Exploring the potential of aloe vera gel-based coating for shelf life extension and quality preservation of tomato

ABSTRACT

Tomato is considered the world’s most important crop owing to its high nutritional profile and flavor. However, its limited shelf life and post-harvest losses impact its marketing. The present study investigated the impact of aloe vera gel-based edible coating on tomato’s post-harvest quality under storage at 8°C for 12 days. The aloe vera-based coating solutions were made with varying concentrations of extracted gel that varied from 0 to 60% with inclusion of chitosan (0.5 to 2%). Physiological, chemical, nutritional, and microbiological analysis of coated and uncoated tomatoes was carried out during storage. It was found that uncoated (control) tomatoes showed maximum weight loss (5.85%), total soluble solids (5.3 ± 0.20 0Brix), change in pH (5.6 ± 0.26), microbial count (3.57 ± 0.12 log cfu/g), decrease in ascorbic acid content (19.23 ± 0.92 mg/100 g), and acidity (0.54 ± 0.01%) as compared to aloe vera-based coatings. However, the coating formulation comprising aloe vera gel (60%) + chitosan (2%) performed much better than other prepared coatings in delaying the weight loss (2.1%), total soluble solid (3.7 ± 0.16 0Brix), change in pH (4.6 ± 0.21), ascorbic acid value (30.47 ± 1.31 mg/100 g), acidity (0.83 ± 0.04%), and microbial load (1.6 ± 0.08 log cfu/g). In addition, it also maintained firmness and color of tomatoes during storage of 12 days. Conclusively, the application of aloe vera-based coating (60% gel) with the inclusion of chitosan (2%) may be proposed for preserving the post-harvest quality of the tomatoes.

KEYWORDS:

• Tomato
• aloe vera
• chitosan
• Edible coating
• Postharvest
• Shelf life

Introduction

Tomato known as (Solanum lycopersicum L.) is highly marketed and the second most significant crop after potato, with an annual yield of approximately 163 million tons.^[1] Tomato is an excellent source of proteins, essential amino acids, fiber, vitamins, minerals, and mono-unsaturated fatty acids. In addition, tomatoes are also high in secondary metabolites (lycopene, carotenoids, phenols, chlorophyll, phenols, flavonoids, and organic acids), which have been linked to protect humans from chronic degenerative diseases like cancer, cardiovascular disease, and neurological disorders.^[2,3] Although tomato is rich in many nutrients and beneficial compounds called secondary metabolites, the postharvest life of tomato is very short.^[4] Because tomatoes are climate-sensitive fruits, they ripen rapidly and lose quality when stored in uncontrolled conditions. Numerous chemical, physical, biological, and physiological changes occur as climacteric fruit ripens.^[5] Postharvest handlings like transport, packaging, and storage are regarded as the main practices which can cause postharvest damage if not managed appropriately.^[6] In addition to postharvest handling, the major causes that affect postharvest quality of fruits are ethylene production, microbe-induced deterioration, respiration, relative humidity, and temperature.^[7] Color, taste, firmness, processing properties, resistance to infection, and shelf life are the quality aspect that decide their market potential.^[8] Tomatoes degrade quickly after harvest, and postharvest losses range from 25–42% globally.^[9] This results in considerable economic loss as well as cause ecological problems (contamination of water, growth of microbes).^[10] In recent years, the growing demand for vegetables and fruits has increased the market’s need for efficient processing and preservation to reduce postharvest losses and maintain quality of fresh produce.^[11,12] Different postharvest techniques are utilized to extend the shelf life and improve the quality of fresh produce. Among them, the utilization of edible coatings has evolved as an efficient technique to enhance the safety and storage life of fresh produce. Edible coatings are thin sheets or layer on the surface of food comprised of hydrocolloids (protein, polysaccharides), lipids, and composites.^[12] Recently, hydrocolloids gained a lot of interest in the food industry with a wide range of food packaging applications. The hydrocolloid biopolymers are widely distributed in nature and are acceptable to be consumed with the food product. They are also safe, nontoxic, and biodegradable.^[13] Among hydrocolloids, aloe vera is a suitable postharvest treatment for an edible coating on fresh products.^[14] Aloe vera is a herbal plant and is widely used for its medicinal benefits which is due to its antioxidant and antimicrobial properties. The antioxidant, antimicrobial properties of aloe vera are due to the presence of bioactive compounds such as aloin, aloetic acid, aloe-emodin, anthranol, isobarbaloin, barbaloin, ester of cinnamic acid, and emodin. These compounds can effectively enhance the shelf life of food, making it a best option for food coatings.^[14,15] Chitosan is a polysaccharide obtained from the deacetylation of naturally occurring chitin. The application of chitosan as a coating for food has demonstrated the possibility of prolonging the storage life and enhancing the fruit quality and is also accepted as a safe biomaterial.^[12] Chitosan possesses numerous essential properties, including the ability to degrade, biocompatibility antibacterial action, and non-harmful nature, and it has been explored for application in variety of fields, including food, agriculture, pharmaceuticals, and ecology. Given many of the claimed properties of chitosan, it might be beneficial as well as secure to use as a coating for different vegetables and fruits.^[16] Numerous papers have been published on the use of chitosan as an edible coating, but a few scientists have combined aloe vera gel with chitosan to develop coating for cucumbers^[17] and blue-berries.^[18] In view of the explained above, the objective of the current study was to investigate the effect of aloe vera-based coating in addition to chitosan on the quality and storage life of Roma tomatoes.

