Use of Aloe Vera Gel-Based Edible Coating with Natural Anti-Browning and Anti-Oxidant Additives to Improve Post-Harvest Quality of Fresh-Cut ‘Fuji’ Apple

: Recently, there is increasing use of edible and biodegradable ﬁlms and packaging that are both environmentally friendly and functional for storage and market distribution. Fresh-cut ‘Fuji’ apples, harvested in an organic farm, were treated, using a spraying technique, with three new edible coatings based on Aloe vera gel (AVG—40% v / w ) and in combination with natural additives: lemon essential oil (LEO—1% v / w ) and hydroxypropyl methylcellulose (HPMC—0.1% v / w ) and compared with untreated sample (CTR), the physicochemical and sensory characteristics and the proximate compounds were evaluated. During cold storage, weight loss, soluble solids content, and color of uncoated slices were reduced, while softening, ripening, browning, and acidity were accelerated. In contrast, the AVG / HPMC treatment signiﬁcantly delayed the above parameters related to post-harvest quality loss, while the AVG / LEO treatment delayed the browning processes, maintaining an excellent color during cold storage. Concerning proximate compounds, the treatments did not alter their concentration in the fruit tissues. Sensory analyses revealed no detrimental e ﬀ ect on taste, aroma, or ﬂavor. Our data evidenced the positive e ﬀ ect of Aloe vera gel in combination with LEO and HPMC on fresh-cut apple quality as an innovative and sustainable technique to maintain fresh-cut apple quality.


Introduction
In recent years, there has been a growing focus on sustainability, starting with the study of the orchard, cultivation techniques, and their impact on the environment [1] until the fruit production supply chain in future climate change scenarios [2].
To date, synthetic antioxidants and artificial additives are still widely used in the food industry to inhibit oxidation and decay of products. To reduce waste and limit losses, researchers study the exclusive use of natural and biodegradable materials to create edible films and packaging that are both environmentally friendly, healthy, and functional for storage and market distribution [3]. In fact, postharvest softening of fresh-cut fruit is a serious commercial problem resulting in quality losses both for growers and distributors. For these reasons, researchers' attention is more focused on fresh, fresh-cut, peeled, sliced, and packaged fruit and vegetables which, if they have physicochemical characteristics suitable for sale on the market, can be sold and appreciated more by consumers, thanks to their freshness, convenience (as a ready-to-eat product), and human health benefits. For example, water loss, browning, and texture are among the most important quality parameters that influence the acceptability of many fruits by consumers [4].
Nonetheless, today no studies have been carried out on the effects of applying an Aloe vera gel-based edible coating in combination with lemon essential oil and hydroxypropyl methylcellulose on the surface of fresh-cut 'Fuji' apple as a sustainable alternative to synthetic by-products.
For this reason, the purpose of this work was to determine how much the proximate compounds, vitamins, physicochemical, and sensory characteristics of fresh-cut 'Fuji' apple slices are influenced by the treatments with an Aloe vera gel-based edible coating and in combination with hydroxypropyl methylcellulose and lemon essential oil, using a spraying technique and simulating commercial storage.

Vegetal Material
Fifteen 'Fuji' apples have been selected and harvested with uniform size (250 ± 10 g) at commercial maturity in an organic farm located near Caltavuturo (37 • 49 N and 850 m a.s.l.). This area is characterized by a typically Mediterranean climate. The soil is of medium texture tending to clayey, with good fertility. Another important aspect is the quantity of water accumulated in the areas of the fields thanks to the presence of several water rivulets. The plants are placed along single rows spaced 4 × 1.5 m, grafted onto M9 rootstocks, and subjected to the ordinary cultivation regime of organic farming.
Fruits were transported to the laboratories of the Department of Agricultural, Food and Forestry Sciences of the University of Palermo, where they were treated with edible coatings.

