Long-term Controlled Atmosphere Storage Techniques on ‘Granny Smith’ Apples

Braam Mouton – Industry Presentation, 5 Nov 2019

Introduction

• The gas composition of the storage environment is adapted according to sensors, enabling adjustment in response to fruit metabolism.
• Three sensor types for monitoring:
  1. Chlorophyll fluorescence (CF)
  2. Respiration quotient (RQ)
  3. Ethanol (ET)

Benefits of Dynamic Controlled Atmosphere (DCA)

• DCA enables:
  • Comparison of fruit quality maintenance between systems.
  • Comparison of respiratory quotient readings and subsequent oxygen control between DCA-CF and DCA-RQ storage systems.
  • Determining the effect of ethylene scrubbing on the storability of fruit under DCA-CF storage.
  • Comparing biochemical data between fruit stored under different long-term storage techniques.
  • Evaluating the effect of different low oxygen storage techniques on the overall sensory sensation of fruit.

Static CA vs. DCA

• Static CA:
  No in situ sensors to monitor fruit response to the modified atmosphere. Low tolerance towards deviations from set gas levels.
• XLO (Extra Low Oxygen):
  • O₂: 1.2–1.5%, CO₂: 0.6–1.0%
  • Better quality maintenance compared to standard CA storage.
• DCA-CF:
  • O₂: 0.3–0.8%, CO₂: 0.3–0.8%
  • Sensors measure chlorophyll fluorescence; a sharp increase shows O₂ stress.
  • Better quality maintenance and reduced incidence of O₂-related disorders compared to standard CA (O₂: 1.5%, CO₂: 1.0%).
• Sensitive ethylene sensors (0.001 ppm) are used.

DCA-RQ: Principle and Benefits

• Sensors measure the CO₂ produced and O₂ consumed during storage; respiratory quotient (RQ) is calculated:
  • Equation: C₆H₁₂O₆ + O₂ → CO₂ + H₂O + energy
  • RQ = CO₂ produced / O₂ consumed (1 = aerobic, >1 = anaerobic)
  • When RQ value is above the set-point, the oxygen partial pressure is raised.
• Benefits of DCA-RQ:
  • Better quality maintenance compared to standard CA storage.
  • Measures the overall metabolic response.
  • Monitors: Flesh firmness, total soluble solids, titratable acidity, starch breakdown, superficial scald incidence/severity, colour change, external defects (e.g., greasiness), internal defects (e.g., core flush, browning).

Experimental Design

• Treatments:
  • DCA-CF
  • DCA-CF + ethylene scrubbing
  • DCA-RQ
  • XLO + ethylene scrubbing
• Evaluation per date, per replicate, per treatment:
  • Maturity indexing
  • Scald development (20 fruit)
  • Remainder: 60 fruit for biochemical, 10 for ethylene

Ethylene and Its Effects

• Ethylene primarily influences:
  • Greasiness
  • Green colour loss
  • Superficial scald incidence/severity
  • Firmness
  • Titratable acidity (TA)

Why Ethylene Matters

1. The synthesis of α-farnesene is ethylene dependent (Watkins et al., 1993; Ju & Curry, 2000).
2. 1-MCP’s efficiency in lowering scald in apples confirms ethylene is the main inducer of scald (Fan et al., 1999; Zanella, 2003).
3. Initial low oxygen stress treatments reduce ethylene production during cold storage, resulting in reduced superficial scald (Pesis et al., 2010).

Practical Implications

1. Regulation of ethylene action or biosynthesis affects volatile production in apple (Defilippi et al., 2005).
2. Ethylene level (tested: 2440, 178, 0.231 ml/l) had no significant influence on flesh firmness and TA retention in ‘McIntosh’ apples stored for 210 days under 1.5% CO₂ + 1.0% O₂ (Lidster et al., 1983).
3. Malic acid degradation is suppressed under low ethylene conditions (Defilippi et al., 2004).
4. In ‘Cox Orange Pippin’, flesh firmness retention was extended by ethylene scrubbing at O₂ levels of 1.25, 1.0, and 0.75%, both after 153 days of storage and after 14 days shelf life (Stow, 1990).
5. Ethylene scrubbing significantly reduced TA acidity loss under CA storage at 0.75% O₂ in ‘Cox Orange Pippin’ stored for 153 days (Stow, 1990).

