Development of a plant-based edible coating for extending the post-harvest shelf life and maintaining the quality of mango fruits

Introduction

Mango (Mangifera indica L.) is among the most economically significant tropical fruits globally, ranked third in worldwide tropical fruit production with over 55 million tonnes harvested annually. In Kenya and East Africa broadly, mango serves dual roles as a major income-generating horticultural crop for smallholder farmers and as a nutrient-dense food rich in vitamins A and C, beta-carotene, and dietary fibre ; however, the highly perishable nature of mango fruits attributable to their climacteric ripening behaviour, high respiratory activity, and susceptibility to fungal pathogens results in post-harvest losses of 20-40% between farm-gate and retail markets across sub-Saharan Africa. These losses translate to an estimated annual economic loss of USD 10-14 billion for tropical fruit producers in developing regions, disproportionately affecting smallholder growers who lack access to cold chain storage and professional packaging infrastructure. Chemical preservatives including fungicides (thiabendazole, imazalil), wax coatings (carnauba, shellac), and surface treatments (ethylene inhibitors, sulfur dioxide) have been widely used in commercial post-harvest management but face increasing regulatory restrictions in export markets due to concerns over residue toxicity, environmental persistence, and consumer health risks. There is consequently a pressing need for safe, effective, affordable, and biodegradable alternatives that can extend mango shelf life while maintaining nutritional and sensory quality. Edible coatings composed of plant-derived International Journal of Agriculture and Food Science https://www.agriculturaljournals.com biopolymers and bioactive extracts have emerged as a scientifically promising post-harvest technology, functioning by creating a semi-permeable physical barrier on the fruit surface that modulates gaseous exchange, reduces transpirational water loss, suppresses microbial surface contamination, and retards enzymatic browning and ripening processes. Among plant-derived coating materials, aloe vera gel (Aloe barbadensis Miller) has attracted considerable research attention owing to its natural antimicrobial compounds (acemannan, aloin, anthraquinones), film-forming polysaccharides, and proven efficacy in delaying climacteric fruit ripening. Moringa (Moringa oleifera) leaf extract contains isothiocyanates, quercetin, and pterygospermin with documented antifungal activity relevant to post-harvest pathogen suppression. Cassava starch-based coatings provide excellent gas-barrier properties and have been combined with plant extracts to enhance their antimicrobial and antioxidant performance. Despite individual reports on each of these materials, direct comparative evaluations of their post-harvest efficacy for East African mango varieties under ambient storage conditions remain limited, creating a practical knowledge gap that impedes adoption by smallholder value chain actors. The present study was therefore designed to develop and comparatively evaluate three plant-based edible coatings (aloe vera gel, moringa leaf extract, and cassava starch composite) for their effectiveness in extending shelf life and maintaining the physicochemical, nutritional, and microbiological quality of 'Apple' mango stored at ambient temperature, hypothesizing that the composite cassava starch-based coating incorporating bioactive plant extracts would provide superior and multi-parametric quality preservation compared to single-source plant coatings and the uncoated control.

Materials and Methods

Materials

Mature-green 'Apple' mango (Mangifera indica L.) fruits at physiological maturity (determined by skin colour change from dark green to light green and starch-iodine index ≥7) were harvested from a commercial orchard in Makueni County, Kenya. Fruits were selected to be uniform in size (300-350 g), free from physical injury and disease, and washed with clean water. Aloe vera (Aloe barbadensis Miller) gel was freshly extracted from mature inner leaf fillet by centrifugation (5,000 × g, 15 min), filtered through a 0.45 μm membrane, and heated to 60 °C for 5 min for pathogen inactivation. Moringa leaf extract (MLE) was prepared by blending fresh moringa leaves in 70% ethanol (1:10 w/v) followed by filtering and rotary evaporation to yield a 20 mg mL⁻¹ stock concentration. Cassava starch (5% w/v) was gelatinized in distilled water at 85 °C for 15 min, cooled, and supplemented with 0.5% glycerol (plasticizer), 1.0% MLE (antimicrobial component), and 0.5% citric acid (pH adjustment and antioxidant stabilizer) to form the composite cassava starch coating (CSC). All reagents used for physicochemical analysis were of analytical grade (Sigma-Aldrich, Germany). Microbiological media (PDA, NA) were obtained from Oxoid Ltd. (Basingstoke, UK). A CR-400 Chroma Meter (Konica Minolta) was used for colour measurements; a texture analyser (TA.XTplus, Stable Micro Systems, UK) with a 3 mm cylindrical probe was used for firmness assessment.

