Effect of a Protein–Polysaccharide Coating on the Physicochemical Properties of Banana (Musa paradisiaca) During Storage

Abstract

Banana (Musa paradisiaca) is a climacteric fruit with high postharvest perishability, limiting its export potential. This study evaluated the effectiveness of a natural protein–polysaccharide edible coating—comprising whey, agar, cassava starch, and glycerol—on maintaining the physicochemical quality of green bananas during 28 days of refrigerated storage (13 °C, 95% RH). Seven formulations were tested, including an uncoated control. Physicochemical parameters such as weight loss, firmness, fruit dimensions, peel color, titratable acidity, pH, and soluble solids (°Brix) were systematically monitored. Significant differences were observed among treatments (ANOVA, p < 0.001). The most effective coating (T5), composed of 16.7% whey, 16.7% agar, 33.3% cassava starch, and 33.3% glycerol (based on 30 g/L solids), reduced weight loss by 58.8%, improved firmness retention by 48.4%, and limited sugar accumulation by 17.0% compared to the control. It also stabilized pH and acidity, preserved peel thickness and color parameters (L*, a*, b*), and delayed ripening. These findings confirm the coating’s capacity to form a cohesive semipermeable barrier that modulates moisture loss and respiration, making it a functional and sustainable alternative for extending banana shelf life in tropical supply chains.

1. Introduction

The postharvest preservation of fruits represents a critical concern in the food industry due to the rapid deterioration that occurs after harvest, leading to significant losses in quality, quantity, and economic value [1,2,3]. Among the most vulnerable tropical fruits is the banana (Musa paradisiaca), which is highly perishable and prone to changes in texture, color, and nutritional composition during storage [2,3]. This situation is particularly relevant in producing countries such as Ecuador, where postharvest losses can reach up to 30%, posing a significant economic, social, and logistical challenge [4,5].

The economic impact of these losses affects not only large exporters but also small-scale producers, who rely on the sale of fresh fruit as their primary source of income. The reduced commercial shelf life of the fruit limits its distribution to international markets and increases food waste, which negatively impacts food security and the sustainability of the agri-food system [3,5]. For this reason, the development of accessible, sustainable, and effective technologies to prolong banana preservation is a priority research area [6].

Edible coatings applied to the surface of fruits are considered a promising strategy to extend the shelf life of fruits and vegetables by reducing water loss, controlling respiration, and delaying ripening [7]. These coatings can be composed of natural and biodegradable ingredients, providing a protective barrier without compromising food safety or nutritional quality [8,9]. The composition of the coating is a factor in determining its effectiveness, as each ingredient directly influences the preservation of the fruit’s physicochemical properties [10].

Several studies have investigated diverse ingredient combinations to formulate effective edible coatings aimed at extending the postharvest shelf life of bananas (Musa paradisiaca) [9]. The incorporation of whey as a primary protein component has been shown to enhance moisture retention and exert antimicrobial activity, both of which are essential for delaying senescence and microbial spoilage [11]. Likewise, natural polysaccharides such as agar and cassava starch exhibit strong film-forming capacity, contributing to a reduction in oxidative reactions and the improvement of mechanical strength, thereby helping to preserve the fruit’s external appearance during storage [12,13,14].

Glycerol, widely recognized for its humectant and plasticizing properties, is frequently included in coating formulations due to its ability to improve film flexibility and prevent cracking or structural failure under postharvest conditions [10,15]. When combined with biopolymers such as whey, its functional efficacy is further enhanced, resulting in significantly reduced water loss and improved firmness retention—both of which are critical for maintaining the physicochemical quality of bananas during prolonged cold storage [15,16].

Additionally, in polysaccharide-based systems, glycerol has been shown to reduce mechanical damage and improve the structural stability of fruits under handling and transport conditions [17,18]. Several studies agree that the combination of natural ingredients, such as proteins, polysaccharides, and plasticizers, not only preserves the fruit’s organoleptic properties but also enhances its resistance to adverse environmental conditions, supporting prolonged storage [19].

These formulations have been successfully applied to fruits such as mango, papaya, and grapes, showing significant improvements in firmness, color retention, acid content, and resistance to physical damage [20,21]. However, in the specific case of bananas, there remains a need to develop coatings tailored to their physiological characteristics, such as high respiration rates and ethylene sensitivity. Moreover, validating these technologies under refrigerated storage conditions is essential, as these are commonly used in the export supply chain.

