Banana Fruit Ripening as Influenced by Edible Coatings

Abstract

The effects of chitosan 1% and 1.5%, calcium chloride (CaCl₂) 1% and 1.5%, chitosan 1% + gibberellic acid 100 ppm, chitosan 1.5% + gibberellic acid 100 ppm, jojoba wax, and glycerol (98%) coatings were evaluated on the shelf life and postharvest quality characteristics of banana fruits stored at 34 ± 1°C and 70–75% relative humidity, while uncoated fruits served as a control. The coatings of chitosan, chitosan + gibberellic acid, and jojoba wax delayed the changes in the weight loss percentage, decay percentage, total soluble solids, pH, titrable acidity, sugar accumulation, pigment degradation, and ascorbic acid compared to uncoated ones. Further, the least disease incidence was found to occur in the banana fruits treated with chitosan and chitosan + gibberellic acid. Hence, it can be concluded that coating with chitosan and chitosan + gibberellic acid has the potential to control decay percentage, prolong the shelf life, and preserve valuable attributes of banana. Calcium chloride and glycerol coatings neither showed any potential to control disease incidence nor prolong the storage life and preserve valuable attributes of banana fruit.

Keywords:

• banana
• edible coating
• postharvest
• shelf life
• quality characteristics

INTRODUCTION

Banana (Musa spp.) is the most widely cultivated and consumed fruit in the tropical and subtropical regions of the world where they constitute a major staple food crop for millions of people (Deka and Choudhury, 2006). India is the largest producer of fruits in the world and banana tops the list with respect to production and area of cultivation (TIFAC Report cited in Surendranathan et al., 2004). Bananas contain nutrients in more balanced proportion than many other fruits. They have nearly all the essential nutrients, including minerals and vitamins (Islam et al., 2001). Bananas are unique due to their high calories and nutritive values. As compared to apples, they contain five times more vitamin A and iron, four times more protein, three times more phosphorus, twice the carbohydrates, and the other vitamins and minerals (Gasster, 1963). They are useful for patients with peptic ulcers, for treatment of infant diarrhea, celiac disease, and colitis (Robinson, 1996). They are also ideal for patients suffering from gout, arthritis, kidney disorders, blood pressure, and heart problems (Stover and Simmonds, 1987).

In many cases, bananas are transported from localities of production great distances for marketing and consumption. Bananas, being a climacteric fruit, have a very short storage life. They are highly perishable and are, therefore, susceptible to several diseases resulting in extensive postharvest losses (Maqbool et al., 2010). In turn, longer shelf life would enhance trade opportunities between nations by extending time constraints under which fresh produce must be delivered to more distant geographic markets or by allowing the use of slower and less expensive modes of transportation (Kader, 1986). But due to absence/non adoption of proper postharvest management practices, the postharvest loss of bananas is highest (22%) among all the fruits (Deka and Choudhury, 2006). Reduction of postharvest losses reduces cost of production, trade and distribution, lowers the price for the consumer, and increases the farmers' income.

The extension of fruit shelf life is an important goal to be attained. Many storage techniques have been developed to extend the marketing distance and holding periods for commodities after harvest. Different preservation methodologies have been studied. One method of extending postharvest shelf life is the use of the edible coatings. Today, use of edible coatings is a common issue that is beneficial to protect nutrients of food, especially fruits and vegetables, and provide a long durability (Raheleh et al., 2008). Edible coatings have long been known to protect perishable food products from deterioration by retarding dehydration, suppressing respiration, improving textural quality, helping retain volatile flavor compounds, and reducing microbial growth (Debeaufort et al., 1998). The objective of this study was to elucidate the effects of edible coatings, such as chitosan [alone and in combination with gibberellic acid (GA₃)], calcium chloride (CaCl₂), jojoba wax, and glycerol on physiological and biochemical changes in harvested banana fruit with a view to optimization of this postharvest technology for green life extension.

