a critical step for its value-added processing and the efficient utilization of its functional components, significantly impacting product quality and process adaptability. This study investigated ultrafine grinding (UFG) as a mechano-physical strategy to improve product quality, systematically analyzing its impact on physical properties (particle size, powder characteristics, color), extraction efficiency, chemical composition, and rheological behavior compared to conventional grinding (CG). The results revealed that UFG treatment induced an extensive disruption of the matrix, reducing particle size by 91.8% (D90 = 18.18 μm) and significantly increasing specific surface area. Notably, this physical modification directly translated into enhanced processing performance. UFG powder exhibited reduced powder flowability, superior solubility and improved color brightness. This structural degradation proved beneficial for extraction, unlocking a substantially higher yield (60.98–66.48%). Concurrently, the aqueous extracts of UFG powder exhibited more fluid-like rheological characteristics. This study confirms the potential of UFG as an effective pretreatment for the intensive processing of T. fuciformis and indicates its promising application in functional food development and the extraction of bioactive components.

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1. Introduction

Tremella fuciformis (silver ear fungus) is a traditional edible and medicinal fungus prized in China. It contains abundant bioactive constituents, such as polysaccharides, proteins, and dietary fiber, and exhibits diverse physiological effects, including immunomodulation, antioxidant, antitumor, antiaging and stabilizing activities [1]. With a long history as a tonic food and herbal ingredient, TF has been used to treat and prevent a variety of diseases, including hypertension, colds and coughs, lung fever, and asthma [2]. Recent studies have also identified Tremella-derived polysaccharides as a potential non-animal source of hyaluronic acid-like compounds with comparable structural characteristics [3]. Comprehensive reviews have summarized the production, structural characteristics, and bioactivities of Tremella polysaccharides, highlighting their functional significance in food and pharmaceutical applications [4]. With a growing emphasis on health and wellness, the demand for T. fuciformis in functional foods, nutraceuticals, and pharmaceuticals is increasing [5]. Various processing techniques such as drying [6], blanching [7], enzymatic treatment [8], and steam explosion [9] have been applied to T. fuciformis to improve its functional properties and extraction efficiency. Grinding represents a critical processing stage that is often overlooked, despite its significant impact on the quality and functionality of the final product. This issue is particularly relevant for T. fuciformis, whose fruiting body exhibits a dense microstructure characterized by rigid polysaccharide-based cell walls composed mainly of chitin and glucan [10]. The hyphae are embedded within a compact gelatinous matrix, forming a substantial barrier to mass transfer. Consequently, conventional crushing is often insufficient to effectively disrupt the cell wall structure, thereby limiting the release and utilization of bioactive components [9].

Ultrafine grinding technology, an emerging physical modification technique, can significantly reduce the particle size, increase the specific surface area, and alter the physicochemical properties of powder materials. For instance, the UFG of wheat bran dietary fiber markedly reduced the particle size and altered the hydration-related properties (water holding capacity, water retention capacity, and swelling capacity), accompanied by a redistribution in fiber fractions and changes in antioxidant-related indices [11]. In fruit byproducts, the superfine grinding of apple pomace improved the powder uniformity and enhanced the techno-functional performance (notably increased water- and oil-holding capacities), while also promoting the release of phenolic and flavonoid compounds and increasing the soluble dietary fiber content [12]. The superfine grinding of T. fuciformis has been shown to improve dough rheological properties and product texture in steamed bun formulations [13]. Similarly, the superfine grinding of soybean residue has been reported to modify the physicochemical properties such as the particle size, color, angle of repose, swelling capacity, water solubility index, and antioxidant activity, supporting its valorization as a functional ingredient [14]. Collectively, these studies indicate that UFG can serve as an effective physicochemical modulation strategy by coupling microstructural refinement with enhanced mass transfer and component accessibility in diverse food systems [15].

UFG also offers a promising technical approach for improving the extraction efficiency of bioactive compounds [15,16]. For instance, Zhuang et al. [17] demonstrated that the superfine grinding of tea powder significantly increased the maximum yields (the theoretical maximum extraction yield (Y∞) predicted by the kinetic model) of polysaccharides, polyphenols, caffeine, and other components, while markedly accelerating the diffusion process compared with untreated samples. Similarly, Meng et al. [18] found that superfine grinding decreased the particle size, thereby enhancing the dissolution rates of polysaccharides and proteins and improving the antioxidant capacity. Xu et al. [19] reported that ultrafine grinding significantly enhanced both the dissolution rate and total extractable number of polysaccharides and ergosterol in Shiitake (Lentinula edodes) and Jew’s ear (Auricularia auricular). Despite these advances across various plant and fungal materials, systematic investigations focusing on the T. fuciformis system remain relatively limited.