A comprehensive evaluation of coatings, considering not only their physical properties but also their structural and chemical effects, is necessary to understand their influence on parameters such as weight loss, firmness, fruit dimensions, peel color, pH, titratable acidity, and soluble solids content (°Brix). These indicators determine the ripening stage, storage stability, and overall fruit quality, which are essential for assessing the commercial viability of the applied coatings [22].

This study transcends coating formulation by incorporating a physicochemical evaluation specifically designed to objectively monitor postharvest quality and physiological deterioration in bananas (Musa paradisiaca). The selected parameters—weight loss, firmness, titratable acidity, pH, soluble solids content (°Brix), and color attributes—are fundamental indicators of ripening progression, metabolic activity, water retention, and senescence. Their systematic assessment allows for a precise evaluation of the coating’s effectiveness in preserving fruit quality during cold storage and provides a solid scientific foundation for its application in postharvest management strategies [23]. Taken together, these indicators provide a comprehensive understanding of the physiological and structural transformations that occur in bananas during refrigerated storage. This insight supports the development of sustainable postharvest technologies aimed at prolonging shelf life and reducing quality losses in highly perishable tropical fruits.

Weight loss percentage is fundamental for assessing the coating’s efficiency in moisture retention and dehydration prevention. This parameter directly correlates with water evaporation, and its control helps extend the fruit’s shelf life.

Changes in fruit dimensions (length and peel thickness) indicate the coating’s effectiveness in preserving structural integrity. Significant changes may reflect accelerated ripening or mechanical damage. Monitoring these parameters helps assess whether the coatings effectively maintain the banana’s physical structure during storage [24].

Firmness, measured with a penetrometer, indicates the fruit’s resistance to deformation. An effective coating should help preserve peel firmness, preventing softening and mechanical injury [25]. Firmness is also linked to consumer perception and visual fruit quality. Color changes, particularly in peel luminosity and chromaticity (a*, b*), serve as visual indicators of ripening and oxidation. Coatings that slow these changes contribute to improved visual quality and consumer acceptance [26].

Chemical parameters such as pH, titratable acidity, and soluble solids content provide insight into the fruit’s internal metabolic state. A suitable coating should help delay acidity loss and the increase in soluble sugars, both associated with overripening [27]. These measurements are fundamental for monitoring the ripening process and determining the coating’s influence on internal fruit chemistry during storage.

This study offers valuable insights into the potential of edible coatings composed of whey, agar, starch, and glycerol as an effective strategy for extending the postharvest shelf life of bananas (Musa paradisiaca). Furthermore, it is part of a broader line of research investigating the use of essential oils as natural antifungal agents to control pathogenic fungi isolated from bananas [28,29,30]. The combined findings may support the development of innovative and integrative preservation technologies applicable to both industrial food chains and small-scale agricultural systems, contributing to a reduction in food losses and the enhancement of food security [24,31].

2. Materials and Methods

Banana samples (Musa paradisiaca) at commercial ripening stage 1 (completely green, uniform size, and free of visible defects) were harvested in Machala (El Oro Province, Ecuador) in December 2023. The fruits were then transported to the laboratory of the National Polytechnic School (EPN, Quito, Ecuador), where they were kept under controlled conditions of temperature (13 ± 1 °C) and relative humidity (approximately 95%). All experimental treatments were conducted under these storage conditions.

2.1. Coating Design

Green bananas were manually harvested and selected for uniform size and absence of physical defects. Coating formulations were prepared using food-grade ingredients: whey powder (Agropur INC., Eden Prairie, MN, USA) as the protein source with film-forming properties; agar-agar (Sigma-Aldrich, St. Louis, MO, USA) as a natural gelling agent; native cassava starch (Industrias Lojanas de Alimentos, Loja, Ecuador) as the structural polysaccharide; and glycerol (Merck, Darmstadt, Germany; ≥99.5% purity) as a plasticizer to enhance flexibility in the coating matrix.

All components were dissolved in distilled water produced in EPN’s laboratory and used without modification, and the coating solutions were freshly prepared before application.

Six different coating formulations (T1, T6) and an uncoated control (T7) were tested. Whey and agar concentrations were constant at 5 g, while cassava starch and glycerol concentrations varied from 5 to 15 g to create different matrix combinations.

Table 1. Composition of coating formulations used for banana treatments.

Treatments	Whey (g)	Agar (g)	Cassava Starch (g)	Glycerol (g)
T1	5	5	5	5
T2	5	5	5	10
T3	5	5	5	15
T4	5	5	10	5
T5	5	5	10	10
T6	5	5	10	15
T7 (Control)	0	0	0	0

presents the detailed compositions of each treatment.

