agriculture

Article
The Combined Effect of Lemon Peel Extract and Calcium
Chloride on the Physical and Biochemical Quality Parameters of
the Dessert Banana (Musa acuminata var. Dwarf
Cavendish) Fruit
Eric-Ivan Ngoko Tchamba 1,2, * , Thorsten Tybussek 3 , Peter Muranyi 3 , Victor Francois Nguetsop 2 ,
Jean Aghofack-Nguemezi 2,† and Wilfried Schwab 1

1 Biotechnology of Natural Products, Center of Life and Food Science Weihenstephan, Technische Universität
München, Liesel-Beckmann Straße 1, 85354 Freising, Germany; wilfried.schwab@tum.de
2 Research Unit of Applied Botany, Department of Plant Biology, Faculty of Science, University of Dschang,
Dschang P.O. Box 67, Cameroon; vfnguetsop@yahoo.fr (V.F.N.)
3 Retention of Food Quality Department, Fraunhofer Institute for Process Engineering and Packaging IVV,
Giggenhauser Straße 35, 85354 Freising, Germany; thorsten.tybussek@ivv.fraunhofer.de (T.T.);
peter.muranyi@ivv.fraunhofer.de (P.M.)
* Correspondence: ngokonet@yahoo.com
† Deceased author.

Abstract: The dessert banana is a popular fruit worldwide, but its ripening process is greatly
accelerated by high temperatures, which eventually leads to an unpleasant taste and the appearance
of spots on the skin of the fruits. To slow down the ripening of bananas, expensive strategies are used,
which are usually not practical for conventional farmers in less developed countries. In this study,
we try to find a less costly alternative. Therefore, the effects of coatings of lemon peel extract (2.5%,
Citation: Ngoko Tchamba, E.-I.; 5%, and 10%), calcium chloride (4%), and glycerol (2%) on the shelf life and postharvest quality of
Tybussek, T.; Muranyi, P.; Nguetsop,
the banana fruit (Cavendish) stored at 19–22 ◦ C and 40–60% relative humidity were investigated.
V.F.; Aghofack-Nguemezi, J.; Schwab,
Treatment with a mixture of 2.5% lemon peel extract and 2% glycerol resulted in an extension of the
W. The Combined Effect of Lemon Peel
shelf life of the dessert banana by up to 6 days and no detectable fungal infestation. The coating
Extract and Calcium Chloride on the
solution is an effective alternative to extend the shelf life and reduce quality losses in bananas.
Physical and Biochemical Quality
Parameters of the Dessert Banana
(Musa acuminata var. Dwarf Cavendish)
Keywords: banana; edible coating; lemon peel extract; physical and biochemical properties; fruit
Fruit. Agriculture 2024, 14, 222. ripening; shelf-life
https://doi.org/10.3390/
agriculture14020222

Academic Editors: Jarosław

1. Introduction
Pobereżny, Elżbieta Wszelaczyńska
and Anna Nogalska Bananas are among the most well-known and frequently consumed fruits worldwide.
It is valued for its convenient size, ease of transport, and sweet and savory taste. However,
Received: 15 December 2023 aside from their delicious flavor, bananas are also very nutritious and have numerous
Revised: 23 January 2024
health benefits. The Cavendish banana variety is the fifth largest agricultural commodity
Accepted: 25 January 2024
in the world trade after cereals, cassava, sweet potato, and yams and the fourth most
Published: 30 January 2024
important foodstuff in the world after rice, wheat, and milk [1]. Banana plays an important
socioeconomic role in developing countries from tropical and subtropical zones, especially
in east, central, and west African countries, Southeast Asia, Central and South America,
Copyright: © 2024 by the authors.
and the Caribbean [2]. Cavendish banana production is currently dominated by Indonesia,
Licensee MDPI, Basel, Switzerland. with the Philippines in second place. The Philippines produced roughly 7.5 million tonnes
This article is an open access article of bananas in 2020, compared to Indonesia’s production of over 11 million tonnes. With
distributed under the terms and 2.3 million, 1.5 million, and 1.1 million tonnes of Cavendish bananas produced in 2020, the
conditions of the Creative Commons United Nations Organization for Food and Agriculture reports that Ivory Coast, Ghana,
Attribution (CC BY) license (https:// and Cameroon are Africa’s top producers of the variety [3].
creativecommons.org/licenses/by/ Banana is a rich source of vitamins A, B, and C, manganese, potassium, and fibers. In
4.0/). addition, 100 g of banana contains approximately 89 kcal calories, 74 g water, 1.1 g protein,

Agriculture 2024, 14, 222. https://doi.org/10.3390/agriculture14020222 https://www.mdpi.com/journal/agriculture

Agriculture 2024, 14, 222 2 of 19

0.3 g lipid, 21.8 g carbohydrate, 2 g fiber, 1 mg sodium, 385 mg potassium, 8 mg calcium,

30 mg magnesium, 0.4 mg iron, 22 mg phosphorous, 11.7 mg ascorbic acid, 40 µg thiamin,
70 µg riboflavin, 610 µg niacin, 80–600 µg pantothenic acid, 470 µg pyridoxine, and 23 µg
folic acid [4].
Banana is a climacteric fruit that ripens quickly after harvesting. Thus, it is a perishable
fruit and has a very short lifespan between harvest and the onset of deterioration [5]. It is es-
timated that post-harvest losses in bananas can differ based on several variables, including
the variety of bananas, the storage conditions, and the handling methods. In developing
countries, post-harvest loss of bananas reaches 30% or higher because of the poor storing
and handling conditions, which are frequently unsatisfactory, while post-harvest losses
are often lower in developed countries with stronger handling and storage infrastructure,
averaging around 5–10% [3]. Many storage methods have been developed to increase
the time and distance between harvest and marketing for commodities. For example, the
fruit is usually harvested when mature and unripe for commercial use and refrigerated
during transportation to the importing nations. Upon arrival at their destination, the green
bananas are held in modified atmospheric rooms at the distribution centers, where they are
treated with chemicals like ethylene gas before selling [6]. By lowering the metabolic rate,
minimizing peel degreening, and preventing fruit degradation, several other preservation
techniques have been investigated, such as regulated and controlled atmospheres [7]. Simi-
larly, low oxygen pre-treatment for two days can prevent bananas from ripening during
storage and shipping [8]. To preserve the color and texture of post-harvest bananas, chemi-
cals are frequently used to delay ripening [9]. Edible coatings [10] and the combinations
of chemical dipping with edible coatings [11] are also used. Small farmers in developing
countries rely on the natural ripening of bananas, which can be considered unsustainable
and unprofitable as these processes are very costly. Because of inadequate storage and
ripening conditions, many ripe bananas are lost or spoiled.
Among all the methods of fruit preservation currently in use, the use of edible coatings
is a popular practice that helps preserve the nutrients of food, particularly fruits, and
vegetables, and offers long shelf lives [12]. Edible coatings help preserve volatile flavor
components, slow down microbial growth, delay dehydration, reduce respiration, improve
textural quality, and prolong the shelf life of perishable food products [13]. The antioxidant
and antifungal qualities of the coating solution give it the ability to delay ripening and
senescence. According to recent studies, fruit seeds and peels may potentially have an-
tioxidant capabilities. Examples include mango seed kernels [14], pomegranate peels [15],
wampee peels [16], and grape seeds and peels [17]. In the past ten years, several researchers
have suggested that citrus waste might be utilized as a natural source of antioxidants [18].
The wealth of this information is invaluable particularly when considering the context of
sub-Saharan Countries such as Cameroon, where it has been observed that 76% of oranges
and 60% of lemons are wasted due to failure to sell, mechanical damage during transporta-
tion, storage conditions, inappropriate used packaging material, and poor hygiene [19].
This led us to use lemon peel as the basis for our coating solution. However, using glycerol
as a plasticizer, calcium chloride has been widely used as a preservative and firming agent
for whole and fresh-cut goods. The use of calcium chloride has also been linked to fruit
firmness, stress tolerance, ripening, and senescence [20]. There is little information about
the combined effect of lemon peel extract and calcium chloride on banana fruits. Therefore,
the objective of this study was to find an alternative solution to extend the shelf life of
bananas by using a combination of lemon peel extract, glycerol, and calcium chloride as
an edible coating solution and study their effect on the physicochemical and biochemical
qualities of the dessert banana fruit.

