Maintaining postharvest quality of cold stored ‘Hass’ avocados by altering the fatty acids content and composition with the use of natural volatile compounds – methyl jasmonate and methyl salicylate

BACKGROUND: Low temperature is often used to reduce metabolic processes and extend the storage of fruit, however, in the case of avocado the temperature below 3 °C would often result in development of physiological disorders associated with chilling injury. The objective of this study was to investigate the ability of methyl jasmonate (MeJA) and methyl salicylate (MeSA) vapours to alleviate the chilling injury in ‘Hass’ avocado fruit kept at 2 °C for 21 d followed by 6-7 d shelf-life at 20 °C, simulating supply chain conditions. RESULTS: The incidence and severity of chilling injury was significantly reduced in MeJA and MeSA exposed fruit, especially at 100 µmol l-1. The mechanism involved improved membrane integrity via alteration of the fatty acids content and composition, down-regulation of LOX gene expression and reduced activity of lipoxygenase. CONCLUSION: Methyl jasmonate and methyl salicylate have the potential for being used with ‘Hass’ avocado fruit shipped at low temperature by reducing their susceptibility to chilling injury

TRANSCRIPTOME DYNAMICS IN MANGO FRUIT PEEL REVEALS MECHANISMS OF CHILLING STRESS

Cold storage is considered the most effective method for prolonging fresh produce storage. However, subtropical fruit is sensitive to cold. Symptoms of chilling injury in mango include red and black spots that start from discolored lenticels and develop into pitting. The response of ‘Keitt’ mango fruit to chilling stress was monitored by transcriptomic, physiological and microscopic analyses. Transcriptomic changes in the mango fruit peel were evaluated during optimal (12°C) and suboptimal (5°C) cold storage. Two days of chilling stress upregulated genes involved in the plant stress response, including those encoding transmembrane receptors, calcium-mediated signal transduction, NADPH oxidase, MAP kinases and WRKYs, which can lead to cell death. Indeed, cell death was observed around the discolored lenticels after 19 days of cold storage at 5°C. Localized cell death and cuticular opening in the lumen of discolored lenticels were correlated with increased general decay during shelf-life storage, possibly due to fungal penetration. We also observed increased phenolics accumulation around the discolored lenticels, which was correlated with the biosynthesis of phenylpropanoids that were probably transported from the resin ducts. Increased lipid peroxidation was observed during chilling injury by both the biochemical malondialdehyde method and a new non-destructive luminescent technology, correlated to upregulation of the α-linolenic acid oxidation pathway. Genes involved in sugar metabolism were also induced, possibly to maintain osmotic balance. This analysis provides an in-depth characterization of mango fruit response to chilling stress and could lead to the development of new tools, treatments and strategies to prolong cold storage of subtropical fruit

Combined Treatments Reduce Chilling Injury and Maintain Fruit Quality in Avocado Fruit during Cold Quarantine.

Quarantine treatment enables export of avocado fruit (Persea americana) to parts of the world that enforce quarantine against fruit fly. The recommended cold-based quarantine treatment (storage at 1.1°C for 14 days) was studied with two commercial avocado cultivars 'Hass' and 'Ettinger' for 2 years. Chilling injuries (CIs) are prevalent in the avocado fruit after cold-quarantine treatment. Hence, we examined the effect of integrating several treatments: modified atmosphere (MA; fruit covered with perforated polyethylene bags), methyl jasmonate (MJ; fruit dipped in 2.5 μM MJ for Hass or 10 μM MJ for Ettinger for 30 s), 1-methylcyclopropene (1-MCP; fruit treated with 300 ppb 1-MCP for 18 h) and low-temperature conditioning (LTC; a gradual decrease in temperature over 3 days) on CI reduction during cold quarantine. Avocado fruit stored at 1°C suffered from severe CI, lipid peroxidation, and increased expression of chilling-responsive genes of fruit peel. The combined therapeutic treatments alleviated CI in cold-quarantined fruit to the level in fruit stored at commercial temperature (5°C). A successful therapeutic treatment was developed to protect 'Hass' and 'Ettinger' avocado fruit during cold quarantine against fruit fly, while maintaining fruit quality. Subsequently, treated fruit stored at 1°C had a longer shelf life and less decay than the fruit stored at 5°C. This therapeutic treatment could potentially enable the export of avocado fruit to all quarantine-enforcing countries. Similar methods might be applicable to other types of fruit that require cold quarantine

Luminescence and light image of ‘Hass’ avocado fruit in response to cold storage.