The coating solutions were homogenized using a magnetic stirrer (Thermo Fisher Scientific, Waltham, MA, USA) approximately 25 °C until solids were fully dissolved. Each fruit was dipped into its corresponding solution for 1 min, then air-dried at room temperature (~25 °C) for 12–15 min to ensure uniform film formation.

A completely randomized design (CRD) was applied to evaluate the effect of seven coating treatments (T1–T7) on the postharvest quality of Musa paradisiaca during 28 days of refrigerated storage at 13 °C and 95% relative humidity. Each treatment was formulated using four core components: whey (protein source), agar (gelling agent), cassava starch (structural polysaccharide), and glycerol (plasticizer). While whey and agar concentrations were kept constant at 5 g in all formulations, cassava starch and glycerol were varied between 5, 10, and 15 g to generate different polymer matrices. Treatments T1 to T6 represent these combinations, whereas T7 served as the uncoated control.

To ensure consistency in storage conditions, temperature and relative humidity were continuously monitored throughout the experiment using a digital thermo-hygrometer (Testo 608-H2, Testo SE & Co. KGaA, Lenzkirch, Germany; accuracy ±2% RH and ±0.5 °C). This controlled environment allowed for the accurate evaluation of coating performance across all treatments.

During storage, several physicochemical parameters were evaluated, including weight loss, firmness, peel color, titratable acidity, pH, soluble solids content (°Brix), fruit length, peel thickness, and structural appearance. These parameters were compared with the uncoated control (T7) to assess the effectiveness of each coating formulation. Samples were taken weekly, and all data were analyzed using one-way ANOVA followed by Tukey’s HSD multiple comparison test (p = 0.05).

2.2. Physical Analysis

The physical parameters of the bananas were evaluated weekly using a total of 10 samples per treatment, following standardized methodologies.

2.2.1. Weight Variation

The weight of each banana was individually measured using a BPS 51 Plus precision balance (Boeco, Hamburg, Germany), with an accuracy of 0.01 g and a maximum capacity of 510 g. The initial weight of each fruit was recorded at the time of coating application. Subsequently, periodic measurements were taken throughout the storage period. Weight loss was calculated as the percentage reduction relative to the initial weight, using the following formula [9]:

$$Weight loss \left(\%\right)={\displaystyle \frac{Initial weight-Final weight}{Initial weight}}\times 100$$

(1)

This measurement was used to assess the effectiveness of each treatment in water retention and dehydration control, which are critical for postharvest preservation.

2.2.2. Fruit Dimensions

The length and thickness of the banana samples were measured using a digital caliper (Truper, CALDI-6MP, Jilotepec, Mexico) with a precision of 0.01 mm. Fruit length was determined from the tip to the base, while thickness was measured at the widest point of the fruit, typically in the middle section [32]. These measurements allowed the evaluation of size variation during storage and its correlation with the applied treatments.

2.2.3. Firmness

Measurements were conducted using a McCormick FT327 penetrometer (McCormick, Forlì, Italy) equipped with an 8 mm diameter plunger. The instrument has a maximum capacity of 13 kgf and a sensitivity of 0.1 kgf. The evaluation focused on peel firmness, as resistance to deformation is an indicator of structural integrity and the peel’s ability to protect the pulp during storage [8,32].

A constant force was applied to the fruit surface, allowing the probe to penetrate slightly into the pulp at a standardized depth. The force required for penetration was recorded, providing a reliable assessment of peel resistance and insights into fruit quality and ripeness progression over time.

2.2.4. Color

Peel color was determined using a Minolta CR-400 tristimulus colorimeter (Konica Minolta, Tokyo, Japan), which records L* (lightness), a* (red–green chromaticity), and b* (yellow–blue chromaticity) values [33]. Measurements were taken in triplicate at three different points on each banana, avoiding visible defects or blemishes to ensure accuracy. The average value was used to characterize surface color as a variable of ripeness, visual quality, and preservation status during storage.

2.3. Chemical Analysis

Chemical measurements were conducted in triplicate to monitor fruit ripening during storage, following internationally recognized standard procedures.