2. Materials and Methods

2.1. Chemicals and Reagents
The standards lutein, alpha-carotene, beta-carotene, sucrose, fructose, and glucose
were obtained from Sigma-Aldrich (Darmstadt, Germany); acetone, acetonitrile, n-hexane,
Agriculture 2024, 14, 222 3 of 19

ethanol (EtOH), methanol (MeOH), methyl tert-butyl ether (MTBE), calcium chloride
(CaCl2 ), and glycerol were purchased from Merck (Darmstadt, Germany). H2 O and ace-
tonitrile were of liquid chromatography grade.

2.2. Plant Materials

Sample Preparation and Storage
Lemon fruits were acquired from a private plantation in Foumbot, Cameroon, which
is located in the western part of the country. After removing all the fruits with physi-
ological and physical abnormalities, such as those that were rotten and immature, the
fruits were immersed for around 2 h in water containing sodium hypochlorite (230 µL·L−1 )
for disinfection. After that, they were rinsed with fresh tap water and the fruit’s peels
were removed using a sharp knife. They were crushed with a conventional grinder af-
ter they had completely dried in the shade, producing a lemon peel powder, and were
transported to the Fraunhofer Institute for Process Engineering and Packaging IVV, depart-
ment of Optimization of the Quality and Shelf-life of Foods, where the experiments were
carried out.
Seven hundred banana fruits from Costa Rica were purchased fresh from a local
supermarket in Germany. They were in the greenest stage conceivable (stage 1), as indicated
by a greenness of level 1. After being delivered to the laboratory, healthy fruits were selected,
disassembled, thoroughly washed with fresh tap water, and dried for about two hours
under ambient temperature (21–24 ◦ C).

2.3. Coatings and Storage Conditions

The different coatings were made of different concentrations of lemon peel extract (0%,
2.5%, 5%, and 10%) which were obtained from the powder using ethanol and distilled water
as solvents (CH3 CH2 OH/H2 O, 1/1 v/v), calcium chloride (4%), and glycerol (2%). The pH
of the solution was adjusted to pH 5.6 using 0.1 mol·L−1 sodium hydroxide. Bananas (54 per
treatment) were dipped into the prepared coating solution for 3 min and allowed to dry
for 1 h. Uncoated bananas, representing control samples (T0), were immersed in distilled
water for the same period. The storage room, which was a purpose-built environmental
chamber for food storage, was equipped with LED (light-emitting diodes, manufactured
by Sylvania Luxine Plus, Erlangen, Germany) light to simulate daylight (F30W/865-T8).
The temperature and relative humidity were controlled throughout the storage period. The
temperature of the storage room was automatically recorded via an internal system and
ranged from 19–22 ◦ C, and the relative humidity was recorded using an Efento sensor
(Krakow, Poland), ranging from 40 to 60% and controlled using an air humidifier (PHILIPS,
Amsterdam, The Netherlands). The coated and uncoated bananas were stored for a period
of 13 d and quality parameters were recorded at 4-d intervals. Visual observations were
made for a further 7 d.

2.4. Experimental Design

Nine edible coating solutions were prepared, and the used concentrations in this
investigation were determined through prior experiments conducted in our laboratory,
undertaken as a preparatory phase preceding the development of our experimental de-
sign: T0 = control sample with only distilled water, T1 = distilled water + glycerol (2%),
T2 = glycerol (2%) + 2.5% lemon peel extract, T3 = glycerol (2%) and 5% lemon peel extract,
T4 = glycerol (2%) + 10% lemon peel extract, T5 = 4% calcium chloride (CaCl2 ), T6 = glycerol
(2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5% lemon peel extract, T8 = glycerol
(2%), CaCl2 (4%) and 5% lemon peel extract, and T9 = glycerol (2%), CaCl2 (4%), and 10%
lemon peel extract. These treatments were arranged in a completely randomized design
(CRD) with three replications. Eighteen banana fruits were used and replicated three times,
for a total of 54 fruits were used for each treatment.
Agriculture 2024, 14, 222 4 of 19

2.5. Weight Loss

The weight of each banana finger was measured using an analytical balance (Sarto-
rius Lab Instruments, GmbH & Co., KG, Göttingen, Germany). The fruit weights were
recorded at 4-d intervals throughout the storage period, and the cumulative weight loss
was determined using the formula below:

IM − FM
WL(%) = × 100
IM
where WL represents the weight loss in percentage and IM and FM represent the initial
mass and the final mass in g, respectively.

2.6. Firmness
The fruit’s textural properties were measured using the texture analyzer (Model TA-
XT, Stable Micro System Ltd., Surrey, UK). The data were recorded using the EXPONENT
6.2.3.0 software. The firmness of the fruit’s flesh was measured by punching the sample,
resulting in a plot of strength vs. time. Compression force measurement mode, pre-test
speed of 1.5 mm·s−1 , test speed of 1.0 mm·s−1 , post-test speed of 10 mm·s−1 , trigger-auto
type of 2 kg, and data acquisition speed were the working circumstances used to measure
the firmness value. The accessories used were a 5 mm cylindrical probe (P/5) and a heavy
platform (HDP/90). Triple readings were taken and recorded at three separate locations (the
middle part, stem end, and distal end) on the fruit while resting on the texture analyzer’s
platform. The average data in kilogram-force (Kgf) were used.

2.7. Color Analysis

A method described by [21] was used with modifications. A D90 digital Nikon camera
and a 35 mm F/2 D Nikon prime lens (Tokyo, Japan) were used for color analysis. Digital
photos were captured under controlled LED illumination using a DigiEye imaging system
(VeriVide Limited, Enderby, Leicester, UK) with the help of DigiEye software version
2.8.0.3. The VeriVide D65 fluorescent tubes are located in the illumination box, which is a
lighting cabinet with light having similar characteristics to natural daylight. Before any
measurement, the system was calibrated using a white uniform board Digitizer Calibration
Pack (version number 4.0) from the Digieye service Pack. Five banana fruits per replicate
(i.e., 15 banana fruits per treatment) were placed on the surface of an additional rectangular
blue plate in the box. The surface of the plate containing the fruits was illuminated by the
mirrors. The blue background of the collected images was removed, and the fruit color was
analyzed using ImageJ version 1.53K (http://imagej.nih.gov/ij (accessed on 26 November
2022)); the results were expressed in RBG (Red-Blue-Green) values and then converted into
La*b* values using Python. These La*b* values determined the total color difference using
the formula below:
∆E = [(∆L)2 + (∆a*)2 + (∆b*)2 ]½
∆E = [(L2 − L1)2 + (a2 − a1)2 + (b2 − b1)2 ]½
where ∆L represents the change in lightness, L2* and L1* are the lightness values of the two
compared samples, a2 and a1 are the red-green color values of the two compared samples, b2,
and b1 are the yellow-blue color values of the two compared samples. The notation—(+ = lighter;
− = darker), (+ = redder, − = greener), (+ = yellow, − = bluer)—describes the positive and
negative changes in lightness (∆L), red-green (∆a), and yellow-blue (∆b) color values.

2.8. Decay Percentage

The percentage of decay or rot was determined through visual observation on day 20.
The survey focused on fruits that were rotten due to physiological and/or microbiological
disorders, and the percentage was estimated using the following formula:

Percentage of decay (%) = (number of decayed fruits) × 100/(Total number of fruits in the treatment)
Agriculture 2024, 14, 222 5 of 19

2.9. Total Soluble Sugar, Titratable Acidity, and pH

A 5 g sample of the banana pulp was prepared from 3 fruits (equal parts of fruit
flesh were collected from the middle and both ends of each fruit) and homogenized with
ultra-turrax and 15 mL of MQ water. The plant material was centrifuged for 10 min at
3000 rpm. Total soluble sugar was determined using a digital refractometer (Atago, Pocket
Brix-Acidity Meter, Tokyo, Japan). A volume of 45 mL of MQ water was used to dilute
and homogenize 5 mL of the fruit juice. The pH was measured using a digital pH meter
(EC-30-PH PHOENIX instrument from ProfiLab24 GmbH, Berlin, Germany). By titrating
the diluted fruit juice using a magnetic stirrer in the presence of phenolphthalein, the
titratable acidity was determined and calculated using the following formula:

Titratable Acidity (TA) = (Volume of NaOH (in mL) × 0.1 (normality of NaOH) × 0.064)/(Total juice volume in mL) × 100

where the volume of NaOH (in mL) is the volume of sodium hydroxide solution (in
milliliters) used to neutralize the acidity in the juice sample during the titration process, 0.1
is the normality of the sodium hydroxide (NaOH) solution and represents its concentration,
0.064 is the citric acid milliequivalent factor, and total juice volume (in mL) is the volume of
the juice sample used in the titration (before the addition of NaOH).

