Optimized High-Pressure Ultrasonic-Microwave-Assisted Extraction of Gingerol from Ginger: Process Design and Performance Evaluation

Abstract

This study employed high-pressure ultrasonic-microwave-assisted extraction (HP-UMAE) to extract gingerols from ginger. The extraction yield and total polyphenol content of the extracts were determined. Their antioxidant activity was assessed by DPPH and ABTS radical scavenging assays, and compared with extracts obtained by leaching extraction, reflux extraction, ultrasonic-assisted extraction (UAE), microwave-assisted extraction (MAE), and ultrasonic-microwave-assisted extraction (UMAE). The results demonstrated that HP-UMAE achieved the highest extraction yield and the strongest ABTS radical scavenging activity among the evaluated methods. Furthermore, HP-UMAE extracts exhibited the highest concentrations of key gingerol constituents: 6-gingerol (14.29 mg/L), 8-gingerol (0.38 mg/L), 10-gingerol (1.95 mg/L), and 6-shogaol (4.32 mg/L). This enhanced efficacy is attributed to the synergistic combination of ultrasonic cavitation and microwave-induced thermal effects under elevated pressure. This synergy creates conditions promoting cellular wall disruption, facilitating the release of intracellular components, while concurrently enhancing solvent penetration and gingerol solubility. Scanning electron microscopy (SEM) analysis confirmed the significant structural damage inflicted on ginger cell walls following HP-UMAE treatment. The process parameters for HP-UMAE were optimized using single-factor experiments. The optimal extraction conditions were determined as follows: microwave power 800 W, ultrasonic power 1000 W, liquid-to-solid ratio 55:1, and temperature 100 °C (corresponding pressure 2 MPa). Under these optimized parameters, the extraction yield and ABTS radical scavenging rate reached their peak performance, yielding values of 4.52% and 43.23%, respectively.

1. Introduction

Ginger (Zingiber officinale), a widely utilized culinary and medicinal plant, contains numerous bioactive components, including gingerols, ginger essential oil, and ginger polysaccharides. Among these, gingerols constitute the primary active ingredients extracted from ginger. These compounds can be classified into subcategories: gingerols, gingerones, gingerdiones, and gingerdiols. The principal constituents of gingerols are phenolic compounds, notably 6-gingerol, 8-gingerol, 10-gingerol, and 6-shogaol. These key phenolics demonstrate significant bioactive properties, including antibacterial, anti-inflammatory, antioxidant, and anti-tumor effects [1,2,3,4]. This multifaceted bioactivity underpins gingerols’ extensive applications across diverse sectors, particularly in the food, cosmetic, and pharmaceutical industries.

At present, the extraction methods of gingerols mainly include leaching extraction [5], reflux extraction [6], microwave-assisted extraction (MAE) [7,8], ultrasonic-assisted extraction (UAE) [9,10], and ultrasonic-microwave-assisted extraction (UMAE) [11]. The leaching extraction method, based on the principle of “like dissolves like”, offers user-friendly operation and cost-effectiveness but suffers from significant limitations including prolonged processing time and suboptimal efficiency [7]. While reflux extraction demonstrates operational simplicity, its extraction yield remains comparatively lower than alternative extraction techniques. In contrast, UAE employs a fundamentally distinct mechanism, utilizing ultrasound-induced cavitation, mechanical effects, and thermal energy to facilitate the release of bioactive compounds from plant matrices [10]. MAE primarily generates thermal effects through electromagnetic wave irradiation (300 MHz–300 GHz), enabling rapid dissolution of plant bioactive components from cellular structures. This technique demonstrates superior extraction efficiency compared to conventional reflux extraction while significantly reducing solvent consumption [12]. Various extraction methods exhibit distinct advantages and limitations. To enhance gingerol extraction efficiency and bioactivity, researchers have explored hybrid extraction techniques, including leaching-ultrasonic extraction [13], UMAE [11], and ultrasonic-supercritical extraction [14]. However, these combined methods often demonstrate insufficient improvement in extraction yield. High-pressure extraction represents an innovative extraction technique that exploits pressure-induced cell wall disruption to generate transmembrane pressure gradients, thereby enhancing the dissolution of bioactive compounds. This method demonstrates notable advantages including operational simplicity, broad applicability, rapid processing efficiency, and successful industrial-scale implementation [15], but it is rarely used in ginger extraction. The integration of high-pressure technology with existing hybrid extraction processes shows considerable promise. Such integration is anticipated to generate a synergistic intensification effect under elevated pressure conditions, potentially leading to a substantial increase in gingerol extraction yield. Nevertheless, the current literature indicates that HP-UMAE has been scarcely applied to the extraction of natural products.

