Composite Edible Coating from Arabic Gum and Mango Peel Hydrocolloids Enriched with Mango Seed Extracts for the Preservation of Grapes (Vitis vinifera) During Storage

Abstract

Composite edible coatings based on arabic gum with mango peel hydrocolloids and mango seed extracts were prepared and used to evaluate grape conservation. Hydroethanolic solutions were used for the obtention of mango seed extracts, by microwave-assisted extraction, with total phenolic compounds (5.48 and 9.85 GAE/g of extract) and antioxidant activity (<13.03 µmol Trolox/g of extract). The extracts were selected for the development of edible coatings. The rheological properties of edible coating solutions present a non-Newtonian behavior-type shear thinning fluid; the addition of extracts improves their viscoelastic properties, favoring their application into grapes. The coated grapes maintained physicochemical parameters, such as weight, pH, acidity, soluble solids, and color during the 15 days of storage. The results of this research offer the possibility of using by-products from fruit industries, especially mango, to obtain functional ingredients and their application in food systems, taking advantage of their biological activity.

1. Introduction

Grapes (Vitis vinifera) are a hard (perennial) and deciduous plant that grows in areas where the temperature is below the freezing point (winter temperatures). Their fruits are not climacteric [1], have a pleasant taste, and also provide several health benefits due to their phytochemical composition [2]. However, grapes (Vitis vinifera) are highly perishable after harvest and undergo several changes during storage, including a loss of firmness and color [3,4]. In this regard, post-harvest practices that aim to maintain the physicochemical composition during storage must be adopted; for example, the use of edible coatings can increase the shelf life of fruits.

Edible coatings aim to extend the useful life presented by food and help form a barrier against moisture, oxygen, and any other cause of deterioration [5]. These are made mainly from edible biopolymers that have film formation properties, such as proteins, carbohydrates, and lipids [6]. Protein-based solutions exhibit excellent barrier properties against oxygen, lipids, and aromas, high water vapor permeability, and moderate mechanical properties; collagen, whey protein, gelatin, corn zein, caseins, wheat gluten, soy protein, quinoa protein, egg white protein, and keratin are examples of proteins used to make this type of coating [7]. Carbohydrate-based solutions are colorless and have a fat-free appearance, and also present barrier properties, the most commonly used being starch, pectin, carrageenan, alginate, chitosan, arabic, and xanthan gum [8,9]. Lipids are excellent barriers against moisture migration [10] due to their low polarity, and they provide gloss and minimize the cost and complexity of packaging [11]; the most commonly used are beeswax, candelilla wax, carnauba wax, triglycerides, acetylated monoglycerides, free fatty acids, fatty alcohols, saccharose esters, and edible terpene resins [12,13]. The interest in coatings has been continuously increasing in research in the food industry, with coatings already applied to various fruits such as apples [14,15], mango [16], guava [17], banana [18], strawberries [19], and grapes [20,21,22]. In the case of arabic gum, it exhibits low flexibility due to strong intermolecular forces within the polymer chains [23]. It has good film formation, solubility, emulsification, and antioxidant activity. Previous studies have proven that the edible coating of arabic gum efficiently reduced post-harvest decay and conserved the general quality of eating of various horticultural crops. The application of an arabic gum coating has been reported in banana [14], guava [15], papaya [16], mango [17], persimmon [18], tomato [19], apricot [20], and mandarin [21].

In addition, composite edible coatings can then be created by mixing two or more of the components listed above [6] to minimize the disadvantages of each of them separately [22,23] and thus achieve the advantages of the good water barrier properties of lipid coatings and the ability to form cohesive films with good gas permeability properties and without the greasy texture of polysaccharides or proteins [23]. Furthermore, natural extracts have been added to improve coating properties, such as essential oils, plant extracts, herbs, and spices. Furthermore, the addition of essential oils and natural extracts still remain, since each polymer presents different properties for protection, viscosity, and adhesiveness that can affect its application on food matrices.

Natural plant extracts have been widely used in the food industry for decades as supplements or ingredients in food production. However, currently, there is an attempt to give their use greater relevance, seeking those plant extracts concentrated in biologically active substances, with the fundamental objective of designing ingredients, due to their antioxidant or antimicrobial, properties [24]. There are several examples of plant extracts authorized as food additives. For example, the use of rosemary extract (E329) obtained with different solvents and/or supercritical carbon dioxide, with a maximum permitted dose of 200 mg/kg or mg/L, is approved as an antioxidant in food formulation (EU Regulation No 1129/2011), or commercial tea made from guava leaves (Psidium guajava L.), authorized in the category of foods related to the prevention of blood sugar levels and recommended in pathologies such as pre-diabetes due to its polyphenol content [25].

The sources of plant extracts are very diverse, including plants, trees, shrubs, and herbs, as well as the parts of plant material from which they can be obtained (stems, seeds, fruits, leaves, roots), giving rise to extracts with very different compositions and therefore with biological activities that provide a wide field of applications. Mango (Mangifera indica) seed contain valuable nutrients such as vitamins (A, B, C, E, K), minerals (Ca, Fe, Mg, K, P), starch, amino acids and oil; also, many research studies confirm that mango seeds are an important source of phenolic compounds, such as xanthonoids, phenolic acids and flavonoids, which possess antioxidant and antimicrobial activities [26,27] with potential use for the development of edible coating alternatives. Furthermore, the use of agricultural waste materials, for the development of sustainable technologies, is convenient for the care of the environment, and the components of these wastes help to ensure food safety. On the basis of the above, the objective of this work was to develop edible coatings based on hydrocolloids from mango peel with the natural extracts of mango seeds and to evaluate their application for grape conservation (Vitis vinifera).

