Notes on the Relationship of Internal Browning and Titratrable Acidity in Fuji Apples
To test the concept that Fuji apples with lower acidity are more susceptible to Internal Browning than those with high acidity.
Materials and Methods
A commercial packer of Fuji apples stored the fruit in CA from harvest to mid-March 1999. He reported that the room was loaded with fruit from 9 orchards over several days. Harvest ran from October 26 to November 3, 1998. Set point CA atmosphere was established 3 days after the room was sealed on Novermber 5. Air temperature was held at 34 ºF. Oxygen was held at 2.4 to 2.5% and carbon dioxide held below 1.0% until December 25, 1998, following which time it slowly rose to 1.5% by March 1, 1999 when the room was opened.
When the room was opened, some fruit had watercore, some had internal browning and others had developed internal cavities. To determine the relationship between postharvest maladies and acidity the fruit were separated by orchard and harvest date, then tested for firmness. Then the fruit were further segregated by whether they had internal browning, cavities or watercore and tested for soluble solids and acidity.
Statistical analysis of the data revealed that post-storage internal browning was positively related to the amount of watercore after storage, and negatively related to the level of acidity. In other words, fruit with internal browning were characterized as having higher watercore, lower firmness and lower acidity than those not affected. Fruit with internal cavities had lower soluble solids. High acid fruit were firmer and had higher soluble solids than those lower in acidity. It is not at all clear why some fruit with watercore develop internal browning while others do not.
In summary it appears from these samples that those fruit that were less mature had less internal browning and less watercore. Maturity leads to lower acidity, less soluble solids, lower firmness, more potential for internal browning and cavities.
Dr. Eugene Kupferman, Postharvest Specialist
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801