Commercial table grape classification method based on saccharic acid content

Abstract

The invention provides a commercial table grape classification method based on saccharic acid content, which comprises the following steps: selecting 76 table grape varieties with higher domestic market share, measuring the contents of soluble solids, titratable acid, glucose, fructose, malic acid, citric acid and tartaric acid, and analyzing the correlation, main components and taste contribution values of the table grape varieties; hierarchical clustering analysis is carried out by using different saccharic acid types, and it is found that grape varieties can be divided into high-sugar high-acid varieties, high-sugar low-acid varieties, low-sugar high-acid varieties and low-sugar low-acid varieties only through the contents of fructose and tartaric acid, so that a simpler, more convenient and more reliable grape classification method is established. Theoretical basis and selection reference are provided for different consumer groups to select and purchase grapes from the aspects of health, taste, quality requirements and the like.

Description

Technical Field

[0001] The invention relates to the field of classification of commercial fresh-table grapes, and in particular to a classification method of commercial fresh-table grapes based on sugar and acid content. Background Art

[0002] Grape (Vitis vinifera L.) is one of the most important economic fruit crops in the world. It has high economic benefits and nutritional value and is widely cultivated around the world. All grape varieties can be roughly divided into three categories according to their consumption: winemaking, dried grapes and fresh-eating grapes. Among them, fresh-eating grapes are the most important subject of the grape industry and are favored by consumers.

[0003] The sweet and sour taste of fruit depends on the content and composition of the sugar and acid components it contains, and is also an important component of its unique flavor. Sweetness and sourness are the intuitive feelings formed by humans for the content and composition of different sugar and acid components, which are mainly determined by the content of soluble sugars and organic acids. There are large differences in the sugar and acid components and contents of different types of fruits, and these differences are the key material basis for the unique flavor of fruits. For example, for fruits with high sweetness such as apples, lychees and pineapples, even if the total sugar content is similar, we can easily identify their quality differences by tasting the difference in sourness in the pulp. In recent years, with the improvement of people's living standards, the output and sales of fresh grapes have also shown an increasing trend year by year. According to the China National Statistical Yearbook, China's grape production increased from 14.998 million tons to 15.378 million tons from 2021 to 2022, a year-on-year increase of 2.53%. At present, the varieties of fresh grapes on the market are becoming more and more abundant, and consumers' choices of varieties have also become diversified, but consumers lack specific information about these varieties, resulting in more time and energy to choose due to different consumption levels, taste preferences and health conditions.

[0004] The existing technical problems are that grape quality is mainly evaluated by the soluble solids and titratable acid content in the sugar and acid components of the grape fruit. The quality and classification of grape varieties are inaccurate, and there is a lack of specific information on fresh grapes on the market. As a result, consumers have to spend more time and energy to make choices due to different consumption levels, taste preferences and health conditions. Summary of the invention

[0005] The present invention provides a classification method for commercial fresh-table grapes based on sugar and acid content, selects 76 fresh-table grape varieties with a high domestic market share, measures the contents of soluble solids, titratable acid, glucose, fructose, malic acid, citric acid and tartaric acid, and analyzes their correlation, principal component and taste contribution value; hierarchical cluster analysis is performed using different types of sugar and acid, and it is found that grape varieties can be divided into four categories of high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid only by fructose and tartaric acid content, thereby establishing a simpler, more convenient and reliable grape classification method. Provides a theoretical basis and selection reference for different consumer groups to purchase grapes from the perspectives of health, taste and quality requirements.

[0006] In one aspect, the present invention provides a method for classifying grapes based on soluble sugar and organic acid content.

[0007] At present, in the planting, production and sales of grapes, the demand increases with the improvement of social living standards, but the quality of grapes is uneven. Some varieties have less sugar, low sweetness and poor taste; some varieties have more sugar, high sweetness and good taste. At the same time, consumers' needs also vary due to various factors such as preferences, tastes, and physical conditions. This leads to people spending more time and energy to choose satisfactory varieties. It can be seen that screening a fast and accurate grape classification method for consumers is of great significance to people's daily consumption choices.

[0008] Consumers' understanding of grapes is mostly limited to popular varieties such as 'Sunny Rose', 'Kyoho', 'Summer Black' and 'Moli Xiang', or the two categories of grapes and raisins, or the distinction between them based on fruit colors such as green, red and black. They are not clear about the specific characteristics of grape varieties, especially the sugar and acid taste of different grape varieties. Sugar and acid are the most direct factors affecting the quality and taste of grapes. Therefore, it is urgent to provide a classification method based on the sugar and acid content of grape fruits, which can classify grape varieties and guide consumers on how to choose.