Coating Formulations
Coating formulations were made on site. Matured leaves of Aloe vera plant were harvested at the experimental field of the University of Palermo. The epidermis was separated from the gel, which was manually cut into portions of 10 ± 1 mm in thickness, and the sample was maintained at 4 • ± 1 • C in a refrigerator. The gelatinous parenchyma was separated from the leaves by means of a stainless-steel knife removing the external epidermis. It was triturated using an ultra-Turrax T25 (Janke and Kunkle, IKa Labortechnik, Breisgau, Germany) for 5 min at 24,500 rpm to form a homogeneous substance, and filtered to remove the fibrous portion [36]. Based on our previous studies, the threshold for sensory acceptance was established at 40% of its volume in 300 mL of water (v/w) due to a bitter taste that occurred at higher concentrations (data not shown). Therefore, the treatments are as follows: Untreated (CTR): only chlorinated water 0.5% (v/w); AVG: 40% (v/w) of Aloe vera gel (AVG); AVG/HPMC: 40% (v/w) of AVG and 0.1% (v/w) of hydroxypropyl methylcellulose (HPMC); AVG/LEO: 40% (v/w) of AVG and 1% (v/w) of lemon essential oil (LEO).
To prevent browning and to maintain the pH value below 3.5, 1% (v/w) of ascorbic acid and 1% (v/w) of citric acid were added to the solutions, except in the CTR.

Experimental Design
'Fuji' apples were cored and sliced into 8 pieces with a 2 cm of thickness, using a stainless-steel knife. The total sample of apple slices (144) was divided into four different lots, which were treated with the spraying technique. Thirty-six slices were coated with AVG treatment, 36 with AVG/HPMC treatment, and 36 with AVG/LEO treatment. The last 36 apple slices were stored as CTR. In all treatments and in the CTR, the apple slices were sprayed for 2 min through an airbrush (0.8 mm nozzle) powered by N 2 . After treatments, three apple slices × PET (polietilentereftalato) tray (12 × treatment) were stored in a passive atmosphere at low temperature (4 • ± 1 • C and 90% ± 5% Relative Humidity (RH) for 9 days. Each tray (125 mm × 115 mm and 150 cc) were thermally sealed on the top with a bi-oriented polypropylene (BOPP) film of 50 mm of thickness. The permeability of the BOPP was 2.004 mL O 2 m −2 d −1 atm −1 and 3.824 mL CO 2 m −2 d −1 atm −1 . All of the analysis was carried out in three replicate and on an interval of three days for nine total days (T0, T3, T6, and T9). All the analyses were Agronomy 2020, 10, 515 4 of 18 carried out in all the trays starting from day 0 of storage. Therefore, the values at T0 are influenced by the weight of the apple slices and the addition of the coating.

Physical Analysis
The weight loss was measured every three days with a two-decimal precision digital scale (Gibertini, Italy). The value was expressed as a relative percentage and calculated as weight loss (%) = (wi − wt)/wi × 100 (where Wi is the initial weight, and Wt is the weight measured during storage).
Three measurements of an apple slice were taken at different locations of each sample to acquire a uniform color measurement.
The firmness of the flesh (kg·cm −2 ) was determined by means of a digital penetrometer TR5325 (Turoni, Forlì Italia) with an 8 mm diameter plunger and a 'Shore A' durometer.

Chemical Analysis
After apple juice extraction by a squeezing-centrifugal machine (Ariete, Italy), we measured the soluble solids content (SSC) as • Brix, by means of an optical digital refractometer ATAGO (Atago Co, Ltd., Tokyo, Japan); the titratable acidity (TA), expressed as malic acid (g/l −1 ), and the pH value, with a Crison Compact titrator pH-meter (Crison Instruments, SA, Barcelona, Spain).

