Alleviation of chilling injury in postharvest banana with protection materials

R E G U L A R A R T I C L E


INTRODUCTION
The banana fruit is harvested and stored in a mature green state.Marketing is complicated by postharvest losses (Hailu et al., 2012).Shelf life extension of banana has been a problem for years due to its climacteric respiration pattern (Sen et al., 2012).Low temperature handling and storage are the most important physical method of postharvest management of banana (Hailu et al., 2013).Green bananas are shipped/stored at 13 to 14°C to delay ripening (Hailu et al., 2013) because are susceptibility to chilling temperature below 13°C (Sen et al., 2012;Wu et al., 2014).
Chilling injury (CI) becomes a major problem in marketability in the banana industry (Hashim et al., 2014).The most common visual CI symptoms include a dull gray peel color, ripening, flavor and increasing physical injury and peel and pulp browning (Hailu et al., 2013).Polyethylene of different densities polypropylene and polyvinyl chloride has been used in the packaging of fruits with direct effect on the permeability to gases and water vapor, with subsequent differential effects on the fruit quality (Mangaraj et al., 2009).
Plastic films have also been found to increase the shelf life (Hailu et al., 2012;Sahay et al., 2015;Sahay et al., 2017) and help the banana fruit tolerate temperatures below 13°C without exhibit CI.The cooking bananas keeps well for nearly 60 days at 9 or 10°C, in a partially evacuated polyethylene bag (Hailu et al., 2013).The use of 16 and 10μm polyethylene films, associated with storage at 12 and 15ºC, shows a retention of the ripening process of the fruits of the cultivars FHIA-02 (AAAA) e Preciosa (PV 4285) (AAAB), (Siqueira et al., 2010), Tropical (AAAB) and Thap Maeo (AAB) (Siqueira et al., 2017).
The purpose of this paper was to investigate the influence of different protection materials on occurrence of CI Storage of bananas at low temperature is limited due to the development of chilling injury (CI).The purpose of this paper was to investigate the influence of different protection materials on occurrence of CI and the characteristics of banana in postharvest.Current paper also investigated temperatures variations in bags.The experiments were conducted with fruits of Musa spp., cultivars Prata (AAB) and Nanica (AAA).Comprised a completely randomized 2x3x6 factorial design, two cultivars, three temperatures (5°C or 10°C for 10 hours and 20°C constant) and five protection materials (blue transparent polyethylene, white non-woven fabric, white opaque polyethylene, bubble wrap, white laminated non-woven fabric) and control (without protection).The different protection materials kept the temperature inside at 1°C higher than environment.The critical temperature for occurrence of chilling injury was 5ºC for 'Prata' banana and 10ºC for 'Nanica' banana.White laminated non-woven fabric induced lower CI index and tended to maintain the peel color characteristics (L*, C* and h o ) higher, compared to other protection materials.'Nanica' fruits stored at 20ºC bagged with white laminated non-woven fabric exhibited lower incidence of Crown rot.Other physicochemical characteristics evaluated were not influenced by low temperature and protection material, only by cultivar.
and the characteristics in banana in postharvest.Current paper also investigated temperatures variations in bags.It was thus expected to establish the best bagging material to protect the fruit from CI and improve the quality of banana.

