FOOD TESTS [CSEC BIOLOGY & HSB]

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SYLLABUS REFERENCE 

HSB

[B1.5] perform tests to distinguish among food nutrients; 

CSEC BIOLOGY

[B2.6] perform tests to distinguish among food substances; 

STARCH TEST - IODINE TEST 

IODINE TEST PROCEDURE 


If starch is present the iodine solution changes colour from yellow-brown to blue-black. 

IODINE TEST - POSITIVE & NEGATIVE RESULTS 


SIMPLE, REDUCING SUGARS - BENEDICT'S TEST 

BENEDICT'S TEST PROCEDURE FOR SIMPLE, REDUCING SUGARS 


If simple sugars are present, the Benedict's solution in the reaction mixture will undergo a colour change. 

Depending on the concentration of sugar in the sample, the colour change will differ. 

Green (lowest) < Yellow < Orange < Brick red (highest) 


Benedict's solution changes colour due to a reduction reaction. (A reduction reaction involves the removal of oxygen atoms from a chemical compound.)  

As a result, the sugars that produce this result are called REDUCING SUGARS. 




COMPLEX, NON-REDUCING SUGARS - MODIFIED BENEDICT'S TEST 

MODIFIED BENEDICT'S TEST PROCEDURE 


The boiling with acid hydrolysed the complex sugar, which broke it down to its simple sugar components. 

Once sugar is present, one gets the same result as for simple sugars, with the same range of colours according to concentration. 


PROTEIN - BIURET TEST 

BIURET TEST PROCEDURE 


If soluble proteins are present in the food sample, the reaction mixture will change colour from blue to pink-violet. 

POSITIVE VS NEGATIVE RESULTS FOR BIURET TEST 


IDEAL POSITIVE RESULT FOR BIURET TEST
 

LIPIDS - GREASE-SPOT OR EMULSION TEST 



If lipids are present, the following occurs:

  • Grease spot: a translucent spot on the paper remains after being left to dry 
  • Emulsion test: the reaction mixture forms a cloudy emulsion after mixing. 





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