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Food Tests

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Introduction

FOOD TESTS Test for proteins Millon's test - 2cm3 of sample were added to 1cm3 of Millon's reagent, the mixture was then heated. If the test is positive for protein, the following test was performed to confirm the result. Biuret test - 2cm3of 5% potassium hydroxide solution were added to 2cm3 of sample. Two drops of 1% copper sulfate solution were added and the mixture was shaken. Test for reducing sugars Benedict's test - 2cm3 of the sample were added to an equal volume of Benedict's solution. The mixture was then heated in a water bath while shaking continuously. If the test is positive for reducing sugars, the following test was performed to confirm the result. Fehling's test - 2cm3 of sample were added to 1cm3 Fehling's A and 1cm3 Fehling's B solution. The mixture was then heated in a water bath. ...read more.

Middle

The mixture was then shaken and an equal volume of cold water was added. Test for Vitamin C (ascorbic acid) A few drops of DCPIP were added to 2cm3 of the sample. Test for cellulose A few drops of Schultz's stain were added to the sample. There are two tests which confirm the presence of proteins: Millon's test - Millon's reagent contains mercury acidified with nitric acid. The amino acid tyrosine contains a phenol group which reacts to give a red mercury complex on boiling. Biuret Test - Biuret reagent is a light blue solution which contains dilute copper sulfate in alkaline conditions. Nitrogen atoms present in the peptide chain, form a purple complex with copper (II) ions. The two tests which confirm the presence of reducing sugars are Benedict's test and Fehling's test. The chemical principal behind these two tests is the same. ...read more.

Conclusion

There are two tests which confirm the presence of lipids: Sudan III - Lipids are stained red and since they are less dense than water, it forms a layer on the surface of the water. Emulsion test - If lipids are present, a cloudy white suspension will form. This is because any lipid present dissolves first in the ethanol, then when the water is added (in which lipid is insoluble), the lipid / ethanol mixture disperses in the water to produce a cloudy white emulsion. Test for Vitamin C (ascorbic acid) involves the addition of a few drops of DCPIP solution to the sample. DCPIP solution which is blue in colour will become colourless in the presence of ascorbic acid. This happens because DCPIP solution is reduced by ascorbic acid which is a strong reducing agent. When a few drops of Schultz's reagent are added to the sample and a purple blue stain is obtained, cellulose is present. This happens because Schultz's reagent dyes the cellulose. ?? ?? ?? ?? ...read more.

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