In this assignment, food analysis involves involve several procedures that have been used to identify the various methods with which the fats, salts, ash and moisture in food are subjected to different conditions to produce results. Several methods have been used with a combination of different solutions that have been able to produce different results. Therefore, this report would include several methods that were applied on fats, salts, ash as well as moisture in food. For instance, soxhlet method would be used in the determination of fat content in foods, Mohr method was used to determine the amount of salt in food, Oven method used in determining the amount of moisture in food and finally determining the amount of ash in the food.
Determination of fat content by soxhlet extractor
The fat content of the food is usually determined by solvent extraction method referred to as soxhlet extractor. For efficient extraction to take place, it is recommended that one should have a dry and finely ground homogenous sample. The amount of fat would in turn depend on the solvent chosen, composition of the food as well as the length of the extraction process. Hot petroleum is used as a solvent in this case as the fat will be extracted from the dried samples in soxhlet apparatus.
The procedures for the determination of fat content would involve the following steps:
- Weigh the evaporating dish
- Add 10g of the sample, weigh and note the accurate weight.
- The dish should be labeled and placed in oven at 1100 C until it dries.
- Place the thimble in the extraction chamber and rinse out the dish with ether and pour the washings into the thimble.
- Pour carefully the ether into the extraction chamber till it is just below the syphon level.
- Weigh a dry and clean 500cm3 round bottomed flask and place it to the bottom of the extraction chamber.
- Fill the chamber with ether until it syphons over twice.
- Set up the apparatus in a fume chamber and confirm that the water supply in the condenser is switched on.
- Switch on the heating mantle and then reflux the ether for a minimum of 2 hours.
- Switch off the heating mantle and let the apparatus cool down.
- Set up the apparatus in the fume chamber. This step involves the removal of the main bulk of the ether.
- Close the tap to prevent the condensing ether returning to flask and continue heating till as small amount of fat remains in the flask.
- Switch off the heating mantle and let the apparatus cool.
- When the apparatus have cooled down, dismantle and place the flask on boiling water bath in the fume cupboard. This will reduce the amounts of ether.
- Place the flasks in the oven at 110o C for about 10 minutes.
- Cool the flask in the desiccator and then weigh.
- Subtract the original weight of flask to determine the amount of fat that has been extracted.
% FAT= Weight of extracted fat * 100
Weight of sample.
= 21.03 *100
172
= 12.23%
Determining amount of salt in food-Mohr method
Sodium chloride is the chemical name that is given to common salt. This method can be used to determine the amount of salt that is available in food. This is particularly essential for persons with health-related complications who are advised to take prescribed amounts of salt in their food. These individuals usually require some kind of limitations on their diets. Salt addition contributes to the total chloride ions that are available in food. Other foods also add to the total number of chloride ions available in different diets. Extraction of salt from food is achieved by ‘ashing’ the sample. The ash is then dissolved in hot water. The Mohr procedure involves the following steps:
- Exactly weighing into a silica dish about 5g of the sample
- Using a Bunsen flame to ignite the sample in a fume chamber
- For one hour, the ash is put in a furnace at 5500C.
- The ash is washed using small amount of distilled water into a No. 54 filter paper. The filtrate is collected in a 100cm3 conical flask.
- Three drops of phenolphthalein are added to the filtrate.
- Drop by drop, add 0.1M of H2SO4. This process continues up to the time the solution is observed to turn colorless.
- Three drops of potassium chromate are added.
- Finally, the burette is filled with 0.1M AgNO3. The sample is then titrated to obtain a red color.
Calculations
1cm3 of 0.1 M AgNO3= 0.0058433 g NaCL
% Salt= Titre* 0.00585 * 100
Weight of sample
Sample A= 13*0.00585 *100
22.10-17.2
= 1.552
Sample B =8* 0.00585 *100
16.05-21.0
=0.945
Average= 1.555+0.945
2
=1.25 %
Determination of Moisture in Food
Two methods can be used to determine the amount of moisture in food; oven method, and infrared by use of Mettler balance.
Oven method
Procedure
- Weigh the evaporation dish, which has to be clean and well-labeled.
- Place 10g of accurately weighed sample in the oven at temperatures of about 110C for around two hours.
- After removing the dish from the oven, place it to cool in the desiccator.
- Replace the dish in the oven for an additional 30 minutes after weighing it.
- Re-weigh the dish after removing and cooling it to determine the final loss in weight.
Infra-red by use of Mettler balance
Procedure
- Use a Mettler balance to weigh a dish of aluminium foil.
- Move the dish to a top-pan balance. Add about two grams of the sample.
- Observe the accurate weight by replacing the dish and sample on Mettler balance.
- Lamp setting selection takes place. The lamp is switched on and loss of weight is observed.
- The process continues until there is no more loss of weight in the sample.
Working formula
% Moisture = Loss in weight * 100
Weight of sample
Determination of Ash content in Food
Procedure
- Into a pre-weighed silica dish that has been coded, weigh 5g of the sample.
- Initially heat the sample in a fume chamber using a small Bunsen flame.
- Increase the intensity of heating up to the point where the sample starts to ignite.
- Carefully move the sample to the Muffle furnace using special tongs and asbestos equipment. Heat the sample for about one hour at 6000C.
- Remove the sample from the furnace, allow it to cool, and then weigh.
- Return the cool sample back to the furnace, heat again, allow it to cool and then weigh. Repeat the procedure until the weight of the sample is constant.
Working Formula
% Ash = Weight of Ash *100
Weight of Sample
% Ash= 17.17 *100
172
=9.98%
Conclusion
Conclusively, when fats, carbohydrates, proteins and salts are exposed to different conditi0ns, they are forced to take different conditions of the processes. Following the above procedures and steps, it was noticeable that several procedures applied help in determining the various components of food. It should be notable that the steps should be followed in the provided order so as to get the required results.
References
Hesselberg, R. J., & Johnson, J. L. (1972). Column extraction of pesticides from fish, fish food and mud. New York: Springer-Verlag.
JOSLYN, M. (1970). Methods in food analysis physical, chemical, and instrumental methods of analysis. (2.ed. ed.). New York: Academic Press.
Michael, L. C., & Cincinnati, O. (1985). Validation of soxhlet extraction procedure for SW-846. Cincinnati, OH: U.S. Environmental Protection Agency, Office of Research and Development, Environmental Monitoring and Support Laboratory ;
Nielsen, S. S. (1998). Food analysis (2nd ed.). Gaithersburg, MD: Aspen Publishers.
Pomeranz, Y., & Meloan, C. E. (1971). Food analysis: theory and practice,. Westport, Conn.: AVI Pub. Co.
Schuck, P., & Dolivet, A. (2012). Analytical methods for food and dairy powders. Chichester, West Sussex: Wiley-Blackwell.
Wood, R., & Nilsson, A. (1998). Quality in the food analysis laboratory. Cambridge: The Royal Society of Chemistry Information Services.
