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Abstract [Objectives] Comprehensive evaluation was made on five peach varieties， in order to select the best varieties.
[Methods] With Tongnan century peach， Chengdu Diao Baifeng， Chengdu ball peach， Wujian yellow peach and Wujian flat peach as research objects， the sensory quality indicators including single fruit weight， fruit shape index and hardness and nutritional quality indicators including soluble solids， total sugar， organic acid， sugar-acid ratio and vitamin C were comprehensively evaluated.
[Results] The single fruit weights of different peach varieties ranked as ball peach>century peach>Diao Baifeng>yellow peach>flat peach; fruit firmness followed an order of yellow peach>flat peach>century peach>ball peach>Diao Baifeng; the fruit shape index ranked as yellow peach>ball peach>century peach>Diao Baifeng>flat peach; the contents of soluble solids showed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach; the total sugar contents followed an order of century peach>ball peach>Diao Baifeng>yellow peach>flat peach; the organic acid contents ranked as by ball peach>Diao Baifeng>century peach>flat peach>yellow peach; the sugar-acid ratios exhibited an order of yellow peach>century peach>Diao Baifeng>ball peach>flat peach; and the vitamin C contents followed an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach. Comprehensive evaluation was performed using the rationality-satisfaction degree multiple value theory， and the results showed that the synthesized rationality-satisfaction degree values ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach.
[Conclusions] Among the five peach varieties in this study， the yellow peach from Wujian town of Yongchuan District was the best， followed by century peach ranking second.
Key words Peach; Sensory quality; Nutritional Quality; Overview
Peach is known as "Shou Tao" and "Xian Tao". Because of its delicious flesh， it is also called "the first fruit in the world". Peaches contain protein， fat， carbohydrates， crude fiber， calcium， phosphorus， iron， carotene， vitamins， and organic acids （mainly malic acid and citric acid）， sugars （mainly glucose， fructose， sucrose and xylose）， and essential oils. This fruit belongs to Amygdalus in Rosaceae， which has been cultivated in China for 4 000 years[1]. According to incomplete statistics， there are currently more than 5 000 peach varieties cultivated in the world， of which more than 700 varieties were selected and introduced in the United States， and more than 1 000 varieties were selected in China[2]. Chinas peach cultivation area is widely distributed， and the quality characteristics vary greatly among varieties. At present， the types of peaches in China are mainly four types： ordinary white-flesh fresh-eating peaches， yellow-flesh processing peach， nectarine， and flat peach. Most of the common peaches are white-flesh fresh-eating peaches[3]. Peach quality is composed of composite evaluation factors of appearance and many internal factors， which can be divided into sensory quality such as fruit size， fruit shape index and firmness， nutritional quality such as sugar， acid， Vc and phenols， and processing quality such as juice yield， viscosity and brown degree. There is close correlation and relative independence between different quality factors， but the relationship between the various factors and their effects on quality are still unknown. There are few reports on this aspect at home and abroad. In the evaluation and research processes of other fruits and vegetables， principal component analysis[9] and cluster analysis method[4] are mostly used. In the quality evaluation of processed foods， some people have adopted rationality-satisfaction degree multiple value theory[5]， but there is no report on the comprehensive evaluation of fruit quality by combining principal component analysis， cluster analysis and rationality-satisfaction degree and multiple value theory.
Sensory quality evaluation methods can be divided into sensory evaluation methods and instrumental measurement methods. Sensory evaluation is to make comprehensive and objective evaluation of the color， aroma， taste， and appearance of foods through the sensory organs of the human body （eyes， nose， mouth， teeth， hands， etc.）， while obtaining real data and performing comprehensive evaluation using mathematical statistics. Zhang et al.[6] organized an evaluation team of 10 people and evaluated the flavor of peach fruit on a 5-point system when evaluating the flavor of peach fruit. Wang et al.[7] adopted the centesimal system to perform sensory evaluation of peach juice in five aspects： color， flavor， aroma， odor and uniformity. Wang et al.[8] performed sensory evaluation of peach cans using the centesimal system from seven aspects： color， soup， tissue state， aroma， hardness， flavor and impurities and statistically analyzed the data. They also evaluated the nutritional quality of peaches by determining and analyzing chemical factors of peaches such as sugar acids， vitamins， etc.
In this study， five peach varieties were comprehensively evaluated based on sensory and nutritional quality， and the best varieties were selected.