Materials and methods

Procurement of raw material

To carry out the experiments, matured Roma tomato fruits were obtained from the local market of Faisalabad, Pakistan. Aloe vera leaves were obtained from the Biochemistry department of Ayub Agriculture Research Institute, Faisalabad, Pakistan. Chitosan, glycerol, and chemicals used in this research were procured from authorized scientific store of Faisalabad, Pakistan.

Pretreatment of tomatoes

Roma tomatoes were taken to the food safety lab (Department of Food Sciences, Government College University Faisalabad, Pakistan) and washed immediately with running tap water. After that, tomato fruits were surface sterilized with 1% sodium hypochlorite solution (v/v) for 2 to 3 minutes and then rewashed with water. Tomatoes were spread and dried at room temperature.

Preparation of Aloe Vera Gel

Fresh gel of aloe vera leaves was prepared according to the procedure as reported by Navarro et al.^[19] Before inner leaf gel separation, spikes along the margins were removed by using sharp stainless steel cutting knife in such a manner that the aloe vera gel could be obtained without difficulty. The colorless gel like material, called hydro parenchyma, was blended in a mixer or a blender to gain a slimy consistency. This solution was then filtered by passing through tea strainer to remove fibrous fraction. Pure aloe vera solution was stored at 5°C in a refrigerator till used to avoid oxidation of phenolic contents.

Preparation of coating solutions

Chitosan percentages (0.5%, 1%, 1.5%, and 2%) were prepared according to procedure as described by Kumar et al.^[20] by dissolving in distilled water contained 1% glycerol. Solutions of chitosan and aloe vera gel were combined and mixed according to Basumatary et al.^[21] with certain modifications. Aloe vera and chitosan in different ratio were mixed as 15:0.5, 30:1, 45:1.5, and 60:2 in the presence of 1% glycerol and mixed in magnetic stirrer for 3 hours before use (Table 1).

Table 1. Development of aloe vera-based coating solutions.

Treatments	Aloe vera (%)	Chitosan (%)
T0	0	0
T1	15	0.5
T2	30	1
T3	45	1.5
T4	60	2

Method of coating

A total of 200 fresh, uncontaminated, and uniform-sized tomatoes were selected for the study and divided into five groups: (A) the control group treated with distilled water; (B) the group treated with 15% aloe vera and 0.5% chitosan; (C) the group treated with 30% aloe vera and 1% chitosan; (D) the group treated with 45% aloe vera and 1.5% chitosan; and (E) the group treated with 60% aloe vera and 2% chitosan. The tomatoes were dipped in the respective coating formulations for 5–7 minutes and left to dry at room temperature. After drying, the treated tomatoes were packed in PET boxes with lids containing 10–12 holes, each with a diameter of 4 mm. These packed boxes were then stored in a cold storage facility at a temperature of 8°C for a duration of 12 days. Throughout the storage period, various physical, chemical, nutritional, and microbial analyses were conducted on the tomatoes at intervals of 0, 4, 8, and 12 days.