2.3.1. pH

Measurements were carried out using a Mettler Toledo SG2-FK digital pH meter (Mettler Toledo, Schwerzenbach, Switzerland), which offers an accuracy of ±0.01 pH units. Prior to each reading, the instrument was calibrated using standard buffer solutions at pH 4.00 and 7.00 to ensure measurement accuracy. Juice was obtained from each fruit by manual or mechanical pressing, and the electrode was immersed directly into the juice to obtain digital readings. AOAC Method 981.12 was followed to pH determination [34]. The data obtained was used to assess the degree of fruit ripeness and chemical stability during the storage period.

2.3.2. Titratable Acidity

Titration was conducted using 0.1 N NaOH, and the results were expressed as a percentage of citric acid, following AOAC Method 942.15. A Brand Titrette digital burette (accuracy ± 0.01 mL) was used to ensure precise volume control during the procedure. Sodium hydroxide was gradually added to the banana juice until the endpoint was reached, as indicated by a color change due to phenolphthalein, confirming neutralization [35]. All determinations were performed in triplicate to ensure measurement reliability. The average values were used to calculate the citric acid concentration in the juice.

2.3.3. Soluble Solids

Measurements were performed using an Atago PAL-1 digital refractometer (Atago, Tokyo, Japan) (range: 0–53 °Brix; accuracy: ±0.2 °Brix), following AOAC Method 932.12. Results were expressed in degrees Brix (°Brix), representing the percentage of soluble solids in the sample [36]. This parameter offered valuable insights into the concentration of sugars and other dissolved compounds in banana juice throughout the storage period.

3. Results

The following section presents the results obtained during the storage of Musa paradisiaca fruits treated with edible coatings, in comparison with an uncoated control group. Physicochemical parameters—including weight loss, firmness, peel color, pH, total soluble solids (°Brix), and titratable acidity—were evaluated to determine the effectiveness of the coatings in preserving postharvest quality.

3.1. Physical Analysis

3.1.1. Weight Variation

Weight loss is one of the most representative indicators of postharvest deterioration in fresh fruits, as it reflects water loss primarily driven by transpiration and respiration. The effectiveness of various edible coating formulations in minimizing the mass loss of Musa paradisiaca was evaluated under refrigerated conditions (13 °C, 95% RH).

Figure 1 displays the cumulative weight loss (%) after 28 days of storage, revealing statistically significant differences among treatments (p < 0.05). The uncoated control group (T7) exhibited the highest weight loss (22.5%), consistent with unprotected water loss. In contrast, the lowest losses were recorded in T5 (9.5%) and T6 (10.0%), indicating superior moisture retention. Treatments T1 (13.5%) and T4 (13.0%) showed intermediate values, which were statistically higher than T3 (10.5%) and T2 (11.5%). According to Tukey’s HSD analysis, the treatments were grouped into distinct statistical categories, with T5 and T6 demonstrating the most effective performance in reducing water loss and preserving fruit mass during storage.

3.1.2. Fruit Dimensions

Banana peel plays a vital role as a protective barrier against moisture loss and mechanical damage. A reduction in peel thickness during storage often indicates progressive dehydration and structural degradation. In this study, peel thickness was measured using a digital caliper with a precision of ±0.01 mm (Truper, Jilotepec, Mexico). Measurements were taken at three equidistant points along the equatorial region of each fruit, and the mean value was recorded. Figure 2 illustrates the percentage of peel thickness loss for each treatment.

Statistically significant differences were observed among treatments (p < 0.05). The uncoated control (T7) exhibited the highest loss (10.5%), indicating severe tissue degradation. Treatments T1 (7.5%) and T4 (6.5%) also showed considerable reductions. In contrast, T5 (5.0%) and T6 (5.3%) demonstrated the lowest loss values, reflecting improved structural preservation. According to Tukey’s HSD test, T5 and T6 formed a statistically distinct group with superior performance, whereas T7 differed significantly from all coated treatments, confirming the protective role of the applied coatings in minimizing peel deterioration.

Fruit length is a relevant physical parameter reflecting the structural integrity and turgor retention of bananas during storage. A reduction in length may result from tissue contraction and water loss, both of which are associated with dehydration and advanced ripening stages. In this study, Figure 3 presents the percentage reduction in fruit length after 28 days of storage, comparing the effectiveness of the different coating formulations.

Statistically significant differences were found among treatments (p < 0.05). The greatest length reduction was observed in the uncoated control (T7), with an average loss of 7.8%. In contrast, treatments T5 (3.8%) and T6 (4.0%) recorded the lowest reductions, indicating better structural preservation. Intermediate decreases were observed in T2, T3, and T4 (4.8%–5.0%), while T1 exhibited a slightly higher reduction (5.5%). According to Tukey’s HSD analysis, the treatments were grouped into distinct statistical categories, reinforcing the capacity of the coatings—particularly those enriched with starch and glycerol—to minimize tissue shrinkage and maintain fruit integrity during refrigerated storage.

