Why does black and white pepper and dehydrated canned onions cause me to have painful gas but i can eat cayenne pepper or chili powder with no disc.

Everyone different: Intolerance to seasoning varies a good deal from person to person as well as in SAME person over time. Although Cayenne and chili powder are strong seasonings they are in fact less IRRITATING to the stomach than white and black pepper..

Food "allergies": Some edible foods or seasonings may produce symptoms such as you describe, but are not "true" allergies. There is no way to "predict" which of these will produce these symptoms, so just avoid the black and white pepper and canned onions, or see a gastroenterologist to determine possible reasons.

Don't know: I do not know the answer to that question but perhaps if you take "BEANO" before you eat it will help.