Methods

The experiment was set up in a completely randomized design (CRD) with four treatments: CT (uncoated control), AVG (aloe vera gel coating), MLE (moringa leaf extract coating, 20 mg mL⁻¹), and CSC (cassava starch composite coating), each replicated three times using five fruits per experimental unit (60 fruits total per treatment). Fruits were dip-coated for 60 s in each coating solution, air-dried at room temperature for 30 min to allow film formation, then stored at ambient conditions (25 ± 2 °C, 65 ± 5% relative humidity) in ventilated plastic crates. Control fruits were dipped in distilled water for 60 s. Quality assessments were conducted at 3-day intervals from day 0 to day 21. Physiological weight loss (PWL, %) was calculated from initial and sampling-day fresh masses. Fruit firmness was measured by a texture analyser at three equatorial points per fruit. Total soluble solids (TSS, °Brix) were determined by hand refractometer (ATAGO PAL-1, Japan) on expressed juice. Titratable acidity (TA) was measured by NaOH (0.1 M) titration. Ascorbic acid (vitamin C) was determined by 2,6-dichlorophenolindophenol (DCPIP) titrimetric method. Peel colour (L*, a*, b*) was measured at four positions per fruit using the Chroma Meter. Total aerobic plate count (APC) and total fungal count (TFC) were determined by serial dilution and plating on nutrient agar and potato dextrose agar (PDA), respectively, followed by 48 h incubation at 28 °C. Overall sensory quality (colour, aroma, texture, taste, overall acceptability) was evaluated by a trained 10-member sensory panel using a 9-point hedonic scale (9 = like extremely; 1 = dislike extremely); acceptability threshold was set at 5.0. All data were subjected to one-way ANOVA and Tukey's HSD test (α = 0.05) at each sampling day using SPSS Statistics v.28 (IBM Corp., Armonk, NY, USA). Repeated measures ANOVA was applied to assess treatment × storage time interactions for weight loss, firmness, and TSS. The CSC treatment was most effective in retarding physiological weight loss, fungal damage and textural softening throughout the 21-day storage period (Table 1). Cumulative weight loss in CSC-coated fruits (8.6% at day 21) was 61.6% lower than the uncoated control (22.4%), while AVG (16.4%) and MLE (15.8%) coatings achieved intermediate but significant reductions compared with CT. The semi-permeable film barrier created by the cassava starch composite effectively reduced transpirational water vapour flux while retaining the selective gas permeability necessary to prevent the build-up of anaerobic conditions. CSC-coated fruits retained significantly higher firmness (3.8 N at day 21) compared with AVG (2.4 N), MLE (2.8 N), and CT (1.2 N), reflecting the coating's capacity to retard cell wall pectin demethylation and depolymerization associated with ethylene-driven ripening. The higher L* and lower a* values in CSC-coated fruits at day 14 indicated delayed chlorophyll degradation and retarded carotenoid development, consistent with modified internal atmosphere effects. The rate of TSS accumulation indicative of starch conversion to soluble sugars during ripening was significantly suppressed in all coated treatments relative to CT throughout storage (Table 2). At day 21, CSC-coated fruits had TSS of 16.8°Brix versus 23.4°Brix in CT, reflecting a 28.2% delay in ripening progression attributable to reduced gas exchange and ethylene synthesis within the coated fruit. Titratable acidity declined significantly faster in CT (0.28% at day 14) compared with CSC (0.54% at day 14), confirming that organic acid catabolism as a substrate for respiration was slowed by coating-mediated atmosphere modification. Ascorbic acid retention was significantly highest in CSC (31.4 mg 100 g⁻¹ at day 21), representing 73.4% of the initial content versus only 43.5% in CT, consistent with the antioxidant capacity of citric acid in the composite coating and reduced surface oxidative reactions under the film barrier. Microbial proliferation was significantly suppressed in all coated treatments relative to CT across all sampling days (Table 3). The CSC treatment was most effective, maintaining APC at 3.4 log₁₀ CFU g⁻¹ at day 21 below the maximum acceptable limit of 5.0 log₁₀ CFU g⁻¹ while CT exceeded this threshold by day 14 (5.1 log₁₀ CFU g⁻¹). The antifungal efficacy of MLE coating was attributable to the isothiocyanate and quercetin compounds in moringa leaf extract, which disrupt fungal cell membrane integrity. The CSC coating achieved the lowest TFC throughout storage (2.1 log₁₀ CFU g⁻¹ at day 21), compared with MLE (3.0), AVG (3.4), and CT (4.6), confirming that the composite formulation synergistically combined the physical barrier effect of cassava starch with the antimicrobial activity of both MLE and citric acid.

Results

Discussion

The marked superiority of the cassava starch composite coating (CSC) across all physicochemical, nutritional, and microbiological quality parameters throughout the 21-day storage period is consistent with the general principle that composite coatings incorporating complementary filmforming, plasticizing, antimicrobial, and antioxidant components achieve superior performance compared to single-component coatings. The exceptional weight loss reduction in CSC-coated fruits (8.6% at day 21) compared to CT (22.4%) reflects the dense semi-permeable film formed by gelatinized cassava starch at 5% concentration, which substantially reduces the water vapour transmission rate while maintaining sufficient O₂/CO₂ selectivity to avoid anaerobiosis. These values are in close agreement with Perdones et al., who reported 60-65% reductions in weight loss of strawberry fruits coated with chitosan-based composite coatings incorporating citrus essential oils, though our study extends these findings to tropical climacteric fruits under warm ambient conditions representative of East African market environments. The significantly higher firmness retention in coated fruits is primarily attributed to coating-mediated reduction of ethylene biosynthesis through modified internal atmosphere modification, as reduced O₂ and elevated CO₂ under the film suppress 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and consequent ethylene production, thereby retarding polygalacturonase (PG) and pectin methylesterase (PME) activity responsible for cell wall softening.

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