Effect of microwave combined with steam pretreatment on the flavor and quality of Tibetan chicken soup

Abstract

Conventional processing relies on time-consuming and intricate stewing methods, which hinder industrial-scale production of chicken soup. To address this limitation, this study investigated the effect of pretreatment cycle number on the quality of chicken meat and the flavor of chicken soup using a microwave combination with steam (MWS) process. Results showed that MWS pre-processing facilitated protein and lipid oxidation, improved the microstructure, and boosted the release and breakdown of nutrients in Tibetan chicken meat. At cycle 9, the concentrations of aldehydes (106.912 μg/kg), alcohols (10.293 μg/kg), and furans (0.717 μg/kg) in the chicken soup reached its maximum value, along with the content of umami amino acids(30.46 %), sweetnamino acids (40.09 %) and 5′-nucleotides (64.65 %) also increased significantly, while the content of bitter amino acids (29.25 %) decreased significantly. 1-octen-3-ol, 2,3-octanedione, and 2-pentylfuran were recognized as the key aromatic substances in chicken soup, while glutamic acid and 5′-inosine monophosphate (5′-IMP) were identified as the primary contributors to its taste. In conclusion, MWS pretreatment significantly enhanced Tibetan chicken meat quality and soup flavor.

Graphical abstract

Highlights

• •The industrial production technologies of chicken soup faces enormous challenges.
• •MWS pretreatment technology promotes the extraction and decomposition of nutrients.
• •1-octen-3-ol, 2,3-octanedione, and 2-pentylfuran are the key aromatic substances.
• •Glutamic acid and 5′-IMP are the primary contributors to taste profile.

1. Introduction

Tibetan chicken, an excellent chicken breed grown in high-altitude areas of China, is renowned for its palatable taste, savory meat flavor, aromatic profile, and high nutritional content. It serves as the sole resource for developing environmentally friendly poultry meat products on the Qinghai-Tibet Plateau, and holds significant culinary importance in the Tibetan region. Tibetan chicken soup, a traditional dish made of stewed Tibetan chicken meat, is esteemed for its rich taste and fragrance, often considered a wonderful tonic. Within traditional Chinese culinary customs, chicken soup holds pivotal significance as a therapeutic nourishment believed to fortify immunity, alleviate cold and flu symptoms, and soothe feelings of unease (Wang et al., 2024). However, the current processing methods of chicken soup mainly involve boiling and stewing, procedures characterized by being time-consuming, inefficient and not conducive to large-scale production (Yue et al., 2025). Consequently, the quest to enhance manufacturing efficiency while preserving and elevating the quality of chicken soup has become a formidable obstacle in advancing the chicken soup industry. Exploring industrial approaches aimed at improving the flavor quality of chicken soup is of considerable importance in addressing this challenge.

In recent years, there has been a growing interest in the application of physical field techniques to improve meat quality. Techniques such as microwave, ultrasonic, and ultra-high pressure processing have been widely applied in enhancing the quality of various meat products, including pork (Mei et al., 2025), fish, and chicken breast. These methods have been demonstrated to be effective in enhancing the solubility and water holding capacity of myofibrillar proteins, thereby preserving the tenderness and juiciness of meat products to the utmost extent. Despite this, reports of physical techniques for enhancing the flavor of soup have been relatively limited. Microwave technology, operating in the spectrum of electromagnetic radiation from 300 MHz to 300 GHz, is a rapid heating method characterized by high efficiency, less time-consuming and convenient (Guo, Sun, Cheng, & Han, 2017). This method not only quickly heats the chicken meat, but also effectively preserves nutrients within the muscle tissue. Nonetheless, microwave heating may result in moisture loss when compared to traditional heating approaches, thus impacting the flavor (Guzik, Szymkowiak, Kulawik, Zając, & Migdał, 2022). Wang et al. (2019) conducted a study comparing microwave heating to conventional water bath heating, discovering that microwave heating could limit the migration of sodium ions from grass carp meat to external free water, thus preserving salt content in the fish and intensifying its salty taste. However, the utilization of microwave heating alone may lead to uneven heating in fish and issues like excessive moisture loss.

To address the issues associated with microwave heating, researchers began combining microwave heating with traditional heating methods. Interestingly, when the two heating methods were used in combination, issues such as uneven heating, moisture loss, and nutrient loss were all resolved (Tsai et al., 2022). Steam heating is frequently coupled with microwave heating due to its advantages such as uniform heating and the ability to effectively maintain the moisture of meat (Mei et al., 2025). Cao et al. (2018) found that microwave-assisted steam heating effectively improves the quality and sensory characteristics of surimi products, resulting in a denser microstructure and significantly increased gel strength.

This study aims to assess the impact of microwave combination with steam (MWS) pre-processing on the flavor and nutrient composition of Tibetan chicken soup. Through varying number of cycle MWS pre-processing on Tibetan chicken meat, the volatile flavor profiles of Tibetan chicken soup were evaluated using electronic nose and gas chromatography–mass spectrometry (GC–MS) technologies. Meanwhile, electron microscopy, thiobarbituric acid reactive substances (TBARS) value, carbonyl group, and total sulfhydryl group analyses were conducted to elucidate the influence of MWS on the flavor of Tibetan chicken soup in terms of protein and fat structure and oxidation. Furthermore, the effect of MWS on the taste profile of Tibetan chicken soup was investigated through electronic tongue analysis, as well as the evaluation of free amino acids and flavor nucleotides. This study seeks to clarify the impact of MWS pretreatment on the flavor quality of Tibetan chicken soup, to provide theoretical and technical support for the processing of Tibetan chicken, as well as to propose theoretical foundations and novel perspectives for advancing the industrialization of Tibetan chicken soup.

2. Materials and methods

2.1. Sample preparation

Tibetan chickens were purchased from Aba Prefecture Bowen Animal Husbandry Technology Co., Ltd., Sichuan, China. Freshly slaughtered Tibetan chickens (head, claws, and internal organs removed) at 400-day-age were transported back to the laboratory under cold chain conditions and stored at −80 °C. prior to treat, the meat was thawed in a refrigerator at 4 °C for 12 h. Subsequently, the chickens were cut into pieces halves of the same weight evenly along the spine using a bone cutter.

Tibetan chicken meat pretreatment: half of the chicken (600 ± 5 g) was randomly divided into five groups. These groups underwent pretreatment using a combination of microwave (1000 W, 30 s) and steam (60 °C, 55 s) under treatment numbers of cycles (0, 3, 6, 9, and 12 cycles). Tibetan chicken meat treated with microwave (1000 W, 30 s) followed by steam (60 °C, 55 s) was one cycle.

