What you see: Brown and black streaks or dots in avocado flesh
What it is: Vascular browning! Mmmm!
Eat or toss? The avocado is edible, but may not taste as good. If the spots are relatively mild (and brown, rather than black), give it a taste test.
The inside of an avocado is a busy place, where nutrients, water and sugars are ferried around. Normally their “transport channels” are invisible to us. Unless, of course, something goes wrong.
In the case pictured above, the avocado's internal thoroughfares may have been ravaged by too-cold storage for too long. The cells that make up the “vascular tissue” weakened and started dying, turning brown and highlighting the avocado highways as lines when the avocado is cut along its long axis, and little dots when it’s cut through its fat middle. (The image below is a long axis cut through the same avocado as the one at the top of this post.)
Elhadi M. Yahia, a professor at the Autonomous University of Querétaro in Mexico who has studied avocado handling after harvest, said a few weeks of refrigeration, likely before you even purchased your avocado, could lead to such vascular browning. The disorder typically becomes visually apparent after the fruit has ripened at room temperature for a couple days.
“I have absolutely no problem eating them,” he said of the little brown dots, with the caveat that palatability will depend on severity. The issue worsens—and creates icky flavor changes—with time. Eventually you’ll find blackened tissue and rancid flavors as the avocado’s fats and enzymes react with oxygen in not-so-tasty ways.
When cold temperatures cause vascular browning, the issue starts in the center of the fruit, Yahia said. While vascular browning doesn't necessarily indicate an infection, when cells weaken and die, they also become more vulnerable to pathogens. It’s also possible for funguses to enter the fruit from the vulnerable spot where the stem attaches and travel along the vascular tissue in something called “stem-end rot.”
But Yahia said that the funguses that tend to attack avocados are not known to be harmful to humans and he was not aware of any food safety outbreaks connected to vascular browning.
Elhadi M. Yahia. Food Science & Post-harvest Handling Professor. Autonomous University of Querétaro, Mexico. Leader of the Phytochemicals and Nutrition Laboratory.
Avocado: Recommendations for Maintaining Post-Harvest Quality. Adel A. Kader and Mary Lu Arpaia. University of California.
The Avocado: Botany, Production, and Uses. Edited by A. W. Whiley, B. Schaffer, B. N. Wolstenholme. 2002. P. 368.
Hot Water Drenching of ‘Hass’ Avocados for Rot Control. MSc Thesis by Emma Terander. Horticulture Program. Institute for Plant Science. Alnarp Sweden.
Avocado Post-harvest Operations - Post-harvest Compendium. Food and Agriculture Organization of the United Nations.
Maturity effects on avocado postharvest physiology in fruits produced under cool environmental conditions. J. G. M. Cutting and B. N. Wolstenholme. Department of Horticultural Science, University of Natal.South Africa. South African Avocado Growers’ Association Yearbook 1991.
G. Hopkirk , A. White , D. J. Beever & S. K. Forbes (1994) Influence of postharvest temperatures and the rate of fruit ripening on internal postharvest rots and disorders of New Zealand ‘Hass’ avocado fruit, New Zealand Journal of Crop and Horticultural Science, 22:3.
Plant Development I: Tissue differentiation and function. Biology 1520. Georgia Tech Biological Sciences