MATERIALS AND METHODS

Fruit Materials

For the present study, hands of mature green bananas were obtained from a local farm in Vallabh Vidyanagar, Gujarat, India. Hands were cut into fingers, and dipped for 3 min in sodium-hypochlorite (500 ppm) fungicide solution to control postharvest diseases, and then were allowed to air dry. Fruits were selected for freedom from visual defects and uniformity of shape, color, and size. Subsequently, these banana fruits were grouped into 8 experimental sets with 20 fruits per set and a control set of 20 fruits. The postharvest treatments (edible coatings) viz. chitosan 1% (T1), chitosan 1.5% (T2), CaCl₂ 1% (T3), CaCl₂ 1.5% (T4), chitosan 1% + GA₃ 100 ppm (T5), chitosan 1.5% + GA₃ 100 ppm (T6), glycerol (T7), jojoba wax (T8), and (uncoated) control (T9) were given for 10 min. After the treatment, the fruits were air dried at an ambient temperature for 30 min in an attempt to reduce possible chemical injury.

The treated banana fruits of experimental as well as control sets were subjected for the following physiological and biochemical analyses at the beginning of the experiment (i.e., 0 days) and after 5 and 10 days of storage in the laboratory with the average maximum and minimum temperature of it at 34 ± 1°C and relative humidity 70–75%.

Weight Loss Percentage (WLP)

The WLP of banana fruit samples was calculated by considering the differences between initial weight and final weight of currently tested banana fruits divided by their initial weight.

Decay or Rotting Percentage

The decay or rotting of the stored banana fruits was determined by their visual observations. Decayed fruits (physiological and microbial decay) were discarded in each sample and decay percent was recorded.

Shelf Life

The shelf life of these banana fruits was calculated by counting the days required for them to attain the last stage of ripening, but up to the stage when they remained still acceptable for marketing.

Total Soluble Solids (TSS), pH, and Titrable Acidity (TA)

The TSS content of the fruit was determined by using a refractrometer (Atago Co., Tokyo, Japan). A homogenous sample was prepared by blending the banana flesh in a blender. The sample was thoroughly mixed and a few drops were taken on the prism of the refractometer and a direct reading was taken by reading the scale in the meter as described in AOAC (1994). The pH of the fruit samples was determined as per the method described by AOAC (1994), while the titrable acidity (expressed as citric acid %) was determined by titrating 5 ml of juice with 0.1 N sodium hydroxide, using phenolphthalein as an indicator (Mazumdar and Majumder, 2003).

Biochemical Analysis

The total soluble sugars and starch content were determined by following the anthrone method, while the dinitrosalicylic acid method was followed for the reducing sugars and non reducing sugar content (Thimmaiah, 1999). The quantitative analyses of pigments, such as total chlorophylls (total chl.), chlorophyll ‘a’ (chl. ‘a’), chlorophyll ‘b’ (chl. ‘b’), and total carotenoids, were carried out as per the methods described by Wang et al. (2005). Ascorbic acid (vitamin C) content was determined by using the titrimetric method with the titration of filtrate against 2, 6-dichlorophenol indophenols, and the results of vitamin C content were expressed as mg.100 g⁻¹ (Mazumdar and Majumder, 2003).

Statistical Analysis

All the performed analyses were carried out in triplicate and the standard deviation was calculated. The experimental design was a completely randomized design with three replicates. Analysis of variance (ANOVA) was used to detect treatment effect. Mean separation was performed by using least significance difference (LSD) at the P < 0.05 level. The data were analyzed using Duncan's multiple range test (Bliss, 1967).

RESULTS AND DISCUSSION

Weight Loss Percentage

Result shows the change of WLPs of coated and uncoated banana (control) during the storage period (Table 1). Coating process caused a significant decrease (P < 0.05) in WLPs as compared with the control samples. All the treatments, except T7, showed a reduction in WLPs compared to that of the control fruits. The control samples had significantly (P < 0.05) higher WLP (15.98%) after 10 days of storage, while banana samples coated with chitosan, chitosan + GA₃, CaCl₂, and jojoba wax had significantly (P < 0.05) lower WLP values. The weight loss in banana during ripening might be due to substrate loss by respiration and loss of water through various physiological mechanisms (Islam et al., 2001). This reduction in weight loss was probably due to the effects of these coatings as a semi-permeable barrier against oxygen, carbon dioxide, moisture, and solute movement, thereby reducing respiration, water loss, and oxidation reaction rates (Baldwin et al., 1999). The obtained results are in accordance with the findings of Garcia et al. (1998) who reported that the chitosan film formed on the surface of the fruit delayed migration of moisture from the fruit into the environment, thus reducing weight loss during storage. The T2 (chitosan 1.5%) treatment was observed to prevent weight loss more than that of other tested treatments throughout the storage period but was less than that of the T5 (chitosan + GA₃) treatment. The combined treatment (i.e., T5 and T6) was clearly effective in conferring a physical barrier to moisture loss and, therefore, retarding dehydration and fruit shriveling. In this experiment, the glycerol and CaCl₂ coating was the least effective in reducing weight loss. CaCl₂ treatments increased weight loss that was due to osmotic potential. Earlier studies by some investigators also indicated that postharvest application of Ca²⁺ accelerated ripening of ‘Cavendish’ bananas (Willis et al., 1982a; Huddar et al., 1991).