The stewing method for Tibetan chicken soup: following the method of Zou et al. (Zou, Xu, Zou, & Yang, 2021) with slight modifications. Pretreated Tibetan chicken meat was cooled, cut into uniform pieces, weighed, and maintained a meat-water ratio of 1:2 (w/w). The meat pieces were placed into a stainless steel cooking pot when the water temperature reached 95 °C ∼ 99 °C. To sustain the temperature within this range throughout the simmering, the induction cooker was adjusted to simmer at 300 W for 20 min, followed by 120 W for 20 min, and then back to 300 W for another 20 min. This process was repeated three times, resulting in a total simmering time of 3 h. During the process, the water level was checked every 30 min, and the boiling water was added to keep the initial water level constant in the pot. After simmering, chicken soup was filtered using double-layered gauze to eliminate the solid substances and surface oils, transferred to 50 mL centrifuge tubes, and after refrigerating overnight at 4 °C, stored in a − 80 °C refrigerator for subsequent usage.

2.2. Extraction of myofibrillar protein (MP)

The chicken breast meat from the pre-processed Tibetan chicken was treated by cutting it into uniform 2 cm × 2 cm pieces, which were then minced using a meat grinder. A 30 g portion of the minced meat was combined with 120 mL of PBS buffer (0.01 mol/L, pH 7.0), homogenized for 3 min, and subsequently centrifuged at 4 °C (4,000 rpm, 5 min). The supernatant was discarded, and the precipitate was collected. The above centrifugation operation was repeated twice. The precipitate was mixed with NaCl solution (0.1 mol/L) at a ratio of 4:1, homogenized for 30 s, and centrifuged at 4 °C (4,000 rpm, 5 min), which was repeated twice. Subsequently, the obtained residue was mixed with NaCl (0.1 mol/L) solution at a 4:1 ratio and filtered through 4 layers of gauze. Adjusted the filtrate to pH 6.5 and then centrifuged at 4 °C (10,000 rpm, 5 min). The resulting pasty precipitate was MP, which was later utilized for determining the protein concentration using a BCA kit (Solabio Technology Co., Ltd., Beijing, China) (Wu et al., 2025).

2.3. Determination of oxidation indicators

2.3.1. Carbonyl content

The carbonyl content was determined following the method of Cheng et al. (2023) with minor modifications. Dilute the MP concentration to 5 mg/mL using a NaCl phosphate buffer (0.04 mol/L, pH 7.0). Transfer 0.5 mL of the diluted MP solution into a centrifuge tube, followed by the addition of 2 mL of 0.2 % DNPH reagent and 2 mol/L HCl. After allowing the reaction to proceed for 1 h at room temperature, 20 % trichloroacetic acid solution was added. The mixture was then centrifuged at 10,000 rpm for 10 min, and the precipitate was washed with 1:1 ethanol-ethyl acetate solution by shaking thoroughly to remove any residual DNPH. This washing process was repeated three times. Finally, the precipitate was dissolved in 6 mol/L guanidine hydrochloride solution and then incubated at 37 °C for 30 min. A centrifugation step was carried out at 10,000 rpm for 10 min to eliminate any insoluble ingredient. The absorbance of the supernatant was measured at 370 nm. The carbonyl content was calculated according to Eq. (1). Each sample was parallel three times and the average were taken.

$$\text{The carbonyl content}\left(\text{nmol}/\mathrm{mg}\right)=\frac{\mathrm{A}\times \mathrm{3000,000,000}}{\mathrm{\epsilon }\times 2500}$$ (1)

where A is the absorbance; ε is the molar absorbance coefficient.

2.3.2. Total sulfhydryl content

The experimental protocol was adapted from Huang et al. (2022a). Dilute the MP concentration to 1 mg/mL using a NaCl phosphate buffer (0.04 mol/L, pH 7.0). An appropriate volume of diluted MP solution was added separately to Tris-glycine solution (containing 6 mmol/L EDTA and 8 mol/L urea, pH 7.2) and centrifuged at 4 °C (10,000 rpm, 15 min). The supernatant was then mixed with 0.01 mol/mL DTNB (dissolved in Tris-glycine solution) and reacted in the dark for 30 min. The control group without the addition of any protein was also prepared following the same steps. The absorption was measured at 412 nm. The total sulfhydryl content was calculated using a molar absorption coefficient of 13,600 L/(mol·cm) according to Eq. (2).

$$\text{Total sulfhydryl content}\left(\text{μmol}/\mathrm{h}\right)=\frac{\mathrm{A}}{\mathrm{C}\times \mathrm{13,600}}\times {10}^6\times 10$$ (2)

where A is the absorbance; C is the concentration of the protein solution; 10 is the dilution factor.

2.3.3. TBARS value

For TBARS analysis, the methodology established by Gong et al. (2024) was implemented. A sample of 0.3 g Tibetan chicken meat was weighed, followed by the addition of an appropriate amount of TBA reagent and TCA-HCl solution, and the reaction system was carried out in a 100 °C water bath for 30 min. After the reaction system was cooled, 5 mL of chloroform was introduced for phase separation prior to centrifugation (10 min, 4000 rpm). The absorbance of the supernatant was analyzed at 532 nm. Each sample was measured three times in parallel, and the average value was recorded.

2.4. Fourier transform infrared spectroscopy(FT-IR)

The chemical structure of the MP lyophilized sample was analyzed using a FT-IR (Nicolet iS 50, Thermo Fisher Scientific, USA) instrument with the following parameters: spectral resolution of 4 cm⁻¹, number of scans of 32, and scan range of 600–4000 cm⁻¹. The amide I band (1600–1700 cm⁻¹) was analyzed spectroscopically using PeakFit 4.12 (Grafiti Holding Inc. Ottawa, Canada), and the relative content of secondary structures was expressed as the ratio of peak areas (Liu et al., 2024).

2.5. Scanning electron microscopy (SEM)

The chicken breast of the Tibetan chicken was sliced into small dimensions of 0.1 cm × 0.1 cm × 0.2 cm along the direction of muscle fibers. The samples were then immersed in 2.5 % glutaraldehyde for 12 h, followed by fixation with a 0.1 mol/L phosphate buffer solution. Gradient dehydration was carried out using a series of ethanol concentration gradients, culminating in freezing at −80 °C in a refrigerator. The samples were ultimately subjected to freeze-drying using a vacuum freeze-dryer. The surface of the freeze-dried sample was sprayed with gold, and then the fleshy structure was observed and photographed by SEM (SU8010 SEM, Hitachi Hi Tech Co., Ltd., Tokyo, Japan) (Wang et al., 2022a).