Physiological analysis

Weight loss, firmness, and color

Weight loss (water loss) was accessed according to the method by Ruelas-Chacon et al.^[22] On the first day fruits from each lot were selected and weighed. Then fruits were weighed again at different storage intervals 0, 4, 8, 12. Loss of weight was expressed in percentage calculated using the equation 1. The fruit firmness was determined by a penetrometer with cylindrical plat probe of 6 mm, inserted from three points of equinoctial line of fruit. The fruit firmness was calculated as means of three measurements for each fruit. A colorimeter was used to assess color using the a* (redness/greenness), the b* (yellowness/blueness), and the L* (brightness) as described by Al-Dairi et al.^[23] Moreover, color index (CI) was measured by using equation 2.:

(1) $\mathrm{\%}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}\mathrm{l}\mathrm{o}\mathrm{s}\mathrm{s}=\hspace{0.17em}\left(\frac{\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}-\mathrm{f}\mathrm{i}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}{\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{w}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}\right)\times 100$(1)

(2) $\mathrm{C}\mathrm{o}\mathrm{l}\mathrm{o}\mathrm{u}\mathrm{r}\mathrm{i}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{x}\left(\mathrm{C}\mathrm{I}\right)\hspace{0.17em}=\hspace{0.17em}\frac{{\mathrm{a}}^{\ast }}{{\mathrm{b}}^{\ast }}$(2)

Chemical analysis

Titratable acidity, total soluble sugars, maturity index, and pH

As method explained by Bhadu et al.^[24], the fruit titratable acidity was determined using a titration method with 0.1 N NaOH and a phenolphthalein indicator. Ten milliliter (ml) of distilled water (DW) was mixed with five grams (g) of sample and then added 2–3 droplets of phenolphthalein as an indicator, and the testing was performed until the color changed to pink, which lasted 15–20 seconds (s) and was marked as the end point. Three replicates were used for each treatment. According to Morad et al.,^[25] the total soluble sugars of prepared juice samples were measured by hand refractometer immediately. The hand refractometer was adjusted using distilled water at the beginning of each usage. A drop of juice (sample) was put on the refractometer’s completely clean prism, and measurements were directly noted as °Brix. Measurements were taken in triplicate. Maturity Index (TSS:TA) was calculated using equation 3. An electronic (digital type) pH meter was used to calculate the pH of the treated tomato juice. The significant sample volume was taken in the beaker in which pH meter electrodes were immersed and test results were achieved as described by Abebe et al.^[26] Analysis were performed in triplicate.

(3) $\mathrm{M}\mathrm{a}\mathrm{t}\mathrm{u}\mathrm{r}\mathrm{i}\mathrm{t}\mathrm{y}\mathrm{I}\mathrm{n}\mathrm{d}\mathrm{e}\mathrm{x}\left(\mathrm{M}\mathrm{I}\right)\hspace{0.17em}=\hspace{0.17em}\frac{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{b}\mathrm{l}\mathrm{e}\mathrm{s}\mathrm{o}\mathrm{l}\mathrm{i}\mathrm{d}\mathrm{s}\left({ }^{\circ }\mathrm{b}\mathrm{r}\mathrm{i}\mathrm{x}\right)}{\mathrm{T}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{A}\mathrm{c}\mathrm{i}\mathrm{d}\mathrm{i}\mathrm{t}\mathrm{y}\left(\mathrm{\%}\right)}$(3)

Nutritional analysis

Ascorbic acid and antioxidant activity

The ascorbic acid concentration of fruit juice was identified using the 2, 6-dichloroindophenol titrimetric procedure reported by Morad et al.^[25] The antioxidant potential test-DPPH (2, 2-diphenyl-l-picrylhydrazyl radical scavenging activity) was determined using the method as described by Azali et al.^[27]

Microbiological analysis

Microbial analysis was performed with slight modification as method described by Ahmed et al.^[28] at storage intervals of 4, 8, and 12 days. In a blender stomacher 3500, homogenization of sample was done for 2 minutes. The sample was prepared in triplets. On the potato dextrose agar 100 mL serial dilutions were spread. After incubation of 5 days at 25°C, the plate count total microbes were done and expressed as log cfu/g.

Statistical analysis

Each experiment was conducted in triplicate, and the data were statistically analyzed. Statistical software (SPSS 22.0) was used to evaluate data by two-way analysis of variance (ANOVA), and the post-hoc test was performed to evaluate significant (p < .05) differences.