3.1.3. Firmness

Firmness is a critical physical attribute for evaluating the postharvest quality of bananas, as it directly influences consumer acceptability, resistance to mechanical damage, and shelf-life stability during storage and distribution. Loss of firmness is commonly associated with cell wall degradation, reduced turgor pressure, and progressive ripening. Figure 4 presents the percentage of firmness loss across treatments, allowing for a comparative assessment of the coatings’ effectiveness in preserving structural integrity.

Statistically significant differences (p < 0.05) were observed among treatments. The uncoated control (T7) exhibited the greatest firmness loss, declining from an initial average of 20.5 N to 14.6 N after 28 days. In contrast, treatment T5 demonstrated the highest firmness retention (17.1 N), followed closely by T6 (17.0 N) and T3 (16.8 N). Intermediate values were recorded for T1, T2, and T4 (15.2 to 15.8 N). These findings suggest that coatings enriched with starch and glycerol significantly contributed to the structural preservation of the fruit, effectively delaying softening during refrigerated storage.

3.1.4. Color

The L* value (luminosity) of banana peel is closely associated with surface brightness and is an indicator of ripening and visual quality. A decrease in L* (ΔL*) is typically linked to enzymatic browning and pigment oxidation, both of which negatively impact the commercial appeal of the fruit. Figure 5 presents the ΔL* values across treatments, illustrating their effects on peel brightness.

The control group (T7) exhibited the most pronounced reduction in luminosity (ΔL* = 12.8), consistent with evident darkening of the peel. In contrast, treatments T5 (ΔL* = 5.3) and T6 (ΔL* = 6.0) retained higher levels of brightness, suggesting more effective inhibition of color degradation. Moderate reductions were observed in T2, T3, and T4, while T1 experienced a slightly greater loss (ΔL* = 8.8). According to Tukey’s HSD test, T5 and T6 were significantly different from the control, forming a distinct group with superior color preservation during storage.

The a* chromaticity value represents the shift in banana peel coloration toward red or brown hues. An increase in this parameter (Δa*) is commonly associated with the progression of visual browning during ripening and the oxidation of phenolic compounds. It serves as a reliable indicator of undesirable color changes and overall deterioration in fruit appearance. In this study, the increase in a* was analyzed refrigerated storage to evaluate the coating’s ability to delay the transition toward darker tones.

Figure 6 displays the Δa* values for each treatment, showing statistically significant differences among them (p < 0.05). The control treatment (T7) recorded the highest increase in a* (Δa* = 5.4), reflecting advanced ripening and chlorophyll degradation. In contrast, treatments T5 (2.4) and T6 (2.7) exhibited the lowest increases, suggesting a more effective delay in pigment transition. Treatments T1 through T4 presented intermediate increases ranging from 2.9 to 3.5. According to Tukey’s HSD analysis, T5 and T6 formed a statistically distinct group from the control, reinforcing their potential to mitigate visual deterioration during postharvest storage.

The b* chromaticity value is associated with the intensity of the characteristic yellow color of banana peel. A decrease in this parameter (Δb*) reflects the loss of warm pigmentation, typically linked to aging, senescence, and carotenoid degradation. In this study, b* variation was assessed at the end of storage to evaluate the effect of the formulated coatings on color preservation.

Figure 7 presents the Δb* values for each treatment, revealing statistically significant differences among them (p < 0.05). The uncoated control (T7) exhibited the highest reduction (6.9 units), indicating a marked decline in brightness and chromatic quality. In contrast, T5 and T6 showed the lowest decreases (3.1 and 3.5, respectively), suggesting improved retention of the yellow hue. Treatments T1 through T4 presented intermediate values, ranging from 4.1 to 4.8. According to Tukey’s HSD analysis, T5 formed a statistically distinct group from the control, supporting its superior performance in delaying pigment degradation and maintaining visual appeal during refrigerated storage.

3.2. Chemical Analysis

All chemical analyses were conducted in triplicate to monitor the progression of fruit ripening during storage, in accordance with internationally recognized standards.