2.6. Determination of nutrient composition of Tibetan chicken soup

The weighing flasks were dried in an oven at 105 ± 2 °C until the weight was constant. Subsequently, 20 mL of chicken soup was placed in the flask and dried at 103 °C until a stable mass was reached, and the soluble solids content was expressed as g/100 mL. Total sugar content was determined by phenol‑sulfuric acid method, using anhydrous glucose as the standard, and the total sugar content was expressed as g/100 mL of soup. After separating the oil layer, the crude fat content was measured through Soxhlet extraction with petroleum ether as the solvent. The crude fat content was expressed as g/100 mL soup. The soluble protein content was calculated using the BCA kit and expressed as mg/mL.

2.7. Determination of volatile flavor compounds

2.7.1. E-nose

Chicken soup samples (10 mL) were drawn into a headspace bottle and heated in a water bath at 85 °C for 15 min before cooling to room temperature for analysis. Measurement parameters included an injection flow rate of 400 mL/min and sampling and washing times of 120 s each. Each sample was measured three times for principal component analysis (PCA) plotting, with the average value utilized for radar plotting.

2.7.2. Volatile flavor compounds

The chicken soup sample (5.00 g) was placed in a headspace vial and equilibrated in a water bath at 50 °C for 5 min. A pre-conditioned extraction needle (50/30 μm DVB/ CAR/PDMS) was inserted to adsorb volatile compounds for 40 min at 50 °C. The needle was then swiftly transferred to the injection port of GC (SHIMADZU GC–MS-QP2010Ultra, Shimadzu, Kyoto, Japan) and subjected to resolution at 230 °C for 3 min.

The GC conditions were as follows: the column utilized was a DB-WAX (30.00 m × 0.25 mm × 0.25 μm), with an inlet temperature of 230 °C. The temperature program initial heating at 40 °C for 3 min, followed by an increase to 70 °C at a rate of 3 °C/min, 180 °C at a rate of 5 °C/min, and eventually reaching 230 °C at a rate of 10 °C/min, where it was maintained for 5 min, leading to a total program duration of 45 min. The mass spectrometry (MS) conditions were as follows: the electron bombardment energy was set at 70 eV, the scan range from 30 to 550 m/z, the ion source temperature was 230 °C, the interface temperature was 210 °C, and the solvent delay was 0.5 min. Using n-ketone C4-C9 (China National Pharmaceutical Group Chemical Reagent Beijing Co., Ltd., Beijing, China) as an external standard, the concentration of the compound was calculated using the area normalization method.

2.8. Determination of non-volatile flavors

2.8.1. E-tongue

Following the method of Dong et al. (2024) with minor modifications. The sample of chicken soup (30 mL) was filtered using four layers of skimmed cotton gauze. The filtered solution was analyzed for taste characteristics using a SA402B E-tongue (INSENT, Tokyo, Japan).

2.8.2. Free amino acids

The free amino acid content of the samples was analyzed using high-performance liquid chromatography (UltiMate3000, Thermo Fisher, Massachusetts, USA). The appropriate amount of amino acid standards were precisely weighed and dissolved in either methanol or water to create a primary standard solution. The accurate volume of each primary standard should be measured out to produce a composite standard solution, which was then diluted by a 1:1 mixture of 10 % methanol formate solution-water to achieve the desired concentration, resulting in a working standard solution. The necessary quantity of isotope standard (Trp-d3) should be weighed and dissolved in a solution comprising 10 % methanol formate-water 1:1 to generate an internal standard master batch at a concentration of 1000 ng/mL.

The pretreatment of chicken soup samples: An appropriate volume of the sample should be transferred into a 2 mL centrifuge tube, followed by the precise addition of 400 μL of a 10 % methanol formate-water solution (1:1, v/v), and then vortex for 30 s. The mixture was centrifuged at 4 °C (12,000 rpm, 5 min). The supernatant should be carefully collected, and 10 % methanol formate-water (1:1, v/v) should be added to dilute it by 50-fold, followed by vortexing for 30 s. Subsequently, 100 μL of the mixed supernatant was blended with 100 μL of a 10 ng/mL Trp-d3 internal standard, and followed by another round of vortexing for 30 s before passing through a 0.22 μm filter membrane. Ultimately, the filtrates were injected into the assay bottles.

The chromatogram conditions were as follows: the use of ZORBAX Eclipse XDB-C18 column (4.6 × 150 mm, Agilent, USA) with a 5 μL injection volume and a column temperature set at 40 °C. The mobile phases of A-10 % methanol in water (containing 0.1 % formic acid) and B-50 % methanol in water (containing 0.1 % formic acid). The gradient elution program involved the following conditions: 0–6.5 min, 10 %–30 % B; 6.5–7 min, 30–100 % B; 7–18 min, 100 % B; 18–18.5 min, 100–10 % B; and 18.5–21 min, 10 % B. The flow rate was set at 0.3 mL/min from 0 to 8 min and then increased to 0.4 mL/min from 8.5 to 21 min.

The mass spectrometry parameters included the use of an electrospray ionization (ESI) source operating in positive ionization mode. The ion source temperature was set at 500 °C, with an ion source voltage of 5500 V, collision gas at 6 psi, air curtain gas at 30 psi, and both atomization and auxiliary gases at 50 psi. Scanning was conducted via multiple reaction monitoring (MRM).

2.8.3. 5′-nucleotides

Each of the three nucleotide standards (10.00 mg) were dissolved with 75 % methanol solution in a 10 mL volumetric flask to acquire the standard stock solution after mixing thoroughly. Subsequently, the standard stock solution (1.0 mg/mL) was withdrawn and diluted with methanol to generate standard working solutions at concentrations of 1 mg/mL, 0.5 mg/mL, 0.25 mg/mL, 0.125 mg/mL, and 0.0625 mg/mL.

The pretreatment of chicken soup samples: Weighed 2.0 g of the sample, followed by the addition of 10.0 mL of 75 % methanol for ultrasonic extraction lasting 10 min. The resulting mixture was centrifuged at 8000 rpm for 10 min and subsequently filtered through a 0.45 μm membrane for liquid-phase analysis. The mobile phases consisted of methanol (A) and a 0.01 mol/L KH₂PO₄ aqueous solution (pH 3.0) (B), both filtered through a 0.45 μm membrane before use. The high-performance liquid chromatograph (HPLC) employed a Thermo Syncronis-C18 column (4.6 μm × 250 mm) at a column temperature of 30 °C, with UV detection at a wavelength of 254 nm and a flow rate of 0.2 mL/min.

2.9. Data processing

Each experiment was performed in triplicate at least. One-way analysis of variance (ANOVA) was conducted to evaluate differences between means, with statistical significance set at P < 0.05. Results are presented as mean ± standard deviation. PCA and PLS-DA analysis using SIMCA 14.1 (Umetrics, Stockholm, Sweden). The data underwent clustering heat map analysis utilizing OmicStudio tools (https://www.omicstudio.cn/tool) and analyzed and plotted using Origin 2023 software (OriginLab Co., Northampton, MA, USA).

