The multi-factorial risks of internal browning in Cripps Pink apples

Fruit- and orchard-specific factors like irrigation practices, pre-harvest spray applications (for which there is currently limited research), maturity, fruit size, current and previous season yield (crop load), and tree age should all be considered as contributing factors to IB development.

Pre-harvest temperature and the accumulation of growing degree days (GDD) above 10 °C from full bloom to harvest, are also important considerations. GDD refers to the thermal time index that quantifies heat accumulation above a defined base temperature (in this case, 10 °C).

A good understanding of the factors involved and the seasonal risk of IB development due to temperature can facilitate effective postharvest management to reduce risk and optimise market planning strategies. Table 1 provides a summary of relevant IB risks that were identified in this study. And below is a comparison of pre- and postharvest factors that influence browning types. This comparative knowledge is instrumental in investigating relevant research gaps (Ramos, 2026).

Pre-harvest

This phase can be thought of as the genesis of IB risks – where it all begins.

Teams in storage facilities must develop a good understanding of relevant pre-harvest risk factors and the apple profiles that they receive. This will equip them to significantly reduce browning risk by adjusting their storage methods and duration accordingly.

Orchard/quality factors

RB risk increased when previous and current yields exceeded 70-80 t/ha and fruit size was below 69 mm, in the current season. CO₂ core browning was most prevalent in orchards with high tree row volumes (>2 200 L) and large fruit (>140 g) with Total Soluble Solids (TSS) <14%. CO₂-induced disorders, including flesh browning and internal cavities, were strongly associated with seedling rootstocks, vigorous canopies, and advanced starch breakdown.
High yields (>79-82 t/ha) helped minimize CO₂ flesh browning and core cavities, and higher acidity [titratable acid (TA) ] reduced browning risks (Ramos, 2026).

Ripening rate

The highest DB incidence was associated with a faster change in ground colour, increase in mass, faster starch breakdown, and a lower blush percentage and colour intensity, and after-storage TA and firmness.

The highest RB incidence was associated with the slowest increase in fruit circumference, mass, seed colour change and starch breakdown.

Temperature

Climatic factors

Thermal conditions during the growing and ripening phases dictate fruit quality maintenance in storage. RB incidence is lower in cooler seasons that have a warmer ripening period shortly before harvest. In contrast, DB is triggered by extreme temperature spikes and high maximum temperatures in the final month before harvest. These temperature surges appear to cause a faster starch breakdown and more mature fruit, reducing the fruit’s tolerance to long-term cold storage.

However, DB risk is lower in longer growing seasons (≥188 days) with a cooler ripening period.

CO₂-induced disorders like core browning and core cavities are least likely after warmer cumulative growing seasons, whereas flesh cavities are exacerbated by low heat units [growing degree hours (GDH) ] in the four weeks leading up to harvest. GDH measures heat accumulation to predict plant development stages (Ramos, 2026).

Harvesting

Harvesting inner and outer canopy fruit together and disregarding their distinct difference in maturity pose a significant risk of IB development when the fruit are stored together.

Other important considerations for risk avoidance include harvesting at optimum maturity and placing fruit in cold storage, soonest after harvesting, to reduce maturity progression before storage.

Unrefrigerated transport over long distances after harvesting in hot conditions causes starch breakdown to reach post-optimum levels, even though fruit were harvested at optimum starch breakdown. This results in high IB during low-oxygen, long-term storage (Ramos, 2026).

Postharvest

Long-term storage regimes

There are various long-term storage regimes available to effectively manage IB incidence.

Long-term storage technology

Dynamic Controlled Atmosphere Chlorophyll Fluorescence (DCA-CF) regulates oxygen at the lowest oxygen limit according to the fluorescence of the fruit, below 1 kPa. And it reduces the risk of browning disorders like superficial scald development in Granny Smith. Controlled atmosphere (CA) regulates oxygen at a constant oxygen level – in this trial, at 1.5 kPa.

Results showed that regardless of low-oxygen storage techniques, maturity played a bigger role in long-term storage than the storage technique employed. Storing fruit with a high starch breakdown in low-oxygen storage, for extended periods of time, will result in high IB (Ramos, 2026).

Literature also shows that in the case of RB, CO₂ levels >1 kPa in CA were found to increase susceptibility. Cripps Pink and its strains are CO₂-sensitive above 1 kPa (Jobling and James, 2008).

