Elsevier

Scientia Horticulturae

Volume 229, 9 February 2018, Pages 117-124
Scientia Horticulturae

Research Paper
Pre-harvest application of hexanal formulation enhances shelf life and quality of ‘Fantasia’ nectarines by regulating membrane and cell wall catabolism-associated genes

https://doi.org/10.1016/j.scienta.2017.10.031Get rights and content

Highlights

  • Enhanced Freshness Formulation (EFF) is proposed to enhance shelf life of nectarines.

  • Hexanal is the key ingredient of EFF with shelf life enhancing effects.

  • Onset of mealiness and internal browning was delayed by a week.

  • Magnitude of incidence of chilling injury symptoms were significantly reduced.

  • Gene expression studies indicated a downregulation of key ripening related genes.

Abstract

Post-harvest technologies play a key role in enhancing shelf life and maintaining quality characteristics of tender fruits such as nectarines (Prunus persica [L.] Batsch var. nectarina). This research investigated the effects of an ‘Enhanced Freshness Formulation’ (EFF) with hexanal as the key ingredient in enhancing shelf life of field grown nectarines. Pre-harvest sprays of EFF on ‘Fantasia’ nectarines, conducted at two commercial orchards in the Niagara region, ON, showed improvement in shelf life. Application of hexanal formulation delayed the incidence of chilling injury symptoms (internal browning and mealiness/woolliness) by one week. As well, treated fruits maintained significantly higher firmness until 38d post-harvest. There were no differences in total soluble solids, titratable acidity and color values between treated and control fruits. qRT-PCR was conducted to evaluate the expression levels of 22 genes potentially involved in ripening, to understand the regulatory effects of the hexanal formulation. EFF application induced a highly significant reduction in transcript levels of three Phospholipase D genes, five N-glycoprotein group genes, and other genes involved in ripening and softening processes. These findings indicate that, a delay in the ripening process caused by hexanal formulation, may be associated with the modulation of the expression of key ripening related genes, enhancing shelf life and quality of nectarines.

Introduction

Nectarines [Prunus persica (L.) Batsch, var. nectarina] are characteristically soft-fleshed tender fruits with a short post-harvest shelf life. In ambient temperatures, they quickly deteriorate in quality, hence, post-harvest technologies are essential to prolong their shelf life and maintain quality attributes of the fruit. Cold storage is the most commercially adopted technique, and a cold chain has been integrated into the post-harvest management systems (Lurie and Crisosto, 2005). However, chilling injury symptoms such as internal browning and mealiness/woolliness have been reported especially when the fruits were stored in the chilling temperature range of 2.2 °C to 7 °C range (Crisosto et al., 1999). Further, these symptoms develop during advanced stages of ripening after cold storage, when the fruits reach the consumer (Bruhn et al., 1991, Crisosto et al., 1995).

Extensive research has been conducted to combat the incidence of these chilling injury disorders. Various techniques such as fertilizer practices, irrigation regimes, crop load adjustments, fruit size, canopy position, application of plant growth regulators, controlled atmosphere storage, use of ethylene inhibitors, intermittent warming (IW), and controlled delayed cooling have been used with varying levels of success (Lurie and Crisosto, 2005). Among them, 1-MCP (1-methyl cyclopropene) has been successfully used to enhance shelf life of many fruits such as apples and pear to maintain firmness, however, it is ineffective at low temperatures which limits its use in extending the post-harvest shelf life of peaches and nectarines (Watkins, 2006). Hence, there is a need to develop more efficient strategies to combat the chilling injury disorders.

Nectarine fruit ripening is a complex process which involves many biochemical changes in the fruit. It is usually characterized by a reduction of organic acid content, an increase in sugar content, breakdown of pectin and starch, all leading to the softening of fruit, changes in color and production of a characteristic aroma (Giovannoni, 2001). As is the case with many stone fruits, nectarines are climacteric, where there is a characteristic rise in respiration corresponding with an increase in ethylene production during ripening and senescence. The fruit development and ripening in nectarine follows a double sigmoid curve with 4 distinct stages (S1–S4) as described by Tonutti et al. (1991). Stage 4 (S4) represents the ripening stage, where the fruit has already reached its full size and is undergoing the process of climacteric ripening. The structural breakdown of different cellular components and other changes occur during this ripening stage (S4) of nectarines (Tonutti et al., 1991).

Cell wall and membrane degradation are two highly complex interrelated processes responsible for softening of most fruits (Paliyath and Murr, 2008). Much attention has been focused on softening of fruits especially due to their economic implications (Crisosto et al., 1995; Brummel and Harpster, 2001). Tender fruits, when softening, are more susceptible to injury during transportation and storage, which may lead to secondary issues such as pathogen attack (Crisosto and Valero, 2008). During softening, the cell wall structure weakens causing a loss of linkage between adjacent cells and cell separation. This process involves the expression of different enzymes that initiate a cascade of reactions which irreversibly degrades the mechanical properties of the cell wall. Several enzymes have been implicated in this process. β-1,4-glucanase degrades cellulose; Pectin methyl-esterase de-esterifies pectin predisposing it to further degradation by polygalacturonase and β-galactosidase (Brummell et al., 2004). Expansins are proteins which facilitate loosening of the cell wall (Rose et al., 1997, Brummell and Harpster, 2001) and a general increase in their expression during ripening of peach has been recorded (Hayama et al., 2003).

