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Postharvest Biology and Technology 91 (2014) 64–71

Contents lists available at ScienceDirect

Postharvest Biology and Technology

journa l h om epa ge : www.elsev ier .com/ locate /postharvbio

ostharvest pigmentation in red Chinese sand pears (Pyrus pyrifoliaakai) in response to optimum light and temperature

ongwang Suna,1, Minjie Qiana,1, Ruiyuan Wua, Qingfeng Niua,uanwen Tenga,∗, Dong Zhanga,b,∗∗

Department of Horticulture, The State Agricultural Ministry Key Laboratory of Horticultural Plant Growth, Development & Quality Improvement, Zhejiangniversity, Hangzhou 310058, Zhejiang Province, ChinaCollege of Horticulture, Northwest A&F University, Yangling 712100, Shaanxi Province, China

r t i c l e i n f o

rticle history:eceived 20 August 2013ccepted 23 December 2013

eywords:ed Chinese sand pearuropean pearnthocyaninolorationemperatureight

a b s t r a c t

The development of red color in the peel of red Chinese sand pears (Pyrus pyrifolia Nakai) is influenced bytemperature and light; however, the response patterns vary among different cultivars. In this study, wesystematically investigated the influence of postharvest treatment with various temperatures (low, high,variant and constant) on detached mature fruit of red Chinese sand pear ‘Mantianhong’ and ‘Meirensu’.Fruit of red apple (Malus domestica Borkh.) ‘Royal Gala’ and red European pear (P. communis L.) ‘Cascade’received the same treatments for comparison. Furthermore, the effects of light quality and irradiance levelon ‘Mantianhong’ pears were evaluated at the optimum temperature for anthocyanin accumulation. Fruitfirmness and concentrations of total soluble sugars and organic acids were measured to determine fruitquality. The effect of temperature on red Chinese sand pear fruit color was similar to that of apples, but notEuropean pear. Moreover, low temperature more effectively induced red coloration in ‘Mantianhong’ and

‘Meirensu’ pears than high temperature; anthocyanin levels increased with increasing irradiance levelfrom 0 to 532 �mol m−2 s−1, and UV-B and visible light synergistically improved the red color of the fruit.Therefore, a combination of low temperature and high intensity of UV-B/visible light could improve thepostharvest coloration of red sand pear fruit. The results will contribute to an improved understandingof the mechanism responsible for the coloration of red Chinese sand pears and will aid development ofnew techniques to improve color in postharvest fruit.

. Introduction

Chinese sand pears are widely cultivated in China, Korea andapan, and the fruit color may vary from yellow or green to russet-rown (Teng and Tanabe, 2004). In recent decades, several cultivarsith red fruit have been discovered and developed in China (Tao

t al., 2004). These red pears are preferred by consumers becausef their attractive appearance and nutritional value; however, theed peel color is not uniform and varies with growing conditionsHuang et al., 2009). Given that red pear fruit are highly coveted, its necessary to develop postharvest treatments that can be used tomprove the red color of fruit that lack sufficient color.

Fruit color mainly depends on the concentration and proportionf three classes of pigments: anthocyanins, carotenoids and chloro-hylls, which contribute red, yellow and green colors, respectively

∗ Corresponding author. Tel.: +86 571 88982803; fax: +86 571 88982803.∗∗ Corresponding author. Tel.: +86 029 87082613; fax: +86 029 87082613.

E-mail addresses: ywteng@zju.edu.cn (Y. Teng), afant@nwsuaf.edu.cn (D. Zhang).1 These authors contributed equally to this work.

925-5214/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.postharvbio.2013.12.015

© 2014 Elsevier B.V. All rights reserved.

(Allan et al., 2008). Anthocyanins belong to the diverse group ofubiquitous secondary metabolites known as flavonoids (Holton andCornish, 1995), which are believed to have multiple physiologicalfunctions and provide potential benefits to human health, includingprotection against cancer, inflammation, coronary heart diseasesand other age-related diseases (Boyer and Liu, 2004; Butelli et al.,2008; Gould et al., 2009).

Temperature and light are important elements that affect fruitcolor. Several studies have reported the influence of differenttemperatures (high, low, variant and constant) and light (qualityand quantity) on fruit color. Low temperature (LT) causes higheranthocyanin accumulation in most apple cultivars compared withhigh temperature (HT). Under UV-B/visible light, apple fruit ofthe ‘Iwai’, ‘Sansa’, ‘Tsugaru’, ‘Homei Tsugaru’ and ‘Akane’ culti-vars treated with a LT of 17 ◦C develop better red color than thosetreated with a HT of 27 ◦C (Ubi et al., 2006). HT is detrimentalfor color development and reduces anthocyanin accumulation in

fruit of ‘Mondial Gala’ and ‘Royal Gala’ apples (Wang et al., 2011).Compared with HT of 27 ◦C, a LT of 17 ◦C promotes UV-B-inducedanthocyanin accumulation and red coloration in ‘Red Delicious’apples (Xie et al., 2012). Furthermore, different apple cultivars show

