Abstract: Background and Objective: Grape brandy and apple cider both have proper varieties for making wine. Faced with so many jujube varieties, in this study determined the suitable choice of jujube variety for brewing high quality brandy. Methodology: Odor activity value, principal component analysis and cluster analysis were used to compare the feature and flavor compounds of eleven kinds of jujube brandies. Data were statistically analyzed by the software of SPSS. Results: Esters are the most important odor-active compounds of jujube brandy, followed by acids and alcohols, specifically including ethyl caproate, ethyl octanoate, ethyl benzoate, ethyl decanoate, octanoic acid, decanoic acid, lauric acid and phenethyl alcohol. Fuping, Xingtang and Huizao jujube brandy had the most odor-active compounds, Junzao had the most unique aroma. Fuping jujube brandy rank first on the total peak area of aroma, followed by Huping, Cangzhou and Yuanling. Conclusion: Jujube variety of Fuping, Huping and Cangzhou are suitable for brewing brandy.
INTRODUCTION
Jujube brandy is produced by solid-state fermentation, solid-state distillation and aging, using Chinese jujube as raw material1-3. However, the development of jujube brandy market is severely restricted because of absence of mature production technology4-6. The brewing technology of grape and apple brandy has already been quite mature and suitable high-quality varieties for brewing wine have been clear7-8. For example, Cabernet Franc, Cabernet Sauvignon, Chardonnay and Riesling are good grape choice for brewing wine and Breakwellings seedling, Nehou, Reine Des Hative and Taylors are suitable apple choice9-11. Faced with a wide variety of jujube, it is essential to determine suitable kinds of jujube for brewing brandy, which is one of the focuses of the jujube brandy manufacturer12-15.
The variety and quality of raw material directly decide the quality of brandy16-17. Plenty of reducing sugar is necessary for fermentation, amino acids are important precursors of many aroma compounds18-19. Fruit ingredient composition is one of the important sources of brandy aroma20-22. Content of sugar, amino acids, flavor compounds in different jujube are not the same due to the different varieties and origin. Choosing the suitable jujube varieties is the key to brew high quality jujube brandy.
Alcohol content and aroma components of jujube brandy are the main assessment criteria. Wine aroma, one of the most important characteristics of wine quality, represents a good balance of several hundred volatile compounds. The quality of wine is closely related to its aroma components23-24. Different groups of volatile compounds, such as alcohols, esters, aldehydes, lactones, terpenes and phenols, have been identified in wines in a wide concentration range. These groups affect wine aroma even at low concentrations. Among the volatiles, alcohols and esters have the highest contents in wines. Esters are important constituents of wine aroma and they possess high fruity nuances25. Higher alcohols are the main byproduct in the fermentation process, can make wine full bodied and mellow26-27. In jujube brandy, isoamyl alcohol and isobutanol are the major higher alcohols, then propanol, butanol and pentanol28-29. Excessive higher alcohols make wine taste bitter, may result in a headache, dizziness and vomiting, low higher alcohols content let the smell thin and heavy water, so proper higher alcohols are one of the evaluation criteria of distillation wine quality30.
The aim of this study was to determine the feature of jujube brandies from different varieties and relationship between jujube variety and aroma compounds of jujube brandies. Odor activity value, principal component analysis and cluster analysis were used to compare the feature and flavor compounds of eleven kinds of jujube brandies, to find suitable jujube choice of making brandy and improve the quality of jujube brandy.
MATERIALS AND METHODS
Samples
Eleven kinds of Jujube varieties: Junzao (Shanxi, 34°36'-40°44' N, 110°15'-14°32' E), Huping (Shanxi, 34°36'-40°44' N, 110°15'-114°32' E), Fuping (Fuping, 38°9'-39°7' N, 113°45'-114°31' E), Cangzhou (Cangzhou, 38°3' N, 116°83' E), Xingtang (Xingtang, 114°23' N, 38°19' E), Huizao (Xinjiang, 34°25'-48°10' N, 73°40'-96°18' E), Hetian (Xinjiang, 34°25'-48°10' N, 73°40'-96°18' E), Goutou (Shanxi, 33.71 N, 110.35 E), Linze (Gansu, 39°13' N, 100°17' E), Xinzheng (Xinzheng, 34°16'-34°39' N, 113°30'-113°54' E) and Yuanling (Shandong, 34°22'-38°23' N, 114°19'-122°43' E). The jujubes selected for this study were harvested in 2015. Jujube brandy is produced by solid fermentation, solid distillation and aging (The average alcohol is 50%), which wine making process was that usual in China1. The study was carried out in September, 2016, 3 replications have been done in each test.