[0009] The existing grape classification method usually uses soluble solids and titratable acid content to evaluate grape quality, which is inaccurate in the classification of grape varieties. This is because grapes contain a variety of soluble solids such as monosaccharides and disaccharides, as well as a variety of titratable acids. Some grapes have a low soluble solids content but still taste very sweet, while some grapes have a high proportion of soluble solids but are still low in sugar; some grapes have a low proportion of titratable acid, but the fruit is very sour, while some grapes have a titratable acid content of half but the sourness is not obvious.

[0010] It can be seen that the existing classification method cannot accurately distinguish grapes into four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid. It can only divide them into two types: high soluble solids content and low soluble solids content.

[0011] Therefore, we need to find a more suitable method to classify grapes, which can accurately divide grapes into four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid, to help consumers (such as diabetics, pregnant women, children and other special groups) accurately select suitable grapes.

[0012] Further, in the method, the grapes include interspecific hybrids: 'Amorai Rose', 'Jungle Rose', 'Crisp Little Red', 'Eastern Star', 'Fuji Glory', 'Gao Qi', 'Han Xiang Mi', 'Red Fuji', 'Red King', 'Red Xia Yin', 'Hu Tai No. 8', 'Golden Queen', 'Golden Finger', 'Golden Field Beauty Finger', 'Kyoho', 'Giant Rose', 'Ju Sheng No. 1', 'Romantic Beauty', 'Roland Rose A', 'Roland Rose B', 'Madonna Ruby', 'Beauty Finger', 'Moldova', 'Queen Nina', 'Dream of Grapes', 'Qinlong Big Spike', 'Shaoxing No. 1', 'Deep Red Seedless', 'Late Kangbao', 'Victoria', 'Future Star', 'Wink', 'Joy', 'Summer Black', 'Xia Yi', 'Wish', 'Xiong Bao' , 'Sunshine Rose', 'Sunshine Thirteen', 'Yinhong', 'Yongfeihong', 'Yonglufei', 'Yongxiangyu', 'Yongzaohong', 'Yongzaolu', 'Yongzijing', 'Yuxuan No. 5', 'Yuxuan No. 1', 'Jade Finger', 'Zaocuixiangti', 'Zaoxiahei', 'Zhichangrongfeng', 'Zhuangyuanhong', 'Zuijinxiang'; Eurasian population: 'White Aolin', 'White Rosa', 'Unicorn' ', 'Royal Rose', 'Black Balado', 'Black Finger', 'Red Balado', 'Red Rosa', 'Royal', 'Koshu Sanshaku', 'Kaneda Rose', 'Seto Koshi', 'Sapphire', 'American Red Grape', 'Sweet Sun', 'Early Kangbao', 'Early Sweet', 'Purple Globe', 'Purple Sweet Seedless'; East Asian population: any one or more of 'Spring Breeze' and 'Thorn Grape'.

[0013] Furthermore, in the method, the soluble sugar includes any one or more of glucose, fructose and soluble solids, and the organic acid includes any one or more of tartaric acid, malic acid, citric acid and titratable acid.

[0014] Glucose, fructose, malic acid, citric acid and tartaric acid are the main sugar and acid components of grapes. Among them, glucose and fructose are the main sugars in grapes, and tartaric acid is the organic acid with the highest content.

[0015] Furthermore, the soluble sugar and organic acid refer to soluble solids and titratable acids, or one or more of glucose, fructose, tartaric acid, malic acid and citric acid, or glucose and tartaric acid, or fructose and tartaric acid.

[0016] Soluble solids and titratable acid are widely used in the production to evaluate the quality of grapes, and are also convenient to measure. However, when grapes are classified according to this combination, only the content of soluble solids in grapes can be distinguished, and the difference in the content of its main components, glucose and fructose, and titratable acid cannot be further distinguished. Therefore, the content of soluble solids cannot determine the taste of grapes. For example, among grape varieties with higher soluble solids content, the content of titratable acid varies greatly, which is not very helpful in people's actual life applications.

[0017] Furthermore, the soluble sugar and organic acid are specifically fructose and tartaric acid.

[0018] Research has shown that this classification method accurately divides 76 grape varieties into four groups: high sugar and high acid, high sugar and low acid, low sugar and high acid, or low sugar and low acid. The sugar and acid content of the grape varieties in each group meets the standards. This method can help consumers quickly select target products.

