Determination of total reducing sugars (TRS)
The DNS (3.5-dinitrosalicylic acid) method developed by Miller
(1959) was used to determine TRS. This determination was
preceded by acid hydrolysis to invert sucrose. A 2-ml aliquot of the
sample was transferred to a 25-ml flask, and 2 ml of hydrochloric
acid (2 molL-1) were added. The flask was heated in water bath at
70°C for 30 min and cooled. The contents were neutralized with 2
ml of 2 molL-1 sodium hydroxide. The sample was transferred to a
100-ml volumetric flask, and the volume was completed with
distilled water. When necessary, samples were further diluted to
obtain concentrations within the linearity range of the calibration
curve.