Jujube brandy brewing process: Brewing process of jujube brandy
| • | Shredded jujube was added to equal water, then soaked 5-6 h |
| • | Boiled, added 1/6 rice hull after cooling |
| • | About 0.5% yeast was taken in 100 mL of 2% glucose water, 40°C water bath for 30 min. Then activated yeast was inoculated, maintained fermentation for 6 days under 28°C |
| • | Jujube brandy sample was obtained by distilling fermentation materials 2 times |
Analysis of enological parameters: The reducing sugar, total acid and alcoholic degree were evaluated following the OIV official analytical methods.
GC-FID analysis of higher alcohols: Higher alcohols of jujube brandy were detected by GC-FID (Agilent 7890A Gas Chromatograph, Santa Clara, USA), quantified using an external standard. A DB-FFAP column (60 m×0.25 mm ID and 0.25 μm film thickness) was used for separation. The working parameters were as follows: Injector temperature of 220°C and FID temperature of 300°C.
| Table 1: | Regression equation, linear range and detection limit of higher alcohols |
The initial temperature was 45°C for 3 min, which was increased to 130°C at a rate of 6°C min–1, then increased to 140°C at a rate of 2°C min–1. The temperature was further raised to 220°C at 15°C min–1. The carrier gas had a flow rate of 2.0 mL min–1. Samples of 0.7 μL were injected using the split mode of 30:1. Ethanol of jujube brandy was detected by alcohol meter. Regression equation, linear range and detection limit show as Table 1.
SPME-GC-MS analysis of flavor compounds: Jujube brandy was diluted by distilled water (10% alcohol content). Sodium chloride (1 g) was added to 7.5 mL of sample solution in a 20 mL sealed glass vial. The sample was exacted at 40°C for 40 min with 50/30 μm DVB/CAR/PDMS fiber, then used to GC-MS analysis.
Flavor compounds of jujube brandy were detected by GC-MS. The contents of flavor compounds were quantified using an internal standard (3-octanol, 99%, Sigma-Aldrich). Wine volatile compounds were analyzed using an Agilent 5975 Mass Spectrometer coupled to an Agilent 7890A Gas Chromatograph (Agilent, Santa Clara, USA). A DB-WAX column (60 m×0.25 mm ID and 0.25 μm film thickness) was used for separation. The working parameters were as follows: Injector temperature of 250°C, EI source of 230°C, MS Quad of 150°C and transfer line of 250°C. The initial temperature was 50°C for 3 min, which was increased to 80°C at a rate of 3°C min–1. The temperature was further raised to 230 at 5°C min–1 and maintained at 230°C for 6 min. The carrier gas had a flow rate of 1.0 mL min–1. Samples were injected using the splitless mode. A mass range of 50-550 m/z was recorded at one scan sec–1. Flavor compounds were identified by Nist 2005 library of GC-MS.
Statistical analysis: Every determination was repeated 3 times and 2 replications of one treatment were performed. All the data were statistically analyzed by the software of SPSS 17.0 (SPSS Inc., Chicago, IL, USA), prominent differences levels including 0.05 (a)-significant differences (p<0.05) and 0.01 (A)-highly significant differences (p<0.01).
