Postharvest Pigmentation in Red Chinese Sand Pears (Pyrus Pyrifolia

Postharvest Biology and Technology 91 (2014) 64–71

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Postharvest Biology and Technology

journal homepage: www.elsevier.com/locate/postharvbio

Postharvest pigmentation in red Chinese sand pears (Pyrus pyrifolia

Nakai) in response to optimum light and temperature

a,1 a,1 a a

Yongwang Sun , Minjie Qian , Ruiyuan Wu , Qingfeng Niu ,

a,∗ a,b,∗∗

Yuanwen Teng , Dong Zhang

Department of Horticulture, The State Agricultural Ministry Key Laboratory of Horticultural Plant Growth, Development & Quality Improvement, Zhejiang

University, Hangzhou 310058, Zhejiang Province, China

College of Horticulture, Northwest A&F University, Yangling 712100, Shaanxi Province, China

a r t i c l e i n f o a b s t r a c t

Article history: The development of red color in the peel of red Chinese sand pears (Pyrus pyrifolia Nakai) is inﬂuenced by

Received 20 August 2013

temperature and light; however, the response patterns vary among different cultivars. In this study, we

Accepted 23 December 2013

systematically 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’.

Keywords:

Fruit of red apple (Malus domestica Borkh.) ‘Royal Gala’ and red European pear (P. communis L.) ‘Cascade’

Red Chinese sand pear

received the same treatments for comparison. Furthermore, the effects of light quality and irradiance level

European pear

on ‘Mantianhong’ pears were evaluated at the optimum temperature for anthocyanin accumulation. Fruit

Anthocyanin

Coloration ﬁrmness and concentrations of total soluble sugars and organic acids were measured to determine fruit

Temperature quality. The effect of temperature on red Chinese sand pear fruit color was similar to that of apples, but not

Light European pear. Moreover, low temperature more effectively induced red coloration in ‘Mantianhong’ and

‘Meirensu’ pears than high temperature; anthocyanin levels increased with increasing irradiance level

−2 −1

from 0 to 532 ␮mol m s , 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 the

postharvest coloration of red sand pear fruit. The results will contribute to an improved understanding

of the mechanism responsible for the coloration of red Chinese sand pears and will aid development of

new techniques to improve color in postharvest fruit.

1. Introduction (Allan et al., 2008). Anthocyanins belong to the diverse group of

ubiquitous secondary metabolites known as ﬂavonoids (Holton and

Chinese sand pears are widely cultivated in China, Korea and Cornish, 1995), which are believed to have multiple physiological

Japan, and the fruit color may vary from yellow or green to russet- functions and provide potential beneﬁts to human health, including

brown (Teng and Tanabe, 2004). In recent decades, several cultivars protection against cancer, inﬂammation, coronary heart diseases

with red fruit have been discovered and developed in China (Tao and other age-related diseases (Boyer and Liu, 2004; Butelli et al.,

et al., 2004). These red pears are preferred by consumers because 2008; Gould et al., 2009).

of their attractive appearance and nutritional value; however, the Temperature and light are important elements that affect fruit

red peel color is not uniform and varies with growing conditions color. Several studies have reported the inﬂuence of different

(Huang et al., 2009). Given that red pear fruit are highly coveted, it temperatures (high, low, variant and constant) and light (quality

is necessary to develop postharvest treatments that can be used to and quantity) on fruit color. Low temperature (LT) causes higher

improve the red color of fruit that lack sufﬁcient color. anthocyanin accumulation in most apple cultivars compared with

Fruit color mainly depends on the concentration and proportion high temperature (HT). Under UV-B/visible light, apple fruit of

of three classes of pigments: anthocyanins, carotenoids and chloro- the ‘Iwai’, ‘Sansa’, ‘Tsugaru’, ‘Homei Tsugaru’ and ‘Akane’ culti-

◦

phylls, which contribute red, yellow and green colors, respectively vars treated with a LT of 17 C develop better red color than those

◦

treated with a HT of 27 C (Ubi et al., 2006). HT is detrimental

for color development and reduces anthocyanin accumulation in

∗ fruit of ‘Mondial Gala’ and ‘Royal Gala’ apples (Wang et al., 2011).

Corresponding author. Tel.: +86 571 88982803; fax: +86 571 88982803. ◦ ◦

∗∗ Compared with HT of 27 C, a LT of 17 C promotes UV-B-induced

Corresponding author. Tel.: +86 029 87082613; fax: +86 029 87082613.

anthocyanin accumulation and red coloration in ‘Red Delicious’

E-mail addresses: [email protected] (Y. Teng), [email protected] (D. Zhang).

