Effects of 1-Methylcyclopropene Treatment on Physicochemical Attributes of “ Hai Jiang ” Yardlong Bean during Cold Storage

e yardlong bean belongs to nonclimacteric fruit. e objective of this study was to investigate the eects of 1-methylcyclopropene (1-MCP) treatment on physicochemical characteristics of yardlong beans during cold storage. Freshly harvested yardlong beans were treated with dierent concentrations of 1-MCP (0, 0.75, 1.0, 1.25, and 1.5 μL ·L) and stored at 8°C for 21 days. e results showed that, compared with the control, the decrease in rmness and good fruit rate and the degradation of chlorophyll and vitamin C (Vc) content could be inhibited, change in skin color could be delayed, activities of superoxide dismutase (SOD) and peroxidase (POD) could be improved, and the increasing of malondialdehyde (MDA) content and weight loss could be inhibited signicantly by 1-MCP treatments. Of the dierent concentrations of 1-MCP, 1.0 μL·L proved to have the best preservative eects, extending storage time and delaying ripening and senescence of yardlong beans. ese results indicated that 1-MCP treatment provided an eective method for delaying the postharvest senescence of fresh yardlong beans.


Introduction
e yardlong bean (Vigna unguiculata (Linn.)subsp.(sesquipedalis)) is a very popular and healthy horticultural product with a high nutritional value.It is commercially cultivated, and its green pods are eaten throughout the tropical and subtropical areas, covering Asia, Africa, South America, and Southern Europe [1][2][3].e yardlong bean, which is a crisp and tender legume, is a good source of proteins, dietary bers, vitamins, anticarcinogenic compounds, etc. [4,5].However, yardlong bean is easy to deteriorate and lose commodity, mainly due to its browning skin color, dehydration, and softening characteristics after harvest, ultimately leading to quality decrease during the transportation and selling [6].
Ethylene is one of the important factors that in uence vegetable preservation, which promote the process of vegetable senescence and accelerate its quality deterioration.1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor that blocked the ethylene signaling transduction by interacting with ethylene receptors in climacteric fruits and vegetables [7].Suppression of ethylene activity neutralizes many adverse e ects on postharvest fruits and vegetables such as increased respiration rate and ethylene production, accelerated softening, senescence, color change, starch breakdown, and other physiological disorders [8][9][10].Commercial application of 1-MCP in edible crops was introduced by Rohm and Haas Company [11].Due to its nontoxic mode of action, low product application rate, and nonexistent residues in postharvested fruits and vegetables, 1-MCP has been widely used in postharvest fruits and vegetables preservation [12].
Yardlong bean belongs to the nonclimacteric group [19].e preservation methods of yardlong bean mainly focused on modi ed storage atmosphere, coating, hot water treatment, chemical treatment, etc. [6,20].In uence of 1-MCP on physicochemical attributes is rarely studied.erefore, the aim of the present study is to investigate the e ects of

Yardlong Bean
Fruit and 1-MCP Treatment.Fresh yardlong beans (cv."Hai Jiang" with dark green color, crisp, and tight flesh) were harvested from a commercial field in Yongxin town, Hainan province, China.Beans were packed into cardboard boxes and transported to the laboratory within 2 h.Pods with uniform size and absence of diseases were selected and then randomly divided into five groups, with ∼150 fruit (30 pods were used for appearance observation, and 120 pods were used for the determination of indexes every three days.)each.Treatments designated as CK (control, distilled water), 0.75 μL•L −1 , 1.0 μL•L −1 , 1.25 μL•L −1 , and 1.5 μL•L −1 of 1-MCP (EthylBloc, Rohm and Haas China, Inc.) were conducted.Yardlong beans were placed in a 38 L container and fumigated with the different concentrations of 1-MCP at 25 °C for 12 h.e yardlong beans were then placed in polyethylene bags (Xin Feng Company, China) and transferred to 8 °C and 85 ± 5% RH and stored for 21 days.ree replicates of fifteen pods were sampled at every third day to determine physicochemical characteristics.