In this study, the investigated parameters were categorized into the physical properties (particle size distribution, density, flowability, color, hydration-related indices), chemical composition (total sugar, protein, and uronic acid contents), extraction yield, and the rheological behavior of aqueous extracts. The objective of this research is to systematically investigate the effects of ultrafine grinding on the powder and processing properties of T. fuciformis powder, as well as on the extraction efficiency of bioactive components and the rheological properties of the T. fuciformis powder extract. This study provides a theoretical basis for the high-value and intensive processing of T. fuciformis.

2. Materials and Methods

2.1. Materials

Dried T. fuciformis slices were supplied by Fujian Sheng’er Biotechnology Co., Ltd. (Gutian, China). The slices were prepared from fresh T. fuciformis by blanching (80 °C for 5 min), followed by homogenization and hot-air drying at 75 °C. Phenol (≥99%), sodium tetraborate (≥99%), pectinase (≥10,000 U/g), D-glucose (≥99%), and D-glucuronic acid (≥98%) were obtained from Macklin Biochemical Co., Ltd. (Shanghai, China). Cellulase (≥10,000 U/g) and neutral protease (≥20,000 U/g) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Sulfuric acid (98%) and ethanol (95%) were acquired from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) and Xilong Scientific Co., Ltd. (Shenzhen, China), respectively. m-Hydroxydiphenyl (≥98%) was purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China), and the Bradford Protein Assay Kit and bovine serum albumin (BSA, ≥98%) were purchased from Beyotime Biotechnology (Shanghai, China). All chemicals were of analytical grade unless otherwise specified and were used without further purification.

2.2. Preparation of T. fuciformis Powder

The conventional grinding (CG) sample was prepared by pulverizing the material using a high-speed pulverizer (FW100, Taisite Instrument Co., Ltd., Tianjin, China) for 3 min, followed by sieving through an 80-mesh screen. For the ultrafine grinding (UFG) treatment, the material was first pre-ground using a graded ultra-fine continuous grinder (KWF-300, Wenzhou Dingli Medical Equipment Co., Ltd., Wenzhou, China). The pre-ground material was subsequently subjected to formal ultrafine pulverization using a large-scale ultra-micro pulverizer (CWF-300S, Dingli Medical Instrument Co., Ltd., Wenzhou, China). During the ultrafine grinding process, the feeding rate was set at 3.0 kg/h, the main shaft speed was set at 5000 rpm, and the equipment was operated under the manufacturer’s recommended speed regulation settings to ensure stable grinding conditions.

Each batch processed approximately 200 g per run. The resulting powders were stored in sealed containers at room temperature under light-protected conditions and used within three months for subsequent analyses.

2.3. Particle Size Distribution

Based on the modified method of Yu et al. [20], the particle size distribution of T. fuciformis powder samples was determined using a laser particle size analyzer (Bettersize2600, Dandong Bettersize Instruments Ltd., Dandong, China) under dry dispersion mode. The measurement range of the instrument was 0.10–2600 μm. Air was used as the dispersing medium (refractive index of 1.00). The refractive index and absorption index of the sample were set to 1.52 and 0.10, respectively. The feeding speed was set at 15 for UFG and 16 for CG, and the dispersion air pressure was maintained at 0.40 MPa. The analysis mode was adaptive, and the particle size distribution was reported on a volume basis. Approximately 0.5 g of powder was measured for each test.

2.4. Microtopography Analysis

The micrographs of T. fuciformis powders were captured using an inverted optical microscope (Leica DM500, Leica Microsystems, Wetzlar, Germany) at 40× magnification.

2.5. Powder Properties

2.5.1. Bulk and Tapped Densities

The bulk and tapped densities were determined according to the previous method with slight modifications [20,21]. Approximately 10 g of T. fuciformis powder was carefully poured into a 50 mL graduated cylinder without compacting, and the initial volume was recorded. The sample was then manually tapped against a rubber mat until no further volume change was observed. The final volume was then recorded. The bulk density (ρ-bulk) and tapped density (ρ-tap) were calculated using the following equations.

$$[eqn]$$ $$[eqn]$$

Here, M1 represents the weight of T. fuciformis powder samples (g), and V1 and V2 are the volumes of the samples before and after tapping (mL), respectively.

