Modified Atmosphere Storage Extends the Shelf Life of ‘Nam Dok Mai Sri Tong’ Mango Fruit

ABSTRACT

Investigation of modified atmosphere packaging (MAP) on changes of fruit quality during cold storage and shelf life extension in mango was conducted with MAP using white ethylene absorbing bag (WEB) and green absorbing bag during storage at 15°C for 30 days. The results found that the mangoes kept in WEB maintained their texture and appearance better than those in package without a plastic bag. Mangoes stored in WEB were more firm than those stored in air (normal atmosphere) during 30 days of storage and could delay the ripening and maintained the quality of the fruits, while the fruit packed without plastic bags extended the shelf life for 24 days. The MAP retarded the ripening process and delayed color development of the mango fruit compared to the mangoes without packing during the cold storage. In particular, WEB effectively reduced respiration rate and weight loss of the fruits stored at 15°C for 30 days. This MAP maintained a higher titratable acidity and firmness of peel and pulp in the mango fruits, while the activities of polygalacturonases in the pulp were reduced. Comprehensive quality analysis indicated that this MAP was the most effective method for improving the quality of mango fruits and extension of shelf life under the cold storage.

KEYWORDS:

• Storage-life extension
• modified atmosphere storage
• pectin methyl esterase
• packaging
• polygalacturonases
• respiration rate

Introduction

Mango (Mangifera indica L.) fruit cv. Nam Dok Mai Sri Tong is one of the leading export products of Thailand. Unlike other mango cultivars, Nam Dok Mai Sri Tong is difficult to handle the fruit because of the thinner skin, and shorter storage life in the normal atmosphere. Modified atmosphere storage has been widely used to increase the shelf life of fruits with incorporation of refrigerating temperature to maintain the food safety and extend the shelf life of climacteric fruit (Oliveira et al., 2015; Werner and Hotchkiss, 2006; Yan and David, 2013). The modification of carbon dioxide and oxygen concentration in the surroundings of products can control the rate of respiration, the activity of enzymes, and the occurrence of oxidation (Rocha et al., 2004). Moreover, the modified atmosphere packaging (MAP) can delay the ripening of the fruit. Therefore, this research aimed to evaluate the influence of modified atmosphere storage using white ethylene absorbing bag (WEB) on the quality of Nam Dok Mai Sri Tong during cold storage.

Material and Methods

Source of Mango Fruits

The mature mango (Mangifera indica L.) fruits of cv. Nam Dok Mai Sri Tong were harvested at 110 days after anthesis from a commercial orchard in Phitsanulok Province of Thailand and transported to the laboratory of Agricultural Science department faculty of Agriculture, Natural resource and environment, Naresuan University, Phitsanulok. The mango fruits were selected with careful attention for size uniformity (350–400 g per fruit) and dipped into 500 mg L⁻¹ of Azoxystrobin (a.i 25% W/V) for fungal prevention.

Preparation of Modified Atmosphere Packaging and Cold Storage Condition

The mango fruits were stored under three packaging conditions: (1) control, (2) plastic 1 – commercially bags (green absorbing bag; GEB), and (3) plastic 2 – polypropylene (WEB). WEB was manufactured from proprietary blends of polymeric materials with specifications of 47 µm thickness, oxygen permeability (O₂P) = 3895.95 cc⁻¹m²d, water permeability (H₂OP) = 8.58 g⁻¹m²d and overall bag dimensions of 20 × 38 cm. All fruits were kept in low-temperature incubators at 15°C with relative humidity at 90–95% for 30 days and physicochemical properties of the fruit were determined every 3 days. Each storage treatment was conducted for 6 replications (one replication per three fruits).

