Journal of Food Engineering 106 (2011) 325–330

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Journal of Food Engineering

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Controlling the weight loss of fresh produce during postharvest storageunder a nano-size mist environment

Duong Van Hung a, Shengnan Tong a, Fumihiko Tanaka b, Eriko Yasunaga c, Daisuke Hamanaka b,Naoya Hiruma d, Toshitaka Uchino b,⇑a Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japanb Laboratory of Postharvest Science, Faculty of Agriculture, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japanc Biotron Institute, Kyushu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japand Mayekawa Manufacturing Company, 3-14-15, Botan koto-ku, Tokyo 135-8482, Japan

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

Article history:Received 6 January 2011Received in revised form 6 May 2011Accepted 20 May 2011Available online 30 May 2011

Keywords:Weight lossChilling injuryStomatal poreNanomistUltrasonic mistPostharvest storage

0260-8774/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.jfoodeng.2011.05.027

⇑ Corresponding author. Tel./fax: +81 92 642 2934.E-mail addresses: hungvanduong@gmail.com (D.V. H

ac.jp (T. Uchino).

Weight loss and chilling injury often occur during the refrigerated storage of fresh produce, leading tosignificant economic costs to horticultural industries. The postharvest quality of three types of horticul-tural produce, eggplant fruit (Solanum melongena), mizuna (Brassica rapa) and fig fruit (Ficus carica), wasinvestigated under storage environments of two kinds of fine mists producing relative humidity as highas 95% at 5.5 and 7 �C for 10, 6 and 8 days, respectively. Mists generated by nanomist humidifiers (nano-mists) had average particle diameters less than 100 nm, while ultrasonic humidifiers (ultrasonic mists)generated average particle diameters of 216 nm. The results show that the weight loss rates of the sam-ples stored under nanomist humidifiers were 3.7%, 5.3% and 8.8% for mizuna, eggplant and fig, respec-tively, while those stored under ultrasonic mist were 7.3%, 8.5% and 14.7%, respectively. The eggplantfruits stored in the nanomist chamber had a lower index of chilling injury than those stored in the ultra-sonic mist. The stomatal pores of the samples exposed to the nanomists closed by 34.7 and 51.5 lm2 formizuna and fig, respectively, compared with their initial openings, while in the ultrasonic mists, theyclosed by 15.8 and 25.5 lm2, respectively. The color of mizuna stored in the nanomist was greener thanthose placed in the ultrasonic mist during the postharvest storage period.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Fresh fruit and vegetables are living tissues that continue to losewater after harvest, but, unlike growing crops, they can no longerreplace lost water from the soil and must rely on the water contentpresent at harvest. The loss of water from fresh produce followingharvest is a serious problem because it causes shrinkage andweight loss. Most commodities become unsalable as fresh produceafter losing 3–10% of their weight (Ben-Yehoshua and Rodov,2003).

The quality and storage life of fresh produce are highly depen-dent upon the vapor pressure gradient between the produce andthe storage atmosphere. Therefore, when the produce and the stor-age environment are maintained at the same temperature (assum-ing factors such as air velocity are held uniform), the transpirationrate is highly correlated with the relative humidity (RH) duringstorage time (Grierson and Wardowski, 1978; Sharkey and Peggie,1984). Transpiration through the actions of the stomata, lenticels,

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ung), toshiu@bpes.kyushu-u.

cuticles and epidermal cells (Ben-Yehoshua and Rodov, 2003) isconsidered the major cause of postharvest weight loss and poorquality in leafy vegetables. Transpiration in produce is a masstransfer process in which water vapor moves from the surface ofplant organs to the surrounding air. This process occurs when thereis a gradient of water vapor pressure between the tissue and thesurrounding air.

Produce is usually stored under a low-temperature environ-ment. For the commodity’s transpiration, however, a high RH stor-age environment plays an important role in maintaining thequality of produce. Recommended RH levels for the storage of freshfruit and vegetables are commodity specific, with levels generallyin the range of 85–95% (Paull, 1999; Rennie et al., 2003; Maguireet al., 2004).