2.5.2. Carr Index

The Carr index was calculated according to the following equation [22].

$$[eqn]$$

Here, $[eqn]$ and $[eqn]$ were determined according to the method described in Section 2.5.1.

2.5.3. Repose Angle

The repose angle (α°) of T. fuciformis powders was measured using a previously described method [23]. For α°, a glass funnel was fixed vertically, above the plane on the testbed. The powder was poured into the funnel until the formed cone made contact with the funnel end. The radius and height were recorded. The α° was obtained via the following equation.

$$[eqn]$$

Here, H represents the height between the outlet of the funnel and the horizontal, and R is the radius of the cone formed by each sample.

2.6. Processing Properties

2.6.1. Color

A high-precision colorimeter (NR10QC, Shenzhen 3nh Technology Co., Ltd., Shenzhen, China) measured the surface color parameters of the T. fuciformis powders, including L*, a*, and b*. Prior to measurement, the instrument was calibrated with a standard white calibration plate (L* = 94.12, a* = −1.08, b* = 2.12). The chroma (C*), Whiteness index (WI) and total color difference (ΔE) were calculated as in the following equations [24,25].

$$[eqn]$$ $$[eqn]$$ $$[eqn]$$

Here, L0, a0, and b0* represent the lightness, green-redness, and blue-yellowness of CG samples, respectively, and L*, a*, and b* represent those parameters of the UFG samples.

2.6.2. Water-Holding Capacity and Oil-Holding Capacity

The water-holding capacity (WHC) of the T. fuciformis powders was determined with slight modifications according to a previously reported method [26]. Briefly, 0.5 g of the sample was placed into a pre-weighed centrifuge tube, mixed with 20 mL of deionized water, and incubated in a water bath at 60 °C for 30 min. The mixture was then centrifuged at 5000 rpm for 20 min. After discarding the supernatant, the precipitate was weighed, and the WHC was calculated according to the following equation.

$$[eqn]$$

Here, $[eqn]$ represents the weight of the T. fuciformis powder sample, and $[eqn]$ represents the weight of the precipitate after centrifugation.

The oil-holding capacity (OHC) of the T. fuciformis powders was determined following the same procedure as that used for WHC, except that deionized water was replaced with corn oil.

$$[eqn]$$

Here, $[eqn]$ represents the weight of the T. fuciformis powder sample, and $[eqn]$ represents the weight of the precipitate after centrifugation.

2.6.3. Water Solubility

The water solubility index (WSI) of the T. fuciformis powders was determined with slight modifications according to a previously reported method [27]. First, 0.5 g of the sample was mixed with 30 mL of deionized water and heated in a water bath at 80 °C for 30 min. The mixture was then centrifuged at 6000 rpm for 10 min. The supernatant was transferred to a pre-weighed dish and vacuum-dried. The mass of the dried precipitate was recorded, and the WSI was calculated using the following equation.

$$[eqn]$$

Here, $[eqn]$ represents the weight of the T. fuciformis powder sample, $[eqn]$ represents the weight of the pre-weighed dish, and $[eqn]$ represents the mass of the precipitate after drying.

2.6.4. Swelling Power

The swelling power (SP) of the T. fuciformis powder was determined with slight modifications according to a previously reported method [28]. Briefly, 0.5 g of the sample was placed in a graduated cylinder to record the initial sample volume (V1). Subsequently, 30 mL of deionized water was added, and the sample was allowed to stand at 25 °C for 24 h. The volume of the swollen sample was then recorded, and the SP was calculated accordingly.

$$[eqn]$$

Here, $[eqn]$ represents the initial volume of T. fuciformis powder sample. $[eqn]$ represents the volume of the swollen sample after absorbing water.

