Mathew, it sounds to me that you have already made up your mind what the cause is, and that you’re not really interested in the truth. If the saliva was the cause of you becoming hungry, half a glass of water would make you ravenous. The saliva that goes into the stomach will do sweet blue all. It’s just water, enzymes and bacteria. The stomach might start secreting digestive juices in anticipation of food that might be coming and this can be interpreted as hunger. It should go away after a couple of minutes if nothing happens.
The only other explanation I can give you is that it’s all in the mind because you can’t keep on fooling your body for long. After a few days of chewing gum it will adapt and know that chewing gum is not followed by food and you should not become hungry. Maybe in your case it doesn’t work like that, but it’s not the case in the general population. Good luck.