Bacteria thrive at temperatures over 40°F but under 135°F. Bacteria cause foodborne illness by releasing toxins. Cooling by refrigeration slows down bacterial growth, but it does not stop it or destroy toxins already produced. Foods left at room temperature for 2 hours, or even 1 hour in hot weather, provide microorganisms with the opportunity to grow. Refrigeration after that time is too late. Diana is correct in wanting to discard the food.
Viruses, bacteria, and other microorganisms in foods cause more than 96% of all food-related illness. Only a small minority of people are susceptible to the health effects of food additives, such as sulfites. The USDA states that most foodborne illnesses arise from poor food-handling practices by consumers. Thus, Joseph’s roommate is at more risk from how he stores and prepares food than from the food additives in the snack cakes he eats on occasion.
