On eating powdered glucose I felt a cold sensation in my mouth. Then I thought it would be a result of the reaction between saliva and glucose. Then I thought that this would imply that the reaction would be endothermic. I don't find myself to be pretty sure and need to know whether I am right or not. Why would the reaction be endothermic in spite of the fact that glucose is readily soluble in saliva?
The dissolution of glucose in an aqueous solution is an endothermic process. As stated in a comment, a reaction need not be exothermic to be spontaneous. Don't forget about the entropy term.
Simply put, the glucose dissolved endothermically in your saliva causing a heat transfer from your mouth to the glucose/saliva solution, resulting in a slight decrease in the temperature of your mouth, making it cooler than it was prior do dissolving the glucose.