Lab Report Experiment Determination of crude protein PDF

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FSTEXPERIMENT 3DETERMINATION OF CRUDE PROTEINNAME:STUDENT ID:GROUP:DATE OF EXPERIMENT IS DONE: 10th NOVEMBER 2020 DATE OF LAB REPORT IS SUBMITTED: 17th NOVEMBER 2020 LECTURER’S NAME:INTRODUCTIONProtein is a macronutrient that is essential for muscle mass building. It is commonly found in animal prod...

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FST556 EXPERIMENT 3 DETERMINATION OF CRUDE PROTEIN

NAME: STUDENT ID: GROUP: DATE OF EXPERIMENT IS DONE: 10th NOVEMBER 2020 DATE OF LAB REPORT IS SUBMITTED: 17th NOVEMBER 2020 LECTURER’S NAME:

INTRODUCTION Protein is a macronutrient that is essential for muscle mass building. It is commonly found in animal products, although other sources, such as nuts and legumes, are also present. Protein chemically consists of amino acids, organic molecules that are composed of carbon, hydrogen, nitrogen, oxygen or sulfur. Amino acids are protein building blocks, and muscles are muscle mass building blocks. According to the USDA, any food made from meat, poultry, fish, beans and peas, eggs, refined soy products, nuts and seeds is considered to be part of the protein category (Szalay, 2015). It is vital to know the protein content in foods as such essential constituents of human diet and hence it is important to have accurate analytical methods. Nitrogen Determination Protein Content Dependent Analysis of the total nitrogen content in the samples is the basis of some of the most commonly used food protein determination methods such as Kjeldahl method. In the Kjeldahl process, nitrogen is released into a strong acid and after neutralization and titration, the content is calculated. Using a conversion factor, crude protein content is determined following the determination of nitrogen. The original conversion factor 6.25, which is still widely used is based on the premise that the general content of nitrogen in food proteins is 16 percent and that all nitrogen in food is protein-bound. However, these are very rough conclusions since the relative content of nitrogen differs between amino acids and the structure of amino acids varies between food proteins (Maehre, 2018). Thus, the aim of this experiment is to determine the amount of crude protein in peanut using Kjedahl method.

OBJECTIVE The objective of this experiment is to determine the amount of crude protein in peanut using Kjedahl method.

MATERIALS The materials used in this experiment are concentrated sulphuric acid, catalyst tablet (potassium sulphate and selenium), 50% sodium hydroxide, 2% boric acid, 0.1 M hydrochloric acid, screen methyl red, Kjedahl digestion and distillation system, digestion tubes, conical flask, spatula, analytical balance, retort stand, burette, beaker and graduated cylinder.

METHODS First, clean and dry Kjeldahl digestion flask was obtained and labeled clearly at varying parts of the flask neck. The digestion tubes were placed in the digestion tube holder on the rack. 0.7 g of sample by difference was weighed into the digestion tube and 2 pills of catalyst mixture which is 5 g potassium sulphate + 5 mg selenium and 20 ml concentrated sulphuric acid was added. Next, the suction module was placed with the fitted gaskets on the digestion tube holder and the water supply was turn on to the condenser and the scrubber unit was switch on. The digestion unit was switch on and the energy regulator was set in position 10. The samples allowed to digested until it is complete and the samples was cleared with no charred material remain. After that, the samples were taken off the digestion block and allowed to cool. The power system of distillation unit was switch on and the system was allowed to warm up at least 2 minutes before the first run. 70 ml 2% boric acid and 3 drops of screened methyl red was filled in as an indicator into the conical flask. The distillation apparatus was set up with the delivery tube dipping below the solution and the sample tube was put in place to make sure it is seated securely. The next step is, 50 ml distilled water was added into the digestion tube and 80 ml 32% NaOH was added into the digestion tube by pressing the NaOH button until desired volume. The STEAM switch was turn on to start distillation process and 200 ml of the distillate was collected. Lastly, the contents of the receiver flask were titrated with 0.1 M HCL and the volume of HCl used for sample and blank was recorded.