Materials and Methods
Experimental materials
Five varieties： Tongnan century peach， Diao Baifeng from Longquanyi district of Chengdu City， ball peach from Longquanyi district of Chengdu City， yellow peach from Wujian Town， Yongchuan District， and flat peach from Wujian Town， Yongchuan District， 10 peaches each. Collection and pretreatment of samples
Sampling was carried out in accordance with the principles of "random"， "equal volume" and "multi-point mixing". From July 2015， samples of the five peach varieties were taken from Tongnan District of Chongqing City， Longquanyi District of Chengdu City， and Wujian peach expo garden of Yongchuan district. The collected peach samples were placed on a clean newspaper and photographed， and then the different varieties were packed and labeled with number， name and date.
Experimental design
In this experiment， five peach varieties were used as experimental materials. Sensory quality indicators such as single fruit weight， fruit shape index and firmness and nutritional quality indicators such as soluble solids， total sugar， organic acid， sugar-acid ratio and vitamin C were to be compared and evaluated comprehensively， so as to select the best peach varieties， which could provide references for the popularization and application in production.
Analysis and determination methods
The single fruit weight was measured by an electronic balance. The maximum longitudinal and transverse diameters of each peach fruit were measured by a vernier caliper， and expressed as the ratio of the fruit longitudinal diameter to the transverse diameter[9]. Fruit firmness was measured with a texture analyzer[9]. Soluble solids were measured with a handheld refractometer[10]. Total sugar was determined using the Filin reagent method[11]. Organic acids were determined by an alkaline titration method[12]. The ratio of total sugar to organic acids was calculated as the sugar-to-acid ratio. Vitamin C was determined by the 2，6-dichloroindophenol titrimetric method[13].
Evaluation methods
Comprehensive evaluation was performed by the rationality-satisfaction degree and multiple value theory. The so-called "rationality-satisfaction degree"[14] refers to the rationality or satisfaction degree that the characteristics of a variety meet the peoples needs. The rationality is expressed by a value between 0 and 1， of which "1" indicates that a certain characteristic of the variety is completely in accordance with the "law"， and "0" means that a certain characteristic is completely out of compliance with the "law". bi represents a certain trait， and if the satisfaction degree of the certain trait is M（bi）， its maximum value will be Max（bi）， and its minimum value will be Min（bi）.
For indicators to which larger is better， the calculation formula of single-factor rationality-satisfaction degree is： M（bi）=[bi-Min（bi）]/[Max（bi）-Min（bi）]（1）
For indicators to which smaller is better， the calculation formula of single-factor rationality-satisfaction degree is：
M（ bi ）=[Max（bi）-bi]/[Max（bi）-Min（bi）]（2）
After obtaining the rationality-satisfaction degree of each single-factor index of different peach varieties， considering that the quality characteristics of a variety cannot be evaluated by single-factor indicators， it is now assumed that their changes are independent and the total contribution to the quality characteristics can be approximated as having no essential difference. And according to consolidation principle of rationality-satisfaction degree and multiple value theory， the single-factor satisfaction degrees are combined into the synthesized rationality-satisfaction degree of quality. A higher synthesized rationality-satisfaction degree of quality proves that the corresponding variety meets peoples requirements for its quality better. The synthesized rationality-satisfaction degree is expressed by formula （3） as following：
V=∑ni=1WiMi（3）
In the formula， V is the synthesized rationality-satisfaction degree; Wi is weight number of the ith indicator， which satisfies 0≤Wi≤1 and is given through the experts score; and Mi is the satisfaction degree of the ith single-factor indicator.
According to the literatures [15-16]， the weight numbers of single fruit weight， firmness， vitamin C， soluble solids， total sugar and total acid are 0.15， 0.10， 0.20， 0.15， 0.20 and 0.20， respectively.
Results and Analysis
Comparison of sensory quality of different peach varieties
Single fruit weights of different peach varieties
Fruit quality is an important indicator for measuring fruit size， as well as an important factor affecting yield and processing adaptability and consumer acceptability， and is greatly affected by variety and maturity[17]. Samples of five peach varieties were weighed with skin using an electronic balance and compared. It can be known from Fig. 1 that ball peach had the largest single fruit weight， which was 8 times of that of flat peach， and the order of single fruit weight was ball peach>century peach>Diao Baifeng>yellow peach>flat peach. However， flat peach had shortest error bar， which indicated that the picked fruit had most even size.