2.10. Sugar Analysis

Ten grams of the banana pulp from each treatment were ground, diluted, and cen-
trifuged at 13,000 rpm for 10 min. The supernatant was collected, dried via lyophilization,
and kept at −4 ◦ C for further analysis. The HPLC system used for analysis was equipped
with an S5200 autosampler and a pump 1000 Smartline with Manager 5000 (Göbel Instru-
mentelle Analytik GmbH, Hallertau, Germany). The detector was an evaporative light
scattering detector (ELSD; PL-ELS 2100, Polymer Laboratories GmbH, Darmstadt, Ger-
many). The column (Grace GmbH, Worms, Germany) was Allsphere Amino 250 × 4.6 mm,
5 µm. MilliQ water (ultrapure water) was utilized as eluent A (20%) and acetonitrile as
eluent B (80%). The flow rate was 1.0 mL·min−1 at 30 ◦ C. The parameters for the ELSD
were Evap: 80, Neb: 45, Gas: 1.6, Pmt: 6, Smth: 1, and LED: 100. The data management
system was Geminix III software, version 1.10.3.9 (Göbel Instrumentelle Analytik). Sucrose,
glucose, and fructose standards were used for identification and quantification.

2.11. Carotenoids Analysis

Ten grams of banana pulp were extracted using ethanol/n-hexane (4:3 v/v). After
centrifugation at 13,500 rpm for 10 min, the yellow supernatant was collected and re-
extracted with the same solvent until it had become colorless. The supernatants were
combined and dried under reduced pressure using a rotatory evaporator. The residues
were dissolved with n-hexane and redried. One hundred µL of ethyl acetate was added to
the dried samples, vortexed, and centrifuged at 10,000 rpm. The analysis was carried out
on the Agilent Technologies 1260 Infinity HPLC (Agilent, Waldbronn, Germany) equipped
with a column size of 250 × 4.6 mm (RP-18; YMC Co., Ltd., Kyoto, Japan). The eluents were
methanol (eluent A: 20%) and tert.-butyl methyl ether (eluent B: 80%). Carotenoids were
detected at 440 nm. The injection volume was10 µL, and the flow rate was 1 mL·min−1 . The
signals were converted and recorded via the OpenLab software version 2.4. Identification
and quantification of individual carotenoids were carried out by comparing retention times
and UV/Vis absorption with those of authentic standards.

2.12. Statistical Analysis

With treatment and storage time as sources of variation, all quantitative parameter data
were subjected to a one-way ANOVA using R version 4.1.2 (1 November 2021) statistical
analysis software with its cross-platform development environment—Rstudio. Data were
expressed as mean plus standard deviation (SD) from the three replicates. Tukey tests,
performed at a significance level of p < 0.05, were used to find differences between treatments.
Agriculture 2024, 14, 222 6 of 19

3. Results and Discussion

3.1. Weight Loss
Due to physiological changes and water loss, banana fruits lose weight during storage.
Therefore, the influence of edible coatings on the physiological weight loss (PWL) of banana
fruits during storage was studied (Figure 1). As the storage time increased, the weight
loss in all the treatments also increased as a result of the normal ripening process, which
is related to the increase in the respiration rate and thus, the loss of water content in the
fruits. On the first day (day 1) after coating, no (0%) physiological weight loss was recorded
in both coated and non-coated banana fruits, meaning that the application of the edible
coating formulation had no immediate effect on the water content of the banana. The
physiological weight loss values varied from 2.4% to 6.2% on day 5, where some treatments
exhibited noticeable differences in PWL compared to the control T0. T1 and T9 showed
higher PWL values of 6.1% and 6.4%, respectively, indicating that the coating might have
limited effectiveness in reducing PWL at this time point, but T2 demonstrated a high
reduction in PWL, with a value of 4.9%, suggesting that the coating formulation in T2 has a
positive impact on preserving banana weight during this period. On day 9, all treatments
displayed a noticeable reduction in PWL compared to the control T0. T2, T3, and T6 showed
a high reduction in PWL, with values of 5.2%, 7.6%, and 4.9%, respectively. The results
indicate that the effect of the edible coating becomes more evident with increasing storage
time. On day 13, when all the fruits were ripe, a high value of WL was observed in all
treatments in comparison to the control T0 (2.3%), which was already at the senescent phase.
T2 continued to show the greatest reduction in WL at 4.9%, implying that the formulation
has an influence on fruit respiration and enables them to produce less water vapor, thus
preserving fruit from weight loss. The main cause of physiological weight loss for fruit and
vegetables is transpiration, which is influenced by the difference in water vapor pressure
between the fruit and the atmosphere [22]. Then, the increased rate of fruit respiration
(where a carbon atom is lost from the fruit in each cycle) during storage, the hastened
evaporation from the fruit surface, and the burning of the fruit surface tissue were the
causes of the greater weight loss in the treated fruit [23]. Similar observations on weight
loss have been made by [24]. Furthermore, edible coatings act as a semipermeable barrier
against oxygen, carbon dioxide, moisture, and solute movement, thus lowering respiration,
water loss, and oxidation reaction rate [25]. The effectiveness of a coating on water retention
depends on its concentration [26]. Our results are not consistent with [27], who reported
that improving pore blockage and forming a thicker layer on the skin of pear offered a
better defense against the friction damage from the brushes and were the main ways by
which increasing coating concentration (and deposit on the skin) reduced fruit drying time.

3.2. Texture Analysis

The changes in texture or firmness of the banana fruit with and without coating during
the storage period are shown in Figure 2. All treatments showed comparable firmness
values (p > 0.05) after one day of storage, which is not surprising given that all fruit was
purchased from the same company, implying that the fruit was handled under the same
conditions. This result for d = 1 also shows that different coating formulations have no
direct influence on the fruit’s firmness. Significant firmness changes between treatments
were observed after 9 days of storage (p < 0.05). In comparison to other treatments, T2 had
the highest firmness value (32.1 ± 3.2 Kg·cm−2 ), followed by T8 (15. 3 ± 19.4 Kg·cm−2 ),
indicating improved firmness preservation. The lowest value measured (2.6 ± 0.3 Kg·cm−2 )
was observed for T9, showing a considerable loss of firmness during storage. At d = 13,
there were still differences between the treatments in the firmness values, which ranged
from 2.3 Kg·cm−2 to 9.6 Kg·cm−2 . However, there were no significant variations between
the treatments (p > 0.05). The firmness of fruits is crucial in determining how resistant they
are to mechanical injury. The different treatments of the samples affected how well the
firmness was preserved during storage. The results thus demonstrate the impact of the
concentration of lemon peel extract (LPE) on the firmness of bananas during storage. T2
Agriculture 2024, 14, 222 7 of 19

had the lowest change in firmness. We speculate that the amount of lemon peel powder con-
tained in T2 was optimized to enhance the fruit’s resistance to physical damage, reducing
the risk of bruising or other injuries during handling and transportation. Another potential
explanation is the dose-response efficiency of the formulation T2, which could have also
provided a protective layer on the surface of the banana, helping to preserve the integrity of
the cellular structures, which contributes to the overall firmness and texture of the banana
during storage. However, bananas treated with CaCl2 alone (T5) were also firmer than
untreated fruits (T0) after 9 and 13 days of storage. This result is consistent with the recent
observation that banana fruits treated with CaCl2 have a slower rate of deterioration and
loss of texture [28]. In addition, CaCl2 treatment has been proven to effectively retain the
firmness of chili pepper [29]. However, others reported that CaCl2 solution accelerates the
ripening process of bananas [30]. Fruit softening and textural changes are brought on by
the depolymerization and solubilization of peptic cell walls, middle lamella constituents,
Agriculture 2024, 14, x FOR PEER REVIEW 7 of 21
cell structure degradation [24,31], and the movement of water from the peel to the pulp
due to the process called osmosis [32].