Herein, HP-UMAE was employed to extract gingerols from ginger, with extraction yield and antioxidant activity serving as the evaluation indicators. The polyphenol content in the extract was quantified by high-performance liquid chromatography (HPLC). Scanning electron microscopy (SEM) was employed to characterize the ginger powder residue post-extraction, evaluating the impact of the extraction process on its structural morphology. Single-factor experiments were conducted to optimize the HP-UMAE process and determine the optimal process conditions. The development of these HP-UMAE parameters for gingerols serves as a reference for the advancement of multi-energy field combined extraction technologies. Additionally, this work establishes a foundation for gingerol applications, highlighting its significant practical relevance.

2. Materials and Methods

2.1. Materials and Reagents

Gingers were sourced from Shangdong Province, China. The raw materials were thoroughly washed, sliced into uniform pieces, and subsequently dried at 50 °C for 24 h in an oven. The dried slices were then ground into fine powder using a grinder. Vanillin (Q) and 1,1-diphenyl-2-picrylhydrazyl (DPPH, ≥98%) were purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). Absolute ethanol (analytical grade), acetic acid (HPLC grade), and acetonitrile (HPLC grade) were obtained from Guangzhou Chemical Reagent Factory (Guangzhou, China). Potassium persulfate (PDS, ≥99%), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, ≥98%), 6-gingerol (6-G, ≥98%), 8-gingerol (8-G, ≥98%), 10-gingerol (10-G, ≥98%), and 6-shogaol (6-S, ≥98%) were supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China).

2.2. Test Method

2.2.1. Determination of Extraction Rate of Gingerol

In this study, the extraction yield of gingerol was quantified by ultraviolet spectrophotometer (Mapada, UV-1800, Shanghai, China) using vanillin as an external standard. A calibration curve was constructed by preparing standard solutions in the following manner: aliquots (1, 2, 3, 4, 5, and 6 mL) of 20 μg/mL vanillin solution were transferred to separate 10 mL volumetric flasks and diluted to the mark with absolute ethanol, yielding final concentrations of 2, 4, 6, 8, 10, and 12 μg/mL, respectively. Using ethanol as the blank control, absorbance measurements were performed at 280 nm. The resulting linear regression equation is y = 15.5090x − 0.8399 (R² = 0.9972).

The gingerol extraction yield was calculated as follows: The supernatant obtained after centrifugation was appropriately diluted with absolute ethanol. Using absolute ethanol as the blank control, absorbance was measured at 280 nm to determine the vanillin-equivalent concentration. The extraction yield was then calculated using the following equation.

$$\eta ={\displaystyle \frac{2.001\times W\times V\times G}{M}}\times 100\mathrm{\%}$$

where 2.001 is conversion factor between gingerol and vanillin; W is concentration of vanillin (μg/mL); V is total volume of extraction solution (mL); G is dilution factor; and M is mass of ginger powder (μg).

2.2.2. Different Extraction Methods of Gingerol

Leaching extraction: Ginger powder (1.24 g) was accurately weighed using an electronic analytical balance (Sartorius, BSA224S, Beijing, China) and mixed with 60% ethanol aqueous solution at a solid-to-liquid ratio of 1:55 (w/v). The extraction was performed at atmospheric pressure and 25 °C for 5 min.

UAE: The ginger powder (1.24 g) was homogenized with 60% ethanol aqueous solution using a solid-to-liquid ratio of 1:55 (w/v). The extraction process was conducted under ultrasonication at a fixed power of 1000 W (25 kHz), with the temperature maintained at atmospheric pressure and 25 °C for 5 min.

Reflux extraction: The ginger powder (1.24 g) was homogenized with 60% ethanol aqueous solution using a solid-to-liquid ratio of 1:55 (w/v). The extraction process was conducted at atmospheric pressure and 60 °C for 5 min.