2. Materials and Methods

2.1. Chemicals

Arabic gum and citric acid were purchased from Tecnas SA (Medellín, Colombia). Ethanol (analytical grade, 99.5%) and hexane and glacial acetic acid (99.5%) were obtained from Panreac (Barcelona, Spain). Sodium hydroxide (NaOH) from EMSURE^® (Merck, Burlington, MA, USA). cetic acid, phenolphthalein, anhydrous sodium carbonate (99.5%), gallic acid standard (>98%), phenylmethyl siloxane (5%), Folin–Ciocalteu reagent, and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, ≥95%) were purchased from Sigma–Aldrich (St. Louis, MO, USA). All other reagents were analytical grade.

2.2. Materials

Mango (Mangifera indica) var. Tommy was purchased from the local market of Cartagena de Indias (Cartagena, Colombia) in a state of organoleptic maturity. All fruits were sanitized by immersion in a sodium hypochlorite solution (100 mg/L) for 10 min and then rinsed and dried with excess water. Peel, pulp, and seed were manually separated with stainless steel knives. Subsequently, the peel was lyophilized for 72 h using Labconco Freezone 1.5 L benchtop equipment. The seed was dried in an oven at 50 °C for 6 h. Subsequently, a reduction in particle size was made in an IKA MF 10.2 mill coupled with a sieve to obtain particle sizes smaller than 250 µm.

The grapes (Vitis vinifera) were purchased from a local market, without any conservation process prior to purchase. They were brought to the laboratory for experimental studies and were used immediately. Grapes were selected for uniformity of color, shape, and size and with the absence of physical defects or decay.

2.3. Obtention of Mango Peel Hydrocolloids

The extraction of mango peel hydrocolloids was carried out following the method described by Marsiglia et al. [28]. Mango peel powder and water in a 1:10 ratio as mixture for 4 h at 80 °C, adjusting at pH 3 using NaOH and acetic acid to solubilize the hydrocolloids. Subsequently, the mixture was filtrated and the filtrate was mixed with absolute ethanol at 5 °C to precipitate the hydrocolloids. The precipitate was dried and stored at 4 °C until used.

2.4. Obtention of Mango Seed Extracts

The mango seed extracts were obtained by microwave-assisted extraction, using the methods described by Quintana et al. [29], evaluating power (180, 360, and 540 W). Next, 1:10 peel/dissolvent (hydroethanolic solution (50% by weight water and 50% by weight ethanol)) ratio was mixed and subjected to microwave-assisted extraction for 3 min using intervals of 30 s. A total of three extracts were obtained. The extracts were stored at 4 °C until use.

2.5. Determination of Total Phenolic Content (TPC) and Antioxidant Activity

The total phenolic content (TPC) of the extracts obtained were determined using the Folin–Ciocalteu singleton method [30]. The antioxidant capacity by the ABTS+ radical scavenging assay following the method described by Re et al. [31], so the results were expressed as TEAC values (µmol of Trolox/g).

2.6. CG-MS Analysis

The identification and quantification of volatile compounds from samples was carried out following the procedures described by Quintana et al. [32], employing a GS-MS-FID 7890A system (Agilent Technologies, Santa Clara, USA) comprising a split/splitless injector, FID detector, and a triple axis mass spectrometer detector 5975C. An HP-5MS capillary column (30 m × 0.25 mm id and 0.25 µm phase thickness) was used. The chromatographic method starts with an initial temperature of 40 °C, then increases to 150 °C, at 3 °C/min, and is held at 150 °C for 10 min, then from 150 to 300 °C, at 6 °C/min, and finally is held at 300 °C for 1 min. A volume of 1 μL of samples was injected in split mode. Helium (99.99%) was employed as carrier gas (1 mL/min flow rate). The temperatures were 250 °C for injector, 230 °C for the mass spectrometer ion source, 280 °C for the interface, and 150 °C for quadrupole.

2.7. Preparation of Composite Edible Coating Solutions

The composite edible coating was prepared using arabic gum (1 %wt.), mango peel hydrocolloids (2.5 and 5.0 %wt.), and mango seed extracts (1 and 3 %wt.) following the procedures described by Ali et al. [33]. Briefly, mango peel hydrocolloids and arabic gum were dissolved in 200 mL of water by constant stirring at 80 °C for 2 h. Subsequently, glycerol was added as a plasticizer. Then, the mango seeds extracts were added by homogenizing using an Ultra Turrax (IKA digital T20 Ultra Turrax, Staufen,, Germany) at 7500 rpm for 3 min. A total of six formulations were obtained (

Table 1. Formulation of composite edible coating solutions based on mango peel hydrocolloid and mango seed extracts.

No.	Code Sample	Mango Peel Hydrocolloid %	Mango Seed Extracts %	Arabic Gum %	Chitosan %	Glycerol %
1.	F_MPH2.5_MSE0	2.5	0	1	1	1
2.	F_MPH2.5_MSE1	2.5	1	1	1	1
3.	F_MPH2.5_MSE3	2.5	3	1	1	1
4.	F_MPH5.0_MSE0	5.0	0	1	1	1
5.	F_MPH5.0_MSE1	5.0	1	1	1	1
6.	F_MPH5.0_MSE3	5.0	3	1	1	1

).

2.8. Rheological Analysis

The stationary and dynamic assays were performed following the methodology described by Mieles et al. [34] using a controlled stress rheometer (Modular Advanced Rheometer System Haake Mars 60, Thermo Fisher Scientific, Waltham, MA, USA), using a rough plate geometry of 35 mm in diameter and 1 mm in the gap to prevent wall slip effects. Each sample was equilibrated 600 s before the rheological test to ensure the same thermal and mechanical history for each sample.

