Efficacy of Postharvest Technologies on Ripening Behavior and Quality of Banana Varieties Grown in Ethiopia

ABSTRACT

Banana is the most important cash and food security crop in Ethiopia. However, the ripening quality and postharvest life of the fruits are not well studied to meet the domestic and international market standards. An experiment was therefore conducted with objectives of describing the ripening behaviors and postharvest qualities of banana varieties and identifying appropriate postharvest technologies for improved ripening and long postharvest life of fruits. The results of the experiment revealed the existence of highly significant variation between banana varieties, ripening temperatures, packaging, and their second- and third-order interactions for length, weight, volume, pulp-to-peel ratio, and pulp diameter. All fruits of the varieties except the local could not ripe well without ripening treatments. Temperatures at 15°C and 20°C were optimum for yellow peel color development. Better eating fruit quality and peel color development were achieved by ripening of fruits at 20°C and 25°C with perforated plastic packaging. Further research on treatments and technologies that can improve the ripening quality and postharvest life of Ethiopian banana like the use of ethylene should be done, and studies on physicochemical changes occurred during fruit maturation and ripening of Ethiopian grown banana varieties in different seasons and agroecologies should also be conducted to reduce the post harvest loss caused by fruit ripening problem.

KEYWORDS:

• Plastic packaging
• post harvest loss
• pulp-to-peel ratio
• ripening
• temperature

Background and justification

Banana comprises an array of species in the genus Musa of the family Musaceae with the majority of cultivated varieties rising from two Musa species: Musa accuminata (A genome) and Musa balbisiana (B genome) as indicated by Simmonds and Shepherd (1955). Banana is a staple food in many tropical countries of the world. It is rich in easily digestible carbohydrates with a caloric value of 67–137 per 100 g of fruit (Bjarnadottir, 2017). Oligosaccharides and various antioxidants are the other important ingredients present in banana fruit that have been found important for weight loss and prevention of various diseases such as colon cancer, diabetes, muscular contraction, regulation of blood pressure, and curing of intestinal disorders (Higgins, 2014; Obrenovich et al., 2011, 2010; Wang et al., 2014). Banana is also a rich source of delightful flavors, total dietary fibers, vitamins, minerals, and phytochemicals which have health benefits (Clark and Slavin, 2013; Ergin et al., 2013; Houston, 2011; Seth et al., 2014).

Banana is the fourth most important crop in world export trade after cereals, oil crops, and sugar. According to FAO (2013), the annual global world production of banana reached over 110 million tons, where India and Brazil are the major sweet banana producing countries in the world. On the other hand, Ecuador, the fifth largest banana producers of the world, exports 67% of its production while European countries and the USA are the major importers of banana (FAO, 2007). Generally, banana and plantains are the most important fruit crops that are grown as main sources of energy for millions of smallholder farmers in Africa, South Asia, and Latin America to sustain their livelihood (Rowe, 1981) where it is available throughout the year (Edmeades et al., 2006).

Banana has great socioeconomic significance in Ethiopia. It is one of the most important fruit security crops especially in the southern part of the country. With the total annual production of 0.3 million tons, Southern Nations, Nationalities, and People's Region (SNNPR) is the major banana growing state in the country followed by Oromia and Amhara Regional states (CSA, 2013). Banana is mostly cultivated in gardens, boundaries of fields, and farms. Recently, however, the cultivation of banana in modern orchards has started with the introduction of different high yielding varieties such as Dwarf Cavendish, William I, Grand Nain, Poyu, Giant Cavendish, and Butazu. As climacteric fruit, dessert bananas are harvested at mature green stage which should be ripened to improve their quality and palatability where postharvest practices influenced the ripening period and quality as well as postharvest loss as described by various researchers (Moradinezhad et al., 2010; Saeed et al., 2001; Savarese 2015; Semple and Thompson, 1988; Stover and Simmonds, 1987; Thompson, 1996; Turner, 1997; Wall, 2004).

Temperature, packaging, concentration, and exposure time of ethylene influenced the ripening process and quality of banana as these factors influence the respiration rate of fruits (Lebibet et al., 1995; Saeed et al., 2001; Smith and Thompson, 1987; Thompson and Seymour, 1982). An increase in storage temperatures between 14°C and 30°C enhances the rate of ripening (Smith, 1989). Jobling (2000) reported that the respiration rate and ethylene production were increased with increasing temperatures. On the other hand, high temperatures can also result in damages on ripened fruit (Liu, 1978; Semple and Thompson, 1988; Smith and Thompson, 1987). Temperatures less than 14°C can cause uneven ripening due to chilling injury (Stover and Simmonds, 1987). Generally, temperature affects the ripening process as well as quality and marketable life of banana fruits.

