Mango is an economically important fruit crop but with a very short shelf life of about 4–9 days in ambient and between 2 and 3 weeks in cold storage. Extending the shelf life and marketing period of mango fruit requires application of quality preservation technologies. This study aimed at evaluating the effect of innovative waxing options on shelf life and postharvest quality of “ngowe” mango fruits stored under different storage conditions. A homogenous sample of mango fruits, variety “ngowe” harvested at mature green stage were subjected to two waxing treatments, namely Shellac or Decco wax™. The waxes were applied by dipping the fruits in wax for five seconds followed by air drying. The waxed fruits were then packed in carton boxes and stored either at ambient room temperature (25°C) or cold room (12°C). Random samples of three fruits from each treatment and storage conditions were taken for measurement of attributes associated with ripening after every 3 and 7 days for ambient and cold storage, respectively. These included cumulative weight loss, respiration, peel firmness, total soluble solids (TSS), total titratable acidity (TTA) and beta carotene content. Results from the study showed that waxing with either Shellac or Decco wax was effective in prolonging shelf life of “ngowe” mango fruits by 3 and 6 days in ambient and cold storage respectively. Untreated fruits in ambient storage lost 5.3% of the initial weight by day 7 compared to an average of 4.5% for the waxed fruit (day 10). Waxed fruits in ambient had low CO2 concentration (59.53 ml/kg hr) compared to a high (88.11 ml/kg hr) CO2 concentration for the untreated fruits. Similarly, other ripening related changes including brix, color, and firmness were significantly slowed down by waxing, especially under cold storage. Findings from this study show the effectiveness of waxing in delaying mango fruit ripening. Waxing can therefore be used to extend the shelf life and marketing period for mango fruit.
Mango (
The function of waxing to extend shelf life and maintain postharvest quality is based on the modification of the internal gas and moisture composition of the produce. Waxing can be applied by either spraying or dipping. Upon drying, the coating forms a thin film around the surface of produce which then creates a modified internal environment [
In order to realize the beneficial effect of waxing, it is important to match the commodity’s characteristics to those of the waxing material. Furthermore, the effectiveness of the waxing material could be improved by addition of active ingredients such as fungicides which help to deter fungal attack [
“Ngowe” mango fruits at mature green stage (color around seed turning cream/yellow) were harvested from commercial farms in Machakos County, Kenya. The fruits were packed in plastic crates lined with wet paper for cushioning and transported to the postharvest laboratory in the University of Nairobi.
Decco wax, Decco clear (food brush sanitizer) and Decco spark (disinfectant) were obtained from United phosphorus Limited, while shellac wax was obtained in flakes form from a commercial trader and the flakes dissolved in 0.01 N sodium hydroxide to make a concentration of 5%, w/w.
In the laboratory, the fruits were sorted for uniformity and then washed with disinfectant water containing calcium chloride (0.18 g/L). A fine brush dipped in Decco clear solution (50% diluted in water) was used to brush dirt on the fruits, after which they were dipped in hot water (45–55°C) for 10 seconds, removed and placed on wire shelves for air drying.
The fruits were then batched into three groups for different treatments which included untreated, 5% Shellac wax and Decco Wax. Wax was applied by dipping the fruits in bowls containing the different waxes and placed on wire shelves for drying. After drying, the fruits were packed in open carton boxes and stored at ambient room temperature (25°C) or under cold storage (12°C). Three fruits from each treatment and storage conditions were randomly sampled after every 3 and 7 days in ambient and cold storage respectively for analysis of attributes associated with ripening and quality. These included weight loss, firmness, respiration, beta carotene, total soluble solids and total titratable acidity. Three replicates of sixty fruits were used per treatment in all experiments. Completely Randomized Design with factorial arrangement was used as the study design.
Treatment protocol was designed by United Phosphorous Limited.
Mass loss for 5 fruits was taken and recorded using a digital balance (Model Libror AEG-220, Shimadzu Corp. Kyoto, Japan). The initial weight (
Mass loss for 5 individual fruits (marked at day 0) from each treatment and storage condition was taken and recorded using a digital balance (Model Libror AEG-220, Shimadzu Corp. Kyoto, Japan) each sampling day. The fruits were then separately incubated in air tight jars fitted with a CO2 gas sensor (Model CM-0187 Cozir AMB, UK) for 2 hours. Gas sample from the headspace was read by the CO2 sensor and a graph drawn from which the slope was used to calculate the amount of CO2 in ml per Kg Hour. The following formula was used to calculate CO2 produced:
where
Five fruits randomly selected from each treatment and storage conditions were sampled and an average of two measurements of firmness along the equatorial area recorded. A penetrometer (CR_100D, Sun Scientific Co. Ltd, Japan) having a 5 mm probe was used to puncture the fruits and the maximum force required to puncture the fruit was recorded. Firmness was expressed as Newton (N).