The stationary viscous flow test was carried out at a temperature of 25 °C, with a shear rate range of 10⁻³ to 10³ s⁻¹. The experimental data were fitted to the Ostwald-de Waele model (Equation (1)):

$$\eta ={k\dot{\gamma }}^{n-1}$$

(1)

where $\eta$ is the apparent viscosity (Pa·s), $k$ is the consistence index, $\dot{\gamma }$ is the shear rate (s⁻¹), and n is the flux index.

A dynamic assay was performed. Initially, a stress sweep was performed at a frequency of 0.1, 1, and 10 Hz, applying an ascending series of stress values from 10⁻³ to 10³ Pa, to determine the range of linear viscoelasticity. Then, frequency sweeps were performed to obtain the mechanical spectrum by applying a stress value, within the linear viscoelastic range, in a frequency range between 10⁻² and 10² rad/s. The viscoelastic parameters obtained were storage modulus ($G^{\prime }$), loss modulus ($G^{″}$), phase angle tangent (Tanδ), and complex viscosity ($\left|\eta \right|$).

2.9. Application of the Coating to Grapes (Vitis vinifera) and Quality Parameters

Grapes (Vitis vinifera) were dipped in six edible coating formulations (Table 1) for 1 min. The fruits were then air dried, packaged in commercial corrugated boxes, and stored at 4.0 ± 0.5 °C. Uncoated grapes were used as a control. Twenty-five berries were used for each coating treatment and the experiments were performed in duplicate. The quality characteristics of the control and coated fruits were determined during storage.

2.9.1. Fungal Decay Percentage

The presence of mold growth was visually evaluated during storage time (15 days). Grapes with visible spoilage were considered to have decayed. The percentage of fungal decay was calculated using Equation (2):

$$\mathrm{F}\mathrm{u}\mathrm{n}\mathrm{g}\mathrm{a}\mathrm{l} \mathrm{d}\mathrm{e}\mathrm{c}\mathrm{a}\mathrm{y}\left(\%\right)={\displaystyle \frac{\mathrm{n}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{d}\mathrm{e}\mathrm{c}\mathrm{a}\mathrm{y}\mathrm{e}\mathrm{d} \mathrm{f}\mathrm{r}\mathrm{u}\mathrm{i}\mathrm{t}\mathrm{s}}{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l} \mathrm{n}\mathrm{u}\mathrm{m}\mathrm{b}\mathrm{e}\mathrm{r} \mathrm{o}\mathrm{f} \mathrm{f}\mathrm{r}\mathrm{u}\mathrm{i}\mathrm{t}\mathrm{s}}}\times 100$$

(2)

2.9.2. Determination of Weight Loss

The grapes were weighed immediately after coating and air drying. The weight was then monitored for 15 days after coating. The percentage of weight loss was calculated using Equation (3):

$$\mathrm{Weight} \mathrm{loss}\%={\displaystyle \frac{\mathrm{Initial} \mathrm{weight}-\mathrm{Final} \mathrm{weight}}{\mathrm{Initial} \mathrm{weight}}}\times 100$$

(3)

2.9.3. Determination of pH and Titratable Acidity

The pH was measured using a pH meter (Hanna HI 9124, Hanna Instruments Inc., Woonsocket, RI, EE. UU.). Titratable acidity was determined by titration of diluted grape juice (10 g fruit in 90 mL of distillated water) at pH 8.2 using 0.1 NaOH. The results were expressed as the percentage of tartaric acid (Equation (4)):

$$\mathrm{T}\mathrm{A}={\displaystyle \frac{\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{e} \mathrm{o}\mathrm{f} \mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\times 0.1\times 0.064}{\mathrm{f}\mathrm{r}\mathrm{u}\mathrm{i}\mathrm{t} \mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}}\times 100$$

(4)

2.9.4. Color Analysis

The variation in color of the coated fruit was evaluated by employing a Konika Minolta CR-20 colorimeter, Japan, following the procedures described by Mieles et al. [34]. Luminance (L*), red-green chromaticity (a*), and blue-yellow chromaticity was registered. The color change was calculated using Equation (5):

$$∆{\mathrm{E}}^{\mathrm{*}}={\left[{\left({∆\mathrm{L}}^{\mathrm{*}}\right)}^2+{\left({∆\mathrm{a}}^{\mathrm{*}}\right)}^2+{\left({∆\mathrm{b}}^{\mathrm{*}}\right)}^2\right]}^{0.5}$$

(5)

2.10. Statistical Analysis

The analysis was carried out in triplicate. The results were expressed as means with standard deviation. The results obtained were statistically analyzed by ANOVA, using the Statgraphics centurion version 16.1 software platform to determine statistically significant differences (p < 0.05) between samples.

3. Results

3.1. Results of Mango Seed Extracts

The natural extracts of mango seed (Mangifera indica) were obtained by microwave-assisted extraction (MAE), using hydroethanolic solvents, varying the power at 180 (MSE180), 360 (MSE360), and 540 W (MSE540). The extraction yield (g of extract/g of seed × 100), total phenolic compounds (mg GAE/g of extract), and antioxidant capacity (µmol Trolox/g of extract) of the natural extracts of mango seed extract are show in

Table 2. Extraction yield % (g of extract/g of seed × 100), total phenolic compounds (mg GAE/g of extract), and antioxidant capacity (µmol Trolox/g of extract) of the natural extracts of mango seed extract.