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arious response patterns to temperature under UV-B/visible light.or example, ‘Jonathan’ apples treated with HT of 25 ◦C develop aore vivid red color than those treated with LT of 15 ◦C (Arakawa,

991). Under UV-B/visible light, a temperature range of 20/6 ◦Cday/night) has a greater effect on anthocyanin accumulation inhe peel of ‘Cripps’ Pink’ apples than a constant 6 ◦C LT treatmentMarais et al., 2001a). Cool nights followed by warm days, whenV-B and light are incident on the fruit peel, are considered toring about blush formation in apple fruit (Reay, 1999). Antho-yanins cannot be detected in the peel of bagged fruit of the redhinese sand pears ‘Meirensu’ and ‘Yunhongli NO. 1’, but rapidlyccumulate when the fruit are re-exposed to light (Huang et al.,009). Studies on red apple cultivars show that UV is the mostffective wavelength band for anthocyanin biosynthesis, whereashite light has almost no effect; UV-B (280–320 nm) has a greater

ffect than UV-A (320–390 nm), and has a synergistic effect withed and white light on induction of anthocyanin accumulationArakawa, 1988a, b; Saure, 1990; Ubi et al., 2006). In a baggingxperiment, fruit of ‘Meirensu’ pear receiving 100%, 80% and 35%unlight showed a graduated decline in anthocyanin accumulationith decreasing exposure to sunlight (Huang et al., 2009).

Anthocyanin accumulation patterns vary among plants. Antho-yanin biosynthesis peaks at two developmental stages in appleruit, initially at the fruitlet stage in both red and non-red cultivars,hich is not of commercial importance, and subsequently at the

ipening fruit stage only in red cultivars (Saure, 1990; Honda et al.,002). In grapes, anthocyanin biosynthesis commences with theeginning of berry ripening and continues throughout the ripeninghase (Boss et al., 1996). Some cultivars of European pear generallyttain their highest anthocyanin concentrations at about midwayetween anthesis and harvest (Dussi et al., 1997; Steyn et al.,004a). Unlike the pigmentation patterns described above, antho-yanin biosynthesis in red Chinese sand pears accompanies fruitaturation and the highest anthocyanin concentration is attained

t maturity. Our previous experiments showed that UV-B/visiblerradiation of debagged ‘Mantianhong’ red Chinese sand pear fruitor 10 days induced good pigmentation; however, ‘Cascade’ Euro-ean pears showed no change in pigmentation with the samereatment, indicating that the two cultivars have different responseatterns to light quality (Qian et al., 2013). The fruit of Europeanear ‘Wujiuxiang’ subjected to a temperature of 4 ◦C showed bettered color than those subjected to 25 ◦C (Li et al., 2012). Our previoustudy showed that, compared with LT of 17 ◦C, HT of 27 ◦C inducedetter red coloration in fruit of ‘Yunhongli No. 1’ Chinese sand pear,hich indicated that red Chinese sand pears respond uniquely to

emperature (Zhang et al., 2012). Nevertheless, few studies havenvestigated the fruit color of red Chinese sand pears in responseo temperature and light.

In this study, we systematically investigated the influence of dif-erent temperatures (low, high, variable and constant) on detachedruit of the red Chinese sand pears ‘Mantianhong’ and ‘Meirensu’.Royal Gala’ apples and ‘Cascade’ pears were treated in parallel tovaluate and compare their pigmentation responses to those of theand pears. In addition, we investigated the effect of different lightualities and irradiance levels on ‘Mantianhong’ pears at 17 ◦C, itsptimum temperature for anthocyanin accumulation. Fruit firm-ess and total concentrations of soluble sugars and organic acidsere determined as measures of fruit quality. It is reported that,

ompared with immature fruit, mature apple and pear fruit areiable to develop red coloration under the same treatment condi-ions (Reay and Lancaster, 2001; Zhang et al., 2013), thus matureruit of apple and pear were used. Our results will be helpful

o understand the mechanism underlying the responses of redhinese sand pear fruit to temperature and light, and will aid theesign of postharvest techniques to enhance fruit coloration inears.

Technology 91 (2014) 64–71 65

2. Materials and methods

2.1. Plant material and experimental treatments

Bagged mature fruit of red Chinese sand pears (Pyrus pyrifoliaNakai) ‘Mantianhong’ and ‘Meirensu’ were obtained from a com-mercial orchard in Zhengzhou city, Henan Province, China. Fruitof red European pear (Pyrus communis L.) ‘Cascade’ was obtainedfrom the Zhengzhou Fruit Research Institute, Chinese Academy ofAgricultural Sciences, Zhengzhou City, Henan Province, China. Fruitof red apple (Malus domestica Borkh). ‘Royal Gala’ was obtainedfrom a commercial orchard in Anyang city, Henan province, China.Five mature trees of ‘Mantianhong’ pear, ‘Meirensu’ pear and ‘RoyalGala’ apple and three mature trees of ‘Cascade’ pear were selectedfor the fruit bagging treatment. These trees were similar in sizeand number of fruit carried and had uniform exposure to sunlight.Sixty fruit of uniform size and growth positions in every selectedtree were bagged 40 days after full bloom. The bagged fruit wereharvested at commercial maturity (165, 165, 145 and 125 days afterfull bloom for ‘Mantianhong’ pear, ‘Meirensu’ pear, ‘Cascade’ pear,and ‘Royal Gala’ apple, respectively), and transported to the lab-oratory immediately. Intact fruit of uniform size were chosen asexperimental material. There were 15 fruit in every treatment andeach treatment had three replicates.

