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Antioxidant capacity, quality, anthochyanins and nutrients content of several peach cultivars [Prunus persica (L.) Batsch] grown in Spain. Gemma Reig, Ignasi Iglesias, Ferran Gatius, and Simó Alegre J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/jf401183d • Publication Date (Web): 28 May 2013 Downloaded from http://pubs.acs.org on June 9, 2013
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Journal of Agricultural and Food Chemistry
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Antioxidant capacity, quality, anthochyanins and nutrients content of several
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peach cultivars [Prunus persica (L.) Batsch] grown in Spain.
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G. Reig1, I. Iglesias1, F. Gatius2, and S. Alegre1
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IRTA, Estació Experimental de Lleida, Av. Rovira Roure, 191, E-25198 Lleida.
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Universitat de Lleida, Department de Química, Av. Rovira Roure, 191, E-25198 Lleida.
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Abstract
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Fruit quality, sensory evaluation, nutrient contents and antioxidant capacity of 106
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peach cultivars from different breeding programmes were evaluated at IRTA - Estació
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Experimental de Lleida (Catalonia Spain) during two growing seasons (2010 and 2011).
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High variability was found among cultivars within each quality trait, where different
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cultivars were scored as the best and the worst. As example, a 5-fold range (2.17 to
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12.07 g malic acid L-1), 6-fold range (144.20 to 711.73 µg Trolox g-1 FW) and 11-fold
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range (0.70 to 11.43 mg 3G kg-1 FW) were observed in titratable acidy (TA), relative
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antioxidant capacity (RAC) and anthocyanins content respectively. Breeding
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programme within each fruit type (melting peach, nectarine and flat peach) and
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qualitative pomological traits had also significant effect on quality. Nevertheless, each
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breeding programme had specific characteristics that distinguished it from the others.
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Even so, within each breeding programme there is high variability among cultivars.
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Therefore, growers should not base their strategy exclusively on the choice of breeding
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programme. PCA analysis for each fruit type (melting peach, nectarine, nonmelting
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peach and flat peach) allowed selecting a set of cultivars from different breeding
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programmes with the highest quality performance. For example, cultivars such as
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‘Azurite’, ‘IFF 1230’,
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‘Mesembrine’ and ‘Platifirst’ hag higher sweetness and flavour compared to others.
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Therefore, this study could help breeders to make decisions for the selection of new
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cultivars able to improve quality features of fruit intake, technicians to know better
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quality performance of peach cultivars, and consumers to meet their expectations for
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fruit with high health-benefits and a specific taste.
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Keywords: Prunus persica, fruit quality, sweetness, sourness, sucrose, malic acid,
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relative antioxidant capacity, anthocyanins content.
‘Amiga’, ‘Fire
Top’,
‘African Bonnigold’,
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‘Ferlot’,
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Introduction
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Peach [Prunus persica (L.) Batsch] is the most important stone fruit crop in Spain,
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which ranks second in European production, after Italy and followed by Greece and
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France.1 Peach is also the most dynamic fruit species in terms of new cultivars released
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per year.2 New cultivars originate from more than 70 active breeding programmes
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which are mainly found in USA, followed by Europe (Italy and France)2, are the source
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of many of the cultivars grown in Spain3. Sometimes, these cultivars show an uncertain
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agronomic, and so qualitative, performance when they are grown under climatic
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conditions that are different from those where they were originally developed.4-6
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Breeders have traditionally selected primarily for external quality (fruit size and
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appearance)7, with organoleptic and nutritional traits being a secondary goal.8-10,2 Today,
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however, health concern is one of the major driving forces of the world food market and
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it is the first or second most important concern of consumers, though it varies
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regionally. Consumers start to realize the connection between diet and health; therefore
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tend to associate their diets with the prevention of cardiovascular disease, vision
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problems, obesity, arthritis/joint pain, and high cholesterol.11,12
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Fruits and vegetables are excellent functional foods as they are high in antioxidant and
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nutritional compounds13. These naturally occurring substances not only play an
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important role in visual appearance (pigmentation and browning) and taste (astringency)
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but also have health-promoting properties, acting as antioxidants by scavenging harmful
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free radicals, which are implicated in most degenerative diseases.14 As a result, there is
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growing interest in fruit quality and nutritional composition in breeding programmes
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worldwide.15 Many of them, in order to improve fruit quality, produce cultivars with
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excellent taste, high sugar levels and balanced sugar:acid ratios.16 Others have directed
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their interest to the identification and quantification of phenolic compounds in fruit in
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order to evaluate their potential health-promoting properties17 and to develop peaches
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with high levels of compounds potentially beneficial to human health.18
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The huge peach cultivar supply and fruit health benefits contrast with the decrease of
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peach consumption in Spain5, as is the case in other western countries (Europe and
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USA)19,20. Poor internal fruit quality, perceived when the fruit is consumed, is the main
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reason claimed by consumers for declining to buy fresh fruit2,5. Internal fruit quality is
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related mainly to two factors: firmness and flavour. Firmness is essential for postharvest
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management, marketing and consumer acceptance. Too soft or too firm flesh impact
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negatively on quality attributes.21 High firmness is a consequence of harvesting
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immature fruits and implies less flavour, aroma, texture and juiciness. As a result, the
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consumer is disappointed and does not buy peaches again during that season3. Many
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authors22,23 have suggested that sensory quality attributes and the nutritive value of
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peach (Prunus persica L.) fruits as well as of other fruits play an important role in
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consumer satisfaction and influence further consumption.
