Testing for Non-Reducing Sugars (Modified Benedict's Test):

If no colour change occurs in the initial test (solution remains blue), the sugar in the sample may be non-reducing. In this case, the test must be modified:

1. Add 2 cm³ of the food sample to 2 cm³ of dilute hydrochloric acid.
2. Heat the mixture in a water bath for 5 minutes. The acid will hydrolyse disaccharides and polysaccharides into their constituent monosaccharides (e.g., glucose and fructose).
3. After heating, carefully add sodium hydrogencarbonate to the solution to neutralise it, checking with pH paper to ensure the solution is no longer acidic.
4. Add 2 cm³ of Benedict's reagent to the neutralised solution and place it in the water bath for another 5 minutes.
5. If a non-reducing sugar is present (like sucrose), the solution will now turn from blue to brick red. The depth of the red colour indicates the concentration of glucose or other reducing sugars in the sample. A more intense red colour signifies a higher glucose concentration.

Estimating Glucose Concentration:

To quantify the glucose concentration, you can compare the test results to a glucose standard curve. This involves preparing solutions of known glucose concentrations and performing the Benedict's test on each. The resulting colour intensities are then measured using a colourimeter and plotted on a graph, allowing you to estimate the concentration of glucose in unknown samples by comparing their colour intensity to the standard curve.