A class of aroma compounds that can characterize the postharvest cold storage time of strawberry-flavored table grapes and their screening method

Abstract

The present invention discloses a type of aroma compound and screening method capable of characterizing the post-harvest cold storage time of strawberry-flavored fresh-eating grape fruits. The ripe fruits of strawberry-flavored fresh-eating grape varieties are used as test materials, and low-temperature cold storage treatment is performed. The types and contents of free and bound aroma substances in the peel and pulp at different cold storage times are determined, and finally the aroma compound capable of characterizing the post-harvest cold storage time of strawberry-flavored fresh-eating grape fruits is screened out. The present invention eliminates the influence of variety differences by mining significantly correlated aroma substances of multiple typical strawberry-flavored (3) varieties at the same time, and has strong reliability. The screened aroma compounds can specifically and accurately characterize the cold storage time of strawberry-flavored fruits. The method is a method with simple operation, good technical and economic performance, and has the advantages of large-scale detection.

Description

Technical Field

[0001] The invention relates to a type of aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored fresh grape fruits and a screening method, and belongs to the field of research and development of post-harvest cold storage technology for fruits. Background Art

[0002] The information disclosed in this background technology section is only intended to increase some understanding of the overall background of the invention, and should not be necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to ordinary technicians in this field.

[0003] Aroma substances are one of the important indicators of the intrinsic quality of grape fruits. Strawberry-flavored grape fruits have a strong strawberry aroma. Low-temperature refrigeration is one of the important ways to extend the supply period of grape fruits in the market and meet the demand for fruits in the off-season. During the low-temperature refrigeration process, the aroma quality of grape fruits will change to varying degrees, and the content of aroma substances will decrease, increase, remain unchanged or have no regularity. At present, post-harvest research on strawberry-flavored grapes mainly focuses on the changing characteristics of the aroma quality of fruits of a single variety, such as how much the compounds have decreased, etc., but there are few studies on the compounds that can be significantly correlated with the length of refrigeration time (i.e., aroma compounds that characterize the post-harvest refrigeration time of strawberry-flavored fresh-eating grape fruits). At present, the flavor change characteristics of some fruits during storage have been reported, and flavor substances that can evaluate the refrigeration time of fruits have been screened out. However, the aroma characteristics of different fruits are different, resulting in different effects of environmental factors on the content and types of aroma substances depending on the fruit type. For example, a total of 54 flavor substances were detected from the fruits of Lunnan white apricots, mainly ketones, alcohols and aldehydes; while up to 100 flavor substances were detected in grape fruits, mainly esters and terpenes. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention measured the concentrations of aroma substances in fruits of three typical strawberry-flavored grape varieties at different cold storage times, and used correlation analysis to screen out aroma compounds that were significantly correlated with cold storage time and had not been reported in the literature.

[0005] The technical solution adopted by the present invention is as follows:

[0006] In a first aspect of the present invention, a method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits is provided, the method comprising the following steps:

[0007] The ripe fruits of strawberry-flavored table grape varieties were used as test materials and were refrigerated at low temperatures. The types and contents of free and bound aroma substances in the peel and pulp at different refrigeration times were determined. Finally, the aroma compounds that can characterize the post-harvest refrigeration time of strawberry-flavored table grape fruits were screened out.

[0008] In one or some embodiments of the present invention, the mature fruits of three typical strawberry-flavored fresh-eating grape varieties (Kyoho, Summer Black and Hutai No. 8) are selected as test materials. The strawberry-flavored fresh-eating grape fruits all contain common aroma substances such as esters and C6 substances, and each variety also contains a small amount of specific aroma substances (substances that do not exist in other varieties). Kyoho, Summer Black and Hutai No. 8 are typical strawberry-flavored fresh-eating grape varieties that have been studied and reported. Selecting these three varieties to detect and screen the common aroma substances can well retain the aroma substances of the aroma type and remove the specific substances of each variety. Therefore, the screened substances more accurately represent strawberry-flavored grapes, and are also applicable to strawberry-flavored grapes other than these three varieties.

