Postharvest Quality of Tommy Atkins Mangoes Coated With Cassava Starch and Chitosan-Based Coatings

This study aimed to evaluate postharvest quality of Tommy Atkins mangoes treated with starch cassava and chitosan based coatings. Mango fruits were collected at physiological maturity. After cleaning, weighing and identification, fruits were submitted to the respective treatments and stored for 35 days in the Laboratório de Tecnologia de Alimentos, with weekly evaluations under refrigeration 13±1 oC and 90±5% RH. The experiment was conducted in a completely randomized design, in factorial scheme with four treatments: control, cassava starch (CS), chitosan (CH), and cassava starch/chitosan (CS/CH) at a concentration of 2%, and six storage periods (0, 7, 14, 21, 28 and 35 days) with four replications. Fruits were evaluated in: appearance, weight loss, external color: luminosity and ΔE, pulp firmness, titratable acidity, soluble solids content, starch, total soluble sugars, reducing sugars and sucrose. Data were submitted to analysis of variance using SISVAR software and compared by Scott-Knott test at 5% of probability. It was observed a reduction in appearance, pulp firmness, titratable acidity, starch and reducing sugars and increase in weight loss, luminosity, ΔE, soluble solids, total soluble sugars and non-reducing sugars during storage. CS/CH coated fruits reported higher notes of appearance, lower weight loss and maintained color. Quality of physicochemical attributes: soluble solids, starch, total soluble sugars, reducing sugars and non-reducing sugars were strongly retarded.


Introduction
Mango (Mangifera indica L.) is one of the most important tropical fruits, appreciated for its taste, aroma, and its typical and attractive colors.World production of mango in 2014 reached over 45 millions of tons, with India as the largest producer holding 40% out of the total.Other important producers of mango worldwide are China (10%), Thailand (8%), Indonesia (5%), Mexico (4%), Pakistan (4%), and Brazil (3%) (FAO, 2017).Brazil exports 9% of what it is produced, with Europe being its biggest importer (Gallo, 2015;FAO, 2017).
Tommy Atkins is the main commercial cultivar exported from Brazil, which has good productivity and capacity to adapt itself to different growing environments, tolerance to diseases, and good postharvest conservation (Andrade et al., 2017).As a climacteric fruit, it quickly ripens in adverse climatic conditions.Decrease in respiratory rate is the main technique used to extend shelf life of fruits and vegetables (Siddiqui, 2017).Currently, refrigeration under 10 to 13 ºC and 85% of RH guarantee mangoes' quality for two to three weeks, depending on maturation stage (Neves, 2009) or refrigeration associated to carnauba wax and plastic packages, which maintain quality for 28 to 35 days, being both used to increase postharvest quality in mangoes fruits intended to exportation.
The use of edible coatings on postharvest conservation of fruits has been announced as an emerging technology with great potential, mainly for use in tropical fruits (Fani et al., 2017;Siddiq et al., 2017).Edible coatings used in postharvest are biodegradable, derived from renewable sources and avoid environmental pollution (Salgado et al., 2015;Kerch, 2015).Studies have been developed aiming tests with edible coatings to increase the use and extend shelf life of fresh products (Dhital et al., 2017;Allegra et al., 2017;Murmu & Mishra, 2017).
Edible coatings do not want to replace conventional materials or even eliminate the use of cold environments, but it presents a functional and supporting performance, since both are capable of reducing fruit weight loss during storage or decrease oxygen absorption and retard respiration, retarding maturation and any alteration in firmness, color, weight, and chemical compounds (Cazón et al., 2017;Yousuf et al., 2018).
Many biopolymers have been assessed on coating formulations.Cassava starch and chitosan have been studied as a primary material on these edible coatings preparation (Castro et al., 2017;Silva et al., 2017;Nair et al., 2018) because they form a resistant and transparent film with good aspect and intense brightness, turning fruits and vegetables more commercially attractive (Garcia et al., 2016).
The use of composite coatings extends quality attributes and increase postharvest shelf life of Tommy Atkins and Palmer mangoes (Azerêdo et al., 2016;Cissé et al., 2015;Medeiros et al., 2012).The combined use of these coatings promoted a uniform and homogenous coat, improving appearance and conservation of fruits quality (Castañeda, 2013).
Due to the importance of mangoes in agribusiness and its perishable nature, the objective of this study is to evaluate postharvest of Tommy Atkins mangoes using cassava starch and chitosan-based coatings.

