Elsevier

Postharvest Biology and Technology

Volume 155, September 2019, Pages 111-119
Postharvest Biology and Technology

Postharvest applications of n-butanol increase greasiness in apple skins by altering wax composition via effects on gene expression

https://doi.org/10.1016/j.postharvbio.2019.05.017Get rights and content

Highlights

  • NBA treatment can accelerate the development of skin greasiness in apples.

  • The accumulations of the fluid wax constituents increase in NBA-treated fruit.

  • The expressions of some genes related to cuticular waxes can be promoted by NBA treatment.

  • NBA treatment does not affect fruit ripening and senescence.

Abstract

The postharvest development of greasiness in apple skin has negative effects on fruit appearance and market quality and causes significant economic losses. The fluid wax constituents responsible for skin greasiness comprise mainly oleate and linoleate esters of (E,E)-farnesol and short-chain alcohols (C3-C5). Butyl esters are also key components. It is believed that accumulations of volatile alcohols affect the development of skin greasiness by offering substrates for the biosynthesis of the greasy esters. To demonstrate the putative role of volatile alcohols on apple skin greasiness, ‘Cripps Pink’ apples were treated with either 10 or 25 μL L−1 n-butanol (NBA) and then stored at 20 °C. The composition of each cuticular wax was analyzed, and the expression levels of the related genes were recorded. There was no significant difference in the time course of fruit ripening or senescence among the two NBA treatments and the control. As expected, accumulations of the fluid wax constituents were indeed promoted in the NBA-treated fruit. On day 42, compared with the control, the butyl ester contents of the skins of the 10 and 25 μL L−1 NBA-treated fruits were 1.7 and 2.9 times higher, respectively. Moreover, the 25 μL L−1 NBA-treated fruit showed higher greasiness levels and looked shinier than the fruit exposed to the lower NBA treatment or the control. Several genes were more highly expressed in the NBA-treated fruit than in the control. These included MdKASIII, MdSAD6, MdWSD1 (related to wax biosynthesis) and MdLTPG1 (related to wax export). We conclude that NBA had no significant effects on fruit ripening or senescence but promoted the development of skin greasiness.

Introduction

Like the organs of most land plants, apple (Malus domestica Borkh.) fruits are covered with hydrophobic organic compounds called cuticular waxes (Pollard et al., 2008). The physical and chemical properties of the cuticular wax determines the appearance of an apple fruit and so significantly affect consumer preference and thus commercial value (Glenn et al., 1990). In apples, the C29 homologues are the most abundant constituents of the wax layer and exist in solid form (Belding et al., 1998; Curry, 2008; Veraverbeke et al., 2001). However, the fluidity of the surface waxes of some apple cultivars, such as ‘Jonagold’ (Veraverbeke et al., 2001), ‘Royal Gala’ (Curry, 2008) and ‘Cripps Pink’ (Yang et al., 2017b) increase during storage, ultimately causing an unpleasant greasy feeling. Skin greasiness can appear either on the tree or later, during storage. Greasiness is associated with an increase in the oil fraction of the cuticular lipids (Dadzie et al., 1995; Fan et al., 1999). It has recently been suggested that skin greasiness may be associated with the accumulation of the long-chain unsaturated fatty acid esters of farnesol (Christeller and Roughan, 2016). Our subsequent work confirmed that significant accumulations of the fluid wax constituents result in a phase change from solid to liquid in the surface waxes of the apple cultivars ‘Cripps Pink’ and ‘Jonagold’ (Yang et al., 2017b). The fluid wax compounds comprise mainly oleate and linoleate esters of (E,E)-farnesol and short-chain alcohols (C3-C5) and lesser amounts of free unsaturated fatty acids.