25

20
Weight loss (%)

15

10

0
WL 1 WL 5 WL 9 WL 13
Storage Time (d)

T0 (control) T1 : Gly(2%), LP(0%), CaCl₂(0%) T2 : Gly(2%), LP(2.5%), CaCl₂(0%)

T3 : Gly(2%), LP(5%), CaCl₂(0%) T4 : Gly(2%), LP(10%), CaCl₂(0%) T5 : Gly(0%), LP(0%),CaCl₂(4%)
T6 : Gly(2%), LP(0%), CaCl₂(4%) T7: Gly(2%), LP(2.5%), CaCl₂(4%) T8 : Gly(2%), LP(5%), CaCl₂(4%)
T9 : Gly(2%), LP(10%), CaCl₂(4%)

Figure 1. Influence of different edible coating formulations on the weight loss of the banana fruits
Figure 1. Influence of different edible coating formulations on the weight loss of the banana fruits
during storage at 19–22 °C and 40–60% relative humidity. Where WL 1, WL 5, WL 9 and WL 13
during storage at 19–22 ◦ C and 40–60% relative humidity. Where WL 1, WL 5, WL 9 and WL 13
represent the weight loss value on day 1, 5, 9 and 13. Each data point consisted of 10 fruits repeated
represent
threethe weight loss value on day 1, 5, 9 and 13. Each data point consisted of 10 fruits repeated
times.
three times.
3.2. Texture Analysis
The changes in texture or firmness of the banana fruit with and without coating dur-
ing the storage period are shown in Figure 2. All treatments showed comparable firmness
values (p > 0.05) after one day of storage, which is not surprising given that all fruit was
purchased from the same company, implying that the fruit was handled under the same
conditions. This result for d = 1 also shows that different coating formulations have no
direct influence on the fruit’s firmness. Significant firmness changes between treatments
were observed after 9 days of storage (p < 0.05). In comparison to other treatments, T2 had
the highest firmness value (32.1 ± 3.2 Kg·cm−2), followed by T8 (15. 3 ± 19.4 Kg·cm−2), indi-
 with the recent observation that banana fruits treated with CaCl2 have a slower rate of
deterioration and loss of texture [28]. In addition, CaCl2 treatment has been proven to ef-
fectively retain the firmness of chili pepper [29]. However, others reported that CaCl2 so-
lution accelerates the ripening process of bananas [30]. Fruit softening and textural
changes are brought on by the depolymerization and solubilization of peptic cell walls,
Agriculture 2024, 14, 222
middle lamella constituents, cell structure degradation [24,31], and the movement of wa-8 of 19
ter from the peel to the pulp due to the process called osmosis [32].

50

45
T0 (control)
40
T1 : Gly(2%), LP(0%),
Banana firmness (kg∙cm−2)

35 CaCl₂(0%)
T2 : Gly(2%), LP(2.5%),
30 CaCl₂(0%)
T3 : Gly(2%), LP(5%),
CaCl₂(0%)
25 T4 : Gly(2%), LP(10%),
CaCl₂(0%)
20 T5 : Gly(0%),
LP(0%),CaCl₂(4%)
T6 : Gly(2%), LP(0%),
15
CaCl₂(4%)
T7: Gly(2%), LP(2.5%),
10 CaCl₂(4%)
T8 : Gly(2%), LP(5%),
5 CaCl₂(4%)
T9 : Gly(2%), LP(10%),
CaCl₂(4%)
0
day 0 day 5 day 9 day 13
Storage period (days)

Figure 2. Influence of different edible coating formulations on the firmness of the banana fruits dur-
Figure 2. Influence of different edible coating formulations on the firmness of the banana fruits during
ing storage at 19–22 °C and 40–60% relative humidity. Each data point consisted of 3 fruits repeated
◦ C and 40–60% relative humidity. Each data point consisted of 3 fruits repeated three
storage at 19–22
three times and on each fruit, 3 values were obtained respectively from the middle and both ends
times
of theand onthe
fruits; each fruit,bar
vertical 3 values werethe
represents obtained respectively
standard from
errors of their the middle and both ends of the
means.
fruits; the vertical bar represents the standard errors of their means.
3.3. Colour Analysis
3.3. Colour Analysis
The La*b* color space offers insightful information about the samples’ color proper-
ties. The La*b*
In this color
study, thespace
changeoffers insightful
in La*b* values information
over time wasabout thefor
studied samples’
variouscolor properties.
treatments
In
in comparison to the control (T0) (Table 1). On day 1, all treatments showed comparable in
this study, the change in La*b* values over time was studied for various treatments
comparison to the control
L* values in comparison to (T0) (Table(T0),
the control 1). On day 1,that
showing all treatments showed
there were no comparable
appreciable vari- L*
values in comparison to the control (T0), showing that there were no appreciable
ations in the samples’ lightness. The a* and b* values were also similar to T0, indicating variations
in thethere
that samples’
were lightness. The differences
no significant a* and b* values
in the were also similar
red-green to T0, indicating
and yellow-blue that there
color compo-
were
nents.no significant
The differences
day 5 analysis showedinthat
theT1
red-green and yellow-blue
had a considerably color
higher a* components.
value than T0 (p < The
day 5 analysis showed that T1 had a considerably higher a* value than T0 (p < 0.05). T1
showed a shift towards a more intense red or green hue compared to T0, with an average a*
value of 91.6 ± 0.5. The L and b* values between treatments did not show any discernible
variations at this time. On day 9, when compared to T0, T2 had significantly lower L levels
(p < 0.05). T2 had a darker appearance than T0, with an average L value of 90.3 ± 1.3.
Furthermore, b values in T2 were considerably lower than in T0 (p < 0.05) and showed
a trend towards a more vivid blue or yellow color with an average b value of 12.4 ± 0.1.
The values between treatments did not show any discernible variations at this period.
However, when compared to the other treatments, T6 displayed a considerably higher b
value at day 9 (7.5 ± 0.1). This suggests that the yellow color of T6 was more pronounced.
However, treatment T2 was greener than the other treatments on day 13. This can be
concluded by the lower a* value of T2 (6.5 ± 4.5) on day 13 in comparison to the other
treatments. The CIELAB color space’s green-red axis is represented by the* value, where
negative values denote greener hues. As a result, T2 had a greener appearance on day 13
than the other treatments. The results show that T3, T4, T9, and T2 effectively retained
the most chlorophyll content (green color) of the fruit, while the other coated fruits are
yellow due to the carotenoid content of the fruit’s peel. The green hue of the banana peel
Agriculture 2024, 14, 222 9 of 19

gradually fades during ripening as a result of the thylakoid membrane breaking and the
chlorophyll being degraded by chlorophyllase and oxidase enzymes, revealing yellow
carotenoid pigments [33]. LPE could effectively retain the green color of banana fruit,
while the combination of LPE and CaCl2 could reduce this effect. This is well observed in
T8, with a 5% concentration of LPE in combination with CaCl2 (4%), which had a lower
effect on the retention of green color during the storage time compared to T3 with 5%
LPE concentration without CaCl2 , which represents a stronger effect on the green color
retention. However, during storage, L values decreased for both coated and uncoated
samples, possibly as a result of surface moisture loss, which could have resulted in the
darker hue observed [34]. Similar results were obtained in the study of an edible coating
based on various concentrations of quince seed gum on banana slices at 4 ◦ C and 40 ◦ C [35].