MAE: The ginger powder (1.24 g) was homogenized with 60% ethanol aqueous solution using a solid-to-liquid ratio of 1:55 (w/v). The extraction process was conducted under microwave irradiation at a constant power of 800 W, with the temperature maintained at atmospheric pressure and 60 °C for 5 min.

UMAE: The ginger powder (1.24 g) was homogenized with 60% ethanol aqueous solution using a solid-to-liquid ratio of 1:55 (w/v). The extraction process was conducted under microwave power of 800 W, ultrasonic power of 1000 W (25 kHz), with the temperature maintained at atmospheric pressure and 60 °C for 5 min.

HP-UMAE: The ginger powder (1.24 g) was homogenized with 60% ethanol aqueous solution using a solid-to-liquid ratio of 1:55 (w/v), and the experimental parameters were set as follows: constant microwave power of 800 W, ultrasonic power of 1000 W (25 kHz), pressure of 2 MPa, and temperature of 100 °C for 5 min.

The extracts obtained from the six different extraction methods were transferred into 10 mL centrifuge tubes and subjected to centrifugation at 3000 r/min for 5 min using a low-speed desktop centrifuge (Cence, LT53, Changsha, China). Subsequently, 1 mL of the supernatant was collected, diluted 100-fold with anhydrous ethanol, and subjected to absorbance measurement at 280 nm using a UV-vis spectrophotometer. The absorbance values were recorded for further analysis.

2.2.3. Optimization of Extraction Process Parameters by HP-UMAE

The HP-UMAE processes were conducted with a high-pressure ultrasonic and microwave collaborative workstation (Xianghu Technologies, XH-300PE, Beijing, China). The schematic diagram and actual picture of the apparatus are presented in Figure 1. Single-factor experiments were systematically conducted to evaluate the effects of various process parameters on both gingerol extraction yield and antioxidant activity, with the objective of determining optimal extraction conditions. The tested parameters are detailed in

Table 1. Technological parameters of HP-UMAE.

Variable	Variable Level	Evaluating Indicator
Solid- to-liquid ratio	1:35, 1:45, 1:55, 1:65, 1:75	Extraction rate, Antioxidant activity
Extraction temperature	80 °C, 90 °C, 100 °C, 110 °C, 120 °C
Ultrasonic power	600 W, 800 W, 1000 W, 1200 W, 1400 W
Microwave power	600 W, 700 W, 800 W, 900 W, 1000 W

.

2.2.4. Antioxidant Activity of Gingerol In Vitro

Determination of DPPH Radical Scavenging Rate

The antioxidant capacity was determined according to Chinese National Standard GB/T 39100-2020 [16], employing both DPPH radical scavenging assays. Following the methods described by Reza with modifications [17], 4 mL of sample was mixed with 4 mL of 0.12 mmol/L DPPH ethanolic solution. The reaction mixtures were shaken and kept in the dark. The mixture was incubated for 30 min in the dark to determine absorbance (S₁), the reaction solution was replaced with anhydrous ethanol to determine absorbance (S₂), while the sample was substituted with anhydrous ethanol to determine absorbance (S₃). Absorbance was measured at 517 nm, and the scavenging rate was calculated using the following equation.

$$P=(1-{\displaystyle \frac{S_1-S_2}{S_3}})\times 100\mathrm{\%}$$

where P is radical scavenging capacity; S₁ is absorbance of DPPH ethanolic solution mixed with sample; S₂ is absorbance of absolute ethanol mixed with sample; and S₃ is absorbance of DPPH ethanolic solution mixed with anhydrous ethanol.

Determination of Radical Scavenging Rate of ABTS

The antioxidant capacity was determined according to Chinese National Standard GB/T 39100-2020 [16], employing both DPPH radical scavenging assays. Based on the method developed by Tranquilino-Rodríguez and Vít with modifications [18,19], we employed 7.25 mmol/L ABTS solution, mixed it with 2.5 mmol/L PDS solution to constant volume, then incubated it in darkness at room temperature for 14 h to generate the ABTS radical cation stock solution, which was subsequently diluted with phosphate-buffered saline to an absorbance of 0.70 ± 0.02 at 734 nm. The reaction mixture was prepared by combining 1 mL of sample with 4 mL of ABTS working solution, followed by 30 min of incubation in the dark. The absorbance (S₄) was measured at 734 nm. For the blank control, the sample was replaced with 1 mL of anhydrous ethanol, and the absorbance (S₅) was measured under identical conditions. The radical scavenging activity was calculated using the following equation.