Although bananas are important food and cash crops for smallholder farmers, research on the ripening behaviors of banana varieties grown in Ethiopia has not been conducted. Ripening of banana in the country is carried out traditionally with smoke treatment where harvested banana bunches are exposed to smoke generated from burning of kerosene stove inside airtight chambers (Berhe et al., 2010). However, smoke treatment is crude and ineffective as it leads to nonuniform ripening and poor peel color development. Moreover, kerosene burning releases gases such as carbon monoxide that impairs human health. Siddiqui and Dhua (2010) reported that most ripening agents are toxic, and their consumption can cause serious heart diseases, skin disease, lung disease, and kidney failure. On the other hand, ripening of banana under the normal ambient temperatures that prevailed in most of the tropical countries are too high for ripening of bananas that leads to poor fruit quality, shorter postharvest life, and high postharvest losses as indicated by Semple and Thompson (1988). Therefore, this research was initiated with the objectives of evaluating the effects of temperature and packaging on the ripening of banana varieties grown in Ethiopia and identifying appropriate postharvest technologies for better fruit quality and long postharvest life.

Materials and method

Description of the experimental site

The experiment was conducted in the Plant Analysis Laboratory of the Department of Botany, College of Science, Bahir Dar University, from January to August 2015, which is located at 11° 37′ N longitude and 37° 27′ E latitude.

Experimental setup and sampling

Fruit samples of seven commonly grown banana varieties (local variety, Dwarf Cavendish, William I, Grand Nain, Poyu, Giant Cavendish, and Butazu) were harvested at green mature stage during the months of January and August 2015 from Weramit Horticultural Research Station, Ade Agricultural Research Center, Bahir Dar, and transported carefully to the laboratory. Bunches were immediately de-handed, and fingers were carefully removed from the hands and washed with clean water. Surface water was allowed to air-dry. Banana hands from the top and bottom of each bunch were discarded as these were not suitable for ripening studies and only uniform-sized fingers were used for the experiment.

Fruit fingers were divided into 10 groups where each group contained about 30 fruits. Five groups were put inside perforated plastic bags and the remaining five groups kept without perforated plastic bags. Two groups of fingers from each variety, one group packed in perforated plastic bag and the other without a perforated plastic bag, were put on the shelves of the incubators separately adjusted at a temperature of 30°C, 25°C, 20°C, and 15°C and relative humidity of 90%. Similarly, two groups of fingers (with and without perforated polyethylene bag) were put at ambient temperature as a control where the maximum and minimum temperatures were about 32°C and 14°C, respectively. Each group of fingers was randomly assigned to each treatment. Moreover, fruits were kept at uniform experimental setup until the time of full color change (color stage 7) and/or the beginning of senescence as indicated by Savories (2015).

Data collection

Both objective and subjective (sensory) methods have been employed to evaluate the postharvest life and quality of banana fruits as well as technologies used for ripening.

Objective methods

Postharvest life (days)

The number of days from the date of harvesting up to the date at which 30% of the sample fruits were spoiled or at senescence stage.

Weight loss (%)

The weight of fruits was measured before the onset and after the end of the experiment using sensitive balance, and the difference between the initial and final weight was expressed as weight loss as a percent of the initial fruit weight.

Fruit length (cm)

The lengths of five randomly selected fruits from each group were measured from the base to the tip using a ruler at ripening, and the mean values were computed and used for analysis.

Fruit diameter (cm)

The diameter of five randomly selected sample fruits was obtained by measuring at the center both on the short and long sides using a caliper and the average of the two was calculated and the mean values were computed and used for analysis.

Pulp–peel ratio

For this purpose, five randomly selected banana fruits from each group were peeled at the time of ripening, and the peels and pulps of the fruits were weighted separately. The pulp weights were divided by the weights of the respective peels, and the mean values were computed and used for analysis.

Fruit volume (cm³)

The volume of five randomly selected banana fruits at the time of ripening was measured by the water displacement method.