3.4. Decay Percentage

The bananas that showed decay after day 13 were counted and expressed as a percent-
age (Figure 3). T2 showed the lowest number of damaged bananas with a decay percentage
of 2.3 ± 0.6%, compared to the other treatments. A low concentration of LPE (2.5%) had a
strong positive effect on the shelf life of the bananas, while a high concentration of LPE
(5% and 10%) accelerated the deterioration of the fruits, e.g., T3 (34.4 ± 1.5%) and T4
(31.3 ± 1.5%), respectively. This low decay percentage observed in the formulation T2
could have happened because of the low weight loss and high firmness value recorded,
implying a delay or disorder in the metabolism of the normal ripening process and as
a result, preventing the fruits from rotting. The first symptoms of dark coloration and
overripe appearance were also perceived as an increase in banana respiration and microbial
activity. We equally assumed that T2 provided a balance in a dose-response efficiency in
its formulation as low (0%) and high (5% and 10%) concentrations of lemon peel powder
had very high decay percentages and then decreased in their visual quality, while the
percentage of lemon peel powder in T2 was optimal, allowing the fruits to preserve their
quality. Similar observations were made by [36]. However, some researchers [26] reported
that the high concentration used in the coating formulation forms a very thick layer on the
fruit surface, which contributes to more clogging of the skin pores, exposing the fruit to
anaerobic respiration that develops an odd taste, which is also a sign of premature decay in
fruits. Similarly, CaCl2 treatment (T5) reduced the decay of banana in comparison with the
control (T0) as only 11.0 ± 1% of the fruits were spoiled compared to T6 (31.6 ± 2.0%), T7
(28 ± 2%), T8 (19.3 ± 2.5%), and T9 (23.6 ± 2.0%). The reduction in the decay of the fruits
after the application of LPE as an edible coating on the surface of fruits could be explained
by the antifungal effect of lemon peel. The effect of the essential oils of lemon, mandarin,
grapefruit, and orange on the growth of molds commonly associated with food spoilage
has already been shown [37].
Agriculture 2024, 14, 222 10 of 19

Table 1. Effect of edible coating formulations on the color of banana storage at 19–22 ◦ C and 40–60% relative humidity.

Color
(CIELab)/ T0 T1 T2 T3 T4 T5 T6 T7 T8 T9
Treatments
L1 61.8 ± 0.1 61.1 ± 0.1 62.3 ± 0.1 61.8 ± 0.1 61.7 ± 0.1 61.1 ± 0.1 61.70 ± 0.1 62.2 ± 0.1 61.8 ± 0.1 61.9 ± 0.1
L2 91.4 ± 0.9 a 91.5 ± 0.5 a 90.3 ± 1.2 a 92.1 ± 0.6 a 91.4 ± 0.8 a 91.8 ± 0.8 a 92.0 ± 0.5 a 92.0 ± 0.6 a 91.5 ± 0.5 a 91.9 ± 1.2 a
L3 91.4 ± 0.9 c 91.5 ± 0.5 a 90.3 ± 1.2 ab 92.1 ± 0.6 bc 91.4 ± 0.8 ac 91.8 ± 0.8 ab 92.0 ± 0.5 ab 92.0 ± 0.6 ac 91.5 ± 0.5 ab 91.9 ± 1.2 bc
L4 66.4 a ± 0.8 a 68.1 a ± 0.8 a 65.8 a ± 0.4 a 67.5 a ± 1.4 a 65.3 a ± 0.2 a 67.5 a ± 1.2 a 68.3 a ± 1.3 a 66.5 a ± 2.2 a 69.8 a ± 4.0 a 66.2 a ± 2.4 a
a1* −9.8 ± 0.1 −5.4 ± 0.1 −8.0 ± 0.1 −7.4 ± 0.1 −6.8 ± 0.1 −5.4 ± 0.1 −6.8 ± 0.1 −8.0 ± 0.1 −9.8 ± 0.1 −5.2 ± 0.1
a2* −243.6 ± 2.9 −240.27 ± 0.71 −241.8 ± 1.5 −237.9 ± 0.6 −240.5 ± 2.6 −239.8 ± 3.5 −239.5 ± 1.2 −239.1 ± 1.9 −240.4 ± 1.5 −238.4 ± 2.3
a3* 14.5 ± 0.2 c 14.6 ± 0.8 a 15.1 ± 0.6 ac 15.3 ± 0.7 ac 15.9 ± 0.2 ac 15.6 ± 0.6 ab 16.0 ± 0.4 ab 16.0 ± 0.4 ac 16.4 ± 1.0 a 17.1 ± 0.4 bc
a4* 12.1 ± 0.3 a 13.4 ± 0.7 a 11.8 ± 0.4 a 12.7 ± 1.5 a 11.8 ± 0.4 a 12.0 ± 1.5 a 12.2 ± 1.3 a 11.0 ± 3.0 a 13.3 ± 3.0 a 12.1 ± 1.6 a
b1* 12.0 ± 0.2 6.2 ± 0.1 12.4 ± 0.1 6.8 ± 0.1 7.5 ± 0.1 6.2 ± 0.1 7.5 ± 0.1 12.4 ± 0.1 12.2 ± 0.1 6.3 ± 0.1
b2* 14.7 ± 0.7 a 15.2 ± 0.2 a 15.4 ± 0.5 a 15.1 ± 0.3 a 15.4 ± 0.3 a 14.6 ± 0.7 a 15.0 ± 0.2 a 15.2 ± 0.4 a 15.3 ± 0.4 a 14.6 ± 0.9 a
b3* 19.7 ± 0.3 d 18.6 ± 0.2 ad 17.9 ± 0.2 ab 19.1 ± 0.4 bd 18.2 ± 0.4 abc 17.7 ± 0.3 a 17.8 ± 0.6 a 18.8 ± 0.5 ad 18.0 ± 0.4 ab 19.3 ± 0.6 cd
b4* 12.4 ± 0.9 a 11.4 ± 1.5 a 12.1 ± 0.3 a 11.6 ± 1.5 a 11.3 ± 0.7 a 12.5 ± 1.5 a 11.8 ± 1.2 a 10.8 ± 0.8 a 11.6 ± 0.8 a 11.3 ± 0.5 a
L1, a1*, and b1* represent the L, a*, and b* values on day 1; L2, a2*, and b2* represent day 5; L3, a3*, b3* represent day 9; L4, a4*, and b4* represent day 13. Means with different lowercase
letters are significantly different in their respective column or rows (p < 0.05). Storage conditions T0–T9 are described in detail in the Materials and Methods section (experimental
design), where T0 = control sample with only distilled water, T1 = distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemon peel powder, T3 = glycerol (2%) and 5% lemon peel
powder, T4 = glycerol (2%) + 10% lemon peel powder, T5 = 4% calcium chloride (CaCl2 ), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5% lemon peel powder,
T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glycerol (2%), CaCl2 (4%), and 10% lemon peel powder. Each data point consisted of 10 fruits repeated three times.
 the control (T0) as only 11.0 ± 1% of the fruits were spoiled compared to T6 (31.6 ± 2.0%),
T7 (28 ± 2%), T8 (19.3 ± 2.5%), and T9 (23.6 ± 2.0%). The reduction in the decay of the fruits
after the application of LPE as an edible coating on the surface of fruits could be explained
by the antifungal effect of lemon peel. The effect of the essential oils of lemon, mandarin,
Agriculture 2024, 14, 222
grapefruit, and orange on the growth of molds commonly associated with food11spoilage of 19
has already been shown [37].

45
g
40 fg
f ef
35
de

Decay on day 13 (%)

30
cd
ce
25 c
20
15
b

10
a
5
0
T0 T1 T2 T3 T4 T5 T6 T7 T8 T9
‐5
Treatments

Figure3.3.Decay
Figure Decaypercentage
percentageofofcoated
coated and
and uncoated
uncoated bananas
bananas on on
dayday
20, 20, where
where T0 =T0 = control
control sample
sample
with only distilled water, T1 = distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemonpeel
with only distilled water, T1 = distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemon
powder, T3 = glycerol (2%) and 5% lemon peel powder, T4 = glycerol (2%) + 10% lemon peel powder,
peel powder, T3 = glycerol (2%) and 5% lemon peel powder, T4 = glycerol (2%) + 10% lemon peel
T5 = 4% calcium chloride (CaCl2), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and
powder, T5 = 4% calcium chloride (CaCl2 ), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2
2.5% lemon peel powder, T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glyc-
(4%) and 2.5% lemon peel powder, T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and
erol (2%), CaCl2 (4%), and 10% lemon peel powder.
T9 = glycerol (2%), CaCl2 (4%), and 10% lemon peel powder.