Results and discussions

Weight loss, firmness, and color

The main problem in tomato fruit is rapid weight loss during storage, which leads to a reduction in shelf life.^[29] The weight loss of coated and uncoated tomatoes significantly (p < .05) increased with storage time (Figure 1). The weight loss in control treatment was higher (p < .05) as compared to coated treatments. On the 12^th day 5.85%, 4.17%, 3.48%, 2.91%, and 2.1% was the observed weight loss for T₀, T₁, T₂, T_3, and T₄. This study clearly indicated that higher weight loss was observed in T₀ (uncoated sample) which is greater than 5%. Moreover, all coated treatments shows less weight loss in comparison to un-coated but the treatment T₄ (aloe gel 60% + chitosan 2%) showed minimum weight loss because of thick coating layer and stand out as a best treatment in retaining the mass of tomato. The primary causes of a quick drop in weight are the loss of water and carbon reserves during respiration.^[30] The rate of loss of water is influenced by the gradient of water pressure over fruit surface and the atmosphere around it. The findings are similar to work described by Imani & Danaee^[31] that aloe vera–chitosan-based coating on tomatoes reduced the percentage of weight loss and enhanced the shelf life of tomatoes while maintaining the quality attributes during storage of 21 days at 4 ± 1°C. Basumatary et al.^[32] reported that chitosan coating in addition with clove oil and aloe vera on pineapple enhance storage life by reducing weight loss. The results were also in line with the work presented by Paul et al.^[33] that chitosan coating in addition with glycerol on tomato delayed the mass loss during storage. Firdous et al.^[34] explained that the aloe vera coating on tomatoes creates a layer that prevent weight loss and extend the shelf life for up to 30 days.

Figure 1. Weight loss percentage of uncoated and coated Roma tomatoes during storage of 12 days.

Texture is one of the vital quality parameters of tomatoes regarding the consumer acceptance. Because of the weakening of the composition of the cell wall, intracellular materials and cell structure the softening of the tomato fruits take place with storage time.^[35] Table 2 shows the remarkable decline in firmness with time period. Uncoated tomatoes showed significantly higher (p < .05) loss of firmness, while all coated samples showed less change in firmness during storage of 12 days. The edible coverings on fruit suppress the loss of firmness by retarding the activities of enzymes responsible for the tissue softening of tomatoes. Among coating treatments, the T₄ (aloe vera 60% + chitosan 2% coated tomato) was declared as best in retaining the firmness throughout storage. Similar work reported by Buendía-Moreno et al.^[36] that firmness of tomatoes decreased with period of storage with untreated tomatoes having highest decline in firmness when compared to fruit coated with active substance. Chrysargyris et al.^[37] reported that the aloe vera gel- and chitosan-based coatings postponed the softening process of tomatoes. According to Shah and Hashmi^[38] and Nia et al.,^[39] the combined coating of aloe vera and chitosan enhances the shelf life of fruits by maintaining their firmness. Utama et al.^[40] also stated that coating of chitosan combined with starfruit leave extract on tomatoes considerably delayed the firmness decline.

Table 2. Firmness (N) of coated and uncoated tomatoes during storage.

	Days
Treatments	0 day	4 day	8 day	12 day
T0	3.53±0.16	3.0±0.12	2.32±0.10	1.57±0.07
T1	3.32±0.14	3.09±0.13	2.64±0.11	2.14±0.10
T2	3.45±0.15	3.23±0.14	2.8±0.12	2.31±0.10
T3	3.37±0.14	3.24±0.14	2.84±0.12	2.45±0.11
T4	3.41±0.15	3.3±0.15	3.02±0.13	2.7±0.12

One of the prime determinants that attracts the consumer attention is color. Consumers prefer the uniform, deep red-colored tomatoes. It is investigated that the chlorophyll content decreased with increasing amount of carotenoids and lycopene during storage. During the ripening process of tomatoes, degradation of chlorophyll and rise in synthesis of lycopene result in characteristic color development. Both flesh and skin color result in the external color of the tomatoes. Table 3 indicates the change in color of tomatoes with storage days. It was noticed that all coated and uncoated treatments resulted in color change a*, b*, L*, and color index during storage. The a* value increased with storage periods, and a significant (p < .05) increase in value (30.04) was noticed in uncoated sample (T₀) on the 12^th day of storage. The rise in a* value with storage time seen lower in coated samples T₁, T₂, T₃, and T₄ and the values at the end day were 28.45, 27.42, 25.86, and 24.37 respectively. Among coated treatments, the significant (p < .05) delay in color change was observed in T₄. Moreover, the b* and L* value declined with the period of storage. The decline was more significant (p < .05) in uncoated treatment (T₀) due to ripening. The value for b* and L* on the initial day was 29.65 and 58.01, while on the 12^th day was 22.2 and 43.17, respectively. However, all coated treatments T₁, T₂, T₃, and T₄ showed lower decline in b* values (24.16), (26.16), (27.0), and (27.7) and L* values (46.3), (49.82), (53.35), and (54.74), respectively. This indicates that aloe-based coverings on tomatoes delayed the color change by delaying the process of ripening. In our study the best treatment that offered tomatoes more lightness and brightness during storage was T₄ (aloe vera gel 60% + chitosan 2%). Sherani et al.^[41] described the characteristics of olive oil/aloe vera gel coating which reduces transpiration that is attributed to metabolic process in fresh process and aids in preventing color quality parameters (L*, a*, and b*). Similar results presented by Basumatary et al.^[32] that addition of active substance in chitosan coating delayed the color alternation during storage. Firdous et al.^[34] stated that edible coating of aloe vera gel (80%) on tomatoes improved the color characteristics and other quality attributes during storage of 30 days. Additionally, the color index (CI) which was calculated by a*/b* ratio showed an increase in CI value in both coated and uncoated fruits with storage time (Table 3). La Scalia et al.^[42]; Al-Dairi et al.^[23] also noticed the same increase in color index with storage time. The coated fruits exhibited a significant (P < .05) delayed in change of CI value as compared to control. The CI value at the 12^th day in T₀, T₁, T₂, T₃, and T₄ was 1.35 ± 0.12, 1.18 ± 0.2, 1.05 ± 0.08, 0.95 ± 0.05, and 0.88 ± 0.07, respectively. The lowest change was observed in T₄ (60% aloe, 2% chitosan) indicated as the best treatment in maintaining the color of tomatoes. The lowest change in CI value of coated fruit was probably due to the impact of coating on delaying ripening process and moisture loss of fruits. Our findings are in accordance with the Shehata et al.^[43] who reported that chitosan-based coating on tomatoes delayed the change in color index during storage.