$$P=({\displaystyle \frac{S_5-S_4}{S_5}})\times 100\mathrm{\%}$$

where P is radical scavenging capacity; S₄ is absorbance of the reaction mixture containing 4 mL ABTS working solution and 1 mL sample; and S₅ is absorbance of the control mixture containing 4 mL ABTS working solution and 1 mL anhydrous ethanol.

2.2.5. Determination of Polyphenols by HPLC

The chromatographic separation was performed using a reverse-phase C18 column (4.6 mm × 150 mm, 5 μm) with the following parameters: detection wavelength at 280 nm, column temperature maintained at 30 °C, injection volume of 10 μL, and flow rate of 1 mL/min. The mobile phase consisted of 1% acetic acid (A) and acetonitrile (B), with gradient elution programmed as 0–6 min (55–65% B), 6–25 min (65–80% B), and 25–30 min (85–55% B), which achieved baseline separation of 6-G, 8-G, 10-G, and 6-S as demonstrated in Figure 2.

A standard stock solution (0.8 μg/mL) was prepared in absolute ethanol for quantitative analysis. The solution was analyzed using a HPLC system (Shimadzu, LC-16, Kyoto, Japan) to establish a calibration curve. The regression equation was derived through linear regression analysis, with the results presented in

Table 2. Gingerol standard curve regression equation.

Ingredient	Regression Equation	Correlation Coefficient
6-G	y = 2.0367 × 10−4x − 0.3678	0.9992
8-G	y = 9.6331 × 10−5x − 0.0523	0.9999
6-S	y = 1.9851 × 10−4x − 0.6842	0.9998
10-G	y = 1.5185 × 10−4x − 0.6500	0.9998

.

Subsequently, 1 mL aliquot of the extract was diluted with absolute ethanol to prepare the test solution, which was then analyzed to determine the concentrations of four target compounds using standard curve regression analysis.

2.2.6. Morphology Test of Ginger Powder

The surface microstructural alterations of ginger samples before and after extraction were examined using SEM (Sigma, 500/VP, Oberkochen, Germany). Following the methodology described by Petrovici [20], the processed ginger residue was lyophilized, uniformly mounted on double-sided conductive tape, and subjected to gold sputter coating. SEM imaging was performed at an accelerating voltage of 5 kV with 2000× magnification.

3. Results and Discussion

3.1. Effect of Different Extraction Methods on the Extraction Rate of Gingerol

Gingerol was extracted using six distinct methods: leaching extraction, UAE, reflux extraction, MAE, UMAE, and HP-UMAE. Gingerol was quantified by ultraviolet spectrophotometer using vanillin as an external standard, and the high determination coefficient (R² = 0.9972, approaching 1.0) of regression equation indicated excellent linearity of the standard curve, confirming the reliability of this spectrophotometric method for quantifying gingerol concentration. To enable a reasonable comparison of extraction efficiency, the same sample mass, solvent composition, and solid–liquid ratio were employed across all methods. However, parameters such as extraction temperature and duration were adjusted according to the operational characteristics of each technique. Under the corresponding experimental conditions, the extraction yields were determined to be 1.58%, 1.63%, 1.79%, 2.03%, 2.20%, and 4.52%, respectively (Figure 3). The comparison of different extraction methods of gingerols is listed in

Table 3. The comparison of different extraction methods of gingerols.