Fruit weight (g)

The weights of five randomly selected banana fruits were weighted using sensitive balance, and the mean values were computed and used for analysis.

Subjective (sensory) methods

Peel color

It was evaluated using the methods described by Savarese (2015), where 1 = all green; 2 = green with trace of yellow; 3 = more green than yellow; 5 = yellow with green tips; 4 = more yellow than green; 6 = all yellow; and 7 = all yellow with brown flecks.

Fruit firmness

The scores for fruit firmness were evaluated using panelists, where 1 = very low firmness; 2 = low firm; 3 = firm; 4 = moderately firm; and 5 = high firmness.

Fruit ripening quality (ready to eat)

It was rated by panelists where 1 = excellent; 2 = good; 3 = fair; 4 = poor; and 5 = bad.

Data analysis

The collected quantitative data were subjected to analysis of variance (ANOVA) as well as descriptive statistics using SAS version 8.1. Tables and graphs were developed to illustrate the results of the experiment.

Results

Combined analysis of variance

The combined analysis of variance revealed the existence of highly significant variation between fruit samples of varieties harvested and ripened at different time, ripening temperatures, perforated plastic packaging, and their second- and third-order interactions for fruit length, fruit weight, fruit volume, pulp–peel ratio, and pulp diameter. The second-order interaction of ripening temperature and perforated plastic packaging was significant only for fruit weight and fruit volume (Table 1). The highly significant variation between fruit samples might be explained because of the difference in genetic makeup of varieties, the difference in preharvest cultural management, climatic condition during fruit development, and maturation and harvesting time. The results indicate that the development of a variety along with production packages, identification of suitable climate, optimum production seasons, and harvesting time needs to be done to improve postharvest quality that meets domestic and international consumer preference.

Table 1. Combined analysis of variance (ANOVA) for quantitative fruit ripening traits.

Source	Df	Mean squares
		FL	FW	FV	PPR	PD
Fruit samples	6	174.4**	9010.1**	4374.7**	5.6**	1.08**
Temperature	4	10.8**	4154.7**	4425.5**	7.4**	0.08**
Rep	4	3.8**	74.6 ns	183.9*	0.1^ns	0.03*
Packaging	1	29.9**	24572.3**	25543.1**	42.4**	1.07**
Fruit samples vs temperature	24	7.6**	425.7**	315.7**	0.45**	0.10**
Fruit samples vs packaging	6	6.6**	921.4**	784.1**	1.04**	0.16**
Temperature vs packaging	4	0.9 ^ns	253.4*	190.5 *	0.64**	0.14**
Fruit samples vs temperature vs packaging	24	3.7**	325.8**	355.6**	0.21**	0.09**
Mean		16.6	95.4	98.9	2.3	2.7
CV		6.1	104	7.7	10.9	3.4
SE		1.1	9.9	7.6	0.3	0.11

Df, degrees of freedom; FL, fruit length; FW, fruit weight; FV, fruit volume; PPR, pulp–peel ratio; PD, pulp diameter; *significant at p ≤ 0.01; **highly significant at p ≤ 0.01; ns, nonsignificant.

The significantly high main effect of packaging happened because of the autocatalytic ethylene gas produced from the cells of banana fruits that diffuse outside, and this gas does not escape but rather stays inside the package and triggers the fruit ripening process. The significant difference between temperatures confirms that temperature plays a significant role in affecting ripening behavior and postharvest quality and indicates the need to identify optimum temperature. Moreover, the significant second-order interaction, i.e. fruits samples of banana varieties harvested on different days (time) and perforated plastic packaging; fruits samples of banana varieties harvested on different days (time) and ripening temperature, indicated that different fruits do not require the same ripening temperature and packaging for optimum ripening and postharvest quality.

Ripening behavior and postharvest quality of banana varieties

Ripening behavior and postharvest quality play a significant role in the commercialization of banana fruits. As described in Table 2, banana varieties grown in Ethiopia are different in their mean ripening qualities and postharvest life. Postharvest life was ranging from 11 to 28 days, while local variety took 11 days to reach the final stage of ripening. Dwarf Cavandish (23 days) and Grand Nain (27 days) took the longest days. Weight loss during the ripening period was high for Poyu and Butazu varieties, but smaller for the local variety. The fruit fingers of William I and Dwarf Cavendish varieties were longer while Grand Nain and Butazu had the heaviest mean finger weights.