Different temperature treatments were applied by placing thefruit in an overhead-lit phytotron (Zeda Instrument Company,AGC-D002Z, Hangzhou, China) for 10 days and 7 days, respec-tively. Two 9 W UV-B lamps (PL-S 9 W/12, 280–315 nm, Philips, TheNetherlands) and four 36 W fluorescent lamps (FSL, T8 36 W/765,China) were installed in the phytotron. The relative humidity wasmaintained at 80%. The photon flux density (PFD) at the bottom ofthe incubator (0.8 m from the light source) was 270 �mol m−2 s−1

(measured with a TES1332A quantum meter, TES Taiwan, China).The temperature treatments applied to each fruit type were as fol-lows: (1) ‘Mantianhong’ pear and ‘Meirensu’ pear fruit were treatedwith five constant temperatures (12, 17, 22, 27 and 32 ◦C) andone variant temperature (27 ± 6 ◦C); (2) ‘Cascade’ pear fruit weretreated with three constant temperatures (17, 22 and 27 ◦C); (3)‘Royal Gala’ apple fruit were treated with four constant tempera-tures (17, 22, 27 and 32 ◦C) and one variant temperature (27 ± 6 ◦C).For the variant temperature treatment, the temperature increasedfrom 21 ◦C to 33 ◦C from 0:00 to 12:00 and decreased to 21 ◦C from12:00 to 24:00 on each day (at the rate of 1 ◦C/h).

To examine the effect of different light treatments, fruit of‘Mantianhong’ pear were placed in the phytotron maintained at aconstant 17 ◦C and 80% RH. The light treatment conditions were asfollows: (1) constant darkness; (2) two 9 W UV-B lamps; (3) eight36 W fluorescent lamps; (4) one 9 W UV-B lamp plus four 36 Wfluorescent lamps; (5) two 9 W UV-B lamps plus four 36 W fluores-cent lamps; (6) two 9 W UV-B lamps plus eight 36 W fluorescentlamps. The PFD at the bottom of the incubator (0.8 m from the lightsource) was measured as described above and reached 0, 28, 504,266, 270, and 532 �mol m−2 s−1, respectively. Treated fruit weresampled after 10 days of irradiation.

Sampled fruit in the two experiments were subjected to mea-surement of color parameters, namely lightness (L*), saturation (C)and color hue (h◦). Peel and flesh samples were separated by peelingfresh fruit with a potato peeler and immediately freezing in liquidN2, then stored at −80 ◦C until use. The peel was used to assay pig-ment concentrations, while flesh was used to assay soluble sugarsand organic acids.

2.2. Fruit measurements

Fruit peel color was measured at the reddest position on the fruitusing a colorimeter (CR-400, Minolta, Japan), which provided CIE L*,

6 gy and Technology 91 (2014) 64–71

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Fig. 1. (A) Peel color of P. pyrifolia cv ‘Mantianhong’ and ‘Meirensu’, P. communis cv‘Cascade’ and P. communis cv ‘Cascade’, M. domestica cv ‘Royal Gala’ irradiated sideof fruit as affected by temperatures during postharvest UV-B/visible irradiation. (B)Peel color of ‘Mantianhong’ pear fruit as affected by different lights treatment. Note:

◦ ◦

6 Y. Sun et al. / Postharvest Biolo

* and b* values. L* represents the relative lightness of color with aange from 0 to 100, being low for dark color and high for light color.oth a* and b* scales extended from −60 to 60. Negative a* values

ndicated greenness and positive values indicated redness, while b*as negative for blueness and positive for yellowness. These valuesere then used to calculate the hue angle degree (h◦ = arctangent

b*/a*]), where 0◦ = red-purple, 90◦ = yellow, 180◦ = bluish greennd 270◦ = blue, and chroma (C* = [a*2 + b*2]1/2), which indicatedhe intensity or color saturation (McGuire, 1992). Fifteen fruit weresed for each measurement.

A TA-XT plus Texture Analyser (Stable MicroSystems, UK) wassed to measure the fruit firmness with a diameter probe of

millimeter (mm), a penetration depth of 5 mm, and a penetrationate of 1 mm s−1. One mm thick sliced peel from two opposite sidesf the fruit was used for these measurements and the thickness wasxpressed in newtons (N).

Total soluble solids of fifteen fruit (two measurements per fruit)ere determined using a digital refractometer (PR-101, Atago,

apan).

