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. 2025 Aug 6;30:102891. doi: 10.1016/j.fochx.2025.102891

Effects of different roasting temperatures on the flavor characteristics of jujube wine: Analysis based on HPLC, HS-GC-IMS, and HS-SPME-GC–MS

Binbin Li a,1, Qian Mu a,b,1, Huijing Guo a, Wenting Jia a, Mengzhen Zhang b, Ya Liu b, Xinwen Jin a,⁎
PMCID: PMC12362083  PMID: 40837087

Abstract

The effects of jujube pretreatment at different roasting temperatures (80–160 °C) on the dynamic changes in free amino acids and volatile organic compounds in jujube wine were evaluated using HPLC, HS-GC-IMS, HS-SPME-GC–MS, and sensory analysis. The results revealed that roasting at 80–100 °C enhanced the accumulation of sweet amino acids in jujube wine, whereas roasting at 140–160 °C increased the bitter amino acid content. As the roasting temperature increased, the contents of esters, alcohols, acids, aldehydes, and ketones in jujube wine rose initially before declining thereafter. Meanwhile, the furan compound content exhibited a continuous increase. Through multivariate statistical analyses, including orthogonal partial least squares-discriminant analysis (OPLS-DA), relative odor activity value (ROAV) calculations, and variable importance in projection (VIP), six key characteristic flavor compounds were identified. These included isoamyl acetate, ethyl hexanoate, and ethyl octanoate. The novel insights derived from this study could guide the improvement of jujube wine flavor.

Keywords: Jujube wine, Roasting, Volatile organic compounds, GC–MS, GC-IMS

Highlights

  • •

    100 volatile compounds were identified by HS-SPME-GC–MS, and 32 by HS-GC-IMS.

  • •

    Significant differences in volatile compounds of jujube wines pretreated at different baking temperatures.

  • •

    The 100 °C group of jujube wines had a higher concentration of esters and ketones.

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    Six key volatile compounds were screened using HS-SPME-GC–MS and HS-GC-IMS.

  • •

    HS-SPME-GC–MS and HS-GC-IMS effectively identified jujube wines pretreated with different roasting temperatures.

1. Introduction

Jujube (Zizyphus jujuba Mill.), a species of jujube belonging to the Rhamnaceae family, has been cultivated for over 4000 years (Li et al., 2011). As a traditional medicinal food, jujube possesses considerable nutritional value and provides several health benefits (Zhang et al., 2021). Jujube fruits are rich in functional compounds and nutrients such as polysaccharides, flavonoids, cyclic adenosine monophosphate, organic acids, and free amino acids (Wang et al., 2020). As a global leader in jujube cultivation, China produces 7.5 million tons of jujube fruits annually, nearly half of which (49 %) originate from Xinjiang (Xin et al., 2021). So far, drying has remained the primary method for jujube processing and product development. However, as a value-added fermented product, jujube wine has emerged as a key competitor in the market due to its unique flavor profile and nutritional composition (Zhang, Ma, et al., 2023).

Jujube wine is produced through the following sequential processing stages: raw material pretreatment, leaching, fermentation, and aging. The first stage—raw material pretreatment—is of particular significance because it influences both flavor development and nutrient retention in the final product. In recent years, researchers have extensively explored the impact of various pretreatment methods on the flavor profile of jujube wine. For instance, Cai, Zhu, et al. (2020) employed headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS) (HS-SPME-GC–MS) to investigate the effects of pretreatment and leaching methods on the flavor profile of jujube wine. They identified a total of 182 volatile compounds in their jujube wine samples and revealed that optimized pretreatment and leaching methods significantly increase the volatile compound content of jujube wine while promoting the formation of characteristic aroma components, including ethyl octanoate and ethyl acetate. Meanwhile, Xu et al. (2019) discovered that pulsed electric field pretreatment improves the extraction efficiency of phenolic compounds in jujube wine while enriching its floral and fruity volatile components. Chun et al. (2012) conducted a comparative study of wines prepared using pitted and unpitted jujubes, employing high-performance liquid chromatography (HPLC) and GC–MS to analyze their amino acid composition. They discovered that the presence of pits alters the amino acid profile of the fermentation system, while pit removal potentially facilitates the release of specific flavor precursors and yields nutritionally enriched jujube wine. Furthermore, Lee et al. (2018) utilized HS-SPME-GC–MS to analyze the volatile compounds in jujube wines produced from fresh and dried fruits. Their research showed that wines fermented from dried jujubes contained higher concentrations of compounds such as isoamyl octanoate, isoamyl decanoate, ethyl laurate, and ethyl myristate than those prepared from fresh fruits. These compounds were found to contribute significantly to the more intense jujube-like aroma characteristic of dried-fruit fermented wines.

Aroma compounds act as key contributors to the sensory quality and market value of wine and other foods (Feng et al., 2022). GC–MS is widely employed to identify aroma compounds in fermented jujube wine. Nearly a hundred volatile components, including alcohols, esters, acids, aldehydes, ketones, and phenolic derivatives, have been detected in jujube wine using GC–MS (Hao et al., 2025). Meanwhile, as an emerging gas-phase separation and detection technology, gas chromatography-ion mobility spectrometry (GC-IMS) enables the faster analysis of volatile compounds and generates spectral data that clearly visualize the differences in volatile profiles between samples, facilitating rapid discrimination. GC-IMS can be conducted at atmospheric pressure, effectively addressing the limitations of GC–MS in terms of the slower analysis speed and potential loss of aromatic compounds during pretreatment. Moreover, it demonstrates higher sensitivity, particularly for low-boiling-point compounds such as aldehydes and sulfur-containing compounds (Huang et al., 2025). Due to its ultra-high sensitivity and speed of analysis, GC-IMS has been widely adopted to detect flavor compounds in alcoholic beverages, such as jujube distilled liquor (Zhang, Ma, et al., 2023) and kiwi wine (Zhang, Sun, et al., 2023). The combination of GC–MS and GC-IMS can provide technical guidance for fermentation process research and yield relatively comprehensive results. For instance, Mou et al. (2025) analyzed the key floral and fruity aroma components in soy sauce-flavored baijiu using GC–MS and GC-IMS. Further, Wang et al. (2025) analyzed the volatile organic compounds in red and black raspberry wine using GC–MS and GC-IMS, demonstrating that red raspberry wine has a significantly higher ester content, whereas black raspberry wine has higher terpenoid compound concentrations. However, few studies have simultaneously applied GC–MS and GC-IMS to analyze the volatile characteristics of jujube wine.