Table 2. Ripening quality and postharvest life of banana varieties. Mean (x) plus or minus standard deviation(s).

No	Variety	PHP	WLR	FL	FW	FV	PPR	PD
		$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$
1	Local variety	13.4$\pm 5.6$	9.5$\pm 4.7$	13.1$\pm 1.2$	79.3$\pm 12.9$	79.3$\pm 14.7$	3.0$\pm 0.6$	3.0$\pm 0.1$
2	Dwarf Cavendish	22.8$\pm 9.8$	10.2$\pm 6.1$	19.9$\pm 2.4$	120.7$\pm 13.9$	120.7$\pm 13.6$	1.8$\pm 0.3$	2.9$\pm 0.1$
3	William I	21.2$\pm 10.0$	11.8$\pm 8.6$	20.1$\pm 1.5$	145.4$\pm 17.7$	145.4$\pm 20.1$	1.9$\pm 0.3$	2.9$\pm 0.2$
4	Grand Nain	28.8$\pm 13.3$	11.3$\pm 3.8$	17.2$\pm$1.1	110.1$\pm 22.2$	110.1$\pm 14.4$	1.8$\pm 0.3$	2.7$\pm 0.2$
5	Poyu	22.8$\pm 8.7$	11.9$\pm 4.1$	15.8$\pm 1.3$	104.3$\pm 11.4$	104.3$\pm 12.5$	1.8$\pm 0.2$	2.7$\pm 0.1$
6	Giant Cavendish	16.2$\pm 5.6$	7.7$\pm 4.0$	17.6$\pm 1.4$	102.4$\pm 14.6$	102.4$\pm 17.2$	1.5$\pm 0.2$	2.6$\pm 0.1$
7	Butazu	18.6$\pm 5.2$	10.0$\pm 8.8$	18.2$\pm 1.8$	114.1$\pm 19.4$	114.1$\pm 12.8$	2.0$\pm 0.2$	2.9$\pm 0.1$

PHP, postharvest life; WLR, water loss; FL, fruit length; FW, fruit weight; FV, fruit volume; PPR, pulp–peel ratio; PD, pulp diameter.

Fruit circumferences are used mainly to determine the size and shape of packaging. The local variety had the largest pulp diameter followed by Dwarf Cavendish. When pulp weight is compared, William I had the highest mean pulp weight followed by Butazu, but the local variety had the least pulp weight (Table 2). Having high peel weight of banana can be considered as advantageous, because it offers protection against mechanical damages, and peel can also be used as animal feed. However, the high peel can also be considered as a disadvantage as it results in lower edible portion. Mechanical damage is an important factor that leads to downgrading of banana fruits in the world market. The present quality rating in the European Union takes into account the percentage of peel damage due to bruising, scarring, and scratching (Santana and Marrero, 1998). The high peel weight of William I, Dwarf Cavendish, and Butazu could be an advantage in offering protection against mechanical damage during transport, handling, and shipping. Thus, fruits of these varieties can be suitable for international banana trade.

The market quality and consumer preference of banana fruits are significantly influenced by the peel color. Therefore, assessment of peel color is an important parameter for the screening of bananas for their postharvest quality (Dadzie and Orchard, 1997). The peel color of all varieties was not the same at the end of the experiment. Poyu and the local variety with and without perforated plastic bags reached the final color stage (color stage 7); however, Giant Cavendish, William I, and Grand Nain could not develop attractive yellow peel color (Table 3). The firmness of banana varieties used in the present study did not vary. Similarly, ripening of banana varieties in perforated plastic bags improved the general ripening (ready to eat) quality of banana fingers where local variety, Poyu, and Butazu were best compared to the others (Table 3).

Table 3. Subjective sensory analysis of banana varieties used in the study. Mean (x) plus or minus standard deviation(s).