2.7. Preparation of T. fuciformis Powder Extract

According to previous research with slight modifications, the T. fuciformis powder extract was prepared using the methods of hot water extraction (HWE), enzymatic extraction (EE), and microwave-assisted extraction (MAE), respectively. For HWE, T. fuciformis slurry was prepared at a solid-to-liquid ratio of 1:70 (w/v) and extracted in a water bath at 90 °C for 4 h [29]. For EE, T. fuciformis slurry was prepared at a solid-to-liquid ratio of 1:80 (w/v), and the pH was adjusted to 6.3. A compound enzyme preparation (1.5%, w/w), consisting of pectinase, cellulase, and neutral protease, was added, followed by enzymatic hydrolysis at 50 °C for 40 min. The enzymes were subsequently inactivated by heating to 80 °C, and the mixture was further extracted at 60 °C for 1 h [30]. For MAE, T. fuciformis slurry was prepared at a solid-to-liquid ratio of 1:100 (w/v) and pre-mixed in hot water for 10 min. The extraction was then performed under microwave irradiation at 1000 W for 25 min using batch microwave equipment (PDBA-6 kW, Changsha Pinyue Technology Co., Ltd., Changsha, China) [31].

After extraction, each extract was centrifuged at 8000 rpm for 20 min to remove the insoluble residues. The supernatant was then concentrated to 1/3–1/2. Subsequently, four volumes of 95% (v/v) ethanol were added, and the mixture was kept at 4 °C overnight to allow ethanol precipitation. After centrifugation, the precipitate was freeze-dried. The extraction yield was calculated as the ratio of the mass of the obtained extract to the mass of the raw powder.

$$[eqn]$$

Here, M_e_ and M_r_ represent the weight of the obtained T. fuciformis powder extract and the raw T. fuciformis powder, respectively.

2.8. Chemical Analysis of T. fuciformis Powder Extract

The total sugar content of the T. fuciformis powder extract was determined by the phenol–sulfuric acid method [9]. D-glucose was used as the standard substance; the standard curve equation was Y = 6.1457X + 0.0871, R^2^ = 0.999.

The protein content of the extract was determined by the Coomassie brilliant blue method [32]. Bovine serum albumin (BSA) was used as the standard substance; the standard curve equation was Y = 0.0042X + 0.3999, R^2^ = 0.9949.

The uronic acid content of the extract was determined by the m-hydroxydiphenyl method [33]. D-glucuronic acid was used as the standard substance; the standard curve equation was Y = 2.3341X + 0.0291, R^2^ = 0.9961.

The experiments here were measured using a multifunctional microplate reader (SpectraMax i3X, Molecular Devices, San Jose, CA, USA).

2.9. Rheological Properties of T. fuciformis Powder Extract

The T. fuciformis powder extract was dispersed in deionized water at a concentration of 1% (w/v) and subjected to rheological measurements using a rheometer (MCR302, Anton Paar, Graz, Austria) at 25 °C. The apparent viscosity and shear stress of the samples were measured over a shear rate range of 1–100 s^−1^. The apparent viscosity–shear rate data were fitted using the power-law model [34], as expressed by the following equation:

$$[eqn]$$

where τ represents the shear stress (Pa), $[eqn]$ is the consistency index (Pa·s^n^), and n is the flow behavior index. When 0 < n < 1, the fluid exhibits pseudoplastic (shear-thinning) behavior, whereas n > 1 indicates dilatant (shear-thickening) behavior.

The dynamic rheological properties were measured using a rheometer (MCR302, Anton Paar, Graz, Austria) equipped with parallel-plate geometry. The tests were performed at 25 °C with a fixed frequency of 1 Hz and a strain amplitude of 1%. Frequency sweep measurements were carried out over an angular frequency range of 1–100 rad/s to determine the storage modulus (G′) and loss modulus (G″) of the samples. The obtained data were fitted to the corresponding model, as expressed by the following equations [35].

$$[eqn]$$ $$[eqn]$$

Here, k′ and k″ indicate the power law constants (Pa·s^n^), n′ and n″ indicate the frequency indexes, and ω indicates the angular frequency (rad/s).

2.10. Statistical Analysis

The experiments were repeated in triplicate except for special instructions. Data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test at a significance level of p < 0.05 via SPSS 16.0. Origin 2018 was utilized for data visualization.

3. Results and Discussion

3.1. Particle Size Distribution and Morphological Characteristics

The particle size distribution is a fundamental determinant of the physicochemical behavior of food powders, governing surface interactions and dissolution kinetics [36,37,38,39]. As illustrated in Figure 1a, the grinding method exerted a profound impact on the granulometric profile of T. fuciformis powders. Notably, ultrafine grinding (UFG) treatment induced a significant comminution effect, shifting the distribution curve toward the sub-100 μm range, with the D_90_ value of 18.18 μm, corresponding to a 91.8% decrease relative to the CG sample. In stark contrast, the conventional grinding (CG) sample displayed a polydisperse distribution characterized by coarse particles (10–1000 μm), with a D_90_ value of 221.52 μm. This mono-dispersion tendency suggests that the high-intensity shear and impact forces during UFG effectively overcame the material’s cohesive strength, shattering the fibrous matrix into micro-scale particulates.