This study combined HPLC, HS-SPME-GC–MS, HS-GC-IMS, and sensory analysis to comprehensively evaluate the impact of jujube pretreatment at different roasting temperatures (0 °C, 80 °C, 100 °C, 120 °C, 140 °C, and 160 °C) on the content of free amino acids (FAAs) and volatile organic compounds (VOCs) in jujube wine. Multivariate statistical analyses, including orthogonal partial least squares discriminant analysis (OPLS-DA), a variable importance of projection (VIP) model, and relative odor activity value (ROAV) calculations, were performed to determine the key aroma compounds in jujube wine pretreated using different roasting temperatures. The results of the study could provide a theoretical reference for flavor and quality optimization in jujube wine.

2. Materials and methods

2.1. Raw material

The raw material consisted of dried Grade II Xinjiang jujubes (Ziziphus jujuba ‘Huizao’), which were obtained from a local orchard in Ruoqiang, Xinjiang Province, China. The jujubes had a moisture content of 18.25 % ± 1.05 % and total soluble solids content of 65.76 % ± 2.34 %. Saccharomyces cerevisiae CECO1 was purchased from Hubei Anqi Yeast Co., China. The reference standards used in this study were of chromatographic grade (purity ≥97 %) and included 2-octanol, normal ketones (C4–C9), and normal alkanes (C6–C26). These were purchased from Sigma-Aldrich (St. Louis, Missouri, USA) and Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Other chemicals were purchased from McLean (Shanghai, China).

2.2. Sample preparation

Jujubes were selected based on the following criteria: plump texture, absence of rot/mold, and lack of pest damage (single fruit weight: 10 ± 1 g; transverse diameter: 24 ± 1 mm). The jujubes were cleaned, pitted, and then cut in half before randomly being divided into six groups. One group served as the normal control (NC) and was not subjected to roasting treatment. Meanwhile, the other five groups were roasted for 30 min at 80 °C, 100 °C, 120 °C, 140 °C, or 160 °C using an electric blower and drying oven (101-1ES, Beijing Yongguangming Medical Instrument Factory, China) (air velocity of 2.0 m/s). Once roasting was complete, the jujubes were removed and cooled naturally to room temperature. Each temperature treatment group included three biological replicates.

2.3. Fermentation

Jujube wine was produced based on a previous method, with slight modifications (Wang, Zhao, et al., 2024). The pretreated jujube fruits were homogenized with distilled water (1:4 w/v ratio) using a juicer. Pectinase (0.35 % w/w, Lallemand Group Co., Ltd., France) was added subsequently, and the mixture was enzymatically treated at 45 °C for 220 min. Then, sucrose was added to adjust the soluble solids content to 22°Brix. Activated commercial wine yeast CECO1 (0.3 g/L) was inoculated for static fermentation at 20–22 °C. Fermentation was terminated by adding 40 mg/L SO2 when the residual sugar content reached ≤4 g/L. Post-fermentation, the must was filtered through sterile gauze to remove the pulp, yielding jujube wine samples (alcohol content: 10.95 ± 0.68 % v/v) that were subsequently stored at 4 °C. Fig. 1 displays the jujube wine samples prepared by fermenting jujubes pretreated at different roasting temperatures.

Fig. 1.

Fig. 1

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Samples of jujube wine prepared by fermenting jujubes subjected to different roasting pretreatments.

2.4. Determination of FAA content

The FAA profile of the jujube wine samples was obtained using an established automated on-line derivatization protocol (Hao et al., 2023). The compounds o-phthalaldehyde (OPA) and 9-fluorenylmethyl chloroformate (FmocCl) were used to derivatize the amino acids. Separation was achieved with an Agilent 1100 HPLC system equipped with a variable wavelength detector (VWD) and a Hypersil ODS reversed-phase column (250 mm × 4.0 mm; 5 μm). Mobile phase A (pH = 7.2) consisted of 27.6 mM sodium acetate, triethylamine, and tetrahydrofuran (500:0.1:2.5, v/v/v). Meanwhile, mobile phase B (pH = 7.2) contained 80.9 mM ammonium acetate, methanol, and acetonitrile (1:2:2, v/v/v). The flow rate was maintained at 1.0 mL/min. Gradient elution was performed using the following elution program: 0 min, 8 % B; 17 min, 50 % B; 20.1 min, 100 % B; and 24.0 min, 0 % B. The column thermostat was maintained at 40 °C. The VWD recorded measurements at 338 nm, while proline was detected at 262 nm.

2.5. HS-SPME-GC–MS analysis

HS-SPME: First, 5 mL of each wine sample was transferred to a 20 mL headspace vial, followed by 20 μL of 2-octanol (internal standard; 5 mg/L); then, the vial was immediately sealed. A DVB/CAR/PDMS fiber (50/30 μm) was inserted into the headspace vial for the extraction of volatile compounds at 50 °C for 30 min. Following extraction, the fiber was subsequently inserted into the gas chromatograph injection port and thermally desorbed at 250 °C for 3 min. The retention indices (RI) of released analytes were determined through automated software calibration against a homologous series of n-alkane standards (C₆-C₂₆) under consistent chromatographic conditions.

The VOCs in jujube wine were analyzed using GC–MS with a Pegasus HRT 4D Plus system (LECO, USA) equipped with a DB-WAX capillary column (30 m × 0.25 mm, 0.25 μm; Agilent, USA). The system was operated in the splitless injection mode, with high-purity helium as the carrier gas at a constant flow rate of 1.0 mL/min. The temperature program consisted of (1) an initial hold at 40 °C for 3 min, (2) a linear ramp at 10 °C/min to 230 °C, and (3) a final hold at 230 °C for 6 min. The additional instrumental parameters were as follows: 250 °C transfer line temperature, 200 °C ion source temperature, and electron ionization (EI+) at 70 eV with 1 mA emission current for mass spectral acquisition. The VOCs were identified by comparing the mass spectra and retention indices against reference standards in the NIST 2014 and Wiley 8.0 mass spectral libraries. The qualitative analysis involved spectral matching and retention index verification. Meanwhile, quantification was achieved through internal standard calibration using the following formula:

Ci=Cx∗AiAx (1)

where Ci is the concentration of VOCs to be measured, μg/L; Ai is the peak area of VOCs to be measured; Cx is the concentration of the internal standard, μg/L; and Ax is the peak area of the internal standard. 2-octanol was used as the standard for the quantitative analysis of volatile compounds.