RESULTS AND DISCUSSION
Comparison of enological parameters: Significant difference appeared about the concentration of reducing sugar, total acid and alcohol in different kinds of jujube varieties (Table 2, p<0.05). Reducing sugar in raw material is power and energy for wine fermentation, lower content of reducing sugar directly influence wine fermentation and the formation of alcohol31. The content of reducing sugar can be divided into three levels from high to low: Fuping, Cangzhou, Xingtang as the first level (49.049-52.843 g/100 g), Xingtang has the highest content, Huizao, Linze, Xinzheng, Yuanling as the second level (38.358-46.178 g/100 g), Junzao, Huping, Hetian, Goutou as the third level (26.191-31.397 g/100 g) and Junzao has the lowest content. Jujube can also be divided into three levels according to total acid concentration. Total acid concentration of Goutou jujube is obviously higher than other varieties (0.83 g/100 g), Junzao, Fuping, Xingtang, Hetian and Linze maintained at about 0.50 g/100 g, the rest jujube varieties with total acid 0.20 g/100 g. Under the same fermentation and one-time distillation condition, Huping has the highest alcohol content (34°C), followed by Hetian, Junzao, Huizao, Goutou, Fuping and Cangzhou, reach 25-30°C, while Xingtang, Linze, Xinzheng and Yuanling has the lowest alcohol content. Therefore, Fuping, Cangzhou, Xingtang jujube had more power and energy for wine fermentation while Huping and Hetian jujube are beneficial for alcohol production. In the previous study, the reducing sugar content of jujube to approximately 42% is very suitable for fermenting alcoholic beverages1. It seems Fuping, Cangzhou, Xingtang jujube are better choice for brewing brandies.
| Table 2: | Comparison of enological parameters |
Values are the Means±standard deviation (n = 3) |
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Comparison of higher alcohols of jujube brandy: The total content of higher alcohols can be divided into three grades: Cangzhou and Huizao take the first grade with content of above 1.9 g L–1, Junzao, Huping, Xingtang, Goutou and Linze take the second grade with content of 1-2 g L–1, Fuping, Hetian, Xinzheng and Yuanling take the third grade with content of 1 g L–1.
Isopropanol was not found in Junzao and Huping, n-butanol can only be detected in Hetian, Goutou, Linze and Xinzheng (Table 3). Excessive and low higher alcohols concentration are not suggested, higher alcohols content of high quality jujube brandy were less than 2 g L–1 30, Junzao, Huping, Xingtang, Goutou and Linze jujube bandies (the second grade) had suitable content of higher alcohols.
Comparison of OAV: Esters are the most important odor-active compounds for jujube brandy, followed by a cids and alcohols, specifically including hexenoic acid ethyl ester, octanoic acid ethyl ester, phenylpropionic acid ethyl ester, decanoic acid ethyl ester, octanoic acid, decanoic acid, lauric acid and phenethyl alcohol. In order to understand the contribution of each compound to odor quality, it is not sufficient just to know whether these compounds are present or absent, one also must have knowledge of how they are perceived at given concentrations32. OAV is a measure of evaluating a compound contributes to aroma and when OAV is greater than 1, it is believed contribute to the aroma, when OAV is greater than 10, it is considered an important aroma component33. The variety of Fuping, Xingtang and Huizao held the most odor-active compounds (11), especially compounds of OAV>500 in Fuping surpass the other two and Goutou showed the least odor-active compounds of all the varieties (7). According to the comparison of odor-active compounds, the rank of jujube varieties is Fuping, Huizao, Xingtang, Cangzhou, Huping, Xinzheng, Yuanling, Goutou, Junzao, Linze, Hetian (Table 4).
Comparison of aroma compounds of jujube brandy: About 194 kinds of flavor compounds were detected in different varieties of jujube brandies, including 70 esters, 14 alcohols, 6 acids, 34 aldehyde and ketone and 34 hydrocarbons (Table 6). Main flavor compounds of jujube are esters, aldehyde and ketone, acids and hydrocarbons. Total peak area of aroma rank: Fuping>Huping, Cangzhou, Yuanling>Hetian, Linze, Huizao, Xingtang, Goutou>Xinzheng, Junzao (Fig. 1).