[0019] Furthermore, the classification method comprises the following steps:

[0020] (1) The components and contents of soluble sugar and organic acid of each grape were measured by refractometer and neutralization titration;

[0021] (2) Based on the test results, each type of grape is classified into high sugar and high acid, high sugar and low acid, low sugar and high acid, or low sugar and low acid.

[0022] In some embodiments, the cluster analysis classification method specifically comprises: performing hierarchical clustering on the original data using the hclust package in the R language, using the ward method as the clustering method, and then calling the ggtree package to convert the clustering results into circles.

[0023] On the other hand, the present invention provides a classification marker combination for grape fruit, including soluble solids and titratable acid, or any one or more of glucose, fructose, tartaric acid, malic acid and citric acid, or glucose and tartaric acid, or fructose and tartaric acid.

[0024] Furthermore, the classification marker combination includes fructose and tartaric acid.

[0025] In another aspect, the present invention provides use of a marker detection reagent for preparing a reagent for improving the accuracy of grape fruit classification, wherein the marker includes fructose and tartaric acid, and the grape fruit classification includes four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid.

[0026] Furthermore, the markers include fructose and tartaric acid.

[0027] In another aspect, the present invention provides a use of a composition for preparing a marker for evaluating the sugar and acid taste of grape fruit, wherein the composition comprises fructose and tartaric acid.

[0028] In another aspect, the present invention provides use of fructose for preparing a marker for evaluating the sugar taste of grape fruit.

[0029] In another aspect, the present invention provides use of tartaric acid for preparing a marker for evaluating the sour taste of grape fruit.

[0030] The present invention has the following advantages and effects:

[0031] 1. Characterize the composition and content of sugar and acid components in ripe fruits of different fresh-table grape varieties, and find that glucose and fructose are the main sugars in grape fruits, and the organic acid with the highest content is tartaric acid; at the same time, it is proved that there is a significant positive correlation between glucose and fructose, and between the three acids, but there is no correlation between sugar and acid components, and the main difference between different varieties comes from the acid component content;

[0032] 2. After evaluating and verifying the effects of sugar and acid composition and content on fruit flavor, it was found that the taste and flavor of ripe grapes are mainly provided by tartaric acid and fructose;

[0033] 3. It was found that only by using fructose and tartaric acid, 76 types of grapes can be accurately divided into four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid. This classification method is more accurate, reliable and practical than the existing classification method;

[0034] 4. It was found that the classification method based on fructose and tartaric acid is not only applicable to the 76 types of grapes, but also to other different types of grapes. They can be accurately divided into four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid. This provides a theoretical basis and selection reference for different consumer groups to purchase grapes from the perspectives of health, taste and quality requirements.

[0035] 5. Provide theoretical basis and selection reference for different consumer groups to purchase grapes from the perspectives of health, taste and quality requirements, and select low-sugar and low-acid grape varieties that are beneficial to the health of the middle-aged and elderly people, such as "Qinlong Dasui", "Victoria" and "Royal" varieties, which are more suitable for middle-aged and elderly consumers who pay more attention to health; select high-sugar and high-acid or high-sugar and low-acid grape varieties with rich taste enjoyment for young people, such as high-sugar and high-acid varieties "Chunfeng", "Cui Xiaohong", high-sugar and low-acid varieties "Hanxiangmi", etc., which are more suitable for young people who pursue taste enjoyment; different groups of people can also choose high-acid or low-acid grape varieties according to their own needs for sour taste. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Shown are the ratios and distributions of sugar and acid components of 76 grape varieties of the present invention;

[0037] Figure 2 Shown is the correlation analysis of sugar and acid components of 76 grape varieties of the present invention;

[0038] Figure 3 Shown is the principal component analysis of sugar and acid components of 76 grape varieties of the present invention;

[0039] Figure 4 Shown is the cluster analysis of soluble solids and titratable acid of 76 grape varieties of the present invention;

[0040] Figure 5 Shown is the cluster analysis of glucose, fructose, malic acid, tartaric acid and citric acid contents of 76 grape varieties of the present invention;

[0041] Figure 6 Shown is the cluster analysis of glucose and tartaric acid content of 76 grape varieties of the present invention;

[0042] Figure 7 Shown is the cluster analysis of fructose and tartaric acid contents of 76 grape varieties of the present invention;

[0043] Figure 8 The figure shows the contribution ratio analysis of flavor substances of 76 grape varieties of the present invention;

[0044] Fig. 9 Shown is the cluster analysis of fructose and tartaric acid contents of 34 grape varieties of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with embodiments. It should be noted that the following specific descriptions are illustrative and are intended to provide further illustration of the present invention. Unless otherwise specified, all scientific and technical terms used in the present invention have the same meanings as commonly understood by persons skilled in the art to which the present invention belongs.