Fruit shape indexes of different peach varieties
The fruit shape index was measured by measuring the maximum longitudinal and transverse diameters of peaches with a vernier caliper， and expressed as the ratio of the longitudinal diameter to the transverse diameter. The peaches could be divided into flat， oval， and pointed round types according to fruit shape index[9，18]. Specifically， a fruit shape index within 0.6-0.8 indicated that the peach was flat， that within 0.9-1.0 stood for oval peaches， and a value larger than 1.0 meant that the peach was pointed round. It can be known from Table 1 that yellow peach had the largest fruit shape index， and the values of different peach varieties followed an order of yellow peach>ball peach>century peach>Diao Baifeng>flat peach. The fruit of century peach， Diao Baifeng and ball peach were all oval， the shape of yellow peach was pointed round， and that of flat peach was flat. Firmness of different peach varieties
Fruit firmness is an important indicator of fruit maturity and shelf life. Fruit firmness affects the length of the fruit supply period， the distance of transportation， and the improvement of economic benefits， and has become a factor limiting the development of peaches. As the circulation of peaches becomes more and more widespread， the requirements for firmness have also increased[9]. Consumers also have new requirements for firmness， that is， the fruit should have certain firmness in the hands of consumers after transportation and sales. The firmness without skin was measured using a texture analyzer according to the instrument instructions. It can be known from Fig. 2 that the firmness of the five varieties ranked as yellow peach>flat peach>century peach>ball peach>Diao Baifeng.
Comparison of nutritional quality of different peach varieties
Soluble solid contents of different peach varieties
Soluble solids are also an important indicator of fruit maturity. The soluble solids in fruits are mainly water-soluble sugars[10]. As the peach fruit matures， more starch is converted into sugars and gradually accumulated in the fruit， and the taste of the fruit also changes from sour to sweet. Generally speaking， the higher the content of soluble solids， the higher the sweetness of the fruit and the better the taste. Therefore， increasing the soluble solid content of peach fruit will also directly increase its market acceptance and improve the competitive advantage of the product[19]. The soluble solids of the peaches were determined using a handheld refractometer following the instrument instructions. It is known from Fig. 3 that the variety with the most soluble solid content was century peach， and the soluble solid contents followed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach. However， Diao Baifeng showed shortest error bar， which also showed that its determination was more accurate.
Agricultural Biotechnology2020
Total sugar contents of different peach varieties
The flavor of a peach depends largely on its sweetness and acidity. The sugar content in fruit is affected by the variety and maturity， and it will vary to some extent depending on the variety. The sugars in peach pulp are mainly sucrose， fructose and glucose. Both fructose and glucose are reducing sugars. Sucrose is a non-reducing sugar， but it produces glucose and fructose after hydrolysis. Therefore， sugar content can be determined according to the Fehling reagent method in the national standard for reducing sugars[11]. It can be seen from Fig. 4 that the variety century peach had the highest total sugar content， and the values of different varieties ranked as century peach>ball peach>Diao Baifeng>yellow peach>flat peach. However， ball peach exhibited the shortest error bar， indicating that its determination was more accurate. Organic acid content of different peach varieties
The organic acids in peach are mainly malic acid， citric acid and quinic acid. The amount of acid content is also an important indicator for evaluating its quality. The acid contents in the samples were determined according to the acid-base titration method in national standards[12]. It can be seen from Fig. 5 that the variety with the highest organic acid content was ball peach， and the values of different varieties ranked as ball peach>Diao Baifeng>century peach>flat peach> yellow peach. The organic acid content of ball peach was nearly 3 times that of yellow peach. The error bar of flat peach was zero， which meant that its determination error was the smallest and more accurate.
Sugar-acid ratios of different peach varieties
Sugar-acid ratio is the main factor affecting peach fruit flavor. It is expressed as the ratio of total sugar to total acid in the fruit. The sugar-acid ratio of each peach obtained in this study was the ratio of the average sugar content to the average organic acid content. From Table 2， it can be seen that yellow peach had the highest sugar-acid ratio， and the values of different varieties ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach， indicating that yellow peach was the sweetest， while flat peach was not as sweet as other varieties.
Vitamin C contents of different peach varieties
Vitamin C has the health care functions of beautifying skin and preventing diseases and the function characteristics of high water solubility and easy absorption. Peach fruit contains a small amount of vitamin C， and its content was determined according to the 2，6-dichloroindophenol titrimetric method in national standard[13]. It can be seen from Fig. 6 that the variety with the highest vitamin C content was flat peach， and the values of different varieties exhibited an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach. However， the content of vitamin C was overall not too high. Century peach had shortest error bar， indicating that its determination results were more accurate.