At present, large mists are used to raise RH in the storage envi-ronment. These mists are occasionally generated by ultrasonichumidifiers, and their average particle diameters vary between2.9 lm (Rodes et al., 1990) and 216 nm (Hung et al., 2010b). Thelarge mists can easily wet the surface of produce, which is coveredby a laminar film of water. The RH of the laminar film is consideredto be nearly 100%. Wetting on the surface of the produce causes thestomata to open (Lange et al., 1971), resulting in water loss. Our

326 D.V. Hung et al. / Journal of Food Engineering 106 (2011) 325–330

previous study showed that nanomists, generated by nanomisthumidifiers, have average particle diameters <100 nm (Hunget al., 2009). Nanomist humidifiers are thought to provide im-proved capability for generating ultrafine mists for high humidifi-cation. Nanomists, because of their very fine particle size,presumably evaporate immediately after atomization. The finemists, which are present on the surface of the produce, also easilyevaporate and therefore do not wet the produce in comparisonwith the larger ultrasonic mists. Nanomists could bring a numberof benefits to the field of postharvest crop storage. Hung et al.(2010a) have demonstrated that the strength of corrugated card-board is well-preserved under a nanomist environment with highrelative humidity. The aim of the present paper is to investigatethe effect of nano- and ultrasonic mists on the control of weightloss and several postharvest quality attributes of three types ofhorticultural produce stored under high relative humidityenvironment.

2. Materials and methods

2.1. Source of materials

Eggplant fruit (Solanum melongena L., cv Chikuyo), mizuna(Brassica rapa L. var. Japonica cv Kyomizore) and fig fruit (Ficus car-ica L., cv Toyomitsu-Hime) were purchased from a Fukuoka whole-sale market. The produce was carefully handled as they weretransported to the laboratory and the experiment. Eggplant fruitspossessing uniform color and weight between 145 and 200 g eachwere chosen for the experiment. Mizuna plants weighing approxi-mately 200 g were packed in polyethylene bags with the leafy por-tion of the plant left open. The figs were sorted to eliminate anythat had defects, and those with a uniform color and a weight ofapproximately 80 grams each were chosen. The experiments wererepeated twice on October 2009 and May 2010 for the mizuna andeggplant and on October and November 2010 for the fig fruit.

2.2. Storage condition

The samples were placed in storage environments at 5.5 �C formizuna and eggplant and 7 �C for fig fruit. A nanomist humidifier(test model, Mayekawa Co. Ltd., Tokyo, Japan) and an ultrasonichumidifier (FT-30 N-14, UCAN Co. Ltd., Japan) were used to main-tain the humidity at approximately 95%. Forty-five eggplant fruitsand 15 mizuna bags were used for each storage condition for theexperiment performed on October 2009, while 10 eggplant fruitsand 8 mizuna bags were used on May 2010. Forty figs were usedin both experiments for each storage condition. To investigatethe effect of particle size on the quality of produce, in addition tothe effect of RH, the eggplant and fig fruits were placed on traysand were directly exposed to the mists, whereas the mizuna bagswere vertically placed into plastic trays with an opening on thetop of each bag. All samples were assessed for weight loss, chillinginjury and color throughout the experiment. Determinations weremade at the beginning of storage and at 3 and 6 days for mizuna, 4and 8 days for fig and 5 and 10 days for eggplant.

The temperature and RH were recorded at 5-min intervals inthe containers using a humidity and temperature transmitter(model HMT337, Vaisala, Helsinki, Finland). This device can mea-sure the accuracy of the temperature to ±0.2 �C and the RH to±1.7% at a range of 90–100%. The nanomist chamber was3060 mm long, 2130 mm high and 2320 mm wide. The ultrasonicchamber was 2600 mm long, 2400 mm high and 1700 mm wide.The chambers were equipped with a cooling system controller, asystem control panel and either a nanomist humidifier or an ultra-sonic humidifier.