Material and Methods
The present study was carried out in the Laboratório de Tecnologia de Alimentos at Universidade Federal Rural do Semi-Árido (UFERSA).Materials used in edible coatings formulation were: cassava starch, chitosan, and bidistilled white glycerin.Tommy Atkins mango fruits were collected at physiological maturity at Fazenda Finobrasa Agroindustrial S/A, located in Ipanguaçu-RN, in the region known as Vale do Açu, semiarid region, classified as "BSwh" according to Köppen-Geiger classification system, dry and hot, with average rainfall rate of 585.5 mm, average annual temperature of 28.1 ºC, and relative humidity of 70%.
In the Laboratório de Tecnologia de Alimentos, fruits were selected and washed in 100-ppm chlorine water and dried at room temperature.Fruits were marked and separated according to the experimental design chosen.The experiment was conducted under a complete randomized factorial design, in factorial scheme, with four treatments: control group (uncoated), and coatings with cassava starch (CS), chitosan (CH), and cassava starch/chitosan (CS/CH), all at a concentration of 2%, and six storage periods (0, 7, 14, 21, 28, and 35 days) under refrigeration of 13±1 ºC and 90±5% of RH, with four replicates per each experimental unit.
Coatings of cassava starch (CS) and chitosan (CH) were prepared with 2.0 g of polymer, 0.2 g of plasticizer (glycerol), in 97.8 g of distilled water (for CS) and 97.8 g of acetic acid (1%) pH 3.0 (for CH).Cassava starch solution was stirred and heated to 70 ºC for 15 minutes using a heater-stirrer.While solution of chitosan was homogenized using a stirrer for 45 minutes until complete homogenization.After preparation of each solution separately, mixture of CS/CH was prepared.
Fruits were individually immersed for one minute in the respective coating solutions of each treatment and dried out in room temperature for one hour, followed by storage under refrigeration at 13±1ºC and 90±5% RH.
The following physicochemical analysis were made for each period of storage: appearance, weight loss, external color: luminosity and total color difference (ΔE), pulp firmness, titratable acidity, soluble solids content, starch, total soluble sugars, reducing sugars, and sucrose.

Weight loss (WL):
Determined by the difference between initial weight and weight at each period of storage, expressed in percentage (%).

External color (EC):
Measured by reflectometry, using a colorimeter CR-10 (Konica Minolta®, Japan), calibrated in white porcelain surface under light conditions.Readings were expressed in L, a* and b* module, which, according to CIE (Commission Internacionale de L'Eclaraige), define color: L corresponds to luminosity (brightness, clarity and reflectance; 0 = dark/opaque and 100 = white) (Minolta Corp, Ltd., Japan).Readings were made in four different equidistant points, in greenish areas, and it was considered the average of readings.From coordinates it was possible to determine the total color difference with the following equation: ΔE = ΔL 2 + Δa 2 + (Δb)², where ∆E represents the difference between each color coordinate from samples at time zero and stored samples.(Siddiq et al., 2017).The decrease in firmness is also associated to the transformation of insoluble pectic fractions to soluble forms during ripening (Siddiqui, 2017).

Titratable Acidity
The use of coatings influenced titratable acidity of fruits during storage (Table 1).At day 14, the type of coating did not change acidity of fruits.However, at day 21 and 28 fruits coated with cassava starch and control reported values statistically superior to the other treatments, which changed in day 35, when fruit acidity did not differ within treatments.Decrease in titratable acidity of fruits coated with chitosan and its mixture with cassava starch from day 21 and fruits coated with cassava starch at day 28 is probably related to the used of acids as carbon skeleton in the respiratory process.The level of acids in plants may decrease with maturation, due the transformation of acids in substrate for phenolic compounds synthesis, lipids, and vegetal aromas (Siddiqui, 2017).
On the other side, an increase in acidity was observed at day 14 in mango fruits regardless of its coating, with reduction of acidity after that period of storage.Fruits did not differ in titratable acidity values within coatings at day 35 of storage.Silva et al. (2017) showed similar results and reported that the increase in acidity of fruits may be assigned to galacturonic acid, from pectin degradation.Gol and Rao (2014), studying coatings, reported that mangoes reach a lower level of titratable acidity (0.2%) at 18 days of postharvest storage.The decline in titratable acidity during storage was assigned to the use of acids as substrates for respiration, as well as its conversion to sugar via gluconeogenesis (Eskin et al., 2013).

Soluble Solids
There was effect of type of coating and storage period on the soluble solids content of fruits (Figure 5). jas.ccsenet.
Figure 5 There was showed th fruits coat compared other. The

Table 1 .
Titratable acidity (% acid citric) of Tommy Atkins mangoes stored with different coatings in function of period of stored at 13 ºC and 90% RH.Mossoró-RN, UFERSA, 2017 Note.* Averages followed by same lowercase letter within lines and same uppercase letter within column did not differ from each other by Scott-Knott test (p < 0.05).