Extraction Method	Optimal Conditions	Extraction Percentage	References
Leaching extraction	solvent: water, solid-to-liquid ratio: 1:25, extraction time: 10 min, extraction temperature: 100 °C	12.25 mg/g	[26]
UAE	solvent: 100% ethanol, solid-to-liquid ratio: 0.302 g ginger sample/20 mL solvent, extraction time: 10 min, extraction temperature: 60 °C, ultrasonic amplitude: 51.8%, ultrasonic period: 0.458 s−1	19.11 mg/g–24.49 mg/g	[10]
	solvent: malic acid–glucose (MA: GLC) in a ratio of 1:1, solid-to-liquid ratio: 1:20, extraction time: 2 min, extraction temperature: keep it below 30 °C, and use ice bath to control the temperature, ultrasonic amplitude: 20%	6-gingerol: 1.90 ± 0.05 mg/g 6-shogaol: 0.20 ± 0.00 mg/g	[27]
MAE	solvent: 87% ethanol aqueous solution, solid- to-liquid ratio: 0.431 g ginger sample/20 mL solvent, extraction time: 5 min, extraction temperature: 100 °C, microwave power: 800 W	15.84 mg/g	[8]
	solvent: 60% ethanol, solid- to-liquid ratio: 1:48.6, extraction time: 1 min	27.89 ± 1.99mg GAE/g	[28]

, and the extraction percentage reported in this study is 45.20 mg/g according to the extraction yield, which exceeds previously reported values in the literature. Notably, HP-UMAE demonstrated the highest extraction efficiency. Significant variations in gingerol extraction yield were observed across different extraction methods. This discrepancy may be attributed to the following factors: The leaching extraction and UAE operate at lower temperatures than HP-UMAE due to inherent technical limitations, resulting in reduced extraction efficiency. In addition, the leaching extraction was performed under short-time, low-temperature conditions to simulate rapid extraction, rather than full equilibrium. Thus, the results reflect initial-stage extraction efficiency rather than maximum yield. MAE may induce degradation or oxidation of thermolabile bioactive compounds during processing, thereby compromising extract quality. In contrast, HP-UMAE synergistically combines multiple energy fields to overcome these limitations, achieving superior extraction performance [21,22]. The reflux extraction, while operationally straightforward, exhibited limited extraction efficiency for gingerol. In contrast, MAE leverages high-frequency electromagnetic energy to rapidly generate thermal energy, enhancing solvent permeability and accelerating component solvation [23]. This mechanism significantly improves gingerol recovery. Synergistic extraction methods demonstrated superior performance, consistent with prior studies [11]. In the HP-UMAE process, elevated pressure disrupts plant tissues, cell walls, membranes, and organelles, thereby enhancing solvent penetration and facilitating the mass transfer of soluble components [15]. Under elevated pressure conditions, ultrasonic waves generate intensified shear forces that markedly enhance cell wall disruption through mechanical action and amplified cavitation phenomena. Concurrent microwave irradiation induces rapid molecular di-pole rotation, producing localized thermal effects that facilitate the liberation of intracellular constituents. The synergistic combination of ultrasonic cavitation and microwave-induced thermal effects under elevated pressure enhanced both the solubility of the target compound and the extraction efficiency [24,25]. This synergistic mechanism enabled HP-UMAE to achieve the highest extraction yield among all tested methods, establishing it as the most effective approach for gingerol isolation.

3.2. Effects of Different Extraction Methods on Antioxidant Activity

The antioxidant activity of extracts obtained through different extraction methods was evaluated using ABTS and DPPH radical scavenging assays (Figure 4). For ABTS radical scavenging, the following order was observed: HP-UMAE (43.23%) > MAE (42.97%) > UMAE (42.88%) > leaching method (40.22%) > reflux method (39.60%) > UAE (38.50%). DPPH radical scavenging activity followed a different trend: UMAE (24.20%) > reflux method (23.88%) > leaching method (23.65%) > HP-UMAE (23.42%) > UAE (22.64%) > MAE (21.76%). Notably, no significant correlation was found between the results obtained by the ABTS and DPPH methods. This discrepancy arises from their distinct chemical properties: DPPH is predominantly hydrophobic, while ABTS exhibits both hydrophilic and lipophilic characteristics. Since antioxidant activity reflects the efficiency of radical scavenging, the solvent affinity between antioxidants and radical systems critically influences measurement accuracy. Specifically, when the antioxidant’s solubility matches the radical’s solvent system, the assay better reflects true antioxidant capacity [29]. Gingerol’s molecular structure contains both hydrophilic moieties (phenolic hydroxyl and methoxy groups) and lipophilic components (C12-C14 alkyl side chains). The ethanol-water extraction system employed in this study demonstrates superior compatibility with the ABTS assay [30]. Furthermore, the DPPH assay exhibits inherent limitations in this system due to its exclusive solubility in organic solvents and susceptibility to interference from steric hindrance, sample impurities, and temperature variations [31], as confirmed by our experimental observations. Consequently, the ABTS assay demonstrates superior suitability for evaluating antioxidant activity in the present study. Accordingly, all subsequent experiments were conducted using the ABTS radical scavenging method as the primary analytical approach.