No.	Code Sample	Power W	Yield %	Total Phenolic Compounds mg GAE/g of Extract	Antioxidant Capacity µmol Trolox/g of Extract
1.	MSE180	180	25.20 ± 1.26 a	25,024.97 ± 937.21 a	404.94 ± 37.22 a
2.	MSE360	360	26.66 ± 1.33 a	24,640.14 ± 589.99 a	428.32 ± 45.07 a
3.	MSE540	540	20.40 ± 1.02 b	16,057.71 ± 625.76 b	425.21 ± 49.47 a

Data are the mean ± standard deviation. Different letters in the same column express statistically significant differences (p < 0.05).

.

3.2. Rheology of Edible Coating Solutions

Different coating-forming solutions were prepared using different percentages of mango peel hydrocolloids and mango peel extracts (MSE360) (Table 1). The flow curves of the coating solutions are shown in Figure 1.

The experimental data of the flow curve was fitted to the Power Law model (Equation (1)); the obtained results (

Table 3. Adjustment parameters of edible composite coating solutions based on arabic gum mango peel hydrocolloids and mango seed extracts (MSE360) in the Ostwald de Waele model.

Code Sample	k $\mathbf{P}\mathbf{a}·{\mathbf{s}}^{\mathbf{n}}$	$\mathbf{n}$	${\mathbf{R}}^2$
F_MPH2.5_MSE0	0.24 ± 0.01 a	0.7.8 ± 0.01 a	0.99
F_MPH2.5_MSE1	4.49 ± 0.03 b	0.55 ± 0.01 b	0.99
F_MPH2.5_MSE3	5.86 ± 0.12 c	0.47 ± 0.01 c	0.95
F_MPH5.0_MSE0	3.51 ± 0.07 d	0.68 ± 0.01 d	0.98
F_MPH5.0_MSE1	4.81 ± 0.02 e	0.57 ± 0.01 e	0.99
F_MPH5.0_MSE3	26.20 ± 0.19 f	0.50 ± 0.01 f	0.99

Data are the mean ± standard deviation. Different letters in the same column express statistically significant differences (p < 0.05).

) indicate that the values of the correlation coefficients were greater than 0.95 (R² ≥ 0.95), indicating a good fit of the experimental data.

Figure 2 shows loss ($G^{\prime }$) and storage ($G^{″}$) modulus as a function of angular frequency (rad·s⁻¹) of coating-forming solutions.

3.3. Application of Edible Coating Solution for the Preservation of Grapes (Vitis vinifera)

Six formulations were used, in which the percentage of hydrocolloids and natural extract of mango seed (Mangifera indica) was varied (Table 1), in addition to a control sample without the coating or extract. The samples with the formulations were stored at 4 °C for 15 days. The visual apparency of uncoated (control) and coated grapes (Vitis vinifera) with arabic gum, mango peel hydrocolloids, and mango seed extracts are shown in Figure 3.

The loss weight, pH, titratable acidity, and soluble solids of uncoated (control) grapes (Vitis vinifera) coated with arabic gum mango peel hydrocolloids and mango seed extracts are shown in Figure 3.

The color parameters a*, b*, L*, and ΔE of uncoated (control) and coated grapes (Vitis vinifera) with arabic gum mango peel hydrocolloids and mango seed extracts are presented in

Table 4. Color parameters of uncoated (control) and coated grapes (Vitis vinifera) with arabic gum mango peel hydrocolloids and mango seed extracts.