Proximate Composition
Ash content was determined through the procedure described in Association of Official Analytical Chemists (AOAC) [37][38][39][40][41], while the Kjeldahl method was used for protein determination. In particular, a sample rate was subjected to acid-catalyzed mineralization to turn the organic nitrogen into ammoniacal nitrogen and, subsequently, was distilled in an alkaline pH. The ammonia formed during this distillation was collected in a boric acid solution and determined through titrimetric dosage. The value of ammoniacal nitrogen was multiplied by 6.25 [42].
The fat content (FAT) was obtained through acid hydrolysis with a 1:4 HCl solution on the sample followed by filtration and dehydration in a heater (70 • C). After solvent evaporation, the extraction in Soxhlet with petroleum ether was determined through a gravimetric method of residual fat.
Complex carbohydrates have a significantly more elaborate biochemical structure than other carbohydrates (simple sugars with a simpler structure, determined with the Fehling reagent). The carbohydrate content (TSG), either free or present in polysaccharides, was obtained with the anthrone method reported in Loewus [43]. Carbohydrates were first hydrolyzed into simple sugars using dilute hydrochloric acid. In hot acidic medium, glucose is dehydrated to hydroxymethyl furfural that with anthrone forms a green-colored product with an absorption maximum at 630 nm.
The contents of K, Na, Ca, Fe, Cu, Mn, and Zn were determined using atomic absorption spectroscopy following wet mineralization, while P was determined using a colorimetric method [44][45][46]. The total content of polyphenols was determined according to the Folin-Ciocalteu method. The extraction of the phenolic compounds was carried out by weighing 0.25 g of sample and adding 5 mL of an 80% (v/v) methanol solution. The mixture was stirred by means of a Vortex shaker for 1 min and then stirred on a magnetic stirrer in a cold room for 30 min. The champion was, therefore, centrifuged for 10 min at 6000 rpm at room temperature. The solid part has separated from the liquid extract. The latter was recovered in a test tube. A counter-extraction was carried out for each sample, resuspending the pellet obtained after centrifugation, according to the above procedure. At the end, it was the supernatant that was recovered and added to the first. The extract thus obtained was further centrifuged to sediment any solid particles left, thus obtaining a clear extract. This extract was transferred in flasks by Rotavapor and was concentrated until the achievement of a final volume of 3 mL. The concentrated extract was resuspended in 80% (v/v) methanol up to a final volume total of 4.5 mL and was placed in Eppendorf Agronomy 2020, 10, 515 5 of 18 and stored at −20 • C until the moment of the analysis, while total, soluble, and insoluble fibers were measured by the chemical-enzymatic method 1995 (AOAC 994.13 [37]).
The riboflavin (vitamin B2) was extracted in an autoclave with a solution of diluted H2SO4, and later, after enzymatic treatment, was determined through HPLC (for the fluorescent spectra) [38].
For the ascorbic acid (vitamin C) determination, the dried methanolic extract (100 mg) was extracted with 10 mL of 1% metaphosphoric acid for 45 min at room temperature and filtered through Whatman No. 4 filter paper. The filtrate (1 mL) was mixed with 9 mL of 2.6-dichlorophenolindophenol, and the absorbance was measured within 30 min at 515 nm against a blank. Ascorbic acid was calculated based on the calibration curve of authentic L-ascorbic acid (0.02-0.12 mg mL −1 ) [47].

Sensory Analysis
The sensory analysis was carried out by a group of judges. All panelists were trained and had broad expertise in sensory evaluation of foods and, in particular, of apples [48]. Panel members were trained using different apple samples to recognize aroma, flavor, and texture attributes during the training session, using references to products and ingredients. Twenty qualitative and quantitative descriptors were considered: appearance (A), flesh color (FC), firmness (F), apple odor (AO), herbaceous odor (EO), honey odor (HO), almond odor (AlO), off-odor (OO), sweetness (S), acidity (AC), bitter (B), astringent (AS), crunchiness (C), flouriness (Fl), juiciness (J), apple flavor (AF), herbaceous flavor (EF), honey flavor (HF), almonds flavor (AlF), off-flavor (OF), overall assessment (OA). The judges assessed the intensity of each attribute on a discontinuous scale from 1 (absence of the descriptor) to 9 (maximum intensity of the descriptor).

Statistical Analysis
All data were tested for differences between treatments and sampling times using the one-way analysis of variance (ANOVA; general linear model) followed by Tukey's multiple range test for p ≤ 0.05. All statistical analysis was conducted using XLSTAT software version 9.0 (Addinsoft, Paris, France).