These authors contributed equally to this work. apples (Xie et al., 2012). Furthermore, different apple cultivars show

Y. Sun et al. / Postharvest Biology and Technology 91 (2014) 64–71 65

various response patterns to temperature under UV-B/visible light. 2. Materials and methods

◦

For example, ‘Jonathan’ apples treated with HT of 25 C develop a

◦

more vivid red color than those treated with LT of 15 C (Arakawa, 2.1. Plant material and experimental treatments

◦

1991). Under UV-B/visible light, a temperature range of 20/6 C

(day/night) has a greater effect on anthocyanin accumulation in Bagged mature fruit of red Chinese sand pears (Pyrus pyrifolia

◦

the peel of ‘Cripps’ Pink’ apples than a constant 6 C LT treatment Nakai) ‘Mantianhong’ and ‘Meirensu’ were obtained from a com-

(Marais et al., 2001a). Cool nights followed by warm days, when mercial orchard in Zhengzhou city, Henan Province, China. Fruit

UV-B and light are incident on the fruit peel, are considered to of red European pear (Pyrus communis L.) ‘Cascade’ was obtained

bring about blush formation in apple fruit (Reay, 1999). Antho- from the Zhengzhou Fruit Research Institute, Chinese Academy of

cyanins cannot be detected in the peel of bagged fruit of the red Agricultural Sciences, Zhengzhou City, Henan Province, China. Fruit

Chinese sand pears ‘Meirensu’ and ‘Yunhongli NO. 1’, but rapidly of red apple (Malus domestica Borkh). ‘Royal Gala’ was obtained

accumulate when the fruit are re-exposed to light (Huang et al., from a commercial orchard in Anyang city, Henan province, China.

2009). Studies on red apple cultivars show that UV is the most Five mature trees of ‘Mantianhong’ pear, ‘Meirensu’ pear and ‘Royal

effective wavelength band for anthocyanin biosynthesis, whereas Gala’ apple and three mature trees of ‘Cascade’ pear were selected

white light has almost no effect; UV-B (280–320 nm) has a greater for the fruit bagging treatment. These trees were similar in size

effect than UV-A (320–390 nm), and has a synergistic effect with and number of fruit carried and had uniform exposure to sunlight.

red and white light on induction of anthocyanin accumulation Sixty fruit of uniform size and growth positions in every selected

(Arakawa, 1988a, b; Saure, 1990; Ubi et al., 2006). In a bagging tree were bagged 40 days after full bloom. The bagged fruit were

experiment, fruit of ‘Meirensu’ pear receiving 100%, 80% and 35% harvested at commercial maturity (165, 165, 145 and 125 days after

sunlight showed a graduated decline in anthocyanin accumulation full bloom for ‘Mantianhong’ pear, ‘Meirensu’ pear, ‘Cascade’ pear,

with decreasing exposure to sunlight (Huang et al., 2009). and ‘Royal Gala’ apple, respectively), and transported to the lab-

Anthocyanin accumulation patterns vary among plants. Antho- oratory immediately. Intact fruit of uniform size were chosen as

cyanin biosynthesis peaks at two developmental stages in apple experimental material. There were 15 fruit in every treatment and

fruit, initially at the fruitlet stage in both red and non-red cultivars, each treatment had three replicates.

which is not of commercial importance, and subsequently at the Different temperature treatments were applied by placing the

ripening fruit stage only in red cultivars (Saure, 1990; Honda et al., fruit in an overhead-lit phytotron (Zeda Instrument Company,

2002). In grapes, anthocyanin biosynthesis commences with the AGC-D002Z, Hangzhou, China) for 10 days and 7 days, respec-

beginning of berry ripening and continues throughout the ripening tively. Two 9 W UV-B lamps (PL-S 9 W/12, 280–315 nm, Philips, The

phase (Boss et al., 1996). Some cultivars of European pear generally Netherlands) and four 36 W ﬂuorescent lamps (FSL, T8 36 W/765,

attain their highest anthocyanin concentrations at about midway China) were installed in the phytotron. The relative humidity was

between anthesis and harvest (Dussi et al., 1997; Steyn et al., maintained at 80%. The photon ﬂux density (PFD) at the bottom of

−2 −1

2004a). Unlike the pigmentation patterns described above, antho- the incubator (0.8 m from the light source) was 270 ␮mol m s

cyanin biosynthesis in red Chinese sand pears accompanies fruit (measured with a TES1332A quantum meter, TES Taiwan, China).

maturation and the highest anthocyanin concentration is attained The temperature treatments applied to each fruit type were as fol-

at maturity. Our previous experiments showed that UV-B/visible lows: (1) ‘Mantianhong’ pear and ‘Meirensu’ pear fruit were treated

◦

irradiation of debagged ‘Mantianhong’ red Chinese sand pear fruit with ﬁve constant temperatures (12, 17, 22, 27 and 32 C) and

◦

for 10 days induced good pigmentation; however, ‘Cascade’ Euro- one variant temperature (27 ± 6 C); (2) ‘Cascade’ pear fruit were

◦

pean pears showed no change in pigmentation with the same treated with three constant temperatures (17, 22 and 27 C); (3)

treatment, indicating that the two cultivars have different response ‘Royal Gala’ apple fruit were treated with four constant tempera-

◦ ◦

patterns to light quality (Qian et al., 2013). The fruit of European tures (17, 22, 27 and 32 C) and one variant temperature (27 ± 6 C).