Comprehensive evaluation based on rationality-satisfaction degree and multiple value theory
Single-factor satisfaction degree with different quality of different peach varieties
The single-factor satisfaction degree of each quality can be calculated from the satisfaction degree formulas （1） and （2）， as shown in Table 3. It can be seen from the table that ball peach had highest satisfaction degree with single fruit weight; the highest satisfaction degree with firmness was observed in yellow peach; the variety having highest satisfaction degree with soluble solids was century peach; century peach exhibited the highest satisfaction degree with total sugar content; the variety having highest satisfaction degree with organic acid content was yellow peach; and flat peach exhibited the highest satisfaction degree with vitamin C content. Satisfaction degree to sensory and nutritional quality of different peach varieties
According to the single-factor satisfaction degree of Table 3， the satisfaction degrees with the sensory quality and nutritional quality of different peach varieties are shown in Table 4. It can be seen from Table 4 that yellow peach had highest satisfaction degree with the sensory quality， and century peach exhibited the highest satisfaction degree with the nutritional quality.
Synthesized rationality-satisfaction degree values of different peach varieties
Formula （3） was used to calculate the synthesized rationality-satisfaction degree of peach fruit quality characteristics， as shown in Table 5. According to Table 5， it was finally concluded that yellow peach had the highest synthesized rationality-satisfaction degree， and the values of different varieties followed an order of yellow peach>century peach>Diao Baitao>ball peach>flat peach. That is to say， the yellow peach variety from Wujian Town， Yongchuan District， Chongqing City was the best， followed by Tongnan century peach variety， Chengdu Diao Baifeng and ball peach were next to them， and the flat peach variety from Wujian Town， Yongchuan District ranked last.
Conclusions and Discussion
The single fruit weights of different peach varieties ranked as ball peach>century peach>Diao Baifeng>yellow peach>flat peach; the firmness of fruit followed an order of yellow peach>flat peach>century peach>ball peach>Diao Baifeng; and the fruit shape index ranked as yellow peach>ball peach>century peach>Diao Baifeng>flat peach. The fruit of century peach， Diao Baifeng and ball peach were all oval， the shape of yellow peach was pointed round， and that of flat peach was flat.
The contents of soluble solids in different peach varieties showed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach; the total sugar contents followed an order of century peach>ball peach>Diao Baifeng>yellow peach>flat peach; the organic acid contents ranked as by ball peach>Diao Baifeng>century peach>flat peach>yellow peach; the sugar-acid ratios exhibited an order of yellow peach>century peach>Diao Baifeng>ball peach>flat peach; and the vitamin C contents followed an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach.
Comprehensive evaluation based on the rationality-satisfaction degree multiple value theory showed that the synthesized rationality-satisfaction degree values ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach. Among the five peach varieties in this study， yellow peach from Wujian Town， Yongchuan District was the best， followed by Tongnan century peach variety， Chengdu Diao Baifeng and ball peach were next to them， and the flat peach variety from Wujian Town， Yongchuan District ranked last. References
[1] YU ML， MA RJ， SHEN ZJ， et al. Research progress of peach germplasm resources in China[J] . Jiangsu Journal of Agricultural Sciences， 2010， 26（6）： 1418-1423. （in Chinese）
[2] CHEN CW， CAO K， WANG LR. Construction of molecular identity cards of chinese peach variety resources and their wild relatives[J]. Scientia Agricultura Sinica， 2011， 44（10）： 2081-2093. （in Chinese）
[3] JIANG Q. Status and trend of peach production in China[J]. Beijing Agricultural Science， 2000， 18（4）： 35-38. （in Chinese）
[4] XU Q， LIU JS， CHEN XH， et al. principle component and cluster analysis of quality characters of pickling cucumber （Cucumis staivus L.）[J]. Journal of Yangzhou University， 2003， 24（4）： 78-81. （in Chinese）
[5] YANG XS， XIE JZ， MA ZX， et al. Sensory and nutritional evaluation of 17 kinds of sympodial bamboo shoots[J]. Applied Research， 2001（2）： 23-27. （in Chinese）
[6] ZHANG HY， HAN T， WANG YN， et al. Selection of peach fruit quality evaluation factors[J] . Transactions of the Chinese Society of Agricultural Engineering， 2006， 22（8）： 235-239. （in Chinese）
[7] WANG LR， ZHU GR， FANG WC， et al. Preliminary Evaluation of Suitable Peach Varieties for Juicing[J]. Acta Horticulturae Sinica， 2006， 33（6）： 1303-1306. （in Chinese）
[8] WANG J， MIAO LJ， ZHANG YC， et al. Effects of different process conditions on the quality of canned peach fruits and soft white peaches[J]. Hubei Agricultural Sciences， 2012， 51（20）： 4592-4594. （in Chinese）
[9] JIAO Y， BI JF， LIU X， et al. Research progress of peach quality evaluation[J]. Agricultural products processing， 2014（4）： 1671-9646. （in Chinese）
[10] DU G， LI M J， MA F W， et al. Antioxidant capacity and the relationship with polyphenol and vitamin C in Actinidia fruits[J]. Food Chemistry， 2009（113）： 557-562. （in Chinese）
