Keeping it Cool: Cold Storage Recommendations for Apples and Peaches

Keeping it Cool: Cold Storage Recommendations for Apples and Peaches

Why do we need cold storage? Fruits such as apples and peaches are highly perishable and thus have a limited market life potential. Cold storage is an efficient way to maintain fruit quality, mitigate losses and maximize harvest potential. At ambient temperatures, fruit quality characteristics are rapidly changing, decreasing storability. Specifically, long-term ambient storage conditions lead to changes in color, texture, flavor (soluble solids, acidity, aroma), and nutritional value. Therefore, cold storage is a key solution to slow down these changes and thus maintain quality for longer periods of time.

Incorporation of cold storage into management practices also expands the market opportunities by extending the shelf life of fruit. With cold storage, local, regional, and even international export is feasible. Additionally, fruit can be sold year-round, regardless of the growing season. Both of these advantages signal increased profitability for the industry. Fruit appearance heavily influences purchasing decisions. Cold storage ensures that the appearance—a presumed indicator of freshness, crispness, and sweetness—is maintained.

Cold Storage Recommendations for Apples

Specific storage conditions and practices not only ensure the quality of fruit but also limit cold-related injury or damage. Mature apples can typically be stored at 32-39°F, depending on the cultivar, for 6 months, but this can be extended to 12 months with close monitoring. If the apples are partially ripe, they can be kept in cold storage for 2-3 months, while fully ripened apples are limited to less than a month in cold storage. However, certain cultivars are chilling sensitive, meaning that they are damaged by exposure to low non-freezing temperatures for a certain amount of time. Chilling sensitivity may occur in Honeycrisp, Granny Smith, Gala, Fuji, Red Delicious, and Cortland apples and can be characterized by disorders such as soft scald (Figure 1), soggy breakdown (Figure 2), and lenticel breakdown among others. Recommended storage temperatures for apples with or without chilling sensitivity can be observed in Table 1.

Delayed cooling or conditioning is the practice of temporarily exposing fruit to 50°F or 68°F for up to 7-10 days before cold storage. This practice is found to be helpful for the chilling sensitive cultivar Honeycrisp, as it decreases fruit susceptibility to chilling injury. There are reports indicating that a 7-day preconditioning period at 50°F dramatically reduced soft scald and soggy breakdown in Honeycrisp apples to be less than 1%, compared to control fruits. However, conditioning treatments have been frequently reported to exacerbate the incidence of bitter pit, another physiological disorder, induced in preharvest due to a nutritional imbalance, that results in small brown flesh lesions and also renders the fruit unmarketable. Bitter pit (Figure 3) is especially common in Honeycrisp apples, and is exacerbated by preconditioning treatments.

Cold Storage Recommendations for Peaches

For peaches, on the other hand, storage life is much shorter than apples, thus they are much more vulnerable to spoilage. Peaches are ideally kept at 32°F, but a range of 29-34°F is acceptable, as shown in Table 2. However, if peaches are continuously stored in cold conditions of 36- 46°F for more than 2 weeks, the physiological disorder of chilling injury becomes a concern. Chilling injury is a physiological disorder caused by prolonged exposure to these temperatures of 36-46°F, but only appears after the ripening process continues at room temperature. It may manifest in peaches via symptoms such as flavor loss, flesh browning, flesh bleeding, flesh mealiness, leatheriness (Figure 4). Flesh bleeding is characterized by an accumulation of red pigments in the flesh, mostly around the peach pit. Mealiness occurs when peach flesh lacks juice, and can often lead to flesh browning. Leatheriness refers to patches in peach flesh that fail to ripen, therefore remaining dry and firm. As chilling injury is only expressed at room temperatures, all of these symptoms are apparent when the peaches reach customers, reducing marketability.

Preventative measures such as postharvest preconditioning and postharvest intermittent warming help avoid chilling injury symptoms. Postharvest preconditioning can be employed by storing peach at 68°F for 1 to 2 days after packing, but prior to cold storage at 32°F. Packing the fruit at cold temperature prevents additional damage, while the warming period allows gentle ripening to prevent chilling injury. Postharvest intermittent warming involves immediate storage at 32°F, with one day of storage at 68°F every 10 to 14 days. This technique ensures gradual ripening throughout the cold storage period.

Additional Storage Considerations

Other factors to consider in postharvest cold storage, in addition to temperature management, include humidity, air circulation, sanitation, and gas content. Controlling storage humidity helps prevent dehydration in peaches and apples, which is a common symptom of chilling sensitivity and injury as well. Ideal storage humidity conditions are 90- 95%. Proper air circulation is essential to maintain a uniform temperature, humidity, and gas content in all areas of the storage room. This can best be achieved by spacing out storage containers to allow for air movement between them, together with appropriate sanitation practices. For apples, low oxygen concentration (1-3%) is essential to prevent fruit respiration. Carbon dioxide levels should also be monitored and kept at least at 3% to prevent undesirable skin and flesh browning in apples.

References

1. Farcuh, M & Moore, K. 2020. What is Chilling Injury in Peaches, What Causes It, and How can you Manage it?; University of Maryland Extension. Link: https://extension.umd.edu/sites/default/files/publications/What%20is%20Chilling%20Injury%20in%20Peaches%20%28Draft%29.pdf
    
2. Lurie, S., & Crisosto, C. 2005. Chilling Injury in Peach and Nextarine. Postharvest Biology and Technology, 37(3), 195-208.
    
3. Moran, R.E., DeEll, J.R., & Murr, D.P. 2010. Effects of Preconditioning and Fruit Maturity on the Ocurrence of Soft Scald and Soggy Breakdown in ‘Honeycrisp’ Apples. HortScience, 45(11), 1719-1722.
    
4. Watkins, C.B., Nock, J.F., Weis, S.A., Jayanty, S., Beaudry, R.M. 2004. Storage Temperature, diphenylamine, and pre-storage delay effects on soft scald, soggy breakdown and bitter pit of ‘Honeycrisp’ apples. Postharvest Biology and Technology, 32(2), 213-221.
    
5. https://extension.umaine.edu/fruit/harvest-and-storage-of-treefruits/ cold-storage-conditions

This article appears on June 10, 2021, Volume 12, Issue 3 of the Vegetable and Fruit News