Microstructural analysis (Figure 1b,c) corroborated the granulometric data. UFG powders presented as fragmented discrete particles with smoothed edges. The significant reduction in particle size considerably increases the specific surface area, thereby expanding the solid–liquid contact interface and diminishing the mass transfer resistance [15]. Such structural modification may therefore facilitate the release of bioactive components, as previously reported in other plant materials subjected to UFG [12,40].

3.2. Powder Properties and Color

The bulk and tapped densities characterize the packing behavior of powders under loose and compacted states, respectively, and are widely used indicators of powder handling, transportation efficiency, and storage stability. In food processing, bulk density is particularly important for determining the packaging volume, dosing accuracy, and material flow in conveying systems, whereas the tapped density provides insight into the compressibility and structural rearrangement of particles under vibration or mechanical stress [41]. Both the bulk and tapped densities decreased significantly following UFG treatment (Table 1). The CG sample exhibited bulk and tapped densities of 0.62 and 0.82 g/mL, respectively, however, these values decreased significantly to 0.29 and 0.45 g/mL for the UFG sample (Table 1). While reduced density often correlates with smaller particle size due to increased inter-particular air voids, it also implies a stronger influence of inter-particle cohesive forces over gravitational forces in finer powders. Crowley et al. [42] indicated that the bulk density of milk protein concentrate powder is affected by the particle sizes. Powders with small particle sizes contribute to the increase in interstitial air volume. Based on this evidence, the smaller particle sizes of the UFG sample (Figure 1) could be a potential explanation for their reduced bulk density.

Flowability refers to the ability of powders to flow freely, regularly, and constantly [43]. This property is a crucial parameter for evaluating the powder handling performance during industrial operations such as storage, transportation, blending, and packaging [36]. In this work, flowability was assessed using the Carr index and the angle of repose. The Carr index, derived from aerated and tapped bulk densities, is widely used to classify powder flowability in industrial practice. According to commonly accepted classification standards, Carr index values of 0–15% indicate good flowability, 15–25% represent medium flowability, 25–30% correspond to poor flowability, and values above 30% indicate very poor flowability [44,45]. In the present study, the Carr index increased significantly from 24.59% for the CG sample to 35.16% for the UFG sample (Table 1), indicating a clear deterioration in flowability following UFG, corresponding to very poor flowability. This phenomenon can be attributed to the substantial increase in the surface-to-volume ratio of the ultrafine particles. As the particle size decreases, van der Waals forces and electrostatic interactions become dominant over gravity, leading to agglomeration and enhanced friction between particles [46]. The angle of repose, defined as the maximum stable inclination of a powder pile relative to the horizontal plane [47], was significantly larger in the UFG sample compared to the CG sample (Table 1). This larger angle corresponds to reduced flowability, which is consistent with the results of the Carr index. This observation aligns with the findings of Li et al. [48] and Gong et al. [49], who reported a significant decrease in the flowability of sweet potato leaf and mushroom powders after superfine grinding. Although reduced flowability may present challenges for automated feeding systems, superfine grinding has been reported to increase the interparticle contact area and packing density, which may enhance the powder compressibility under certain conditions [50].

Color is a critical indicator affecting the sensory quality and consumer acceptability of food ingredients and final products, where a bright white appearance is commonly associated with high quality. UFG significantly altered the color parameters of the T. fuciformis powder (Table 2). The lightness (L*) significantly increased from 89.35 to 95.68, while the chroma (C*) decreased, resulting in a visually whiter and less saturated powder. In addition to L*, a*, and b*, the whiteness index (WI) was calculated to more comprehensively evaluate the visual whiteness of the powder. The WI value increased significantly after UFG treatment, further confirming the enhancement of whiteness and visual brightness.

Chroma (C*) reflects color saturation, where lower C* values indicate reduced color intensity and a shift toward a more neutral or white appearance. The decrease in redness (a*) and yellowness (b*) suggested that the rapid high-energy grinding process may have physically disrupted pigment–protein complexes [51] or limited the oxidative browning compared to the prolonged heat exposure often associated with conventional milling.

