Characterization of aroma-impact compounds in dry jujubes (Ziziphus jujube Mill.) by aroma extract dilution analysis (AEDA) and gas chromatography-mass spectrometer (GC-MS)

Profiling the Major Aroma-Active Compounds of Microwave-Dried Jujube Slices through Molecular Sensory Science Approaches

To discriminate the aroma-active compounds in dried jujube slices through microwave-dried treatments and understand their sensory attributes, odor activity value (OAV) and detection frequency analysis (DFA) combined with sensory analysis and analyzed through partial least squares regression analysis (PLSR) were used collaboratively. A total of 21 major aromatic active compounds were identified, among which 4-hexanolide, 4-cyclopentene-1,3-dione, 5-methyl-2(5H)-furanone, 4-hydroxy-2,5-dimethyl-3(2H)furanone, 3,5-dihydroxy-2-methyl-4-pyrone were first confirmed as aromatic compounds of jujube. Sensory evaluation revealed that the major characteristic aromas of dried jujube slices were caramel flavor, roasted sweet flavor, and bitter and burnt flavors. The PLSR results showed that certain compounds were related to specific taste attributes. 2,3-butanedione and acetoin had a significant positive correlation with the roasted sweet attribute. On the other hand, γ-butyrolactone, 4-cyclopentene-1,3-dione, and 4-hydroxy-2,5-dimethyl-3(2H)furanone had a significant positive impact on the caramel attributes. For the bitter attribute, 2-acetylfuran and 5-methyl-2(5H)-furanone were positively correlated. Regarding the burnt flavor, 5-methyl-2-furancarboxaldehyde and 3,5-dihydroxy-2-methyl-4-pyrone were the most influential odor-active compounds. Finally, 2-furanmethanol and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one were identified as the primary sources of the burnt and bitter flavors. Importantly, this work could provide a theoretical basis for aroma control during dried jujube slices processing.

Determination and Risk Assessment of Flavor Components in Flavored Milk

This study aimed to determine chemical composition and assess exposure in flavored milk among Chinese residents, based on risk assessment methodologies of acceptable daily intake (ADI) and toxicological concern threshold (TTC). Esters (32.17%), alcohols (11.19%), olefins (9.09%), aldehydes (8.39%), and ketones (7.34%) comprised the majority of the flavoring samples. Methyl palmitate (90.91%), ethyl butyrate (81.82%), and dipentene (81.82%) had the highest detection rates in flavor samples. This study screened fifteen flavor components of concern and discovered that 2,3,5-trimethylpyrazine, furfural, benzaldehyde, and benzenemethanol were detected in 100% of flavored milk samples. Benzenemethanol was found in the highest concentration (14,995.44 μg kg^-1). The risk assessment results revealed that there was no risk for Chinese residents in consuming flavored milk, and the maximum per capita daily consumption of 2,3,5-trimethylpyrazine, furfural, and benzenemethanol were 226.208 g, 140.610 g, and 120.036 g, respectively. This study could provide guidelines for amounts of flavor additive ingredients in milk.

Influence of Deamidation on the Formation of Pyrazines and Proline-Specific Compounds in Maillard Reaction of Asparagine and Proline with Glucose

Maillard reaction products obtained from the model system of binary amino acids (asparagine and proline) with glucose were first studied. GC-MS results showed that proline-specific aromatic compounds, 2,3-dihydro-1H-pyrrolizines and cyclopent[b]azepin-8(1H)-ones, were dominant among overall products, followed by pyrazines at different temperatures. Aspartic acid was first applied to model reactions as the precise control of asparagine deamidation, and lysine was further introduced into model systems for improving pyrazine formation. Quantitative results of model reaction products demonstrated that pyrazines were not significantly increased in deamidated states (Asn-Asp-Pro and Asp-Pro) while proline-specific compounds had a rapid enhancement at the same time. With excellent ability to form pyrazines, lysine did help to increase the formation of pyrazines, but still far fewer than pyrrolizines and azepines. It was assumed that proline would preferentially react with α-dicarbonyl compounds in Maillard reaction cascades with lower activation energies.