◦

pear ‘Wujiuxiang’ subjected to a temperature of 4 C showed better For the variant temperature treatment, the temperature increased

◦ ◦ ◦ ◦

red color than those subjected to 25 C (Li et al., 2012). Our previous from 21 C to 33 C from 0:00 to 12:00 and decreased to 21 C from

◦ ◦ ◦

study showed that, compared with LT of 17 C, HT of 27 C induced 12:00 to 24:00 on each day (at the rate of 1 C/h).

better red coloration in fruit of ‘Yunhongli No. 1’ Chinese sand pear, To examine the effect of different light treatments, fruit of

which indicated that red Chinese sand pears respond uniquely to ‘Mantianhong’ pear were placed in the phytotron maintained at a

◦

temperature (Zhang et al., 2012). Nevertheless, few studies have constant 17 C and 80% RH. The light treatment conditions were as

investigated the fruit color of red Chinese sand pears in response follows: (1) constant darkness; (2) two 9 W UV-B lamps; (3) eight

to temperature and light. 36 W ﬂuorescent lamps; (4) one 9 W UV-B lamp plus four 36 W

In this study, we systematically investigated the influence of dif- fluorescent lamps; (5) two 9 W UV-B lamps plus four 36 W fluores-

ferent temperatures (low, high, variable and constant) on detached cent lamps; (6) two 9 W UV-B lamps plus eight 36 W ﬂuorescent

fruit of the red Chinese sand pears ‘Mantianhong’ and ‘Meirensu’. lamps. The PFD at the bottom of the incubator (0.8 m from the light

‘Royal Gala’ apples and ‘Cascade’ pears were treated in parallel to source) was measured as described above and reached 0, 28, 504,

−2 −1

evaluate and compare their pigmentation responses to those of the 266, 270, and 532 ␮mol m s , respectively. Treated fruit were

sand pears. In addition, we investigated the effect of different light sampled after 10 days of irradiation.

◦

qualities and irradiance levels on ‘Mantianhong’ pears at 17 C, its Sampled fruit in the two experiments were subjected to mea-

optimum temperature for anthocyanin accumulation. Fruit ﬁrm- surement of color parameters, namely lightness (L*), saturation (C)

◦

ness and total concentrations of soluble sugars and organic acids and color hue (h ). Peel and ﬂesh samples were separated by peeling

were determined as measures of fruit quality. It is reported that, fresh fruit with a potato peeler and immediately freezing in liquid

◦

compared with immature fruit, mature apple and pear fruit are N2, then stored at −80 C until use. The peel was used to assay pig-

liable to develop red coloration under the same treatment condi- ment concentrations, while ﬂesh was used to assay soluble sugars

tions (Reay and Lancaster, 2001; Zhang et al., 2013), thus mature and organic acids.

fruit of apple and pear were used. Our results will be helpful

to understand the mechanism underlying the responses of red 2.2. Fruit measurements

Chinese sand pear fruit to temperature and light, and will aid the

design of postharvest techniques to enhance fruit coloration in Fruit peel color was measured at the reddest position on the fruit

pears. using a colorimeter (CR-400, Minolta, Japan), which provided CIE L*,

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

a* and b* values. L* represents the relative lightness of color with a

range from 0 to 100, being low for dark color and high for light color.

Both a* and b* scales extended from −60 to 60. Negative a* values

indicated greenness and positive values indicated redness, while b*

was negative for blueness and positive for yellowness. These values

◦

were then used to calculate the hue angle degree (h = arctangent

◦ ◦ ◦

[b*/a*]), where 0 = red-purple, 90 = yellow, 180 = bluish green

◦ 2 2 1/2

and 270 = blue, and chroma (C* = [a* + b* ] ), which indicated

the intensity or color saturation (McGuire, 1992). Fifteen fruit were

used for each measurement.

A TA-XT plus Texture Analyser (Stable MicroSystems, UK) was

used to measure the fruit ﬁrmness with a diameter probe of

5 millimeter (mm), a penetration depth of 5 mm, and a penetration

−1

rate of 1 mm s . One mm thick sliced peel from two opposite sides

of the fruit was used for these measurements and the thickness was

expressed in newtons (N).

Total soluble solids of ﬁfteen fruit (two measurements per fruit)

were determined using a digital refractometer (PR-101, Atago,

Japan).

