Elsevier

Food Research International

Volume 105, March 2018, Pages 384-392
Food Research International

Thap Maeo bananas: Fast ripening and full ethylene perception at low doses

https://doi.org/10.1016/j.foodres.2017.11.007Get rights and content

Highlights

  • Thap Maeo banana cultivar is highly sensitive to ethylene.

  • The effective dosage for ethylene treatments can be redefined by up to 100 times lower than those commercially applied.

  • Banana fruit volatile profile is differentially affected by various ethylene treatments.

Abstract

Brazil is a major producer and consumer of various banana types. Thap Maeo is a promising cultivar for the market due to its resistance to Black and Yellow Sigatoka disease. However, a lack of information and postharvest technologies concerning Thap Maeo physiology seems to be a significant problem limiting its expansion in the market. Thus, this study aims to establish Thap Maeo fruit's physical, biochemical, and physiological aspects, defining the best ethylene dosage for treatment considering fruit ripening parameters. Bananas were harvested and monitored during both natural and ethylene-induced ripening processes. Assessments of pulp firmness, peel color and endogenous ethylene production showed different profiles between ethylene-treated and non-treated fruits, whereas the ethylene responses concerning the carbohydrates and hormones profiles, as well as the ethylene receptors expression, were observed in all ethylene-treated fruits, even applying low concentrations of the hormone. It thus indicated the high ethylene-sensitivity of Thap Maeo cultivar. Such postharvest behaviors reverberate in lower ethylene requirements for treatment, which was established at 10 μL L 1. Ethylene-inducible changes in fruit volatile compounds throughout ripening are also discussed.

Introduction

Bananas are a key crop for Brazilian fruit production. They are the most consumed fruit in natura, and Brazil is the fourth largest producer and the second largest consumer market on the planet (FAOSTAT, 2016, POF/IBGE, 2008). In addition to banana production for exportation, Brazil produces many banana cultivars that are specifically cultivated in each region of the country (POF/IBGE, 2008).

As a typical climacteric fruit (Burg & Burg, 1965), bananas must be harvested in a pre-climacteric stage and artificially ripened by induction through ethylene treatment in commercial sheds (Marriott & Palmer, 1980). For this reason, the period during which bananas can be transported and sold is known as ‘greenlife’, comprising the number of days between harvest and the initiation of the natural ripening process (Peacock & Blake, 1970). Climacteric fruit ripening is thus characterized by an increase in ethylene autocatalytic production and respiratory rates (Burg and Burg, 1965, Kumar et al., 2014, Marriott and Palmer, 1980). However, different banana cultivars can present different profiles of ethylene production and respiratory rates during postharvest life (Mota et al., 1997, Soares et al., 2011), which indicates that ethylene sensitivity in response to exogenous treatment can vary by cultivar.

During the banana ripening process, a dynamic interplay of plant signaling substances, transcription factors and hormones triggers a highly coordinated sequence of events. These events include color and texture changes in fruit pulp and peel due to both the degradation of starch (Shiga et al., 2011) and the cell wall polysaccharides, likewise the volatile synthesis (Wyllie & Fellman, 2000). The fruit flavor formation throughout ripening results from the fruit sweetening, the degradation of organic acids, and the synthesis of aroma-related volatile compounds (Seymour, 1993).

The regulation of the banana ripening seems to be also associated with a balance between indol-3-acetic acid (IAA) and abscisic acid (ABA) levels, wherein IAA plays a negative role on triggering ripening once its levels decrease concurrently with the activation of metabolic events of ripening (Purgatto, Lajolo, Nascimento, & Cordenunsi, 2002).

Concerning the starch metabolism, it has been shown that IAA and ABA are closely related to starch breakdown in banana fruit (Purgatto et al., 2002). The exogenous application of IAA delays the transcription and activity of β-amylase (Purgatto, Lajolo, Nascimento, & Cordenunsi, 2001), one of the key enzymes related to the starch breakdown in banana fruit (Nascimento et al., 2006). Therefore, IAA plays retarding the conversion of starch into soluble sugars which leads to the fruit sweetening and the softening process together with the cell wall degradation in banana fruit (Lohani et al., 2004, Mota et al., 1997, Shiga et al., 2011).