Table 3. Change in color parameters (a*, b*, L*, CI) of uncoated and aloe vera-based coated Roma tomatoes during storage.

Color Parameters
a* value	Treatments	Days
		0th day	4th day	8th day	12th day
	T0	24.3±1.01	26.21±1.04	28.13±1.01	30.04±1.08
	T1	24.23±0.98	25.63±0.98	27.05±1.01	28.45±1.04
	T2	24.05±0.96	25.15±0.97	26.3±0.98	27.42±1.05
	T3	23.59±0.95	24.3±0.93	25.08±0.95	25.86±0.1
	T4	23.29±0.96	23.61±0.93	24.0±0.91	24.47±0.97
b* value
	T0	29.65±1.09	27.45±1.01	24.8±0.98	22.2±1.02
	T1	29.03±1.07	27.53±1.07	25.86±1.01	24.16±0.1
	T2	29.57±1.01	28.47±1.03	27.32±1.01	26.16±1.02
	T3	29.35±1.02	28.58±1.19	27.79±1.20	27.0±1.11
	T4	29.03±1.05	28.61±1.04	28.14±1.02	27.7±1.03
L* value
	T0	58.01±2.71	53.55±2.72	48.51±2.66	43.17±2.74
	T1	58.45±2.70	54.87±2.74	50.64±2.78	46.3±2.75
	T2	58.32±2.61	55.68±2.65	52.76±2.66	49.82±2.74
	T3	58.68±2.60	57.0±2.64	55.17±2.71	53.35±2.71
	T4	58.74±2.71	57.42±2.73	56.13±2.74	54.74±2.75
Color index (CI)
	T0	0.82±0.07	0.95±0.08	1.13±0.1	1.35±0.12
	T1	0.83±0.06	0.93±0.07	1.04±0.07	1.18±0.2
	T2	0.81±0.06	0.88±0.07	0.96±0.07	1.05±0.08
	T3	0.80±0.06	0.85±0.07	0.9±0.07	0.95±0.05
	T4	0.80±0.06	0.82±0.06	0.85±0.06	0.88±0.07

Acidity, total soluble solids, maturity index, and pH

Acidity constitutes a crucial quality aspect that greatly affects the fruit taste. Tomatoes are highly susceptible to after harvest respiration activity because the organic acid, especially citric acid, undergoes metabolism to provide mediators to the tricarboxylic acid cycle with a rise in respiration. Tomato titratable acidity decreases during ripening.^[5] As shown in Figure 2, results indicated that the acidity of all the coated and uncoated samples decreased with storage periods. The uncoated tomatoes experienced significantly (p < .05) greater reduction in acidity from initial day (0) to end day of storage (12) and the value drops from 1.01% to 0.55%. The coated tomatoes showed a slower decline in acidity. The slower decline in acidity values in samples that were coated indicated a decrease in the rate of transpiration due to a decreased accessibility of organic acids, that is important for acidity in fruits.^[44] Among coated samples, the aloe vera-based coating with 60% gel and chitosan 2% (T₄) showed least change in acidity from initial to end of trial (0.97% − 0.83%) and retain the taste of tomatoes during storage. Similar result reported by Sree^[45] that the tomatoes with a combined aloe vera- and chitosan-based coating retained a higher acidity percentage as compared to tomatoes with a single aloe vera coating during storage of 30 days. According to Tarangini et al.,^[46] the sericin coating in addition with aloe vera and chitosan enhanced the shelf life of tomatoes and retained the taste by retarding its acidity change during storage. Morad et al.^[25] explained that casein/chitosan coating in addition with oregano oil as antimicrobial maintained the acidity of tomatoes during storage of 32 days at 4°C. Wang et al.^[47] described that coating of chitosan with inclusion of ascorbic acid on Annona squamosa maintained their acidity during storage of 12 days at temperature 15°C.