3.3. Effects of Different Extraction Methods on the Content of Gingerol

To elucidate the contribution of gingerols to antioxidant activity, HPLC analysis was performed on extracts obtained by different extraction methods (Figure 5). The 6-gingerol (6-G) content followed the following order: HP-UMAE > UMAE > MAE > leaching extraction > UAE > reflux extraction. Similarly, 8-gingerol (8-G) content exhibited the following trend: HP-UMAE > UMAE > leaching extraction > reflux extraction > MAE > UAE; For 6-shogaol (6-S) and 10-gingerol (10-G), the concentration decreased as HP-UMAE > UMAE > reflux extraction > leaching extraction > MAE > UAE.

Table 4. Content of 6-G, 8-G, 6-S, 10-G for different extraction methods.

Extraction Method	6-G (mg/L)	8-G (mg/L)	10-G (mg/L)	6-S (mg/L)	Total Capacity (mg/L)
Leaching extraction	12.93	0.32	1.68	3.56	18.49
UAE	12.25	0.16	1.50	3.22	17.13
Reflux extraction	11.95	0.29	1.75	3.66	17.65
MAE	13.21	0.24	1.58	3.47	18.50
UMAE	13.90	0.37	1.91	4.08	20.26
HP-UMAE	14.29	0.38	1.95	4.32	20.94

demonstrates that the extraction efficiency for the four phenolic compounds followed this order: HP-UMAE > UMAE > MAE > leaching extraction > reflux extraction > UAE. Comparative analysis revealed that 6-S exhibited the strongest antioxidant capacity among the four compounds, attributable to its α,β-unsaturated ketone moiety. Among the gingerols (6-G, 8-G, and 10-G), 10-G showed superior antioxidant activity, with its extended carbon chain length being a critical determinant of this property; while 6-G displayed measurable antioxidant effects, its potency was relatively lower compared to the other gingerols [32]. The antioxidant assay results may be influenced by additional bioactive constituents present in the extracts beyond the characterized gingerols. Importantly, HP-UMAE yielded the highest content and total quantity of all four gingerols, with these findings being consistent with both the extraction yields and ABTS radical scavenging rates.

3.4. Effects of Different Extraction Methods on Cell Structure of Ginger

To comparatively analyze the extraction efficiency differences between conventional reflux extraction and HP-UMAE, we examined the microstructural changes in ginger powder post-extraction. As illustrated in Figure 6, scanning electron microscopy revealed distinct morphological differences: reflux-extracted ginger maintained largely intact oval cell structures, whereas HP-UMAE-treated samples exhibited significant cellular deformation into rod-shaped fragments with evident wall collapse. This pronounced structural disruption in HP-UMAE-processed ginger suggests more severe cellular damage, likely attributable to ultrasonic cavitation-induced cell wall rupture [33,34]. Such mechanical disruption presumably enhances the liberation of bioactive compounds (particularly gingerols) into the solvent matrix, thereby explaining the observed improvements in both extraction yield and target compound concentration.

3.5. Optimization of Processing Parameters for HP-UMAE

3.5.1. Effect of Solid–Liquid Ratio on Extraction Rate and Gingerol Antioxidant Capacity In Vitro

The extraction system was maintained at 100 °C with an ultrasonic power of 1000 W, pressure of 2 MPa, and microwave power of 800 W while varying the solid-to-liquid ratio to evaluate its impact on gingerol yield and in vitro antioxidant activity. As depicted in Figure 7a, when the solid-to-liquid ratio was adjusted from 1:35 to 1:75, both gingerol extraction efficiency and ABTS radical scavenging activity initially increased, peaking at a solid-to-liquid ratio of 1:55 (w/v), followed by a gradual decline. This trend suggests that gingerol extraction reached saturation beyond this optimal ratio, as excessive solvent volume reduced the concentration gradient and mass transfer efficiency [35,36]. Consequently, a solid-to-liquid ratio of 1:55 (w/v) was identified as the optimal condition for maximizing gingerol recovery.