Plant materials and experimental design
The experiments were conducted with fruits of 70 bunches of Musa spp., AAB group, subgroup Prata, cv.Prata and Musa spp., AAA, Cavendish subgroup, cv.Nanica harvested on two plots in a 5 th crop cycle in Jacupiranga, state of São Paulo,Brazil (24º43' 6.2' S and 48º2'53.2' W).The bunchs were harvested with 30mm diameter and sum thermal of 1005 and 917 degree-days, respectively, for the 'Prata' and "Nanica'.
The four central hands of each bunch were collected and cut into bouquets of five fruits, without any defect or blemish.The bouquets were then washed, dried and bagged with blue transparent polyethylene (BTP) with 3µ of thickness and highly transparent; white non-woven fabric (WNF) with 3µ of thickness and moderately transparent; white opaque polyethylene (WOP) with 60µ of thickness; bubble wrap (BW) with 3µ of thickness and highly transparent; white laminated non-woven fabric (WLNF) with 1µ of thickness and translucent.Bouquets without protection (WP) were the control.BTP, BW and WOP were manufactured with low density polyethylene, and WNF and WLNF with polypropylene, all sealed and non-perforated.After bagging, the fruits underwent different temperatures and exposure times, as follows: 5°C for 10 hours; 10°C for 10 hours, and 20°C (constant) in a refrigerated chamber.The experimental design was completely randomized in a factorial 2 x 3 x 6 (cultivar x temperature x protection material), with seven replications.The incidence of the Cladosporium spot and Crown rot due to occurring in only one cultivar were analyzed according to completely randomized in a factorial 3 x 6 (temperature x protection material), with seven replications.
Temperatures were taken on the peel and pulp surface during low temperature exposure by a Datallogger with sensors, coupled to an automatic acquisition of periodic data readings.Until reached maturity stage 6 (von Loesecke, 1950), all plots were maintained at at 20°C and 90% relative humidity.The camera space was ventilated for 15 min every 12 h to avoid the build-up of ethylene.

Evaluation of physicochemical characteristics and phytosanitary quality of the fruits
The shelf life, was defined as the time from harvest to when fruit reached the maturity stage 6; the mass loss, was determinated by the equation ML=[(Mf-Mi)/ Mi]*100, where Mi is the initial mass and Mf is mass at maturity; and the firmness of pulp, estimated with penetrometer equipped with conical probe of 0,8 cm diameter.The pH was determinated in pH-meter after homogenization of pulp with water and the titratable acidity, after homogenization of pulp with water and titration with NaOH (AOAC, 2005); the total soluble solid, determined after homogenization of pulp with water using digital refractometer (Tressler and Joslyn, 1961).The soluble sugars were determined after extracting with hot ethanol and reaction with anthrone (Hodge and Hodfreiter, 1962), whiles starch, quantified in residue from ethanol extraction of soluble sugars (McCready et al., 1950;Patel, 1970).The incidence of rot (Cladosporium spot, Anthracnose and Crown rot) in mature fruits was also estimated.All analyses were made in triplicates.

Statistical analysis
Was carried out with Sisvar 4.2.Analysis of variance was then performed with F-test and the differences in means were compared by Tukey´s test.The data of disease incidence were transformed in arc sen (x/100) 1/2 .Correlation study (r) was performed by Pearson´s method based on the significance of t-test.