Attributes	Packaging	Banana varieties
		Local variety	Dwarf Cavendish	Grand Nain	Poyu	Giant Cavendish	William I	Butazu
		$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$
Peel color	With packaging	6.5$\pm$0.7	6.1$\pm$1.4	5.9$\pm$1.4	6.7$\pm$0.6	6.2$\pm$1.4	6.3$\pm$0.7	6.4$\pm$1
	Without packaging	6.3$\pm$0.7	4.5$\pm$1.6	5.1$\pm$0.9	4.7$\pm$1.0	5.3$\pm$1.9	3.9$\pm$1.4	5.0$\pm$1.3
Firmness	With packaging	4.9$\pm$0.3	4.4$\pm$0.6	4.7$\pm$0.5	4.9$\pm$0.3	4.6$\pm$0.5	3.9$\pm$0.7	4.1$\pm$0.7
	Without packaging	4.4$\pm$1.0	3.8$\pm$0.8	3.7$\pm$1.1	3.8$\pm$1.1	4.6$\pm$0.5	4.1$\pm$1.1	4.3$\pm$0.7
Ripening quality	With packaging	1.3$\pm$0.5	1.7$\pm$0.9	2.0$\pm$1.4	1.2$\pm$0.4	1.4$\pm$0.9	2.0$\pm$1.3	1.5$\pm$1.0
	Without packaging	1.6$\pm$0.7	3.0$\pm$1.4	2.9$\pm$1.2	2.8$\pm$0.7	2.3$\pm$1.2	3.3$\pm$1.1	2.9$\pm$1.2

Peel color: 1– all green, 2 – green with trace of yellow, 3 – more green than yellow, 4 –more yellow than green, 5 – yellow with green tips;  6– all yellow, 7 – all yellow with brown flecks.

Firmness: 1 – bad firmness, 2 – low firm, 3 – firm, 4 – moderately firm, 5 – high firmness.

Ripening (quality): 1 – excellent, 2 – good, 3 – fair, 4 – poor, 5 – bad.

Postharvest quality at different ripening temperatures

The results of the experiment indicated that weight losses of banana fruits mostly occurred at higher temperatures of 30°C and 25°C (Figure 1). The fruits that were kept at lower (15°C) temperature took a significantly longer time (32 days) to ripe while that of fruits at a higher temperature of 30°C took 14 days and the control about 13 days. This is because climacteric fruits give off ethylene during ripening (Sacher, 1973), and the sensitivity of bananas to ethylene is very low within the range of 0.01−1.0 ppm (Thompson and Seymour, 1982). Bananas kept at higher temperatures showed shorter finger length compared to those stored at low temperatures. A similar trend was recorded for fruit volume, fruit weight, peel weight, and pulp weight.

Figure 1. Effect of ripening temperature and packaging on postharvest life (a), weight loss (b), fruit weight (c), fruit volume (d), pulp–peel ratio (e), and pulp diameter (f) of banana.

This indicates that the role of temperature is pronounced in affecting the quality and life of perishable tropical fruits like banana that are harvested green and consumed after ripenening. Therefore, cold storages and transportation and precooling infrastructures need to be set up in the market chains, and these commodities need to be handled in the cold chain. Comparably, higher pulp–peel ratio was also observed at 30°C and 25°C compared to those ripened at a lower temperature. Better peel color was developed for banana fruit samples ripened at 25°C, but poor color development was observed at higher temperature (30°C) (Table 4). Banana fruits stored at higher temperature and the control soften fast whereas bananas stored at lower temperature stayed firm. In terms of overall ripening quality, banana fruits ripened at 20°C, 25°C and the control were preferable; however, banana ripened at 30°C and 15°C showed poor overall quality development. The effect of temperature on fruit ripening was studied on banana fruits by Saeed et al. (2001) and similar results were obtained.

Table 4. Subjective sensory analysis of banana varieties as influenced by ripening temperatures and packaging. Mean (x) plus or minus standard deviation(s).

Attributes	Perforated plastic packing	Temperatures
		15°C	20°C	25°C	30°C	Control
		$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$	$\pm \mathrm{S}$
Peel color	With packaging	6.4$\pm$1	6.4$\pm$0.8	6.7$\pm$0.6	4.8$\pm$1.5	6.6$\pm$0.9
	Without packaging	5.5$\pm$1.4	5.6$\pm$102	4.4$\pm$1.4	3.9$\pm$1.4	5.7$\pm$1.3
Firmness	With packaging	3.8$\pm$1	4.0$\pm$1.1	4.6$\pm$0.6	4.7$\pm$0.4	4.7$\pm$0.5
	Without packaging	3.6$\pm$1.3	4.0$\pm$0.9	4.5$\pm$0.8	4.5$\pm$0.8	4.0$\pm$0.9
Ripening quality	With packaging	1.3$\pm$1	1.3$\pm$0.6	1.2$\pm$0.5	3.1$\pm$1.3	1.2$\pm$0.5
	Without packaging	2.7$\pm$1.2	2.2$\pm$1.0	3.0$\pm$1.1	4.0$\pm$1.0	2.9$\pm$0.8

Peel color; 1 – all green, 2 – green with trace of yellow, 3 – more green than yellow, 4 – more yellow than green, 5 – yellow with green tips;  6–all yellow, 7 – all yellow with brown flecks.