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The high number of new cultivars on the market makes their technical management and
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their quality performance identification difficult for both growers and technicians. As
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far as known, no analyses have been performed on fruit quality (flesh firmness, soluble
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solids content, titratable acidity), sensory evaluation (sweetness, sourness and flavour)
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and nutrients contents and antioxidant capacity (individual and total sugars content,
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individual and total acids content, relative antioxidant capacity and anthocyanins
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content) of peach commercial cultivars from different breeding programmes grown
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under Mediterranean climate conditions. Therefore, the aims of this work were: (1)
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characterization of 106 peach cultivars by measuring fruit quality, sensory, nutrients and
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antioxidant capacity traits, (2) to study the influence of breeding programme and
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pomological traits in the quality, sugars, acids, anthocynins content and relative
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antioxidant capacity profile in Prunus persica fruits, (3) examine relationships among
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all variables evaluated and (4) to select commercial peach cultivars with enhanced fruit
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quality, sensory, nutrient and antioxidant capacity traits by PCA analysis.
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Material and Methods
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Plant material
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The study was carried out during the 2010 and 2011 seasons on fruits of 106 peach
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cultivars from an experimental collection plot located at the IRTA-Estació Experimental
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in Lleida, (Catalonia, Spain). Their breeding programme, fruit type, flesh colour and
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fruit shape are described in Table 1. In order to simplify the analysis, both flat peach
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and flat nectarine cultivars were considered flat peach cultivars.
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The experimental orchard contained three trees per cultivar planted in a single block,
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trained in central axis system, grafted on INRA®GF-677 rootstock and spaced 4.5 m x
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2.5 m. The rows were oriented from NE to SW. Trees were trickle-irrigated using drip
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irrigation with two drips per tree delivering 4 litres per hour. Standard commercial
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management practices recommended for the area were followed including, fertilization,
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plant disease and pest control, in accordance with the guidelines of integrated fruit
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production. The weather conditions for the period 2010-2011 were usual for this warm
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Mediterranean area: high summer temperatures (>30ºC) and low rainfall (379 mm per
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season). Hand thinning in early May was performed each season.
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At harvest date, when firmness ranged from 39 to 49N, 24 fruits per cultivar (8 fruits
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per tree), and season were picked in order to make the following determinations. The
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fruits were picked from the periphery of the tree and at 1.5–2.0 m above ground level.
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Fruit quality determinations
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Eighteen of 24 fruits per cultivar and season were assessed for flesh firmness (FF),
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soluble solids content (SSC) and titratable acidity (TA). Flesh firmness of two opposing
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cheeks (the most and least exposed to light) of each fruit was measured using an 8 mm
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tip penetrometer fixed in a drill stand (Penefel; Copa-Technology; CTIFL, Saint Etienne
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du Gres, France). SSC and TA were determined on flesh juice extracted by an automatic
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juicer (Moulinex, Type BKA1). SSC was determined using a digital calibrated
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refractometer (Atago PR-32, Tokyo, Japan) and the results were expressed in º Brix. TA
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was measured with an automatic titrator (Crison GLP 21, Barcelona, Spain) and
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determined by titrating 10 mL of juice with 0.1 M NaOH to a pH endpoint of 8.2.
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Results were given as grams of malic acid per litre. Ripening index (RI) was then
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calculated as SSC/TA ratio. In order to characterize the cultivars, two groups were
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established according to the TA value24: sweet (6 g. malic acid per litre).
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Sensory determinations
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Three of the 24 fruits per cultivar and season were subjected to sensory evaluation by a
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panel of four experts. Based on Oraguzie et al.25, the panel was set up using the
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following criteria: (1) membership of the IRTA-Fruit Growing area, (2) at least 3 years
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of experience in stone fruit sensory evaluation and (3) participation in a sensory training
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exercise. Before the assessments and for each season, the experts undertook a week long
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course of specific training on peach sensory attributes (Table 2) according to the
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procedures determined by the International Organization for Standardization (no. 8586-
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1, 1993) provided by IRTA sensory group. An overall sensory score, from 1 to 10, was
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used to understand the influence of all sensorial attributes together, representing a fair
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and indicative value of threshold acceptability for consumers.26 Each sample for sensory
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evaluation consisted of 3 pieces of 1.5 cm3 (without skin), one from each of three fruits
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per cultivar. Peeled fruit samples were identified by a random 2-digit code and
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presented to the expert in white plastic cups in random order. Intensity of each sensory
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attribute was recorded on 150 mm unstructured line scales, anchored at 0 (absent) and
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150 (extreme). The experts were instructed to use mineral water and crackers were
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provided as a palate cleanser between each sample assessment.
