Why are polysaccharides non-reducing sugars?
For polysaccharides made with only glucose (starch, cellulose, glycogen, etc), only 1 unit can be reduced from hundreds, thousands or tens of thousands of units. With the same mass of dextrose and starch, the amount reduced for starch is 1/100, 1/1000 or 1/10000 the amount for dextrose. This is usually below the detection limit for most ways of detecting the reaction.