The results showed that treatment of litchi by hot water at 47 oC for 7 min., then dipped in a
oxalic acid solution (pH = 3 for 6 min.), finally packed in MAP bags with the thickness of 30 µm
(incorporated 3-5 % silica additives) and stored at 4 ± 1oC, 90 % humidity can extend the storage
time to 35 days (5 weeks) at the decay incidence < 10 %, the quality of fruit change
insignificantly compared initial state, color pericarp is of stability and low disease index.
This result is the basis for preserving postharvest litchi on a large scale, helping to extend
shelf life, maintaining fruit quality, suitable for the storage and transport over long distances.
Acknowledgement. Authors would like to thank Vietnam Academy of Science and Technology and Bac
Giang Department of Science and Technology for providing financial support to conduct this research
(VAST.NĐP.16/15-16 topic).
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Vietnam Journal of Science and Technology 55 (4) (2017) 411-419
DOI: 10.15625/2525-2518/55/4/8630
1
EFFECT OF MODIFIED ATMOSPHERE PACKAGING (MAP) AND
POSTHARVEST TREATMENTS ON QUALITY OF LITCHI
FRUITS DURING STORAGE
Pham Thi Thu Ha1, *, Nguyen Thi Mien1, Duong Thu Hien2, Nguyen Thanh Tung1,
Nguyen Thi Trang2, Nguyen Thu Huong2
1Institute of Chemistry, VAST, 18 Hoang Quoc Viet, Cau Giay, Hanoi
2Lac Trung Technology and Trading Service Company Limited, 350 Lac Trung, Hai Ba Trung,
Ha Noi
3Natural Science Faculty, Hai Duong College, Lien Hong, Gia Loc, Hai Duong
*Email: haptt6@gmail.com
Received: 19 August 2016; Accepted for publication: 19 April 2017
ABSTRACT
In this article, effect of modified atmosphere packaging (MAP) and different postharvest
treatments on quality of litchi (Litchi chinensis Sonn.) fruit was investigated. Quality indexes of
litchi during cold storage at 4 ± 1 0C were measured in terms of decay, total soluble solids,
titratable acidity, color, anthocyanin content and incidence of microbiological infection. These
indexes were determined at harvest and 7, 14, 21, 28 and 35 days after storage. The results
suggested that after 35 days of storage, the pericarp browning and fruit quality deterioration can
be improved compared to the control by dipping fruit in hot water at 47 0C in 7 min., followed
by oxalic acid solution (pH = 3 in 6 min.) and finally packed in MAP bag (LDPE, thickness of
30 µm incorporated 3 - 5 % silica additive) and stored at 4 ± 1 0C and relative humidity of 90 %.
Keywords: litchi, modified atmosphere packaging, postharvest treatment, storage, fruit quality.
1. INTRODUCTION
Litchi (Litchi chinensis Sonn.) is a tropical to subtropical fruit, highly admired for its
characteristic appealing bright red color, delicious taste, and attractive aroma, were grown in
Luc Ngan district, Bac Giang province of Vietnam. However, the litchi fruits are consumed
mainly in the domestic market, exported partially (5 - 10 %) to the close markets such as
Southeast Asian countries, Australia, etc.[1]. Pericarp browning, desiccation and postharvest
decay have been identified as major problems which greatly reduce its market value around the
globe.
Previous studies have shown that the pericarp browning of the litchi fruit is related to the
oxidation of phenolic compounds by peroxidase (POD) and polyphenol oxidase (PPO),
membrane lipid peroxidation, degradation of anthocyanins, and redox imbalance resulting from
overproduction of reactive oxygen species (ROS) and decreased antioxidant capacity. Therefore,
Pham Thi Thu Ha, et al.
412
the inhibition of these physiological processes could be important for controlling the pericarp
browning and extending the shelf life of harvested litchi fruit. The litchi industry commercially
uses sulphur dioxide (SO2) fumigation to overcome these problems. However, SO2 fumigation
leaves undesirable residues, alters the fruit taste, and results in health hazards for consumers and
pack house workers [2].
Many studies have shown that pericarp color was maintained well by dipping in dilute acid
solution (at low pH). Either treatment with acid solution such as oxalic acid, chlohydric acid,
citric acid, ascorbic acid... or combining acids and chitosan was significantly inhibited PPO
enzyme activity and maintained anthocyanin in pericarp at high level. Among them, treatment
with oxalic acid solution controlled pericarp browning the best due to increasing uniformity of
the cell membrane and inhibiting activity of PPO enzyme during storage. Moreover, oxalic acid
is a natural antioxidant and a metabolic product that is distributed among different organs of
plants, play an important role in the natural and artificial preservation of oxidized materials [3-
5].