Weight Loss
During storage, there was a difference in weight loss between the uncoated and coated fresh-cut apples. At the beginning of the experiment, CTR apple slices weighed 44.14 g, AVG apple slices weighed 48.9 g, AVG/HPMC apple slices weighed 45.4 g, and AVG/LEO apple slices weighed 44.8 g. After three days of storage, the apple slices uncoated (CTR) and AVG treatment lost 3.44% and 0.52%, respectively, by weight, giving a result (expressed in grams) of 42.62 g and 48.64 g. The fruits treated with AVG/HPMC, instead, weighed 45.13 g (showing a weight loss percentage of 0.54%), while the AVG/LEO treatment showed a weight loss of 0.96% (the tray weighs 44.35 g). After 6 days of storage, the tray with the untreated slices (CTR) weighed 42.10 g (it lost 4.62% in weight), the slices treated only with AVG weighed 47.85 g, showing a weight loss of 2.13%. One percent weight loss was detected for AVG/HPMC treatment (which had a weight of 44.92 g), while AVG/LEO had a weight loss of 1.50%, reaching 44.10 g. Finally, after 9 days of storage, the weight of the CTR and the AVG-treated apple slices decreased to 41.94 g and 47.47 g, respectively, whereas the apple slices coated with AVG/HPMC and AVG/LEO weighed 44.70 g and 44.08 g, respectively. The results at the end of the storage period indicated that the CTR and the AVG-treatment lost 4.98% and 2.92%, respectively, while the AVG/HPMC and AVG/LEO treatments minimized weight loss (1.50% and 1.56%, respectively) by maintaining the water content in fresh-cut apple. In fact, this weight loss is probably caused by the water evaporation on the fruit surface and is a leading cause of quality loss, such as shriveling of the surface and decreased juiciness [6,42]. Nonetheless, there are not many studies available in the literature concerning the mixing of HPMC with Aloe vera gel and lemon essential oil to form edible or biodegradable films or packages, to compare with our data. Bai, J. et al. [49] also reported that the coatings were effective in preventing weight loss in apples. In particular, the Aloe vera gel-based edible coating acts as a very efficient barrier for oxygen, carbon dioxide, and lipids, but with poor resistance to water vapor transport [50]. Moreover, Klangmuang and Sothornvit [51] have been combined Aloe vera gel with other lipids to reduce water vapor permeability and to reduce weight loss, as Velickova et al. [52] they did before on strawberries. Edible films and coatings based on HPMC have been extensively studied to improve the shelf life and quality of whole citrus fruit. Navarro-Tarazaga et al. [53] and Perez-Gago et al. [54] have contributed to maintaining the quality of the fruits by reducing its weight loss and improving its mechanical integrity. HPMC has also been studied in combination with different components, such as fatty acids [12] or cellulose nano-particles [55] but never with Aloe vera. In fact, on fresh-cut apples, the effect of edible coating based on HPMC, whey proteins, and beeswax was only studied [56].
Regarding the use of lemon essential oil, Perdones A. et al. [31] applied an edible coating based on chitosan and lemon essential oil to strawberries cv. Camarosa, and found significant differences, compared to untreated fruits, as the coated products slowed the respiration rate of the samples when lemon essential oil was added.

Color Analysis
As regards color parameters (Table 1 and Figure 1), initial Lightness (L*), redness (a*) and yellowness (b*) values of the apple slices were 78.28 ± 1.40, −4.01 ± 0.86, and 34.44 ± 0.55, respectively. For all treatments and uncoated apple slices, there was no difference in the b* value. Conversely, the L* value and a* value, respectively, decrease and increase during storage, according to Iglesias, Echeverría, and Lopez [57] and Marquina et al. [58]. Table 1. Color characteristics of fresh-cut apples at 0, 3, 6, and 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH (relative humidity) after all treatments.  From the sixth day of storage, the a* (redness) coordinate decreased for both coated and uncoated samples, but only the AVG/HPMC treatment maintained a constant value until the 9th day. This increase in redness is probably due to an increase in the respiration rate and enzymatic processes that lead to a loss of quality of the fruit [59].
Concerning yellowness (b*), no significant differences (p ≤ 0.05) were found between treated and untreated fruits.
Treatments with an edible coating effectively delay color loss of fresh−cut apples during storage. Only two coating formulations (AVG/HPMC and AVG/LEO) led to a significant reduction in color loss, in terms of brightness (L*) and redness (a*), compared to uncoated apple slices and AVG treatment, which undergo rapid color deterioration.
Aloe vera gel slows down the ripening process and the respiration rate of apple slices [50]. Aloe vera gel applied to table grapes [60], cherries [50], and plums [61], has shown excellent results in terms of improving product presentation and reducing browning of treated fruits. Similar results were also found by Marpudi SK., Ramchandaran P. and Srividya N. [62] for figs coated with Aloe vera gel, which maintained the color of the fruit, its texture, and ripeness during storage.
On the other hand, the gloss and transparency of the films are relevant properties since they have a direct impact on the appearance of the coated product. In general, significant differences were associated with the nature and amount of the essential oil (EO). Sánchez−González, L. et al. [63] observed that the addition of EO to the HPMC matrix led to a reduction in gloss (L*), despite concentration. The reduction in gloss in lipid−containing composite films has also been observed by several authors [63,64]. The gloss of the films is related to the surface morphology achieved during the drying of the film. In general, the smoother the surface, the glossier it is.
Additionally, the amorphous state of the HPMC has allowed limiting the crystallization of the coating on the surface of the apple slice, maintaining almost unchanged the properties of brightness and transparency of the coating. The amorphous state of the HPMC was reported by Kou et al. [65] through X−ray diffraction analysis.
Rojas−Graü et al. [27] covered apple slices with alginate−based edible coating and essential oils of oregano, lemongrass, and vanillin, showing significantly smaller differences in color data than in the control. In our case, the edible coating enriched with lemon essential oil showed better color retention values than the control.