[0009] In one or some embodiments of the present invention, the temperature of the low temperature refrigeration treatment is 4-8°C, preferably 4°C.

[0010] In one or some embodiments of the present invention, the method for determining the type and content of flavor substances comprises the following steps:

[0011] (1) Extraction of free aroma substances

[0012] The fruit is peeled, the stem and seeds are removed, the peel is centrifuged to remove the pulp, the peel is placed in an extracting solution and extracted on a shaker; the supernatant is centrifuged and used for the determination of peel aroma substances; vitamin C is added to the pulp, crushed, centrifuged, filtered, and the supernatant is used for the determination of pulp aroma substances.

[0013] (2) Extraction of bound aroma substances

[0014] The solid phase column is activated with methanol and ultrapure water in turn, and the peel extract or juice supernatant is washed with ultrapure water and dichloromethane; methanol is added for elution, evaporated to dryness, dissolved with citric acid / phosphate buffer, glucosidase is added, and under the action of glucosidase, the released compounds are extracted by heat bath using SPME.

[0015] (3) Extraction of aroma substances

[0016] The extract, NaCl and internal standard were added into the headspace bottle, which was sealed with nitrogen gas; the extraction head was inserted into the extraction.

[0017] (4) Quantitative and qualitative analysis of aroma substances

[0018] Gas chromatography-mass spectrometry (GC-MS) was used to identify and quantify aroma compounds.

[0019] In one or some embodiments of the present invention, based on the types and content data of aroma compounds of strawberry-flavored grape varieties, correlation analysis is performed between the cold storage time (2-8 weeks of cold storage) and the compound content in different parts and forms of each variety, and significantly correlated compounds of each variety are screened out; then, the significantly positively correlated compounds that exist in common in the variety are used as the final characterization compounds; and the cold storage time is identified by detecting and comparing the contents of these substances in samples at different cold storage times.

[0020] In a second aspect of the present invention, a class of aroma compounds capable of characterizing the postharvest cold storage time of strawberry-flavored table grape fruits is provided, comprising 2-ethylhexanol, α-terpineol, 2-octanone, hexanal and butanol.

[0021] Preferably, the aroma compounds are 2-ethylhexanol and α-terpineol in the free state of the pulp, 2-octanone in the peel-bound state, hexanal and butanol in the pulp-bound state. The content of these substances gradually increases during the cold storage process, specifically: 8 weeks of cold storage> 6 weeks> 4 weeks> 2 weeks, and are easy to detect.

[0022] More preferably, the aroma compound is hexanal, and the content thereof exceeds 5 μg / kg.

[0023] Compared with the related art known to the inventor, one of the technical solutions of the present invention has the following beneficial effects:

[0024] The present invention eliminates the influence of variety differences by mining the significant correlation aroma substances of multiple typical strawberry aroma (3) varieties at the same time, has strong reliability, and the selected aroma compounds can specifically and accurately characterize the cold storage time of strawberry aroma fruits. The method is a method with simple operation, good technical and economic efficiency, and has the advantages of large-scale detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 Venn diagram: The number and names of compounds with significant positive correlation between the changes in the content of aroma substances in different grape varieties under low-temperature refrigeration and the refrigeration time. Note: FS: free skin, FP: free pulp, BS: bound to skin, BP: bound to pulp.

[0027] Figure 2 Venn diagram: The changes in the content of aroma substances in different grape varieties under low-temperature cold storage and the number of compounds that are significantly negatively correlated with the cold storage time. Note: FS: free skin, FP: free pulp, BS: bound to skin, BP: bound to pulp.

[0028] Figure 3 The average contents of five aroma compounds in three varieties that were significantly correlated with changes in refrigeration time during refrigeration.

