Analysis of macro nutrients

1. Analysis of Macro and
Micro Nutrients in
Foods

2. FOOD
Proximate Analysis:

3. It is important for a number of different
reasons:
 Legal and Labeling Requirements
 Microbial Stability
 Food Quality
 Food Processing Operations.

4.  Moisture content of a food material is defined
through the following equation:
 % Moisture = (mw/msample)* 100
 Where mw - mass of water;
 msample - mass of sample

6. 1. Drying Methods
◦ Oven drying methods
2. Distillation method
◦ Dean and Stark Method
3. Chemical Methods
◦ Karl Fisher
◦ Gas production
4. Physical Methods

7. Principle:
 Measuring the mass of water in a known mass
of sample.
 Measuring the mass of a food before and after
water is removed by evaporation
 % moisture = (Minitial – Mdried) × 100
Minitial

8.  MINITIAL and MDRIED are mass of the sample before
and after drying, respectively.
 Basic principle of this technique is that water has a
lower boiling point than other major components
within foods
e.g., lipids, proteins, carbohydrates and minerals.

9.  Total solids, is reported as a measure of the
moisture content.
 It is the amount of material remaining after all
water has been evaporated
 % Total Solids = (Mdried) × 100
(Minitial)
 Thus, %Total solids = (100 - %Moisture)

10. You have the following gravimetric results:
 weight of dried pan and glass disc = 1.04 g,
 weight of pan and liquid sample = 4.63 g,
 weight of the pan and dried sample =1.73 g.
 Calculate the percent moisture and the percent solids
of the sample.

11.  % moisture = (4.63-1.04) – (1.73-1.04) x 100
(4.63 - 1.04)
= 3.59 – 0.69 x 100
3.59
= 80.78 %
 % solids = 0.69 x 100 or (100 – 80.78)
3.59
= 19.22 %

12.  Weighed samples are placed in an oven for a specified
time and temperature and they are dried until they reach
constant mass.
◦ 1. Convection ovens.
◦ Disadv: Greatest temperature variations - because hot air
slowly circulated with out the aid of fan, air movement is
obstructed further by pans placed in the oven

13.  Samples with high carbohydrates or volatile
materials should not be dried in a
convection or forced draft oven.
2. Forced Draft Oven
 The least temperature difference across interior (< 1oC).
 Air is circulated by a fan that forces air movement
throughout the oven cavity

14. 3. Vacuum oven.
 Weighed samples are placed under reduced pressure (25 –
100 mm Hg) in a vacuum oven for a specified time and
temperature and their dried mass is determined.
 Boiling point of water is reduced when placed under vacuum.
 A number of advantages over conventional oven drying
techniques.
i. If sample is heated at same temperature, drying can be
carried out much quicker.
ii. Alternatively, lower temperatures can be used to remove
the moisture (e.g. 70oC instead of 100 oC),
iii. Degradation of heat labile substances can be reduced.

15. 1. Sample dimensions.
Greater the surface area (fine particles), faster
the rate of moisture removal.

16. 2. Clumping and surface crust formation.
 Some samples form clumps / a semi-
permeable surface crust during drying.
 Loss of moisture is restricted by clumps or
crust.
 To avoid, samples are mixed with dried sand.

17. 3. Water type.
 Easy removal of water depends on its
interaction with other components present.
 Free water is most easily removed.
 More severe conditions required to evaporate
chemically or physically bound water.

18. 4. Decomposition of other food components.
 Decomposition of heat-sensitive components.
 Eg. Decomposition of carbohydrates
C6H12O6 6C + 6H2O
 Water released by this reaction lead to an overestimation
of true moisture content.
 Many chemical reactions occur at elevated temperatures
lead to water absorption. e.g., sucrose hydrolysis
 (sucrose + H2O fructose + glucose)
 lead to an underestimation of true moisture content.

19. 5. Volatilization of other food components.
 For foods that have significant amounts of volatile
components (e.g. spices and herbs) must use
alternative methods e.g., distillation, chemical or
physical methods.

20. 1. Organic compounds:
◦ Carbohydrates
◦ Lipids
◦ Proteins
◦ Nucleic acids
◦ Vitamins
◦ Organic acids
2. Inorganic Compounds:
- Minerals
“Ash content” - total amount of minerals present
within a food.

21.  Ash - inorganic residue remaining after water and
organic matter removed by heating in the presence
of oxidizing agents.
 Principle: Minerals are not destroyed by heating,
and they have low volatility compared to other
food components.

22.  Main types Ashing: dry ashing, wet ashing, plasma
ashing
 Method chosen depends on the reason for carrying
out analysis, type of food analyzed and equipment
available

23.  Representative sample.
Typically, samples of 1-10g are used.
Solid foods are finely ground and carefully mixed
(representative sample).

24.  Before ash analysis, samples high in moisture are
dried to prevent spattering.
 High fat samples are defatted by solvent extraction
 Avoid contamination of samples by minerals in
grinders, glassware or crucibles etc.

25.  Use a high temperature muffle furnace (To between 500
and 600oC).
 Water and other volatile materials are vaporized and
organic substances are burned in the presence of O2 in
air to CO2, H2O and N2.
 Most minerals are converted to oxides, sulfates,
phosphates, chlorides or silicates.

26.  Some minerals are volatile and may be partially lost,
e.g., iron, lead and mercury.
 For such minerals - use an alternative ashing method
that uses lower temperatures.

27.  Food sample is weighed before and after ashing to
determine the concentration of ash present.
 The ash content can be expressed on either a dry or
wet basis:

28.  The following data was obtained on a sample of hamburger:
sample wt, 2.034 g ; wt after drying, 1.0781 g; and wt of ash,
0.0233 g.
What is the percentage ash on a) a wet weight basis and b)
dry-weight basis?
Wet Basis Ash % = (0.0233 / 2.034) *100
= 1.15 %
Dry Basis Ash % = (0.0233 / 1.0781) * 100
= 2.16 %

29.  Different types of crucible - quartz, Pyrex,
porcelain, steel and platinum.
 Selection depends on sample being analyzed and
furnace temperature used.
 Most widely used - porcelain (relatively
inexpensive, resistant to high temperatures
(< 1200oC) and easy to clean).

30. Platinum
Pyrex
Porcelain
Quartz

31.  Advantages: Safe, few reagents are required, many
samples can be analyzed simultaneously, not labor
intensive, and ash can be analyzed for specific
mineral content.
 Disadvantages: Long time required (12-24 hours),
muffle furnaces are quite costly to run due to
electrical costs, loss of volatile minerals at high
temperatures, e.g., Cu, Fe, Pb, Hg, Ni, Zn.

32. Topic: Analysis of crude fat content (by Soxhlet
extraction method) and crude protein content (by
Kjeldhal method) of foods.
 Sample preparation techniques
 Equipment and method
 Calculation
 Advantages and disadvantages of technique
 Reference: Chapter 18, Nielsen, S.S. (Ed.) Food Analysis
– Food Science Texts Series (4th ed.) Springer 2003