[11] GB/T 5009.7-2008 Determination of reducing sugar in foods. （in Chinese）
[12] GB/T 12456-2008 Method for determination of total acid in foods. （in Chinese）
[13] GB 6195-1986 Determination of vitamin C in vegetables and fruits （2，6-dichloroindophenol titration method）. （in Chinese）
[14] JIAO Y， BI JF， LIU X， et al. Quality evaluation of white-flesh peach juices from different cultivars[J]. Food and Fermentation Industries， 2014， 40（8）： 114-119，125. （in Chinese）
[15] HUANG SG， YANG GL， FANG CJ. Evaluation on the fruit quality of 40 pear varieties by multiple value theory[J]. Hunan Forestry Science & Technology， 2003， 30（4）： 26-27. （in Chinese）
[16] FANG CJ. Evaluation of the Fruit Quality of 19 Kiwi Fruit Varieties with the Multiple Value Theory[J]. Journal of Anhui Agricultural Sciences， 2004， 32（3）： 489-490. （in Chinese）
[17] WANG LR， ZHU GR， FANG WC， et al. The evaluating criteria of some fruit quantitative characters of peach （Prunus persica L.） genetic resources[J]. Acta Horticulturae Sinica， 2005， 32（1）： 1-5. （in Chinese）
[18] WANG LR， ZHU GR， FANG WC， et al. The evaluating criteria of some botanical quantitative characters of peach genetic resources[J]. Scientia Agricultura Sinica， 2005， 38（4）： 770-776. （in Chinese）
[19] LIU HQ， CHEN Y， FANG Y， et al. Effects of selenium fertilizers on selenium content and nutrient quality of kiwi fruit[J]. Journal of Agricultural Resources and Environment， 2004， 31（6）： 565-569. （in Chinese）
[Methods] With Tongnan century peach， Chengdu Diao Baifeng， Chengdu ball peach， Wujian yellow peach and Wujian flat peach as research objects， the sensory quality indicators including single fruit weight， fruit shape index and hardness and nutritional quality indicators including soluble solids， total sugar， organic acid， sugar-acid ratio and vitamin C were comprehensively evaluated.
[Results] The single fruit weights of different peach varieties ranked as ball peach>century peach>Diao Baifeng>yellow peach>flat peach; fruit firmness followed an order of yellow peach>flat peach>century peach>ball peach>Diao Baifeng; the fruit shape index ranked as yellow peach>ball peach>century peach>Diao Baifeng>flat peach; the contents of soluble solids showed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach; the total sugar contents followed an order of century peach>ball peach>Diao Baifeng>yellow peach>flat peach; the organic acid contents ranked as by ball peach>Diao Baifeng>century peach>flat peach>yellow peach; the sugar-acid ratios exhibited an order of yellow peach>century peach>Diao Baifeng>ball peach>flat peach; and the vitamin C contents followed an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach. Comprehensive evaluation was performed using the rationality-satisfaction degree multiple value theory， and the results showed that the synthesized rationality-satisfaction degree values ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach.
[Conclusions] Among the five peach varieties in this study， the yellow peach from Wujian town of Yongchuan District was the best， followed by century peach ranking second.
Key words Peach; Sensory quality; Nutritional Quality; Overview
Peach is known as "Shou Tao" and "Xian Tao". Because of its delicious flesh， it is also called "the first fruit in the world". Peaches contain protein， fat， carbohydrates， crude fiber， calcium， phosphorus， iron， carotene， vitamins， and organic acids （mainly malic acid and citric acid）， sugars （mainly glucose， fructose， sucrose and xylose）， and essential oils. This fruit belongs to Amygdalus in Rosaceae， which has been cultivated in China for 4 000 years[1]. According to incomplete statistics， there are currently more than 5 000 peach varieties cultivated in the world， of which more than 700 varieties were selected and introduced in the United States， and more than 1 000 varieties were selected in China[2]. Chinas peach cultivation area is widely distributed， and the quality characteristics vary greatly among varieties. At present， the types of peaches in China are mainly four types： ordinary white-flesh fresh-eating peaches， yellow-flesh processing peach， nectarine， and flat peach. Most of the common peaches are white-flesh fresh-eating peaches[3]. Peach quality is composed of composite evaluation factors of appearance and many internal factors， which can be divided into sensory quality such as fruit size， fruit shape index and firmness， nutritional quality such as sugar， acid， Vc and phenols， and processing quality such as juice yield， viscosity and brown degree. There is close correlation and relative independence between different quality factors， but the relationship between the various factors and their effects on quality are still unknown. There are few reports on this aspect at home and abroad. In the evaluation and research processes of other fruits and vegetables， principal component analysis[9] and cluster analysis method[4] are mostly used. In the quality evaluation of processed foods， some people have adopted rationality-satisfaction degree multiple value theory[5]， but there is no report on the comprehensive evaluation of fruit quality by combining principal component analysis， cluster analysis and rationality-satisfaction degree and multiple value theory.
