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

Authors: Zitao Jiang; Jiaoke Zeng; Yunke Zheng; Hong Tang; Wen Li
Journal: Journal of Food Quality
 (2018)

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## Abstract

The yardlong bean belongs to nonclimacteric fruit. The objective of this study was to investigate the effects of 1-methylcyclopropene (1-MCP) treatment on physicochemical characteristics of yardlong beans during cold storage. Freshly harvested yardlong beans were treated with different concentrations of 1-MCP (0, 0.75, 1.0, 1.25, and 1.5μL ·L−1) and stored at 8°C for 21 days. The results showed that, compared with the control, the decrease in firmness 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 significantly by 1-MCP treatments. Of the different concentrations of 1-MCP, 1.0 μL·L−1 proved to have the best preservative effects, extending storage time and delaying ripening and senescence of yardlong beans. These results indicated that 1-MCP treatment provided an effective method for delaying the postharvest senescence of fresh yardlong beans.


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## Body

## 1. Introduction

The 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 [1–3]. The yardlong bean, which is a crisp and tender legume, is a good source of proteins, dietary fibers, 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 influence 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 effects on postharvest fruits and vegetables such as increased respiration rate and ethylene production, accelerated softening, senescence, color change, starch breakdown, and other physiological disorders [8–10]. 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].Previous studies reported that 1-MCP has positive effects on delaying ripening and senescence of climacteric fruits and vegetables, such as guava [13], pear [9], plum [10], and tomato [14]. However, it has been found that 1-MCP may also show significant preservation effects on inhibition of senescence, physiological disorders development, degreening, and color change in some nonclimacteric fruit and vegetables [15], e.g., eggplant [16], jujube [17], broccoli [18], and pitaya [15].Yardlong bean belongs to the nonclimacteric group [19]. The preservation methods of yardlong bean mainly focused on modified storage atmosphere, coating, hot water treatment, chemical treatment, etc. [6, 20]. Influence of 1-MCP on physicochemical attributes is rarely studied. Therefore, the aim of the present study is to investigate the effects of different concentrations of 1-MCP on physicochemical characteristics, including skin color, firmness, weight loss, and content of Vc and MDA, and the effects on activities of SOD and POD were investigated too.


## 2. Materials and Methods

### 2.1. 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), 0.75μL·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. The 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. Three replicates of fifteen pods were sampled at every third day to determine physicochemical characteristics.


### 2.2. 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]. The 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). The measurement was conducted with the penetration depth of 10 mm, and five equally position of single side were performed. Three replicates with three pods were performed, and the results were expressed in Newton (N).


### 2.3. Determination of Color and Chlorophyll Content

Pod color parameters ofL∗, 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. The mixture was left to stand for about 3–5 min. The homogenate was then filtered into 50 mL brown volumetric flasks through filter paper. The mortar, pestle, and the residue were rinsed several times with 80% acetone until the filter paper and residue showed no green coloration. The filtrate was diluted with 80% acetone to a final volume of 25 mL. The 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.


### 2.4. Determination of Vc Content

The 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. The solution was slightly red in color and not fading in 30 s. The amount of the solution was measured.


### 2.5. Determination of MDA Content

The 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. The homogenate was centrifuged at 12,000 g for 20 min at 4°C. Then 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). The reaction mixture (5 mL) contained 50 mM sodium phosphate buffer (pH 7.8), 130 mM methionine, 750 μM nitroblue tetrazolium (NBT), 100 μM EDTA-Na2, 20 μM riboflavin, and 0.1 mL enzyme extract. The 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.


### 2.7. 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 (1 mmol PEG, 4% PVPP and 1% Triton X-100). The homogenates were centrifuged at 12,000 g for 30 min at 4°C. The 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% H2O2; 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.


### 2.8. 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.


## 2.1. 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), 0.75μL·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. The 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. Three replicates of fifteen pods were sampled at every third day to determine physicochemical characteristics.


## 2.2. 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]. The 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). The measurement was conducted with the penetration depth of 10 mm, and five equally position of single side were performed. Three replicates with three pods were performed, and the results were expressed in Newton (N).


## 2.3. Determination of Color and Chlorophyll Content

Pod color parameters ofL∗, 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. The mixture was left to stand for about 3–5 min. The homogenate was then filtered into 50 mL brown volumetric flasks through filter paper. The mortar, pestle, and the residue were rinsed several times with 80% acetone until the filter paper and residue showed no green coloration. The filtrate was diluted with 80% acetone to a final volume of 25 mL. The 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.


## 2.4. Determination of Vc Content

The 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. The solution was slightly red in color and not fading in 30 s. The amount of the solution was measured.


## 2.5. Determination of MDA Content

The 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. The homogenate was centrifuged at 12,000 g for 20 min at 4°C. Then 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). The reaction mixture (5 mL) contained 50 mM sodium phosphate buffer (pH 7.8), 130 mM methionine, 750 μM nitroblue tetrazolium (NBT), 100 μM EDTA-Na2, 20 μM riboflavin, and 0.1 mL enzyme extract. The 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.


## 2.7. 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 (1 mmol PEG, 4% PVPP and 1% Triton X-100). The homogenates were centrifuged at 12,000 g for 30 min at 4°C. The 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% H2O2; 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.