2.3. Extraction and measurement of total anthocyanin

The total anthocyanin concentration was measured using a

pH differential method and was presented as mg cyanidin-3- Fig. 1. (A) Peel color of P. pyrifolia cv ‘Mantianhong’ and ‘Meirensu’, P. communis cv

galactoside per 100 g fresh tissue (Dussi et al., 1995). One gram ‘Cascade’ and P. communis cv ‘Cascade’, M. domestica cv ‘Royal Gala’ irradiated side

of fruit as affected by temperatures during postharvest UV-B/visible irradiation. (B)

of fruit peel was mixed with methanol containing 0.1% HCl

◦ Peel color of ‘Mantianhong’ pear fruit as affected by different lights treatment. Note:

followed by centrifugation at 4 C and 12,000 rpm for 20 min. ◦ ◦

T, Temperatures; DI, Days of irradiation; 27c, 27 C constant temperature; 27v, 27 C

◦

The absorbance of each 100 ␮L extract was assessed using a

variable temperature (27 ± 6 C); 7/10, 7 and 10 days of irradiation for apple and pear

DU800 spectrophotometer (Beckman Coulter, Fullerton, CA, U.S.) at respectively; DI, Days of irradiation; “−”, without UV-B or visible light; 1, 2, 4 and

8, the number of lamps.

510 nm and 700 nm in buffers of pH 1.0 and 4.5. Anthocyanin con-

centration was calculated using the equation: A = [(A510 − A700) ◦

80% ethanol and shaken for 10 min at 35 C. The homogenate was

pH1.0 − (A510 − A700) pH4.5] with a molar extinction coefﬁcient of

4 ﬁltered and the residue was re-extracted twice with 80% ethanol.

cyanidin-3-galactoside of 3.02 × 10 .

The combined extracts were centrifuged at 6500 rpm for 5 min, and

◦

the supernatant was evaporated under a vacuum at less than 35 C

2.4. Extraction and measurement of total chlorophyll and

until the ethanol was removed and then adjusted to the volume of

carotenoid

1 mL with distilled water for analyses of soluble sugars and organic

acids using HPLC (Beckman, USA). System Gold Software (Beckman,

One gram of ground fruit peel was homogenized in 6 mL of 80%

◦ USA) was used to run the HPLC and to process the results.

cold acetone and centrifuged at 4 C and 12,000 rpm for 20 min.

A 20 ␮L aliquot of eluate was injected into a 5.0 ␮m NH2

Absorbance of the extract was measured using a DU800 spectro-

(4.6 mm × 250 mm) column (GL Sciences Inc., Japan) and the eluted

photometer (Beckman, USA) at 440, 645 and 663 nm. From the

peaks were detected with a refractive index detector RI-1530 (Jasco

data, chlorophyll concentration was calculated using the equation:

Corp., Japan). Acetonitrile: water (70:30) was used as the mobile

Ct = 20.2 A645 + 8.02 A663, and carotenoid concentration was cal- −1

phase with a ﬂow rate of 1.0 mL min . Quantiﬁcation of soluble

−

culated based on the equation: Ck = 4.7 A440 0.27Ct (Chen and

sugars was made by comparison with the peak area of standard

Wang, 2002).

sugars (Sigma chemical, St. Louis, USA).

A 20 ␮L aliquot of eluate was injected into an ODS C18

2.5. Extraction and measurement of total ﬂavonoids

(4.6 mm × 250 mm) column (Beckman, USA). The ﬂow rate was

−1

0.5 mL min using 3% methanol − 0.01 M K2HPO4 as the solvent.

Flavonoid concentration was determined by a colorimetric assay

The mobile phase was adjusted to pH 2.55 using H3PO4. Organic

(Jia et al., 1999) with slightly modiﬁcation. One gram of fruit peel

◦ acids were detected at a wavelength of 210 nm. The eluted peaks

was mixed with 6 mL 80% ethanol for 24 h at 4 C in the dark.

were detected with a 166 UV–vis detector (Beckman, USA), and

After centrifugation for 20 min at 12,000 rpm, 0.5 mL of the super-

quantiﬁcation of individual organic acids was made using peak area

natant was transported into a new tube, 0.3 mL 8% NaNO2, 0.3 mL

of standard acids (Sigma chemical, St. Louis, USA).

10% Al (NO3)3, 2 mL 2 M NaOH, 4.9 mL ethanol were added to

the tube in that order. The absorbance of each sample was mea-

2.7. Statistical analysis

sured 10 min later at 510 nm using a DU800 spectro-photometer

(Beckman, USA). The result was expressed as milligram of rutin

LSDs (a = 0.05) were calculated for mean separations using the

(Sigma Chemical, St. Louis, USA) equivalent on a fresh weight basis,

−1 Data Processing System (DPS, version 3.01, Zhejiang University,

mg rutin g FW.

