Dynamic controlled atmosphere: Effects on the chemical composition of cuticular wax of ‘Cripps Pink’ apples after long-term storage

Highlights

• Long-term CA and DCA apple storage affect peel wax composition.

• DCA increases the total wax content on 'Cripps Pink' apple in shelf life period.

• Esters, ursolic and oleanolic acids and C16:0 are related to greasiness.

• DCA-RQ decreases the incidence of greasiness after long-term storage.

Abstract

The effects of controlled atmosphere (CA) and dynamic controlled atmosphere based on chlorophyll fluorescence (DCA-CF) and respiratory quotient (DCA-RQ; RQ = 1.3 and 1.5) on the metabolism, decay incidence, concentration and chemical composition of ‘Cripps Pink’ apple peel wax after 8 months of storage plus shelf life at 20 °C were studied. DCA-RQ1.3 stored fruit had the lowest respiration rate, evidencing low metabolism, corroborating with the highest number of healthy fruit and consequently being the best storage condition. The mean wax concentration found 21.23 g m⁻², although it was lower for the DCA-RQ1.5 condition after 7 d. There was increase in wax concentration for DCA treatments from 7 to 14 d of shelf life. Chromatographic analysis allowed the identification of palmitic, stearic, oleic and linoleic fatty acids, with an increase in cis-11,14-eicosadienoic acid in all treatments and in palmitic acid in CA at 14 d. Triterpenoids, such as ursolic acid and oleanolic acids, were higher in CA, while alcohols such as 10-nonacosanol was higher in both DCA-RQ treatments. All treatments had high concentrations of nonacosane and tetracosanal. DCA-RQ decrease the incidence of greasiness. The supposed induction of anaerobic metabolism by extremely low oxygen levels and consequently higher concentration of ethanol, which were monitored by the two levels of RQ, induced the formation of compounds that may favor some mechanisms of adaptation against the low oxygen partial pressure (pO₂).

Introduction

‘Cripps Pink’ (Malus × domestica Borkh) was developed by crossing ‘Golden Delicious’ and ‘Lady Williams’ apples. This is a promising cultivar due to its sensorial attributes, which are mainly related to flavor and crunchy texture (Cripps et al., 1993). Apples are seasonal and perishable fruit, although they can be stored for long periods, significantly increasing commercial interest by promoting the development of novel storage technologies that increase the availability of fresh apples and preserve the quality of the final product (Mditshwa et al., 2018).

Controlled atmosphere (CA) is one of the most used methods to store apples and uses low (1 kPa) (Brackmann et al., 2005) or ultra-low (0.8, 0.7 and 0.5 kPa) (Both et al., 2014) O₂ partial pressure (pO₂) combined with similar CO₂ partial pressure (pCO₂). However, these gases are maintained at static concentration, and do not reflect physiological changes of the fruit throughout the storage period, and are above the lower oxygen limit (LOL). The quality of the apple is maintained when it is closer to LOL, due to lower mitochondrial respiration (Wright et al., 2015). Several dynamic controlled atmosphere (DCA) systems have been proposed to determine LOL and maintain fruit at safe concentrations during storage. Thus, LOL can be monitored based on ethanol production by fruit (DCA-ethanol) (Veltman et al., 2003), fruit chlorophyll fluorescence emission (DCA-CF) (Prange et al., 2007), or respiratory quotient (DCA-RQ) (Brackmann, 2015; Van Schaik et al., 2015; Weber et al., 2015; Bessemans et al., 2016).

Recent studies have shown important aspects regarding the cuticle of the epidermis and the postharvest performance of fruit: permeability and water loss, susceptibility to infections and physiological disorders, and mechanical properties that define texture (Lara, 2018; Lara et al., 2014). Cuticular wax is composed of very long chain fatty acids (VLCFAs) and their derivatives, including primary and secondary alcohols, aldehydes, alkanes, ketones, wax esters, as well as those derived from other precursors such as triterpenoids (Lara et al., 2015). Therefore, it is necessary to relate the properties and/or composition of this cuticular layer with the quality attributes during the postharvest period.

‘Cripps Pink’ apple is characterized by a very dense pulp as well as a greasy and waxy cuticle that develops mainly during the ripening and storage. Besides ‘Pink Lady’, other apple cultivars have been reported to become greasy during storage, including ‘Jonagold’, ‘Royal Gala’, and ‘Granny Smith’ (Fan et al., 1999; Veraverbeke et al., 2001; Curry, 2008; Yang et al., 2017b, 2017a). Excessive greasiness is considered a disagreeably sensorial quality attribute for fresh fruit consumers (Richardson-Harman et al., 1998). Greasiness is a physical and chemical fruit-surface phenomenon that may occur both in development and during storage and is associated with changes in wax constituents (Curry, 2008; Dong et al., 2012). Many of these changes have been shown to be regulated by ethylene (Li et al., 2017; Yang et al., 2017a). DCA use, mainly DCA-RQ, reduces ethylene production (Both et al., 2018; Donadel et al., 2019), and may affect the characteristics and chemical composition of this cuticular layer of stored apples.

The production and composition evaluation of apple peel wax will provide important data on fruit metabolism and its relation to quality attributes, especially when stored for long-term periods under different DCA methods. Therefore, the objective of this study was to evaluate the changes in the concentration and chemical composition of ‘Cripps Pink’ apple peel waxes after storage under CA, DCA-CF and DCA-RQ conditions for eight months of storage plus 7 and 14 d shelf life at 20 °C. In addition, the results of the concentration and chemical composition of apple peel wax were related to the metabolism,decay incidence, and greasiness of fruit.