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Extraction and quantification of sugars and organic acids
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In order to extract and quantify the main soluble sugars and organic acids per cultivar
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and season, 10 mL of flesh juice were pooled. An aliquot of 5 mL was taken and diluted
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in ultrapure water (1:1). The mixture was vortexed (10 sec) and filtered using triple
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sterile gauze. 2 mL were extracted and immediately frozen in liquid nitrogen and
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storage at -25ºC until analysis. In the moment of analysis, extracts were defrosted at 4ºC
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followed by centrifugation at 11000 rpm for 15 min at 4ºC. 500 µl of supernatant were
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extracted and clarified by a Whatman syringe filter PVDF (13 mm, 0.22 µm, ref. 6779-
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1302) and purified using a Sep Pak light 130 mg C18 (Waters. WAT023501). Sep Pak
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was previously activated with 1 mL of methanol and conditioned with 1 mL of water.
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To ensure the total elution of the compounds of interest, 500 µL of Milli-Q water was
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finally added. 100 µL of filtrate were diluted with ultrapure water (1:10) in a 1 mL
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HPLC vial. Sugars and organic acids were analysed by a Waters HPLC system.
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In the case of sugars, 10 µl from the HPLC vial were injected and isolated by a strong
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Hamilton HC-75 (Ca2+) cation-exchange resin column (305 x 7.8 ; 9 µm Teknokroma,
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Barcelona, Spain, ref. HC-79476) at 90ºC. Flow rate was set at 0.6 ml min-1 using
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ultrapure water as a mobile phase. Compounds were detected by a 2414 Refractive
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Index Detector (x16) at 30ºC. External calibration was performed at 6 calibration levels
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by dilution of a stock solution composed of 2.5 g·L-1 of sucrose, 0.6 g·L-1 of glucose and
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fructose and 0.25 g·L-1 of sorbitol. In this case, the lowest calibration level for sorbitol
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was taken as the instrumental limit of quantification (LOQ) because of its low
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concentration present in the samples. Calibration curves showed good linearity, and
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their determination coefficients (R2) were higher than 0.99. Results from individual
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sugars were expressed as mean of the proportion (%) respect to total sugar content, and
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total sugar content as g·L-1 of flesh juice.
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To determine the organic acids, 20 µL from the HPLC vial were injected and isolated
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by a reverse phase strong Hamilton HC-75 (Ca2+) cation-exchange resin column (305 x
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7,8 ; 9 µm Teknokroma, Barcelona, Spain, ref: HC-79476) at 90ºC. Flow rate was set at
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1 mL·min-1 using ultrapure water as a mobile phase buffered at pH 3. Compounds were
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detected by a 2414 Refractive Index Detector (x16) at 30ºC. External calibration was
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performed at 6 calibration levels by dilution of a stock solution composed of 1.0 g·L-1 of
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malic acid, citric acid and quinic acid and 0.05 g·L-1 of shikimic acid. The lowest
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calibration level for sorbitol was taken as the LOQ because of its low concentration
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present in the samples. Calibration curves showed good linearity, and their
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determination coefficients (R2) were higher than 0.99. Results from individual organic
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acids were expressed as a mean of the proportion (%) respect to total acids content, and
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the total acids content as g·L-1 of flesh juice.
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Sweetener potency was defined as the number of times the compound was sweeter than
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sucrose, based on its equi-sweetness.27 The equi-sweet concentrations used were 1, 1.75
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and 0.75 for sucrose, fructose and glucose, respectively28 and 0.6 for sorbitol.29
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Relative antioxidant capacity (RAC) and anthocyanins content.
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Three of the 24 fruits were chosen from each cultivar and season to measure
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anthocyanins content and RAC as described by Cantín et al.
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the 2,2-dipyridyl,1,1-diphenyl-2-picrylhydrazyl (DPPH) radical method adapted from
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RAC was quantified by
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Brand-Williams et al.30 The results were expressed in µg of Trolox per gram of fresh
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weight (FW). Total anthocyanins content analysis was determined by the method of
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Fuleki and Francis31 adapted to peach tissue. Anthocyanins were quantified as
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milligrams of cyaniding-3-glucoside per kg of FW using a molar extinction coefficient
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of 25965 cm-1 M-1 and a molecular weight of 494.32
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Statistical Analysis
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Three replications for each parameter evaluated and season were used for each cultivar.
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To obtain basic statistics for the entire plant material studied, the number of observed
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cultivars, maximum, minimum and mean values, mean standard error and standard
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deviation for each trait were recorded. All data were treated by means of analysis of
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variance (GLM procedure) using the SAS program package.33 Differences between fruit
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type were tested with Tukey’s honestly significant difference (HSD) test at a
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significance level of 0.05 (p