3.2.1. pH

This chemical parameter serves to assess the physiological status of the fruit during storage, as increased pH values are typically associated with the breakdown of organic acids and the progression of ripening. More stable pH levels reflect reduced internal alteration and improved regulation of postharvest metabolic processes. In this study, the final pH of the banana pulp was evaluated. Figure 8 presents a comparative boxplot of the treatments, illustrating data dispersion, central tendencies, and statistical differences in pH stability based on the coating formulation applied.

Statistically significant differences (p < 0.05) were observed among treatments. The control group (T7) exhibited the highest mean pH value (5.52), indicating advanced ripening and loss of biochemical stability. In contrast, treatment T5 maintained the lowest pH (5.30), followed by T6 (5.33), suggesting a delay in senescence. Intermediate pH levels were recorded in T1 to T4, ranging from 5.36 to 5.39. According to Tukey’s HSD analysis, T5 and T6 formed a statistically distinct group from the control, confirming their effectiveness in buffering pH increases and modulating postharvest metabolic activity.

3.2.2. Titratable Acidity

Expressed as a percentage of citric acid, titratable acidity is an indicator of fruit maturity and chemical stability during storage. Its progressive decline typically reflects the consumption of organic acids through respiratory and fermentative processes. An effective coating is expected to help preserve acidity levels, thereby delaying senescence. Figure 9 presents a boxplot comparing the titratable acidity across coated and uncoated treatments, highlighting their impact on the fruit’s acid profile.

Statistically significant differences were observed among treatments (p < 0.05). The control group (T7) exhibited the lowest acidity (mean ≈ 0.25%), consistent with advanced ripening. In contrast, T5 (0.38%) and T6 (0.37%) retained the highest acidity values, suggesting a slower metabolic transition. Treatments T2 and T3 also maintained relatively high levels (0.35%–0.36%), while T1 and T4 showed intermediate values (0.33%–0.34%). According to Tukey’s HSD analysis, T5 and T6 formed a significantly distinct group from the control, confirming their effectiveness in preserving acidity during cold storage.

3.2.3. Soluble Solids

Soluble solids content, expressed in degrees Brix (°Brix), reflects the concentration of soluble sugars in the fruit and is closely associated with the ripening process. A rapid increase in °Brix typically indicates accelerated starch-to-sugar conversion, which may shorten the fruit’s shelf life. Figure 10 presents a comparative boxplot of all treatments, illustrating their effect on sugar accumulation and the modulation of ripening metabolism.

Significant differences (p < 0.05) were observed among treatments at the end of storage. The control group (T7) recorded the highest °Brix value (mean ≈ 20.6), indicative of advanced ripening and sugar accumulation. In contrast, treatments T5 and T6 showed the lowest values (≈17.1 and 17.5, respectively), suggesting a delay in the metabolic transition. Intermediate values were observed in treatments T1 to T4 (18.2–18.7). According to Tukey’s HSD test, T5 and T6 formed a statistically distinct cluster, demonstrating their effectiveness in modulating postharvest ripening.

4. Discussion

The results obtained in this study demonstrate that the application of edible coatings had a significant effect on preserving the physicochemical properties of Musa paradisiaca fruits during storage, in comparison to the untreated control. The coatings contributed to maintaining structural integrity and slowing down biochemical changes associated with ripening and senescence.

4.1. Physical Analysis

4.1.1. Weight Loss

All treatments showed progressive weight loss throughout storage. However, treatment T5 was the most effective, recording the lowest cumulative loss (9.4% ± 0.3), in contrast to the control (T7), which exhibited a significantly higher loss (22.8% ± 0.8).

The effectiveness of T5 is attributed to the synergistic combination of whey, agar, cassava starch, and glycerol. The film-forming properties of starch and agar contribute to the formation of an effective moisture barrier, while glycerol enhances the flexibility of the coating matrix without causing stickiness [37]. Whey contributes antimicrobial and antioxidant properties, which may reduce respiration rates and enhance fruit integrity. Conversely, coatings with excessive glycerol (e.g., T3 and T6) showed intermediate losses, suggesting that high plasticizer concentrations may weaken film structure and barrier capacity.

These findings are consistent with previous studies reporting that cassava starch–beeswax coatings reduced weight loss in papaya by 40% after 21 days of storage [38], and that chitosan–starch blends achieved similar reductions in banana weight loss to those observed in treatments T2 and T3 [9,39]. Additionally, significant mass loss reduction was observed in plums coated with pectin and essential oils, underscoring the potential of incorporating bioactive compounds to enhance coating functionality [40].