The Grade of Dried Jujube (Ziziphus jujuba Mill. cv. Junzao) Affects Its Quality Attributes, Antioxidant Activity, and Volatile Aroma Components

Jujube (Ziziphus jujuba Mill. cv. Junzao) has attracted a large number of consumers because it is rich in nutrients, such as carbohydrates, organic acids, and amino acids. Dried jujube is more conducive to storage and transportation, and has a more intense flavor. Consumers are affected by subjective factors, and the most important factor is the appearance of the fruit, including size and color. In this study, fully matured jujubes were dried and divided into five grades according to their transverse diameter and jujube number per kilogram. In addition, the quality attributes, antioxidant activities, mineral elements, and volatile aroma components of dried jujube were further analyzed. As the dried jujube grade increased, the total flavonoid content increased, which was positively correlated with the antioxidant activity. The results showed that small dried jujube had a higher total acidity and lower sugar-acid ratio than large and medium dried jujube, thus, large and medium dried jujube had a better flavor than small dried jujube. However, the antioxidant activity and mineral elements of medium and small dried jujube were superior to large dried jujube. From the edible value analysis of dried jujube, medium and small dried jujube were better than large dried jujube. Potassium is the highest among the measured mineral elements, with contents ranging from 10,223.80 mg/kg to 16,620.82 mg/kg, followed by Ca and Mg. Twenty-nine volatile aroma components of dried jujube were identified by GC-MS analysis. The main volatile aroma components were acids including n-decanoic acid, benzoic acid, and dodecanoic acid. The fruit size affected the quality attributes, antioxidant activity, mineral elements, and volatile aroma components of dried jujube. This study provided a piece of reference information for further high-quality production of dried jujube fruit.

The Discrimination and Characterization of Volatile Organic Compounds in Different Areas of Zanthoxylum bungeanum Pericarps and Leaves by HS-GC-IMS and HS-SPME-GC-MS

The pericarps of Zanthoxylum bungeanum (ZBP) and leaves of Zanthoxylum bungeanum (ZBL) are popular spices in China, and they have pharmacological activities as well. In this experiment, the volatile organic compounds (VOCs) of the pericarps of Zanthoxylum bungeanum in Sichuan (SJ) and its leaves (SJY) and the pericarps of Zanthoxylum bungeanum in Shaanxi (SHJ) and its leaves (SHJY) were analyzed by headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS) and headspace solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). The fingerprint of HS-GC-IMS and the heat maps of HS-SPME-GC-MS were established. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed. The results showed that a total of 95 components were identified, 62 components identified by HS-SPME-GC-MS and 40 components identified by HS-GC-IMS, of which 7 were the same. The analysis found that SJ and SHJ were obviously distinguished, while SJY and SHJY were not. There were considerably fewer VOCs in the leaves than in the pericarps. In the characterization of the VOCs of ZBL and ZBP, the flavor of ZBP was more acrid and stronger, while the flavor of ZBL was lighter and slightly acrid. Thirteen and eleven differential markers were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. This is helpful in distinguishing between SHJ and SJ, which contributes to their quality evaluation.

Unravelling the key aroma compounds in the characteristic fragrance of Dendrobium officinale flowers for potential industrial application

Dendrobium officinale Kimura et Migo, one of the most important orchids because of its medicinal and edible value, has a typical Dendrobium Sw. flora scent, which has great application potential and commercial value to be characterized. The aroma-active compounds originating from D. officinale fresh flowers (DFF) were investigated using a sensomics approach. A combined solid phase microextraction and solvent-assisted flavor evaporation method were used to accurately capture the overall aromatic profile. Exactly 34 odorants were detected and identified by aroma extract dilution analysis (AEDA) coupled with gas chromatography/olfactometry-mass spectrometry (GC/O-MS) in DFF, of which nine odorants had a flavor dilution (FD) factor ≥27. All 34 odorants were further quantified. The odor activity values (OAVs) were calculated with the highest value of 7444, in which 18 compounds were confirmed to be key odorants, including 1-octen-3-ol, hexanal, nonanal, phenylacetaldehyde, linalool, 4-oxoisophorone, theaspirane, methyl salicylate, etc. Among the studies above, 42 out of 78 volatiles and 14 out of 34 odorants were identified in DFF for the first time. Then, the aroma profile of the DFF was simulated successfully by aroma recombination experiments based on the quantitation results, and the omission test suggested that alcohols are the decisive type of compounds in the DFF key odorants. In addition, a progressive addition test showed that the aroma recombinate prepared with 18 reference key odorants was able to reconstruct the characteristic aroma of DFF. In comparison, the recombinate constituted by mixing all 34 reference odorants in the same concentrations as determined in the DDF sample could mimic the flower scent and closely match the sensory attributes of the original D. officinale fresh flower.