<p>Luminescence and light image were captured and visualized after 15 days of cold storage at 5°C or 1°C or 1°C with the combined treatments (MJ, MA, LTC). (A) Luminescence (20 min of autoluminescence, emission: 647–770 nm) indicating lipid peroxidation. (B) Light image.</p

Evaluation of physiological parameters of ‘Ettinger’ fruit during cold-quarantine treatments.

<p>Physiological parameters of treated [modified atmosphere (MA), methyl jasmonate (MJ), low-temperature conditioning (LTC)] or non-treated ‘Ettinger’ after cold storage (black column) and further shelf storage (white column). (A) Overall decay displayed in percentage. (B) Firmness displayed in Newton. (C) Blossom-end rot displayed in percentage. Data are mean ± SE.</p

Chilling Stress Upregulates α‑Linolenic Acid-Oxidation Pathway and Induces Volatiles of C₆ and C₉ Aldehydes in Mango Fruit

Mango-fruit storage period and shelf life are prolonged by cold storage. However, chilling temperature induces physiological and molecular changes, compromising fruit quality. In our previous transcriptomic study of mango fruit, cold storage at suboptimal temperature (5 °C) activated the <i>α-</i>linolenic acid metabolic pathway. To evaluate changes in fruit quality during chilling, we analyzed mango “Keitt” fruit peel volatiles. GC–MS analysis revealed significant modulations in fruit volatiles during storage at suboptimal temperature. Fewer changes were seen in response to the time of storage. The mango volatiles related to aroma, such as <i>δ</i>-3-carene, <i>(Z)-β-</i>ocimene, and terpinolene, were downregulated during the storage at suboptimal temperature. In contrast, C₆ and C₉ aldehydes and alcoholsα-linolenic acid derivatives 1-hexanal, <i>(Z)</i>-3-hexenal, <i>(Z)</i>-3-hexenol, <i>(E)-</i>2-hexenal, and nonanalwere elevated during suboptimal-temperature storage, before chilling-injury symptoms appeared. Detection of those molecules before chilling symptoms could lead to a new agro-technology to avoid chilling injuries and maintain fruit quality during cold storage at the lowest possible temperature

Chilling symptoms of ‘Ettinger’ after cold-quarantine treatments.

<p>Evaluation of chilling-injury (CI) symptoms in treated [modified atmosphere (MA), methyl jasmonate (MJ), low-temperature conditioning (LTC)] and non-treated ‘Ettinger’ after cold-quarantine treatments (15 days at 5°C or at 1°C, then storage at 5°C for the rest of the overall 3 weeks in cold storage), followed by 7 days of shelf storage. (A) Representative pictures of ‘Ettinger’ fruit after 3 weeks of cold storage followed by shelf storage. (B) CI severity ranked from 1–3 after cold storage (black column) and further shelf storage (white column). Data are mean ± SE. Different letters (lowercase letters and uppercase letters refer to after cold storage and shelf life, respectively) indicate significant differences at <i>P</i> < 0.05 by one-way ANOVA and Duncan's multiple range test.</p

Evaluation of physiological parameters of ‘Hass’ fruit during cold-quarantine treatments.

<p>Treated (LTC 3d or 5d: 3 or 5 days of low-temperature conditioning, MCP: 1-MCP 150 ppm) or non-treated ‘Hass’ fruit were checked for physiological parameters after cold storage (15 days at 5°C or at 1°C, then storage at 5°C for the rest of the overall 3 weeks in cold storage), followed by 7 days of shelf storage at 20°C. (A) Chilling injuries (CI index 1–3). (B) Overall decay displayed in percentage. (C) Firmness displayed in Newton. Data are mean ± SE. Different letters indicate significant difference at <i>P</i> < 0.05 by one-way ANOVA and Duncan's multiple range test.</p

Chilling symptoms of ‘Hass’ fruit during cold-quarantine treatments.

<p>Evaluation of chilling-injury (CI) symptoms in ‘Hass’ during cold-quarantine treatments (15 days at 5°C or at 1°C, then storage at 5°C for the rest of the overall 3 weeks of cold storage), followed by 7 days of shelf storage. (A) Representative pictures of ‘Hass’ fruit after 3 weeks of cold storage followed by shelf storage. (B) CI severity ranked from 1–3 after cold storage (black column) and further shelf storage (white column). Data are mean ± SE. Different letters indicate significant differences at <i>P</i> < 0.05 by one-way ANOVA and Duncan's multiple range test.</p