.3. Extraction and measurement of total anthocyanin

The total anthocyanin concentration was measured using aH differential method and was presented as mg cyanidin-3-alactoside per 100 g fresh tissue (Dussi et al., 1995). One gramf fruit peel was mixed with methanol containing 0.1% HClollowed by centrifugation at 4 ◦C and 12,000 rpm for 20 min.he absorbance of each 100 �L extract was assessed using aU800 spectrophotometer (Beckman Coulter, Fullerton, CA, U.S.) at10 nm and 700 nm in buffers of pH 1.0 and 4.5. Anthocyanin con-entration was calculated using the equation: A = [(A510 − A700)H1.0 − (A510 − A700) pH4.5] with a molar extinction coefficient ofyanidin-3-galactoside of 3.02 × 104.

.4. Extraction and measurement of total chlorophyll andarotenoid

One gram of ground fruit peel was homogenized in 6 mL of 80%old acetone and centrifuged at 4 ◦C and 12,000 rpm for 20 min.bsorbance of the extract was measured using a DU800 spectro-hotometer (Beckman, USA) at 440, 645 and 663 nm. From theata, chlorophyll concentration was calculated using the equation:t = 20.2 A645 + 8.02 A663, and carotenoid concentration was cal-ulated based on the equation: Ck = 4.7 A440 − 0.27Ct (Chen and

ang, 2002).

.5. Extraction and measurement of total flavonoids

Flavonoid concentration was determined by a colorimetric assayJia et al., 1999) with slightly modification. One gram of fruit peelas mixed with 6 mL 80% ethanol for 24 h at 4 ◦C in the dark.fter centrifugation for 20 min at 12,000 rpm, 0.5 mL of the super-atant was transported into a new tube, 0.3 mL 8% NaNO2, 0.3 mL0% Al (NO3)3, 2 mL 2 M NaOH, 4.9 mL ethanol were added tohe tube in that order. The absorbance of each sample was mea-ured 10 min later at 510 nm using a DU800 spectro-photometerBeckman, USA). The result was expressed as milligram of rutinSigma Chemical, St. Louis, USA) equivalent on a fresh weight basis,

g rutin g−1FW.

.6. Extraction and measurement of total soluble sugar andrganic acid

Soluble sugars and organic acids were extracted by the methodf high performance liquid chromatograph (HPLC) (Ding et al.,002). Three grams of ground flesh was homogenized in 6 mL of

T, Temperatures; DI, Days of irradiation; 27c, 27 C constant temperature; 27v, 27 Cvariable temperature (27 ± 6 ◦C); 7/10, 7 and 10 days of irradiation for apple and pearrespectively; DI, Days of irradiation; “−”, without UV-B or visible light; 1, 2, 4 and8, the number of lamps.

80% ethanol and shaken for 10 min at 35 ◦C. The homogenate wasfiltered and the residue was re-extracted twice with 80% ethanol.The combined extracts were centrifuged at 6500 rpm for 5 min, andthe supernatant was evaporated under a vacuum at less than 35 ◦Cuntil the ethanol was removed and then adjusted to the volume of1 mL with distilled water for analyses of soluble sugars and organicacids using HPLC (Beckman, USA). System Gold Software (Beckman,USA) was used to run the HPLC and to process the results.

A 20 �L aliquot of eluate was injected into a 5.0 �m NH2(4.6 mm × 250 mm) column (GL Sciences Inc., Japan) and the elutedpeaks were detected with a refractive index detector RI-1530 (JascoCorp., Japan). Acetonitrile: water (70:30) was used as the mobilephase with a flow rate of 1.0 mL min−1. Quantification of solublesugars was made by comparison with the peak area of standardsugars (Sigma chemical, St. Louis, USA).

A 20 �L aliquot of eluate was injected into an ODS C18(4.6 mm × 250 mm) column (Beckman, USA). The flow rate was0.5 mL min−1 using 3% methanol − 0.01 M K2HPO4 as the solvent.The mobile phase was adjusted to pH 2.55 using H3PO4. Organicacids were detected at a wavelength of 210 nm. The eluted peakswere detected with a 166 UV–vis detector (Beckman, USA), andquantification of individual organic acids was made using peak areaof standard acids (Sigma chemical, St. Louis, USA).

2.7. Statistical analysis

LSDs (a = 0.05) were calculated for mean separations using theData Processing System (DPS, version 3.01, Zhejiang University,Hangzhou, China), and Origin8.0 (USA) was used as drawing tool.

