Proximate Analysis

What is proximate analysis?

• It is a system of analysis that provides top level results in analytical determinations of food and feed component as moisture content, protein , crude fat, crude fiber, ash, total lipids and total sugars.

Moisture

Moisture Content

• Determination of moisture defines the dry matter composition of food.

• Determination of moisture content based on physical removal of water

Oven drying at 105o

• Applicable in most foods except those rich in sugar and fat – causes caramelization of sugars and degradation of unsaturated fats.

• Sample is heated in an oven at 105o for5 hours .

Kjeldahl Method

• Method used for protein determination through total nitrogen.

• Uses Selenium mixture as catalyst.• Adds Sodium thiosulphate in the

solution to prevent and break ammonium and catalyst complex

Digestion with sulphuric acid

• Oxidation of oxygen and hydrogen into carbon dioxide and water.

• Conversion of bound nitrogen into ammonium ion.

• Results in colorless solution.

Sample + H2SO4 → (NH4)2SO4(aq) + CO2(g) + SO2(g) + H2O(g)

Distillation with naoh

• (NH4)2SO4 is distilled with NaOH which is then converted to ammonia. Consequently, the generated gas is trapped in Boric acid upon distillation.

(NH4)2SO4(aq) + 2NaOH → Na2SO4(aq) + 2H2O(l) + 2NH3(g)

B(OH)3 + NH3 → NH4+ + H2BO3

–

Titration with acid• The generated ammonium

ion is in equilibrium with boric acid, thus titration with acid (HCl) of the boric acid gives the amount of total nitrogen present in the sample.

H2BO3– + H3O+ → + B(OH)3(aq) + H2O

Crude Fat

goldfisch method• Continuous solvent extraction method• Solvent continuously boils over sample held in

ceramic thimble.• Extracts lipids through non-polar solvents like

diethyl ether, hexane, petroleum ether or methylene chloride

• Extraction times range from 4-16 hrs• Solvent is removed by evaporation• Fat content is measured by weight loss of the

sample or by weight of fat removed.

Weende Method

• Developed in 1884 by Hennenburg and Stohman for determiation on crude fiber.

• Uses boiling sulphuric acid to to separate fiber from other component by hyrolyzing carbohydrates and other protein components.

• Uses Sodium hydroxide as alkali slution for saponifying remaining lipids and dissolving remaining minerals.

• Sample is ignited at 600o to oxidize fiber.

ASH

• Gives an index of total mineral content of the sample

• Can detect possible adulterations in the sample such as soil, salt, dirt etc.

• Sample is ignited at 600o until white ash.

• Ash content is determined through difference in sample weight.

Phenol-Sulphuric method

• Sample is degraded by sulphuric acid to furfural • Addition of phenol creates a orange colored complex

• Color intensity is related to sugar content• Sugar content is measured spectrophotometrically at 490nm.

Phosphorus

Ascorbic acid method

• Requires full conversion of phosphorus content to orthophosphate

• Uses acidic medium for reaction to tae place

• Ammonium-molybdate and antimony-potassium tartrate reacts with orthophosphate dilute solution to form intense blue complex.

• Complex not stable so must be read within 30 min upon addition of mixed reagent.

• Formed complex is proportional to the Phosphorus content and thus spectroscopic analysis at 880 nm gives total phosphorus content.

Nesvita Cereal Milk Drink

Experimental Results

Moisture content

Weight of container + sample, g 25.6852 28.1863

Constant wt. of sample upon drying, g 25.614 28.1188

% moisture content 0.277 % 0.2394 %

Average moisture content, % 0. 2563 %

Literature value n/a

ASh

Weight of container + sample, g 23.0186 26.4774

Constant wt. of sample upon ignition, g 22.7328 25.2412

% ash content 8.1202% 4.195%

Average ash content, % 6.1577%

Literature value 7.333%

Crude Fat

Weight of sample, g 1.0077 1.0103

Constant wt. of goldfisch beaker, g 54.0026 63.7501

Constant wt. of sample upon analysis, g 54.0618 63.8053

% crude fiber content 5.875 % 5.464%

Average crude fiber content, % 5.669%

Literature value 7.667%

Crude Fiber

Weight of sample, g 0.2980 0.2960

Constant wt. of sample before ignition, g 25.5280 17.6608

Constant wt. of sample after ignition, g 25.5186 17.6546

% crude fiber content 3.1543 % 2.0946 %

Average crude fiber content, % 2.584%

Literature value 6.333%

Crude Protein

Weight of sample, g 0.1012 0.1009

Normality of HCl, N 0.1010 0.1010

Average Normality of HCl, N 0.1022

% Total N 2.373 % 2.554 %

% crude protein content 14.00 % 15.07 %

Average crude fiber content, % 14.53%

Literature value 12.oo%

Total Sugars

Weight of sample, g 0.0515 0.0498

Absorbance reading at 490 nm (corrected) 0.026 0.032

Concentration of sample, mg/ml 57.4667 64.2570

Average Concentration of sample, mg/ml 60.8619

Literature value 66.67%

Total Phosphorus

Weight of sample, g 1.1858 1.2900

Absorbance reading at 490 nm (corrected) 0.619 0.734

Concentration of sample, mg/100 g 16.129 18.186

Average Concentration of sample, mg/100 g 17.157

Literature value n/a

Conclusion

• The experimental value of the Nesvita Cereal Milk drink is almost as close to the literature value cited from the product.

Some errors

• For moisture analysis- excess experimental value could be attributed to formation of milliard product (protein:carbohydrate complex) which can be mistaken for moisture loss.

• For ash- volatilization of some elements due to hi temperature process

• For fat- incomplete extraction may have made

• For protein – slight difference may be due to assumption that all nitrogen present is in the form of protien.

• For fiber- acid and base solubilize some of the true fiber (particularly hemicellulose, pectin and lignin)

• Cellulose too is partially lost. Hence, crude fiber underestimates true fiber.

THE END