By contrast, ABA appears to induce the banana ripening process since its application increases respiratory rates in three days in advance compared to untreated fruit (Vendrell, 1985). ABA treatment also stimulates genes involved in cell wall degradation even independently of ethylene action, indicating that this hormone can act directly in some ripening events (Lohani et al., 2004). Moreover, early ripening caused by biotic stress during banana fruit development is associated with higher levels of ABA and lower levels of IAA (Saraiva et al., 2013). Hence, all these results support that IAA and ABA levels are directly involved in at least some events of the ripening process.

The primary challenge to banana crops in Brazil and many other Latin American countries is the fungal disease Black Leaf Streak Disease, or Black Sigatoka, which is caused by the fungus Mycosphaerella fijiensis Morelet (anamorph: Paracercospora fijiensis (Morelet) Deighton). This is a very aggressive foliar disease that causes severe damage and losses (Ploetz, 2006), premature ripening (Castelan, Saraiva, Lange, Cordenunsi, & Chillet, 2012), and fruit metabolic disorder (Saraiva et al., 2013). Black Sigatoka control is predominantly undertaken through aerially spraying fungicide, which represents a substantial portion of production costs (Ploetz, 2006). Thus, the development of a genetic resistance to Black Sigatoka has become a major focus of banana breeding programs (Jahnabi et al., 2015, Ploetz, 2006).

Thap Maeo is a Brazilian banana cultivar derived from Mysore (Creste, Neto, Silva, & Figueira, 2003). It is a tall plant with a high number of tillers at flowering (around four) and a higher number of fruits and hands per bunch than 24 other cultivars (Mattos et al., 2010). Particularly, Thap Maeo is resistant not only to Black Sigatoka, but also to Yellow Sigatoka and Fusarium wilt (Jesus et al., 2009).

However, like its parent cultivar Mysore, Thap Maeo fruits develop a distinct ripening behavior in which ripening events appear to occur quickly (Shiga et al., 2011, Soares et al., 2011). It demands a careful handling (even higher than Cavendish fruit) and can also show finger drop and peel browning as postharvest defects (personal communication with Thap Maeo producer).

Given the potential of the Thap Maeo as a promising cultivar for the Brazilian market and the lack of information and technologies allowing for its commercial expansion, this work aims to establish the physical, biochemical and physiological aspects of Thap Maeo fruit. It aims to define the best ethylene dosage for treatment, taking into account the fruit ethylene sensitivity assessed by the transcripts levels of genes encoding the ethylene receptors and ethylene biosynthesis enzymes, and also to characterize the ripening concerning the volatile compounds in ripe fruit and the IAA and ABA levels.

Section snippets

Materials

Thap Maeo Bananas (Musa acuminata, AAB, cv. Thap Maeo) were harvested at a commercial plantation located in Itapetininga, São Paulo State, Brazil. Samples were collected from an irrigated area of approximately 50,000 m2 (23°32′15.04″S; 47°59′27.53″W) at a latosol soil location and an average temperature of 21 °C throughout the experiment. Organic fertilizations were conducted by the farmer based on compost and manure applications. Necrotic leaf removal was also performed for disease and pest

Fruit characterization

In order to determine a range of physical and physiological parameters of Thap Maeo bananas, ten different sample collections were performed. The diameter of Thap Maeo fruit was found to range from 30.8 to 35.8 mm, weight from 67.2 to 94.3 g, and length from 11 to 13.3 cm (Table 2). Thap Maeo fruit is thus smaller fruit than Nanicão and Prata cultivars – diameter and length from 37.7 and 14.8 cm, respectively. Those are the types usually marketed in Sao Paulo state (Donato et al., 2006).

Harvests

Acknowledgment

We are thankful to Helena Pontes Chiebao for the ethylene receptors primer design and validation, and the technical assistance of Dr. Tania Shiga and Lucia Helena Justino da Silva. We also thank João Luiz Brandão Martins Junior for providing a well-managed banana field for this trial.

This work were supported by FAPESP (grant 2012/07220-3) and FoRC (FAPESP 2013/07914-8).

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