Esters: Main esters in jujube brandy are ethyl esters of lauric acid, decanoic acid, octylic acid and nonanoic acid, followed by ethyl esters of undecanoic acid, tetradecanoic acid, heptanoic acid and hexanoic acid. About 107 kinds of esters were detected in different varieties of jujube brandies, including 12 straight-chain ethyl esters, 3 branched-chain acid esters, 12 branched-chain alcohol esters, 10 unsaturated esters, 11 aromatic esters, 4 acetate, 6 methanol esters. Straight-chain ethyl esters were also main esters. Fuping has the most ester peak area, followed by Huping and Yuanling.
| Table 3: | Comparison of higher alcohols of different kinds of jujube brandies |
Values are Mean±SD, letters (a, b, c, d, etc) represent significance difference (p<0.05) in total values, Unit: g L–1 |
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| Table 4: | OAV value of eleven jujube varieties |
Four unique compounds can be found in Junzao, including Benzoic acid, ethyl ester, Ethyl 9-decenoate, Ethyl trans-2-decenoate and Benzoic acid, 2-hydroxy-, ethyl ester. Butanoic acid, 3-methyl-, ethyl ester, 10-Bromodecanoic acid, ethyl ester, Nonanoic acid, 9-bromo-, ethyl ester and Decanedioic acid, diethyl ester can only be detected in Yuanling, Xingtang, Cangzhou and Fuping, respectively (Table 5).
Alcohols and acids: Main alcohols in jujube brandy are isopentanol, phenylethanol, isobutanol and hexanol. Cangzhou and Huping jujube brandy have more unique alcohols. Cangzhou has unique trans-2-Undecen-1-ol, 1-Decanol and (Z)-3-Nonen-1-ol. Huping has 1-Octanol and 1-Dodecanol. Junzao has Benzyl alcohol. Main acid in jujube brandy are decanoic acid and lauric acid, followed by octoic acid.
| Table 5: | Comparison on peak area of aroma compounds of different kinds of jujube brandies |
Peak area values are expressed in scientific notation, letters (a, b, c, d, etc) represent significance difference (p<0.05) in total values |
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| Table 6: | Comparison of flavor compounds of jujube brandy |
| Fig 1: | Comparison of flavor peak area of different kinds of jujube brandies Bars are Mean±SD, Letters (a,b,c,d, etc) represent significance difference(p<0.05) |
Types and content of acids in Junzao and Xingtang jujube brandy were significantly higher than other varieties. Heptanoic acid was unique for Junzao and Goutou brandy. But no acids were detected in Huping brandy.
Aldehydes and ketones: Main aldehydes and ketones in jujube brandy are 2-Tridecanone, 2-Undecanone, Decanal, Furfural and (E)-1-(2,6,6-trimethyl-1,3-cyclohexadien-1-yl)-2-Buten-1-one. Most unique aldehydes and ketones are unsaturated. Xingtang has 6-methyl-5-Hepten-2-one, Huping has (E)-2-Nonenal, Junzao has 6-methyl-5-Hepten-2-one and (E)-2-Tridecenal, Cangzhou has 8-oxo-2-Nonenal, Linze has 5-Methyl-2-phenyl-2-hexenal. For saturated aldehydes and ketones, Tetradecanal and Undecanal were only detected in Linze and Yuanling, respectively. For unique aldehydes and ketones, Junzao and Xinzheng have 3,4-dihydro-2H-1-Benzopyran-2-one and 3-methyl-2(3H)-Benzofuranone. Besides these, Junzao has more unique aldehydes and ketones, like 2-Nonanone and (E)-6,10-dimethyl-5,9-Undecadien-2-one. Linze has unique 1-Methyl-2-phenylpiperidin-4-one, Huping has 2-Pentadecanone. In addition, 3 characteristic aldehydes and ketones((E)-6,10-dimethyl-5,9-Undecadien-2-one, alpha-ethylidene-Benzeneacetaldehyde and dihydro-5-pentyl-2(3H)-Furanone) were also found in jujube brandy.
Hydrocarbon and others: Main hydrocarbon in jujube brandy is Styrene, then Pentadecane. Type and content of hydrocarbon in Junzao were obviously higher than others. For other flavor compounds, main flavor coponents are Naphthalene, followed by Methoxy-phenyl-oxime. Many kinds of flavor compounds were found, like 3 Terpenoids (longifolene, V6-cedrene and thujopsene), 2 furans (2, 5-dihydro-furan and 2-amyl-furan), 3 kinds of phenols (3, 4-dimethyl-phenol, 2,4-bis (1,1-dimethylethyl)-phenol and phenol), 1 ether (Vinyl Ether) and anethole.