Sensory quality evaluation methods can be divided into sensory evaluation methods and instrumental measurement methods. Sensory evaluation is to make comprehensive and objective evaluation of the color， aroma， taste， and appearance of foods through the sensory organs of the human body （eyes， nose， mouth， teeth， hands， etc.）， while obtaining real data and performing comprehensive evaluation using mathematical statistics. Zhang et al.[6] organized an evaluation team of 10 people and evaluated the flavor of peach fruit on a 5-point system when evaluating the flavor of peach fruit. Wang et al.[7] adopted the centesimal system to perform sensory evaluation of peach juice in five aspects： color， flavor， aroma， odor and uniformity. Wang et al.[8] performed sensory evaluation of peach cans using the centesimal system from seven aspects： color， soup， tissue state， aroma， hardness， flavor and impurities and statistically analyzed the data. They also evaluated the nutritional quality of peaches by determining and analyzing chemical factors of peaches such as sugar acids， vitamins， etc.
In this study， five peach varieties were comprehensively evaluated based on sensory and nutritional quality， and the best varieties were selected.
Materials and Methods
Experimental materials
Five varieties： Tongnan century peach， Diao Baifeng from Longquanyi district of Chengdu City， ball peach from Longquanyi district of Chengdu City， yellow peach from Wujian Town， Yongchuan District， and flat peach from Wujian Town， Yongchuan District， 10 peaches each. Collection and pretreatment of samples
Sampling was carried out in accordance with the principles of "random"， "equal volume" and "multi-point mixing". From July 2015， samples of the five peach varieties were taken from Tongnan District of Chongqing City， Longquanyi District of Chengdu City， and Wujian peach expo garden of Yongchuan district. The collected peach samples were placed on a clean newspaper and photographed， and then the different varieties were packed and labeled with number， name and date.
Experimental design
In this experiment， five peach varieties were used as experimental materials. Sensory quality indicators such as single fruit weight， fruit shape index and firmness and nutritional quality indicators such as soluble solids， total sugar， organic acid， sugar-acid ratio and vitamin C were to be compared and evaluated comprehensively， so as to select the best peach varieties， which could provide references for the popularization and application in production.
Analysis and determination methods
The single fruit weight was measured by an electronic balance. The maximum longitudinal and transverse diameters of each peach fruit were measured by a vernier caliper， and expressed as the ratio of the fruit longitudinal diameter to the transverse diameter[9]. Fruit firmness was measured with a texture analyzer[9]. Soluble solids were measured with a handheld refractometer[10]. Total sugar was determined using the Filin reagent method[11]. Organic acids were determined by an alkaline titration method[12]. The ratio of total sugar to organic acids was calculated as the sugar-to-acid ratio. Vitamin C was determined by the 2，6-dichloroindophenol titrimetric method[13].
Evaluation methods
Comprehensive evaluation was performed by the rationality-satisfaction degree and multiple value theory. The so-called "rationality-satisfaction degree"[14] refers to the rationality or satisfaction degree that the characteristics of a variety meet the peoples needs. The rationality is expressed by a value between 0 and 1， of which "1" indicates that a certain characteristic of the variety is completely in accordance with the "law"， and "0" means that a certain characteristic is completely out of compliance with the "law". bi represents a certain trait， and if the satisfaction degree of the certain trait is M（bi）， its maximum value will be Max（bi）， and its minimum value will be Min（bi）.
For indicators to which larger is better， the calculation formula of single-factor rationality-satisfaction degree is： M（bi）=[bi-Min（bi）]/[Max（bi）-Min（bi）]（1）
For indicators to which smaller is better， the calculation formula of single-factor rationality-satisfaction degree is：
M（ bi ）=[Max（bi）-bi]/[Max（bi）-Min（bi）]（2）
After obtaining the rationality-satisfaction degree of each single-factor index of different peach varieties， considering that the quality characteristics of a variety cannot be evaluated by single-factor indicators， it is now assumed that their changes are independent and the total contribution to the quality characteristics can be approximated as having no essential difference. And according to consolidation principle of rationality-satisfaction degree and multiple value theory， the single-factor satisfaction degrees are combined into the synthesized rationality-satisfaction degree of quality. A higher synthesized rationality-satisfaction degree of quality proves that the corresponding variety meets peoples requirements for its quality better. The synthesized rationality-satisfaction degree is expressed by formula （3） as following：
V=∑ni=1WiMi（3）
In the formula， V is the synthesized rationality-satisfaction degree; Wi is weight number of the ith indicator， which satisfies 0≤Wi≤1 and is given through the experts score; and Mi is the satisfaction degree of the ith single-factor indicator.