The total color difference (ΔE) between the CG and UFG samples was 9.28. According to commonly accepted color difference standards, ΔE values between 1 and 3 are slightly noticeable, 3–6 indicate clearly visible differences, and values above 6 represent large or obvious color differences [25]. Therefore, the ΔE value of 9.28 indicates a pronounced and easily perceptible color change after UFG treatment. These changes can be primarily attributed to the particle size reduction, which enhances light scattering and increases surface reflectance, thereby elevating lightness [52].

In practical terms, WI values above 90 are generally associated with high whiteness in food powders, which is desirable for consumer perception and product formulation. The achieved higher WI and reduced chroma therefore indicate the improved visual acceptability of T. fuciformis powder as a food ingredient.

3.3. Processing Properties

The water-holding capacity (WHC) and oil-holding capacity (OHC) are important functional properties that describe the capacities of powder materials to retain water and oil, providing insight into their hydration characteristics and suitability for food formulation [53]. Interestingly, UFG treatment resulted in divergent trends for WHC and OHC (Table 3), with the WHC declining from 19.69 g/g (CG) to 18.08 g/g (UFG). This decrease is probably due to the reduced particle size. In CG powders, the intact physical voids retain water via capillary action; however, UFG destroys these capillaries, leaving water retention to rely primarily on surface adsorption [11]. Meanwhile, more compact packing limits the pores available for water penetration and retention [54,55]. These results align with the findings of Tsai et al. [56], who also reported a decline in the WHC with decreasing particle size in T. fuciformis powder. Conversely, the OHC increased significantly in the UFG sample (0.92 g/g). The liberation of hydrophobic groups from the interior of the protein–polysaccharide matrix, coupled with the increased specific surface area, provided more binding sites for lipid absorption. Notably, the WHC values for both samples considerably exceeded their respective OHC values, indicating that T. fuciformis powder retains favorable thickening properties.

The water solubility index (WSI) is an indicator widely adopted to reflect the improvement in the solubility of powder samples. The swelling power (SP) is an important functional parameter that provides insight into hydration behavior and structural responsiveness in aqueous systems [57]. Notably, the WSI and SP were dramatically enhanced by UFG, with the WSI increasing 4.4-fold to 29.33%. This solubility enhancement is a direct consequence of the mechanical activation effect: the disruption of the cell wall matrix eliminates the physical barrier to dissolution, while the reduction in particle size accelerates hydration kinetics according to the Noyes–Whitney equation [15]. In addition, the concurrent increase in SP (33.45 mL/g) indicated that, once dissolved, the exposed polysaccharides rapidly hydrate to form an expansive network. The increase in SP is a direct consequence of the improved WSI. Rapid hydrolysis and the subsequent expansion of abundant hydrophilic components enable the formation of a high-viscosity gel-like network [58]. Macroscopically, this appears as a significant volumetric increase [57]. Thus, this increase in SP is attributed primarily to enhanced molecular-level hydration, rather than to changes in powder bed porosity. These properties suggest that UFG powders are superior instant thickening agents compared to their coarse counterparts.

3.4. Extraction Yields and Chemical Component of T. fuciformis Powder Extracts

The extraction yield serves as a macroscopic indicator of how effectively the intracellular matrix is solubilized under different processing conditions. The grinding method exerted a determinant role in the extraction efficiency across all tested modalities, including hot water extraction (HWE), enzymatic extraction (EE), and microwave-assisted extraction (MAE). Generally, the UFG-treated samples exhibited a substantial improvement in extraction yields compared to their CG counterparts, with increments ranging from approximately 1.7-fold to 3-fold depending on the extraction method (Figure 2a).

Specifically, in the HWE and EE groups, the yields for the UFG samples surged to over 60%, whereas the CG samples hovered around 35% (Figure 2a). The most striking contrast was observed in the MAE group, where the yield for the CG sample was merely 20.38%, while the UFG treatment propelled it to over 60% (Figure 2a). The extraction process is governed by the diffusion of solvent into the solid matrix and the subsequent diffusion of solutes out into the bulk solution [59]. UFG treatment pulverizes the tissue matrix, drastically increasing the specific surface area and reducing the diffusion path length to the micro-scale. This structural disruption effectively eliminates the physical barrier of the cell wall, exposing the intracellular contents directly to the solvent and thermal/microwave energy, thereby shifting the solid–liquid equilibrium toward rapid solubilization [45].