Long-term storage temperature

Similarly, the research team was confronted with the dilemma of decreased DB incidence when storing fruit at 3 °C, but with compromised fruit quality. Low storage temperatures possibly result in a stress response in fruit, increasing reactive oxygen species (ROS). And this physiological postharvest factor possibly overcomes the cell antioxidant capacity, giving rise to DB development. Research team member Heleen Tayler proved that step-down cooling from 3 to 1 °C works well in inhibiting disorder development, which is why it is included in three storage regimes in the industry best practice guidelines (Store-it Group, 2022).

For RB, an incidence decrease was also observed in these same trials when step-down cooling was applied from 3 to 1 °C. Therefore, the research team advises following the best practice guidelines closely to minimise overall IB incidence (Store-it Group, 2022).

1-Methylcyclopropene and Diphenylamine

Lower DB incidence was recorded in 1-Methylcyclopropene (1-MCP)-treated fruit (Butler, 2015; Crouch et al., 2015; de Jong, 2023; James, 2007; Majoni et al., 2013). These fruit also exhibited lower IB incidence (Majoni et al., 2013; Store-it Group, 2022). 1-MCP inhibits ethylene action, thereby retarding ripening and extending shelf life.

Regarding CO₂-related browning, the application of Diphenylamine (DPA) – a postharvest chemical antioxidant – reportedly reduces the incidence of IB by retaining ascorbic acid levels and decreasing H2O2 production (de Castro et al., 2008).

Unfortunately, DPA is not allowed in many of our major markets, including the EU and UK.

Devising an effective, robust risk mitigation strategy for IB remains dependent on ongoing research.

Acknowledgements

• Researchers: Dr Elke Crouch (project lead)
• Research team: Heleen Tayler (a student at the time), Daniël Viljoen and Ian Crouch (both ExperiCo), Tara Southey (TerraClim), Garth Stevens [Centre for Geographical Analysis (CGA), Stellenbosch University (SU) ], and Dr Mariana Jooste (Hortgro).
• Stakeholders: Hortgro and Pink Lady® SA
• Technical assistance: ExperiCo Agri Research Solutions, G. Lötze (Horticultural Science, SU), DuToit Agri Maturity Indexing Lab, Koukamma Fruit Packers (Joubertina, Eastern Cape), Langkloof Fruit Solutions (Misgund, Eastern Cape).
• Statistical assistance: Marieta Van der Rijst (ARC, Infruitec), Martin Kidd (SU), Adriaan Van Niekerk (CGA, SU), and Caley Higgs and Michaela Nortjé (TerraClim).
• Growers: Farm owners and managers
• Participating students: Ineke de Jong, Daniela Ramos, Heleen Tayler.

References

• Butler, L, 2015. “Internal flesh browning of ‘Cripps Pink’ apple (Malus domestica Borkh.) as influenced by pre-harvest factors and the evaluation of near infrared reflectance spectroscopy as a non-destructive method for detecting browning.” (Master of Science). Stellenbosch University.
• Crouch, E.M., Jooste, M., Majoni, T.J., Crouch, I.J., Bergman, H, 2015. “Harvest maturity and storage duration influencing flesh browning in South African ‘Cripps Pink’ apples.” Acta Hortic. 1079: 121-127.
• de Castro, E., Barrett, D., Jobling, J., Mitcham, E., 2008. Biochemical factors associated with a CO₂-induced flesh browning disorder of Pink Lady apples 48, 182-191.
• De Jong, I, 2023. “‘Cripps Pink’ fruit quality affected by pre-harvest temperature, orchard factors, canopy position and long-term DCA-CF storage.” (Master of Science). Stellenbosch University.
• James, H.J. (2007). “Understanding the flesh browning disorder of ‘Cripps Pink’ apples”. (Doctor of Philosophy). The University of Sydney.
• Jobling, J., James, H.J., 2008. “Managing the flesh browning disorder of ‘Cripps Pink’ apples. A summary of Australian research investigating the causes and management of the problem.”
• Majoni, T.J., Jooste, M., Crouch, E.M, 2013. “The effect of 1-MCP and storage duration on the storage potential and flesh browning development on ‘Cripps Pink’ apples stored under controlled atmosphere conditions.” Acta Hortic. 1007: 49-56.
• Ramos, D., 2026. “Internal browning and other defects of ‘Cripps Pink’ apples – the effect of growing region temperature, canopy position and dynamic controlled atmosphere – chlorophyll fluorescence on fruit quality after long-term storage.” (Master of Science). Stellenbosch Universiy.
• Store-it Group, 2022. “Best-practice guidelines for ‘Cripps’ Pink.”