Figure 2. Acidity (%) of uncoated and coated treatments with storage days.

The amount of sugar present in the fruits represents the TSS value. Among the quality parameters, it is the main parameter for determining the freshness of fruit.^[48] In a present work, it was observed that at initial day TSS content was found to be lower in all coated and uncoated tomatoes (Table 4). However, with storage time the increased trend was seen and the significant increase (p < .05) in TSS was observed in T₀ at the end day of storage (5.3 °Brix). The TSS values for other coated treatments T₁, T₂, T_3, and T₄ which were 4.6, 4.3, 4, and 3.7 °Brix. This clearly indicated that soluble solid content of all coated tomatoes was found lower compared to uncoated ones. The lowered change in soluble solids content in edible covered fruits may be related to a reduction in tomato respiration rate, which delays metabolic processes like pectin and other carbohydrate breakdown, incomplete protein hydrolysis, and glycoside decomposition.^[49] According to our work, the T₄ (aloe vera 60% + chitosan 2%) stands out as the best treatment in retaining the soluble content at end day of storage. Similar work reported by Khatri et al.^[50] who found that aloe vera-chitosan coating on tomatoes retained the total sugar content during 32 days of storage. Same results reported by SALARIA et al.^[51] that combined coating of aloe vera, chitosan, and extract of mint leaves on sponge gourd retained the TSS and other quality attributes during 10 days of storage.

Table 4. Total soluble solid (⁰Brix) and pH of coated and uncoated Roma tomatoes during storage of 12 days.

Total soluble solid (TSS)
		Days
	Treatments	0th day	4th day	8th day	12th day
	T0	3.3±0.14	4±0.18	4.6±0.20	5.3±0.20
	T1	3.2±0.14	3.8±0.17	4.2±0.18	4.6±0.20
	T2	3.4±0.15	3.7±0.17	4±0.18	4.3±0.20
	T3	3.4±0.15	3.6±0.16	3.8±0.17	4.0±0.17
	T4	3.5±0.16	3.5±0.16	3.6±0.16	3.7±0.17
pH
	T0	4.28±0.16	4.7±0.23	5.1±0.25	5.6±0.26
	T1	4.2±0.20	4.5±0.21	4.82±0.23	5.1±0.25
	T2	4.35±0.2	4.6±0.22	4.8±0.24	4.95±0.25
	T3	4.2±0.15	4.5±0.20	4.7±0.22	4.8±0.23
	T4	4.4±0.20	4.4±0.20	4.5±0.2	4.6±0.21

The maturity index (MI) increased along with increased storage time in both untreated and treated tomatoes (Figure 3). The increase in MI with an extended storage period is related to an increase in sugar content and a decrease in acid content of the tomatoes.^[52] However, the value of MI showed a significant difference (p < .05) between coated and uncoated tomatoes. At the end of the trial (12^th), the control treatment had the greatest TSS/TA ratio (9.58) compared to the coated treatments T₁, T₂, T₃, and T₄, which were 6.8, 5.8, 4.8, and 4.4, respectively. The lowest MI value in coated fruits could be attributed to a barrier effect induced by the coatings, which reduces the fruits’ metabolism. Furthermore, it was obvious that among all treatments, T₄ responded very well and had a significantly (p < .05) lower TSS/TA ratio at the 12^th day of storage. Peralta-Ruiz et al.^[53] studied the effect of chitosan-based coating on tomatoes during storage of 12 days. The authors suggested that chitosan-based coated tomatoes showed least change in TSS/TA ratio during storage of 12 days compared to control. Our findings are also in line with those of Abebe et al.^[26] who found that chitosan-coated tomatoes delayed the change in value of MI during storage for 22 days. Similarly, Pobiega et al.^[54] examined the impact of pullulan-based coatings on tomatoes and found that pullulan in combination with ethanolic extract of propolis (5%, 10%) reduced the maturation time of cherry tomatoes.

