Food and Nutrition in
Humans
Food Test and Storage
Food Test theory

Heat is required ONLY for Benedict’s test for
reducing and non-reducing sugars

Reducing sugars are so called because they
reduce blue copper sulphate (CuSO4) in
Benedict’s solution to a reddish precipitate
Food Test theory cont’d

Simple sugars are reducing sugars

Some complex sugars are also reducing
sugars e.g. maltose

Sucrose, a complex sugar is a non-reducing
sugar
Food Test theory cont’d

There is no direct test for non-reducing sugars

A non-reducing sugar can be broken down to simple sugars by
heating it with a dilute acid like HCl (hydrolysis)

The resulting mixture is acidic and must first be neutralized by
adding a small amount of alkali like NaHCO3

The test for reducing sugar can then be carried out

The red precipitate obtained confirms that a non-reducing sugar
was originally present
Table summarizing the method and results of food tests
FOOD
SUBSTANCES
METHOD
OBSERVATIONS FOR
POSITIVE RESULTS
Starch
Add 2-3 drops of iodine
Blue-black
Reducing sugar
Add Benedict’s solution and heat
Blue-green, yellow, orange red
precipitate
Non-reducing
sugar
i)
ii)
iii)
Add Benedict’s solution and heat to boiling
Add (to fresh solution) dilute hydrochloric
acid and heat. Add solid sodium hydrogen
carbonate until fizzing stops.
Add Benedict’s solution and heat
I.
II.
Remains blue
Blue-green, yellow,
orange red precipitate
Protein
Add sodium hydroxide solution. Add 3-4 drops 1%
copper sulphate solution
Purple or violet
Fat or Oil
Test 1. Rub or place a drop on absorbent paper
Test 2.
i)
Add alcohol and shake
ii)
Pour clean liquid into water
Grease spot (translucent)
White emulsion
Complete the following table to indicate where and in
what forms the named organisms store food
ORGANISMS
FOOD STORED
SITE OF STORAGE
(i)
(ii)
(i)
(ii)
Sugar cane
Irish potato
Onion
Mango
Man
Complete the blank spaces in the following tale which
shows the method and positive results of selected
food tests
PROCEDURE
RESULT
CONCLUSION
Protein Present
Add Benedict’s
solution and heat
Blue-black colour
Essay Type



(a) State clearly how you would test a sample of
flour for
(b) Include the apparatus and materials you would
use
(c) Describe the procedure and the results expected
if positive




Starch
Reducing Sugar
Protein
Fat
TYPE OF
STORAGE ORGAN
STORAGE AREA
EXAMPLE
TYPE OF FOOD
STORED
Root tubers
Root
Cassava, sweet
potato
Starch, small
amount of protein
Tap roots
Root
Beetroot, carrot
Sucrose glucose
Stem tubers
Stem
Yam, Irish potato
Starch, small
amount of protein
Rhizome
Stem
Ginger
Starch, oils
Corm
Stem
Dasheen
Starch
Bulb
Leaves
onion
glucose
FOOD RESERVES AND SITES OF
STORAGE IN SOME COMMON SEEDS
STORAGE AREA
PLANT EXAMPLE
COTYLEDON(S) Peas and Beans
Nuts
Sunflower Seeds
Cocoa
ENDOSPERM
Corn, Rice
Coconut
Castor Oil
TYPE OF FOOD
STORED
Protein, Starch
Protein, Oil
Protein, Oil
Fat
Starch, Protein
Oil
Oil, Protein