Firmness
AVG/LEO treatment limits, especially during the first six days, the loss of firmness (N) compared to CTR, while AVG and AVG/HPMC do not seem to have an improving effect on this parameter ( Table 2). From the sixth day of storage, the a* (redness) coordinate decreased for both coated and uncoated samples, but only the AVG/HPMC treatment maintained a constant value until the 9th day. This increase in redness is probably due to an increase in the respiration rate and enzymatic processes that lead to a loss of quality of the fruit [59].
Concerning yellowness (b*), no significant differences (p ≤ 0.05) were found between treated and untreated fruits.
Treatments with an edible coating effectively delay color loss of fresh-cut apples during storage. Only two coating formulations (AVG/HPMC and AVG/LEO) led to a significant reduction in color loss, in terms of brightness (L*) and redness (a*), compared to uncoated apple slices and AVG treatment, which undergo rapid color deterioration.
Aloe vera gel slows down the ripening process and the respiration rate of apple slices [50]. Aloe vera gel applied to table grapes [60], cherries [50], and plums [61], has shown excellent results in terms of improving product presentation and reducing browning of treated fruits. Similar results were also found by Marpudi SK., Ramchandaran P. and Srividya N. [62] for figs coated with Aloe vera gel, which maintained the color of the fruit, its texture, and ripeness during storage.
On the other hand, the gloss and transparency of the films are relevant properties since they have a direct impact on the appearance of the coated product. In general, significant differences were associated with the nature and amount of the essential oil (EO). Sánchez-González, L. et al. [63] observed that the addition of EO to the HPMC matrix led to a reduction in gloss (L*), despite concentration. The reduction in gloss in lipid-containing composite films has also been observed by several authors [63,64]. The gloss of the films is related to the surface morphology achieved during the drying of the film. In general, the smoother the surface, the glossier it is.
Additionally, the amorphous state of the HPMC has allowed limiting the crystallization of the coating on the surface of the apple slice, maintaining almost unchanged the properties of brightness and transparency of the coating. The amorphous state of the HPMC was reported by Kou et al. [65] through X-ray diffraction analysis.
Rojas-Graü et al. [27] covered apple slices with alginate-based edible coating and essential oils of oregano, lemongrass, and vanillin, showing significantly smaller differences in color data than in the control. In our case, the edible coating enriched with lemon essential oil showed better color retention values than the control.

Firmness
AVG/LEO treatment limits, especially during the first six days, the loss of firmness (N) compared to CTR, while AVG and AVG/HPMC do not seem to have an improving effect on this parameter Agronomy 2020, 10, 515 8 of 18 (Table 2). These data are in agreement with Hye-Yeon Song [32], according to whom the treatment of edible coating with aloe vera gel allowed the maintenance of a constant firmness of the fresh-cut apple flesh compared to the untreated fruits. The differences between the results observed in this work rely on the high initial level of firmness values of apple slices, as this cv has intrinsic compactness characteristics Rojas-Graü, M. A. et al., [27]. Table 2. Physico-chemical traits of fresh-cut apples at 0, 3, 6, and 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH after all treatments..

