This is known as White Core. White Core is a physiological disorder usually the result of high heat.
What is happening the high heat is preventing the formation of lycopenes (the red color).When the weather cools down the new tomatoes are usually better.
Sometimes this is the result of either too much fertilizer, especially high nitrogen liquid fertilizer or stress on the plant.
Tomatoes that are more juicy or heirlooms tend to be more susceptible to white core.