[0046] Example 1: Screening of table grape variety classification methods

[0047] (I) Classification of 76 table grape varieties

[0048] The mature fruits of 76 grape varieties with large market shares (Table 1) were selected as materials. According to the regional division standards, the 76 grape varieties can be divided into three categories: East Asian populations, Eurasian populations and interspecific hybrids. There are 2 East Asian populations, 19 Eurasian populations and 51 interspecific hybrids.

[0049] Table 1 Names of 76 grape varieties

[0050]

[0051] (II) Sugar and acid composition and content determination and composition variation analysis

[0052] Soluble solids include soluble sugars such as monosaccharides, disaccharides and polysaccharides in fruits, which are mostly used to measure the maturity of fruits. Therefore, soluble solids cannot be used to distinguish whether grape fruits are high-sugar or low-sugar. It is necessary to find more suitable markers that can distinguish high-sugar or low-sugar grapes. Glucose and fructose are the main sugars in grape fruits, so this embodiment considers adding the determination of glucose and fructose in grape fruits.

[0053] Take 1g of grape pulp powder, place it in 10mL of deionized water, and mix well. Heat in an 80℃ water bath for 30min, cool to room temperature, and centrifuge at 4200rpm for 30min. Take 1mL of supernatant, dilute to 10mL, filter through 0.25μm, and use LC-MS to determine the glucose and fructose content. Use a portable refractometer to determine the soluble solids. Set up three biological replicates for each variety. The glucose, fructose and soluble solids content in grape fruits were analyzed. The test results are shown in Table 2, and the statistical analysis results are shown in Table 3 and Figure 1 .

[0054] Tartaric acid is the highest content of organic acid in grape fruit, followed by malic acid, and citric acid is the least, and citric acid is almost undetectable in some varieties. Take 1g of grape pulp powder, place it in 10mL of 0.2% metaphosphoric acid solution, and mix well. Heat in an 80℃ water bath for 30min, then cool to room temperature and centrifuge at 4200rpm for 30min. Take 1mL of supernatant, dilute to 10mL, filter through 0.25μm, and use LC-MS to determine the content of malic acid, citric acid and tartaric acid. The titratable acid was determined by neutralization titration. The test results are shown in Table 2, and the statistical analysis results are shown in Table 3 and Figure 1 .

[0055] Table 2 Test results of sugar and acid content of 76 grape varieties

[0056]

[0057]

[0058] Table 3 Statistical analysis results of sugar and acid content of 76 grape varieties

[0059]

[0060]

[0061] The results of the determination of soluble solids, glucose, and fructose showed that the glucose content in the fruit was the highest, with an average of 73.49 g·kg -1The varieties with the highest content were 'Chunfeng' (110.04), 'Cui Xiaohong' (98.02) and 'Zaotian' (95.93); the fructose content was second, with an average of 67.84 g·kg -1 , among which the varieties with the highest content are 'Chunfeng' (97.68), 'Cui Xiaohong' (94.74) and 'Fujizhihui' (90.85); the average soluble solids value is 16.41, among which the varieties with the highest content are 'Chunfeng' (21.80), 'Cui Xiaohong' (21.50) and 'Yongxiangyu' (21.10), and only varieties such as Thorn Grape have lower content.

[0062] The results of organic acid determination showed that the average tartaric acid content was 6.41 g·kg -1 , accounting for 67.90% of the total organic acid content, among which the varieties with the highest content are 'Red King' (11.37), 'Crisp Little Red' (10.43) and 'Sunshine Rose' (9.30). The average malic acid content is 2.33g·kg -1 The highest content of citric acid in grapes was 'Sunny Rose' (5.52), 'Sweet Sun' (4.60) and 'Thorn Grape' (4.50). The average citric acid content was 0.65 g kg -1 The highest content of titratable acid was 5.20 mol / L, and the highest content was found in the varieties of 'Purple Earth', 'Yongzaolu' and 'Yangguangmei'.

[0063] The analysis of sugar and acid component variation showed that the coefficient of variation of soluble solids content in grape fruit was the smallest, at 16.60%; the coefficient of variation of citric acid content was the largest, at 51.01%; the coefficients of variation of glucose and fructose content were 18.27% and 19.00%, respectively, which were significantly smaller than tartaric acid (23.03%), malic acid (38.35%) and citric acid (51.01%), indicating that the main difference between different varieties comes from the acid component content ( Figure 1 ). KS test was performed on each index, and it was found that the contents of glucose, fructose, tartaric acid and titratable acid in the seven indexes were normally distributed (P>0.05), while the remaining three indexes were skewed ( Figure 1 ).