TABLE 1 Effect of Edible Coatings and Their Combinations With Different Chemicals on Weight Loss Percentages (WLPS) and Decay Percentage of Banana Fruit During Storage at 34 ± 1°C

	Treatments
Storage period (day)	T1	T2	T3	T4	T5	T6	T7	T8	T9	LSD (P < 0.05)
WLP
0	0.00g	0.00g	0.00g	0.00g	0.00g	0.00g	0.00g	0.00g	0.00g	0.00
5	3.76 ± 0.74c	4.78 ± 0.66c	8.31 ± 1.37b	6.86 ± 0.92b	4.43 ± 0.58c	3.21 ± 0.58c	7.63 ± 1.41b	3.75 ± 0.53c	10.35 ± 0.99a	1.5759
10	9.67 ± 1.01d	6.20 ± 0.36f	15.02 ± 0.73b	12.20 ± 1.41c	6.00 ± 0.44f	7.18 ± 0.62ef	21.27 ± 1.12a	7.83 ± 1.02e	15.98 ± 0.71b	1.5207
Decay percentage
0	0.00f	0.00f	0.00f	0.00f	0.00f	0.00f	0.00f	0.00f	0.00f	0.00
5	7.03 ± 1.76e	5.58 ± 0.53e	21.00 ± 1.00c	23.50 ± 1.32b	5.45 ± 0.40e	6.83 ± 0.68e	30.50 ± 0.50a	9.50 ± 0.50d	31.33 ± 1.26a	1.6983
10	13.17 ± 1.61d	10.25 ± 0.25e	38.27 ± 1.55b	35.33 ± 0.29c	9.90 ± 0.56e	13.00 ± 1.80d	39.17 ± 0.76ab	11.50 ± 1.32de	40.67 ± 0.76a	1.9492
Means with the same letters within rows are not significantly different at P < 0.05 using LSD. Each value is the mean for three (n = 3) replicates. The values represented (a–g) in the results indicate the range from higher to lower rank. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

Decay Percentage

Data summarized in Table 1 show the changes in decay percentage values of coated and uncoated bananas (control) during the storage period. Coatings significantly (P < 0.05) reduced the decay percentage as compared to that of control samples during the storage period. Decay percentage of control samples at the end of storage period was approximately four to five times higher than that of the banana fruits coated with chitosan, chitosan + GA₃, and jojoba wax. Among all the presently tested treatments, T2 (i.e., 10.3%) and T5 (i.e., 9.9%) treatments were superior in controlling the decay percentage. Chitosan in combination with GA₃ (T5) significantly reduced the decay level, i.e., 9.9% compared to all other treatments and control samples. This is consistent with the reports that chitosan has antifungal properties against several postharvest pathogens (Jiang and Li, 2001). El-Ghaouth et al. (1992a) suggested that chitosan induces chitinase, a defense enzyme, and catalyzes the hydrolysis of chitin, a common component of fungal cell walls, thus preventing the growth of fungi on the fruits. The results of the present study show that the banana fruits treated with jojoba wax had a lower decay percentage, i.e., 11.5% after 10 days of storage. Similar results were obtained by Ahmed et al. (2007) in orange fruit that was coated with jojoba wax and had lower decay percentage compared to the control fruits.