3.5. Total Soluble Sugar

The total soluble sugar (TSS, ◦ Brix) of the coated and uncoated bananas was deter-
mined during storage (Figure 4). All treatments had TSS values between 2.1 and 2.1% Brix
after an initial storage period of 1 day. The TSS values significantly differed between the
treatments after the 5-day storage period. In comparison to other treatments, T0, T1, T4, T8,
and T9 exhibited higher TSS values (ranging from 3.0 to 3.4◦ Brix), indicating a faster ripen-
ing of these bananas in comparison with the fruits treated differently. The TSS readings
continued to deviate when the storage duration increased. TSS values for T0, T3, and T4
showed the highest values, with 16.8 ± 0.2, 16.6 ± 0.1, and 16.5 ± 0.1◦ Brix, respectively on
day 9. Similarly, results differed significantly on day 13. TSS values for T0 were highest at
17.8 ± 0.1◦ Brix, indicating that all other treatments slowed the ripening process. These
results of the effect of edible coatings are similar to those obtained on strawberries [38]
and bananas [39]. The T2 treatment was found to be the most effective in retaining TSS
during the storage period. This could be because only a moderate concentration of lemon
peel is required for the effective preservation of the banana fruit. High concentrations also
had an effect on the titratable acidity during the ripening process of the bananas but not
enough to make the coating effective. Similarly, the effect of CaCl2 was not significant
enough to maintain TSS compared to other edible coating formulations. The coating film
on the surface of the banana reduces the internal respiration rate and vital processes, which
reduces the ripening process and keeps the TSS value low. Physiologically, the noticeable
general increase of TSS over the storage time is due to the breakdown of starch into soluble
sugars [40]. Similar results have been reported in another study [24].
 enough to make the coating effective. Similarly, the effect of CaCl2 was not significant
enough to maintain TSS compared to other edible coating formulations. The coating film
on the surface of the banana reduces the internal respiration rate and vital processes,
which reduces the ripening process and keeps the TSS value low. Physiologically, the no-
Agriculture 2024, 14, 222
ticeable general increase of TSS over the storage time is due to the breakdown of12 starch
of 19
into soluble sugars [40]. Similar results have been reported in another study [24].

25

20
Total soluble sugar (° Brix)

15

10

0
day 1 day 5 day 9 day 13
Storage time (days)

T0 (control) T1 : Gly(2%), LP(0%), CaCl₂(0%)

T2 : Gly(2%), LP(2.5%), CaCl₂(0%) T3 : Gly(2%), LP(5%), CaCl₂(0%)
T4 : Gly(2%), LP(10%), CaCl₂(0%) T5 : Gly(0%), LP(0%),CaCl₂(4%)
T6 : Gly(2%), LP(0%), CaCl₂(4%) T7: Gly(2%), LP(2.5%), CaCl₂(4%)
T8 : Gly(2%), LP(5%), CaCl₂(4%) T9 : Gly(2%), LP(10%), CaCl₂(4%)

Figure 4. Influence of different edible coating formulations on the titratable acidity of the banana fruits
Figure 4. Influence of different edible coating formulations on the titratable acidity of the banana
during storage at 19–22 °C and 40–60% relative humidity, where T0 = control sample with only dis-
fruits during storage at 19–22 ◦ C and 40–60% relative humidity, where T0 = control sample with only
tilled water, T1 = distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemon peel powder, T3 =
distilled water, T1 = distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemon peel powder,
T3 = glycerol (2%) and 5% lemon peel powder, T4 = glycerol (2%) + 10% lemon peel powder, T5 = 4%
calcium chloride (CaCl2 ), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5%
lemon peel powder, T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glycerol
(2%), CaCl2 (4%), and 10% lemon peel powder. Each data point was a pooled sample of fresh material
from 3 fruits repeated thrice and the vertical bar represents the standard errors of their means.

3.6. Titratable Acidity, and pH

The changes in the pH of control and treated banana fruits during the storage period
were determined (Figure 5). The pH increased as the storage time increased. On day 1,
there was no difference between the pH of the coated and the control fruits, whose value
varied between 3.7 and 3.8. By day 9 and 13, the pH values increased uniformly and
T2 showed the lowest pH throughout the storage period, with values of 4.3 and 4.8 on
days 9 and 13, respectively, while the control sample had values of 5.2 and 6.6 on days
9 and 13, respectively. No significant differences were found in the other formulations
compared to the control samples. The TA gradually decreased as the storage time increased
(Figure 6). On the first day, the TA values for all treatments, including the control, were
almost identical. This could be because the fruits were all handled under the same storage
conditions. We can conclude from this observation that the different formulations had no
direct influence on the TA value of the fruits. On day 5, we observed a general decrease
in the TA value for all treatments, but with a small slope value for T2. This observation
was even more pronounced on day 9, where T2 had a TA value of 0.24 g citric acid/100 mL
juice, while the other treatments, including the control (T0 = 0.23 g citric acid/100 mL juice),
 Agriculture 2024, 14, 222 13 of 19

had a TA value between 0.192 and 0.2048 g citric acid/100 mL juice. By day 13, the values
of TA for all the treatments were higher than the control, and in particular, T2 was higher
than all the other treatments. This indicates that T2, which contained a moderate amount
of lemon peel, was effective in maintaining the titratable acidity by reducing the metabolic
activity and lowering the respiration in the fruits. Lemon concentration plays an important
role in the formation of organic acids during the ripening process of bananas, which are
very crucial for their final flavor. Organic acids, such as citric or malic acid are considered
to be the primary substrates for the respiration process [41]. Edible coatings reduce the rate
of respiration and may therefore delay the utilization of these organic acids [42]. In contrast
to the results of [43], there was a direct relationship between pH and titratable acidity
Agriculture 2024, 14, x FOR PEER REVIEW in 21
14 of
different samples. These results are in accordance with the results obtained on bananas
coated with chitosan alone and with a combination of chitosan and gibberellic acid [25].

7.5

6.5

6
pH values

5.5

4.5

3.5

3
day 0 day 5 day 9 day 13
Storage Time (d)

T0 (control) T1 : Gly(2%), LP(0%), CaCl₂(0%)

T2 : Gly(2%), LP(2.5%), CaCl₂(0%) T3 : Gly(2%), LP(5%), CaCl₂(0%)
T4 : Gly(2%), LP(10%), CaCl₂(0%) T5 : Gly(0%), LP(0%),CaCl₂(4%)
T6 : Gly(2%), LP(0%), CaCl₂(4%) T7: Gly(2%), LP(2.5%), CaCl₂(4%)
T8 : Gly(2%), LP(5%), CaCl₂(4%) T9 : Gly(2%), LP(10%), CaCl₂(4%)

Figure
Figure5.5.Influence
Influenceofofdifferent
differentedible coating
edible formulations
coating onon
formulations thethe
pHpHof of
thethe
banana fruits
banana during
fruits stor-
during
age at 19–22 °C and 40–60% relative humidity. Each data point was a pooled sample of fresh material
storage at 19–22 ◦ C and 40–60% relative humidity. Each data point was a pooled sample of fresh
from 3 fruits repeated thrice and the vertical bar represents the standard errors of their means.
material from 3 fruits repeated thrice and the vertical bar represents the standard errors of their means.
Agriculture 2024, 14,
Agriculture 22214, x FOR PEER REVIEW
2024, 15 of 2114 of 19

Titratable acidity (g citric acid/100 ml juice) 0.35

0.3

0.25

0.2

0.15

0.1
day 1 day 5 day 9 day 13
Storage Time (d)

T0 (control) T1 : Gly(2%), LP(0%), CaCl₂(0%)

T2 : Gly(2%), LP(2.5%), CaCl₂(0%) T3 : Gly(2%), LP(5%), CaCl₂(0%)
T4 : Gly(2%), LP(10%), CaCl₂(0%) T5 : Gly(0%), LP(0%),CaCl₂(4%)
T6 : Gly(2%), LP(0%), CaCl₂(4%) T7: Gly(2%), LP(2.5%), CaCl₂(4%)
T8 : Gly(2%), LP(5%), CaCl₂(4%) T9 : Gly(2%), LP(10%), CaCl₂(4%)