[0064] The correlation analysis of sugar and acid components found that there was a significant positive correlation between glucose and fructose content, indicating that the accumulation trend of these two sugars in grape berries was consistent. The contents of the three organic acids also showed a significant positive correlation. However, there was no correlation between sugar and acid components ( Figure 2 ).

[0065] (III) Principal component analysis of sugar and acid components

[0066] Glucose, fructose, tartaric acid, malic acid and citric acid were used as different dimensions for PCA analysis (Table 4). The eigenvalues ​​of the first two principal components were greater than 1, and the cumulative variance contribution rate of the two reached 78.76%. This shows that under the premise that the variables are not lost, the two principal components can contain 78.76% of the information of the original data. Therefore, the two principal components can be used to represent the five indicators of glucose, fructose, malic acid, citric acid and tartaric acid for analysis and evaluation.

[0067] According to the principal component factor value of the gluconic acid component, two principal component factors were selected and a scatter plot of grape varieties was made on the PC1-PC2 plane ( Figure 3 ). The distance between glucose and fructose is small, indicating that the contribution of glucose and fructose to grape quality is highly repeatable, and one of them can be selected as the main component. The distance between malic acid, citric acid and tartaric acid is small, especially malic acid and citric acid, indicating that tartaric acid can be used as the main component of the acid component.

[0068] Table 4 Principal component analysis of sugar and acid components of 76 grape varieties

[0069]

[0070] (IV) Cluster analysis of sugar and acid components

[0071] Soluble solids and titratable acid content are widely used in grape maturity and quality evaluation in production because of their convenient determination. Based on the soluble solids and titratable acid content, the hclust package in R language was used to perform hierarchical clustering on the original data. The clustering method was the sum of squares of deviations (ward), and the ggtree package was used to convert the clustering results into circles. The 76 grape varieties can be roughly divided into two groups ( Figure 4 ).

[0072] Group 1, high soluble solids content: 'Spring Breeze', 'Cui Xiaohong', 'Yong Xiangyu', 'Giant Rose', 'Mi Guang', 'Yong Zijing', 'Xia Hei', 'Zui Jinxiang', 'Yong Lufei', 'Jufeng', 'Yong Zaohong', 'Red Fuji', 'Zhichang Rongfeng', 'Bai Aolin', 'Golden Finger', 'Han Xiang Mi', 'Red Balado', 'Black Balado', 'Hutai No. 8', 'Jusheng No. 1', 'Roland Rose B', 'Zao Cui Xiangti', 'Red King', 'Roland Rose A', 'Zao Sweet', 'Yuxuan No. 1', 'Fuji's Glory', 'Queen Nina', 'Red Natsune', 'Yongzaolu', 'Romantic Beauty', 'Sunshine Thirteen', 'Koshu Sansha', 'Kaneda Beauty Fingers', 'Chrysanthemum Dream', 'Top Scholar Red', 'Victoria', 'Jade Fingers', 'Jungle Rose', 'Early Kangbao', 'White Rosa', 'Kaneda Rose', 'Red Rosa', 'Guifei Rose', 'Yuxuan No. 5', 'American Red Grape', 'Gaoqi', 'Madonna Ruby', 'Sunshine Rose', and 'Yinhong'.

[0073] Group 2, low soluble solids content: 'Wink', 'Thorn Grape', 'Yongfei Red', 'Moldova', 'Future Star', 'Joy', 'Xiayi Grape', 'Royal', 'Shaoxing No. 1', 'Golden Queen', 'Black Finger', 'Seto Koshi', 'Early Summer Black', 'Purple Sweet Seedless', 'Sapphire', 'Deep Red Seedless', 'Unicorn', 'Beauty Finger', 'Eastern Star', 'Sweet Sun', 'Wish', 'Late Kangbao', 'Xiongbao', 'Purple Earth', 'Armona Rose', 'Qinlong Big Spike'.

[0074] However, this classification method can only distinguish the content of soluble solids in grapes, and cannot further distinguish the difference in the content of its main components, glucose and fructose, and titratable acid. Therefore, the content of soluble solids cannot determine the sweetness and sourness of grapes. For example, in grapes with high soluble solids content, the content of fructose and glucose may be low, the total acidity is high, and the grapes taste sour. In this embodiment, for example, 'Sunshine Rose' and 'Madonna Ruby', which are clustered in the same branch of the high soluble solids group, have similar soluble solids content, but their titratable acid content is very different.