In addition, the approaches which inhibit the growth of microorganisms have been
investigated. Using synthesis antifungal incorporated cooling is a highly effective method.
However, if the treatment method, dosage and isolation duration etc. were not controlled strictly,
it could be harmful to humans and the environment. Hot water treatment (by spraying, dipping
or brushing...) not only slow the growth of pathogens but also inhibit the possibility of infection
of fruits. This method can be alternative to sulphur-dioxide fumigation method, applied easily at
commercial scale, not affect human health. Combined with acid treatment obtained more safe
and higher quality litchi fruits [6].
Modified atmosphere packaging (MAP) is the best method for litchi fruit preservation and
storage. The successful use of MAP is based on the specific permeation properties of polymer
films to O2 and CO2 to generate atmospheres that are suitable for the postharvest life of many
horticultural commodities. This technology also provides three advantages: (1) it helps to reduce
browning, (2) to control postharvest diseases and (3) it maintains a high humid environment for
litchi fruit inside the sealed plastic film [5].
In previous studies, the effect of various MAP materials on postharvest quality retention of
litchi has been investigated. The results showed that there are insignificant difference in the
quality litchi between storing in MAP bags produced by the Institute of Chemistry and CE44
bags from Korea after 4 weeks storage. The weight loss of fruits packed in these film was
4.37 % and 4.24 %, respectively. While the incidence of decay of fruits packed in PE (with the
same thickness) is 100 % after 4 weeks storage [7]. The objective of this study was to investigate
various postharvest treatment methods combined with packaging in MAP to reduce incidence of
microbiological infection, extend shelf-life and maintain, improve sensory quality and the
commercial value of litchi fruit.
2. MATERIALS AND METHODS
2.1. Materials
- Litchi (Litchi chinensis Sonn.) fruits which were harvested in Quy Son commune, Luc
Ngan district, Bac Giang province, reached harvest maturity 2 (80 - 85 days after full bloom). In
the study, chlohydric acid, citric acid, oxalic acid, standard sodium hydroxide solution,
phenolphthalein (China). Modified atmosphere packaging (MAP) bags, the commercial product
with GreenMAP trademark, was manufactured in Institute of Chemistry, Vietnam Academy of
Effect of modified atmosphere packaging (MAP) and postharvest treatments.....
413
Science and Technology from polyethylene incorperated 3 - 5 % silica additive. The thickness of
the bags was 30 µm (size 25 cm × 30 cm).
2.2. Postharvest treatment
Litchi fruits were harvested, subjected to preliminary hydro-cooling (0 oC) by keeping in
insulated container containing ice and transported to laboratory within 4 - 6 h. Fruits of uniform
size with the length of stalk 2 - 3 mm, free off physical damage, injury caused by insects and
fungal infection were selected. The experiment samples were listed as follows:
(CT1) - Control, fruits were untreated
(CT2) - Fruits were dipped in hot water at 47 oC for 7 minutes
(CT3) - After treating with hot water, fruits were dipped in hydrochloric acid solution
(CT4) - After treating with hot water, fruits were dipped in citric acid solution
(CT5) - After treating with hot water, fruits were dipped in oxalic acid solution
For applying hot water treatment, the fruits were dipped in hot water kept at 47 oC for 7
min., air dried (18 – 20 oC). For applying hot water treatment and different acids, hot water
treated fruits were dipped in pH 3 acid solutions for 6 min., air dried (18 – 20 oC). The air dried
fruits were distributed into groups of 2 kg and then placed inside the MAP bags, kept for
observations under cold storage conditions (4 ± 1 oC). Each experiment had three replicates.
Fruits from each replication were taken for determine changes of terms of decay, total soluble
solids, titratable acidity, color, anthocyanin content and incidence of microbiological infection
after 7, 14, 21, 28, 35 days of storage and the end result was the average value.
2.3. Methods
2.3.1. Decay
Decay was defined as the ratio of decayed fruit weight (fruits were caused of fungi,
pericarp browning, physical damage) and initial fruit weight.
2.3.2. Total soluble solids content
Total soluble solids content is determined according to TCVN 7771:2007 standard using a
digital refractometer (PR-101 Atago, Japan).
2.3.3. Titratable acidity content
Total acidity content is determined according to TCVN 5483-91 standard using the
automated voltage titration device Titrino 702SM, Metrohm (Switzerland).