Weight Loss, Good
Fruit Rate, and Firmness.Weight loss was determined for 30 pods from each treatment group [21].Pods were weighed individually before packing and during storage.Good fruit rate (%) was evaluated by determining the percentage of surface area showing healthy status and measured based on the method reported in [22].e sensory quality, in terms of changes in visual appearance and acceptability, was rated on a nine-point Hedonic Scale: 9, excellent (fully characteristic of the product, color, freshness, hardness, and juiciness; like very much); 7, very good (faint loss of sepal greenness, freshness, hardness, and juiciness; like moderately); 5, good (further loss of freshness, hardness, and juiciness; like, limited marketability); 3, fair (faint tissue disruption; neither like nor dislike, limited edible quality), and 1, poor (distinct tissue disruption; dislike very much, inedible quality).Firmness was measured using a firmness tester (FMH-1, Takemura Motor Manufacturing, Matsumoto, Japan).
e measurement was conducted with the penetration depth of 10 mm, and five equally position of single side were performed.
ree replicates with three pods were performed, and the results were expressed in Newton (N).

Determination of Color and Chlorophyll Content.
Pod color parameters of L * , a * , and b * were evaluated using a colorimeter (Konica Minolta, CM-700d, Osaka, Japan) with an 8 mm aperture and a d65 illuminant setting.Chlorophyll was determined using a colorimetric method [23].Samples from pods of approximately 0.5 g were grounded in a mortar with a small amount of quartz sand, calcium carbonate powder, and 5 mL of 80% acetone to produce a homogenate, and then 10 mL of 80% acetone was added until the mixture became white.e mixture was left to stand for about 3-5 min.e homogenate was then filtered into 50 mL brown volumetric flasks through filter paper.e mortar, pestle, and the residue were rinsed several times with 80% acetone until the filter paper and residue showed no green coloration.e filtrate was diluted with 80% acetone to a final volume of 25 mL.e supernatant was used in the chlorophyll assay using colorimetric determination with a T6-spectrophotometer (model: T6, Beijing Purkinje General Instrument Company, Beijing, China) at 440 nm, 645 nm, and 663 nm colorimetric wavelengths, with three replicates of each sample.

Determination of Vc Content.
e contents of Vc were measured by 2,6-dichlorophenolindophenol titration [17,24].Vc concentration was calculated according to the titration volume of 2,6-dichlorophenolindophenol and expressed as mg•100 g −1 .Samples from pods of approximately 2.0 g were grounded in a mortar with a small amount of quartz sand and 5 mL of 2% oxalic acid to produce a homogenate.After centrifugation, the supernatant was extracted with oxalic acid to 50 mL, and the 10 mL sample was titrated with 2,6-dichlorophenolindophenol.e solution was slightly red in color and not fading in 30 s. e amount of the solution was measured.

Determination of MDA Content.
e pod MDA content was determined using the thiobarbituric acid (TBA) reaction [25,26].A 2 g sample of pod tissue was homogenized in 10% trichloroacetic acid.
e homogenate was centrifuged at 12,000 g for 20 min at 4 °C.en 3 mL supernatant and 3 mL 0.6% thiobarbituric acid were added to a 10 mL test tube, the mixture was heated in a boiling water bath for 20 min, and cooled immediately.Absorbance was then measured at 450 nm, 532 nm, and 600 nm, using distilled water as a blank.Data were expressed as mmol g −1 .
2.6.Assay of SOD Activity.SOD activity in pod tissue was estimated using the method discussed in [27].Approximately 1.0 g samples of pod tissue were weighed and grounded with a pestle in an ice-cold mortar with 5 mL extracting solution in 50 mM sodium phosphate (pH 7.8).
e mixture was illuminated by light (60 mol m −2 s −1 ) for 20 min, and the absorbance was then determined at 560 nm.Identical solutions kept in the dark served as blanks.SOD activity was expressed as U g −1 , where one unit was defined as the amount of enzyme that caused a 50% decrease of the SOD inhabitable NBT reduction per mass of fruit pulp per hour.