Code Sample	Day 0	Day 4	Day 8	Day 12	Day 15
a*
Control	1.70 ± 0.26 a	0.86 ± 0.05 ac	0.60 ± 0.30 ab	1.60 ± 0.40 ad	1.73 ± 0.20 ab
F_MPH2.5_MSE0	0.46 ± 0.05 de	1.00 ± 0.17 c	1.83 ± 0.23 d	1.96 ± 0.55 d	2.02 ± 0.17 b
F_MPH2.5_MSE1	1.30 ± 0.26 b	1.53 ± 0.25 d	2.10 ± 0.10 d	2.86 ± 0.37 e	0.96 ± 0.30 c
F_MPH2.5_MSE3	0.36 ± 0.05 e	0.66 ± 0.11 a	1.20 ± 0.02 c	1.40 ± 0.20 ab	1.56 ± 0.18 a
F_MPH5.0_MSE0	0.76 ± 0.05 c	0.78 ± 0.07 ac	0.86 ± 0.20 b	0.94 ± 0.05 b	0.98 ± 0.12 c
F_MPH5.0_MSE1	0.63 ± 0.05 cde	0.10 ± 0.00 b	0.43 ± 0.15 a	0.33 ± 0.05 c	0.26 ± 0.02 d
F_MPH5.0_MSE3	0.73 ± 0.15 cd	1.43 ± 0.30 d	0.70 ± 0.00 ab	1.40 ± 0.20 ab	0.33 ± 0.23 d
b*
Control	−2.13 ± 0.40 a	−1.23 ± 0.15 ab	−1.43 ± 0.25 a	−0.46 ± 0.05 a	−0.30 ± 0.10 ab
F_MPH2.5_MSE0	−0.96 ± 0.30 c	−0.90 ± 0.28 b	−0.73 ± 0.05 c	−0.15 ± 0.07 b	−0.13 ± 0.05 a
F_MPH2.5_MSE1	−1.33 ± 0.60 bc	−0.96 ± 0.57 ab	−1.00 ± 0.10 b	−1.30 ± 0.36 e	−1.20 ± 0.10 c
F_MPH2.5_MSE3	−1.50 ± 0.17 bc	−1.43 ± 0.20 a	−1.23 ± 0.11 ab	−0.56 ± 0.05 ac	−0.39 ± 0.04 b
F_MPH5.0_MSE0	−1.16 ± 0.05 bc	−1.40 ± 0.26 ab	−0.53 ± 0.11 cd	−0.96 ± 0.11 d	−1.02 ± 0.07 c
F_MPH5.0_MSE1	−1.40 ± 0.36 bc	−0.93 ± 0.23 ab	−1.23 ± 0.25 ab	−0.80 ± 0.17 cd	−0.30 ± 0.23 ab
F_MPH5.0_MSE3	−1.56 ± 0.15 ab	−0.93 ± 0.15 ab	−0.43 ± 0.15 d	−0.40 ± 0.17 ab	−0.37 ± 0.07 b
L*
Control	7.66 ± 0.11 ab	5.33 ± 0.05 a	5.56 ± 0.25 a	6.63 ± 0.11 a	9.23 ± 0.32 a
F_MPH2.5_MSE0	7.36 ± 0.15 a	11.70 ± 0.20 f	10.40 ± 0.36 e	9.66 ± 0.32 c	8.44 ± 0.21 c
F_MPH2.5_MSE1	9.20 ± 1.34 c	7.06 ± 0.47 b	8.36 ± 0.05 bc	8.40 ± 0.34 b	7.46 ± 0.32 d
F_MPH2.5_MSE3	8.43 ± 0.37 bc	9.50 ± 0.45 d	8.06 ± 0.05 b	7.06 ± 0.30 a	6.84 ± 0.22 e
F_MPH5.0_MSE0	8.50 ± 0.20 bc	8.70 ± 0.45 c	8.60 ± 0.26 c	8.30 ± 0.53 b	8.13 ± 0.21 c
F_MPH5.0_MSE1	11.26 ± 0.32 d	10.23 ± 0.20 e	9.73 ± 0.32 d	10.43 ± 0.15 d	11.2 ± 0.26 b
F_MPH5.0_MSE3	9.36 ± 0.20 c	11.83 ± 0.15 f	10.63 ± 0.25 e	10.33 ± 0.40 d	9.67 ± 0.34 a
$∆\mathrm{E}$
Control	-	2.63 ± 0.10 a	2.47 ± 0.09 ab	1.96 ± 0.08 c	2.41 ± 0.09 b
F_MPH2.5_MSE0	-	4.37 ± 0.17 a	3.34 ± 0.16 b	2.86 ± 0.13 c	2.07 ± 0.10 d
F_MPH2.5_MSE1	-	2.18 ± 0.08 a	1.20 ± 0.03 c	1.75 ± 0.05 b	1.77 ± 0.07 b
F_MPH2.5_MSE3	-	1.11 ± 0.03 a	0.95 ± 0.02 b	1.96 ± 0.06 c	2.28 ± 0.08 d
F_MPH5.0_MSE0	-	0.31 ± 0.01 a	0.64 ± 0.02 b	0.33 ± 0.01 a	0.45 ± 0.01 c
F_MPH5.0_MSE1	-	1.25 ± 0.03 a	1.55 ± 0.05 b	1.06 ± 0.04 c	1.16 ± 0.03 d
F_MPH5.0_MSE3	-	2.64 ± 0.08 a	1.70 ± 0.06 b	1.65 ± 0.05 b	1.29 ± 0.04 c

Data are the mean ± standard deviation. Different letters in the same column express statistically significant differences (p < 0.05).

.

4. Discussion

4.1. Mango Seed Extracts

The extracts obtained have a visual appearance of granular powder with a brown color. The extraction yields of the natural extracts of mango seed (Mangifera indica) were 25.20 ± 1.26, 26.66 ± 1.33, and 20.40 ± 1.02 for MSE180, MSE360, and MSE540, respectively (Table 2), decreasing with the power applied (p > 0.05) associated with interaction of compounds with the other biomolecules present in the mango seed, such as carbohydrates, lipids, and proteins, attributed to the fact that the irradiation power is influenced by the ionic condition and the dielectric properties of the solvent, increasing molecular movements and temperature [35].

4.1.1. Total Phenolic Compounds and Antioxidant Capacity

The total phenolic compound (TPC) content of the mango seed extracts presents values of 25,024.97 ± 937.21, 24,640.14 ± 589.99, and 16,057.71 ± 625.76 mg GAE/g of extract for MSE180, MSE360, and MSE540, respectively (Table 1), evidencing a decrease (p < 0.05) in the power employed in relation to the irradiation process and an accumulation of heat produced in the solvent due to the absorption of microwave energy, which is channeled toward the cell matrix, increasing intermolecular interactions, causing the faster mass transfer from inside the cell to the solution. The results obtained are higher compared to other mango seed extracts; that is, Martinez-Olivo et al. [36] obtained the natural extracts of the Ataulfo mango seed variety, with ultrasound-assisted extraction, resulting in 6568.61 ± 406.91 mg GAE/g of extract; and Abdel et al. [37] achieved TPC values of 21.97 mg GAE/100 g using conventional methods in mango seed, and similarly for Pereira-Farias et al. [38]. Found a total phenolic content of 95.50 mg GAE/100 g for an ethanolic extract of mango seed.

The mango seed extracts have TEAC values of 404.94 ± 37.22, 428.32 ± 45.07, and 425.21 ± 49.47 µmol Trolox/g of extract for MSE180, MSE360, and MSE540, respectively (Table 3). Then, extraction with hydroethanolic solvents led to the extraction of more bioactive compounds from the internal organelles of the sample, and the polarity of the solvent plays an important role in solubilization. Different investigations have reported that using this type of mixture as a solvent allows the solubilization of hydrophobic and hydrophilic compounds, allowing a higher concentration of phenolic and non-phenolic compounds in the extracts, resulting in greater antioxidant activity [39,40,41]. The results obtained from the mango seed extracts are lower than those by Pereira Farias et al. [38] for the ethanolic extract (518.68 μmol TEAC/g), and higher than those of Bernal et al. [42] for the hydroethanolic (7:3, ethanol/water) (4205.7 ± 13.15 μmol TEAC/g). These differences are due to the fact that the level of synthesis of secondary metabolites and their properties vary between extraction conditions, species, and mango varieties. Therefore, all mango seed extracts showed a great response to stabilize the ABTS radical, which presents a great antioxidant activity, which can be used in the development of innovative foods, in the preparation of coatings and edible films with bioactive activity.