Pulp color change in the fruit was measured at 2 different spots along the equator using Minolta color difference meter (Model CR-200, Osaka, Osaka Japan) which had been calibrated on a white and black standard tile. To access the pulp, the fruit was cut open longitudinally. The L∗, a∗ and b∗ values were recorded and used to calculate the hue angle (H) using the below formula:
The TTA was determined by titration. Ten grams of the fruit pulp was ground and diluted with 90 mL of distilled water. 10 ml of the dilute solution was obtained, mixed with 2-3 drops of phenolphthalein indicator (colorless in acid medium) for titration against 0.1 N sodium hydroxide with constant shaking, till the mixture showed appearance of pink color. The TTA was expressed as percentage citric acid content of the fruit juice.
An Atago hand refractometer (Model 500, Atago, Tokyo, Japan) was used to determine the TSS levels. Fruits from each treatment were randomly picked and a blender used to macerate the pulp. The pulp was then placed on the glass prism and an average of three readings recorded.
The
where
There was a gradual weight loss in all the fruits in the different storage conditions but the loss was significantly (
Changes in cumulative weight loss (%) for “ngowe” mango fruits which were treated with either 5% Shellac wax or Decco wax or left Untreated (Control) and stored at ambient room temperature, 25°C (a) or cold room, 12°C, (b) top bars represent least significant difference (LSD) of means (
The rate of Carbon dioxide concentration is an indicator of the metabolic activity which signals on the possible shelf life of a given produce. Carbon dioxide concentration increased in all fruits as ripening progressed during the storage period (Figures
Changes in CO2 concentration (ml/kg hr) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Decco wax or left Untreated (Control) and stored at ambient room temperature, 25°C (a) or cold room, 12°C, (b) top bars represent least significant difference (LSD) of means (
In both storage conditions, a general decrease in peel firmness was observed regardless of treatment, but the rate was slower for the treated fruits compared to untreated (Figures
Changes in Peel firmness (N) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Decco wax or left Untreated (Control) and stored at ambient room temperature, 25°C (a) or cold room, 12°C, (b) top bars represent least significant difference (LSD) of means (
A general decrease in pulp Hue angle was observed in all fruits as ripening progressed irrespective of treatment or storage conditions. Cold storage (12°C) significantly (
A general decrease in TTA content was observed in all fruits as ripening progressed, but the rate was significantly (
Changes in Pulp color (H°) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Mango Decco wax or left Untreated (Control) and stored in cold storage (12°C).
Days in storage | |||||
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Treatment | 0 | 8 | 15 | 22 | 28 |
Untreated | 92.51a | 83.7a | 81.69a | 78.39a | |
5% Shellac wax | 92.51a | 84.86a | 85.55a | 84.48b | 80.6a |
Decco wax | 92.51a | 83.48a | 83.9a | 81.68b | 81.66a |
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Mean | 92.51 | 84.01 | 83.75 | 81.98 | 82.27 |
LSDs | 1.093 | 4.264 | 4.626 | 1.878 | 3.329 |
Means within each column followed by different letter differ significantly at (
Changes in Pulp color (H°) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Mango Decco wax or left Untreated (Control) and stored at ambient (25°C).
Days in storage | ||||
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Treatment | 0 | 3 | 7 | 10 |
Untreated | 115.42a | 81.8a | 76.38a | |
5% Shellac wax | 115.42a | 89.3b | 80.78b | 81.05a |
Decco wax | 115.42a | 85.8b | 81.19b | 82.57a |
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Mean | 115.42 | 85.63 | 79.45 | 81.81 |
LSDs | 2.196 | 3.543 | 2.844 | 4.92 |
Means within each column followed by different letter differ significantly at (
Changes in Total Titratable acidity (% citric acid) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Mango Decco wax or left Untreated (Control) and stored in ambient (25°C).
Days in storage | ||||
---|---|---|---|---|
Treatment | 0 | 3 | 7 | 10 |
Untreated | 0.755a | 0.378a | 0.103a | |
5% Shellac wax | 0.755a | 1.15b | 0.18a | 0.288a |
Decco wax | 0.755a | 1.133c | 0.467b | 0.274a |
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Means | 0.755 | 0.887 | 0.25 | 0.281 |
LSDs | 0.265 | 0.230 | 0.112 | 0.081 |
Means within each column followed by different letter differ significantly at (
Changes in Total Titratable acidity (% citric acid) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Decco wax or left Untreated (Control) and stored in cold storage (12°C).
Days in storage | |||||
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Treatment | 0 | 8 | 15 | 22 | 28 |
Untreated | 0.755a | 0.352a | 0.395a | 0.205a | |
5% Shellac wax | 0.755a | 0.778b | 0.66b | 0.404b | 0.244a |
Decco wax | 0.755a | 0.667b | 0.533c | 0.364b | 0.222a |
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Means | 0.742 | 0.599 | 0.531 | 0.324 | 0.233 |
LSDs | 0.2529 | 0.106 | 0.065 | 0.118 | 0.049 |
Means within each column followed by different letter differ significantly at (
An increase in TSS was observed in fruits in both storage conditions, but the rate was slower in cold storage compared to ambient storage (Tables
Changes in total soluble solids (°Brix) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Decco wax or left Untreated (Control) and stored in ambient (25°C).
