**4.2 Hydrazide method of p-hydroxy-benzoic acid (Blakeney & Mutton, 1980)**

This method is based on determination of reducing sugar before and after the digestion by invertase using acid for p-hydroxy benzoic acid hydrazide – PAHBAH. In this method, with some modifications, there is possible to perform the colorimetric determination of glucose, fructose and sucrose, during this analysis procedure with invertase. The major subject of the methodology described in this chapter is for determination of reducing sugar. The phydroxy benzoic acid hydrazide also has the advantage that glucose and fructose when reacting produce the same intensity of colour, and then all free monossacharides present in the sample can be determined.