Fruit Quality Evaluation and Statistical Analysis

Fruit color (peel and pulp) was measured with a colorimeter (Minolta Model DR-20; Konica Minolta Sensing Americas, Inc; USA). The measurement area of ø8 mm, a 10o standard observer angle and a D65 Illuminant. CIE L*a*b* values were determined for each sample. The L*value is a measure of the lightness, the a* value of the greenness-redness and the b* value of the blueness-yellowness of a sample.(Carolien et al., 2018) Firmness was evaluated using a texture analyzer machine (QTS 25, Book field; USA), as the maximum force (N) to the lateral radial surface of the mango. The firmness of peel and pulp, each fruit was measured twice in the equatorial region, on opposite sides, after the skin was removed; the results were expressed in Newtons (N). The weight was calculated with the following equation:

$\mathrm{W}\mathrm{L}=\frac{\left({\mathrm{W}}_{\mathrm{i}}-{\mathrm{W}}_{\mathrm{f}}\right)}{{\mathrm{W}}_{\mathrm{i}}}\times 10$

where WL is the weight loss (%), W_i is the initial weight (g), and W_f is the weight at each storage time (g) (Ochoa-Velasco and Guerrero-Beltrán, 2016). Soluble solid content (SSC) was determined in the juice by using a digital refractometer (PAL-1, Atago, Japan) and expressed as %Brix. The titratable acidity (TA) was expressed as the percentage of citric acid content, g/100 g fresh weight. Respiration rate was estimated according to Park and Lee (2008). Enzyme extraction was carried out following the method of Ahmed and Labavitch (1980) with some modification. The pectin methyl esterase (PME) enzyme activity in pulp was measured using the method of Nagel and Patterson (1967) with slight modification. The polygalacturonases (PG) enzyme activity in pulp was measured using the method of Nelson (1944) with slight modification. Protein content was determined according to the method of Bradford (1976). To test significant difference among the mean of treatments, Generalized Linear Models were applied using SPSS 17.0. Significant differences between treatments were tested by Duncan’s Multiple Range Test at P≤ 0.05 and considered to be a statistically significant difference at 95%.

Results

Color of Peel and Pulp

Mango fruits stored in the air exhibited the highest color changes (a* and b* of peel and pulp). Those fruit color of in the WEB and GEB packaging had similar changes of peel color. L* of peel values all decreased following the application of MAP treatments. Significant differences of color differed were found between packaging and storage condition (P ≤ 0.05) (Figures 1, 2).

Figure 1. Color change of peel a* (A), b* (B), and L* (C) of mango cv.Nam Dok Mai Sri Tong after 30 days of storage at 15°C and 95% RH. The experimental data are represented by the different symbols.

Figure 2. Color change of pulp a* (A) and b* (B) of mango cv.Nam Dok Mai Sri Tong after 30 days of storage at 15°C and 95% RH. The experimental data are represented by the different symbols.

Firmness of Peel and Pulp

Firmness of peel decreased over the storage period. Fruit packed in the WEB plastic bag retained the firmness of the peel and pulp throughout the duration of storage time. In contrast, the mango fruit packed in the GEB plastic bag and non-packed (control) had similar pulp firmness throughout the storage except over the last days of storage and the pulp firmness of the fruit GEB was significantly lower than that in WEB (Table 1).

Table 1. Effect of modified atmosphere storage on firmness (N) of peel and pulp of ‘Nam Dok Mai Sri Tong’ mango fruit during cold storage

Storage period (Days)	Treatments
	Control (no bag)	WEB	GEB
	Firmness (N) of peel
0	2.93 a^1	2.93 a	2.93 a
6	1.80 a	2.81 a	1.96 a
12	0.97 b	2.50 a	0.91 b
18	0.22 b	2.13 a	0.78 b
24	0.06 b	0.95 a	0.09 b
30		0.77 a	0.06 b
	Firmness (N) of pulp
0	2.93 a^1	2.93 a	2.93 a
6	1.80 a	2.81 a	1.96 a
12	0.97 b	2.50 a	0.91 b
18	0.22 b	2.13 a	0.78 b
24	0.06 b	0.95 a	0.09 b
30		0.77 a	0.06 b

¹The values within a row with different letters super scripted are significantly different at p ≥ 0.05% according to the Duncan’s multiple range test. WEB = white ethylene absorbing bag. GEB = green ethylene absorbing bag.

Weight Loss

Weight loss increased during the storage of all MAP and control. In the control, the weight loss increased from 0.00% to 15.75% after 24 days of storage at 15°C while in plastic bag GEB and WEB were found around 5.50 and 3.55%, respectively at the end of the same storage time. The weight loss of the fruit rapidly increased during 30 days of storage time at 15 °C for all packaging (Figure 3).