2.3. Methods for parameter assessment

2.3.1. Weight lossWeight loss was measured as a reduction in the weight of the

produce stored and was expressed as the percentage of weightchange compared with initial weight, namely, the weight loss rate.

2.3.2. Chilling injury (CI) index in eggplant fruitOn the day of sampling, the external CI symptoms were visually

observed on a subjective scale. The level of CI severity was calcu-lated according to the following scale, similar to that proposedby Concellón et al. (2007) and Lederman et al. (1997): 1 = no dam-age, 2 = low damage, 3 = regular damage, 4 = moderate damageand 5 = severe damage. The CI index (CI) was expressed as follows:

CI ¼P5

i¼1ðLiNiÞNTotal

ð1Þ

where Li is the chilling injury level, Ni is number of fruits on the le-vel and Ntotal is the total number of fruits in the treatment.

2.3.3. Determination of colorThe color of eggplant skins and mizuna leaves was measured

using a chromameter (Minolta CR 200, Japan). The measurementswere expressed as L⁄ values (dark to light), and parameters a⁄

and b⁄ represent redness to greenness and yellowness to blueness,respectively. Three readings were taken from the lower, centraland upper sections of each eggplant fruit, and the average of thevalues for each fruit was calculated. Ten fruits were used for eachmeasurement. For the mizuna leaf, the determination of color wasmade from three leaves per pack and eight packs were employedfor each storage condition.

To evaluate the browning of the pulp tissue of the eggplant,only the lightness of the pulp tissue indicated by parameter L⁄

was used. Two slices (thickness = 1 cm) were cut at the central sec-tion of each fruit, and the reading was taken from one side of eachslice immediately after cutting. The results were expressed as L�0,which was calculated as the mean of five fruits per storage timeand condition.

2.3.4. Examination of stomatal apertureThe stomatal data were collected following the method de-

scribed by Hirose et al. (1992). A glass slide with a small drop ofinstant adhesive was attached to the epidermal surface of the min-uza leaf and the skins of the figs for approximately 30 s. Afterremoving the leaves and skins, the glass slide was placed on amicroscopic base to observe the stomatal image through a confocallaser scanning system (CLSM) (Olympus Fluoview FV-300, Tokyo,Japan). The collection of stomatal impressions using instant adhe-sive was performed inside a storage environment under low lighton six glass slides from six leaves/fruits per storage time and con-dition. From each glass slide, two images were taken at 20-foldmagnification with a size of 1024 � 1024 pixels. The stomatal areawas measured using ImageJ 1.42q (Wayne Rasband, National Insti-tute of Health, USA). Twenty stomata for minuza and six stomatafor fig were randomly selected from each image to study the sto-matal area, and a total 240 and 72 stomata were used to calculatestomatal the area for mizuna and fig, respectively, in eachtreatment.

2.4. Statistical analysis

The experimental data are presented as the mean ± SE of twoindependent experiments. An analysis of variance was performedusing the statistical software GenStat (Discovery Version 3, VSNInternational Ltd., UK). Differences between the means of

D.V. Hung et al. / Journal of Food Engineering 106 (2011) 325–330 327

attributes were compared by a least significant difference (LSD)test at a significance level of P 6 0.05.

3. Results and discussion

The temperature and RH monitored in all experiments duringpostharvest storage are shown in Table 1. From the results in Ta-ble 1, it can be seen that the average temperature recorded fromthe two storage environments was nearly the same in each exper-iment. The average RH measured from the nanomist was equal toor smaller than those measured from ultrasonic storage except forfig in experiment 1. For instance, in the second experiments formizuna and eggplant, the RH recorded from the nanomist was1.2% and 1.4% smaller than those in the ultrasonic chamber,respectively. Fig. 1 presents the changes in temperature and RHduring fig storage as an example. The graphs show various patternsof RH readings obtained from the two chambers. The points withan RH over 100% reflect supersaturation, which occurs when wateris present in the form of tiny droplets (Rodov et al., 2010). Morereadings with an RH over 100% were observed in the ultrasonicchamber than in the nanomist chamber. This difference could beone reason that the number density of mists produced by the ultra-sonic humidifier was four times greater than the nanomist humid-ifier (Hung et al., 2010b).