2.6. HS-GC-IMS analysis

Headspace vials containing 2 mL of wine samples were incubated at 60 °C for 30 min, with the injection needle at 90 °C. Then, 300 μL of each sample was automatically aspirated using a headspace autosampling device. Headspace gas was separated at 45 °C using a DB-WAX capillary column (30 m × 0.32 mm). High-purity nitrogen (≥99.999 %) served as both the carrier gas and drift gas, and the flow program was as follows: 2 mL/min (0–2 min), 30 mL/min (1–10 min), 100 mL/min (10–20 min), and 130 mL/min (20–45 min). To prevent cross-contamination, 30-s pre-analysis and 5-min post-analysis nitrogen purging was implemented. RIs were determined using an automated mass spectrometry system, with C4–C9 ortho-ketone standards (China National Pharmaceutical Chemical Reagent Beijing Co., Ltd.) as external references. VOC identification was performed by comparing the drift times and RI values of different ions with those of the standards in the GC-IMS library (Yang et al., 2024), while relative quantification was conducted based on HS-GC-IMS peak intensities.

2.7. ROAV calculation

The ROAVs were analyzed to determine the contribution of individual volatile compounds to the overall aroma profile of jujube wine. ROAVs were calculated according to the following equation:

ROAVi=Ci×TmaxTi×Cmax×100 (2)

Here, Cmax and Tmax represent the relative content (%) and odor threshold, respectively, of the compound that contributes most dominantly to the overall flavor profile of the sample. Meanwhile, Ci and Ti denote the relative content and threshold value of the target compound, respectively (Miao et al., 2024).

2.8. Sensory evaluation

Sensory evaluation was conducted using quantitative descriptive analysis (QDA) based on Zhao et al. (2022) methodology, with some modifications. The panel consisted of 12 rigorously selected assessors (six women and six men), all of whom completed a systematic one-week training program encompassing standard odor recognition, intensity scale calibration, and sample evaluation consistency. Each member consented to participate in the study, and informed consent was obtained before participation. During preliminary tests for six jujube wine samples, the panel established six aroma descriptors: floral (phenethyl alcohol), fruity (isoamyl acetate), grassy (hexanal), alcoholic (ethanol), nutty (2-acetylpyrrole), and caramel-like (2-acetylfuran). To ensure standardized evaluation, reference compounds were dissolved in ultrapure water at concentrations 100 times their respective odor thresholds. All samples were presented in standard wine glasses coded with random three-digit numbers and evaluated in a temperature-controlled environment (20 ± 1 °C). Intensity was expressed on a 10-point scale (1 indicating that the compound could not be detected and 10 indicating that the attribute was extremely strong). Testing was conducted in triplicate to ensure methodological reliability. The study was reviewed and approved by the ethics board of the College of Food Science, Shihezi University.

2.9. Statistical analysis

Experimental data were collected based on triplicate measurements and presented as the mean ± standard deviation. Statistical analysis was conducted using SPSS 22.0 (IBM Corp., USA) for one-way ANOVA (significance threshold: p < 0.05) and SIMCA 14.1 (Umetrics AB, Sweden) for OPLS-DA with VIP assessment. Data visualization was conducted by employing multiple platforms, such as OmicShare Tools, TBtools, and OriginPro 2024.

3. Results and discussion

3.1. Quantification of FAAs in jujube wine

FAAs contribute significantly to the flavor of fruit wines, not only by providing nutrients for microbial growth during fermentation but also by acting as flavor precursors (Hu et al., 2014). Supplemental Table S1 presents the FAA composition of jujube wines processed at varying roasting temperatures. In total, 17 amino acids were identified, including eight amino acids (i.e., lysine, phenylalanine, methionine, threonine, isoleucine, leucine, valine, and histidine). Among the nine non-essential amino acids detected, proline, glutamic acid, aspartic acid, and alanine showed the highest concentrations, all exceeding 0.0160 g/100 g. These findings were consistent with a previous report by Zhao et al. (2022). The amino acid composition of jujube wine remained similar before and after roasting pretreatment, with only quantitative changes observed in amino acid concentrations. The control group (NC) exhibited a total FAA content of 0.8869 g/100 g. The total FAA content demonstrated a parabolic trend as the roasting temperature increased, initially rising before subsequently declining. Comparative analysis revealed that the 100 °C group showed the highest amino acid content (23.33 % increase versus NC), while the 160 °C group displayed the lowest concentration (77.21 % reduction relative to NC). This trend reflected the effect of roasting temperature on the dynamic balance between protein degradation and amino acid transformation. At 100 °C, moderate heating promoted the enzymatic and non-enzymatic (e.g., thermal denaturation) breakdown of proteins, leading to the accumulation of free amino acids (Mesías et al., 2016). Previously, Wang et al. (2018) reported that phenylalanine, tryptophan, and tyrosine serve as key precursors for the synthesis of benzene derivatives via specific metabolic pathways, particularly the Maillard reaction. In this study, at 120–160 °C, the rate of the Maillard reaction increased with the rise in roasting temperature, causing FAAs to combine with reducing sugars to produce melanoidins and other products. Meanwhile, the deamination or decarboxylation of some amino acids was likely the primary reason for the decreased amino acid content (Cai, Tang, et al., 2020).