2.3.4. Color
Color of the whole litchi fruit was measured by a ColorTec 5974-01 Colorimeter (Mexico)
and the results were expressed as L, a, b (Hunter value). The “L” scale ranges from no reflection,
i.e., black (L = 0) to perfect diffuse reflection, i.e., white (L = 100). The “a” scale ranges from
negative values for green (-60) to positive values for red (+60), and the “b” scale ranges from
negative values for blue (-60) to positive values for yellow (+60).
∆E color index indicates the level difference in the pericarp color of stored fruits and the
pericarp color of initial fruits, ∆E = .
Pham Thi Thu Ha, et al.
414
2.3.5. Anthocyanin content
Anthocyanin content was determined by differential pH method (AOAC Official Method
2005.02).
2.3.6. Incidence of microbiological infection
Incidence of microbiological infection index was assessed by using the scale (Table I). The
method outlined by Khan et al. [8] was used to determine this index.
Table 1. Scales used for incidence of microbiological infection index.
Scale Incidence of microbiological infection
1 no fruit infected
2 0 - 5 % infected fruits
3 5 - 10 % infected fruits
4 10 - 25 % infected fruits
5 25 - 50% of infected fruits
6 50 % of infected fruits
3. RESULTS AND DISCUSSION
3.1. Decay
Table 2. Effect of treatments on the decay (%).
Weeks
Samples
1 2 3 4 5
CT1 3.21 ± 0.17 5.14 ± 0.81 8.75 ± 0.25 12.61 ± 1.12 17.52 ± 1.24
CT2 2.91 ± 1.08 3.76 ± 0.55 4.62 ± 0.31 6.32 ± 0.93 9.73 ± 1.34
CT3 4.75 ± 0.72 5.62 ± 0.47 6.48 ± 0.19 8.21 ± 1.05 11.66 ± 0.98
CT4 0.00 0.00 4.05 ± 0.52 6.28 ± 0.37 8.32 ± 2.31
CT5 0.00 0.00 3.63 ± 0.36 5.62 ± 0.22 7.45 ± 1.34
Decay is an important indicator to determine if the preservation methods is successful.
Results are presented in Table 2.
The results showed that the pretreatment methods before storage significantly reduces the
rate of deterioration compared with using only modified atmosphere packing (MAP). However,
there is a difference about the effectiveness of each method for pretreatment process.
Actual observations showed that the hot water treatment is able to limit the development of
pathogenic mold, fungi and microorganisms on pericarp, but it didn’t limit the pericarp
browning. Process should be a certain percentage of fruit damaged by pericarp browning. Litchi
fruits being treated with hydrochloric acid solution are nice red. However, because the litchi is
fruit wood pericarp, easily subjected to strong acids leading to softening of shells and there are
many cracks which lost market value since the first weeks of storage. Meanwhile, the structure
Effect of modified atmosphere packaging (MAP) and postharvest treatments.....
415
of pericarp of litchi fruits which were pre-treated with a solution of citric acid and oxalic acid
did not change. In addition, they still showed good performance, i.e. valuable hardness and
relatively good sense.
3.2. Total soluble solids
Total soluble solids (TSS) is one of the important indicators to determine the quality during
storage of litchi. The change of TSS in the preservation process is shown in Figure 1.
Figure 1. Effect of the treatment methods on the total soluble solids content.
The total soluble solids content trends to decrease during storage, due to these substances
are still taking part in the process of metabolism to maintain the life of the fruit. However, the
TSS content went down insignificantly and there wasn’t the difference between the samples
treated with different agents. After 3 weeks storage, the rate of change of TSS content in most of
the samples tends to be significantly increased. After 5 weeks of storage, the TSS content in CT5
least reduced (approximately 94 % compared the initial value) and decreased the most in CT1
(about 79 % from the initial state).
3.3. Titratable acid
The goal of preservation is to reduce to a minimum the loss of organic acid content in the
litchi to maintain the sensory value of the fruit. Results of studying the total acid content in the
preservation process is shown in Figure 2.
Figure 2. Effect of the treatment methods on the change of titratable acid content.
Pham Thi Thu Ha, et al.
416
In the process of preserving, the total acid content tends to decrease, which proved partly
flesh had been transformed. However, after the first 2 weeks of storage, the difference of the
total acid content in the samples is negligible. The total acid content in the fruit treated with acid
solution remain around 88 % - 90 % from the initial value after 5 weeks of storage. This result is
consistent with the report by Khan et al. [8] studying the preserving litchi on the cool condition.
3.4. Color
For litchi, the color is the first criterium of evaluation affecting the purchase decisions of
consumers. In the process of preserving, the litchi fruit pericarp tended to be browning that leads
to their commercial viability to be a serious decline. The results of the effects of treatment
methods to change the color of the pericarp is presented in Table 3.