Firmness: 1 – bad firmness, 2 – low firm, 3 – firm, 4 – moderately firm, 5 – high firmness.

Ripening (quality): 1 – excellent, 2 – good, 3 – fair, 4 – poor, 5 – bad.

Packaging on ripening behavior and postharvest quality of banana fruits

Banana fruits ripened with perforated plastic packaging showed no difference for the mean postharvest life (Figure 2(a)). Nevertheless, higher weight loss was measured for fruits ripened without perforated plastic packaging than with packaging as indicated in Figure 2(b). Banana fruits ripened without perforated plastic bags were shorter (Figure 2(c)) and light in weight (Figure 2(d)) as well as had smaller pulp diameters (Figure 2(e)) compared to those fruits ripened in perforated plastic bags. Fruits ripened without packaging recorded higher pulp–peel ratio (Figure 2(f)) compared to fruits ripened inside perforated plastic bags. The overall results of the experiment indicated that better fruit quality, firmness, and color development were achieved by the ripening of banana fruits with perforated plastic packaging than without it (Table 4).

Figure 2. Effect of packaging on postharvest life (a), weight loss (b), fruit length (c), fruit weight (d), pulp diameter (e), and pulp–peel ratio (f) of banana.

In the Ethiopian market chain, banana fruits are handled without packaging and hence experience high postharvest losses both in quality and quantity. The results of this experiment indicated that ripening and postharvest handling of the fruit with perforated packaging is much better than the normal practice (without packaging) as it protects the fruits against mechanical damages during transportation as well as insect pests and sun burning.

Ripening behavior and postharvest quality of fruits as affected by temperature and packaging

The ripening behavior and postharvest quality of banana fruits were influenced by the interaction effect of temperature and packaging. The results in Figures 3 and 4 show that banana varieties ripened at 15°C with perforated plastic packaging took the longest postharvest period (32 days) whereas the shortest were observed in fruits ripened without packaging in 30°C (12 days). It was observed that packaging of fruits at lower temperature brought longer postharvest life than without packaging. Weight loss was higher for fruits ripened at high temperature without packaging than fruits ripened at higher temperature with packaging. It is possible to generalize that weight losses of Ethiopian banana varieties ripened in perforated plastic packaging were lower than those ripened without perforated plastic packaging. Similar results were observed for fruit lengths, weights, and diameters of pulps. Moreover, good peel color was developed on fruits ripened with perforated plastic packaging at 20°C and 25°C (Table 4). Therefore, packaging and postharvest handling of the fruit at a temperature range between 15°C and 25°C and relative humidity (90%) is required for Ethiopian grown improved banana varieties for optimum ripening (bright yellow peel color development), whereas for local variety, all these treatments may not be required. Therefore, physicochemical changes occur during fruit maturation, and ripening of Ethiopian grown varieties in different seasons and agroecologies is important for further improvement in the reduction of postharvest losses caused by the problem of ripening.

Figure 3. Interaction effects of ripening temperature and packaging on fruit weight (a), pulp diameter (b), and pulp–peel ratio (c) of bananas grown in Ethiopia.

Figure 4. Effects of temperature and perforated plastic packaging on ripening behavior of banana fruits: A = 15°C without packaging; B = control without packaging, C = 15°C with packaging; D = 25°C with packaging; E = 20°C with packaging; and F = experimental setup.

Discussion

As climacteric fruit, banana is harvested at green mature stage and should be ripened under natural or controlled ripening room (Rao and Rao, 1979). Ripening under natural ripening room with ambient temperature, however, results in inconsistent ripening with dull peel and pale yellow color which is unattractive to the consumers that leads to postharvest loss. Therefore, to obtain fruits that have bright yellow peel color with firm pulp texture and good flavor, bananas are best ripened artificially in a controlled condition where ethylene, temperature, relative humidity, and gas compositions of the ripening room are optimum in the ripening process (Saeed et al., 2006, 2001).