Subsequently, the 17 FAAs were categorized into five flavor groups based on their taste characteristics (Fig. 2a): umami/sour (Asp, Glu) (Lee et al., 2019), sweet (Ala, Lys, Thr, Pro, Ser, Gly), bitter (Phe, Arg, Ile, Leu, His, Tyr, Met, Val), and unflavored (Cys) (Tian et al., 2024). These five amino acid classes accounted for 85.66 %, 7.73 %, 7.73 %, 6.07 %, and 0.54 % of total free amino acids in the NC group, respectively. In contrast, their relative proportions in the 80–160 °C treatment groups were 28.87–88.04 %, 6.98–37.53 %, 4.61–32.45 %, and 0.37–1.15 %, respectively. The observed shifts in free amino acid distribution could be attributed to enhanced Maillard reaction activity at elevated roasting temperatures (Hao et al., 2023).

Fig. 2.

Fig. 2

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Changes in the types and contents of FAAs in jujube wines prepared with jujubes pretreated at different roasting temperatures (a). FAA heatmap of jujube wines based on Z-score normalization (b). The color gradient indicates the changes in the content of individual amino acids at different temperatures (red: above the group mean, blue: below the group mean, color scale range: −2.0 to +2.0 SD). The bubble size represents the original content (g/100 g). Cluster analysis was performed based on Pearson correlation analysis (Ward's method). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

As shown in Fig. 2b, the content of sweet-tasting amino acids (e.g., proline and serine) initially increased and then decreased with rising roasting temperatures, peaking at 100 °C. Among all detected amino acids, the bitter-tasting types were the most abundant. Notably, the levels of arginine, valine, and leucine increased significantly (p < 0.05) when the roasting temperature rose from 120 °C to 160 °C. While the absolute contents of umami and sour amino acids (Asp, Glu) showed no statistically significant variations across roasting temperatures (p > 0.05), normalized heatmap analysis (Fig. 2b) revealed the relative enhancement of these flavor-active amino acids in the 100–160 °C treatment groups.

3.2. Volatiles in jujube wine identified with HS-SPME-GC–MS

3.2.1. Identification of VOCs

The VOCs in jujube wine samples treated at different roasting temperatures were analyzed using HS-SPME-GC–MS. A total of 100 VOCs were identified, including 38 esters (27.95–40.22 %), 18 alcohols (43.44–53.50 %), 12 acids (4.97–6.99 %), 9 ketones (1.14–3.34 %), 8 aldehydes (0.06–0.49 %), 4 furans (0.35–2.07 %), and 11 miscellaneous volatile compounds (7.61–12.95 %) (Table S2, Fig. 3c). As shown in Fig. 3a, the number of VOCs differed across the jujube wine samples prepared using different roasting temperatures. Among them, the 100 °C group contained the highest diversity of VOCs (67 compounds), followed by the 160 °C (63 compounds) and 80 °C (62 compounds) groups. Meanwhile, the NC group showed the lowest variety of VOCs (56 compounds). This indicated that the aroma characteristics of the 80 °C, 100 °C, and 160 °C groups were richer than those of the other groups (Fig. 3a). Among the various VOCs detected, esters were found to be predominant. The 100 °C group contained the highest numbers of both esters (34) and aldehydes (6). Meanwhile, alcohols were more abundant in the NC and 80 °C groups (13 compounds each), whereas the 160 °C group had a higher number of furan derivatives (4 compounds). These results indicated that jujube pretreatment at different roasting temperatures leads to the production of jujube wines with different aroma characteristics.

Fig. 3.

Fig. 3

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Identification of volatile organic compounds (VOCs) in jujube wine via HS-SPME-GC–MS. (a) Column stacking plot of VOC species. (b) UpSet plot. The blue bars indicate the total number of VOCs in the jujube wine samples from each treatment group, the black dots represent the VOCs present, the lines connecting the dots indicate the shared VOCs, and the orange bars represent the number of shared VOCs. (c) Circos plot showing the relative concentration of VOC species. (d) Clustering heat map of VOCs. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

To intuitively depict the overlap of volatile compounds in different jujube wine samples, an UpSet plot was created (Fig. 3b). Notably, 35 volatile substances— including isoamyl acetate, ethyl propionate, ethyl butyrate, ethyl hexanoate, phenethyl alcohol, isoamyl alcohol, octanoic acid, and hexanoic acid— were shared by the six groups of jujube wines. The 160 °C treatment group had the most unique volatile compounds (11), including ethyl formate, 2-furanmethanol, and geranyl acetone. The 100 °C treatment group had seven unique compounds, such as octyl formate, γ-decalactone, and 4,6-dimethyl-2-heptanone. The 120 °C treatment group had three unique compounds, while the NC, 80 °C, and 140 °C treatment groups had two unique VOCs. These compounds imparted characteristic aromas to these wines, distinguishing them from other jujube wines. The differences were closely related to the roasting temperature, and the fruit wine prepared using jujubes pretreated at 160 °C seemed to have the most recognizable flavor.

Alcohols, as secondary metabolites of yeast, are synthesized through glycolysis or via the dehydrogenation and decarboxylation of amino acids (Tian et al., 2024), and their concentrations are influenced by the available content of sugars and amino acids. In the present study, as the roasting temperature increased, the alcohol concentration first rose and then decreased (Table S2). The alcohols consistently detected across all temperature treatments were 3-methyl-1-butanol, phenethyl alcohol, and isobutyl alcohol. Of these, 3-methyl-1-butanol (2628.94 μg/L) and phenethyl alcohol (1239.60 μg/L) showed the highest content in the 120 °C group. 3-Methyl-1-butanol, which was among the most abundant alcohols across all samples in this study, is known to have an apple brandy flavor and grassy aroma (Hao et al., 2023). In this study, its concentration tended to first rise and then decline with increasing roasting temperatures. Phenethyl alcohol, which contributes significantly to the floral rose-like and fruity aromas of wine (Tian et al., 2024), showed a similar trend of variation as 3-methyl-1-butanol. Isobutyl alcohol, a higher alcohol with a wine- and acetone-like aroma, showed the highest levels (111.38 μg/L) in the 140 °C group. In addition, (S)-1,2-propanediol and D-citronellol were only detected in the NC group, while serinol and furfuryl alcohol were exclusively detected in the 160 °C group. The presence of these specific alcohols suggested that roasting temperature markedly affects the composition of alcohols in jujube wine.