3. Results

3.1. Effects of different temperature and light treatments on fruit color

The peel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple fruitwas a similar white color before treatment, whereas the peel of ‘Cascade’ pearfruit was yellow (Fig. 1A). Treatment with different temperatures resulted in a

Y. Sun et al. / Postharvest Biology and Technology 91 (2014) 64–71 67

Fig. 2. (A) Effect of different temperatures on lightness (L*), chroma (C) and hue angle (h◦) of fruit in coordination with UV-B/visible irradiation. (B) Lightness (L*), chroma(C) and hue angle (h◦) of ‘Mantianhong’ pear fruit as affected by different light treatment. Note: T, Temperatures; DI, Days of irradiation; 27c, 27 ◦C constant temperature;2 ple an4

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7v, 27 ◦C variable temperature (27 ± 6 ◦C); 7/10, 7 and 10 days of irradiation for ap and 8, the number of lamps.

olor change in ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple fruito different degrees of red, whereas the color of ‘Cascade’ pear fruit showed no sig-ificant change (Fig. 1A). The optimum temperatures for red color development in

Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple were LTs of 17 ◦C, 12 ◦C,nd 17 ◦C, respectively (Fig. 1A). Red coloration decreased with increasing tempera-ure (Fig. 1A). ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple exhibitedoor color at constant 27 ◦C and variable (27 ± 6 ◦C) temperatures, although variantemperature appeared to be more effective than a constant temperature in generalFig. 1A). Untreated fruit showed high L*, high h◦ and low C values, as indicated byhe bright, yellow–white, and low saturation color (Fig. 2A). The lowest values of L*nd h◦ and the highest value of C for ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royalala’ apple were attained at low temperatures, which indicated that LT induced

ed coloration of the fruit. However, the color of ‘Cascade’ pear was not affectedignificantly by any temperature (Fig. 2A).

Fruit color was also affected by variation in light quality. The fruit of ‘Mantian-ong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple showed red color formation inesponse to visible light treatment, but the color remained unchanged followingnly UV-B irradiation (Fig. 1B). A combination of UV and visible light was moreffective at inducing development of a brighter red hue in the fruit of ‘Mantianhong’

ear, ‘Meirensu’ pear, and ‘Royal Gala’ apple. Two UV-B lamps were more effectivehan irradiation from one UV-B lamp with four visible-light lamps; similarly, eightisible-light lamps were more effective than four visible-light lamps with two UV-Bamps (Fig. 1B), which suggested that a high irradiance level imparts better red col-ration. In addition, treatment with two UV-B lamps plus eight visible-light lamps

d pear respectively; DI, Days of irradiation; “−”, without UV-B or visible light; 1, 2,

induced a greater response than separate application of both treatments (Fig. 1B).Measurements of color parameters were in agreement with the visual observations;lower values of L* and h◦ and higher values of C were attained with visible-light irra-diation, but not UV-B (Fig. 2B). With increasing number of lamps, the values of L* andh◦ declined, whereas the values of C increased. The highest values of C and lowestvalues of L* and h◦ were attained under irradiation with two UV-B lamps plus eightvisible-light lamps (Fig. 2B).

3.2. Effects of different temperature and light treatments on pigmentconcentration in fruit peel

Anthocyanins were undetectable in bagged fruit of ‘Mantianhong’ pear,‘Meirensu’ pear, and ‘Royal Gala’ apple, but rapidly accumulated after removal of thebag and exposure to UV-B/visible-light irradiation (Fig. 3A). Significant accumulationof anthocyanins was observed in ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘RoyalGala’ apple post-treatment for all temperatures except 32 ◦C, and the concentrationranged from 2.9 to 8.2 mg Cy-3-gla 100 g−1 FW (Fig. 3A). ‘Cascade’ pear showed traceanthocyanin accumulation in response to all three temperature treatments and theanthocyanin concentration did not exceed 0.5 mg Cy-3-gla 100 g−1 FW (Fig. 3A).

The optimum temperatures for anthocyanin accumulation in ‘Mantianhong’ pear,‘Meirensu’ pear, and ‘Royal Gala’ apple were 17 ◦C, 12 ◦C and 17 ◦C, respectively,and the maximum anthocyanin concentration at the three temperatures were 5.03,5.04 and 8.2 mg Cy-3-gla 100 g−1 FW, respectively (Fig. 3A). Anthocyanin concentra-tion declined as temperature rose above the optimum, and the lowest values were

68 Y. Sun et al. / Postharvest Biology and Technology 91 (2014) 64–71

Fig. 3. (A) Effects of different temperatures on anthocyanin, flavonoids, chlorophyll and carotenoid concentration of fruit in coordination with UV-B/visible irradiation. (B)Effects of different kinds of light treatment on anthocyanin, flavonoids, chlorophyll and carotenoid concentration of ‘Mantianhong’ pear peel. Note: T, Temperatures; DI, Dayso 7 ± 6i

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f irradiation; 27c, 27 ◦C constant temperature; 27v, 27 ◦C variable temperature (2rradiation; “−”, without UV-B or visible light; 1, 2, 4 and 8, the number of lamps.

ecorded at 32 ◦C (Fig. 3A). Variant temperature (27 ± 6 ◦C) was more effective thanonstant 27 ◦C in inducing anthocyanin accumulation in the peel of ‘Mantianhong’ear, ‘Meirensu’ pear, and ‘Royal Gala’ apple, but the difference was not significantFig. 3A).