The practice of banana ripening in Ethiopia is traditional which is done in most cases by burning of kerosene stove inside airtight chambers where temperature and relative humidity are not controlled. The use of ethylene and temperature control for ripening of banana is not common in the country. Thus, bananas found in the local market of the country are poor in quality and experience high postharvest losses. Most commercial cultivars of bananas and plantains require exposure to ethylene for 24–48 h at temperatures ranging from 14.4°C to 18°C (Saeed et al., 2001; Thompson and Burden, 1995). Akter et al. (2013) also observed a variation in the ripening of banana cultivars for different postharvest treatments including ethylene trigger. Kulkarni et al. (2011) studied that 500 ppm of ethrel solution was optimum for inducing uniform ripening of banana at 20°C. According to them, the concentration can be increased to 1000 μL L⁻¹ in case the ripening rooms are not airtight. It has been reported that exogenous application of ethylene in the form of ethrel accelerates ripening, increase color and eating quality with reduced spoilage in different varieties of mango (Saltveit 1999; Singh and Janes, 2001). In line with this, the results of the present study indicated that except the local variety all other improved varieties of banana require postharvest treatment including ethylene trigger for optimum ripening and best eating quality. Banana fruits ripened in perforated plastic bags showed better ripening perhaps due to autocatalytic ethylene action produced inside the cells of banana fruits in the climacteric phase (Sacher, 1973) that may foster uniform ripening of fruits inside the package.

Ripening room temperatures also have a great influence on the physiological processes that occurred during the ripening of climacteric fruits including bananas (Esguerra et al., 1992). An increase in temperature between 14°C and 30°C enhances the rate of ripening, and the fruit softens at a faster rate and becomes palatable (Smith, 1989). On the other hand, high temperature can also cause damages on ripening fruits like weight loss through transpiration and increase respiration that deteriorate the quality of banana and reduce yellow color development (Semple and Thompson, 1988; Smith and Thompson, 1987; Yang et al., 2011) which is in line with the results of the present study. Furthermore, high temperatures influence the production and its effect of ethylene which in turn affects the ripening of banana fruits (Jobling, 2000; Liu, 1978). On the other hand, temperature less than 14°C can cause uneven ripening due to chilling injury (Stover and Simmonds, 1987).

Ripening and postharvest handling temperatures that prevail in tropical countries such as Ethiopia are ranging from 14°C to 32°C with an average of 25°C. As indicated in the present study, banana fruits that were ripened at a higher temperature (30°C) failed to develop the bright yellow color of the peels which is in line with the findings of Yang et al. (2011). Banana fruits ripened at constant temperatures of 20°C and 25°C had better yellow peel color which can be accepted by the consumers. In line with the present study, Thompson and Burden (1995) recommended that temperatures around 20°C and relative humidity ranging from 90% to 95% are necessary for optimum ripening of improved banana varieties.

In addition to ethylene and temperature management, packaging affects the shelf life of fresh fruits including banana by reducing the respiration rate as well as affecting the ripening process (Sen et al., 2012). The results of the present study depict that better yellow color development, firmness, and eating quality of banana fruits were achieved when fruits were ripened in perforated plastic bags at 20°C and 25°C. This is probably due to gas composition changes that occurred inside the perforated plastic bag during the course of ripening where the concentration of oxygen decreased while that of carbon dioxide and ethylene increased which in turn improved ripening.

Conclusion

Banana is the most important cash and food security crop in Ethiopia. However, the ripening behaviors of the banana varieties which are important for the reduction of postharvest losses of the crop are not yet studied in the country. Therefore, the present study was conducted to characterize the postharvest behaviors of banana varieties grown in the country and identify technologies that help reduce losses of the crop where one local and six improved banana varieties were used. Based on the findings of the present study, both qualitative and quantitative traits of banana varieties including shelf life, weight loss, and ripening quality were significantly influenced by the ripening temperatures as well as packaging systems used. Better fruit quality and peel color development were generally achieved by the ripening of banana fruits at 20°C and 25°C with perforated plastic packaging. Research on technologies and treatments that can further improve the ripening quality and postharvest life of Ethiopian banana, like the use of ethylene, is recommended. Moreover, further research on physicochemical properties of the fruits that occurred during maturity and ripening should be also conducted.