Membrane degradation during ripening has been studied in great detail (Paliyath and Droillard, 1992). During the natural ripening process, lipid degradation leads to destabilization of the membrane. This can result in progressively increasing Ca2+ concentration in the cytoplasm due to leakage and inactivation of calcium pumps, which activates Phospholipase D (PLD), the key enzyme involved in membrane lipid catabolism. This in turn has been proposed to drive the autocatalytic cascade of lipid catabolic reactions leading to progressive degradation of the lipid membranes (Paliyath and Droillard, 1992). Subsequent studies on PLD (Wang, 2001) have revealed several isoforms of PLD, such as PLD-α, PLD-β, PLD-γ, etc, which are involved in several interrelated processes and are activated by different levels of calcium (Paliyath and Murr, 2008).

N-Glycoproteins also play an important role in various physiological processes of ripening. The activity of this class of enzymes results in the production of free glycans, which stimulate fruit ripening by activating the ethylene synthesis pathway (Priem and Gross, 1992). Among the N-glycoprotein degrading enzymes, α-mannosidase, β-hexosaminidase and xyloglucan endotransglucosylase/hydrolase play prominent roles in the N-glycosylation pathway. Inhibition of these enzymes in peaches and tomatoes slow the rate of the softening of these fruits (Cao et al., 2014, Ghosh et al., 2011, Meli et al., 2010).

Most of the technologies used to enhance the shelf life of fruits have focused on ethylene biosynthesis and cell wall degradation pathways to decelerate the ripening process. However, inhibition of lipid metabolic pathways has also been used to inhibit PLD in order to enhance the shelf life of fruits, vegetables and flowers (Paliyath et al., 2003). PLD is an autocatalytic enzyme which initiates the cascade of ripening related catabolic pathways. Recent advancements in increasing the shelf life of fruits, vegetables and flowers has witnessed the successful use of hexanal based formulations, which inhibits the PLD induced membrane catabolism (Paliyath et al., 2003, Paliyath and Murr, 2007). Hexanal, a C6 aldehyde with GRAS (generally regarded as safe) status, is naturally produced in the lipid peroxidation pathway mediated by lipoxygenase and hydroperoxide lyases (Paliyath et al., 2003).Hexanal has been found to downregulate the expression of PLD, and several other ripening related genes, resulting in enhanced shelf life of fruits such as apple, sweet cherry, guava and strawberry (Paliyath and Subramanian, 2008). At present, several studies are being conducted to study the ability of hexanal based technologies in enhancing post-harvest characteristics of fruits and vegetables.

The main objective of this study was to determine the effect of Enhanced Freshness Formulation, a hexanal based formulation, as a pre-harvest spray in enhancing post-harvest shelf life of Fantasia nectarines. Further, we also studied the expression pattern of 22 genes, encoding proteins involved in lipid and cell wall metabolism, to better understand the mechanism of regulation of ripening by the hexanal formulation on nectarine fruits.

Section snippets

Trial location

Experiments were conducted at two commercial nectarine orchards in the Niagara region of Ontario, to determine the effect of the EFF (Enhanced Freshness Formulation) as a pre-harvest spray in enhancing post-harvest shelf life of ‘Fantasia’ nectarines. The nectarines orchard sites were located at Jordan, ON (Site A) (43°10ˈ14 ̎ N, 79°90ˈ54 ̎ W) and Beamsville, ON (Site B) (43°11ˈ32 ̎ N, 79°29ˈ3 ̎ W). The trees at Jordan, ON were 5–6 years of age and the trees at Beamsville, ON were 10–15 of age.

Plant material and postharvest treatments

Firmness

The results showed a significant effect of the repeated measure ‘days post-harvest’ (P < 0.0001) and treatment (P = 0.0009). The day*treatment effect was not significant indicating the consistency of the trends seen in the firmness results. Fruit firmness decreased over time in both treatments, but EFF treated fruits always maintained a significantly higher firmness at most time points of at least 5 N/cm from 8d post-harvest (Table 1). The significant advantage of the EFF treatment was maintained,

Discussion

Peaches and nectarines are highly perishable soft fleshed fruits with a short market life. Cold storage at near 0 °C has been integrated into the post-harvest storage chain to enhance shelf life and ensure the freshness of fruits until they reach the market (Crisosto and Valero, 2008). However, the fruits are exposed to the development of chilling injury symptoms such as internal browning and mealiness, thus reducing the taste, flavor and consumer acceptance of these fruits (Lurie and Crisosto,

Acknowledgements

This work was supported by a grant from Canada’s International Development Research Centre (IDRC), www.idrc.ca, and financial support from Global Affairs Canada (GAC), an entity of the Government of Canada. We also thank Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) for the support of this work. Thanks are also due to Glen Alm (Sr. research technician), Varsha Jayasankar and Olivia Colling (summer assistants) who helped with the field work conducted in this project. We also

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