PCA and cluster analysis of flavor compounds: The PCA was conducted using the concentrations of main volatile compounds in jujube brandy samples from different varieties as analytical variables. This was done to reduce the dimensionality within the data set, to analyze the main sources of variation within the data set and to detect similarities and/or differences among wine samples. This demonstrated the effects of different varieties on the volatile composition of jujube brandy, as well as the correlations/relationships between compounds and wine samples.
A bi-plot showing the score plots as well as the loadings plots of the first two principal components (PC1 and PC2, respectively), PC1 and PC2 accounted for 87.045% of the total variability for jujube brandy samples, with 73.054 and 13.991% of the variability being explained by PC1 and PC2, respectively as provided by Fig. 2.
| Fig. 2: | Main components scattered diagram of flavor compounds and load scatter plot |
For the observed sample distribution, the loadings show the relative importance of each individual volatile compound. Generally, the distribution of the different volatiles will reflect the differences observed among jujube brandies from different varieties.
Eleven jujube brandies were all distributed in the positive axis of PC1. Wine samples of Huping, Fuping, Cangzhou, Hetian, Linze, Yuanling had a relation with hexanoic acid ethyl ester (A1), octylic acid ethyl ester (A2), heptanoic acid ethyl ester (A4), pelargonic acid ethyl ester (A5), 3-methyl-1-butanol (A7), 1-hexanol (B1), 2-undecanone (D2) and 2-tridecanone (D3). Similar methods were used and reported in previous studies34. In the loadings plots of compounds, all kinds of flavor components were distributed in four quadrants. Phenylethyl alcohol (B2), dodecoic acid (B2), beta-Damascenone (D4) gathered, which were distributed in the second quadrant. Tetradecanoic acid ethyl ester (A6), octanoic acid (B3), decanal (D1) gathered, which were distributed in the third quadrant (Fig. 2).
| Fig. 3: | Cluster analysis on flavor compounds of eleven jujube brandies Sample 1: Junzao, sample 2: Huping, sample 3: Fuping, sample 4: Cangzhou, sample 5: Xingtang, sample 6: Huizao, sample 7: Hetian, sample 8: Goutou, sample 9: Linze, 10: Xinzheng, sample 11:Yuanling |
| Table 7: | Cluster analysis on flavor compounds of jujube brandy |
| , | |
Cluster analysis was carried out in order to evaluate the number of subsets of similar samples appearing in the complete data set (Table 7). We can clearly recognize the three main clusters, (1) Huping, (2) Fuping and (3) The rest of the wine samples, which represent the rest of the wine samples held high similarity and they were obviously different with wine samples of Huping and Fuping wine samples (Fig. 3).
In the current study, fruit variety is very important in making wine and brandy. Nutrients difference cause different flavor and quality of liquor. Similar findings were reported in previous studies35-37.
CONCLUSION
Odor activity value, principal component analysis and cluster analysis were used to compare the feature and flavor compounds of eleven kinds of jujube brandies. Odor-active compounds of jujube brandy include ethyl caproate, ethyl octanoate, ethyl benzoate, ethyl decanoate, octanoic acid, decanoic acid, lauric acid and phenethyl alcohol. Fuping, Xingtang and Huizao jujube brandy had the most odor-active compounds, Junzao had the most unique aroma. Fuping jujube brandy rank first on the total peak area of aroma, followed by Huping, Cangzhou and Yuanling. The aroma of Huping and Fuping jujube brandy were unique and the other brandy samples had high similarity by cluster analysis. Therefore, Fuping, Huping and Cangzhou jujube are found suitable for brewing brandy, which is beneficial for improving the quality of jujube brandy.
SIGNIFICANCE STATEMENTS
This study discovered the key and unique flavor compounds of different jujube brandies that can be beneficial for highlighting the feature and characteristic. This study help the researcher to uncover the critical areas of selection of brewing varieties that many researchers were not able to explore. Thus a new theory on brewing characteristics may be arrived at.
ACKNOWLEDGEMENTS
This research was supported by the National Natural Science Foundation of China:
| • | Research of Methanol and Fusel Oil Formation Mechanism and Control Measures in Traditional Chinese Jujube Brandy (Founding No.31171725) |
| • | Study on the flavor character and its formation mechanism of Chinese date brandy (Funding No. 31371815) |