Soluble Solids Content
With respect to soluble solids content (SSC), also shown in Table 2, both the three treatments and the control follow the same evolution. The AVG/LEO treatment was able to limit the loss of soluble solids content from the first three days of the storage period by maintaining this behavior until the last day of observation. The other treatments did not differ from the control. Studies concerning a decrease in the sugar content during apple storage confirm that this behavior could be attributed to the conversion of sugar into starch [66], and malic acid is consumed by the fruit as respiratory substrates and for the synthesis of new compounds during storage [67]. Moreover, the coating seemed to decrease the permeability to CO 2 and O 2 , with the result of a decrease in the respiration rate of apples [49]. The SSC allows the evaluation of the degree of sugar and, correlated with the titratable acidity (TA), gives useful feedback on the satisfaction of the fruit by the consumer. Together with these results, our findings indicate that coating apple slices with the AVH/HPMC and AVG/LEO treatments was effective with respect to the soluble solids content found in untreated fruits (CTR) during the 9 days of storage.

Titratable Acidity and pH
With respect to TA and pH, these two parameters are important for assessing the freshness of fruit and are strongly correlated because the pH value depends on the presence of acid compounds. As can be seen from Table 2, the presence of edible coating slowed down the increase in pH and, consequently, stabilized the titratable acidity (TA). Moreover, the evidence that the fruits coated with edible coating had a stabilized pH around 3.7 is an interesting aspect because, at this pH value, both polyphenol oxidase and microbial activities are slowed down [68]. The acid content in the fruit tends to decrease over time, probably due to the oxidation of organic acids that occurs with the ripening of the fruit [69]. Therefore, a pH increase is expected during the storage period. Compared to other studies, the results on pH and TA obtained with the application of HPMC, AVG, and LEO edible coatings were positive, especially compared with the untreated fruits or treated with AVG edible coating. As Soares and Fonseca report [70], intrinsic and extrinsic factors, such as treatment, variety, and storage conditions, are essential to determine the degree of acidity variation. The latter had the opposite trend to the evolution of pH observed by other authors [28,71,72].

Proximate Compounds
The proximate compounds into the treated and untreated apple slices were analyzed (Table 3). All the samples have values similar to the USDA Nutrient Database during the storage period.
The results show that the samples evaluated contained high variability of proximate compounds in all treatments and CTR during the 9 days of storage, according to other researchers [12,73], which explained this behavior related to different cultivars studied, growing conditions, and methodology used to determine these compounds. The increase in values during storage time is probably due to the reduction in water content and closely related to weight loss. Ca, K, and P, together with a low Na intake, are associated with protection against bone demineralization, arterial hypertension, insulin resistance, and overall cardiovascular risk [74]. As regards the essential elements (Mn, Zn, Cu, Fe) involved in many biochemical processes, there were no significant differences between treatments and CTR.
During storage, there were very low significative differences between treated and untreated apple slices. In particular, the CTR showed the highest loss of moisture during cold storage, unlike the other treatments. Concerning protein content, there were very low significative differences between treated and untreated apple slices.
In FAT content, the AVG treatment had a major increase. In carbohydrate content, AVG/HPMC treatment had a major increase. AVG/LEO treatment had a major content increase in sugars. Concerning fibers, AVG/LEO treatment had the highest content at the end of the storage period. Finally, as regards total phenolic content, AVG treatment had a greater range of variability from day 0 to day 9 of storage.
From the results obtained, it is possible to see that the treatments did not alter the nutrients content inside the treated apple slices but kept it throughout the storage time. Table 3. Ca, K, Na, P, Mn, Zn, Cu, and Fe in fresh-cut apples at 0, 3, 6, and 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH after all treatments. Data correspond to the means ± standard deviation of three replicates. Means with different letters are significantly different at p ≤ 0.05 using Tukey's test. ns = not significant. Different capital letters denote significant differences (p < 0.05) among different treatments for the same sampling time. Different lowercase letters denote significant differences (p < 0.05) among different sampling times for the same treatment. "%" is the percentage variation from t0.