Statistical analysis confirmed a highly significant treatment effect (F = 190.71, p < 0.0001). T5 outperformed all other treatments in reducing water loss, due to its balanced composition of hydrophilic polymers and plasticizers, which produced a cohesive, semipermeable film that effectively regulated transpiration and gas exchange.

4.1.2. Fruit Dimensions

Structural parameters such as peel thickness and fruit length provide insights into tissue dehydration and shrinkage, which affect overall fruit integrity and postharvest quality [41].

ANOVA indicated highly significant effects of coating type on both peel thickness loss (F = 123.88, p < 0.0001) and length reduction (F = 84.66, p < 0.0001). Model assumptions were validated (Shapiro–Wilk and Levene’s tests), ensuring statistical robustness.

T5 preserved structure most effectively, with minimal peel thickness (4.9% ± 0.2) and length reduction (3.7% ± 0.2). The control (T7) showed the greatest contraction (10.3% ± 0.5 and 7.6% ± 0.4, respectively), with statistically significant differences.

This performance is attributed to the structural cohesion of the T5 matrix, formed by interactions among starch, agar, glycerol, and whey proteins, which reinforce the mechanical integrity of the coating and reduce cellular collapse during storage [39]. Comparable outcomes were reported in mangoes and litchis coated with polysaccharide- and protein-based films [38,42].

4.1.3. Firmness

Firmness, a quality attribute, declined in all treatments due to cell wall degradation and turgor loss. ANOVA revealed a significant treatment effect (F = 139.41, p < 0.0001), with assumptions satisfied (Shapiro–Wilk: p = 0.787; Levene: p = 0.775).

T5 maintained the highest firmness (15.2% ± 0.4 loss) versus T7 (28.7% ± 0.7), likely due to its ability to reduce enzymatic activity (e.g., pectinases) and water loss. The film also contributed to a stable microenvironment that mitigated senescence [43]. Overall, T5 proved highly effective in preserving tissue integrity and delaying softening, confirming its potential as a functional postharvest technology for tropical fruits [44,45].

Previous research supports these findings: coatings based on polysaccharides and proteins preserved firmness in strawberries and bananas [34,41]. Glycerol’s plasticizing effect likely helped prevent cracking, maintaining barrier function.

4.1.4. Color Parameters

The L* value, representing luminosity, declined in all treatments. Treatment T5 preserved brightness best (ΔL* = 5.5 ± 0.2), while T7 exhibited the greatest loss (ΔL* = 12.5 ± 0.5). ANOVA confirmed a significant effect (F = 152.28, p < 0.0001), with validated assumptions.

The reduced browning in T5-treated fruits may result from its oxygen-limiting film, which inhibits PPO activity and delays pigment oxidation [46]. These results are consistent with earlier studies using protein- and polysaccharide-based coatings to limit chromatic degradation [47,48].

Chromaticity a* (Δa*) also increased with storage, indicating browning. T5 again showed the smallest change (2.4 ± 0.2) versus T7 (5.4 ± 0.4), supporting its role in limiting enzymatic oxidation.

Chromaticity b* (Δb*) measures yellow intensity. T5 minimized its reduction (3.3 ± 0.2) compared to the control (6.9 ± 0.4), indicating better carotenoid preservation. Similar outcomes have been reported for tropical fruits like papaya and mango coated with biopolymers [42,47,49].

Together, these results confirm treatment T5 is effective in preserving visual attributes—for consumer acceptance and marketability.

4.2. Chemical Analysis

4.2.1. pH

This parameter serves as an indicator of the fruit’s physiological and microbiological condition during storage. A noticeable increase is typically associated with the degradation of organic acids and the onset of fermentative metabolic pathways linked to ripening [50].

One-way ANOVA revealed a highly significant effect of treatment on final pH values (F = 70.87, p < 0.0001). Model assumptions were validated by the Shapiro–Wilk test (W = 0.921, p = 0.090) and Levene’s test (F = 0.696, p = 0.657), confirming the robustness of the statistical approach. The T5 treatment exhibited the most stable pH, ending at 5.31 ± 0.01—closely aligned with its initial value of 5.20. In contrast, the uncoated control (T7) rose to 5.52 ± 0.02, indicating increased metabolic degradation.

These findings are consistent with previous studies reporting that edible coatings reduce pH shifts during storage by forming semipermeable barriers that limit gas exchange, thereby slowing acid loss and respiration [41,43]. The ability of T5 to maintain acid–base equilibrium reinforces its value in postharvest preservation.