Hangzhou, China), and Origin8.0 (USA) was used as drawing tool.

2.6. Extraction and measurement of total soluble sugar and 3. Results

organic acid

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

Soluble sugars and organic acids were extracted by the method

The peel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple fruit

of high performance liquid chromatograph (HPLC) (Ding et al.,

was a similar white color before treatment, whereas the peel of ‘Cascade’ pear

2002). Three grams of ground ﬂesh was homogenized in 6 mL of fruit 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;

◦ ◦

27v, 27 C variable temperature (27 ± 6 C); 7/10, 7 and 10 days of irradiation for apple and pear respectively; DI, Days of irradiation; “−”, without UV-B or visible light; 1, 2,

4 and 8, the number of lamps.

color change in ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple fruit induced a greater response than separate application of both treatments (Fig. 1B).

to different degrees of red, whereas the color of ‘Cascade’ pear fruit showed no sig- Measurements of color parameters were in agreement with the visual observations;

◦

niﬁcant change (Fig. 1A). The optimum temperatures for red color development in lower values of L* and h and higher values of C were attained with visible-light irra-

◦ ◦

‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple were LTs of 17 C, 12 C, diation, but not UV-B (Fig. 2B). With increasing number of lamps, the values of L* and

◦ ◦

and 17 C, respectively (Fig. 1A). Red coloration decreased with increasing tempera- h declined, whereas the values of C increased. The highest values of C and lowest

◦

ture (Fig. 1A). ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple exhibited values of L* and h were attained under irradiation with two UV-B lamps plus eight

◦ ◦

poor color at constant 27 C and variable (27 ± 6 C) temperatures, although variant visible-light lamps (Fig. 2B).

temperature appeared to be more effective than a constant temperature in general

◦

(Fig. 1A). Untreated fruit showed high L*, high h and low C values, as indicated by

3.2. Effects of different temperature and light treatments on pigment

the bright, yellow–white, and low saturation color (Fig. 2A). The lowest values of L*

concentration in fruit peel

◦

and h and the highest value of C for ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal

Gala’ apple were attained at low temperatures, which indicated that LT induced

Anthocyanins were undetectable in bagged fruit of ‘Mantianhong’ pear,

red coloration of the fruit. However, the color of ‘Cascade’ pear was not affected

‘Meirensu’ pear, and ‘Royal Gala’ apple, but rapidly accumulated after removal of the

signiﬁcantly by any temperature (Fig. 2A).

bag and exposure to UV-B/visible-light irradiation (Fig. 3A). Signiﬁcant accumulation

Fruit color was also affected by variation in light quality. The fruit of ‘Mantian-

of anthocyanins was observed in ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal

◦

hong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple showed red color formation in

Gala’ apple post-treatment for all temperatures except 32 C, and the concentration

−

response to visible light treatment, but the color remained unchanged following 1

ranged from 2.9 to 8.2 mg Cy-3-gla 100 g FW (Fig. 3A). ‘Cascade’ pear showed trace

only UV-B irradiation (Fig. 1B). A combination of UV and visible light was more

anthocyanin accumulation in response to all three temperature treatments and the

−

effective at inducing development of a brighter red hue in the fruit of ‘Mantianhong’ 1

anthocyanin concentration did not exceed 0.5 mg Cy-3-gla 100 g FW (Fig. 3A).

pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple. Two UV-B lamps were more effective

The optimum temperatures for anthocyanin accumulation in ‘Mantianhong’ pear,

◦ ◦ ◦

than irradiation from one UV-B lamp with four visible-light lamps; similarly, eight

‘Meirensu’ pear, and ‘Royal Gala’ apple were 17 C, 12 C and 17 C, respectively,

visible-light lamps were more effective than four visible-light lamps with two UV-B

and the maximum anthocyanin concentration at the three temperatures were 5.03,

−

lamps (Fig. 1B), which suggested that a high irradiance level imparts better red col- 1

5.04 and 8.2 mg Cy-3-gla 100 g FW, respectively (Fig. 3A). Anthocyanin concentra-

oration. In addition, treatment with two UV-B lamps plus eight visible-light lamps

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, Days

◦ ◦ ◦

of irradiation; 27c, 27 C constant temperature; 27v, 27 C variable temperature (27 ± 6 C); 7/10, 7 and 10 days of irradiation for apple and pear respectively; DI, Days of

irradiation; “−”, without UV-B or visible light; 1, 2, 4 and 8, the number of lamps.