4.1.2. CG-MS

The identification of compounds allows for a better understanding of the potential bioactive and functional properties of mango (Mangifera indica) seeds. A chromatographic analysis of mango seed extracts with higher antioxidant activity (MSE360) revealed the presence of some compounds with bioactive properties, such as diethyl phthalate (6.22%), hexadecanoic acid (2.51%), methyl ester, and octadecanoic acid. Its presence in the natural extracts of mango seeds may be associated with the lipid content of the seeds; diethyl phthalate is commonly used in industrial and pharmaceutical applications, where the presence of this compound in the aqueous extract of mango leaves has been reported [43]; similarly, hexadecanoic acid and methyl ester have been reported to be present in various food matrices, including the natural extracts of mango seeds of Egyptian and Indian origin [44,45], and octadecanoic acid is expected due to its lipid content and has been reported in mango extracts and seeds [46].

In addition, mango seed is considered an important source of polyphenols with antioxidant capacity; some identified compounds may have functional and health properties; for example, the fatty acids present may have beneficial effects on cardiovascular health and metabolism regulation [47].

4.2. Rheological Properties of Edible Coating Solution

Different film-forming solutions were prepared using different percentages of mango peel hydrocolloids and mango peel extracts (MSE360) (Table 1). The rheological characteristics of the coating solutions play a fundamental role, since they affect the structure and apparent viscosity of the film to be formed. The uniformity, spreadability, and thickness of the coating can be strongly influenced by the flow properties of the solution used [48].

4.2.1. Stationary Behavior

Figure 1 shows the flow curve of different prepared edible coating solutions. All samples show a decrease in viscosity as a function of the shear rate characteristic of the non-Newtonian fluid-type shear thinning, indicating that the structures of the polymer chains in the system were destroyed and the molecular chains aligned in the direction of the shear force [49]; similar behavior has been observed in coatings composed of fish gelatin and bitter almond gum [50] and edible coatings composed of cellulose, pectin, and blackberry pomace [51].

Similarly, the experimental data of the flow curve were fitted to the Power Law model (Equation (1)); the results obtained (Table 3) indicate that the values of the correlation coefficients were greater than 0.95 (R² ≥ 0.95), indicating a good fit of the experimental data. The behavior of the shear-thinning fluid was confirmed, since all samples of the film-forming solution had flow index (n) values lower than 1. This behavior is the most common in this type of fluid, which will allow the performing of successful unit operations such as pump and fill [51]. Then, a variation in n vas was observed, when the percentage of hydrocolloids and extracts increased (p < 0.05) due to the reduction in intermolecular interactions with high concentrations of extracts, as observed at low shear rates. The values of k ranged from 0.24 to 26.20 Pa.sⁿ, increasing with the percentage of hydrocolloids (p < 0.05) attributed to the ability of the hydrocolloids to increase viscosity at higher concentrations. Furthermore, a similar behavior was observed for extracts (p < 0.05), associated with an improvement in resistance to entanglements in the polymeric matrix [52]. Silva-Weiss et al. [53] have reported similar behaviors for film-forming solutions based on hydro colloids from extracts from ant murta leaves, Cofelice et al. [54] for dispersions of essential oils of alginate, and Vigilato-Rodrigues et al. [52] for the extracts of an edible coating solution of grape and jaboticaba peel, when phenolic extracts influence the flow parameters.

4.2.2. Dynamic Behavior

To determine the linear viscoelastic zone of the coating-forming solutions, stress sweep tests were performed at a temperature of 25 °C in a range of 0.01 to 1000 Pa, at a constant frequency of 1 Hz, where a stress of 1 Pa was established in the linear viscoelastic range, enabling frequency tests to be performed from 0.1 to 100 Hz at a temperature of 25 °C, and providing information on the structure (elastic or viscous material) and the stability of the material at rest and during transport [55].

Figure 2 shows the loss ($G^{\prime }$) and storage ($G^{″}$) modulus as a function of angular frequency (rad/s). $G^{\prime }$ and $G^{″}$ increase proportionally to frequency, showing a strong dependence on angular frequency, characteristic of the formation of entanglements in the network of polymeric components that consolidate the structure [56]. For the control sample (F_MPH2.5_MSE0), $G^{\prime }$ was higher than $G^{″}$ at a low frequency, followed by a crossover at $\approx$ 30 rad/s and an inverse crossover frequency, indicating the elasticity of these fluids; then, the addition of mango peel extracts modified the behavior when $G^{\prime }$ was slightly lower than $G^{″}$. In all cases, improving the elastic properties is a characteristic of a network system of intertwined macromolecules: molecular rearrangements are feasible, which gives these results at a low frequency [57]; as the frequency increased, a crossover was evidenced between $G^{\prime }$ and $G^{″}$, known as the crossing point ($G^{\prime }$ = $G^{″}$), in this case indicating that as the frequency increases, the lattice structure becomes more rigid and dense. This may be due to phenomena such as the aggregation of molecules, formation of hydrogen bonds, polymerization, and gelation. This greater rigidity in the lattice structure hampers the ability of the solution to store elastic energy, which is reflected in an increase in the loss modulus $G^{\prime }$ [55]. Therefore, at a high frequency, $G^{″}$ was observed more than $G^{\prime }$; similar behaviors have been observed in film-forming solutions based on different mixtures of hydrocolloids [53], in film-forming solutions composed of banana flour and hydrocolloids [58], and in a gel emulsion made from whey protein isolate and xanthan gum enriched with curcumin [59], suggesting that the extract used modifies the viscoelastic properties of film formation solutions.