SHELF LIFE

The shelf life of banana fruit has been extended significantly (P < 0.05) with some of the treatments tested in the current study (Table 2). The banana fruits treated with the T6 treatment were found to extend their shelf life to the maximum duration of 17.2 days as compared to that of other presently tested treatments (Table 2). The treatment of 1% and 1.5% of chitosan caused the extension of shelf life of banana fruits tested in the current study by 15.3 and 16.2 days, respectively, as compared (i.e., 11.3 days) for fruits of the control set (Table 2). These results also support the view of Zhang and Quantick (1998) who reported that the application of a chitosan coating improved the quality and storability in strawberries and raspberries. The positive effect of a chitosan coating on storage life could probably be due to modifying the atmosphere within as in modified atmosphere (MA) storage. The depolymerization process of metabolism substrates is possibly influenced by the MA created inside fruits. The MA created can, therefore, delay ripening by delaying ethylene production and by reducing the level of internal oxygen and consequently prolonging the storage life of fruits (El-Ghaouth et al., 1992b). Among the tested postharvest treatments, the fruits treated with chitosan and GA₃ (T6) exhibited longer shelf life and reduced spoilage (Table 2). Rao and Chundawat (1988) suggested that postharvest dipping of fruits in GA₃ delayed the conversion of starch to sugars and reduced peroxidase activity and ethylene production. In the present study, calcium treatments showed a depressing impact on the shelf life. Studies carried out by other investigators also indicate that postharvest application of Ca²⁺ accelerated ripening of ‘Cavendish’ bananas (Willis et al., 1982a; Huddar et al., 1991). The hastened color development may be linked to faster achievement of senescence leading to shorter shelf life. A previous study on bananas showed a tendency towards a negative correlation of lesion diameter of anthracnose and fruit firmness (Perera et al., 1999). These results appear to suggest that firmness reduction observed in Ca²⁺-treated bananas may develop a susceptibility to anthracnose and, hence, reduction of shelf life.

TABLE 2 Effect of Edible Coatings and Their Combination With Different Chemicals on Shelf Life (Days) and Total Soluble Solids (TSS) of Banana During Storage at 34 ± 1°C

	Treatments
Storage period (day)	T1	T2	T3	T4	T5	T6	T7	T8	T9	LSD (P < 0.05)
Shelf life (days)
At the end of the storage period	15.26d	16.16b	11.23f	12.13e	16.36b	17.16a	11.40f	15.66c	11.30f	0.3975
TSS (%)
0	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	11.2 ± 0.8f	1.3742
5	14.34 ± 0.59c	14.01 ± 0.02c	17.67 ± 0.58b	18.68 ± 0.59ab	12.36 ± 0.56d	12.68 ± 0.56d	18.67 ± 1.15ab	13.01 ± 0.01d	19.03 ± 0.04a	0.9878
10	16.33 ± 0.58c	15.02 ± 0.03d	20.17 ± 0.76ab	19.67 ± 0.58b	14.69 ± 0.54de	14.02 ± 0.03e	19.68 ± 0.59b	14.02 ± 0.03e	20.7 ± 0.61a	0.8590
Means with the same letters within rows are not significantly different at P < 0.05 using LSD. Each value is the mean for three (n = 3) replicates. The values represented (a–f) in the results indicate the range from higher to lower rank. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

Total Soluble Solids

Changes in the TSS of bananas over the storage time are shown in Table 2. The TSS of control fruit increased with storage time, while the banana fruits coated with chitosan, chitosan + GA₃, and jojoba experienced a slower increase during the 10 days of storage. Data showed that control samples without coating treatments had significantly (P < 0.05) higher levels of TSS with 20.7% at 10 days of storage period. TSS values of banana treated with T1, T2, T5, T6, and T8 after 10 days of storage were approximately 1.3, 1.4, 1.4, 1.5, and 1.5 times lower, respectively, than the TSS values of control samples without coating. The concentrations of free sugars progressively increased with storage; this increase was quite markedly delayed by chitosan, chitosan + GA₃, and jojoba coatings. This was probably due to the semi-permeable chitosan film, which formed on the surface of the fruits, causing the modification of internal atmosphere and the endogenous CO₂ and O₂ concentrations of the fruit, thus retarding ripening as shown by Bai et al. (1988). Other reports indicated a slow rise in TSS of mango and banana treated with chitosan (Kittur et al., 2001), which might be due to chitosan's effect on slowing down the ripening, respiration rise, and metabolism processes of the fruits. The combined treatment of chitosan and GA₃ had a greater effect in reducing the TSS during storage compared to other tested treatments. During the 10 days of storage, the least amount of TSS (i.e., 14.0%) was seen in the T6- and T8-treated banana fruits.