3.5.2. Effect of Temperature on Extraction Rate and Antioxidant Capacity of Gingerol In Vitro

The extraction system was maintained at a fixed solid-to-liquid ratio of 1:55 (w/v) with constant ultrasonic power of 1000 W, pressure of 2 MPa, and microwave power of 800 W while varying the temperature to evaluate its impact on gingerol yield and in vitro antioxidant activity. As presented in Figure 7b, both the gingerol yield and ABTS radical scavenging activity exhibited a similar biphasic response to increasing temperature, characterized by initial enhancement followed by gradual decline beyond the optimal point. This behavior can be attributed to the competing influences of thermal and cavitation effects: while elevated temperatures facilitate mass transfer through thermal activation, they simultaneously attenuate ultrasonic cavitation intensity [37]. The observed maximum extraction efficiency at 100 °C corresponds to the optimal balance between these opposing mechanisms.

3.5.3. Effect of Microwave Power on Extraction Rate and Antioxidant Capacity of Gingerol In Vitro

Keep the solid-to-liquid ratio at 1:55 (w/v), the temperature at 100 °C, the ultrasonic power at 1000 W and the pressure at 2 MPa constant, and change the microwave power to explore the influence of microwave power on the extraction rate of gingerol and its antioxidant capacity in vitro. As shown in Figure 7c, gingerol extraction efficiency exhibited a biphasic response to microwave power intensification: increasing significantly from 600 W to 800 W, followed by gradual decline at higher power levels. This trend paralleled the ABTS radical scavenging activity, which peaked at 800 W. The initial enhancement can be attributed to improved microwave energy absorption, which elevates intracellular temperature and disrupts cellular structures, thereby facilitating gingerol dissolution [38]. Conversely, excessive microwave power induces instantaneous thermal degradation of gingerol and compromises solvent permeability [39], ultimately reducing extraction efficiency. Consequently, 800 W was established as the optimal microwave power for gingerol extraction.

3.5.4. Effect of Ultrasonic Power on Extraction Rate and Antioxidant Capacity of Gingerol In Vitro

Under the conditions of keeping the material–liquid ratio of 1:55 (w/v), temperature of 100 °C, microwave power of 800 W, and pressure of 2 MPa, the influence of ultrasonic power on both gingerol extraction efficiency and in vitro antioxidant activity was investigated. As demonstrated in Figure 7d, when the ultrasonic power increased from 600 W to 1400 W, both the gingerol extraction yield and ABTS radical scavenging activity demonstrated a bell-shaped response, reaching their maxima at 1000 W before declining. The observed trend may be explained by the dual effects of ultrasonic power on cavitation phenomena. Moderate ultrasonic power enhances cavitation effects, effectively disrupting ginger cell walls [40], thereby promoting gingerol release and consequently improving both extraction efficiency and antioxidant activity. Excessive ultrasonic power induces overproduction of cavitation microbubbles, resulting in significant energy dissipation through inter-bubble interactions, which ultimately diminishes the effective energy available for gingerol extraction [41].

4. Conclusions and Perspectives

This study pioneers the application of integrated ultrasonication and microwave irradiation under elevated pressure for the extraction of gingerols, representing the first reported instance of this synergistic approach. Operating at 2 MPa pressure, 100 °C, 1:55 solid–liquid ratio, 800 W microwave, and 1000 W ultrasonic power, HP-UMAE achieved a gingerol yield at 4.52%, which 141% higher than reflux extraction and 105% superior to UMAE methods. This remarkable efficiency improvement stems from a novel pressure-synergy mechanism: pressure-amplified cavitation induces catastrophic cell wall disruption verified by SEM characterization. HP-UMAE sets a new benchmark for sustainable bioactive extraction.

Building on the breakthrough efficiency of HP-UMAE for gingerol extraction, future research should prioritize the following: (1) Process scale-up and techno-economic validation: conducting pilot-scale studies to assess industrialization feasibility and cost-effectiveness, (2) Extract stability and composition analysis: evaluating stability of extract during storage/processing and establishing comprehensive phytochemical profiles, (3) Green process enhancement: exploring sustainable solvents under pressurized systems while developing efficient solvent recovery strategies.