◦ ◦ ◦

recorded at 32 C (Fig. 3A). Variant temperature (27 ± 6 C) was more effective than at 27 C, and their concentration increased with increasing temperature from

◦ ◦ ◦ ◦

constant 27 C in inducing anthocyanin accumulation in the peel of ‘Mantianhong’ 17 C to 27 C (Fig. 3A). Variant temperature (27 ± 6 C) caused accumulation of

pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple, but the difference was not signiﬁcant ﬂavonoids and carotenoids in peel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and

◦

(Fig. 3A). ‘Royal Gala’ apple, whereas constant 27 C resulted in accumulation of chlorophyll

The concentrations of ﬂavonoids, chlorophyll and carotenoids were measured (Fig. 3A).

prior to temperature treatment. Carotenoid concentrations were highest in ‘Cas- The anthocyanin concentration in peel of ‘Mantianhong’ pear treated solely with

−1 −1

cade’ pear, followed by ‘Mantianhong’ pear and ‘Meirensu’ pear, and were lowest in UV-B or visible light was 0.12 mg Cy-3-gla 100 g FW and 1.14 mg Cy-3-gla 100 g

‘Royal Gala’ apple (Fig. 3A). The accumulation patterns of ﬂavonoids and chlorophyll FW, respectively (Fig. 3B). Anthocyanin concentration in the peel of fruit treated

in all fruit tested were the same, and their concentration increased as temperatures with two UV-B lamps was 20.47% higher than that with one UV-B lamp plus four

◦ ◦ ◦

increased from 12 C to 27 C. However, temperatures higher than 27 C were not visible-light lamps; similarly, anthocyanin concentration in the peel of fruit treated

ideal for pigment accumulation (Fig. 3A). Carotenoid concentrations in ‘Mantian- with eight visible-light lamps was 48.11% higher than that of fruit treated with four

−1

hong’ pear and ‘Meirensu’ pear reached a maximum of 1.53 and 1.40 mg 100 g visible-light lamps (Fig. 3B). Irradiation with UV-B and visible light together resulted

◦

FW, respectively, at 17 C, and their concentration decreased with increasing tem- in better color development than with solely UV-B or visible-light treatment. The

◦ ◦ −1

perature from 17 C to 32 C. The carotenoid concentration in ‘Cascade’ pear and concentration of anthocyanin was 7.45 mg Cy-3-gla 100 g FW after 10 days of

−1

‘Royal Gala’ apple reached a maximum of 1.86 and 0.81 mg 100 g FW, respectively, treatment with UV-B/visible light (Fig. 3B).

Y. Sun et al. / Postharvest Biology and Technology 91 (2014) 64–71 69

Light treatment signiﬁcantly induced accumulation of ﬂavonoids, chlorophyll studies, which suggest that the optimum temperature for red color

and carotenoids in the peel of ‘Mantianhong’ pear, but the effect varied among the

development differs among red Chinese sand pear cultivars. Fur-

different pigments. Compared with untreated fruit, the concentration of pigments

thermore, UV-B/visible-light irradiation resulted in a vivid red hue

was unchanged when only one UV-B lamp was used, but signiﬁcantly increased

in the fruit of ‘Mantianhong’ pear and ‘Meirensu’ pear treated with

when irradiated with eight visible-light lamps. Moreover, the concentration was

unchanged with increasing number of UV-B lamps, but declined as the number of LT. However, a combination of UV-B/visible light did not induce the

visible-light lamps decreased (Fig. 3B). These observations clearly indicated that the same response at HT.

concentrations of ﬂavonoids, chlorophyll and carotenoids were inﬂuenced by the

Studies of apple and grape showed that variant temperature is

irradiance level of visible light but not UV-B.

more effective than constant temperature in improving red col-

oration (Marais et al., 2001b; Mori et al., 2005). In the present study,

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

the concentration of anthocyanin in the peel of ‘Mantianhong’ pear

◦

The fruit ﬁrmness of ‘Mantianhong’ pear, ‘Meirensu’ pear, ‘Royal Gala’ apple, and ‘Meirensu’ pear treated with variant (27 6 C) temperature

and ‘Cascade’ pear prior to treatments were 20.1, 16.2, 10.9 and 26.3 N, respec-

was slightly, but non-signiﬁcantly, higher than that with con-

tively (Fig. 4A). For ‘Cascade’ pear, fruit ﬁrmness declined to 12.8, 9.4, and 8.4 N ◦

◦ ◦ ◦ stant 27 C treatment (Fig. 3A). However, given that the treatment

after 10 days of treatment with 17 C, 22 C, and 27 C, respectively; thus, ﬁrmness

temperature was not the optimum temperature for anthocyanin

decreased in amplitude by more than 50%. In contrast, ﬁrmness in the other fruit

types declined by no more than 10%. The ﬁrmness of ‘Royal Gala’ apple fruit declined accumulation in these cultivars, it would be unwise to reﬂect upon

slightly as temperature increased, but no signiﬁcant difference in fruit ﬁrmness of this observation.