pH and Titrable Acidity

Uncoated (control) fruit was observed to have higher pH values compared with other coated fruits (Table 3). Chitosan 1.5% and chitosan (1.5%) + GA₃ (100 ppm) coating proved to be significantly better (P < 0.05) in maintaining low pH, compared to uncoated fruits and CaCl₂-coated fruits. The combined treatment of chitosan and GA₃ showed the changes in pH effectively, delaying fruit ripening and senescence. All the coated fruits have shown lower pH compared to that of uncoated fruits. The pH in both coated and uncoated fruits increased, while their titrable acidity decreased significantly (P < 0.05) along with increased storage time (Table 3). These results are in accordance with those reported by Garcia et al. (1998) that the decrease of acidity during storage demonstrated fruit senescence. The change in pH is associated with a number of reasons; it might be due to the effect of coating on the biochemical condition of the fruit and slower rate of respiration and metabolic activity (Jitareerat et al., 2007). Coating slowed the changes of pH and TA by effectively delaying fruit senescence. The higher level of TA in the fruits coated with chitosan and the combination with GA₃ (Table 3) may be due to a protective O₂ barrier or reduction of O₂ supply to the fruit surface that inhibited the respiration rate (Jiang and Li, 2000). Increased activity of citric acid during ripening or reduction in acidity may be due to their conversion into sugars and their further utilization in the metabolic processes of the fruit. The chitosan coating treatment [i.e., T1 (4.4%) and T2 (4.2%)] showed significantly (P < 0.05) higher amounts of TA than that of chitosan + GA₃ [i.e., T5 (3.3%) and T6 (3.2%)] during 10 days of storage. Slowing down the banana ripening by means of coating (chitosan and jojoba) and GA₃ causing inhibition of enzyme activity could be the reason for delay in the use of organic acids in the enzymatic reactions of respiration. This result was consistent with reports of Garcia et al. (1998) and Zhang and Quantick (1998) who reported that TA of chitosan or starch-based coated strawberries kept under cold storage decreased with time, but to a lesser extent than that of uncoated fruit.

TABLE 3 Effect of Edible Coatings and Their Combination With Different Chemicals on pH and Titrable Acidity (TA) of Banana During Storage at 34 ± 1°C

	Treatments
Storage period (day)	T1	T2	T3	T4	T5	T6	T7	T8	T9	LSD (P < 0.05)
pH
0	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	2.08 ± 0.025j	0.0432
5	5.05 ± 0.020e	4.93 ± 0.015f	5.43 ± 0.010d	5.53 ± 0.017c	4.86 ± 0.006g	4.61 ± 0.01h	5.70 ± 0.02a	4.48 ± 0.015i	5.59 ± 0.012b	0.0251
10	5.17 ± 0.006g	5.13 ± 0.021h	6.13 ± 0.026c	6.27 ± 0.01b	5.31 ± 0.006f	5.04 ± 0.006i	5.91 ± 0.006d	5.40 ± 0.012e	6.31 ± 0.015a	0.0238
TA (%)
0	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.92 ± 0.013e	0.0220
5	1.72 ± 0.187d	1.55 ± 0.154d	3.48 ± 0.108b	3.68 ± 0.138b	1.70 ± 0.109d	1.64 ± 0.129d	3.96 ± 0.198a	2.82 ± 0.234c	4.03 ± 0.103a	0.2705
10	4.35 ± 0.118b	4.16 ± 0.134b	2.77 ± 0.085d	2.89 ± 0.077d	3.32 ± 0.108c	3.23 ± 0.110c	2.85 ± 0.096d	4.66 ± 0.147a	2.92 ± 0.113d	0.1926
Means with the same letters within the rows are not significantly different at P < 0.05 using LSD. Each value is the mean for three (n = 3) replicates. The values represented (a–j) in the results indicate the range from higher to lower rank. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