The concentrations of flavonoids, chlorophyll and carotenoids were measuredrior to temperature treatment. Carotenoid concentrations were highest in ‘Cas-ade’ pear, followed by ‘Mantianhong’ pear and ‘Meirensu’ pear, and were lowest inRoyal Gala’ apple (Fig. 3A). The accumulation patterns of flavonoids and chlorophylln all fruit tested were the same, and their concentration increased as temperaturesncreased from 12 ◦C to 27 ◦C. However, temperatures higher than 27 ◦C were not

deal for pigment accumulation (Fig. 3A). Carotenoid concentrations in ‘Mantian-ong’ pear and ‘Meirensu’ pear reached a maximum of 1.53 and 1.40 mg 100 g−1

W, respectively, at 17 ◦C, and their concentration decreased with increasing tem-erature from 17 ◦C to 32 ◦C. The carotenoid concentration in ‘Cascade’ pear and

Royal Gala’ apple reached a maximum of 1.86 and 0.81 mg 100 g−1 FW, respectively,

◦C); 7/10, 7 and 10 days of irradiation for apple and pear respectively; DI, Days of

at 27 ◦C, and their concentration increased with increasing temperature from17 ◦C to 27 ◦C (Fig. 3A). Variant temperature (27 ± 6 ◦C) caused accumulation offlavonoids and carotenoids in peel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and‘Royal Gala’ apple, whereas constant 27 ◦C resulted in accumulation of chlorophyll(Fig. 3A).

The anthocyanin concentration in peel of ‘Mantianhong’ pear treated solely withUV-B or visible light was 0.12 mg Cy-3-gla 100 g−1 FW and 1.14 mg Cy-3-gla 100 g−1

FW, respectively (Fig. 3B). Anthocyanin concentration in the peel of fruit treatedwith two UV-B lamps was 20.47% higher than that with one UV-B lamp plus fourvisible-light lamps; similarly, anthocyanin concentration in the peel of fruit treated

with eight visible-light lamps was 48.11% higher than that of fruit treated with fourvisible-light lamps (Fig. 3B). Irradiation with UV-B and visible light together resultedin better color development than with solely UV-B or visible-light treatment. Theconcentration of anthocyanin was 7.45 mg Cy-3-gla 100 g−1 FW after 10 days oftreatment with UV-B/visible light (Fig. 3B).

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Light treatment significantly induced accumulation of flavonoids, chlorophyllnd carotenoids in the peel of ‘Mantianhong’ pear, but the effect varied among theifferent pigments. Compared with untreated fruit, the concentration of pigmentsas unchanged when only one UV-B lamp was used, but significantly increasedhen irradiated with eight visible-light lamps. Moreover, the concentration wasnchanged with increasing number of UV-B lamps, but declined as the number ofisible-light lamps decreased (Fig. 3B). These observations clearly indicated that theoncentrations of flavonoids, chlorophyll and carotenoids were influenced by therradiance level of visible light but not UV-B.

.3. Effect of different temperature and light treatments on fruit quality

The fruit firmness of ‘Mantianhong’ pear, ‘Meirensu’ pear, ‘Royal Gala’ apple,nd ‘Cascade’ pear prior to treatments were 20.1, 16.2, 10.9 and 26.3 N, respec-ively (Fig. 4A). For ‘Cascade’ pear, fruit firmness declined to 12.8, 9.4, and 8.4 Nfter 10 days of treatment with 17 ◦C, 22 ◦C, and 27 ◦C, respectively; thus, firmnessecreased in amplitude by more than 50%. In contrast, firmness in the other fruitypes declined by no more than 10%. The firmness of ‘Royal Gala’ apple fruit declinedlightly as temperature increased, but no significant difference in fruit firmness ofMantianhong’ pear and ‘Meirensu’ pear was observed in response to the differ-nt temperature treatments (Fig. 4A). For ‘Mantianhong’ pear, ‘Meirensu’ pear, and

Royal Gala’ apple, fruit firmness decreased more markedly under variant temper-ture (27 ± 6 ◦C) than under constant 27 ◦C, but the difference was not significantFig. 4A). These results indicated that declining fruit firmness may be attributed toatural softening but not to temperature. Compared with untreated fruit, the con-entrations of soluble solids, total soluble sugars and organic acids in the flesh ofreated fruit were slightly increased; however, the different temperature treatmentsid not affect the concentrations of soluble solids, sugars and organic acids in theruit (Fig. 4A).

Fruit firmness of ‘Mantianhong’ pear was slightly decreased, but not signifi-antly, among the different light treatments (Fig. 4B), which indicated that thisecrease may be also attributed to natural softening and not light treatment. After 10ays of irradiation, the concentration of soluble solids and organic acids all slightly

ncreased, but no significant differences between treated fruit and the control werebserved; total sugars concentration increased significantly, but there were no sig-ificant differences among the light treatments (Fig. 4B), which indicated that theifferent light treatments had no effect on fruit internal quality.