The results shown in Table 1 indicate that the weight loss ratesof the samples stored in the nanomist were 3.7%, 5.3% and 8.8% formizuna, eggplant and fig, respectively, while those stored in theultrasonic mist were 7.3%, 8.5% and 14.7%, respectively. From thesedata, it can be observed that storing fresh fruit and vegetables inthe nanomist chamber reduced the weight loss rates (3.6%, 3.2%and 5.9% for mizuna, eggplant and fig, respectively) compared withthose stored under the ultrasonic mists. The differences in theweight losses of the produce between the two treatments can beexplained using Fick’s law of diffusion. According to Ben-Yehoshuaand Rodov (2003), the flow rate of water vapor through the surfaceof fruit or vegetables is proportional to the difference between thehumidity of the internal atmosphere of the produce and thehumidity of the storage atmosphere, behaving according to Fick’slaw of gas diffusion. This model has been applied to estimate thetranspiration rate of mushrooms (Mahajan et al., 2008). Therefore,the weight loss of fresh produce in a chamber in which the RHchanges with time can be calculated based on Fick’s law and is ex-pressed as follows:

J ¼ kPs � PRdTA

� �ð2Þ

where J is the mass flux of water vapor; k is the mass transfer coef-ficient; Rd is the gas constant of water vapor per mass unit; TA is theabsolute temperature and (Ps � P) is the vapor pressure deficit(VPD).

VPD also can be expressed as

Table 1Temperature, RH, cumulative VPD and weight loss of produce measured from all experim

Produce Experiment Nanomist

Temperature(�C)

RH (%) Cumulative VPD(Pa)

Weight(%)

Minuza 1 5.9 ± 1.2 96.9 ± 3.8 49885.5 3.1 ± 0.62 5.5 ± 0.7 94.4 ± 5.7 93925.4 4.2 ± 0.2

Eggplant 1 5.9 ± 1.1 97.4 ± 3.8 66448.3 4.4 ± 0.12 5.5 ± 0.7 94.4 ± 5.7 119986.8 6.2 ± 0.1

Fig 1 7.1 ± 0.5 94.3 ± 4.1 117216.1 7.8 ± 0.22 7.0 ± 0.4 93.3 ± 3.9 143102.4 9.9 ± 0.2

Data except for cumulative VPD are the mean and accompanied by the standard error o

VPD ¼ Psð100� RHÞ=100 ð3Þ

where RH is the actual RH (%) and Ps is the saturated vapor pressurein pascals (Pa) and is calculated using Tetens’s equation, as pre-sented by Rodov et al. (2010):

Ps ¼ f a � expbT

c þ T

� �� �ð4Þ

a = 611.21, b = 17.502, c = 240.97 and f = 1.0007 + 3.46 � 10�8 P,where T = temperature in degrees Celsius (�C) and P = atmosphericpressure in pascals, with u (decimal) = RH/100 and VPD = Ps(1 � u).

Eq. (2) can be rewritten as

1A

dmdt¼ KPsðus �uÞ ð5Þ

where m is the mass of water vapor and t is the time.

K ¼ kRdTA

ð6Þ

As the rate of change of absolute temperature during the experi-ment is extremely small, TA can be considered constant.