RESULTS AND DISCUSSION
The analysis of the temperature near the surface of fruit peels at 10 and 5°C revealed no significant changes when comparing the temperatures of bagged fruit with different types.However, temperature rose when bagging was employed (Figure 1).On an the average, the protection of fruits with different types of material kept the temperature higher by 0.71 and 0.66°C for banana cultivars 'Nanica' and 'Prata', respectively, when compared to fruits without protection during 10 hours exposure at 10°C (Figure 1).From 0.44 and 0.49°C during exposure to 5°C, respectively.In short, there was a less than 1°C increase in temperature with bagging.During the exposure of fruits to 5 or 10°C during 10 hours, regardless of the cultivar, the temperature of the pulp was always higher than that of the peel.
CI index was influenced by interaction cultivar x temperature and (Table 1) and temperature x protection material (Table 2).For 'Prata' fruits, CI index was low at 10 and 20°C and increased at 5°C, while for 'Nanica' increased already at 10°C and differed between the three temperatures of storage (Table 1).Regardless of temperature, CI index was always lower in fruits of the cv.Prata, indicating superior tolerance at low temperature.
For both cultivars, CI index increases with the reduction of storage temperature, regardless of the protection material used (Table 2).At 20°C, there were no significant differences in CI index between the protection materials.However, at 5 and 10ºC, fruits protected with WLNF exhibited lower CI index.
Browning has a significant impact on colour of peel.L*, C* e h o were affected by interaction cultivar x temperature x material.The unfolding of interaction revealed there was a marked difference in color characteristics between the cultivars (Table 3).Regardless of temperature and protection materials, fruits 'Nanica' exhibited L*, C* and h o lower than 'Prata', a sign of greater internal browning.L* of fruits 'Prata' stored at 10°C did not differ from fruits stored at 20°C, different from the 'Nanica', which exhibited a significant reduction.
For 'Prata' fruits kept at 20ºC, the highest values of L* in the peel occurred for WP, followed by WLNF and last of the other materials, which did not differ (Table 3).WLNF also promoted higher L* in fruits of the same cultivar maintained at 5 and 10ºC.For 'Nanica' fruits, there were no differences for L* between protection materials at any storage temperature.
The color intensity (C*) was more intense for 'Prata' fruits at 20ºC with WOP, at 10ºC with BW and at 5ºC with WLNF.For 'Nanica' fruits, independent of storage temperature C* was higher for WLNF.
Due to CI, the color angle (h o ) decreased and shifted towards the reddish region, as a result of the discoloration of peel colour into brown (Hashim et al., 2012) (Table 3), associated with the accumulation of oxidized polyphenols within the vascular tissues (Hashim et al., 2014).Response that occurred to 'Nanica' banana already at 10ºC, while for 'Prata' only without protection fruits exposed to 5°C.For fruits 'Prata' stored at 10 and 20ºC, hº was higher with bagging with WLNF, while at 5ºC there were no differences between the protection materials (Table 3).For 'Nanica' fruits, h o at 5 and 20ºC did not differ between treatments, while at 10ºC, it was higher for WLNF and lower for WP.
Fruits cv.Prata storage at 5ºC without protection (WP) always showed the lowest values of L*, C* h°, indicating that regardless of the nature of the material protection the presence of the bag was beneficial for maintaining the visual quality.Response does not observe in fruits cv.Nanica (Table 3).
Color characteristics presented significant negative correlation (p<0.01) with CI index of the fruit peel 'Prata' (-0.82 for L* and -0.75 for C*) and of the 'Nanica' (-0.83 for L*, -0.74 and -0.85 for h o ), indicating that the visual analysis of peel browning was adequate.
The incidence of Anthracnose was not influenced by the cultivar x temperature x protection material interaction, nor isolated effects of these factors, presenting an average value of 3.51 and 3.85%, respectively, for 'Prata' and 'Nanica', without significant difference (p<0.01).Cladosporium spot occurred only in fruits 'Prata', with an average incidence of 25.39%, unaffected by temperature and protection material (p<0.01).
Crown rot is one of the most important postharvest diseases of banana, very common in bananas of subgroup Cavendish, is caused by several fungi, sometimes in association with other microorganisms such as bacteria (Hailu et al., 2013).Indeed, only 'Nanica' fruits showed Crown rot, which was affected by the interaction temperature and protection material (Table 4).The unfolding of this interaction revealed a lower incidence of Crown rot in fruits stored at 20 o C with LNFW, followed by WNF, and finally of the other treatments.All fruits stored at 5 and 10 o C exhibited Crown rot.Cold stress in postharvest promotes reduced resistance to pathogens (Gamal et al., 2010).
The effect of the protection material on the CI index, peel color and incidence of Crown rot may be related to the composition (Tables 2, 3 and 4).BTP, WOP and BW are composed of low-density polyethylene.WNF and WLNF are made of polypropylene.Polypropylene have higher barrier gases (higher ratio of CO 2 to O 2 permeability) e water vapor than polyethylene (Mangaraj et al. 2009).Because it is very porous, polypropylene tends to has lower heat transfer, without however has significantly affect the surface temperature of the fruit peel (Figure 1).
The atmosphere with low in O 2 and / or high in CO 2 to influence the metabolism of banana being packaged or the activity of decay-causing organisms to increase storability and/or shelf life (Hailu et al., 2013).Nguyen et al. (2004) observed that that the use of non-perforated polyethylene bags has raised ratio CO 2 to O 2 and reduced CI symptom in sucrier bananas (Musa AA Group cv.Kluai Khai) stored at 10 o C, response related to lower activity of enzymes phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO).
Recently, based on the respiration rate and permeability of the packaging materials, the best suitable packaging films obtained for the modified atmospheric packaging of fruits of Musa balbisiana at different storage temperatures) was found to be polypropylene, and polyvinyl chloride film (Ghosh and Dash, 2018).Despite possible differences in moisture and gas content inside the bagging, there were no differences in shelf life and mass loss, as well as in other physicochemical characteristics, between the protection materials.Shelf life has not prolonged (Table 4), possibly because after exposure to low temperature the fruits were kept at 20°C, temperature that allows high metabolic activity.Exposure to low temperature (5 and 10°C) also did not affect the ripening and conversion of starch to soluble sugars, though the pulp has reached the stress temperature (Figure 1).This fact may be related to the stress temperature and duration or to the type of the tissue.The shelf life, mass loss, total soluble solid, pH, titratable acidity, soluble sugars and starch in the pulp were affected only by the cultivar, with mean values characteristic of each genomic group (Table 5).The symptoms of CI are dependent on the genomic group (der Agopian et al., 2011).In this study cultivar 'Prata' was more tolerant to CI than 'Nanica' (Table 1).Really, in Brazil, the cv.Nanicão, a member of the AAA group, is commercially relevant but less tolerance to low temperatures than Prata, the cultivar of the AAB group (der Agopian et al., 2011).The B genome appears to confer cold resistance (der Agopian et al., 2011).Goldfinger' banana (AAAB) showed tolerance keeping L* and h° of the peel unchanged even when submitted to storage at 10°C, compared to control 20°C.
It is suggested to carry out new studies using microperforated LNWF of different thicknesses, in order to extend the shelf life of the banana with a lower temperature than usual (13 ºC), for cv.Prata between 5 and 10ºC and cv.Nanica between 10 and 13ºC.