[0075] Glucose, fructose, malic acid, citric acid and tartaric acid are the main sugar and acid components of grape fruit. According to the content of glucose, fructose, malic acid, citric acid and tartaric acid, the 76 grape varieties can be roughly divided into two groups by hierarchical clustering method ( Figure 5 ).

[0076] Group 1, high in glucose and fructose: 'Spring Breeze', 'Crispy Little Red', 'Red King',

[0077] 'Fuji's Glory', 'Yongzaolu', 'Red Summer Sound', 'Chrysanthemum Dream', 'Joy', 'White Aolin', 'Summer Black', 'Red Rosa', 'Golden Queen', 'Hanxiang Mi', 'Sunshine Thirteen',

[0078] 'White Rosa', 'Madonna Ruby', 'Yongxiangyu', 'Jungle Rose', 'Zaokangbao', 'Spring Breeze', 'Zaotian', 'Zuijinxiang', 'Zhuangyuanhong', 'Yong Zijing', 'Jintian Rose', 'Giant Rose', 'Purple Sweet Seedless', 'Yongzaohong', 'Jintian Meizhi', 'Zaocui Xiangti',

[0079] 'Zhichang Rongfeng', 'Golden Finger', 'Red Fuji', 'Romantic Beauty', 'Honey Light', 'Yuxuan No. 1', 'Kyoho', 'Roland Rose A', 'Tota No. 8', 'Yonglufei', 'Koshu Sansha', 'Queen Nina'.

[0080] Group 2, low in glucose and fructose: 'Unicorn', 'Wink', 'Purple Earth',

[0081] 'Thorn Grape', 'Sunny Rose', 'Shaoxing No. 1', 'Qinlong Big Spike', 'Victoria', 'Gaoqi', 'Late Kangbao', 'Wish', 'Jade Finger', 'Guifei Rose', 'Xia Yi', 'Royal', 'Black Balado', 'Sweet Sun', 'Future Star', 'Yuxuan No. 5', 'Yongfei Red', 'Black Finger', 'Armona Rose', 'Seto Koshi', 'Deep Red Seedless', 'Red Balado', 'Roland Rose B', 'Jusheng No. 1', 'Early Summer Black', 'Eastern Star', 'Moldova', 'Xiongbao', 'Beauty Finger', 'Sapphire', 'American Red Grape', and 'Yinhong'.

[0082] However, this classification method cannot further distinguish the differences in malic acid, citric acid and tartaric acid content. For example, 'Hong Xia Yin' and 'Pu Zhi Meng', which are clustered in the same branch of the high glucose and fructose group, both have high glucose and fructose contents, but their tartaric acid contents are very different.

[0083] Principal component analysis showed that glucose / fructose and tartaric acid could represent the effects of glucose, fructose, malic acid, citric acid and tartaric acid content on grape quality. According to the content of glucose and tartaric acid, the 76 grape varieties could be accurately divided into 4 groups ( Figure 6 ).

[0084] Group 1, high sugar and high acid: 'Jufeng', 'Xiahei', 'Cui Xiaohong', 'Red King',

[0085] 'Sunshine Rose', 'Deep Red Seedless', 'Moldova', 'Early Summer Black', 'Fuji Glory', 'Jusheng No. 1', 'Roland Rose A', 'Summer Black', 'White Olin', and 'Koshu Sanshaku'.

[0086] Group 2, high sugar and low acid: 'Spring Breeze', 'Mi Guang', 'Giant Rose', 'Yong Fei Green',

[0087] 'Dream of Chrysanthemum', 'Queen Nina', 'Tota No. 8', 'Red Fuji', 'Red Natsune', 'Romantic Beauty', 'Yuxuan No. 1', 'Yongzaolu', 'Jintian Meizhi', 'Zhuangyuanhong', 'Giant Rose', 'Golden Fingers', 'Drunken Golden Fragrance', and 'Early Sweetness'.

[0088] Group 3, low sugar and high acid: 'Black Balado', 'Wink', 'Yinhong', 'Thorn Grape', 'Black Finger', 'Eastern Star', 'Armona Rose', 'Royal', 'Sapphire', 'Sweet Sun', 'Seto Koshi', 'American Red Grape', 'Beauty Finger', 'Yongfei Red', 'Future Star', 'Roland Rose B', 'Joy', 'Red Rosa', 'Golden Queen', 'Sunshine Thirteen', 'Red Balado', 'Hanxiang Honey', and 'Yuxuan No. 5'.

