Ptyalin (salivary amylase), maltase, lactase, and sucrase are all digestive enzymes. Salivary amylase acts on starch and gives only one by-product i.e. maltose. The enzymes maltase, lactase and sucrase act on maltose, lactose and sucrose respectively. Maltose, lactose and sucrose are broken up by these enzymes to produce two molecules of glucose, one molecule of glucose and one molecule of galactose, one molecule of glucose and one molecule of fructose respectively.

Hence, all enzymes except salivary amylase give two by-products by acting on their substrate and acts on disaccharides. Thus, it is an odd one.