Figure 3. Change in maturity index (TSS:TA) during storage for both uncoated and coated Roma tomatoes.

pH is one of the quality parameters used to calculate the quality of tomato fruits. Due to the organic acid consumption for the metabolic process in the course of respiration, the pH of the fruit always rises for the duration of maturation.^[55] The results of the current study also showed that pH increased with storage periods. This rise in pH during storage indicates that the organic acids in tomatoes degrade during storage. From mean table results (Table 4), the highest change in pH was seen in T₀ (uncoated sample) >1 from day first to end day of trial. However, the other treated tomatoes showed the lowest change in pH of tomatoes in comparison to uncoated ones. Edible coverings reduced change in pH during storage by modifying the internal environment and slowing down the metabolic process.^[56] Moreover, the study suggested that among all coated treatments T₄ (aloe-based gel 60% + chitosan 2%) showed significantly (p < .05) lower pH at the end day of storage (12th). Similar results reported by Mani et al.^[57] that edible coatings on fruit in addition with aloe vera extend the shelf life of fruit by delaying the change in pH. Abebe et al.^[26] stated that edible coating of pectin and chitosan on tomatoes not only extended the storage life of fruit but also maintained the pH and other quality attributes during storage.

Ascorbic acid (vitamin C) and free radical scavenging potential (DPPH)

Ascorbic acid is a prime nutritive factor, and as compared with the other nutrients it is sensitive to deterioration during processing and storage.^[38] High levels of ascorbic acid present in tomato fruits provide several health benefits. Ascorbic acid has a vital role in various physical and metabolic functions of plant.^[58] The content of vitamin C declines as the fruit ripens. As seen in Table 5, the ascorbic acid level for control tomatoes on the first day was 40.32 mg/100 g. During storage a rapid decrease was noticed in the control sample and at 12^th day the observed value of ascorbic acid was 19.23 mg/100 g. In contrast with uncoated (T₀), the coated tomatoes have shown a significant difference (p < .05). At end day of trial the observed values for other treatments T_1, T₂, T₃ and T₄ were 23.18, 25.16, 28 and 30.47 mg/100 g. The retention in ascorbic acid content may be greatly preferred by the existence of oxygen and the coverings on fruit surface that restrict diffusion of oxygen and thus better retain the ascorbic acid content.^[28] Among coating treatments, T₄ (aloe vera gel 60% + chitosan 2%) showed be the best in retaining vitamin C content. In accordance with our work, Tzortzakis et al.^[59] described a decreased in vitamin C content during storage of tomatoes that was conserved by aloe vera gel-based coating. Another findings reported by Firdous et al.^[60] that aloe vera gel-based coating on tomatoes delayed the decrease in ascorbic acid content during storage of 30 days. Adetunji et al.^[17] demonstrated that aloe vera coating combined with chitosan is a more effective approach for extending the shelf life of fruits while maintaining their ascorbic acid content than individual aloe vera coating. Khatri et al.^[50] studied the synergetic effect of aloe vera and chitosan coating on tomatoes and found that aloe vera + chitosan retained the ascorbic acid of tomatoes during storage for 42 days at 4 ± 1°C.

Table 5. Ascorbic acid (mg/100 g) and free radical scavenging activity (DPPH) value of uncoated and aloe vera-based treated tomatoes.

Ascorbic acid contents
		Storage
	Treatments	0th day	4th day	8th day	12th day
	T0	40.32±1.95	34.15±1.46	27.78±1.05	19.23±0.92
	T1	39.77±1.92	34.61±1.47	29.33±1.09	23.18±0.94
	T2	39.51±1.92	34.89±1.5	29.96±1.11	25.16±0.96
	T3	38.2±1.87	35.42±1.57	31.54±1.27	28.0±0.1
	T4	39.86±1.92	37.43±1.61	34.17±1.31	30.47±0.1
DPPH
	T0	67.8±3.25	74.27±3.66	81.1±3.75	88.0±3.78
	T1	67.3±3.15	73.1±3.65	79.32±3.73	85.54±3.75
	T2	66.4±3.11	71.4±3.62	76.72±3.72	81.72±3.74
	T3	66.7±3.12	70.3±3.6	74.2±3.65	78.0±3.66
	T4	67.8±3.14	69.6±3.57	72.7±3.64	75.82±3.65