CONCLUSIONS
The different protection materials kept the temperature inside at 1°C higher than environment.The critical temperature for occurrence of chilling injury was 5ºC for 'Prata' banana and 10ºC for 'Nanica' banana.In terms of chilling injury and peel color, the laminated non-woven fabric white was the best material.Other physicochemical characteristics were not influenced by low temperature and protection material, only by cultivar.

Figure 1 .
Figure 1.Temperature at the surface of the peel of banana 'Prata' and 'Nanica' without protection (WP Surface Peel), pulp (WP Surface Pulp) and average temperatures on the peel surface of fruits bagged with different materials (MP Surface Peel) during exposure to 10 and 5°C.

Table 2 : CI index bagged with different protection materials, depending on temperature Protection materials
, without protection; BTP, blue transparent polyethylene; WNF, white non-woven fabric; WOP, white opaque polyethylene; BW, bubble wrap; WLNF, white laminated non-woven fabric.Data are means ± standard deviation.Means followed by the same uppercase letters in the columns and lowercase letters in the lines do not differ from each other by the Tukey test (p<0.05) WP

Table 4 : Incidence of Crown rot of the peel of banana 'Nanica' bagged with different protection materials, depending on temperature Protection materials
, without protection; BTP, blue transparent polyethylene; WNF, white non-woven fabric; WOP, white opaque polyethylene; BW, bubble wrap; WLNF, white laminated non-woven fabric.Data are means ± standard deviation.Means followed by the same uppercase letters in the column and lowercase letters in the line do not differ from each other by Tukey test (p<0.05).Means followed by the same uppercase letters in the column and lowercase letters in the line do not differ from each other by Tukey test (p<0.05) WP