Various studies have shown that the provision of exogenous substrates to the seeds and fruits of some plants promotes the synthesis of the corresponding esters and that the synthesis of a particular ester is selective to the substrate (Bartley et al., 1985; Berger and Drawert, 1984; Yu et al., 2018). For example, the synthesis of volatile esters can be enhanced by supplying alcohols (C2-C8) as a substrate, in which n-butanol (NBA) and n-pentanol are converted maximally into their corresponding esters, with ester production increasing with increasing concentrations of the exogenous alcohols (Bartley et al., 1985; Berger and Drawert, 1984). Our recent studies show that the unsaturated fatty acid esters of short-chain alcohols accumulate extensively during the development of skin greasiness in ‘Cripps Pink’ apples, in which the butyl ester content is particularly high (Yang et al., 2017a, 2017b). Moreover, studies have shown that NBA is the most abundant volatile alcohol during postharvest storage of ‘Cripps Pink’ apples (Carmen et al., 2008; Villatoro et al., 2008). Accordingly, we speculated that volatile biosynthesis affects the development of skin greasiness by providing the volatile alcohol substrates for greasy ester production (Yang et al., 2017b). Hence, it is worthwhile to conduct a thorough study of the effects of NBA on the development of apple skin greasiness.

Here, we compare wax composition and the expression levels of genes related to wax biosynthesis and wax export in control and NBA-treated ‘Cripps Pink’ apples stored at 20 °C. The aim is to gain new insights into skin greasiness by analyzing the effects of applications of exogenous volatile alcohol substrates on skin greasiness in apple fruit during storage at ambient temperatures.

Section snippets

Plant materials and treatments

Mature ‘Cripps Pink’ apple fruit was picked from an orchard in Fufeng County, Shaanxi Province, China, on 30 October 2017. Apples of uniform size (60 mm in diameter) without any physical damage were selected and randomly divided into three groups. One group was the control, and the other two groups were treated with NBA vapor using the method reported by Berger and Drawert (2010) with some modifications. Apples and a glass vessel with filter paper soaked with liquid NBA were enclosed in a

Effects of NBA on respiration rate, ethylene production and fruit firmness during postharvest ripening at 20 °C

The respiratory rate of control and NBA-treated fruit showed a similar trend (Fig. 1A). During the first days of storage, from day 0 to day 7, there was a slight increase in the respiration rates of all three groups of fruit. After a slight decline, the respiration rate then began to rise rapidly on day 14 and reached a climacteric on day 21. Subsequently respiration showed a downward trend until the end of storage. Changes in the ethylene production of the NBA-treated fruit during storage

NBA treatment promotes the accumulation of liquid esters in waxes, thus accelerating the development of skin greasiness

Certain apple cultivars develop a greasy surface during ripening, such as ‘Jonagold’ (Veraverbeke et al., 2001), ‘Royal Gala’ (Curry, 2008) and ‘Cripps Pink’ (Yang et al., 2017b). Skin greasiness is commercially undesirable. Although there has been significant research on the cuticular waxes of apples (Curry, 2008; Veraverbeke et al., 2001), the causes of skin greasiness have not been fully explained. Previously, Christeller and Roughan (2016) presumed that the accumulations of the liquid

Conclusion

The accumulation of liquid waxes in ‘Cripps Pink’ apples during storage was promoted by NBA treatment, which also accelerated the development of skin greasiness. Meanwhile, neither earlier ripening nor senescence were affected. Chemical analyses show that the content of fluid wax components contributing to skin greasiness (free linoleic and oleic acids and their corresponding esters, especially butyl esters) increased significantly in NBA-treated fruit. The results suggest that the level of

Acknowledgment

This work was supported by the National Industry Technology System of China for Apple (CARS-27).

References (33)

  • D. Allan et al.

    Arabidopsis LTPG is a glycosylphosphatidylinositol-anchored lipid transfer protein required for export of lipids to the plant surface

    Plant Cell

    (2009)
  • B.M. Barney et al.

    Altering small and medium alcohol selectivity in the wax ester synthase

    Appl. Microbiol. Biotechnol.

    (2015)
  • I.M. Bartley et al.

    Synthesis of aroma compounds by apples supplied with alcohols and methyl esters of fatty acids

    J. Sci. Food Agric.

    (1985)
  • R.D. Belding et al.

    Composition and variability of epicuticular waxes in apple cultivars

    J. Am. Soc. Hortic. Sci.

    (1998)
  • R.G. Berger et al.

    Changes in the composition of volatiles by post-harvest application of alcohols to red delicious apples

    J. Sci. Food Agric.

    (1984)
  • V. Carmen et al.

    Long-term storage of Pink Lady apples modifies volatile-involved enzyme activities: consequences on production of volatile esters

    J. Agric. Food Chem.

    (2008)
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