Assay of POD Activity.
POD activity in pod tissue was estimated by using the method reported in [28].Approximately 1.0 g samples (pod) were weighed and grounded with a pestle in an ice-cold mortar with 5 mL extracting solution 2 Journal of Food Quality (1 mmol PEG, 4% PVPP and 1% Triton X-100).
e homogenates were centrifuged at 12,000 g for 30 min at 4 °C.e resulting supernatants were used to determine enzymatic activities.Crude enzyme extraction solution was assayed using 3 mL of 25 mM guaiacol as the substrate.Enzyme extraction solution (30 μL) was added to 50 μL of 30% H 2 O 2 ; the reaction started by rapid mixing.At start time, the reaction mixture was transferred into a cuvette and placed in the spectrophotometer sample chamber.With distilled water as a reference, the absorbance values were recorded at 470 nm per 15 s, and one unit of POD was defined as the enzyme activity changes of 0.01 in the 470 nm absorbance in one minute.Results were expressed as U g −1 min −1 .

Statistical Analysis.
All data were expressed as mean values ± standard error and analysed using SPSS version 17.0 (SPSS, China, Zhejiang University).Data at each time point were subjected to one-way analysis of variance (ANOVA), and differences between pairs of means were measured using Tukeys HSD.P < 0.05 was considered as a significant difference.

Effect of 1-MCP Treatment on the Weight Loss, Good Fruit
Rate, and Firmness.Weight loss, good fruit rate, and firmness were recognized as quality attributes of postharvest yardlong bean that affect pod texture and freshness.As shown in Table 1, 1-MCP treatments exhibited significantly (P < 0.05) lower losses of weight than control group after 21 days storage, and 1.0 μL•L −1 concentration of 1-MCP exhibited the most retarded effect.Compared with control, weight loss of 1.0 μL•L −1 1-MCP decreased from 1.90% to 0.8% at 3 d and from 26.0% to 16.7% at 21 d.1-MCP treatment delayed the softening and maintained the healthy characteristic of yardlong bean during 21 days of storage.After being stored at 8 °C for 21 days, significant differences were observed between control and 1-MCP-treated beans, and highest values were found in the group treated with 1.0 μL•L −1 concentration of 1-MCP, with 51% of good fruit rate and 4.2 N of firmness at 21 day, respectively (Table 1).us, 1.0 μL•L −1 1-MCP treatment could effectively reduce the rate of weight loss and suppress the decline of the good fruit and firmness.Similar results have also been reported in avocado [29], Chinese chive scape [30], and eggplant fruit [16] that 1-MCP treatment effectively reduced weight loss, maintained higher firmness, and good fruit rate.

Effect of 1-MCP Treatment on the Color and Chlorophyll
Content.Skin color is one of the important indicators of vegetable quality.1-MCP significantly delayed (P < 0.05) the increase of a * and b * values and the decrease of L * value as compared to the pods in the control group (Figures 1(a)-1(c)).On day 21, a * and b * values of 1.0 μL•L −1 1-MCP-treated pods were higher by 1.06 and 1.26 than those of controls, respectively (Figures 1(b), and 1(c)).A sharp decrease in chlorophyll content was observed in the untreated pods after  21 days of storage (Figure 1(d)).After 21 days of storage, yardlong bean treated with 1.0 μL•L −1 1-MCP had the highest chlorophyll content (0.18 mg g −1 ).
ese results were in agreement with that of the previous studies that 1-MCP treatment delayed the color change of broccoli floret [18,31], Strawberry [15], and eggplant [16].