Vitamin Content
Epidemiological studies show that diets high in vitamin C-rich fruits and vegetables are associated with a lower risk of cardiovascular disease, stroke, and cancer, and increased longevity [75].
From the results obtained concerning Vitamin C, CTR and AVG/HPMC treatments had a different trend than the others. In fact, as can be seen in Table 4, AVG and AVG/LEO treatments had the same trend up to day 3; the AVG/HPMC treatment had a constant value up to day 3, from day 6 to day 9, it decreased. According to Leahu,A. et al. [76], this behavior could be associated with the presence of Cu, sugars, and a pH of around 4.
The Riboflavin (Vitamin B2) is important for the prevention of cardiovascular disease, cancer, incipient diabetic nephropathy, and retinopathy. With regard to vitamin B2, Table 5 shows a lower loss of concentration of this vitamin in all treatments. Only CTR treatments underwent a marked decrease in B2 values from day 3. In addition, Thornalley, P. J. [77] showed in their studies, an unstable downward trend during the entire shelf life. Table 4. Water, Protein, FAT, carbohydrate, sugars, fibers, and total polyphenol content of fresh-cut apples at 0, 3, 6, and 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH after all treatments. Data correspond to the means ± standard deviation of three replicates. Means with different letters are significantly different at p ≤ 0.05 using Tukey's test. ns = not significant. Different capital letters denote significant differences (p < 0.05) among different treatments for the same sampling time. Different lowercase letters denote significant differences (p < 0.05) among different sampling times for the same treatment. "%" is the percentage variation from t0. Table 5. Vitamin content of fresh-cut apples at 0, 3, 6, and 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH after all treatments.  Figure 2 shows moderate to severe symptoms of dehydration and browning of the control apple slices after 9 days of storage at 4 • ± 1 • C and 90% ± 5% RH and mild for treated slices even at the last sampling date. Browning and dehydration are phenomena that typically develop during storage. This behavior is associated with fruit ripening [78,79]. Therefore, the AVG/HPMC and AVG/LEO coatings delayed the loss of sensory quality of fresh-cut apples during the 9 days of storage. This behavior could be attributed to their power of water diffusion inhibition and anti-browning agents. In fact, Lanciotti, R. et al. [80] reported that the addition of 0.02% (v/w) citrus, mandarin, cider, lemon, and lime EOs to a minimally processed fruit mix (apple, pear, grape, peach, and kiwifruit) inhibited the microbiota proliferation and extended the shelf life of the fruit salad without affecting its sensory properties. AVG/HPMC was the most effective treatment in terms of color, firmness, and crunchiness, while AVG/LEO treatment showed superior results in terms of sweetness, color, odor, and flavor. The opposite happens in CTR and AVG, which showed "off flavors" since day 3 of cold storage. In addition, the judges did not perceive the development of "off flavor " in fresh-cut apples as a result of treatments.

Sensory Analysis
Agronomy 2020, 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/agronomy (apple, pear, grape, peach, and kiwifruit) inhibited the microbiota proliferation and extended the shelf life of the fruit salad without affecting its sensory properties. AVG/HPMC was the most effective treatment in terms of color, firmness, and crunchiness, while AVG/LEO treatment showed superior results in terms of sweetness, color, odor, and flavor. The opposite happens in CTR and AVG, which showed "off flavors" since day 3 of cold storage. In addition, the judges did not perceive the development of "off flavor " in fresh−cut apples as a result of treatments.

Conclusions
The obtained results showed the best performances on treated apple slices than in the untreated (CTR). In particular, the aloe vera gel associated with HPMC gave at the apple slices an attractive natural shine, quite similar to that of freshly harvested fruit. While the AVG/LEO treatment showed the best characteristics in terms of soluble solids content, titratable acidity, and pH, in relation to a reduction in senescence processes. The analysis of proximate compounds, such as minerals, essential elements, nutrients, and vitamins content, showed that the treatments did not alter the intrinsic characteristics of the treated samples while maintaining constant values during the storage period. The results obtained were confirmed by sensory analysis, which revealed higher values of appreciation for fresh-cut 'Fuji' apple treated with AVG/HPMC and AVG/LEO, compared to CTR and AVG. In a system that comes ever closer to sustainability, a balance between ecological and socio-economic conditions is expected. In fact, the exclusion of chemical-based food coatings eliminates the need to remove toxic waste, reducing environmental pollution as the plant material is covered by an entirely edible coating.
Funding: This research received no external funding.