To find the change in mass, namely, water loss Dm, we integrateEq. (5) as follows:

Dm ¼Z

dm ¼ KAZ

Psðus �uÞdt ð7Þ

By discretizing Eq. (7), we obtain Eq. (8)

Dm ¼ KADtXn

i¼1

Psiðus �uiÞ ð8Þ

where Dm is the mass of water transpirated from the produce (kg),Dt = ti � ti�1 is partial storage time (s), us is the equilibrium of theRH in the tissue of the produce (intercellular RH is described be-low), ui(decimal) is the RH of the storage environment at time ti,A is the surface of the produce through which water vapor passes(m2) and K is a constant related to the mass transfer coefficient,as expressed by Eq. (6) (s m�1).

The expression Psiðus �uiÞ in Eq. (8) is the vapor pressure def-

icit (VPD), which shows the difference in the partial pressure ofwater vapor between the storage environment and the produce.The rate of transpiration from fresh produce is proportional tothe VPD of the surrounding atmosphere at a given temperature ifK and A are constant. The higher the VPD, the greater the waterloss.

In both empirical and theoretical studies, it has been well dem-onstrated that intercellular water vapor in the tissues of fresh pro-duce is very close to saturation with a us of approximately 0.995(Nobel, 1974; Ben-Yehoshua and Rodov, 2003). We can calculatethe cumulative VPD using Eq. (9) based on the RH and temperaturedata from each experiment. The values of ui more than or equal to0.995 were not calculated because, at this level of ui, the transpi-ration process does not occur.

ents.

Ultrasonic-mist

loss rate Temperature(�C)

RH (%) Cumulative VPD(Pa)

Weight loss rate(%)

5.8 ± 0.9 97.3 ± 5.1 45765.5 8.4 ± 0.55.5 ± 0.8 95.8 ± 7.1 89440.2 6.2 ± 0.6

5.8 ± 0.8 97.5 ± 4.9 64230.5 7.3 ± 0.35.6 ± 0.8 95.6 ± 7.1 118418.6 9.7 ± 1.1

7.0 ± 0.5 94.0 ± 5.7 133325.8 13.3 ± 0.37.0 ± 0.5 93.6 ± 5.9 139136.6 16.2 ± 0.2

f the means. RH: relative humidity, VPD: vapor pressure deficit.

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Rel

ativ

e hu

mid

ity (%

)

0

2

4

6

8

10

12

14

16

Tem

pera

ture

(o C

)

RH

T

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8Time (days)

Rel

ativ

e hu

mid

ity (%

)

0

2

4

6

8

10

12

14

16

Tem

pera

ture

(o C)

RH

T

a

b

Fig. 1. Changes in temperature (T) and relative humidity (RH) under two environments of nanomist (a) and ultrasonic mist (b) during postharvest storage of fig.

328 D.V. Hung et al. / Journal of Food Engineering 106 (2011) 325–330

Cumulative VPD ¼Xn

i¼1

Psiðus �uiÞ ð9Þ

The data on cumulative VPD calculated from each experiment areshown in Table 1. If we hypothesize that parameters A and K inEq. (8) are the same in both storage environments, the weight lossof the produce then depends on the cumulative VPD. We can seethat the cumulative VPDs obtained from the experiments exposedto the nanomists were higher than those treated with the ultrasonicmists, except for fig in experiment 1. Although the cumulative VPDsof the experiments stored with nanomists were higher than those ofthe ultrasonic mists, the weight loss rates of the nanomist-exposedproduce were always smaller than those under the ultrasonic mists.Furthermore, the mean RH recorded in the ultrasonic mists ofexperiment 2 was 1.2% and 1.4% higher than that in the nanomistsfor mizuna and eggplant, respectively; the weight loss rate of theproduce stored in the ultrasonic mists would have been lower thanthose in the nanomist. There was one case in which the cumulativeVPD of the nanomist experiment was smaller than the ultrasonic,but the ratio of cumulative VPD for ultrasonic to nanomist (1.1)was very different, with a weight loss rate ratio of ultrasonic tonanomist of 1.7. Therefore, it can be concluded that one of thetwo above-mentioned parameters (K, A) in both storages was notthe same. It is also possible that the weight losses of the producemay be influenced by the particle size, resulting in the partial clos-ing of the stomata pores which is relative to the A parameter in Eq.(8), as indicated below.