## 2.8. 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.


## 3. Results and Discussion

### 3.1. 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 Table1, 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). Thus, 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.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.
1-MCP treatments
Weight loss (%)
Good fruit (%)
Firmness (N)
3 d
21 d
3 d
21 d
3 d
21 d
Control
1.9aZ
26.0a
75.0d
32.0
7.2 ± 0.001e
3.3 ± 0.004e
0.75μL·L−1
1.6b
17.1d
90.0a
47.0b
7.3 ± 0.05d
4.0 ± 0.014b
1.0μL·L−1
0.8c
16.7e
89.0b
51.0a
7.4 ± 0.015c
4.2 ± 0.001a
1.25μL·L−1
0.9c
18.3c
80.0c
43.0c
7.5 ± 0.016b
3.8 ± 0.007c
1.5μL·L−1
1.6b
22.6b
80.0c
36.0d
7.6 ± 0.001a
3.5 ± 0.014d
ZMean values (weight loss; good fruit n = 30; firmness n = 9; ±SE) in each column followed by different lower case letters are significantly different at P≤0.05 using Tukeys HSD.


### 3.2. 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). These 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].Figure 1
Effects of 1-MCP treatment onL∗ (a), a∗ (b), b∗ (c) values, and chlorophyll content (d) of yardlong bean during storage at 8°C. Each data point is the average of nine pods. Error bars represent the standard error of the means. Control (✲), 0.75 μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).
(a)
(b)
(c)
(d)


### 3.3. 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 (Figure2). 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. Thus, 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. This 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].Figure 2
Effects of 1-MCP on Vc content of yardlong bean fruit during storage at 8°C. Error bars represent standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).


### 3.4. 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 progressively, with a lower level of 1-MCP-treated pods than in the control after 21 days storage (Figure3). 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].Figure 3
Effects of 1-MCP treatment on MDA content of yardlong bean during storage at 8°C. Each data point is the average of nine fruits. Error bars represent the standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).


### 3.5. 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]. The 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). The 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. The treated beans had higher POD activities after 9 days of storage, and POD activity in 1.0 μL·L−1 1-MCP-treated bean was the highest of all the treatments (Figure 4(b)). The 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. The similar enzyme activities enhanced by 1-MCP were reported in green asparagus [36], Chinese chive scape [30], and eggplant [16].Figure 4
Effects of 1-MCP treatment on SOD (a) and POD (b) activities of yardlong bean during storage at 8°C. Each data point is the average of nine fruits. Error bars represent the standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).
(a)
(b)


## 3.1. 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 Table1, 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). Thus, 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.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.
1-MCP treatments
Weight loss (%)
Good fruit (%)
Firmness (N)
3 d
21 d
3 d
21 d
3 d
21 d
Control
1.9aZ
26.0a
75.0d
32.0
7.2 ± 0.001e
3.3 ± 0.004e
0.75μL·L−1
1.6b
17.1d
90.0a
47.0b
7.3 ± 0.05d
4.0 ± 0.014b
1.0μL·L−1
0.8c
16.7e
89.0b
51.0a
7.4 ± 0.015c
4.2 ± 0.001a
1.25μL·L−1
0.9c
18.3c
80.0c
43.0c
7.5 ± 0.016b
3.8 ± 0.007c
1.5μL·L−1
1.6b
22.6b
80.0c
36.0d
7.6 ± 0.001a
3.5 ± 0.014d
ZMean values (weight loss; good fruit n = 30; firmness n = 9; ±SE) in each column followed by different lower case letters are significantly different at P≤0.05 using Tukeys HSD.


## 3.2. 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). These 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].Figure 1
Effects of 1-MCP treatment onL∗ (a), a∗ (b), b∗ (c) values, and chlorophyll content (d) of yardlong bean during storage at 8°C. Each data point is the average of nine pods. Error bars represent the standard error of the means. Control (✲), 0.75 μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).
(a)
(b)
(c)
(d)


## 3.3. 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 (Figure2). 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. Thus, 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. This 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].Figure 2
Effects of 1-MCP on Vc content of yardlong bean fruit during storage at 8°C. Error bars represent standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).


## 3.4. 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 progressively, with a lower level of 1-MCP-treated pods than in the control after 21 days storage (Figure3). 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].Figure 3
Effects of 1-MCP treatment on MDA content of yardlong bean during storage at 8°C. Each data point is the average of nine fruits. Error bars represent the standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).


## 3.5. 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]. The 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). The 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. The treated beans had higher POD activities after 9 days of storage, and POD activity in 1.0 μL·L−1 1-MCP-treated bean was the highest of all the treatments (Figure 4(b)). The 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. The similar enzyme activities enhanced by 1-MCP were reported in green asparagus [36], Chinese chive scape [30], and eggplant [16].Figure 4
Effects of 1-MCP treatment on SOD (a) and POD (b) activities of yardlong bean during storage at 8°C. Each data point is the average of nine fruits. Error bars represent the standard error of the means. Control (✲), 0.75μL·L−1 (■), 1.0 μL·L−1 (•), 1.25 μL·L−1 (◆), and 1.5 μL·L−1 (▲).
(a)
(b)


## 4. 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 1.0μL·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.



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*Source: 7267164-2018-09-09.xml*