Figure 6. Influence of different edible coating formulations on the titratable acidity of the banana
Figure 6. Influence of different edible coating formulations on the titratable acidity of the banana fruits
fruits during storage at 19–22 °C and 40–60% relative humidity. Storage conditions T0–T9 are de-
during storage at 19–22 ◦ C and 40–60% relative humidity. Storage conditions T0–T9 are described
scribed in detail in the Materials and Methods section (experimental design). Each data point was a
in detail
pooledinsample
the Materials
of fresh and Methods
material from section (experimental
3 fruits repeated design).
thrice and Each data
the vertical point was the
bar represents a pooled
standard
sample errors
of fresh of their means.
material from 3 fruits repeated thrice and the vertical bar represents the standard
errors of their means.
3.7. Influence of Different Edible Formulation Coatings on the Sugar Content of the Banana
3.7. Influence of Different
Glucose, Edible
fructose, and Formulation
sucrose Coatings
are the main on the
sugars Sugar Content
in bananas of the Banana
during ripening, and
these sugarsfructose,
Glucose, increase in andconcentration
sucrose areduring the main ripening
sugars [44]. The concentration
in bananas of these and
during ripening,
sugars in coated and uncoated bananas was determined during
these sugars increase in concentration during ripening [44]. The concentration (Figure the storage period of these sug-
ars 7). In general, the sugar content increased as the storage time increased. The concentra-
in coated and uncoated bananas was determined during the storage period (Figure 7). In
tions were not significantly different from each other up to the first 9 days of storage. By
general, the sugar content increased as the storage time increased. The concentrations were
day 9, the highest sucrose concentration was in T0 (2.1 mg·g−1), T6 (2.0 mg·g−1), and T7 (1.8
notmg·g
significantly different from each other up to the
−1), while the lowest sucrose concentration was in T8 (0.8 mg·g−1), and first 9 days of storage. By day 9, the
T2 (1.3 mg·g−1).
highest sucrose concentration was in T0 (2.1 mg · g −1 ), T6 (2.0 mg·g−1 ), and T7 (1.8 mg·g−1 ),
The sucrose concentration of T0 dropped to 0.7 mg·g−1 on day 13, while the sucrose content
while the lowest
increased in all sucrose
the coated concentration
samples. T1, T2, was and inT5T8showed
(0.8 mg ·g−
the
1 ), and T2 (1.3 mg·g−1 ). The
highest sucrose concentra-
sucrose mg·2.2 − 1
tions concentration
on day 13, withof 2.3T0 dropped
mg·g to 0.7
−1, 2.2 mg·g −1, and g mg·g on day 13, while the
−1, respectively. Thesucrose
fructosecontent
con- in-
creased in all the
centrations werecoated
highersamples.
in most of T1,
the T2, and T5
coated showed
fruits compared the highest sucrose
to the control concentrations
samples. By
on day
day 9,13,the
with 2.3 mg·g−1of, 2.2
concentration mg·g−
fructose 1 , and
and glucose2.2 mgwere·g−highest
1 , respectively.
in T4 (1.2Themg·g fructose
−1 and 1.2 concen-
mg·g−1were
trations , respectively),
higher in T7 most (1.8ofmg·g
the −1 and 1.1
coated mg·g
fruits −1, respectively), T6 (1.1 mg·g−1 and 1.1
compared to the control samples. By day 9,
themg·g of fructose and glucose were highest in T4 (1.2 mg·g−1 and
−1, respectively), and T3 (1.1 mg·g−1 and 1.1 mg·g−1, respectively), while
concentration 1.2 mg·g−1 ,
the lowest
content was observed in T2 (0.7 mg·g
respectively), T7 (1.8 mg·g and 1.1 mg·g , respectively), T6 (1.1 mg·g and 1.1and
− −1 and − 0.7 mg·g −1, respectively). T0 had 0.8 − mg·g mg·g−1 ,
1 1 1 −1

0.8 mg·g −1 of fructose and glucose, − 1 respectively. −T0

1 fructose
respectively), and T3 (1.1 mg·g and 1.1 mg·g , respectively), while the lowest content and glucose concentrations
wasdropped to 0.7 mg·g−1 and 0.7 −
in T2 (0.7 mg·g mg·g
−1, respectively, on day 13, while the concentration of
observed 1 and 0.7 mg·g−1 , respectively). T0 had 0.8 mg·g−1 and
sugars−in the coated fruits continued to increase. However, among the coated fruits, low
0.8 mg·g 1 of fructose and glucose, respectively. −1T0 fructose and glucose concentrations
fructose-glucose content was found in T8
−1 and 0.7 mg·g−1 , respectively, (0.9 mg·g and 1.1 mg·g−1, respectively), T1 (0.8
dropped to 0.7 mg · g on
mg·g and 0.8 mg·g , respectively), and T2 (0.8 mg·g and 0.8 mg·g−1, respectively). A
−1 −1 −1 day 13, while the concentration
of sugars in the coated fruits continued to increase.
complicated regulatory process changes the metabolism during banana ripening, However, among the coated fromfruits,
low fructose-glucose content was found in T8 (0.9 mg·g−1 and 1.1 mg·g−1 , respectively),
T1 (0.8 mg·g−1 and 0.8 mg·g−1 , respectively), and T2 (0.8 mg·g−1 and 0.8 mg·g−1 , respec-
tively). A complicated regulatory process changes the metabolism during banana ripening,
from starch synthesis to starch breakdown, resulting in the accumulation of soluble sug-
ars, primarily sucrose, which significantly affects the taste and flavor of the fruit. This
conversion of starch into sucrose appears to be responsible for sweetening the pulp and
 Agriculture 2024, 14, x FOR PEER REVIEW 16 of 21
Agriculture 2024, 14, 222 15 of 19

starch synthesis to starch breakdown, resulting in the accumulation of soluble sugars, pri-
marily sucrose,
providing energywhich significantly
for metabolic affects thethat
processes tastelead
and flavor
to theofdevelopment
the fruit. This conversion
of other quality
characteristics of ripe bananas, such as color change, synthesisthe
of starch into sucrose appears to be responsible for sweetening of pulp and compounds,
volatile providing and
evenenergy for metabolic processes that lead to the development of other quality characteris-
softening of the pulp, which greatly affects the quality of the finished fruit [45]. In all
tics of ripe bananas, such as color change, synthesis of volatile compounds, and even sof-
the samples, a higher concentration of sucrose than fructose and glucose was detected. In
tening of the pulp, which greatly affects the quality of the finished fruit [45]. In all the
fact,samples,
during athe ripening
higher process,ofglucose
concentration and fructose
sucrose than fructoseand areglucose
formed was from sucrose
detected. molecules.
In fact,
When during the ripening process, glucose and fructose are formed from sucrose molecules. under
the climacteric peak is reached, this sucrose concentration starts decreasing
the When
effect the
of saccharolytic
climacteric peakenzymes,
is reached,while fructose
this sucrose and glucose
concentration startsconcentrations
decreasing under increase.
Several authors
the effect have tracked
of saccharolytic the concentration
enzymes, while fructose ofand
starch, sucrose,
glucose glucose, increase.
concentrations and fructose as
wellSeveral
as theauthors
activitieshaveoftracked
various theenzymes
concentration of starch,
involved in sucrose, glucose,ofand
the synthesis fructose
sucrose as In the
[46].
well as the activities of various enzymes involved in the synthesis of
control sample T0, a typical natural ripening was observed (Figure 5), as demonstrated by sucrose [46]. In the
control sampleof
the degradation T0,sucrose
a typicalonnatural ripening
day 13, whilewas all observed
the coated (Figure 5), asshowed
samples demonstrated
a highbysucrose
the degradation of sucrose on day 13, while all the coated samples showed a high sucrose
content on day 13. From an organoleptic point of view, the coated fruits could be sweeter
content on day 13. From an organoleptic point of view, the coated fruits could be sweeter
because the the
because total content
total contentof of
sweet-tasting
sweet-tastingsugars
sugarsisishigher
higher ininthe
the coated
coated fruit
fruit samples,
samples, which
is anwhich
important criterioncriterion
is an important for consumer acceptance.
for consumer acceptance.