Fingerprints and changes analysis of volatile compounds in fresh-cut yam during yellowing process by using HS-GC-IMS

The purpose of this study was to investigate the dynamic change in volatile components during the yellowing process. The volatile components were analyzed by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and the critical enzyme activities were determined by commercial kits. The results revealed that 29 signal peaks for 20 compounds were identified, which were quantified in all samples: 1 furan, 1 ester, 15 aldehydes, 3 ketones, and 9 alcohols. The contents of most of these compounds increased first and then decreased at 36 h, which were basically consistent with the enzyme activities of LOX, HPL, ADH and AAT. Subsequently, principal component analysis (PCA) results clearly showed that the fresh-cut yams for different yellowing processes were well distinguished by the volatile compounds. These results showed that the potential of HS-GC-IMS-based approaches to evaluate the volatile compound profiles of fresh-cut yam at different stages in the yellowing period.

Effects of High Hydrostatic Pressure Combined with Vacuum-Freeze Drying on the Aroma-Active Compounds in Blended Pumpkin, Mango, and Jujube Juice

A combination process of completely non-thermal processing methods involving high hydrostatic pressure (HHP) and vacuum-freeze drying (VFD) for producing a new snack from fruit and vegetable blends was developed, and the effect of the process on flavor quality was investigated. The HHP-VFD treatment did not significantly reduce volatile compound contents compared to single HHP or VFD. Gas chromatography-olfactometry showed that HHP-VFD raised the contents of floral-like volatile compounds (e.g., β-ionone) compared to the untreated sample. Sensory evaluation analysis confirmed that the overall liking was unchanged after the HHP-VFD treatment. The HHP-VFD combined treatment is effective in maintaining the flavor and extending shelf life, and is convenient for the portability and transportation of ready-to-drink juice.

Analysis of volatility characteristics of five jujube varieties in Xinjiang Province, China, by HS-SPME-GC/MS and E-nose

In this study, headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC/MS) was used to identify individual volatile compounds in five jujube varieties, and E-nose was used to identify their flavor. The results showed that a total of 45 volatile compounds were detected by GC-MS in the five varieties, and the proportion of acids was the highest (38.29%-54.95%), followed by that of aldehydes (22.94%-47.93%) and esters (6.33%-26.61%). Moreover, different varieties had obviously different volatile components. E-nose analysis showed that the R7 and R9 sensors were more sensitive to the aroma of jujube than other sensors. The strong response of R7 sensor was attributed to terpenes (or structurally similar substances) in jujube fruit, such as 1-penten-3-one, 2-octenal, (E)-2-heptanaldehyde, and (E)-2-hexenal and that of R9 sensor was attributed to the cyclic volatile components such as benzaldehyde, benzoic acid, and methyl benzoate. The multivariate data analysis (PCA, OPLS-DA, and HCA) of the results of GC/MS and E-nose showed that the five varieties could be divided into three groups: (1) Ziziphus jujuba Mill. cv. Huizao (HZ) and Z. jujuba cv. Junzao (JZ). Acids were the main volatile components for this group (accounting for 47.44% and 54.95%, respectively); (2) Z. jujuba cv. Hamidazao (HMDZ). This group had the most abundant volatile components (41), and the concentrations were also the highest (1285.43 µg/kg); (3) Winter jujube 1 (Z. jujuba cv. Dongzao, WJ1) and Winter jujube 2 (Z. jujuba cv. Dongzao, WJ2). The proportion of acids (38.38% and 38.29%) and aldehydes (40.35% and 38.19%) were similar in the two varieties. Therefore, the combination of headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry and E-nose could quickly and accurately identify the volatile components in jujube varieties from macro- and microperspectives. This study can provide guidance for the evaluation and distinguishing of jujube varieties and jujube cultivation and processing.