Figure 3. Weight loss (%) and respiration rates (mg CO₂kg⁻¹h⁻¹) of mango cv.Nam Dok Mai Sri Tong after 30 days of storage at 15°C and 95% RH. Treatment are control (○), white ethylene absorbing bag (WEB) (□), green ethylene absorbing bag (GEB) (∆). Vertical bars represent the standard deviation.

TA, SSC, and Total Soluble Solids to Titratable Acidity Ratio (TSS/TA)

TA decreases after 12 days of storage in all MAP and control (Table 3) and continued to decline during 30 days of storage. Fruit storage in WEB tended to be higher TA than that in the fruit of other MAP and control. The SSC value of mango stored in MAP were stable around 8.2 that the SSC value was continually increased during storage time (Table 3). The mango stored in WEB had lower SSC than that in the fruits stored in air after 30 days. At the end of storage time, the SSC was evolved from the initial 8.20% to 12.70% (WEB) (Table 3). The SS/TA of mango fruits increased gradually during storage corresponding to the decrease of TA in all MAP, and the significant differences of TA, SSC, and ratio SS/TA of mango stored in normal atmosphere and MAP were found after 30 days at 15°C (P ≤ 0.05) (Table 3).

Table 2. Effect of modified atmosphere storage on PME activity and PG activity (units.mg protein⁻¹) of ‘Nam Dok Mai Sri Tong’ mango fruit during cold storage.

Storage period (Days)	Treatments
	Control (no bag)	WEB	GEB
	PME activity (units.mg protein^−1)
0	75.67 a^1	75.67 a	75.67 a
6	68.76 b	71.95 a	66.16 c
12	56.72 b	69.32 a	64.03 a
18	43.10 b	64.62 a	60.94 ab
24	35.60 c	60.92 a	53.62 b
30		45.95 a	41.64 b
	PG activity (units.mg protein^−1)
0	5.67 a1	5.67 a	5.67 a
6	10.25 a	9.99 a	10.06 a
12	11.88 a	11.08 b	10.75 b
18	13.24 a	11.79 b	11.22 b
24	14.50 a	12.42 b	12.18 b
30		13.90 a	13.18 b

¹The values within a row with different letters super scripted are significantly different at p ≥ 0.05% according to the Duncan’s multiple range test. WEB = white ethylene absorbing bag. GEB = green ethylene absorbing bag.

Table 3. Effect of modified atmosphere storage on soluble solid concentration (%), titratable acidity (%) and SSC/TA of ‘Nam Dok Mai Sri Tong’ mango fruit during cold storage.

Storage period (days)	Treatments
	Control (no bag)	WEB	GEB
	Soluble solid concentration, SSC (%)
0	8.20 a^a^1	8.20 a	8.20 a
6	9.90 a	8.80 b	8.47 b
12	13.57 a	10.40 c	11.00 b
18	14.73 a	10.57 c	12.30 b
24	16.13 a	10.97 c	13.87 b
30		12.07 b	14.10 a
	Titratable acidity, TA (%)
0	2.71 a	2.71 a	2.71 a
6	2.29 a	2.23 a	2.37 a
12	1.67 b	2.05 a	1.72 b
18	0.98 c	2.00 a	1.69 b
24	0.38 c	1.94 a	1.57 b
30		1.60 a	1.38 b
	SSC/TA
0	0.39 a	0.39 a	0.39 a
6	4.35 a	3.45 b	3.57 b
12	8.11 a	5.07 c	6.58 b
18	16.54 a	5.44 c	7.26 b
24	41.02 a	5.87 b	8.18 b
30		7.31 b	11.00 a

¹The values within a row with different letters are significantly different at P ≥ 0.05% according to Duncan’s Multiple Range Test. WEB = white ethylene absorbing bag. GEB = green ethylene absorbing bag.

Respiration Rate

Respiration rate of mango fruits packed in plastic bag GEB and WEB increased slowly during the storage period, but the mangoes in non-packing of plastic bag had higher respiration rates. The mango packed in plastic bag of WEB had the lowest respiration rate at 150.23 mg CO₂kg⁻¹h⁻¹ after 30 days at 15°C, with statistical significant difference compared to other packaging and storage treatments (P ≤ 0.05) (Figure 3).