4.2.2. Titratable Acidity

Closely tied to flavor and microbial stability, this parameter tends to decline as organic acids are consumed in respiratory processes and converted into volatiles during ripening.

Analysis of variance revealed highly significant differences among treatments (F = 29.11, p < 0.0001), with the Shapiro–Wilk test (W = 0.921, p = 0.090) and Levene’s test (F = 0.696, p = 0.657) confirming statistical assumptions. T5 showed the smallest reduction, with acidity decreasing from 0.45% to 0.39% citric acid. By contrast, the control group (T7) dropped from 0.38% to 0.25%, evidencing a higher degree of metabolic activity.

The previous literature supports these results. Fruits coated with starch, chitosan, or Aloe vera exhibited slower declines in acidity due to the restricted gas diffusion afforded by these biopolymers [34,41,43]. The preservation of organic acids in T5-treated fruits strengthens its profile as a coating capable of extending freshness and flavor retention.

4.2.3. Soluble Solids

The accumulation of soluble sugars during ripening is reflected in °Brix values, which increase as enzymatic hydrolysis transforms starch reserves into simple sugars.

Treatments differed significantly in their °Brix progression (F = 67.00, p < 0.0001). Statistical assumptions were validated (Shapiro–Wilk W = 0.946, p = 0.282; Levene F = 0.478, p = 0.814). While all treatments experienced increases over the storage period, T5 showed the most moderate rise, from 15.7 to 17.3 ± 0.2 °Brix. In contrast, the control (T7) reached 20.7 °Brix, indicating faster ripening and complete starch conversion.

These results align with previous studies where chitosan- or starch-based coatings delayed sugar accumulation and modulated the ripening rate by reducing respiration and restricting ethylene exposure [38,42]. The slower sugar conversion in T5 highlights its effectiveness in prolonging postharvest freshness.

4.3. Statistical Analysis

All evaluated physicochemical variables—including weight loss, firmness, structural integrity, color parameters, titratable acidity, pH, and soluble solids content (°Brix)—exhibited statistically significant differences among treatments (p < 0.0001), with treatment T5 consistently achieving superior performance across most parameters. This treatment minimized deterioration while maintaining internal biochemical stability, suggesting effective modulation of both metabolic and physiological processes.

The statistical analysis was validated through assumption checks: the Shapiro–Wilk test confirmed the normality of data distribution, and Levene’s test verified the homogeneity of variances among treatment groups.

Tukey’s HSD post hoc test (α = 0.05) further confirmed that treatment T5 differed significantly from the control (T7) in nearly all assessed variables. T5 was consistently grouped among the highest-performing treatments.

The enhanced performance of T5 can be attributed to its balanced composition of whey, agar, cassava starch, and glycerol. This formulation formed a cohesive and functional semipermeable barrier that reduced gas exchange, limited enzymatic degradation, and retained moisture content—thereby delaying the ripening process without compromising the overall fruit quality.

The results strongly support the use of treatment T5 as an effective and sustainable edible coating to extend the postharvest shelf life of bananas.

5. Conclusions

The findings of this study demonstrate that the application of edible coatings significantly enhances the postharvest preservation of bananas (Musa paradisiaca). Among the formulations tested, the treatment composed of 5 g of whey (16.7%), 5 g of agar (16.7%), 10 g of cassava starch (33.3%), and 10 g of glycerol (33.3%)—based on a total of 30 g of solids per liter of distilled water—proved to be the most effective in maintaining the physicochemical quality of the fruit.

This formulation notably reduced weight loss, preserved firmness, and minimized structural changes—such as peel thickness reduction and fruit length shrinkage—when compared to the uncoated control. It also contributed to better color retention (lower loss of luminosity and chromaticity), moderated the increase in pH and decline in titratable acidity, and limited the rise in total soluble solids (°Brix), all of which indicate a slower and more controlled ripening process.

Statistical analyses, including ANOVA and Tukey’s HSD post hoc test, confirmed that this formulation (referred to as T5) produced statistically significant differences across most evaluated variables. Its consistent performance highlights its efficacy in preserving the physicochemical properties of bananas during storage. These results support the use of this coating as a functional, sustainable, and low-impact postharvest strategy capable of extending shelf life without compromising sensory attributes or commercial value.

Further studies are needed to evaluate the performance of this coating under real-world postharvest storage and commercial distribution conditions. Future research should also include microbiological analyses and sensory evaluations to determine its potential to inhibit fungal and bacterial growth during storage. In addition, the incorporation of bioactive compounds could be explored to enhance their functional properties.