. Discussion

A previous report showed that the pattern of anthocyanin accu-ulation differed between European pears and Asian pears (Qian

t al., 2013). In the present study, 10 days irradiation with UV-B andisible light under different temperature treatments (except 32 ◦C)esulted in a gradual increase in anthocyanin concentration in theeel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ appleruit, whereas anthocyanin concentration in the peel of ‘Cascade’ear fruit showed no significant change (Figs. 1A, 2A and 3A). Theseesults indicated that the various temperature treatments affectnthocyanin biosynthesis in red Chinese sand pears in a mannerimilar to that observed in apple, but not European pear.

Temperature is one environmental factor that influences antho-yanin accumulation in fruit peel. It is widely believed that LTnduces the biosynthesis of anthocyanin while HT causes antho-yanin degradation. Several studies report that LT is more effectivehan HT for inducing coloration in apple and pear fruit (Ubi et al.,006; Ban et al., 2007; Li et al., 2012). Artificial heating of on-treeruit caused a dramatic reduction in peel anthocyanin concentra-ion (Wang et al., 2011). HTs during the maturing period acceleratehe degradation of anthocyanin in the peel of European pear ‘Rose-

arie’ (Steyn et al., 2004b). Some studies show that the responseattern to temperature treatments varies among species and cul-ivars. In ‘Jonathan’ apple, Arakawa (1991) showed that underV-B/visible light, fruit treated with 25 ◦C developed better color

han those treated with 15 ◦C. Similarly, our preliminary resultshowed that, compared with 17 ◦C, 27 ◦C more effectively induceded coloration in red Chinese sand pear ‘Yunhongli No. 1’ fruitZhang et al., 2012).

In the present study, under UV-B/visible-light irradiation theptimum temperatures for anthocyanin accumulation in ‘Man-ianhong’ pear and ‘Meirensu’ pear fruit were 17 ◦C and 12 ◦C,espectively (Fig. 3A). These results concur with those of previous

Technology 91 (2014) 64–71 69

studies, which suggest that the optimum temperature for red colordevelopment differs among red Chinese sand pear cultivars. Fur-thermore, UV-B/visible-light irradiation resulted in a vivid red huein the fruit of ‘Mantianhong’ pear and ‘Meirensu’ pear treated withLT. However, a combination of UV-B/visible light did not induce thesame response at HT.

Studies of apple and grape showed that variant temperature ismore effective than constant temperature in improving red col-oration (Marais et al., 2001b; Mori et al., 2005). In the present study,the concentration of anthocyanin in the peel of ‘Mantianhong’ pearand ‘Meirensu’ pear treated with variant (27 ± 6 ◦C) temperaturewas slightly, but non-significantly, higher than that with con-stant 27 ◦C treatment (Fig. 3A). However, given that the treatmenttemperature was not the optimum temperature for anthocyaninaccumulation in these cultivars, it would be unwise to reflect uponthis observation.

Light is an essential factor for accumulation of anthocyanin,and both light quality and quantity play important roles in antho-cyanin biosynthesis. The concentration of anthocyanin in baggedfruit of ‘Meirensu’ pear was below detectable limits, but rapidlyaccumulated when the fruit were re-exposed to light (Huanget al., 2009). ‘Mantianhong’ pear cultivated in Kunming, Yunnanprovince, where the irradiance level is higher, show better fruitcolor development than in those cultivated in Xingyang, Henanprovince, where the irradiance level is lower (Yu, 2012). In thepresent study, anthocyanin concentration in the peel of untreatedand dark-treated fruit was below the detectable threshold (Fig. 3B),which indicated that light is indispensable for anthocyanin accu-mulation. Our results showed that anthocyanin accumulation waselevated with increasing light quantity in the peel of ‘Mantianhong’pear, which was in agreement with previous studies in pear (Huanget al., 2009) and apple (Arakawa, 1988b).

Previous studies in apple showed that compared with visible,red and blue light, UV is the most efficient light for inducing antho-cyanin biosynthesis in the peel of apple fruit (Arakawa, 1988b;Saure, 1990; Ubi et al., 2006). UV-B and visible light, however, have asynergistic effect in inducing anthocyanin accumulation in the peelof apple fruit (Arakawa, 1988a,b). In the present study, the concen-tration of anthocyanin in the peel of ‘Mantianhong’ pear treatedsolely with visible light was 9.5-fold higher than in fruit treatedsolely with UV-B, which was inconsistent with the conclusion thatUV-B is more effective than visible light in inducing accumulationof anthocyanin in red apple (Arakawa, 1988b; Ubi et al., 2006). Pre-vious studies in apple showed that UV-B and visible light interactto induce coloration (Arakawa, 1988a,b). Our results also indicatethat combined UV-B/visible-light irradiation is significantly moreeffective on fruit color than use of either type of light alone.

Light treatment significantly influenced accumulation of differ-ent pigments in the current study. The concentration of chlorophyll,carotenoids and flavonoids in the peel of ‘Mantianhong’ pearincreased in response to different levels of irradiation. Further-more, the respective proportions of chlorophyll, carotenoids andanthocyanin increased approximately from 1:1:0 (control) to 2:4:9(after 10 days of irradiation). In the present study, the maximumproportion of anthocyanin among the three main pigment typeswas attained at LT, which suggested that LT enhances color byimproving not only the concentration, but also the proportion ofanthocyanin in the fruit peel.