(E)-2-Heptenal in Soymilk: A Nonenzymatic Formation Route and the Impact on the Flavor Profile

Flavor is an essential quality characteristic of soymilk. (E)-2-Heptenal has a fatty and fruity flavor with the sensory threshold value of 13 μg/L in water. This study demonstrated that the formation of (E)-2-heptenal was independent of the lipoxygenase (LOX) and hydroperoxide lyase (HPL) activity as well as oxygen concentration but was related to the presence/absence of Fe²⁺ and chelators. In a dry matter base, soybean hypocotyls generated a much higher amount of (E)-2-heptenal than cotyledons. A phospholipid hydroperoxide was purified from the chloroform/methanol extract of soybean hypocotyls and was identified as 1-palmitoyl-2-(12-hydroperoxyoctadecadienoyl)-sn-glycerol-3-phosphatidylethanol-amine (12-PEOOH). The decomposition of 12-PEOOH in the presence of ferrous ions to form (E)-2-heptenal was studied in a model system. The rate of decomposition decreased sharply at pH values higher than 6, but the molar conversion of 12-PEOOH to (E)-2-heptenal increased with an increase of pH. At a constant pH of 5.8, the decomposition rate of 12-PEOOH was positively linearly related to the Fe²⁺ concentration, while the molar conversion to (E)-2-heptenal was 74% and independent of the Fe²⁺ concentration. The formation of radicals LOO^• and R^• showed similar pH and Fe²⁺ concentration dependence with those of (E)-2-heptenal. (E)-2-Heptenal displayed an enhancement of bean aroma and fruity flavor of soymilk at low concentrations, but a fatty flavor was noticed at high concentrations.

Effects of pretreatment methods and leaching methods on jujube wine quality detected by electronic senses and HS-SPME-GC-MS

Conventional analysis, electronic senses and HS-SPME-GC-MS were applied to evaluate the effects of pretreatment methods and leaching methods on jujube wine quality. Significant differences (p < 0.05) in the levels of alcohol content, color, taste and aroma were observed among all the jujube wine samples, in which the pulp and pectase fermented jujube wine was the best among all. Moreover, rather than taste, aroma is the most significantly (p < 0.05) affected. In regard to aroma, a total of 182 volatile compounds were identified by HS-SPME-GC-MS. It was found that the blended-into-pulp treatment and the leached-by-pectase treatment had notable positive effects on jujube wine. The pulp and pectase fermented jujube wines exhibited the highest concentration of total volatile compounds as well as alcohols, esters, acids and aldehydes. Thus, the optimal pretreatment method and leaching method for jujube wine fermentation are blended-into-pulp and leached-by-pectase respectively.

Characterization of Volatile Component Changes in Jujube Fruits during Cold Storage by Using Headspace-Gas Chromatography-Ion Mobility Spectrometry

Volatile components in jujube fruits from Zizyphus jujuba Mill. cv. Dongzao (DZ) and Zizyphus jujuba Mill. cv. Jinsixiaozao (JS) were analyzed under different cold storage periods via headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). Results identified 53 peaks that corresponded to 47 compounds and were mostly alcohols, aldehydes, esters, and ketones. Differences in the volatile components of jujube fruits were revealed in topographic plots and fingerprints. For DZ, 3-pentanone was the characteristic component of fresh fruits. After storage for 15 days, dipropyl disulfide became the most special substance. Moreover, when stored for 30 and 45 days, the fruits had some same volatile components, like 2-pentyl furan and diallyl sulfide. However, for DZ stored for 60 days, esters were the prominent constituent of the volatile components, simultaneously, some new alcohols appeared. For JS, 2-ethyl furan was the representative of fresh fruits, and 2-butoxyethanol content was the most abundant after 15 and 30 days of storage. Different from that in DZ, the content of ester in JS increased after storage for 45 days. Substances such as amyl acetate dimer, methyl salicylate, and linalool greatly contributed to the jujube flavor during the late storage period. Principal component analysis (PCA) showed that fresh samples and refrigerated fruits were effectively distinguished. Heat map clustering analysis displayed the similarity of volatile components in different samples and was in accordance with PCA results. Hence, the volatile components of jujube fruits can be readily identified via HS-GC-IMS, and jujube fruits can be classified at different periods based on the difference of volatile components.