‘Mantianhong’ pear and ‘Meirensu’ pear was observed in response to the differ-

Light is an essential factor for accumulation of anthocyanin,

ent temperature treatments (Fig. 4A). For ‘Mantianhong’ pear, ‘Meirensu’ pear, and

and both light quality and quantity play important roles in antho-

‘Royal Gala’ apple, fruit ﬁrmness decreased more markedly under variant temper-

◦ ◦ cyanin biosynthesis. The concentration of anthocyanin in bagged

ature (27 6 C) than under constant 27 C, but the difference was not signiﬁcant

(Fig. 4A). These results indicated that declining fruit ﬁrmness may be attributed to fruit of ‘Meirensu’ pear was below detectable limits, but rapidly

natural softening but not to temperature. Compared with untreated fruit, the con-

accumulated when the fruit were re-exposed to light (Huang

centrations of soluble solids, total soluble sugars and organic acids in the ﬂesh of

et al., 2009). ‘Mantianhong’ pear cultivated in Kunming, Yunnan

treated fruit were slightly increased; however, the different temperature treatments

province, where the irradiance level is higher, show better fruit

did not affect the concentrations of soluble solids, sugars and organic acids in the

fruit (Fig. 4A). color development than in those cultivated in Xingyang, Henan

Fruit ﬁrmness of ‘Mantianhong’ pear was slightly decreased, but not signiﬁ- province, where the irradiance level is lower (Yu, 2012). In the

cantly, among the different light treatments (Fig. 4B), which indicated that this

present study, anthocyanin concentration in the peel of untreated

decrease may be also attributed to natural softening and not light treatment. After 10

and dark-treated fruit was below the detectable threshold (Fig. 3B),

days of irradiation, the concentration of soluble solids and organic acids all slightly

which indicated that light is indispensable for anthocyanin accu-

increased, but no signiﬁcant differences between treated fruit and the control were

observed; total sugars concentration increased signiﬁcantly, but there were no sig- mulation. Our results showed that anthocyanin accumulation was

niﬁcant differences among the light treatments (Fig. 4B), which indicated that the elevated with increasing light quantity in the peel of ‘Mantianhong’

different light treatments had no effect on fruit internal quality.

pear, which was in agreement with previous studies in pear (Huang

et al., 2009) and apple (Arakawa, 1988b).

4. Discussion Previous studies in apple showed that compared with visible,

red and blue light, UV is the most efﬁcient light for inducing antho-

A previous report showed that the pattern of anthocyanin accu- cyanin biosynthesis in the peel of apple fruit (Arakawa, 1988b;

mulation differed between European pears and Asian pears (Qian Saure, 1990; Ubi et al., 2006). UV-B and visible light, however, have a

et al., 2013). In the present study, 10 days irradiation with UV-B and synergistic effect in inducing anthocyanin accumulation in the peel

◦

visible light under different temperature treatments (except 32 C) of apple fruit (Arakawa, 1988a,b). In the present study, the concen-

resulted in a gradual increase in anthocyanin concentration in the tration of anthocyanin in the peel of ‘Mantianhong’ pear treated

peel of ‘Mantianhong’ pear, ‘Meirensu’ pear, and ‘Royal Gala’ apple solely with visible light was 9.5-fold higher than in fruit treated

fruit, whereas anthocyanin concentration in the peel of ‘Cascade’ solely with UV-B, which was inconsistent with the conclusion that

pear fruit showed no signiﬁcant change (Figs. 1A, 2A and 3A). These UV-B is more effective than visible light in inducing accumulation

results indicated that the various temperature treatments affect of anthocyanin in red apple (Arakawa, 1988b; Ubi et al., 2006). Pre-

anthocyanin biosynthesis in red Chinese sand pears in a manner vious studies in apple showed that UV-B and visible light interact

similar to that observed in apple, but not European pear. to induce coloration (Arakawa, 1988a,b). Our results also indicate

Temperature is one environmental factor that inﬂuences antho- that combined UV-B/visible-light irradiation is signiﬁcantly more

cyanin accumulation in fruit peel. It is widely believed that LT effective on fruit color than use of either type of light alone.

induces the biosynthesis of anthocyanin while HT causes antho- Light treatment signiﬁcantly inﬂuenced accumulation of differ-

cyanin degradation. Several studies report that LT is more effective ent pigments in the current study. The concentration of chlorophyll,

than HT for inducing coloration in apple and pear fruit (Ubi et al., carotenoids and ﬂavonoids in the peel of ‘Mantianhong’ pear

2006; Ban et al., 2007; Li et al., 2012). Artiﬁcial heating of on-tree increased in response to different levels of irradiation. Further-

fruit caused a dramatic reduction in peel anthocyanin concentra- more, the respective proportions of chlorophyll, carotenoids and

tion (Wang et al., 2011). HTs during the maturing period accelerate anthocyanin increased approximately from 1:1:0 (control) to 2:4:9

the degradation of anthocyanin in the peel of European pear ‘Rose- (after 10 days of irradiation). In the present study, the maximum

marie’ (Steyn et al., 2004b). Some studies show that the response proportion of anthocyanin among the three main pigment types

pattern to temperature treatments varies among species and cul- was attained at LT, which suggested that LT enhances color by

tivars. In ‘Jonathan’ apple, Arakawa (1991) showed that under improving not only the concentration, but also the proportion of

◦

UV-B/visible light, fruit treated with 25 C developed better color anthocyanin in the fruit peel.

