The yellowing of white tomato powder may be caused by some chemical reactions or storage conditions. Tomato powder is usually made from fresh tomatoes, which contains a natural pigment called carotenoid, which will change under certain conditions. Here are some possible reasons why white tomato powder turns yellow:

1. Oxygen exposure: Carotenoids are sensitive to oxygen. When tomato powder comes into contact with air, carotenoids in it may be oxidized and turn yellow.

2. Illumination: Exposure of tomato powder to sunlight or strong light may also cause carotenoids to oxidize and turn yellow.

3. Humid or high-temperature environment: When storing tomato powder, high-temperature and humid conditions may also accelerate the oxidation reaction of carotenoids and make them discolor.

To prevent tomato powder from turning yellow, the following measures can be taken:

-Store in a dry and cool place, away from direct sunlight.

-Try to reduce the contact between tomato powder and air, store it in a sealed container, and add food-grade moisture absorbent or oxygen absorber to reduce the oxygen concentration.

-Pay attention to the shelf life of tomato powder and avoid using expired products.

Although the yellowing of tomato powder may change its appearance, it usually has no obvious effect on its safety or taste. If the discoloration is due to the storage conditions rather than the quality of the product itself, it can still be safely eaten. If you are uneasy about the discoloration of tomato powder, you'd better consult the customer service of the manufacturer or brand for more information.