[0089] Group 4, low sugar and low acid: 'Unicorn', 'Qinlong Dasui', 'Wan Kangbao', 'Jade Finger', 'Guifei Rose', 'Wish', 'Xia Yi', 'Xiong Bao', 'Gao Qi', 'Victoria', 'Shaoxing No. 1' and 'Purple Earth'.

[0090] However, in this classification method, the 'Red King' and 'Crisp Little Red', which are clustered in the same branch of the high-sugar and high-acid group, have similar glucose contents, but quite different tartaric acid contents; the 'Early Summer Black', 'Moldova', 'Deep Red Seedless' and 'Sunshine Rose', which are clustered in the same branch of the high-sugar and high-acid group, have similar glucose and tartaric acid contents, but lower tartaric acid contents, and should belong to the low-acid group.

[0091] According to the fructose and tartaric acid content, the 76 grape varieties can be accurately divided into 4 groups by hierarchical clustering method ( Figure 7 ).

[0092] High sugar and high acid: 'Spring Breeze', 'Crisp Little Red', 'Fuji Glory', 'Sunshine Rose', and 'Red King'.

[0093] High sugar and low acid: 'Honey Light', 'Han Xiang Mi', 'Xia Hei', 'Yu Xuan No. 1', 'Romantic Beauty', 'Red Summer Sound', 'Chrysanthemum Dream', 'Sunshine Thirteen', 'Drunk Golden Fragrance', 'Early Sweet', 'Red Fuji', 'Giant Rose', 'Golden Finger', 'Yong Zao Lu', 'Yong Zi Jing', 'Queen Nina', 'Red Balado', 'Yong Lu Fei', 'Hu Tai No. 8', 'Roland Rose B', 'Koshu Sanshaku', 'Future Star', 'Roland Rose A', 'White Ao Lin', 'Joy', 'Kyoho', 'Zao Cui Shanti', 'Jintian Meizhi', 'Zhichang Rongfeng', 'Madonna Ruby', 'Zhuangyuanhong', 'Yongzaohong', 'Golden Queen', 'Yongxiangyu', 'Jungle Rose', 'White Rosa', 'Jintian Rose', 'Late Kangbao', and 'Gaoqi'.

[0094] Low sugar and high acid: 'Black Balado', 'Wink', 'Early Summer Black', 'Thorny Grape', 'Black Finger', 'Deep Red Seedless', 'Eastern Star', 'Moldova', and 'Jusheng No. 1'.

[0095] Low sugar and low acid: 'Unicorn', 'Qinlong Big Spike', 'Yinhong', 'Victoria', 'Purple Earth', 'Shaoxing No. 1', 'Wish', 'Xiongbao', 'Amona Rose', 'Xiayi', 'Zaokangbao', 'Guifei Rose', 'Jade Finger', 'Purple Sweet Seedless', 'Royal', 'Beauty Finger', 'Sweet Sun', 'Yuxuan No. 5', 'Red Rosa', 'American Red Grape', 'Seto Koshi', 'Sapphire', and 'Yongfei Red'.

[0096] This classification method is more reasonable than the other four.

[0097] (V) Evaluation of the effects of sugar and acid content on the taste and flavor of grape berries

[0098] Flavor contribution refers to the degree to which a chemical in a food or beverage contributes to its flavor. These contribution values ​​are usually calculated based on data from chemical analysis and sensory evaluation to determine the contribution of different chemical components to flavor. By understanding these contribution values, the food and beverage industry can better control the taste characteristics of products, improve product quality and taste, and meet consumer taste needs.

[0099] Flavor substance contribution value = flavor substance content / taste threshold of the flavor substance. Among them, the taste thresholds of glucose and fructose are 6.75g·kg -1 and 3.24 g kg -1 The taste thresholds of tartaric acid, malic acid and citric acid are 0.047 g·kg -1 , 0.042g·kg -1 and 0.057 g kg -1 Among the grape fruit sugar components, fructose contributed the most to sweetness (20.6), which was significantly higher than glucose (10.7, P < 0.01). Among the grape acid substances, tartaric acid contributed an average of 136.0 to the taste and flavor of grapes, which was significantly higher than citric acid (11.5) and malic acid (56.2, P < 0.01) (Table 5 and Figure 8 ). These data indicate that organic acids may play a more important role than soluble sugars in the flavor evaluation of fresh grapes. At the same time, from the overall data of the composition and content of fruit flavor substances, the taste and flavor of mature grapes are mainly provided by tartaric acid and fructose. In addition, by recruiting volunteers to taste and evaluate different varieties of grapes, the results showed that the grape varieties classified by fructose and tartaric acid were consistent with the public taste evaluation, which also proved the reliability of clustering grape varieties according to fructose and tartaric acid content.