◦

than those treated with 15 C. Similarly, our preliminary results Red Chinese sand pears are eaten at a ﬁrm and crisp stage soon

◦ ◦

showed that, compared with 17 C, 27 C more effectively induced after harvest or storage (Zhang et al., 2012), and therefore fruit

red coloration in red Chinese sand pear ‘Yunhongli No. 1’ fruit ﬁrmness is an essential parameter to be considered. Different tem-

(Zhang et al., 2012). perature treatments had no signiﬁcant effect on ﬁrmness of treated

In the present study, under UV-B/visible-light irradiation the sand pear fruit (Fig. 4). Our results indicated that good fruit ﬁrmness

optimum temperatures for anthocyanin accumulation in ‘Man- was maintained, and concentrations of soluble solid, total soluble

◦ ◦

tianhong’ pear and ‘Meirensu’ pear fruit were 17 C and 12 C, sugars and organic acids were slightly increased, in treated fruit.

respectively (Fig. 3A). These results concur with those of previous 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 .communis

cv ‘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 lights

◦

on 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 constant

◦ ◦

temperature; 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-B

or visible light; 1, 2, 4 and 8, the number of lamps; total soluble sugar concentration was expressed as the sum of sucrose, glucose, fructose and sorbitol concentrations. Total

organic acid concentration was expressed as the sum of malic acid, citric acid, quinic acid, tartaric acid and oxalic acid concentrations.

‘Mantianhong’ pear and ‘Meirensu’ pear could be maintained by LT sand pear ‘Mantianhong’ cultivated in Kunming (which experiences

◦ ◦

of 17 C and 12 C, respectively. relatively lower temperatures and higher irradiance) developed a

Fruit bagging is widely used for production of high quality, better red coloration than in fruit cultivated in Zhengzhou (which

unblemished apple and pear fruit. It is believed that bagging has relatively higher temperatures and lower irradiance) (Yu,

increases the light sensitivity of fruit and stimulates increased 2012). In apple, low temperature and high irradiance can also pro-

anthocyanin synthesis when fruit are re-exposed to light follow- mote anthocyanin accumulation in attached and detached fruit

ing bag removal (Ju et al., 1995; Huang et al., 2009). In the present (Ubi et al., 2006). These results infer that the response of attached

experiment, UV-B/visible-light irradiation for 10 days under LT fruit to temperature and light is consistent with that of detached

conditions induced development of a uniform red color in fruit of fruit. Therefore, to develop a good red color in non-bagged, attached

‘Mantianhong’ pear and ‘Meirensu’ pear after bag removal (Fig. 1A), pear fruit, growing regions with a relatively low temperature and

which was in agreement with the above-mentioned results. Simi- strong illumination during the fruit harvest period were pref-

larly, for attached fruit, our previous study showed that red Chinese erentially chosen. Furthermore, application of pulsed overhead

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

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tree sprinkler irrigation on fruit color and ﬁrmness in ‘Sensation Red Bartlett’

face would be a favorable measure to improve fruit color in warm

pear. Hortechnology 7, 55–57.

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color and weight. HortScience 42, 91–96.

color (Van den Dool, 2006; Glenn and Puterka, 2007). However, the

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This work was supported by the National Natural Science Foun-

communis L.) under bagging treatment and postharvest UV-B/visible irradiation

dation of China (Nos. 31272141, 31301753), the earmarked fund

conditions. Sci. Hortic. 151, 75–82.

for Modern Agro-industry Technology Research Systems (nycytx- Reay, P.F., 1999. The role of low temperatures in the development of the red blush

29), the Doctoral Program of Higher Education of China (no. on apple fruit (Granny Smith). Sci. Hortic. 79, 113–119.

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20130204120004), the Natural Science Foundation of Shaanxi

sides in ‘Gala’ and ‘Royal Gala’ apple fruit skin with UV-B-visible irradiation:

province of China (No. 2013JQ3005) and the Science Foundation

modifying effects of fruit maturity, fruit side, and temperature. Sci. Hortic. 99,

from the Northwest A&F University (No. QN2013015). 57–68.

Saure, M.C., 1990. External control of anthocyanin formation in apple. Sci. Hortic.

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