3. Results and discussion

3.1. Protein oxidation

Carbonyl groups and total sulfhydryl groups are important indicators for measuring protein oxidation, reflecting the degree of protein oxidation and structural alterations. Both elevated carbonyl levels and decreased total sulfhydryl content signify heightened levels of oxidation (Huang et al., 2022). The effect of MWS on protein oxidation of Tibetan chicken breast meat is depicted in Fig. 1a and b. Following pretreatment of chicken meat with MWS, there was a gradual elevation in carbonyl content with an increase in the number of cycles (Fig. 1a), accompanied by a gradual reduction in total sulfhydryl content (Fig. 1b). These outcomes suggested an augmentation in the protein oxidation of chicken meat subsequent to MWS pretreatment. The observed phenomenon may be attributed to the rapid internal temperature elevation of chicken meat during MWS treatment, facilitated by microwave heating, and the subsequent steam pretreatment further accelerated the creation of a high-temperature milieu, intensifying the breakdown of proteins and amino acids, consequently amplifying the degree of oxidation. Li et al. (2019) demonstrated that a controlled level of protein oxidation can liberate additional flavor precursor compounds (e.g., free amino acids, peptides, etc.). These precursors further engaged in the Maillard reaction and Strecker degradation processes during stewing to generate a wider array of flavor substances (e.g., aldehydes, ketones, sulfur-containing compounds, etc.), thus contributing to the flavor enhancement of soup.

Fig. 1.

The effects of microwave combined with steam pretreatment on the protein oxidation (a, b), lipid oxidation (c), secondary structure (d), and microstructure (e) of Tibetan chicken meat.

3.2. Lipid oxidation

During thermal processing, high temperature can lower the activation energy necessary for hydroperoxide breakdown, facilitating the production of free radicals and expediting the oxidative breakdown of lipids into flavor compounds (Yan et al., 2025; Wang et al., 2022b). As can be seen from Fig. 1c, the TBARS value of chicken meat increased notably after MWS treatment. This was due to MWS destroying the muscle fiber structure of chicken meat, causing fat to leak out of the meat and heat damage to membrane phospholipids, making the fat more susceptible to oxidation (Broncano, Petrón, Parra, & Timón, 2009). In addition, with the increase in the number of MWS cycles, the TBARS values of chicken meat exhibited a tendency of initial increase followed by decrease, peaking at 0.18 mg/kg at 9 cycles. For cycles ≤9, the elevation in TBARS value of chicken meat may be linked to the higher number of cycles and extended cooking duration, resulting in heightened lipid oxidation and consequent TBARS value escalation. Sánchez del Pulgar, Gázquez, and Ruiz-Carrascal (2012) found that elevated temperatures and prolonged cooking durations contribute to increased lipid oxidation occurrences. In cases where the number of cycles ≥9, a reduction in the TBARS value of chicken meat appeared. This decline may be due to the higher number of cycles, leading to the interaction of secondary lipid oxidation products with other compounds present in the meat, thereby resulting in a decrease in TBARS value.

3.3. Secondary structure

MP plays a crucial role in meat and meat products as they contribute to both the structural and textural attributes of meat, and also enhance its flavor profile by forming complexes with flavor compounds like ketones, alcohols, esters, and aldehydes (Zhang, Xiao, & Ahn, 2013). However, alterations in the structure of MP can affect their ability to bind with flavor compounds (Li, Song, Jiao, Geng, & Lin, 2025). Fig. 1d illustrated that the impact of MWS on the secondary structure of MP. The results in Fig. 1d revealed significant modifications in the secondary structure composition of MPs induced by MWS treatment. Notably, the α-helix and β-turn contents decreased, while the β-sheet and irregular coil contents exhibited an increasing trend, indicating a transition in protein structure from ordered to disordered states (Zhang et al., 2025). These variations in the secondary structure may enhance the binding affinity of MP with flavor substances, thereby enriching the overall flavor characteristics (Xingwei Wang et al., 2020). The findings of Xu, Wang, Zhao, Yin, and Li (2020) demonstrated that the reduction in myosin α-helix content and the rise in β-folding and irregular coil content following heat treatment result in the exposure of sulfhydryl groups and active amino acids, thereby providing additional binding sites and improving the protein's capacity to bind flavor compounds. Moreover, the escalation in the quantity of MWS cycles correlates with an augmentation in β-folding content, promoting the formation of protein gels.

3.4. Microstructure

The effect of MWS on the microstructure of Tibetan chicken meat is shown in Fig. 1e. Compared to the untreated samples, the chicken meat subjected to MWS cycles exhibited gaps and disruptions between muscle fibers, attributed to muscle fiber contraction, protein denaturation, and cell membrane damage. In addition, an increase in the number of MWS cycles led to a transition of the meat surface from smooth to a state in which attachments appeared on the surface, which were due to the heat denaturation of proteins (Yarmand & Homayouni, 2009). Within the MWS processing, the endomysium and myolemma of chicken meat underwent dissolution, accompanied by protein solubilization and denaturation due to heat, resulting in protein coverage on muscle fiber surfaces and the formation of observable attachments on the meat samples. Meanwhile, with the increase in the number of cycles and extended processing duration, the degree of protein denaturation escalated, culminating in protein gelation and a progressive augmentation in adhesions on the surface of the meat samples. These adhesions dissolve rapidly during the initial stages of stewing, leading to an increase in the soluble solids content of the chicken broth. As stewing time increases, the unfolding of protein structures caused by MSW processing promotes the release of soluble substances from deeper muscle groups, which also facilitates the transfer of macromolecular substances from the chicken meat to the broth, thereby enhancing the nutritional value and flavor of the chicken broth. This is consistent with the results of our nutritional component research.

3.5. Nutritional ingredient

Following MWS treatment of the Tibetan chicken meat, the chicken soup exhibited a tendency of increasing and then decreasing in nutrient levels, including soluble solids (Fig. 2a), proteins (Fig. 2b), sugars (Fig. 2c), and fats (Fig. 2d), peaking at nine cycles before declining. Microwave could induce varying extents of thermal denaturation in meat proteins, reduce the water holding capacity of meat and dissolve soluble components, thereby increasing the content of nutrients such as proteins and fats in the soup (Gawat, Boland, Chen, Singh, & Kaur, 2024). Conversely, as the pretreatment cycles >9, all the nutrients in the chicken soup showed a decreasing trend. This phenomenon could be attributed to prolonged processing time and an immoderate number of cycles leading to excessive protein denaturation and mass nutrient loss during processing, ultimately resulting in diminished nutrient content in the Tibetan chicken soup.

Fig. 2.

Effect of microwave combined with steam pretreatment on the nutrient content of Tibetan chicken soup (a: soluble solids content; b: protein content; c: total sugar content; d: crude fat content).