[0029] Figure 4 The content of pulp-bound hexanal in Hutai No. 8 variety during cold storage. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0032] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0033] Example 1

[0034] The ripe fruits of three typical strawberry-flavored table grape varieties (Kyoho, Xiahei and Hutai No. 8) were used as test materials and refrigerated at 4°C. The types and contents of free and bound aroma substances in the peel and pulp after 0, 2, 4, 6 and 8 weeks of refrigeration were determined, and finally the aroma compounds that can characterize the post-harvest refrigeration time of strawberry-flavored table grape fruits were screened out. The specific method is as follows:

[0035] (1) Extraction of free aroma substances

[0036] The fruit was peeled, the stem and seeds were removed, and the peel was centrifuged to remove the pulp. To prevent oxidation, the peel was quickly placed in the extracting solution and extracted at 20℃ for 24h on a shaker. The supernatant was centrifuged at 4℃ (12000rpm) for 15min and used for the determination of peel aroma substances. Vc was added to the pulp, crushed in a juicer for 1min, centrifuged at 4℃ (10,000rpm) for 10min, filtered, and the supernatant was used for the determination of pulp aroma substances.

[0037] (2) Extraction of bound aroma substances

[0038] The solid phase column was activated with methanol and ultrapure water in turn, 25 mL of peel extract or juice supernatant was taken, and ultrapure water and dichloromethane (20 mL each) were taken for washing. 25 mL of methanol was added for elution, and the mixture was evaporated to dryness on a rotary evaporator at 40°C, and dissolved with 25 mL of pH=5 citric acid / phosphate buffer, and 2 mL of AR2000 enzyme was added. Under the action of AR2000 enzyme, the mixture was placed in a metal bath at 40°C for 16 hours. The released compounds were extracted with SPME.

[0039] (3) SPME procedure for aroma compound extraction

[0040] The extract, NaCl, and internal standard (2-octanol) were added to a 20 mL headspace bottle (1 / β=0.5), which was sealed with nitrogen. The 50 / 30-μm DVB / CAR / PDMS extraction head was inserted into the automated extraction system optimized in the early stage for extraction for 30 min.

[0041] (4) Quantitative and qualitative analysis of aroma substances

[0042] The aroma compounds were qualitatively and quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The compounds were qualitatively analyzed by the mass spectrometry of full ion scanning (Scan), and the grape compounds were qualitatively analyzed according to the chromatographic retention time and mass spectrum information of the standard samples, the comparison information of the NIST 2016 standard spectral library and related scientific research literature to determine the types of aroma compounds. The simulated solution was prepared. The grape juice simulated solution (1L): pH 3.9, 100g glucose, 100g fructose, 50mg Vc and 10g D-gluconolactone. The grape skin simulated solution (1L): pH 3.2, 3g tartaric acid, 50mg Vc and 10g D-gluconolactone. Standard sample: Take 25mL of grape juice and grape skin simulated solutions, add 25μL of mother solution and 20μL of internal standard respectively, and prepare various aroma mixtures into mother solution continuous gradient dilutions of 12 different concentrations to establish the standard curve of aroma substances and calculate the content of aroma compounds.

[0043] According to the types and content data of aroma compounds of three strawberry-flavored grape varieties, the correlation analysis between cold storage time and compound content in different parts (skin, flesh) and different forms (free state, bound state) of each variety was performed, and the significantly correlated compounds of each variety were screened out (significant P value <0.05, correlation coefficient |r|>0.6). Through Venn diagram analysis, it was found that there were only 5 common compounds in the three varieties that were significantly positively correlated with cold storage time ( Figure 1 ), while there was no compound with significant negative correlation with cooling time ( Figure 2 The five significant positively correlated compounds common to the three varieties were 2-ethylhexanol and α-terpineol in the free state of the pulp, 2-octanone in the bound state of the peel, hexanal and butanol in the bound state of the pulp ( Figure 1 ).