4.3. Application of Edible Coating Solution for the Preservation of Grapes (Vitis vinifera)

Six formulations were used, in which the percentage of hydrocolloids and natural extracts of mango seed (Mangifera indica) was varied (Table 2), in addition to a control sample without coating or extract. The samples with the formulations were stored at 4 °C for 15 days.

4.3.1. Physicochemical Properties

The coated grapes showed a slightly darker color than the uncoated samples (control); however, the coated grapes felt bright and uniform in appearance. The formation of the coating in grapes depends on the rheological parameters of the coating solutions, which present different shear stress and viscoelastic properties. The amount of coating solution adhered to grapes during application strongly depends on the viscosity and surface tension of the coating solutions. Some authors determined that solutions with high viscosity and low surface tension promote a better film-forming surface [60]. In this study, F_MPH2.5_MSE0 presents the lower viscosity values, and the coating with extracts (F_MPH2.5_MSE1, F_MPH2.5_MSE3, F_MPH5.0_MSE0 F_MPH5.0_MSE1, and F_MPH5.0_MSE3) was higher; the viscoelastic properties were also improved, which allowed better surface extensibility in berries, forming thinning coatings with higher uniformity and adherence, which can be associated with the better physical appearance observed (Figure 3).

The efficacy of edible hydrocolloid coatings of mango peels with seed extracts was visually evaluated to verify their effect on the inhibition of molds and fungi in grapes. All coated samples visually showed better conservation appearance conditions, compared to the control sample, which had a greater deterioration, which could be evidenced from day 8 with a lower visual quality and with the presence of mold from day 12. As can be seen in Figure 3, F_MPH2.5_MSE3 and F_MPH5.0_MSE3 presented the best visual appearance and conservation results during all storage days.

4.3.2. Loss of Weight

Weight loss in fruits and vegetables is generally considered an important parameter to assess post-harvest quality and freshness in storage and is mainly due to the loss of water through respiration and transpiration processes [61]. The percentages of weight loss of grapes were in the range of 0.11 to 5.53%, as shown in Figure 3a; these values are slightly lower than those reported by Kantetis et al. [62] for the case of grapes with a chitosan coating incorporated with extracts of Salvia fruticosa Mill, which were between 0.38 and 9.05%. Regardless of the different coating treatments, the weight loss of the grapes increased in all coated and uncoated grapes with the storage time. This phenomenon was more evident on day 15, which had the highest weight loss values and was associated with an increase in the metabolic activity of the fruit [63]. Furthermore, weight loss was more noticeable in uncoated grapes (control), while coated grapes provided significant barrier properties to the fruit. Grapes containing the formulations F_MPH5.0_MSE0 and F_MPH5.0_MSE3 decreased approximately 43 to 45% in weight compared to the control formulation during storage time.

Samples with a higher percentage of hydrocolloids (F_MPH5.0_MSE0, F_MPH5.0_MSE1, and F_MPH5.0_MSE3) had lower weight loss values, and then the increase in hydrocolloids in edible coatings reduced the transfer of moisture, by producing a more resistant layer on the surface of the fruit. Similar behaviors have been observed in edible coatings for fruits with formulations of other hydrocolloids such as low methoxyl pectin, carboxymethylcellulose, persian gum, chitosan, and gum tragacanth [64,65]. Then, samples with a higher percentage of extracts (F_MPH2.5_MSE3 and F_MPH5.0_MSE3) showed lower weight loss values compared to samples that did not contain natural extracts (F_MPH2.5_MSE0 and F_MPH5.0_MSE0), this is due to the fact that natural extracts are hydrophobic in nature and their incorporation into edible coatings can control and reduce the respiration of fruits and with it the transpiration, moisture loss, and other processes that affect and influence weight loss. The results observed in this study are consistent with those reported by Hosseini et al. [66], who prepared edible coatings with the addition of savory and/or tarragon essential oils, applied to the fruits of kumquat and Tesfay and Magwaza [67], who designed edible coatings based on chitosan and CMC, with the addition of moringa leaf extract, applied to avocado fruit (Persea americana Mill.)

4.3.3. pH and Titratable Acidity (TA)

Acidity is an important parameter for determining the maturity and flavor of fruit. The pH values of the coated grapes were higher during storage days, compared to the uncoated (control) (p > 0.05), as shown in Figure 3b. An increase in pH values with respect to storage time was observed for all samples, except for formulations that contained 5% hydrocolloids and extracts of 1%–3% (F_MPH5.0_MSE1 and F_MPH5.0_MSE3); therefore, it can be inferred that the content of hydrocolloids in edible coatings can affect pH values. Quintana-Martinez et al. [29] applied edible chitosan coatings to strawberries with the incorporation of Licorice extract, and Vieria et al. [68] applied edible chitosan coatings to blueberry fruits and aloe vera extracts. In general, the application of coatings with natural extracts delays the increase in pH, which decreases the effect of ripening on the fruit as a result of the consumption of organic acids.