Fig. 2 shows the stomatal opening of the mizuna leaves and thefig fruit stored in the nanomist (a) and the ultrasonic mist (b). Thestomatal pore is presented in Table 2. Significant differences werefound in stomatal area between the samples stored in the nano-mist and ultrasonic conditions. The average value of the stomatalarea measured prior to storage was 99.2 and 172.5 lm2 for mizunaand fig, respectively. At that time, the recorded temperature andRH were 23 �C and 61%, respectively, under light. Nevertheless,the stomata of the samples partially closed during storage, espe-cially the stomatal pores of the samples stored in the nanomistchamber, which closed by 34.7 and 51.5 lm2 for mizuna and fig,respectively, compared to their initial openings, while in the ultra-sonic chamber, they were closed by 15.8 and 25.5 lm2, respec-tively. The variation in stomatal area between the twotreatments could be the reason for the differences in weight loss.Open or partially closed stomata will affect parameter A, therebychanging the water loss, as shown in Eq. (8). The partial closureof the stomata observed in the nanomist chamber could be dueto the following reasons. Lange et al. (1971) found that the openingof the stomatal aperture depends on the wetness of the surface ofthe plant, which suggests that less water on the outer surface ofthe epidermis results in a closing of the stomata, while air that isnearly saturated leads to maximal opening of the stomata. Further-more, the structure and function of stomata are described as fol-lows. Stomata are composed of two guard cells. These cells havewalls that are thicker on the inner side than the outer side. This un-equal thickening of the paired guard cells causes the stomata toopen when they take up water and close when they lose water.

Fig. 2. Stomatal opening of mizuna leaves and fig fruit stored in the nanomist (a) and in the ultrasonic mist (b).

Table 2Several quality attributes of three commodities preserved under two environments of nanomist and ultrasonic mist during postharvest storage.

Products Treatments Storage time (days) Stomatal pore (lm2) Color CI index Pulp color (L�0)

L⁄ a⁄ b⁄

Mizuna Nanomist 0 99.2 ± 5a 45.9 ± 0.3a �18.4 ± 0.2a 25.4 ± 0.3a3 69.4 ± 3b 46.0 ± 0.2a �18.2 ± 0.2a 25.1 ± 0.4a6 64.5 ± 2b 46.2 ± 0.4a �18.4 ± 0.2a 25.5 ± 0.4a

Ultrasonic-mist 0 99.2 ± 5a 45.9 ± 0.3a �18.4 ± 0.2a 25.4 ± 0.3a3 83.4 ± 3.7a 45.5 ± 0.3ab �17.1 ± 0.2b 23.7 ± 0.4b6 87.6 ± 2.2a 45.0 ± 0.3b �17.2 ± 0.2b 23.0 ± 0.4b

Eggplant Nanomist 0 27.0 ± 0.2a 2.2 ± 0.3a �0.9 ± 0.1a 86.4 ± 0.3ab5 25.8 ± 0.2b 2.7 ± 0.4a �0.8 ± 0.1a 2.6 ± 0.2c 86.7 ± 0.2ab

10 24.5 ± 0.4c 2.6 ± 0.4a �0.7 ± 0.1a 3.2 ± 0.2b 87.1 ± 0.3a

Ultrasonic-mist 0 27.3 ± 0.2a 2.2 ± 0.3a �0.9 ± 0.1a 86.4 ± 0.3a5 25.6 ± 0.2b 2.6 ± 0.5a �0.7 ± 0.1a 3.1 ± 0.1b 85.9 ± 0.3ab

10 23.6 ± 0.2d 2.2 ± 0.4a �0.7 ± 0.1a 4.4 ± 0.2a 85.7 ± 0.3b

Fig Nanomist 0 172.5 ± 10.6a4 113.9 ± 4.9c8 121.3 ± 4.4c

Ultrasonic-mist 0 172.5 ± 10.6a4 147.0 ± 6.3b8 170.5 ± 6.8a

Data are the mean of two experiments (No. 1 and 2 shown in Table 1) except for pulp color of eggplant and stomatal pore of fig and accompanied by the standard error of themeans. Pulp color of eggplant and stomatal pore of fig were obtained from experiment No. 2. Different letters in one column separated by products show significant differenceby statistical programme at P < 0.05.