According to the literatures [15-16]， the weight numbers of single fruit weight， firmness， vitamin C， soluble solids， total sugar and total acid are 0.15， 0.10， 0.20， 0.15， 0.20 and 0.20， respectively.
Results and Analysis
Comparison of sensory quality of different peach varieties
Single fruit weights of different peach varieties
Fruit quality is an important indicator for measuring fruit size， as well as an important factor affecting yield and processing adaptability and consumer acceptability， and is greatly affected by variety and maturity[17]. Samples of five peach varieties were weighed with skin using an electronic balance and compared. It can be known from Fig. 1 that ball peach had the largest single fruit weight， which was 8 times of that of flat peach， and the order of single fruit weight was ball peach>century peach>Diao Baifeng>yellow peach>flat peach. However， flat peach had shortest error bar， which indicated that the picked fruit had most even size.
Fruit shape indexes of different peach varieties
The fruit shape index was measured by measuring the maximum longitudinal and transverse diameters of peaches with a vernier caliper， and expressed as the ratio of the longitudinal diameter to the transverse diameter. The peaches could be divided into flat， oval， and pointed round types according to fruit shape index[9，18]. Specifically， a fruit shape index within 0.6-0.8 indicated that the peach was flat， that within 0.9-1.0 stood for oval peaches， and a value larger than 1.0 meant that the peach was pointed round. It can be known from Table 1 that yellow peach had the largest fruit shape index， and the values of different peach varieties followed an order of yellow peach>ball peach>century peach>Diao Baifeng>flat peach. The fruit of century peach， Diao Baifeng and ball peach were all oval， the shape of yellow peach was pointed round， and that of flat peach was flat. Firmness of different peach varieties
Fruit firmness is an important indicator of fruit maturity and shelf life. Fruit firmness affects the length of the fruit supply period， the distance of transportation， and the improvement of economic benefits， and has become a factor limiting the development of peaches. As the circulation of peaches becomes more and more widespread， the requirements for firmness have also increased[9]. Consumers also have new requirements for firmness， that is， the fruit should have certain firmness in the hands of consumers after transportation and sales. The firmness without skin was measured using a texture analyzer according to the instrument instructions. It can be known from Fig. 2 that the firmness of the five varieties ranked as yellow peach>flat peach>century peach>ball peach>Diao Baifeng.
Comparison of nutritional quality of different peach varieties
Soluble solid contents of different peach varieties
Soluble solids are also an important indicator of fruit maturity. The soluble solids in fruits are mainly water-soluble sugars[10]. As the peach fruit matures， more starch is converted into sugars and gradually accumulated in the fruit， and the taste of the fruit also changes from sour to sweet. Generally speaking， the higher the content of soluble solids， the higher the sweetness of the fruit and the better the taste. Therefore， increasing the soluble solid content of peach fruit will also directly increase its market acceptance and improve the competitive advantage of the product[19]. The soluble solids of the peaches were determined using a handheld refractometer following the instrument instructions. It is known from Fig. 3 that the variety with the most soluble solid content was century peach， and the soluble solid contents followed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach. However， Diao Baifeng showed shortest error bar， which also showed that its determination was more accurate.
Agricultural Biotechnology2020
Total sugar contents of different peach varieties
The flavor of a peach depends largely on its sweetness and acidity. The sugar content in fruit is affected by the variety and maturity， and it will vary to some extent depending on the variety. The sugars in peach pulp are mainly sucrose， fructose and glucose. Both fructose and glucose are reducing sugars. Sucrose is a non-reducing sugar， but it produces glucose and fructose after hydrolysis. Therefore， sugar content can be determined according to the Fehling reagent method in the national standard for reducing sugars[11]. It can be seen from Fig. 4 that the variety century peach had the highest total sugar content， and the values of different varieties ranked as century peach>ball peach>Diao Baifeng>yellow peach>flat peach. However， ball peach exhibited the shortest error bar， indicating that its determination was more accurate. Organic acid content of different peach varieties
The organic acids in peach are mainly malic acid， citric acid and quinic acid. The amount of acid content is also an important indicator for evaluating its quality. The acid contents in the samples were determined according to the acid-base titration method in national standards[12]. It can be seen from Fig. 5 that the variety with the highest organic acid content was ball peach， and the values of different varieties ranked as ball peach>Diao Baifeng>century peach>flat peach> yellow peach. The organic acid content of ball peach was nearly 3 times that of yellow peach. The error bar of flat peach was zero， which meant that its determination error was the smallest and more accurate.