Esters are the primary aroma constituents of fermented wines, imparting them with typical fruity characteristics (Yang et al., 2024). As shown in Table S2, the total ester concentration of jujube wine tended to first increase and then decrease with increasing roasting temperatures, in line with the changes in alcohol levels. Ester formation occurs through two primary pathways: (1) the reaction of acyl-CoA with ethanol to produce ethyl esters and (2) the reaction of acetyl-CoA with higher alcohols to form acetate esters (Chen et al., 2023). The predominant volatile ethyl esters detected in jujube wine were ethyl acetate, ethyl hexanoate, and ethyl caprylate (Fig. 3d and Table S2). The 100 °C group exhibited higher concentrations of ethyl hexanoate (36.99 % of total esters) and ethyl acetate (8.12 % of total esters). In contrast, the ethyl caprylate content in the 120 °C group was significantly elevated (p < 0.05), reaching levels 1.09 times higher than those in the NC group. Moreover, isoamyl acetate—the main volatile ethyl ester—accounted for 7.71 % to 17.21 % of the total ester concentration. Interestingly, certain ester compounds were only discovered at specific roasting temperatures. For instance, γ-decalactone was detected only in the 100 °C group, whereas propanoic acid, 2-hydroxy-, ethyl ester was detected only in the 160 °C group (Fig. 3d). These findings demonstrated that the roasting temperature has a remarkable impact on the synthesis, accumulation, and release of ester compounds in jujube wine (Liu et al., 2022).

Acids are mostly derived from raw fruits and yeast metabolism during fermentation (Wang, Chen, et al., 2024), playing an auxiliary role in the harmonization and balance of fruit wine flavors due to their high odor threshold. In this study, the proportion of acid compounds among the total VOCs progressively increased with increasing roasting temperatures, peaking in the 160 °C group (6.99 %, Fig. 3c). As the most representative volatile acid in fruit wines, acetic acid contributes significantly to wine quality. Previous studies have indicated that acetic acid concentrations exceeding 80,000 μg/L can generate distinct sour off-odors that are detrimental to wine flavor (Vilela, 2017). In the current study, the concentrations of acetic acid (88.58–208.49 μg/L) were well within the optimal range across all treatment groups. Notably, the progressive increase in acetic acid levels with increasing roasting temperatures enhanced the aromatic complexity of jujube wine, without the acetic acid content reaching negative thresholds. Acid compounds typically serve dual functions in fruit wines: they contribute to characteristic flavor profiles while also acting as precursors for ester synthesis (Cai, Zhu, et al., 2020). In this study, the concentrations of hexanoic acid and octanoic acid both showed the tendency to first increase and then decrease with the increase in roasting temperature, highly consistent with the variation patterns of ethyl hexanoate and ethyl caprylate. Hexanoic acid, as a direct substrate for esterification reactions, is converted into ethyl hexanoate, which has fruity characteristics. Similarly, octanoic acid is converted into ethyl caprylate, which has sweet and fragrant characteristics. These esters impart desirable creamy and fruity aromas to jujube wine while also enhancing its overall complexity and richness.

Aldehydes show limited concentrations in fruit wines but play an essential role in aroma development due to their low odor threshold (Wang, Chen, et al., 2024). Aldehydes are mainly generated through yeast-mediated sugar metabolism, amino transfer, or amino acid degradation (Ma et al., 2023). In this study, a total of eight aldehydes were detected in the six groups of jujube wine, and their relative contents gradually increased with the increase in roasting temperature (Fig. 3c). Nonanal was consistently detected across all samples, reaching peak concentrations of 25.03 μg/L in the 160 °C group. This compound is known to impart characteristic citrus notes to the aroma profile of wine. Meanwhile, methyl-containing short-chain aldehydes such as (E)-2-butenal (107.76 μg/L)—a Maillard reaction product derived from isoleucine (Duan et al., 2024)—add distinct nutty and toasted bread aromas. Decanal, a saturated aliphatic aldehyde with sweet orange and lemon flavors, showed significant accumulation (26.44 μg/L) in the 80 °C group. Conversely, 3-furaldehyde (imparting floral and fruity notes) exhibited peak concentrations (11.56 μg/L) in the 100 °C group. These compositional variations underscore the profound impact of roasting temperature on the flavor evolution of jujube wine.

Ketones are primarily formed through the oxidation and degradation of unsaturated fatty acids (Zhang et al., 2024). In the present study, the concentration of these compounds first increased and then decreased with increasing roasting temperatures. The main ketones detected in jujube wine were β-damascenone, p-hexylacetophenone, and geranylacetone (Table S2). Among them, β-damascenone exhibited the highest concentration in the 100 °C group (Fig. 3d), accounting for 63.64 % of the total ketones, and could provide rose and honey flavors to the fruit wine (Osorio Alises et al., 2024). Furthermore, p-hexylacetophenone (2.64–4.72 μg/L), detected exclusively in the roasted treatment groups, could impart floral and fruity odors to jujube wine, potentially enriching its overall aroma profile.

Furans are known for their characteristic caramel, nutty, and baking flavors and are mainly derived from the Melad and Strecker degradation reactions (Crews & Castle, 2007). In total, four furans were detected in this study, namely, furan, 2,5-dimethyl-; 2-acetylfuran; dihydro-2-methyl-3(2H)-furanone; and 1-propanone, 1-(2-furanyl)-. When the roasting temperature was higher than 120 °C, furans were generated in large quantities, and their concentrations increased linearly with the roasting temperature. Of these compounds, 2-acetylfuran (71.85 μg/L) showed the highest concentration in the 140 °C group, meaning that higher temperature promoted lipid oxidation and meladic reactions.

3.2.2. Identification of aroma-active substances based on ROAVs

The aromatic profile of fruit wines is complex. Notably, the concentration and diversity of VOCs do not necessarily correlate with prominent aromas because factors such as odor thresholds also play a key role. To accurately identify the key flavor compounds in jujube wine, we conducted a more in-depth analysis of volatile flavor substances using the ROAV method, which integrates both concentration and odor threshold data. Generally, components with ROAV ≥1 are considered primary volatile components of a target sample, while those with 0.1 ≤ ROAV <1 play an important role in modifying the overall flavor of the samples. In this study, 12 potential key aroma compounds with ROAV ≥1 were screened from 100 volatile organic compounds.