The extraction yield reflects the total quantity of solubilized solids, while the chemical composition analysis reveals how physical disruption selectively influences the release of specific macromolecular components. Previous studies have demonstrated that drying and grinding techniques significantly influence the chemical composition and nutritional properties of fungal polysaccharides [60]. In this study, the total sugar content, representing the primary polysaccharide fraction, remained the dominant component in all extracts (68.39–79.41%), yet its proportion was differentially modulated by the interaction between grinding and extraction methods (Figure 2b). The total sugar content is substantially higher than that reported for other plant materials [29], demonstrating considerable potential for the industrial extraction of active ingredients from T. fuciformis.

In the HWE system, UFG treatment significantly increased the total sugar purity compared to CG (p < 0.05, Figure 2b). This increase can be attributed to the intensive mechanical forces generated during ultrafine grinding, which reduce the particle size and disrupt cell wall structures, thereby enhancing the accessibility and extractability of polysaccharides, leading to a higher proportion of total sugars in the hot water extract. Conversely, in the EE system, the UFG sample displayed a statistically lower total sugar content than the CG sample. This reduction may be related to the synergistic effect of enzymatic hydrolysis and ultrafine grinding. The increased surface area and structural disruption caused by UFG not only enhance polysaccharide solubilization but may also promote the co-extraction of non-sugar components, such as proteins, phenolics, and other soluble solids. As a result, although the absolute amount of extracted material increases (Figure 2a), the relative proportion of sugars in the final dry extract decreases, leading to an apparent dilution effect.

Crucially, the protein content provided biochemical evidence for the extent of cell wall disruption. The protein content in the aqueous extracts was generally low (<5%). However, the protein content in all UFG-treated samples was consistently and significantly higher than in the CG samples (p < 0.05, Figure 2b). It was indicated that UFG effectively ruptured the cell wall matrix, liberating proteoglycans or intracellular proteins that remain inaccessible in coarse powders. This observation is consistent with the findings reported by Gong et al. [49] for mushrooms.

The content of uronic acid remained relatively stable across all groups (15%) and was largely independent of the grinding method (Figure 2b). It was revealed that while the high-intensity shear forces of UFG are sufficient to shatter physical cellular structures and promote the release of macromolecules, they are not destructive enough to cleave the glycosidic bonds of the uronic acid moieties or degrade the primary chemical structure of the active polysaccharides. Similar findings have been reported for other food powders, where different grinding methods markedly modified the particle morphology and functional properties but caused no significant changes in the main chemical structures [61].

3.5. Rheological Properties of T. fuciformis Powder Extract

3.5.1. Static Rheological Measurements

The gelation of fungal polysaccharides is vital for enhancing food texture and sensory properties, allowing them to function as thickeners, stabilizers, gelling agents, and adhesives in various food products. Their rheological properties significantly impact extraction processes, food design, sensory evaluation, product development, and shelf life [60]. The rheological behavior of T. fuciformis aqueous extracts is an important factor governing their applications in food and cosmetics, constituting a key parameter for guiding industrial production. The apparent viscosity of all the extract solutions declined with the increasing shear rate at 25 °C, demonstrating characteristic pseudoplastic (shear-thinning) flow (Figure 3a,b). The power-law model was effectively fitted to the rheological data, with high coefficient of determination (R^2^ > 0.981) confirming the model’s suitability. All samples exhibited a flow behavior index (n) below 1 (ranging from 0.320 to 0.616) (Table 4), which further verifies their non-Newtonian shear-thinning nature. This rheological profile is principally attributed to the high content and polymeric nature of Tremella polysaccharides in the extracts. The presence of polymer chain entanglements and hydrogen bonds promotes a partially associated molecular conformation, yielding high viscosity under low-shear conditions [62]. The decrease in viscosity with increasing shear rate suggests that the imposed shear forces induce chain alignment and temporary disentanglement, weakening intermolecular associations and facilitating flow [63].

The CG samples demonstrated higher consistency coefficients (κ), reflecting their greater apparent viscosity. Specifically, the CG-HWE sample exhibited the strongest structural integrity (κ = 3.894 Pa·s^n^, η_1_ = 2760.5 mPa·s, Table 4), whereas the CG-MAE sample displayed the highest shear sensitivity (n = 0.320, η_1_/η_100_ = 19.27, Table 4). However, both the viscosity and the extent of shear-thinning were noticeably reduced under the UFG treatment, with the UFG-HWE sample displaying the lowest viscosity and the mildest shear-thinning response (κ = 0.659 Pa·s^n^, n = 0.616, Table 4). This decrease can be primarily attributed to polysaccharide chain scission and the reduced molecular weight induced by the intense mechanical shear during UFG processing, which weakens intermolecular entanglement [64]. Collectively, these results indicate that both the grinding method and the extraction technique are capable of modulating the structural properties of Tremella polysaccharides, thereby regulating their rheological behavior.