3.6. Volatile flavor compounds

3.6.1. E-nose

To investigate the differences in the aroma of soup derived from Tibetan chicken meat pretreated with varying numbers of cycles of MWS, the overall aroma profile of the chicken soup was assessed using an electronic nose. The electronic nose radargram is shown in Fig. 3a. The response values from sensors W1W, W2W, W5S, W2S, and W5C were higher compared to the other sensors, indicating the possible presence of high levels of sulfides, aromatic compounds, alcohols, aldehydes, and short-chain alkane compounds in the chicken soup. Specifically, the W1W sensor exhibited the highest response value for the chicken soup at 9 cycles, surpassing the responses at other cycle numbers. The PCA plot (Fig. 3b) illustrated significant differences in the flavors of chicken soup treated with MWS cycles compared to untreated samples. The contribution of PC1 and PC2 in the PCA model was 76.4 % and 11.4 %, respectively, with a total contribution of 87.8 %, indicating that they could respond to most of the information of the samples. The plot shows that samples treated 0 times and 3 times are closer together, indicating similarity in odor, which may be attributed to the lower oxidation degree and limited release of flavor compounds at lower MWS cycle numbers. In contrast, the distance between samples treated 9 times and others was greater, suggesting a distinct flavor profile. This difference could be attributed to higher protein and lipid oxidation levels after 9 MWS cycles, leading to the release of a greater variety of flavor compounds.

Fig. 3.

Effect of microwave combined with steam pretreatment on the overall flavor of Tibetan chicken soup. (a: e-nose radar plot; b: e-nose PCA plot; c: GC–MS OPLS-DA plot, d: VIP plots, e: clustered heat map).

3.6.2. Gc–MS

The volatile flavor compounds present in MWS treated Tibetan chicken soup were analyzed qualitatively and quantitatively using GC–MS (Table 1). A total of 28 volatile compounds were identified, comprising 13 aldehydes, 8 alcohols, 2 ketones, 2 acids, 1 alkane, 1 ester, and 1 furan compound. Among them, aldehydes constituted the highest proportion of the total volatile flavor constituents in chicken soup, accounting for approximately 46.43 % of the total. Aldehydes are crucial flavor components in chicken soup, primarily originating from lipid oxidation. Apart from imparting a distinctive fat aroma to the meat, aldehydes play a significant role in shaping the overall flavor profile of chicken soup due to their low odor detection threshold (Barola, SimoneGiusepponi, FabiolaSaluti, GabrieleBrambilla, & Roberta., 2020).

Table 1.

Effects of MWS on volatile flavor compounds in Tibetan chicken soup.

Class	Compound name	CAS	Molecular formula	Content(μg/kg)					Flavor description
				0	3	6	9	12
Aldehydes	Hexanal	66–25-1	C6H12O	18.11 ±  1.50c	19.61 ±  1.28c	28.36 ±  1.96b	36.13 ±  4.46a	21.88 ±  1.59c	Grass scent or green plant scent
	Heptanal	111–71-7	C7H14O	4.01 ±  0.19c	4.12 ±  0.09c	4.52 ±  0.10b	5.31 ±  0.18a	4.66 ±  0.07b	Fatty odor, similar to the aroma of fruit
	2-Heptenal	18,829–55-5	C7H12O	2.15 ±  0.10d	2.39 ±  0.12c	2.66 ±  0.12b	2.87 ±  0.06a	2.50 ±  0.09bc
	Octanal	124–13-0	C8H16O	7.09 ±  0.29c	7.40 ±  0.41c	9.91 ±  0.70a	10.48 ±  0.72a	8.76 ±  0.76b	Strong fruity aroma, sweet orange or citrus scent
	(E)-2-Octenal	2548-87-0	C8H14O	3.67 ±  0.15d	4.19 ±  0.19c	4.45 ±  0.10bc	5.19 ±  0.23a	4.65 ±  0.08b	Fat and meat aroma
	Nonanal	124–19-6	C9H18O	10.76 ±  0.96c	12.71 ±  0.84bc	14.21 ±  1.52ab	15.72 ±  0.61a	13.73 ±  1.28ab
	(2E)-2-Nonenal	18,829–56-6	C9H16O	1.89 ±  0.07d	2.17 ±  0.16c	2.35 ±  0.11bc	2.60 ±  0.17a	2.48 ±  0.12ab	Floral and woody notes, with subtle hints of grass and sweetness.
	(4E)-4-Nonenal	2277-16-9	C9H16O	–	–	0.35 ±  0.13a	0.58 ±  0.17a	0.34 ±  0.08a
	Decanal	112–31-2	C10H20O	0.36 ±  0.02c	0.41 ±  0.03b	0.48 ±  0.01a	0.44 ±  0.03ab	0.40 ±  0.03bc
	(E)-2-Decenal	3913-81-3	C10H18O	6.38 ±  0.17d	6.98 ±  0.14c	6.87 ±  0.08c	10.24 ±  0.17a	7.76 ±  0.19b	Fruity aroma
	(2E,4E)-2,4-Decadienal	25,152–84-5	C10H16O	2.14 ±  0.08d	2.14 ±  0.12d	2.47 ±  0.09b	2.82 ±  0.08a	2.32 ±  0.04c
	Trans-2-Undecenal	53,448–07-0	C11H20O	0.22 ±  0.02d	0.26 ±  0.01c	0.29 ±  0.01b	0.35 ±  0.01a	0.27 ±  0.02c
	Undecenal	1337-83-3	C11H20O	3.84 ±  0.25c	4.09 ±  0.07c	5.74 ±  0.14a	4.61 ±  0.05b	5.50 ±  0.13a	Clean green aldehydic rose
Alcohols	Pentanol	13,403–73-1	C5H12O	0.45 ± 0 .0.12ab	0.46 ±  0.08ab	0.35 ±  0.07b	0.56 ±  0.04a	0.51 ±  0.02a
	1-Hexanol	111–27-3	C6H14O	0.25 ±  0.02d	0.27 ±  0.01cd	0.29 ±  0.03c	0.40 ±  0.01a	0.33 ±  0.01b	Green fragrance, wine fragrance, sweet fragrance
	1-Heptanol	111–70-6	C7H16O	1.34 ±  0.10d	1.47 ±  0.03c	1.58 ±  0.03bc	1.93 ±  0.10a	1.64 ±  0.03b	A sweet and gentle fragrance of wax flowers.
	1-Octen-3-ol	3391-86-4	C8H16O	2.59 ±  0.10c	2.60 ±  0.04c	2.95 ±  0.07b	3.20 ±  0.02a	3.06 ±  0.11ab	Aromas of mushroom, lavender, rose, and hay.
	2-Octen-1-ol	18,409–17-1	C8H16O	0.09 ±  0.01c	0.10 ±  0.02c	0.25 ±  0.04b	0.38 ±  0.04a	0.27 ±  0.03b	Sweet fruity
	1-Octanol	111–87-5	C8H18O	2.16 ±  0.20c	2.12 ±  0.19c	2.67 ±  0.07b	3.17 ±  0.17a	2.78 ±  0.03b	Sweet rose fragrance
	1-Nonanol	143–08-8	C9H20O	0.18 ±  0.05d	0.29 ±  0.03c	0.42 ±  0.01b	0.55 ±  0.04a	0.46 ±  0.02b	Rose, fruity, and green citrus aromas
	1-nonen-3-ol	21,964–44-3	C9H18O	0.10 ±  0.03a	0.11 ±  0.01b	0.12 ±  0.04b	0.14 ±  0.02b	0.10 ±  0.01b	Green earth and mushroom smell
Ketone	2,3-Octandione	585–25-1	C8H14O2	1.27 ±  0.10d	1.50 ±  0.10c	1.66 ±  0.66bc	2.88 ±  0.20a	1.88 ±  0.11b	Sweet cream aroma and slight butter aroma
	Geranylacetone	3796-70-1	C13H22O	0.05 ±  0.00c	0.07 ±  0.01b	0.07 ±  0.01ab	0.10 ±  0.02a	0.09 ±  0.02ab	Floral fragrance with fruity and rose notes
Acids	Palmitic acid	57–10-3	C16H32O2	0.48 ±  0.02e	0.58 ±  0.05d	0.7 ±  0.05c	1.06 ±  0.07a	0.88 ±  0.03b
	Stearic acid	57–11-4	C18H36O2	0.56 ±  0.11d	0.67 ±  0.02cd	0.79 ±  0.10c	1.45 ±  0.11a	1.03 ±  0.06b	Slightly buttery or waxy smell
Alkanes	Decane	124–18-5	C10H22	2.95 ±  0.11d	3.20 ±  0.07c	3.46 ±  0.10b	3.74 ±  0.11a	3.44 ±  0.15b
Esters	Vinyl hexanoate	3050-69-9	C8H14O2	0.08 ±  0.03cd	0.05 ±  0.01d	0.22 ±  0.04b	0.40 ±  0.07a	0.15 ±  0.05bc	Green apple, jackfruit, cellar mud aroma
Furans	2-Amylfuran	3777-69-3	C9H14O	0.39 ±  0.04d	0.43 ±  0.04d	0.53 ±  0.05c	0.72 ±  0.04a	0.63 ±  0.03b	Sweet paste cocoa and coffee aroma.

