Many people think that the fresher tomatoes are, the better they taste and the more nutritious they are. Blue tomatoes should be fresher. However, this is not the case. Tests show that immature green tomatoes contain solanine, a toxic substance, which also exists in blue germinated potatoes. Green tomato tastes bitter, and may have poisoning symptoms such as nausea, dizziness and vomiting after eating. It may be life-threatening in severe cases. So it's best to choose ripe tomatoes and cook them by heating.