RESULT Sample: Peanut Weight of sample: 0.7 g Table 1.1: Data of crude protein analysis using Kjeldahl method Blank

Sample titration

titration Volume used (ml) (final – initial)

0.30

% crude protein

Trial #1

Trial #2

Trial #3

18.20

18.10

18.70

19.55

19.44

20.09

Average ± SD 19.69 ± 0.35

Conversion factor for peanut = 5.46 (AOAC International, 2000)

CALCULATIONS 1 ml 0.1 M HCL = 1.4 mg N Therefore, total nitrogen (g) per 100 g food sample =

(titre −blank ) X 1.4 X 100 1000 X sample weigh(g)

Crude protein (g) per 100g food sample = total nitrogen X conversion factor for foodstuff analyzed use appropriate conversion factor. Trial 1 Total nitrogen = (

(18.20 −0.30) X 1.4 X 100 ¿ 1000 X 0.7 g

= 3.58

Crude protein (%) = 3.58 X 5.46 = 19.55 %

Trial 2 Total nitrogen = (

(18.10 −0.30) X 1.4 X 100 ¿ 1000 X 0.7 g

= 3.56

Crude protein (%) = 3.56 X 5.46 = 19.44 % Trial 3 Total nitrogen = (

(18.70 −0.30) X 1.4 X 100 ¿ 1000 X 0.7 g

= 3.68

Crude protein (%) = 3.68 X 5.46 = 20.09 %

Mean 19.55 +19.44 + 20.09 3

= 19.69

Standard deviation SD =

√

( 19.55 −19.69 ) 2+( 19.44 −19.69 ) 2+( 20.09−19.69 ) 2 2

= 0.35

DISCUSSION In experiment Kjedahl method peanut was used as a food sample. Based on the results, trial 1 has 19.55% of crude protein, trial 2 has 19.44% crude protein and trial 3 has 20.09% of crude protein. The average of peanut crude proteins content is 19.69 ± 0.35. For theoretical value of crude protein content for peanuts or nuts is ranged within 1 – 40 % (Arya, 2016). Thus, from the result obtained it the sample was proven that the crude protein content is within the theoretical value for trial 1, trial 2 and trial 3. There are 4 stages in this experiment which is digestion, neutralization, distillation and titration. In digestion, the food sample to be analyzed is weighed into a digestion flask and then digested in the presence of sulfuric acid (H2SO4) an oxidizing agent that digests the food. Potassium sulfate used to increase the rate of organic decomposition and shorten the digestion time by raising the boiling point of the acid and used to increase the rate of organic decomposition and shorten the digestion time by increasing the boiling point of the acid. In neutralization, the digested sample is neutralized by converting (NH4)2SO4 (ammonium sulfate) into ammonia gas with an alkali solution of NaOH. In distillation, the ammonia gas is distilled into a solution of boric acid. The solution-freed NH3 gas transfers to the receiving flask containing boric acid. Low pH transforms NH3 into NH4 ion and boric acid to borate ion, causing a change in color or pH value. In titration, is to measure in the receiving solution the sum of ammonia. The addition of acid (HCl) neutralizes the ammonium-borate complex and causes a reverse shift in colour or pH value. Amount of acid used is the same as the amount of digested organic N. The results of this analysis represent the crude protein content of peanut since nitrogen also comes from non-protein components.

QUESTIONS 1. Why conversion factors used in the calculation? Why is it different between foods? Conversion factor is needed to convert measured N concentration to a protein concentration. The conversion factor is different between foods because there are some changes happened during cooking such as water absorption, water reduction, and fat absorption.

2. Comment on the robustness, reproducibility and precision of this method. This method generally considered as the standard method of determining protein concentration since the Kjeldahl method does not explicitly measure the protein content, a conversion factor (F) is needed to convert the measured concentration of nitrogen to the concentration of protein. For certain applications, a conversion factor of 6.25 equivalent to 0.16 g of nitrogen per gram of protein is used, but this is just the mean value, because each protein has a different conversion factor depending on its amino acid composition. However, this method is applicable to all types of food and accurate even it is not give the measure of true protein.

CONCLUSION In a conclusion, the experiment was achieved because able to determine the amount of crude protein in peanut using Kjedahl method. The amount of crude protein obtained is 19.55%, 19.44% and 20.09%.

REFERENCES Arya, S. S., Salve, A. R., & Chauhan, S. (2016). Peanuts as functional food: a review. Journal of food science and technology, 53(1), 31-41. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4711439/ Maehre, H. K., Dalheim, L., Edvinsen, G. K., Elvevoll E. O., & Jensen, I. J. (2018). Protein determination method matters. Foods, 7(1), 5. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5789268/ Szalay, J. (2015, December 10). Live Science. Retrieved from What is Protein?: https://www.livescience.com/53044-protein.html...