Sugars

Gradual increase was seen in the content of total sugars, reducing sugars, and non reducing sugars in coated and uncoated banana fruits, but the accumulation of the sugars in coated fruits was found to be less (Fig. 1A, B, C). It is clear from the results that at the time of harvest the sugars were very low, but with the passage of time, total sugars increased with ripening. An increase in reducing sugar might be attributed to enzymatic conversion of starch to reducing sugar and also to conversion of some non reducing sugar to reducing sugar through the process of inversion. The coatings of chitosan, chitosan + GA₃, and jojoba wax were found to lower the total sugars, reducing sugars, and non reducing sugars compared to fruits of the control set. Among all the coated fruits, the fruits of T8 (34.2 mg.g⁻¹), T6 (36.6 mg.g⁻¹), and T5 (39.2 mg.g⁻¹) sets showed significantly (P < 0.05) lower amounts of total sugar content compared to that of control fruits (52.8 mg.g⁻¹) (Fig. 1A, B, C). This view is supported by Hoa and Ducamp (2008) who studied the effects of different coatings on biochemical changes of ‘cat Hoa loc’ mangoes in storage and observed that the content of reducing sugars and total sugars were lower with respect to that of control fruits. A maximum amount of reducing sugars (9.1 mg.g⁻¹) in control fruits (Fig. 1B) might be due to rapid conversion of starch to sugars as a result of moisture loss and decrease in acidity by physiological changes during storage.

FIGURE 1 Effect of edible coatings on content of total sugars (A), reducing sugar (B), non reducing sugar (C), and starch (D) of banana fruit during storage at 34 ± 1°C. Vertical bars represent ±SE of means for three replicates. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

Starch

Starch is bulk polysaccharides in banana fruit and its degradation results in pronounced softening (Prasanna et al., 2007; Zhang et al., 2010). Significant (P < 0.05) variation was found in respect to starch content in the coated banana fruits during storage period (Fig. 1D). However, degradation of starch in coated fruit was slow as compared with control fruit and was accompanied by a delay in the increase of soluble sugar content. The result of the present study further reveals that the amount of starch content was very high at the beginning of their storage period and thereafter started to decline. A decrease in starch content during banana ripening was also observed by Chacon et al. (1987). At the storage of 10 days interval, the fruits coated with T8 and T6 have shown the maximum amount of starch content, i.e., 146.6 mg.g⁻¹ and 122 mg.g⁻¹, respectively. Thus, the results of the present study indicate that the least value of starch content (i.e., 34.4 mg.g⁻¹ and 52.2 mg.g⁻¹) was perceived in the T3 and T9 (control) treated fruits, respectively (Fig. 1D), and these are in line with that obtained by Islam et al. (2001) who reported that the banana fruits coated with waxol had a higher amount of starch compared to the control fruits.

Pigments

The data obtained pertaining to the total chlorophyl (chl.) and total carotenoids as affected by the coatings tested under the current study are presented in Figures 2 and 3. The quantitative analysis of photosynthetic pigments indicates that they occur more in the coated fruits in both pulp and peel. In contrast, control fruits exhibit weaker stimulation on total chl. accumulation. All the treatments, except T7, showed significantly (P < 0.05) more amounts of total chl. in peel as compared to that of the control set (Fig. 2A). During the end of the storage period, the fruits coated with chitosan, chitosan + GA₃, and jojoba coating have shown a higher impact on the accumulation of photosynthetic pigments (chl. ‘a’, chl. ‘b’, and total chl.) in peel as well as pulp. The retardation of color development in the banana fruit coated with chitosan and chitosan + GA₃ in this investigation can be attributed to the modified internal fruit atmosphere, which caused slowing down of the ripening process indicating by lower change of peel color of fruits. The coating reduced the fruit respiration and ethylene production (Eryani Raqeeb et al., 2009). The slow respiration and reduced ethylene synthesis, in turn, delayed ripening and senescence, resulting in less change in the greenish yellow color of fruits (Kader et al., 1989). Higher amounts of chl. ‘a’ (37.1 μg.g⁻¹), chl. ‘b’ (12.9 μg.g⁻¹), and total chl. (48.0 μg.g⁻¹) in the peel was seen in T6, T8, and T6, respectively, at the 10 days of storage period (Figs. 2A, B, C). In the case of pulp, the fruits treated with T6 treatment have revealed a greater amount of total chl., i.e., 6.0 μg.g⁻¹ (Fig. 2D). The control fruits have shown higher impact on their chlorophyll degradation. The least amount of total chl. was seen in the uncoated fruits in peel as well as pulp, i.e., 9.2 μg.g⁻¹and 1.3 μg.g⁻¹, respectively (Fig. 2A, D), compared to the fruits coated with chitosan, chitosan + GA₃, and jojoba wax. The loss of green color was the most obvious change in bananas, which was probably due to the physicochemical changes by degradation of the chlorophyll structure and increase in carotenoid pigments during storage. The principal agents responsible for this degradation might be the oxidative system, pH change, and enzymes, such as chlorophyllase (Willis et al., 1982b). The data of the present study suggested that the level of carotenoid content progressively increased in both the coated as well as uncoated fruits during their storage periods (Fig. 3). The increase in carotenoid content during storage might be due to a series of physicochemical changes, such as the breakdown of chlorophyll and increase in carotenoid pigments of the peel caused by the enzymatic oxidation and photo degradation. The delay in ripening and degradation of chlorophyll and retention of green color for a longer period also depend on the types of coating (Kittur et al., 2001).