Table 1 presents the ROAVs and sensory descriptors of key aroma compounds in jujube wines fermented from jujubes treated at different roasting temperatures. Two characteristic esters—isoamyl acetate (ROAV range: 1.91–36.27) and ethyl hexanoate (22.77–100)—were consistently detected in all wine samples, imparting distinctive banana-, grape-, and apple-like aromas to the jujube wines. These compounds collectively appeared to establish the fundamental aroma profile of jujube wine. Our findings demonstrated that the enhanced floral and fruity characteristics of wine correlated strongly with increased ester concentrations (Li et al., 2020). Notably, ethyl butyrate, ethyl heptanoate, and nonanoic acid were identified as key aroma compounds (ROAV >1) exclusively in the NC group, contributing fruity, berry, and green aromas. γ-Decalactone (peachy flavor) had an ROAV >1 only in the 100 °C group, while 2-acetyl pyrrole—which typically has a nutty and roasted aroma profile—had an ROAV >1 only in the 140 °C (87.37) and 160 °C groups (77.83). Notably, ethyl caprylate (0.35–7.49) provided sweet, fruity, and floral aromas; ethyl caprate (0.12–2.85) imparted a faint rose aroma; and nonanal (0.39–3.11) offered a citrus aroma. These temperature-dependent variations provided compelling evidence that different roasting conditions generate distinct flavor profiles in jujube wine.

Table 1.

ROAVs of VOCs detected using HS-SPME-GC–MS in jujube wine prepared following pretreatment at different roasting temperatures.

NO. Compound Threshold (μg/L) 1 Aroma description 2 ROAV
NC 80 °C 100 °C 120 °C 140 °C 160 °C
1 Ethyl butyrate 20a Fruity 2.67 0.95 0.65 0.91 0.22 0.16
2 Isoamyl acetate 30a Banana, pear, apple 36.27 12.98 4.77 10.60 2.74 1.91
3 Ethyl hexanoate 14a Pineapple 100.00 100.00 39.37 100.00 34.16 22.77
4 Ethyl heptanoate 220a Berry, plum 1.33 0.57 0.24 0.66 0.19 0.11
5 Ethyl caprylate 147a Sweet, fruity, floral 7.49 2.41 1.13 3.10 0.68 0.35
6 Ethyl caprate 200a Fruit, with a light rose aroma 2.85 0.92 0.47 1.06 0.22 0.12
7 γ-Decalactone 0.7b Peach, lactone-like – – 6.27 – – –
8 Nonanoic acid 26c Green, fatty 1.06 0.43 0.17 – 0.12 –
9 Nonanal 15a Fatty, citrus, green 3.11 0.81 0.39 1.36 0.87 0.67
10 Decanal 1c Soap, orange peel, tallow – 35.30 0.55 – 8.07 11.35
11 β-Damascenone 0.05a Strong rose-like aroma – – 100.00 – 100.00 100.00
12 2-Acetyl pyrrole 0.12c Nutty, caramel – – – – 87.37 77.83
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Note: 1 All thresholds were determined in an aqueous matrix.

2

From the flavornet database (https://www.femaflavor.org; http://www.flavornet.org; http://www.thegoodscentscompany.com; accessed on February 23, 2025).

“-” indicates that the volatile compounds were not detected.

The superscripts a, b, and c, located in the “Threshold” column, represent the references for threshold data. (Wei et al. (2023); Feng et al. (2022); Zheng, Wei, et al. (2024)).

3.2.3. Multivariate statistical analysis

An OPLS-DA model was constructed based on the VOC concentrations in jujube wines prepared after pretreatment at different roasting temperatures. This model demonstrated excellent fit parameters (R2Y = 0.998, Q2 = 0.988) (Fig. 4a). All groups of wine samples were relatively independent and could be effectively distinguished from each other. The samples clustered distinctly according to the roasting temperature, with distances of spatial separation reflecting compositional differences. Notably, the 160 °C group showed the greatest separation, which reflected its unique aromatic characteristics. Model validity was confirmed through 200 permutation tests, where the negative Q2 intercept (R2 = 0.226, Q2 = −0.994) (Fig. 4b) excluded the possibility of overfitting. VIP analysis revealed the presence of 19 discriminant volatiles (VIP >1) based on HS-SPME-GC–MS data (Fig. 4c). Phenylethyl alcohol showed the highest VIP score (3.92), followed by ethyl hexanoate (3.52), 3-methyl-1-butanol (3.47), ethyl caprylate (2.05), and other compounds.

Fig. 4.

Fig. 4

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Comparative analysis of HS-SPME-GC–MS-derived VOCs in jujube wines processed using different roasting temperatures. (a) OPLS-DA Score plot. (b) Cross-validation plot based on 200 permutation tests. (c) VIP score distribution, where red denotes characteristic flavor compounds with VIP values >1. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The contribution of volatile compounds to the characteristic flavor profile of jujube wine depends on both concentration and sensory thresholds. Notably, certain compounds can have a significant impact on flavor despite low concentrations and thresholds (Zheng, Oellig, et al., 2024). Therefore, to evaluate the contribution of individual compounds to the overall flavor, four key differential volatile compounds were screened out based on the criteria ROAV ≥1 and VIP > 1, namely, isoamyl acetate, ethyl hexanoate, ethyl caprylate, and ethyl caprate.

3.3. HS-GC-IMS identification of VOCs in jujube wine

3.3.1. Identification of VOCs

In addition to HS-SPME-GC–MS, HS-GC-IMS was also used to identify VOCs and explore the impact of roasting temperature on the volatile characteristics of jujube wine. As shown in Fig. 5a, the peak intensities of VOCs varied across jujube wine samples prepared after pretreatment at different roasting temperatures. Due to the high similarities among the 3D spectra of the volatiles in each group, which made direct visual comparisons challenging, a downscaling process was carried out to obtain the 2D planar top-view spectra (Fig. 5b). Most signal peaks appeared within retention times of 200–900 s and drift times of 1.0–1.5 ms. By analyzing these parameters, 32 compounds were identified, including 12 previously uncharacterized VOCs. The characterized compounds comprised 15 esters, 7 alcohols, 7 aldehydes, 1 ketone, 1 acid, and 1 furan (Table S3). The concentrations of these VOCs varied across the six groups. Subsequently, differential spectrograms were constructed based on the topography of the NC group (Fig. 5c). The contents of several compounds were significantly higher or lower in the roasting treatment groups versus the NC group, indicating that the roasting temperature could obviously influence the volatile content of jujube wine.

