What would cause a whitish ring inside tomatoes? The outside is nice and red, plants appear to be healthy. These are grown in a greenhouse.
There are several possible causes for a white ring inside tomatoes. It can be caused by high temperatures or a potassium deficiency at the time the tomato is ripening, or a combination of the two. Potassium deficiency manifests itself as orange shoulders at the top of the tomato, as well as white rings, or white fleshy areas inside the tomato. Sufficient potassium is important for all stages of growth of tomatoes, including fruit development. The latter because potassium is important for pigment synthesis and the sugar levels. Research examining potassium levels in the soil as well as in the foliar tissue of tomato plants has shown that while potassium levels may be appropriate in soil in which tomatoes are growing, there can nonetheless be a deficiency of potassium in the plant itself. I suggest testing the soil to determine if there is a potassium deficiency. If so, apply high potassium fertilizer before the growing season. A high potassium spray could also be applied during the season if there are indications of potassium deficiency. Such indications include brown leaf edges; yellowing along the veins in leaves and stunted plant growth.
Tomatoes with potassium deficiency are safe to eat – simply cut away the white growth – which is likely be unpalatable.
Here is a link to research paper from the University of Maryland Extension on potassium deficiency in tomatoes which you might find interesting: https://extension.umd.edu/sites/extension.umd.edu/files/_docs/articles/TomatoRipeningProblemsRoleOfPotassium.pdf