Sugar-acid ratios of different peach varieties
Sugar-acid ratio is the main factor affecting peach fruit flavor. It is expressed as the ratio of total sugar to total acid in the fruit. The sugar-acid ratio of each peach obtained in this study was the ratio of the average sugar content to the average organic acid content. From Table 2， it can be seen that yellow peach had the highest sugar-acid ratio， and the values of different varieties ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach， indicating that yellow peach was the sweetest， while flat peach was not as sweet as other varieties.
Vitamin C contents of different peach varieties
Vitamin C has the health care functions of beautifying skin and preventing diseases and the function characteristics of high water solubility and easy absorption. Peach fruit contains a small amount of vitamin C， and its content was determined according to the 2，6-dichloroindophenol titrimetric method in national standard[13]. It can be seen from Fig. 6 that the variety with the highest vitamin C content was flat peach， and the values of different varieties exhibited an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach. However， the content of vitamin C was overall not too high. Century peach had shortest error bar， indicating that its determination results were more accurate.
Comprehensive evaluation based on rationality-satisfaction degree and multiple value theory
Single-factor satisfaction degree with different quality of different peach varieties
The single-factor satisfaction degree of each quality can be calculated from the satisfaction degree formulas （1） and （2）， as shown in Table 3. It can be seen from the table that ball peach had highest satisfaction degree with single fruit weight; the highest satisfaction degree with firmness was observed in yellow peach; the variety having highest satisfaction degree with soluble solids was century peach; century peach exhibited the highest satisfaction degree with total sugar content; the variety having highest satisfaction degree with organic acid content was yellow peach; and flat peach exhibited the highest satisfaction degree with vitamin C content. Satisfaction degree to sensory and nutritional quality of different peach varieties
According to the single-factor satisfaction degree of Table 3， the satisfaction degrees with the sensory quality and nutritional quality of different peach varieties are shown in Table 4. It can be seen from Table 4 that yellow peach had highest satisfaction degree with the sensory quality， and century peach exhibited the highest satisfaction degree with the nutritional quality.
Synthesized rationality-satisfaction degree values of different peach varieties
Formula （3） was used to calculate the synthesized rationality-satisfaction degree of peach fruit quality characteristics， as shown in Table 5. According to Table 5， it was finally concluded that yellow peach had the highest synthesized rationality-satisfaction degree， and the values of different varieties followed an order of yellow peach>century peach>Diao Baitao>ball peach>flat peach. That is to say， the yellow peach variety from Wujian Town， Yongchuan District， Chongqing City was the best， followed by Tongnan century peach variety， Chengdu Diao Baifeng and ball peach were next to them， and the flat peach variety from Wujian Town， Yongchuan District ranked last.
Conclusions and Discussion
The single fruit weights of different peach varieties ranked as ball peach>century peach>Diao Baifeng>yellow peach>flat peach; the firmness of fruit followed an order of yellow peach>flat peach>century peach>ball peach>Diao Baifeng; and the fruit shape index ranked as yellow peach>ball peach>century peach>Diao Baifeng>flat peach. The fruit of century peach， Diao Baifeng and ball peach were all oval， the shape of yellow peach was pointed round， and that of flat peach was flat.
The contents of soluble solids in different peach varieties showed an order of century peach>yellow peach>ball peach>Diao Baifeng>flat peach; the total sugar contents followed an order of century peach>ball peach>Diao Baifeng>yellow peach>flat peach; the organic acid contents ranked as by ball peach>Diao Baifeng>century peach>flat peach>yellow peach; the sugar-acid ratios exhibited an order of yellow peach>century peach>Diao Baifeng>ball peach>flat peach; and the vitamin C contents followed an order of flat peach>Diao Baifeng>century peach>yellow peach>ball peach.
Comprehensive evaluation based on the rationality-satisfaction degree multiple value theory showed that the synthesized rationality-satisfaction degree values ranked as yellow peach>century peach>Diao Baifeng>ball peach>flat peach. Among the five peach varieties in this study， yellow peach from Wujian Town， Yongchuan District was the best， followed by Tongnan century peach variety， Chengdu Diao Baifeng and ball peach were next to them， and the flat peach variety from Wujian Town， Yongchuan District ranked last. References
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