Days in storage | ||||
---|---|---|---|---|
Treatment | 0 | 3 | 7 | 10 |
Untreated | 10.5a | 15.97a | 20.03a | |
5% Shellac wax | 10.5a | 13.43b | 18.85a | 18.5a |
Decco wax | 10.5a | 14.55b | 19.15a | 19.4a |
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Mean | 10.5 | 14.65 | 19.34 | 18.95 |
LSDs | 1.427 | 1.647 | 1.889 | 3.258 |
Means within each column followed by different letter differ significantly at (
Changes in total soluble solids (°Brix) for “ngowe” mango fruits which were treated with either 5% Shellac wax, Decco wax or left Untreated (Control) and stored in cold storage (12°C).
Days in storage | |||||
---|---|---|---|---|---|
Treatment | 0 | 8 | 15 | 22 | 28 |
Untreated | 10.5a | 18.37a | 21.43a | 16.54a | |
5% Shellac wax | 10.5a | 16.5a | 19.55b | 15.9a | 17.2a |
Decco wax | 10.5a | 15.65a | 15.45c | 16.13a | 22.2b |
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Mean | 10.5 | 16.84 | 18.81 | 16.19 | 19.7 |
LSDs | 1.427 | 2.866 | 2.055 | 2.984 | 3.082 |
Means within each column followed by different letter differ significantly at (
There was a gradual increase in
Changes in Beta carotene (
Storage temperature is one of the most important factors that influences the deteriorative rate of harvested produce. For every 10°C increase in temperature, the rate of deterioration of most perishable commodities increases two to three-fold. The rate of respiration of harvested commodities increases with increase in temperature, thus contributing to a quicker senescence. Relative humidity (moisture content of the atmosphere, expressed as a percentage) is retained depending on temperature and vapor pressure deficit. Increase in temperature causes an increase in the capacity of the air to hold moisture and this affects the rate at which water is lost from stored produce to the environment. Cuticle, a natural waxy layer that prevents water loss and gaseous exchange on the surface of produce is often lost during handling operations. Artificial waxing helps to reinforce the natural wax or replace in cases where most of the cuticle has been removed. Waxing limits the amount of water leaving the produce through transpiration by reducing the number and sizes of the lenticels, thus leading to a water saturated internal environment and also regulates gaseous exchange on the surface of the fruit leading to a high CO2 and low O2 level inside the fruit [
Normally, water is lost by diffusion through the skin to the atmosphere. Previous studies [
Reduced respiration rate is an indicator of low metabolic response due to low temperature and O2 level. Fruits stored in ambient (25°C) exhibited higher respiration compared to those in cold storage(25°C). For every 10°C increase in temperature, the rate of deterioration of most perishable commodities increases two to three-fold. An increased rate in the rate of metabolism has been shown to result into quick deterioration of climacteric fruits such as mango [
Color change from green to orange is attributed to the loss of chlorophyll and appearance of other pigments [
Decrease in firmness during ripening is associated with activities of the enzymes involved in cell wall metabolism including pectin methylesterase (PME), polygalacturonase (PG), endo-B-1,4- glucanase (EGase) and pectatelyase activities [
Increase in total soluble solids (TSS) during ripening is associated with the breakdown of stored carbohydrates to yield respiratory substrates necessary for maintaining the metabolic activities [
Untreated fruits total titratable acidity reduced faster compared to Decco and shellac wax treated fruits. This could be due to the utilization of the acid as a respiratory product during ripening [
The change in color of the mango pulp (cream to yellow/orange) is attributed to accumulation of beta carotene. In the current study, beta carotene content increased with storage time and as the fruits ripened but the increase was gradual for cold stored fruits compared to ambient stored, which could be attributed to reduced enzymatic activities due to low temperature. Beta carotene content development for the waxed fruits in both storage conditions was delayed compared to untreated fruits probably due to delayed synthesis and accumulation of beta carotene as a result of low O2 and high CO2, which interfered with the enzymes involved in the synthesis or unmasking of preexisting color pigments [
The findings from this study show that Decco wax and Shellac wax can delay mango fruit ripening and therefore extend the shelf life and consequently the marketing period for the fruits. Waxing coupled with cold storage resulted in more than two times the storage period for mangoes under ambient storage. This implies that cold storage is important to realize the potential benefits of waxing to preserve quality and extend the shelf life of mango fruit.
The data used in the development of this manuscript are available upon request, by reaching out to,
The authors declare that there are no conflicts of interest.
The mango wax and supportive funding for this research was provided by UPL Limited and the Rockefeller Foundation under the YieldWise Initiative.