[0100] Table 5 Analysis of contribution values ​​of each component of 76 grape varieties

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[0102] Example 2: Verification of the best classification method

[0103] This example adopts the classification method provided in Example 1 to measure the fructose and tartaric acid contents of the mature fruits of 34 hybrid offspring (Yong 1-34) of 'Sunshine Rose'×'Black Balado' (Table 6), and uses the hclust package in the R language to perform hierarchical clustering on the original data, the clustering method is the sum of squares of deviations method (ward), and then calls the ggtree package to convert the clustering results into circles. The specific classification results are as follows:

[0104] Classification results ( Fig. 9 ) are high sugar and high acid: 9 accessions, including Yong 1, Yong 9, Yong 10, Yong 11, Yong 17, Yong 19, Yong 20, Yong 25 and Yong 32; high sugar and low acid: 13 accessions, including Yong 2, Yong 4, Yong 6, Yong 12, Yong 13, Yong 15, Yong 16, Yong 23, Yong 24, Yong 28, Yong 31, Yong 33 and Yong 34; low sugar and high acid: 6 accessions, including Yong 3, Yong 4, Yong 7, Yong 14, Yong 22 and Yong 26; low sugar and low acid: 6 accessions, including Yong 5, Yong 18, Yong 21, Yong 27, Yong 29 and Yong 30.

[0105] Table 6 Analysis of fructose and tartaric acid content in 34 grape varieties

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[0108] Table 7 Analysis of contribution values ​​of each component of 34 grape varieties

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[0110] The contribution values ​​of flavor substances in 34 grape varieties were analyzed (Table 7). It was found that fructose in the grape fruit sugar components contributed the most to sweetness (23.9), significantly higher than glucose (12.4, P < 0.01). Among the grape acid substances, the average contribution value of tartaric acid to grape taste and flavor was 162.4, significantly higher than citric acid (15.4) and malic acid (57.8, P < 0.01) (Table 5).

[0111] The flavor evaluation results once again verified the reliability of clustering grape varieties according to fructose and tartaric acid content. It can be seen that the classification method provided by the present invention is also suitable for the accurate classification of the 34 grape varieties.

[0112] In summary, the above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, improvements and modifications can be made without departing from the core technology of the present invention, and these improvements and modifications should also fall within the scope of patent protection of the present invention. Any changes within the meaning and scope equivalent to the claims of the present invention should be considered to be included in the scope of the claims.

Claims

1. A method for classifying grapes, characterized in that: By testing the soluble sugar and organic acid content in grape fruits, grapes are classified into four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid.

2. The classification method according to claim 1, characterized in that: The soluble sugar includes any one or more of glucose and fructose, and the organic acid includes any one or more of tartaric acid, malic acid, and citric acid.

3. The classification method according to claim 2, characterized in that: The soluble sugar and organic acid refer to one or more of glucose, fructose, tartaric acid, malic acid and citric acid, or glucose and tartaric acid, or fructose and tartaric acid.

4. The classification method according to claim 3, characterized in that: The soluble sugar and organic acid are fructose and tartaric acid.

5. The classification method according to claim 4, characterized in that: The following steps are involved: (1) Determine the composition and content of soluble sugar and organic acid of each grape; (2) Based on the test results, each type of grape is classified into high sugar and high acid, high sugar and low acid, low sugar and high acid, or low sugar and low acid.

6. A classification marker combination for grape fruit, characterized in that: It comprises any one or more of soluble solids and titratable acid, or glucose, fructose, tartaric acid, malic acid and citric acid, or glucose and tartaric acid, or fructose and tartaric acid.

7. The classification marker combination according to claim 6, characterized in that: Includes fructose and tartaric acid.

8. Use of a marker detection reagent for preparing a reagent for improving the accuracy of grape fruit classification, characterized in that: The grape fruit classification includes four categories: high sugar and high acid, high sugar and low acid, low sugar and high acid, and low sugar and low acid. The markers include one or more of glucose, fructose, tartaric acid, malic acid and citric acid, or glucose and tartaric acid, or fructose and tartaric acid.

9. The use according to claim 8, characterized in that The markers include fructose and tartaric acid.

10. Use of a composition for preparing a marker for evaluating the sugar and acid taste of grape fruit, characterized in that: The composition includes fructose and tartaric acid.

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