Biochemical Parameters Under Different Low O₂ Storage Techniques

• Parameters per evaluation date, per replicate, per treatment:
  • ROS, MHO & ACC, α-farnesene, internal gases
  • EtOH, CTols (frozen), O₂, CO₂, C₂H₄
  • 10–20 fruit per reading

Analytical Methods

• Headspace volatile analysis: α-farnesene, MHO, ethanol (GC-MS, 3 replicates, 10 fruit per replicate, in duplicate)
• Reactive oxygen species (ROS) production: Fluorescent confocal microscopy (3 replicates, 10 fruit per replicate)
• Conjugated trienols (CTols): HPLC, UV spectrophotometry (3 replicates, 20 fruit/rep)
• Fruit peel frozen with liquid nitrogen, stored at -80°C until analysis

Expected Outcomes

1. Fruit quality storage profiling for different long-term methods.
2. Understanding control of O₂ & CO₂ under different methods.
3. Comparison of RQ values of DCA-CF and DCA-RQ storage methods.
4. Does ethylene scrubbing influence long-term DCA/CA storage quality?
5. Biochemical data between fruit stored under different long-term storage methods:
   • Mechanisms (e.g., α-farnesene vs. internal ethylene/ACC)
   • Ethanol levels in DCA-RQ vs. DCA-CF vs. XLO
6. Sensory experience between fruit stored under different long-term storage methods.

Sensory and Storage Observations

1. Core flush incidence decreases with decreasing O₂ concentrations in long-term storage for ‘Granny Smith’ (Zanella, 2003), but ethylene scrubbing under low O₂ (1.25, 1.0, 0.75%) increased core flush in ‘Cox Orange Pippin’ (Stow, 1990).
2. Modified atmosphere of 1.0% O₂ decreased ethylene accumulation and suppressed ethylene and CO₂ production at end of storage compared to conventional CA (Lidster et al., 1983). Is additional ethylene scrubbing economical?
3. Ethylene is an important modulator in aroma compound biosynthesis under normoxia (Defilippi et al., 2005).

References

• Bessemans, N., et al. (2016). A novel type of dynamic controlled atmosphere storage based on the respiratory quotient (RQ-DCA). Postharvest Biology and Technology, 115, 91-102.
• Both, V., et al. (2016). Effect of low oxygen conditioning and ultralow oxygen storage on the volatile profile, ethylene production and respiration rate of ‘Royal Gala’ apples. Scientia Horticulturae, 209, 156-164.
• Defilippi, B.G., et al. (2004). Impact of Suppression of Ethylene Action or Biosynthesis on Flavor Metabolites in Apple (Malus domestica Borkh) Fruits. J. Agric. Food Chem., 52, 5694-5701.
• Defilippi, B.G., et al. (2005). Relationship of Ethylene Biosynthesis to Volatile Production, Related Enzymes, and Precursor Availability in Apple Peel and Flesh Tissues. J. Agric. Food Chem., 53, 3133-3141.
• Fan, X., et al. (1999). Development of Apple Superficial Scald, Soft Scald, Core Flush, and Greasiness Is Reduced by MCP. Agric. Food Chem., 47, 3063-3068.
• Ju, Z. & Curry, E. (2000). Evidence that α-farnesene biosynthesis during fruit ripening is mediated by ethylene regulated gene expression in apples. Postharvest Biol Technol., 19, 9-16.
• Lidster, P.D., et al. (1983). Fruit quality and respiration of ‘McIntosh’ apples in response to ethylene, very low oxygen and carbon dioxide storage atmospheres. Scientia Hortic., 20, 71-83.
• Pesis, E., et al. (2010). Short anaerobiosis period prior to cold storage alleviates bitter pit and superficial scald in Granny Smith apples. J Sci Food Agric., 90, 2114-2123.
• Stow, J. (1990). The effects of removal of ethylene from low oxygen storage atmospheres on the quality of ‘Cox’s Orange Pippin’ apples. Scientia Hortic., 43, 281-290.
• Wang, Y. (2016). Storage Temperature, Controlled Atmosphere, and 1-Methylcyclopropene Effects on a-Farnesene, Conjugated Trienols, and Peroxidation in Relation with Superficial Scald, Pithy Brown Core, and Fruit Quality of ‘d’Anjou’ Pears during Long-term Storage. J. Am. Soc. Hortic. Sci., 141(2), 177-185.
• Watkins, C.B., et al. (1993). Relationships between α-farnesene, ethylene production and superficial scald development of apples. Acta Hortic., 343, 155-160.
• Wright, A.H., et al. (2012). Dynamic controlled atmosphere (DCA): Does fluorescence reflect physiology in storage? Postharvest Biology and Technology, 64, 19-30.
• Zanella, A. (2003). Control of apple superficial scald and ripening—a comparison between 1-methylcyclopropene and diphenylamine postharvest treatments, initial low oxygen stress and ultra low oxygen storage. Postharvest Biology and Technology, 27, 69-78.