[0044] Further analysis of the average contents of the five substances in the three varieties revealed that only the hexanal content in the pulp-bound state was higher (more than 5 μg / kg), and showed a trend of gradual increase (2-8 weeks of refrigeration) ( Figure 3 ). Therefore, the hexanal bound to the pulp is taken as the most preferred characterizing compound. In order to verify whether the content of this substance gradually increases with the refrigeration time, the present invention analyzed its average content in the refrigerated Hutai-8 variety. The number of samples was 28, taken from different grape producing areas. The results showed that its content gradually increased during the 2-8 weeks of refrigeration, and was positively correlated with the refrigeration time ( Figure 4 ). Although the aroma quality is more affected by environmental factors than sugar and acid quality, the aroma substances are stable under the influence of fixed factors (refrigeration). Therefore, the selected characterization substances can effectively characterize the refrigeration time.

[0045] Similarly, the present invention also verified other varieties of strawberry-flavored fresh-eating grape varieties such as Kyoho and Summer Black, and found that their content gradually increased during 2-8 weeks of cold storage, and was positively correlated with the cold storage time.

[0046] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for screening aroma compounds that can characterize the post-harvest cold storage time of strawberry-flavored table grapes, characterized in that: The method comprises the following steps: The ripe fruits of strawberry-flavored table grape varieties were used as test materials and were refrigerated at low temperatures. The types and contents of free and bound aroma substances in the peel and pulp at different refrigeration times were determined. Finally, the aroma compounds that can characterize the post-harvest refrigeration time of strawberry-flavored table grape fruits were screened out.

2. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grapes according to claim 1, characterized in that: The mature fruits of three typical strawberry-flavored table grape varieties were selected as experimental materials, namely Kyoho, Xiahei and Hutai No.

8.

3. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 1, characterized in that: The temperature of low temperature refrigeration treatment is 4-8℃.

4. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grapes according to claim 1, characterized in that: The method for determining the type and content of aroma substances comprises the following steps: (1) extracting free aroma substances; (2) extracting bound aroma substances; (3) extracting aroma substances; and (4) quantitative and qualitative analysis of aroma substances.

5. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 4, characterized in that: step( The specific method of 1) is as follows: peel the fruit, remove the stem and seeds, centrifuge the peel to remove the pulp, put the peel into the extracting solution, and extract on a shaking table; centrifuge the supernatant and use it for the determination of the aroma substances in the peel; add vitamin C to the pulp, crush, centrifuge, filter, and use the supernatant for the determination of the aroma substances in the pulp.

6. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 4, characterized in that: The specific method of step (2) is as follows: the solid phase column is activated with methanol and ultrapure water in turn, the peel extract or juice supernatant is taken, and ultrapure water and dichloromethane are taken for washing; methanol is added for elution, evaporated to dryness, dissolved with citric acid / phosphate buffer, glucosidase is added, and under the action of glucosidase, the released compound is extracted by heat bath using SPME.

7. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 4, characterized in that: The specific method of step (3) is: adding the extract, NaCl and internal standard into the headspace bottle, filling with nitrogen and sealing; inserting the extraction head into the extraction.

8. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 4, characterized in that: The specific method of step (4) is: using gas chromatography-mass spectrometry (GC-MS) to qualitatively and quantitatively identify the aroma compounds.

9. The method for screening aroma compounds capable of characterizing the post-harvest cold storage time of strawberry-flavored table grape fruits as claimed in claim 1, characterized in that: According to the types and content data of aroma compounds of strawberry-flavored grape varieties, correlation analysis was conducted on the cold storage time and compound content in different parts and forms of each variety, and significantly correlated compounds of each variety were screened out; the significantly positively correlated compounds that existed in common in the varieties were taken as characterizing compounds.

10. A class of aroma compounds that can characterize the post-harvest cold storage time of strawberry-flavored table grapes, characterized in that: The aroma compounds include 2-ethylhexanol and α-terpineol in the free state of pulp, 2-octanone in the peel-bound state, hexanal and butanol in the pulp-bound state; preferably, the aroma compound is hexanal in the pulp-bound state.

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