Fig. 5.

Fig. 5

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VOCs detected using HS-GC-IMS in jujube wine following jujube pretreatment at different roasting temperatures. (a) Three-dimensional spectra. (b) Two-dimensional spectra. (c) Difference spectra. (d) Fingerprinting. Monomers and dimers are denoted by M and D, respectively. Due to the incomplete nature of the IMS database, 12 compounds remained uncharacterized and were marked with numbers in the fingerprints.

To visualize temperature-dependent variations in the volatile composition of jujube wine, a fingerprint spectrum was constructed (Fig. 5d). The NC group exhibited higher concentrations of ethyl acetate-M, isoamyl acetate-M, 2-propanol, and butanol. Notably, as the roasting temperature increased, a progressive decrease in isoamyl acetate-M levels and a gradual increase in 3-methylbutyric acid, 3-methylbutanal, and methyl isovalerate levels were observed. Moreover, the contents of VOCs such as ethyl acetate-D, methyl acetate, propan-1-ol, and butanal displayed an increasing and then decreasing trend, with the highest contents detected in the 100 °C group. In contrast, the contents of some VOCs, such as methyl isovalerate, butanol, and 2-methyltetrahydrofuran-3-one, tended to first decrease and then increase as the temperature increased. These findings highlighted the critical role of roasting temperature in modulating the flavor profile of jujube wine.

3.3.2. Comparison of HS-SPME-GC–MS and HS-GC-IMS in the identification of jujube wine VOCs

By comparing the results of HS-SPME-GC–MS and HS-GC-IMS analysis for VOC detection in jujube wine, we found that HS-SPME-GC–MS performed better in terms of detection range and the accuracy of qualitative and quantitative results, identifying a greater number of compounds (a total of 100). This technique was particularly effective at identifying long-chain volatile compounds. Meanwhile, although HS-GC-IMS could only identify 32 volatile compounds in the jujube wine samples, some of these (including six esters, four alcohols, four aldehydes, and one ketone) were compounds that HS-SPME-GC–MS failed to identify. This indicated that HS-GC-IMS also demonstrated strong detection capabilities for volatile components in jujube wine samples. Despite the significant differences in the types and concentrations of detected VOCs between the two methods, 13 VOCs—including ethyl acetate, isoamyl acetate, 3-methyl-1-butanol, and isovaleric acid—were consistently detected using both GC–MS and GC-IMS. Nevertheless, the observed differences could be attributed to two key factors. First, GC–MS and GC-IMS have different sensitivities for compounds with different molecular weights. GC-IMS shows excellent sensitivity for smaller molecules (C2–C10), while GC–MS is more sensitive to C10–C15 compounds (Wang et al., 2023). Further, during SPME, volatile compounds undergo different degrees of enrichment and concentration, which changes their proportion in the tested volatile sample. Therefore, the combination of HS-GC-IMS and HS-SPME-GC–MS provides more comprehensive insights into the aroma characteristics of jujube wine.

3.3.3. ROAV analysis

The analysis of ROAVs revealed 11 aroma-active compounds (ROAV >1) across different groups of jujube wines (Table S4). Of these, ethyl heptanoate, which had an apple and pineapple-like aroma, showed the highest ROAV (7.03–11.16) and contributed the most to the aroma of the 80 °C group. High ROAVs were also detected for butanal (6.16–7.28) and 1-penten-3-one (4.33–7.95), which were dominated by fruity and grassy aromas. Conversely, isoamyl acetate-M (0.87–1.09) and isoamyl acetate-D (1.54–3.60), with a distinct banana aroma, had a higher ROAV in the NC group, which clearly differentiated the aroma profiles of the control samples from those of the other samples.

3.3.4. Multivariate statistical analysis

OPLS-DA effectively differentiated among the sample groups while identifying significant variables responsible for intergroup variations. The clear separation among samples (Fig. 6a) and excellent model parameters (R2Y = 0.973, Q2 = 0.831) demonstrated the robust explanatory and predictive capacity of the model. Model reliability was confirmed through 200 permutation tests (Fig. 6b), with the negative Q2 intercept (R2 = 0.676, Q2 = −1.24) validating the model's stability without overfitting. The VIP values of key compounds are shown in Fig. 6c. Thirteen compounds had VIP values >1, namely, isoamyl acetate-D, ethyl acetate-D, 3-methyl-1-butanol, ethyl hexanoate, 3-methylbutanoic acid, ethyl propanoate, 2-propanol, 3-methylbutanal-D, 3-methylbutanal-M, pentyl acetate, ethyl butyrate, propan-1-ol, 2-methylbutanol, and methyl acetate. Candidate differential VOCs with VIP values >1 in the OPLA-DA model were subjected to further analysis. By combining the ROAVs of each substance and their odor characteristic descriptions, isoamyl acetate-D, ethyl hexanoate, pentyl acetate, and ethyl butyrate were identified as key differential VOCs among the different groups of jujube wine.

Fig. 6.

Fig. 6

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Comparative analysis of HS-GC-IMS-derived VOCs in jujube wines processed using different roasting temperatures. (a) OPLS-DA score plot. (b) Cross-validation plot based on 200 permutation tests. (c) VIP score distribution, where red denotes characteristic flavor compounds with VIP values >1. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Overall, by combining GC–MS and GC-IMS analyses, a total of six key aroma-contributing compounds were identified in jujube wines prepared from jujubes pretreated at different roasting temperatures: isoamyl acetate, ethyl hexanoate, ethyl caprylate, ethyl caprate, pentyl acetate, and ethyl butyrate.