Effect of 1-MCP Treatment on the Vc Content.
One of the nutritional importance of yardlong bean focused on vitamin C (Vc).A shape decrease of Vc content of all the five treated yardlong beans were observed over the storage time (Figure 2).1-MCP treatment retarded the Vc content decline on 5% level as compared to the control (Figure 2).1.0 μL•L −1 concentration of 1-MCP treatment obviously restrained the Vc decreasing rate, as the Vc decreasing rate at 1.0 μL•L −1 1-MCP-treated beans was 58.2%, which was remarkably lower than that (93.3%) of the controls after 21 days storage.us, the results indicated that 1-MCP treatment had the positive role in maintaining Vc content of yardlong bean, especially treated with 1.0 μL•L −1 1-MCP. is result was in agreement with previous studies that Vc content lost more than half in broccoli during postharvest storage, and 1-MCP treatment maintained significantly better retention of Vc [18,32].

Effect of 1-MCP Treatment on the MDA Content.
MDA is a major product of membrane lipid peroxidation, reflecting cellular membrane integrity.MDA content in both control and 1-MCP-treated yardlong beans increased    Journal of Food Quality progressively, with a lower level of 1-MCP-treated pods than in the control after 21 days storage (Figure 3).MDA content of untreated fruit increased remarkably after 9 days of storage (Figure 3).In the middle of the storage period (12 days), MDA content of the control beans was higher by 0.83, 0.72, 0.54, and 0.46 mmol g −1 than that in 0.75, 1.0, 1.25, and 1.5 μL•L −1 1-MCP-treated beans, respectively.Hong et al. [13] found that 1-MCP treatment inhibited the increase of MDA content in early storage, but the effect was not significant at the latter period of storage, which is similar to the conclusions of this study.However, no effect of 1-MCP treatment on MDA was reported in field-grown cotton [33].

Effect of 1-MCP Treatment on the SOD and POD
Activities.SOD and POD are important enzymes related to fruit and vegetable senescence and defense responses, protecting cells from oxidative damage by scavenging reactive oxygen species [34,35].e SOD activity decreased in the first three days of storage, then increased rapidly, and peaked at day 6 (control and 1-MCP at 1.5 μL•L −1 ), day 9 (1-MCP at 0.75 and 1.25 μL•L −1 ), and day 12 (1-MCP at 1.0 μL•L −1 ).e 1-MCP-treated samples exhibited higher SOD activities than those in the controls after 3 days of storage (Figure 4(a)).POD activity in the control beans increased and peaked at the 6th day and then declined.POD activities in treated beans showed two fluctuation and peaked at the 9th day and 15th day.e treated beans had higher POD activities after 9 days of storage, and POD  Journal of Food Quality activity in 1.0 μL•L −1 1-MCP-treated bean was the highest of all the treatments (Figure 4(b)).e results suggested that 1-MCP treatment could significantly induce SOD and POD activities, and 1-MCP at 1.0 μL•L −1 had the significant effect on improving the activities of SOD and POD. e similar enzyme activities enhanced by 1-MCP were reported in green asparagus [36], Chinese chive scape [30], and eggplant [16].

Conclusion
Positive effects of 1-MCP treatments were reported in this study on physicochemical quality of yardlong bean during cold storage.We demonstrated that the application of 1-MCP suppressed the change in skin color and the decrease in firmness and reduced the increase in weight loss, the degradation in chlorophyll, and Vc content of yardlong beans.In addition, 1-MCP improved activities of antioxidant enzymes, such as SOD and POD, and reduced the accumulation of MDA in yardlong beans.1-MCP at a concentration of 1.0 μL•L −1 proved to be the most suitable concentration of all the treatments.Our results suggest 1-MCP at 1.0 μL•L −1 maintains postharvest quality of yardlong beans and has the potential for commercial application in the future.

Table 1 :
Effects of 1-MCP treatment on weight loss, good fruit, and firmness of yardlong bean during storage at 8 °C.Firmness values are mean ± standard error from three replicates.Photograph showing the effects of 1-MCP treatment on yardlong bean fruit after 21 days of storage at 8 °C.CK 0.75 μL L -1 1.0 μL L -1 1.25 μL L -1