2.5
Sugar concentration (mg.g−1)

1.5

0.5

0
Sucrose

Sucrose

Sucrose

Sucrose

Sucrose

Sucrose

Sucrose

Sucrose

Sucrose

Sucrose
Fructose

Fructose

Fructose

Fructose

Fructose

Fructose

Fructose

Fructose

Fructose

Fructose
Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

Glucose

T0 T1 T2 T3 T4 T5 T6 T7 T8 T9
Treatments

Day 1 Day 5 Day 9 Day 13

Figure 7. The concentration of sugars in coated and non-coated bananas during the storage period
Figure 7. The
at 19–22 °Cconcentration of sugars
and 40–60% relative in coated
humidity, where and non-coated
T0 = control samplebananas during
with only the
distilled storage
water, T1 period
at 19–22 ◦ C and 40–60% relative humidity, where T0 = control sample with only distilled water,
= distilled water + glycerol (2%), T2 = glycerol (2%) + 2.5% lemon peel powder, T3 = glycerol (2%)
T1 =and 5% lemon
distilled peel
water + powder,
glycerolT4 = glycerol
(2%), (2%) + 10%
T2 = glycerol lemon
(2%) peel powder,
+ 2.5% T5 =powder,
lemon peel 4% calcium T3chloride
= glycerol (2%)
(CaCl2), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5% lemon peel powder,
and 5% lemon peel powder, T4 = glycerol (2%) + 10% lemon peel powder, T5 = 4% calcium chloride
T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glycerol (2%), CaCl2 (4%), and
(CaCl2 ), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5% lemon peel powder,
T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glycerol (2%), CaCl2 (4%), and
10% lemon peel powder. Each data point was a pooled sample of fresh material from 3 fruits repeated
thrice and the vertical bar represents the standard errors of their means.

3.8. Influence of Different Edible Formulation Coatings on the Carotenoid Contents of the Banana
The distinctive yellow color of ripe banana peels is solely the result of chlorophyll
breakdown, which obscures the yellow hue of unripe bananas. As a result, the carotenoid
Agriculture 2024, 14, 222 16 of 19

content in bananas changes as fruit ripening and maturation proceed. The concentration
of carotenoids (lutein and alpha- and beta-carotene) obtained from the calibration curve
calculations using high-performance liquid chromatography (HPLC) was analyzed in the
coated and non-coated bananas during the storage period (Figure 8). The concentration of
carotenoids increased with increasing storage time. Lutein was the major carotenoid, followed
by alpha- and beta-carotene. A large difference in carotenoid concentration was observed
particularly on day 5 of the storage time, when all the treated banana fruits had a higher lutein
concentration compared to the control samples, which had a concentration of 0.2 mg·g−1 . The
highest concentration was detected in T1 (0.3 mg·g−1 ), T2 (0.38 mg·g−1 ), T7 (0.37 mg·g−1 ),
and T9 (0.30 mg·g−1 ), while the alpha- and beta- carotene content remained low. On day 9,
alpha- and beta-carotene concentrations were particularly high in T2, with 0.14 mg·g−1 and
0.05 mg·g−1 , respectively. In the control, beta-carotene was not detected on day 9. The highest
concentration of lutein was found in the control sample T0, with 0.5 mg·g−1 on day 13. Fruits
like bananas produce a large amount of carotenoids, which are produced from terpenoids as
the chloroplast to chromoplast transition occurs [47]. During the ripening process, the fruit
color changes due to the production of carotenoids and the destruction of chlorophylls. Similar
to regular ripening, the highest level of lutein content was found in T0 and T5 compared to
Agriculture 2024, 14, x FOR PEERthe other coated samples on day 13. This indicates that T0 and T5 may be in a more
REVIEW 18 of advanced
21

stage of the ripening process; thus, coating delays the ripening of the banana.

0.6
Carotenoid concentration (mg.g−1)

0.5

0.4

0.3

0.2

0.1

0
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car
Lutein
α-Car
β-Car

T0 T1 T2 T3 T4 T5 T6 T7 T8 T9
Treatments

Day 1 Day 5 Day 9 Day 13

Figure 8. Concentration of carotenoids in coated and non-coated bananas during the storage period
Figure 8. Concentration
at 19–22 °C and 40–60%of carotenoids
relative humidity,in coated
where T0and non-coated
= control samplebananas
with onlyduring
distilledthe storage
water, T1 period
at 19–22 ◦ C and
= distilled water40–60% relative
+ glycerol (2%), T2humidity,
= glycerol where T0 =lemon
(2%) + 2.5% control
peelsample
powder,with
T3 = only distilled
glycerol (2%) water,
T1 =and 5% lemon
distilled peel+powder,
water glycerolT4(2%),
= glycerol
T2 = (2%) + 10%
glycerol lemon
(2%) peel powder,
+ 2.5% lemon peelT5 = powder,
4% calcium T3chloride
= glycerol (2%)
(CaCl2), T6 = glycerol (2%) + CaCl2 (4%), T7 = glycerol (2%), CaCl2 (4%) and 2.5% lemon peel powder,
and 5% lemon peel powder, T4 = glycerol (2%) + 10% lemon peel powder, T5 = 4% calcium chloride
T8 = glycerol (2%), CaCl2 (4%) and 5% lemon peel powder, and T9 = glycerol (2%), CaCl2 (4%), and
(CaCl 2 ), lemon
10% T6 = glycerol (2%) +
peel powder. CaCl
Each 2 (4%),
data pointT7 = glycerol
was a pooled (2%),
sample CaCl 2 (4%)
of fresh and 2.5%
material fromlemon
3 fruitspeel
re- powder,
T8 =peated
glycerolthrice and CaCl
(2%), the vertical
2 (4%) bar
andrepresents
5% lemonthe standard
peel errors
powder, of
and their
T9 means.
= glycerol (2%), CaCl 2 (4%), and
10% lemon peel powder. Each data point was a pooled sample of fresh material from 3 fruits repeated
4. Conclusions
thrice and the vertical bar represents the standard errors of their means.
Our results suggest that banana fruits coated with lemon peel extract-based formu-
lations post-harvest retain significant fruit chlorophyll content despite a reduction in fruit
firmness. The addition of CaCl2 in the formulation reduced the effect of the lemon peel
extract but was not enough to be considered important. The use of a concentration of 2.5%
lemon peel extract in the formulation of an edible coating for the post-harvest preservation
of bananas showed significant retention of color, sugar, firmness, and carotenoids of the
fruit, which are very important parameters for quality control, as shown by treatment T2
Agriculture 2024, 14, 222 17 of 19

4. Conclusions
Our results suggest that banana fruits coated with lemon peel extract-based formula-
tions post-harvest retain significant fruit chlorophyll content despite a reduction in fruit
firmness. The addition of CaCl2 in the formulation reduced the effect of the lemon peel
extract but was not enough to be considered important. The use of a concentration of 2.5%
lemon peel extract in the formulation of an edible coating for the post-harvest preservation
of bananas showed significant retention of color, sugar, firmness, and carotenoids of the
fruit, which are very important parameters for quality control, as shown by treatment T2
throughout the storage period. On the other hand, a high percentage of lemon peel extract
(in this case, 10% in T3) in the edible coating solution applied to the surface of bananas
caused the fruit to ripen very quickly compared to the control samples. These data provide
significant and helpful information for maintaining the quality of bananas in fresh produce
post-harvest management industries. The findings of this research contribute significantly
to the income improvement for farmers, processors, and distributors to market bananas
in developing and emerging countries and toward the use of plastic-free packaging in the
fruits and vegetable industries.

Author Contributions: E.-I.N.T.: Conceptualization, investigation, methodology, analysis, writing—

original draft, and writing review and editing. W.S.: Supervision, conceptualization, investigation,
methodology, analysis, resources, writing—review and editing, and validation. V.F.N.: supervision,
methodology, project administration, and visualization. J.A.-N.: supervision, project administration,
conceptualization, investigation, and methodology. P.M.: conceptualization, methodology, and
analysis. T.T.: conceptualization, methodology, formal analysis, software, and data curation. All
authors have read and agreed to the published version of the manuscript.
Funding: This work was supported by the DAAD (Deutscher Akademischer Austauschdienst) and
the Professorship Biotechnology of Natural Products.
Institutional Review Board Statement: Not applicable.
Data Availability Statement: The data presented in this study are available upon request from the
corresponding author.
Acknowledgments: Thomas Hoffmann, Anja Forstner, Mechthild Mayershofer, and Sadiq Mareai are
acknowledged for their technical support.
Conflicts of Interest: The authors declare no conflicts of interest.

Abbreviations
LPE: Lemon peel extract

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