Red Chinese sand pears are eaten at a firm and crisp stage soonafter harvest or storage (Zhang et al., 2012), and therefore fruitfirmness is an essential parameter to be considered. Different tem-perature treatments had no significant effect on firmness of treated

sand pear fruit (Fig. 4). Our results indicated that good fruit firmnesswas maintained, and concentrations of soluble solid, total solublesugars and organic acids were slightly increased, in treated fruit.These results showed that fruit firmness and internal quality of

70 Y. Sun et al. / Postharvest Biology and Technology 91 (2014) 64–71

Fig. 4. (A) Effects of different temperatures on firmness, total soluble solids, total sugars and total organic acids of P. pyrifolia cv ‘Mantianhong’ and ‘Meirensu’, P .communiscv ‘Cascade’ and P. communis cv ‘Cascade’, M. domestica cv ‘Royal Gala’ irradiated side of fruit in coordination with UV-B/visible irradiation. (B) Effects of different lightson firmness, total soluble solids, total sugars and total organic acids in fruits of ‘Mantianhong’ pear. Note: T, Temperatures; DI, Days of irradiation; 27c, 27 ◦C constanttemperature; 27v, 27 ◦C variable temperature (27 ± 6 ◦C); 7/10, seven and ten days of irradiation for apple and pear respectively; DI, Days of irradiation; “−”, without UV-Bo was eo ic acid

‘o

uiaiec‘wl

r visible light; 1, 2, 4 and 8, the number of lamps; total soluble sugar concentrationrganic acid concentration was expressed as the sum of malic acid, citric acid, quin

Mantianhong’ pear and ‘Meirensu’ pear could be maintained by LTf 17 ◦C and 12 ◦C, respectively.

Fruit bagging is widely used for production of high quality,nblemished apple and pear fruit. It is believed that bagging

ncreases the light sensitivity of fruit and stimulates increasednthocyanin synthesis when fruit are re-exposed to light follow-ng bag removal (Ju et al., 1995; Huang et al., 2009). In the presentxperiment, UV-B/visible-light irradiation for 10 days under LT

onditions induced development of a uniform red color in fruit ofMantianhong’ pear and ‘Meirensu’ pear after bag removal (Fig. 1A),

hich was in agreement with the above-mentioned results. Simi-arly, for attached fruit, our previous study showed that red Chinese

xpressed as the sum of sucrose, glucose, fructose and sorbitol concentrations. Total, tartaric acid and oxalic acid concentrations.

sand pear ‘Mantianhong’ cultivated in Kunming (which experiencesrelatively lower temperatures and higher irradiance) developed abetter red coloration than in fruit cultivated in Zhengzhou (whichhas relatively higher temperatures and lower irradiance) (Yu,2012). In apple, low temperature and high irradiance can also pro-mote anthocyanin accumulation in attached and detached fruit(Ubi et al., 2006). These results infer that the response of attachedfruit to temperature and light is consistent with that of detached

fruit. Therefore, to develop a good red color in non-bagged, attachedpear fruit, growing regions with a relatively low temperature andstrong illumination during the fruit harvest period were pref-erentially chosen. Furthermore, application of pulsed overhead

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vaporative cooling to reduce the temperature at the fruit sur-ace would be a favorable measure to improve fruit color in warmreas, and laying reflective film on the ground and removal of leaveslso may be used to increase the irradiance level to improve fruitolor (Van den Dool, 2006; Glenn and Puterka, 2007). However, theesponse of non-bagged red Chinese sand pears to light and tem-erature under postharvest conditions was not examined in theresent study and needs further investigation.

. Conclusion

Under UV-B/visible-light irradiation, the pattern of responseso temperature treatments in red Chinese sand pears was similaro that of apple, but differed from European pear. The optimumemperature for fruit coloration differed among the species andultivars, and variant temperature may induce enhanced accu-ulation of anthocyanin than constant temperature. Both light

uantity and light quality were crucial for coloration of red Chi-ese sand pear fruit, and UV-B and visible light had a synergisticffect on anthocyanin accumulation in the peel of red Chinese sandear. These results indicated that LT and high light quantity result

n fruit with an enhanced red color and good firmness and internaluality. The use of artificial lamps providing a high quantity of UV-/visible light in conjunction with low temperature is a favorabletrategy to improve the postharvest color of red Chinese sand pearruit.

cknowledgements

This work was supported by the National Natural Science Foun-ation of China (Nos. 31272141, 31301753), the earmarked fundor Modern Agro-industry Technology Research Systems (nycytx-9), the Doctoral Program of Higher Education of China (no.0130204120004), the Natural Science Foundation of Shaanxirovince of China (No. 2013JQ3005) and the Science Foundationrom the Northwest A&F University (No. QN2013015).

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