Note: “—”indicates that the substance was not detected. Different letters in the same row indicate significant differences in data.

In order to demonstrate more clearly and intuitively the effects of different numbers of MWS treatment cycles on the content of volatile flavor compounds in chicken soup, orthogonal partial least squares discriminant analysis (OPLS-DA) was conducted on the 28 identified volatile flavor compounds (Huang et al., 2022). OPLS-DA is a multivariate statistical detection technique whose principle is employed to emphasize the distinctions of these compounds across different samples by leveraging the signal intensities of the flavor substances. As shown in Fig. 3c, the cumulative variance contribution ratio of PC1 and PC2 was 87.15 %, indicating that principal component 1 and principal component 2 effectively respond to the information from the original data. Furthermore, Fig. 3c illustrated that samples with 0 cycles and those with 3 cycles exhibited similar odors, aligning with the findings of the electronic nose analysis. Contrasted with other cycle counts, chicken soup prepared with 9 cycles is situated in the third quadrant alone, showcasing more pronounced differences in aroma compared to the other cycle variations. The Variable Projection Importance (VIP) scores obtained from the OPLS-DA analysis (Fig. 3d) revealed that 1-octen-3-ol, 1-pentanol, 2-pentylfuran, n-hexanol, vinyl hexanoate, and 2,3-octanedione were identified as the primary volatile flavor compounds in the chicken soups impacted by the number of MWS treatment cycles (VIP > 1).

To further intuitively respond to the impact of different pretreatment cycles of MWS on the volatile flavor compounds in chicken soup, a clustered heat map was generated to visualize the 28 identified volatile compounds, as depicted in Fig. 3e. A noteworthy increase in the content of volatile compounds was observed in the chicken soup treated with MWS cycles compared to the untreated group (P < 0.05). The majority of volatile compounds exhibited a pattern of initially rising and then dropping in content with the number of cycles, with the total volatile compounds content peaking at 9 cycles. Among them, the notable increase in aldehyde content can be attributed to the promotion of lipid oxidation in chicken meat by the MWS cycling treatment, which enhanced the flavor profile. Simultaneously, the MWS facilitated the adsorption of aldehydes by MP, further augmenting the aldehyde content in the Tibetan chicken soup. However, when the number of cycles reached 12, there was a decrease in aldehyde content in the soup. This decline may be due to excessive lipid oxidation at this point, leading to the further oxidation of aldehydes into other compounds, resulting in the reduction of aldehyde content (Su et al., 2025).

Besides, the MWS treatment also resulted in a growth in the levels of alcohols, alkanes, and furans in chicken soup. Among them, the production of alkanes was mainly linked to the breakdown of fatty acid alkoxy radicals (Hu, Cui, Zhou, Wang, & Xu, 2025), although alkanes contributed minimally to the overall flavor of the chicken soup due to their higher taste threshold. Within the alcohol group, 1-octen-3-ol played a significant role in enhancing the taste of the soup, albeit less so to the odor than the aldehydes (T. X. Liu & Zhao, 2010). On the other hand, 1-pentanol and hexanol imparted sweet and floral fragrances to the chicken soup, bringing a distinct aroma to the soup (Yue et al., 2025). Furans, which are also produced through lipid oxidation, are known for their sweet properties and their ability to enhance the flavor of meat products. Specifically, 2-pentylfuran imparts a robust meaty flavor along with a plant-like aroma that is indispensable to the flavor profile of chicken soup (Guan et al., 2025). Meanwhile, 2,3-octanedione contributes a fruity, floral, herbaceous, and creamy scent, which contributes to the overall flavor of the chicken soup (Wang et al., 2024). Moreover, traces of esters, ketones, and acids were detected in the compositional analysis of the chicken soup. When esters and ketones coexist, they work together to harmonize and balance the overall flavor of the chicken soup.

3.7. Non-volatile flavors compounds

3.7.1. E-tongue

As shown in Fig. 4a, the pretreatment of MWS dramatically improved the sweetness and freshness of the chicken soup samples compared to samples without MWS treatment. This improvement could be attributed to the ability of microwave heating to expedite protein hydrolysis and the thermal breakdown of nucleotides. The sweetness and freshness of the soup samples peaked at 9 cycles of MWS. To further investigate the taste variations of chicken soup with MWS, PCA model analysis was conducted on the electronic tongue data (Fig. 4b). Among them, PC1 and PC2 accounted for 50.2 % and 35.1 %, respectively, with a cumulative contribution of 85.3 %. This suggests that PC1 and PC2 effectively captured the overall taste profile information of the chicken soup samples. From the Fig., it can be seen that the taste difference from the other samples was more pronounced when the number of cycles was 9 times.