FIGURE 2 Effect of edible coatings on content of total chlorophylls (peel) (A), chlorophyll ‘a’ (peel) (B), chlorophyll ‘b’ (peel) (C), and total chlorophylls (pulp) (D) of banana fruit during storage at 34 ± 1°C. Vertical bars represent ±SE of means for three replicates. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

FIGURE 3 Effect of edible coatings on carotenoid content of banana peel during storage at 34 ± 1°C. Vertical bars represent ±SE of means for three replicates. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

Ascorbic Acid

Ascorbic acid is one of the most abundant antioxidants present in fruits. Ascorbic acid was found to maintain with postharvest application of chitosan, chitosan + GA₃, and jojoba coating. Chitosan treatment with GA₃ (T6) had the highest content (26.2 mg.100 g⁻¹) of ascorbic acid compared with other coatings and control (14.9 mg.100 g⁻¹) fruits during 10 days of their storage periods (Fig. 4). On the other hand, CaCl₂-coated banana fruits have not shown any significant differences with control sets. Chitosan coating at 1 and 1.5% maintained the loss of ascorbic acid compared to the uncoated ones. This study has demonstrated that the combined treatment (chitosan + GA₃) delayed the increase of ascorbic acid and the loss at the ripening stage of the banana. After 10 days of storage, all the coatings, except CaCl₂ and glycerol, were much more effective in reducing the ascorbic acid loss of banana fruits than the uncoated (control) fruit. The present study showed that vitamin C content of chitosan and chitosan+GA₃-coated bananas were highest among all the treatments at the end of the storage. This may be due to the effect of chitosan coating on retarding ripening and slowing down the metabolism activity, which causes oxidation of ascorbic acid. The reason for high vitamin C content in coated fruit can be attributed to the slow ripening rate of chitosan-treated fruit. This view is also shared by Abbasi et al. (2009), who reported that the ascorbic acid contents in irradiated Crab chitosan-coated mango fruits were higher than unirradiated chitosan-coated fruits at the end of the storage. Oxidation of ascorbic acid may be caused by several factors, including exposure to oxygen, metals, light, heat, and alkaline pH (Abbasi et al., 2009). As Ayranci and Tunc (2003) stated, slowing down of vitamin loss was attributed to the low oxygen permeability of the coating.

FIGURE 4 Effect of edible coatings on ascorbic acid content of banana fruit during storage at 34 ± 1°C. Vertical bars represent ±SE of means for three replicates. T1—chitosan (1%); T2—chitosan (1.5%); T3—calcium chloride (1%); T4—calcium chloride (1.5%); T5—chitosan (1%) + gibberellic acid (100 ppm); T6—chitosan (1.5%) + gibberellic acid (100 ppm); T7—glycerol (98%); T8—jojoba oil; T9—control (uncoated).

CONCLUSIONS

The results of the current investigation indicate that banana fruit coated with chitosan alone, chitosan in combination with gibberellic acid, and jojoba coatings cause a significant delay in the change of weight loss, decay percentage, total soluble solids, pH, titrable acidity, sugar accumulation, pigment degradation, and ascorbic acid content compared to uncoated ones. Chitosan 1.5% and chitosan 1.5% + gibberellic acid 100 ppm was more effective as a protective coating on banana fruits by maintaining the quality characteristics, prolonging the shelf life, and preserving the valuable attributes of banana fruits during the storage period. Hence, these coatings, being environmentally friendly, provide good handling procedures to enhance banana export to long distances with minimum losses.

ACKNOWLEDGMENT

Neeta B. Gol is grateful to the University Grant Commission (UGC), New Delhi for financial support under the program of Meritorious Fellowship.