3.5.2. Dynamic Rheological Properties

Dynamic rheological measurements were conducted to further probe the viscoelastic network structure. Both the storage modulus (G’) and loss modulus (G″) for all samples increased with the angular frequency, a characteristic feature of entangled biopolymer solutions or weak gels (Figure 4). In the low-frequency region, the viscous component dominated (G″ > G’), whereas at higher frequencies, the elastic component prevailed (G’ > G″). This frequency-dependent crossover indicates a transition from liquid-like flow to solid-like elastic response [65], driven by the varying time scales of molecular relaxation. Furthermore, UFG treatment induced a shift of the G′–G″ crossover to a higher frequency, which corresponds to a shorter characteristic relaxation time and suggests more rapid structural rearrangement within the system [58]. It should be noted that an atypical crossover was detected at low frequency for the UFG-HWE group (Figure 4a). This anomaly may be due to the measured moduli approaching or falling below the instrument’s reliable detection threshold, which could also account for the variability in the viscoelastic parameters reported for this group, as shown in Table 5. Therefore, this low-frequency crossover should be interpreted with caution and is unlikely to represent an intrinsic viscoelastic transition of the system.

The quantitative viscoelastic parameters derived from the power-law fitting (Table 5) reveal the extent of structural weakening caused by UFG. The power-law constants for the storage modulus (k’), which reflect the strength of the elastic network, were significantly lower in UFG samples. Specifically, for the HWE group, k’ decreased by an order of magnitude from 2.040 Pa·s^n^ (CG) to 0.169 Pa·s^n^ (UFG). This aligns perfectly with the static viscosity data, confirming that UFG treatment disrupts the formation of a strong elastic network. Moreover, the frequency exponents (n’ and n″) provide insight into the nature of the interactions. A true gel typically exhibits frequency-independent moduli (n’~0). In contrast, the UFG samples displayed significantly higher n’ values (0.910 for UFG-HWE, 0.535 for CG-HWE, Table 5), indicating a strong dependence on frequency. This high frequency sensitivity suggests that the UFG extracts behave more like dilute or semi-dilute solutions rather than structured networks.

Overall, both the static and dynamic rheological measurements consistently demonstrate that UFG effectively modulates the molecular organization of T. fuciformis extracts. The viscosity, G′ and G″ were all markedly reduced after UFG treatment, with more pronounced effects observed in the HWE samples, whereas relatively minor changes were detected in the MAE and EE samples (Figure 4, Table 5). These results indicate a transition of the system from a highly entangled gel-like network toward a more fluid-like dispersed state. This transformation is primarily attributed to the mechanical degradation of polysaccharide chains induced by UFG, leading to a reduction in the hydrodynamic volume and chain entanglement density, thereby weakening the viscoelastic network structure.

4. Conclusions

This study systematically investigated the effects of UFG on the physical properties of T. fuciformis powder (particle size, density, flowability, color, hydration-related indices), as well as the extraction yield, chemical composition (total sugar, protein, and uronic acid), and rheological behavior of aqueous extracts obtained by different extraction methods (HWE, EE, and MAE). The results demonstrate that UFG markedly modified the powder and processing properties of T. fuciformis powder and significantly enhanced the extraction yield of aqueous extracts. UFG treatment influenced the distribution of the extract components, leading to variations in the total sugar content, while the contents of protein increased, and uronic acid remained relatively stable. In addition, UFG effectively regulated the rheological behavior of the aqueous extracts, resulting in reduced apparent viscosity, storage modulus (G′), and loss modulus (G″), together with enhanced frequency dependence, which collectively reflect a transition toward more fluid-like viscoelastic characteristics. Overall, UFG represents an efficient physical modification strategy for T. fuciformis, capable of improving the powder processability, promoting the extraction efficiency of bioactive components, and tailoring the rheological properties of aqueous extracts. This work provides a mechanistic insight and technical guidance for the intensive processing of T. fuciformis and its application in food, cosmetic, and related products.