Fig. 4.

Effect of microwave combined with steam pretreatment on flavor substances of Tibetan chicken soup. (a: e-tongue radar plot; b: e-tongue PCA plot; c: free amino acid content; d: free nucleotide content).

3.7.2. Free amino acid

Free amino acids are crucial constituents that contribute to the flavor of food, impacting taste directly and playing a role in aroma formation as precursors of aromatic compounds (Wang, Zhao, et al., 2024). As shown in Fig. 4c, the total free amino acid content in chicken soup exhibited an upward trend after MWS pretreatment. Specifically, the levels of sweet and umami amino acids remarkably increased (P < 0.05), reaching peak values of 34.01 mg/100 mL and 44.06 mg/100 mL, respectively, at 9 cycles (Table 2). This represented a growth of 40.07 % and 30.43 %, respectively, compared to 0 cycles. Free amino acids are the final products resulting from protein hydrolysis, and the heat treatment from MWS accelerated the breakdown of proteins, thereby augmenting the free amino acid levels in the soup. Protein and peptide hydrolysis, along with degradation due to lipid oxidation, resulted in the production of additional sweet and fresh amino acids, as reported by Fu et al. (2024). At 12 cycles, there was a subsequent decline in the sweet and fresh amino acid content in the soup, which could be attributed to the reduction in protein content within the meat samples, consequently leading to a decline in the sweet and fresh amino acid content present in the soup obtained through stewing. However, the bitter amino acid content of chicken soup expressed a notable reduction by 29.25 % (P < 0.05) after MWS treatment. This phenomenon could be explained by the involvement of bitter amino acids in the Maillard reaction following MWS treatment, resulting in a decline in the bitter amino acid content present in the chicken soup (He et al., 2023).

Table 2.

Effects of MWS on the content of free amino acids in Tibetan chicken soup.

		Threshold(mg/100 mL)	Content(mg/100 mL)
			0	3	6	9	12
Sweet amino acids	Gly	130	5.45 ± 0.12d	5.52 ± 0.12d	6.13 ± 0.07c	8.25 ± 0.10a	7.22 ± 0.11b
	Ala	60	6.94 ± 0.11e	7.65 ± 0.15d	8.07 ± 0.06c	9.17 ± 0.04b	9.77 ± 0.18a
	Ser	150	6.53 ± 0.03e	7.07 ± 0.16d	8.03 ± 0.11c	9.39 ± 0.03a	8.51 ± 0.06b
	Thr	260	5.36 ± 0.05e	5.67 ± 0.14d	5.87 ± 0.07c	7.21 ± 0.06a	6.82 ± 0.13b
Bitter amino acids	Val	40	6.39 ± 0.11a	6.13 ± 0.15a	5.61 ± 0.18b	4.23 ± 0.07d	5.01 ± 0.17c
	Ile	90	4.86 ± 0.14a	4.39 ± 0.17b	4.13 ± 0.12b	3.29 ± 0.14d	3.83 ± 0.18c
	Leu	190	8.24 ± 0.16a	7.93 ± 0.13b	7.57 ± 0.16c	6.45 ± 0.14d	6.14 ± 0.12e
	Lys	50	11.42 ± 0.26a	8.55 ± 0.25b	8.43 ± 0.21b	6.83 ± 0.04d	7.71 ± 0.18c
	Met	30	3.24 ± 0.09a	3.17 ± 0.06ab	3.02 ± 0.12b	2.45 ± 0.08c	2.40 ± 0.16c
	His	20	5.18 ± 0.13a	4.83 ± 0.13b	4.29 ± 0.15c	3.86 ± 0.06d	3.96 ± 0.13d
	Phe	90	4.54 ± 0.06a	4.42 ± 0.09a	3.92 ± 0.09b	3.29 ± 0.11d	3.50 ± 0.08c
	Arg	50	6.74 ± 0.12a	6.24 ± 0.13b	6.03 ± 0.16b	4.83 ± 0.05d	5.27 ± 0.12c
	Tyr	90	4.99 ± 0.09a	4.32 ± 0.12b	4.27 ± 0.15bc	4.09 ± 0.13c	3.50 ± 0.06d
Fresh amino acids	Asp	100	3.73 ± 0.16e	4.48 ± 0.06d	4.87 ± 0.21c	6.40 ± 0.05a	6.14 ± 0.10b
	Glu	30	30.05 ± 0.29d	31.24 ± 0.90cd	32.73 ± 1.15bc	37.67 ± 0.88a	33.53 ± 1.19b
Odorless amino acids	Cys	–	ND	0.02 ± 0.00d	0.09 ± 0.00c	0.23 ± 0.02a	0.18 ± 0.02b
Other amino acids	GABA	–	0.01 ± 0.00e	0.02 ± 0.00d	0.03 ± 0.00c	0.08 ± 0.00a	0.04 ± 0.00b
	Gln	–	7.62 ± 0.20d	9.43 ± 0.16c	9.74 ± 0.13c	12.10 ± 0.02a	11.26 ± 0.26b

Note: “ND” indicates that the substance was not detected. Different letters in the same row indicate significant differences in data.

3.7.3. 5′-nucleotides

Nucleotides in chicken soup were derived from the breakdown of proteins and nucleic acids that occurred during the stewing of chicken. These nucleotides can interact with amino acids and other volatile flavor compounds to improve the overall taste of the chicken soup. In particular, 5′-nucleotides are crucial for enhancing the umami taste (Davila, Muniz, & Du, 2022). As can be seen in Fig. 4d, the nucleotide content in chicken soup was substantially increased (P < 0.05) by the MWS cycle treatment. Among them, the content of 5’-IMP represented the largest proportion of the three nucleotides. The variation in its content exhibited a tendency of initially increasing and then decreasing with an increase in the number of MWS cycles. The content peaked at 59.68 mg/100 g when the cycles reached 9, reflecting a 64.59 % increase in 5’-IMP content. This trend might be related to the efficient heating of microwaves. The accelerated thermal degradation of nucleotides caused by microwave likely contributed to the higher nucleotide content observed in chicken soup following the pretreatment (Yin et al., 2022). Therefore, MWS presented a beneficial effect on the umami taste of chicken soup. It is worth noting that when the number of cycles reached 12, the nucleotide content decreased once more. This decline could be attributed to the extended duration of the MWS cycles and heating time, resulting in the loss of water-soluble nucleotides along with water from the chicken meat during the pretreatment process. As a consequence, the nucleotide content in the final soup samples was reduced.