The antioxidant potential of tomato fruit was investigated by DPPH method. The antioxidant (DPPH) value of fruit increased gradually with time of storage (Table 5). Uncoated tomato fruits showed a significant (p < .05) increase in DPPH value from day first to end day of trial, while the coated sample in comparison to uncoated showed resistance against change in DPPH value during storage. Sharp increase in uncoated tomatoes presents the rapid ripening process and decay of postharvest fruit. Edible coverings aid in slowing down the process of decaying and ripening of fruit. Among coverings, the aloe vera-based coatings with gel 60% and chitosan 2% showed to be the one treatment in retaining the DPPH value during storage of 12 days. A similar work presented by Tahir et al.^[61] that coating of strawberry fruit maintained the value of DPPH during storage by delaying the process of maturation and senescence. According to Noorbakhsh & Danaee,^[62] the coating of aloe vera and chitosan preserves the antioxidant activity and other nutritional quality of the fruits while extending their shelf life. Tzortzakis et al.^[59] stated that aloe vera coating in addition with sage essential oil maintained antioxidants of tomatoes during 12 days of storage. Mondal et al.^[63] described that addition of ethanol extract of green algal in chitosan coating delayed the change in DPPH value of tomato during storage.

Microbiological analysis

Due to high susceptibility of microbial spoilage, the quality of tomatoes deteriorates rapidly.^[64] The growth of microbes increased with time. From Table 6 no significant (p > .05) increase in decay was observed in all treatments for up to 4 days. However, on the 8th day a sharp rise in microbial growth was observed and uncoated treatment (T₀) showed a significantly (p < .05) higher value 2.47 log cfu/g whereas for coated treatments T₁, T₂, T₃, T₄ the values were 2.01, 1.74, 1.53, 1.38 log cfu/g. On the end day (12^th) of storage a similar trend was seen the microbial count for T₀ was 3.57 log cfu/g and for other treatments T₁, T₂, T₃, T₄ was 2.67, 2.12, 1.8, 1.6 log cfu/g. It can be seen that aloe vera-based coating treatment showed slower growth of microbes in comparison to uncoated. This is because edible coating not only repairs damage on the fruit’s surface but also provides a layer of protection that keeps the food from decaying. In this study, we found that T₄ coating treatment delivered the best results in terms of microbial inhibition. In accordance with our work Vieira et al.^[18]; Imani & Danaee^[31] demonstrated that applying a chitosan coating comprising aloe vera to the fresh produce surface after harvesting creates an extra barrier to prevent postharvest contamination by microorganisms. Lin et al.^[64] reported that the combination of Bacillomycin D. and chitosan overcomes the prevalence of gray mold and soft rot in cherry tomatoes during the storage at room temperature and extended the shelf life. Other studies by Peralta-Ruiz et al.^[53], Guerra et al.^[65], and Ramos-García et al.^[66] stated that the addition of essential oil as antimicrobial agent in chitosan coating prevented the tomato from decay.

Table 6. Microbial count of coated and uncoated tomatoes during storage.

	Days
Treatments	0	4	8	12
T0	1.06±0.05	1.56±0.08	2.47±0.11	3.57±0.12
T1	1.03±0.05	1.4±0.07	2.01±0.10	2.67±0.11
T2	1.04±0.05	1.34±0.06	1.74±0.08	2.12±0.01
T3	1.05±0.05	1.26±0.06	1.53±0.07	1.8±0.08
T4	1.01±0.05	1.17±0.06	1.38±0.07	1.6±0.08

Conclusion

The results of the study proved that aloe vera-based coating in combination with chitosan is a successful and effective way for prolonging the shelf life and sustaining the quality attributes of tomatoes during storage of 12 days at 8°C. All aloe vera-based coatings delayed the physiological, chemical, nutritional, and microbial changes in tomatoes during storage as compared to uncoated ones. However, the best coating combination in case of sustaining the quality attributes was 60% aloe vera + 2% chitosan (T₄). T₄ coated tomatoes showed maximum retention of changes in weight, firmness, color, acidity, soluble solids, maturity index, pH, ascorbic acid, and antioxidant activity. Additionally, this coating treatment lowered the overall microbial count, which reduced fruit decay susceptibility and improved microbial safety during storage of 12 days. To summarize, 60% aloe gel with 2% chitosan edible coatings can be suggested for preserving tomato fruit postharvest quality. However, further research is required to explore the effect of this novel organic, edible coating on quality conservation of other fruits and to commercialize it in the food industry.

Acknowledgments

The authors express their thanks to Government College University for giving us a platform for gathering literature.

Disclosure statement

No potential conflict of interest was reported by the author(s).