Enzyme Activity of PME and PG

Fruits packed in the WEB plastic bag showed considerable delay reduction in the activity of PME compared with the product in GEB bag and control. The control mango had the highest loss in PME enzyme activity throughout the storage time. For the GEB, the PG activity decreased from 75.67 to 47.47 units/mg activity/protein over the storage time increasing from 0 days to 27 days at 15°C. This PG enzyme activity value was decreasing by 37.34% in the PG activity after 27 days. In all packaging, the PG enzyme activity increased with increasing of storage time. Fruits stored in the air had the highest increase in PG enzyme activity. However, fruits packed in both WEB and GEB bags were significantly difference (P ≤ 0.05) with slower increase in PG activity than that in the control (Table 2).

Discussion

Fruits packed in WEB plastic bags maintained lower color changes (a* and b* of peel and pulp) compared to other treatments. This result is likely to be similar to that found by Rocha et al. (2004) who found that apples kept in the modified atmosphere can reduce weight loss and change color more than when kept under normal air-storage condition. Nurten and Mustafa (2014) reported that pomegranate fruits stored in MAP had a higher L*, C*, and lower H° values than in other treatments. MAP could delay the loss of firmness in both peel and pulp compared to control fruits. Retention of fruit firmness can be attributed to high humidity and mango fruits stored in WEB had minimal weight loss (Jessica and Juan, 2016). The suitable WEB plastic bag suitable for prolonging the shelf life of mango is better than plastic bags GEB. Because, it more was effectiveness of reducing respiration rate and ethylene production on the fruit (Lange and Kader, 1997; Okan et al., 2016; Sivakumar et al., 2012).

The SSC of the mango were increased in all MAP during cold storage at 15°C after 6 days. Ghafir et al. (2010) reported that pomegranate fruits had significant increase in SSC during storage. Mango fruits packed in plastic bags WEB tend to have less soluble solids than in other MAP treatments. The modified atmosphere combined with hot water treatment slowed down the changes in TSS and delayed ripening (Akbudak et al., 2007). MAP and low temperature may delay and retard ripening (Zainon et al., 2004). TA of the control and MAP treatments rapidly decrease from 3 days of storage life while mangoes stored in the plastic bags WEB was decreased less than all treatments during storage. Titratable acidity of the control and GEB treatments rapidly decrease from 12 days of storage life while mangoes stored in the plastic bags WEB was decreased less than all treatments.

Mango fruits packed in white ethylene absorbing bag (WEB) affect the quality of fruit being better than other treatments. Modified atmosphere treatment could decrease the respiration rate and ethylene production rate while MAP could reduce weight loss, lycopene biosynthesis, and the formation of red color (Fagundes et al., 2015). The atmosphere generated by MAP has been shown previously to delay the ripening of certain subtropical and tropical fruits, including mango (Kader, 1994).

The plastic bags WEB and GEB under cold storage were the effective methods for inhibiting PG activity in comparison with control. The physiological maturity in tree-ripe mango fruit was reported to be associated with a decrease in PME activity (Mitra and Baldwin, 1997). Chin et al. (1999) presented the collective significance of these wall-modifying enzymes for softening of the carambola fruit during storage and ripening. MAP-stored nectarines showed significantly reduced rate of chilling injury  (CI) and polyphenol oxidase, PG and PME activities as well as lower hue angles (H°) and TSS contents. The PME activity of fruits significantly increased depending on the storage time and the increase was at lower rate in MAP treatments, compared to control.

Conclusion

The present investigation showed senescence inhibition for mango cv. Nam Dok Mai Sri Tong packaged in the WEB and kept at 15°C. The MAP treatment was potential to reduce respiration rate, weight loss, firmness of peel and pulp, and the activities of pectin methyl esterase (PME) and polygalacturonase (PG). Although, the MAP storages effectively reduce softening and inhibit of the soluble solids content and SSC/TA ratio, these results suggest that a combination of MAP and low temperature resulted in better mango quality and extended their postharvest life up to 30 days at 15°C.

Acknowledgments

We extend our thanks to the Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) Ph.D. Program for financial support, as well as the Center of Excellence Research in Postharvest Technology, Naresuan University, and the Postharvest Technology Innovation Center, Commission of Higher Education, for granting the use of scientific instruments.

Additional information

Funding

This work was supported by Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) Ph.D. Programme through the Thailand Research Fund (TRF) for financial support.