Ripening produces an enzymatic reaction of the sugars and the amounts of acids present tend to decrease; it is also one of the factors that helps determine the shape and storage time [69]. TA values are observed in Figure 3b. These values oscillate between 6.37 and 1.53% of tartaric acid; in general, TA values decreased as storage time elapsed, which can be attributed to the increase in ethylene production and respiration rate during the ripening process [70]. The control sample had a slightly greater decrease in titratable acidity than that of the coated grape formulations; the grapes coated with the formulations, which contained 2.5% and 5% hydrocolloids, respectively, and a natural mango seed extract value of 1% (F_MPH2.5_MSE1 and F_MPH5.0_MSE1), had fewer changes in acidity values; this indicates that the application of coatings on the surface of the grape significantly reduces the loss of organic acids (p < 0.05) and helps the grape maintain a higher acidity content, which could be attributed to elimination of the oxidative reduction process of organic acids [71]. Furthermore, edible coatings have played a positive role in delaying the ripening and senescence processes of the fruit and therefore a greater retention of acidity in the coated fruit as demonstrated by Elanany et al. [72] in apples coated with edible coatings based on soy gum and guava fruits with edible coatings based on chitosan [64].

4.3.4. Soluble Solids

Soluble solids are directly related to the maturity state in fruits [73]; they are responsible for providing sweetness and palatability, which can influence consumer preference, since it is related to the pleasure experienced when eating a fruit [74]. Therefore, strategies that maintain this quality parameter at an adequate level are necessary, as is the case with edible coatings and/or films. In the present study, all samples showed a significant increase (p < 0.05) in the soluble solids content compared to the storage days (Figure 3d). This is mainly due to the fact that during storage fresh fruits can lose moisture content and possibly also due to the conversion of complex organic metabolites (polysaccharides) into simple molecules or the hydrolysis of starch into sugar [75,76]. The previous application of the coatings on the surface of the grapes positively influenced the decomposition of complex sugars or starch and delayed the increase in the concentration of TSS in the grapes during the storage period analyzed. Therefore, it can be inferred that the coatings retarded the metabolic and respiratory process of the grape; therefore, the ripening and senescence process of the fruit was slower. Similar results have been found in the preservation of mandarins with an edible coating made of guar gum and chitosan [75] and in the preservation of blueberries with edible coatings based on carboxymethylcellulose, xanthan gum, guar gum, and acacia gum [77].

4.3.5. Color Properties

Color is one of the most characteristic and important characteristics of food products, especially fruit, and this is a key quality indicator of consumer preference [78]. In the case of grape fruits, coloring occurs during the ripening process, since there is a loss of chlorophyll that gives rise to the final dyes that form the characteristic color of these, this process begins at veraison, which is the beginning of ripening, when the color of the grape changes, this being the beginning of the transition between the growth of the berries and the ripening of the grapes [79]. A colorimetric analysis was carried out in the color plane (a* and b*) in the CIELAB space, as well as a representation of the L* values, which are defined as the luminosity of a sample, a visual sensation attribute according to which a given visual stimulus appears to be more or less clear. The L* values for the grape samples coated in each formulation did not have a significant variation (p < 0.05), with the exception of the control sample, as shown in Table 4. The control sample was observed to have a variation in luminosity on day 4 of 5.33 ± 0.05 and on day 15 of 9.23 ± 0.32. The results showed that the edible coatings retained the natural color of the grapes throughout the storage time. When the values of the coated grapes were compared with those of the control sample, it was evident that they had a higher luminosity, indicating that the untreated grapes showed a darker color than the others. Other authors have found results that coincide with these, for strawberries with edible coatings based on chitosan-oleic acid and alginate [80,81], and in Brazilian grapes [82].

The values of a* and b* were also determined, which correspond to the two coordinates of the field, where a* takes positive values for reddish colors and negative values for greenish colors, and b* takes positive values for yellowish colors and negative values for bluish colors [83]. Values of a* were obtained for all samples (Table 4); that is, the coated grapes were characterized by being more red. Compared to green, this color is associated with the content of anthocyanins present in the skin of the grape, which provides the characteristic color of this fruit [84]. The values were maintained during storage time for all formulations in which the highest values were obtained from the control samples and F2.5-0 samples. On the other hand, the values of b* were negative and increased with the storage time for all samples (Table 4), indicating that they were more blue than yellow; however, the results show that the percentage of yellow color increased as a function of days of storage. Similar results have been found for different varieties of grapes, such as Figueiredo-González et al., and Serratosa et al., [85,86]. Finally, the total color variation in the coated grapes was determined using Equation (4), as shown in Table 4. The ΔE values on day 4 were significantly (p < 0.05) higher than on the other days of storage; however, the high levels of hydrocolloids (5.0%) and natural extracts allowed the grapes to maintain their color. Initially and in general, the values of L* a* and b* corroborated that the edible coatings had a positive impact on color preservation compared to the control sample.

5. Conclusions

The microwave-assisted extraction method proved to be effective for the extraction of natural extracts of mango seed (Mangifera indica), showing extraction yields greater than 17%. The biological activity of the mango seed extracts presented considerable TPC and TEAC values, and compounds such as diethyl phthalate, hexadecanoic acid, methyl ester, and 9, 12 octadecanoic acid, where MSE360 has a higher antioxidant capacity and was chosen for the development of edible coatings. The composite edible coating solutions showed a non-Newtonian behavior-type shear-thinning fluid, which could be described by the Power Law or the Ostwald-de Waele model (R² ≥ 0.95). Their viscoelastic behavior changes with the addition of mango peel extracts, presenting a good mixture and stable intertwining in solution with the mango peel hydrocolloids. The coating-forming solutions were successfully applied to the grapes (Vitis vinifera), showing a uniform visual appearance with good compatibility. The coated grapes maintained physicochemical parameters, such as weight, pH, acidity, soluble solids, and color throughout storage (15 days), compared to the uncoated grapes. Finally, the results of this research offer the possibility of taking advantage of by-products from fruit industries, especially mango, to obtain functional ingredients and their application in food systems, taking advantage of their biological activity, and presenting new alternatives to the use of polluting non-biodegradable materials for the environment.