3.7.4. Cluster analysis

Free amino acids and nucleotides can not only be used as precursors of volatile flavor compounds, but also as flavor presenting substances to influence the taste of the food, playing a crucial role in shaping the final flavor profile of chicken soup. In order to more intuitively analyze the effect of the number of MWS cycles on the nonvolatile flavor compounds in chicken soup, the identified free amino acids and nucleotides were subjected to PLS-DA analysis, and the results were shown in Fig. 5a. It can be seen that the cumulative contribution of PC1 and PC2 was 94.57 %, indicating that the five sample groups were well-distinguished in the PLS-DA model, suggesting that varying the number of MWS pretreatment cycles can markedly alter the nonvolatile substances in chicken soup.

Fig. 5.

Effect of microwave combined with steam pretreatment on key taste substances of Tibetan chicken soup (a: PLS-DA plots; b: VIP plots; c: clustered thermogram analysis).

To further assess the variances in nonvolatile substances in chicken soup treated with varying cycle number of MWS, a clustered heat map analysis was conducted. Specifically, the coloration of the heat map reflects the relative content of substances, enabling a visual examination of the distinctions between the data through different color gradients. As shown in Fig. 5, the levels of sweet amino acids such as glycine, alanine, serine, and threonine, and umami amino acids such as glutamic acid and aspartic acid exhibited a remarkable growth, reaching their peak at 9 cycles. Conversely, the content of bitter amino acids like lysine, arginine, leucine, and valine saw a marked decrease. These findings revealed that the MWS pretreatment method substantially enhanced the umami taste while diminishing the bitter taste, thereby optimizing the distinctive flavor profile of Tibetan chicken soup. What's more, the umami of chicken soup was not solely influenced by sweet and umami amino acids; rather, the combined effect of nucleotides and various flavor compounds also played a significant role in enhancing its umami. Notably, the data illustrated a notable increase in the levels of 5′-adenosine monophosphate (5’-AMP) and 5’-IMP with an escalation in cycle times. Especially, the IMP has been discovered as the primary material foundation for the umami taste attributes of chicken soup, with higher levels of IMP correlating to superior umami flavor of the chicken soup (Lei et al., 2025). VIP scores also demonstrated that glutamic acid and 5-IMP were the most noteworthy nonvolatile flavor compounds impacted by the MWS pretreatment.

3.8. Correlation analysis

Pearson correlation analysis was employed to investigate the possible relationship between the crucial volatile and non-volatile flavor components in Tibetan chicken soup, and the results are shown in Fig. 6a and b. Among them, 1-octen-3-ol exhibited a positive correlation with several amino acids like glutamate and cysteine, as well as nucleotides such as 5’-IMP. Conversely, it displayed a significant negative correlation solely with lysine and leucine. 1-Octen-3-ol is typically generated through the oxidation of linoleic acid and arachidonic acid, which are considered to be compounds with the aroma of mushrooms or green grasses. It can enhance the overall flavor of food products through chemical or sensory synergistic interactions with umami amino acids (Wang, Li, et al., 2022). Consequently, it is positively associated with amino acids like glutamic acid. In Fig. 4b, it was evident that 5’-IMP and 5’-AMP exhibited substantial positive correlations with volatile flavor components such as trans-2-decenal, n-hexanol, and vinyl hexanoate. Wang et al. (2024) also found that 5’-IMP and 5’-AMP were the most crucial 5-nucleotides in duck soup. The synthesis of 5’-AMP mainly occurs through the adenosine triphosphate (ATP) enzymatic hydrolysis pathway. Within this pathway, ATP is broken down enzymatically to produce 5’-AMP, while 5’-IMP is predominantly formed through the deamination of 5’-AMP catalyzed by 5-adenylate deaminase. Furthermore, 5’-IMP and 5’-AMP displayed synergistic effects and dramatically boosted the umami taste of chicken soup. Additionally, it was observed that 2,3-octanedione and 2-pentylfuran were also strongly positively correlated with most amino acids. 2,3-octanedione is known for its fruity and cheesy flavor. It is primarily stemmed from the enzymatic oxidation of linoleic acid, which has been reported to possess a close association with amino acid breakdown or the Maillard reaction in recent years (Wan et al., 2024). On the other hand, 2-pentylfuran is a low-threshold non-carboxylic compound with a pronounced sweetness and nutty aroma, playing an essential role in the aroma profile of chicken soup (Liao et al., 2024).

Fig. 6.

Correlation analysis between key flavor substances and key taste substances in microwave combined with steam pretreatment Tibetan chicken soup (a: correlation network diagram; b: correlation clustering heat map).

4. Conclusions

Tibetan chicken was primarily processed through traditional stewing methods, which were time-consuming and complex. Therefore, there was an urgent need to develop new technologies for the industrial production of chicken soup. This study investigated the impact of different cycles of microwave-steam combined treatment on the flavor of Tibetan chicken soup.The results indicated that microwave-steam pre-treatment significantly improved the quality of Tibetan chicken meat and enhanced the soup's flavor, with the optimal pre-treatment cycle identified as nine. This method not only enhanced the microstructure of the meat but also facilitated the breakdown and leaching of macromolecules such as proteins, carbohydrates, and fats, promoting their oxidation and contributing to the formation of flavor compounds in the soup. E-nose and GC–MS analyses revealed that microwave-steam pre-treatment notably increased both the variety and concentration of volatile compounds in Tibetan chicken soup. At 9 cycles, the levels of aldehydes and furans were maximized, enriching the soup's flavor profile. Additionally, this pre-treatment improved the taste of the soup, with significant increases in umami and sweet amino acids, and a decrease in bitter amino acids. Key aroma-active components identified included 1-octen-3-ol, 2,3-octanedione, and 2-pentylfuran, while glutamic acid and 5’-IMP were recognized as crucial non-volatile flavor compounds.Future research could explore various industrial processing techniques on Tibetan chicken and soup, combining thermal and non-thermal pre-treatments to innovate flavor enhancement technologies for industrial chicken soup production.

CRediT authorship contribution statement

Kai Dong: Writing – review & editing, Writing – original draft, Investigation, Formal analysis. Xinyuan Huang: Writing – review & editing, Writing – original draft, Investigation, Formal analysis. Yingmei Wu: Methodology, Investigation, Formal analysis. Zhendong Liu: Investigation, Formal analysis. Yufang Guan: Investigation, Formal analysis. Hongbo Song: Software, Data curation. Fengping An: Software, Data curation. Xin Li: Supervision, Funding acquisition. Erhao Zhang: Validation, Supervision. Qun Huang: Funding acquisition, Conceptualization.

Ethical guidelines

Ethics approval was not required for this research.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

No data was used for the research described in the article.