3.4. Correlation between flavor and sensory characteristics

The results of sensory evaluation are shown in Fig. 7a. The aroma of the six jujube wine samples was assessed based on their “alcohol,” “botanical,” “fruity,” “floral,” “nutty,” and “caramel” attributes. Compared with the NC group, the 80 °C group showed greater “nutty” aroma, while the 100 °C and 120 °C groups showed stronger “fruity,” “floral,” and “nutty” aroma. The intensity of “fruity,” “floral,” and “nutty” aromas was greatly enhanced in the 100 °C and 120 °C groups, likely due to the presence of esters, alcohols, and aldehydes. Meanwhile, the “caramel” aroma was stronger in the 140 °C and 160 °C groups, while the intensity of “alcohol” and “botanical” attributes was lower. This difference was attributed to the presence of 2-acetylfuran, which provides a unique roasted aroma. Overall, the results of sensory analysis were in line with the GC data, indicating that GC-IMS and GC–MS are effective methods for detecting VOCs in jujube wine.

Fig. 7.

Fig. 7

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(a) Radar plots for the sensory analysis of jujube wine prepared using jujubes treated with different roasting temperatures. (b) Correlation network heatmap between sensory characteristics and key aroma compounds, as well as FAAs. Pearson correlation analysis was used. The color of each block within the circles in the right heatmap indicates the type of correlation (positive and negative), while the size of the block represents the magnitude of the correlation. The Mantel test was used to test the significance of the correlations, with smaller Mantel P values indicating more significant correlations. The thickness of the lines on the left indicates the strength of the correlation, while the color of the lines indicates the degree of significance.

To further characterize the relationships among the sensory characteristics of jujube wine and the key aroma compounds and FAAs present in these samples, a three-dimensional interactive network heatmap was constructed for systematic analysis (Fig. 7b). The results revealed that pentyl acetate exhibited a significant positive correlation with the nutty aroma (r = 0.707, p < 0.001). Meanwhile, unflavored acid not only had a strong correlation with the alcohol aroma (r = 0.774, p < 0.005) but was also significantly associated with the botanical aroma (r = 0.679, p < 0.005), likely owing to its unique molecular structure and volatility characteristics. In terms of fruity characteristics, ethyl hexanoate was significantly correlated with the fruity aroma (r = 0.629, p < 0.05), confirming that this ester served as the main contributor to the fruity aroma of jujube wine. Noteworthily, bitter amino acids were highly correlated with the caramel aroma (r = 0.699, p < 0.005), highlighting the key role of the Maillard reaction in the flavor formation of jujube wine. Heatmap analysis not only verified the aroma characteristics of each key flavor compound but, more importantly, revealed the dual role of free amino acids in directly contributing to taste and indirectly regulating the release of volatile compounds.

4. Conclusions

An integrated analysis of FAAs and VOCs in jujube wine fermented from jujubes pretreated at different roasting temperatures was performed using HPLC, HS-SPME-GC–MS, HS-GC-IMS, and sensory analysis. The results revealed that roasting pretreatment at 80–100 °C increased the sweet amino acid content of jujube wine, while roasting pretreatment at 140–160 °C promoted the accumulation of bitter amino acids. Moreover, roasting temperatures significantly affected the VOC composition of jujube wine. With the increase in roasting temperature, the contents of esters, alcohols, acids, aldehydes, and ketones first increased and then decreased, while the content of furans continuously increased. The highest content of esters was found in the 100 °C and 120 °C treatment groups, the highest content of acids and aldehydes/ketones in the 140 °C group, and the highest content of furans in the 160 °C group. VOC analysis based on OPLS-DA, ROAV calculations, and VIP values illustrated that six key aroma compounds (isoamyl acetate, ethyl hexanoate, ethyl caprylate, ethyl caprate, pentyl acetate, and ethyl butyrate) contribute significantly to the characteristic aroma of jujube wine. This study uncovers the impact of roasting temperatures on the flavor characteristics of jujube wine, providing a theoretical foundation for the development of high-quality jujube wines with varying flavor profiles. Future studies should integrate gas chromatography-olfactometry (GC-O), electronic tongue analysis, and other advanced techniques to investigate how various jujube cultivars and roasting methods influence the flavor profiles of jujube wine. Such research would facilitate the establishment of predictive models for optimizing specific volatile profiles, particularly key flavor compounds, in jujube wine.

CRediT authorship contribution statement

Binbin Li: Writing – review & editing, Writing – original draft, Software, Methodology, Investigation. Qian Mu: Writing – review & editing, Writing – original draft, Visualization, Data curation. Huijing Guo: Methodology, Investigation. Wenting Jia: Validation, Methodology. Mengzhen Zhang: Data curation. Ya Liu: Methodology, Conceptualization. Xinwen Jin: Supervision, Funding acquisition, Conceptualization.

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.

Acknowledgment

The research was supported by Agriculture Research System of China (CARS-30-5-04)

Footnotes

Appendix A

Supplementary data to this article can be found online at https://doi.org/10.1016/j.fochx.2025.102891.

Appendix A. Supplementary data

Supplementary material: Table S1: Content of free amino acids in jujube wines processed at different baking temperatures. Table S2: Concentrations of volatile compounds in jujube wines pretreated with different roasting temperatures, analyzed by HS-SPME-GC-MS. Table S3: Contents of volatile compounds in jujube wines pretreated with different roasting temperatures, determined by HS-GC-IMS. Table S4: ROAVs (Relative Odor Activity Values) of volatile organic compounds (VOCs) detected by HS-SPME-GC-MS in jujube wine prepared with different roasting temperature pretreatments.

mmc1.docx (80.5KB, docx)

Data availability

Data will be made available on request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplementary material: Table S1: Content of free amino acids in jujube wines processed at different baking temperatures. Table S2: Concentrations of volatile compounds in jujube wines pretreated with different roasting temperatures, analyzed by HS-SPME-GC-MS. Table S3: Contents of volatile compounds in jujube wines pretreated with different roasting temperatures, determined by HS-GC-IMS. Table S4: ROAVs (Relative Odor Activity Values) of volatile organic compounds (VOCs) detected by HS-SPME-GC-MS in jujube wine prepared with different roasting temperature pretreatments.

mmc1.docx (80.5KB, docx)

Data Availability Statement

Data will be made available on request.

Articles from Food Chemistry: X are provided here courtesy of Elsevier

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