D.V. Hung et al. / Journal of Food Engineering 106 (2011) 325–330 329

The opening and closing of stomata is governed by increases or de-creases of water in the guard cells, which cause them to take up orlose water, respectively (Masuda, 1989; Taiz and Zeiger, 2003).

In our study, we observed that the stomata of the producestored in the nanomist closed more than those stored in the ultra-sonic mist. The reason may be that under the nanomist environ-ment, the number of nanomist particles on the surface of theproduce is smaller than that of the ultrasonic mist. Moreover, thevery fine mists present on the surface of the produce are believedto evaporate quickly, therefore not wetting the produce and thusmaking the stomata close more than those stored in the ultrasonic,where the large mists and their number, which directly drop on theproduce and do not easily evaporate, are thought to wet the surfaceof the samples.

The CI index of the eggplant fruits increased by day 5 (Table 2).The CI of the fruits stored in the nanomist chamber was lower thanthat of the ultrasonic mist, and the CI symptoms increased withstorage time. Concellón et al. (2004) reported that a high CI index(CIi = 4) of eggplant fruits was observed on day 12 at 5 �C, similar tothe CI of the eggplant fruits stored in the ultrasonic chamber. Mois-ture loss has been implicated as the causal factor in the CI of grape-fruit (Purvis, 1984) and eggplant fruit (Fallik et al., 1995). Severe CImay induce water loss by the destruction of cuticles and the soft-ening of the tissue. Because the CI was not severe in our experi-ment, the reduction of CI in the eggplant fruit stored undernanomist is probably due to the reduced water loss from the fruit.

Changes in the color parameters of mizuna, eggplant fruit andthe pulp of eggplant during the storage period are shown in Table 2.

330 D.V. Hung et al. / Journal of Food Engineering 106 (2011) 325–330

For mizuna, the L⁄ value was different between the two storageconditions at the end of the experiment. Moreover, the a⁄ and b⁄

values showed a significant difference between the samples storedin the two environments. A more negative a⁄ (greenness index) va-lue was recorded for the samples stored in the nanomist, whichmeans that the leaves were greener than those stored in the ultra-sonic chamber. For eggplant, the lightness of skin (L⁄) was reducedslightly over the storage period and was not significantly differentat day 5, though it was significantly different between the twotreatments during storage at the end of experiment. Parametersa⁄ and b⁄ were not different between the two treatments and wereconstant throughout storage. The variations in parameter L⁄ be-tween the two treatments were attributed to differences in surfaceCI symptoms. Concellón et al. (2007) suggested that CI symptomsare related to variations in the color parameter. The lightness ofeggplant pulp (L�0) was a good indication of the browning evolutionof the fruit tissue during cold storage. As shown in Table 2, the L�0readings of the fruits stored under nanomist were constant overstorage time and were similar to the initial value, which wasaround 87. However, a significantly lower value was observed inthe fruit stored under ultrasonic mist, indicating the browning ofseed and pulp. The difference in the lightness of eggplant pulpmay be attributed to the difference in chilling injury.

In summary, it is possible to conclude that nanomists are usefulfor raising humidity to control the weight loss of fresh fruit andvegetables during cold storage or transportation. Further researchregarding the impact of nanomists on postharvest diseases of fruitis highly recommended.

Acknowledgements

The authors would like to acknowledge financial support forthis research from research and development projects funded bythe Ministry of Agriculture, Forestry and Fisheries, Japan and bythe Ministry of Education, Science, Sports and Culture, Japan (Pro-ject No. 22380138).

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