Table 3. Effect of treatment methods on the color change of pericarp (∆E).
Weeks
Samples
0 1 2 3 4 5
CT1 0 2.81 ± 0.16 5.31 ± 0.09 8.25 ± 0.27 11.90 ± 0.37 16.18 ± 0.54
CT2 0 2.71 ± 0.24 5.42 ± 0.15 7.90 ± 0.51 10.38 ± 043 15.34 ± 0.31
CT3 0 2.38 ± 0.11 4.56 ± 0.20 6.89 ± 0.23 9.02 ± 0.64 13.27 ± 0.16
CT4 0 1.95 ± 0.18 3.89 ± 0.36 5.72 ± 0.34 8.13 ± 0.31 11.16 ± 0.41
CT5 0 1.01 ± 0.21 2.01 ± 0.13 3.84 ± 0.07 5.67 ± 0.15 9.33 ± 0.32
During the storage period, the pericarp browning increased with increasing period of
storage because PPO enzyme decaying the anthocyanins, thus forming brown-color by-products.
The higher value of ∆E, the higher the color change.
The results showed that the ∆E index tends to increase in all the samples in the preservation
process. After 5 weeks of storage, the ∆E indexes of the samples which were treated with
organic acid solution were lowest. This result proves the effect of the treatment process with
acid in the maintenance of pericarp color due to the activity of the PPO enzyme was inhibited at
low pH levels, so the color change of the litchi fruit occurs more slowly. In addition, the red
color of the samples treated with hydrochloric acid solution remain good, but because of the
influence of microorganisms, the brightness of pericarp was not maintained such as the fruits
which were dipped with citric and oxalic acid solution.
3.5. Anthocyanin content
The pericarp browning phenomenon of litchi occurs mainly due to the oxidation of
anthocyanin compounds forming brown products under the effect of the PPO enzyme, O2 and
H2O2 which is produced when vitamin C is decomposed. The analytical results of the
anthocyanin content in pericarp during storage is shown in Figure 3.
Effect of modified atmosphere packaging (MAP) and postharvest treatments.....
417
Figure 3. The effect of treatment methods on the anthocyanin content.
It can be seen that the anthocyanin content decreases during the storage period, especially
CT1, CT2 and CT4. The reduction of the anthocyanin content in CT3 and CT5 is not significant
and this value is maintained at a high level after 5 weeks of preservation. Oxalic acid is oxidized
easily by H2O2, this process competes with the oxidation reaction of anthocyanin. So it helps the
red color of pericarp remain for more long time than the fruits treated with citric acid solution.
3.6. Incidence of microbiological infection
The diseases caused by microorganisms is a major cause of reduced the storage period and
commercial value of litchi. The results of studying the growth of diseases caused by
microorganisms during storage are shown in Table 4.
Table 4. The effect of the treatment methods in the development of diseases caused by microorganisms.
Weeks
Samples
0 1 2 3 4 5
CT1 1.0 2.0 2.5 3.0 3.5 4.0
CT2 1.0 1.0 1.0 2.0 2.0 2.5
CT3 1.0 2.0 3.0 3.5 4.0 4.5
CT4 1.0 1.0 1.0 1.5 2.0 2.0
CT5 1.0 1.0 1.0 1.0 2.0 2.0
The results showed that after 2 weeks of storage, the disease indicators in CT2, CT4 and
CT5 are similar when harvested fruit. After 5 weeks of storage, the disease indicators in CT4
and CT5 increased up only 2 points (corresponding to < 5 % of the pericarp is infected). The
sample treated with hydrochloric acid solution (CT3) have signs of cracking, so microorganisms
can penetrate easily, causing increased the amount of infected fruits.
4. CONCLUSIONS
The results showed that treatment of litchi by hot water at 47 oC for 7 min., then dipped in a
oxalic acid solution (pH = 3 for 6 min.), finally packed in MAP bags with the thickness of 30 µm
(incorporated 3-5 % silica additives) and stored at 4 ± 1oC, 90 % humidity can extend the storage
time to 35 days (5 weeks) at the decay incidence < 10 %, the quality of fruit change
insignificantly compared initial state, color pericarp is of stability and low disease index.
Pham Thi Thu Ha, et al.
418
This result is the basis for preserving postharvest litchi on a large scale, helping to extend
shelf life, maintaining fruit quality, suitable for the storage and transport over long distances.
Acknowledgement. Authors would like to thank Vietnam Academy of Science and Technology and Bac
Giang Department of Science and Technology for providing financial support to conduct this research
(VAST.NĐP.16/15-16 topic).
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