Proximate Analysis of Food

What is the total lipid content of a food commonly determined by?

• Organic solvent extraction methods

• Alkaline hydrolysis

• Acid hydrolysis

• All of the above

What does the accuracy of direct solvent extraction methods depend on?

• Solubility of the lipids in the solvent used

• Ability to separate the lipids from complexes

• Both A and B

• None of the above

What is the ideal sample for fat analysis?

• As close as possible in all intrinsic properties

• Moist and fresh

• Dried and ground

• None of the above

What is the effect of drying the sample at elevated temperatures?

• Enhances lipid extraction

• Causes some lipids to bind to proteins

• Makes the sample easier to grind

• None of the above

What is the Kjeldahl method used for?

• Analyzing organic nitrogen

• Measuring protein content

• Both A and B

• None of the above

What is the main disadvantage of the Dumas method?

• Requires hazardous chemicals

• Expensive equipment is required

• Not suitable for all samples

• None of the above

What does infrared spectroscopy measure?

• Absorption of radiation by molecules

• Protein content in food

• Both A and B

• None of the above

What color is produced in the Biuret method?

• Violet-purplish

• Green

• Blue

• Red

What are the disadvantages of the biuret reaction?

• Not very sensitive requires at least 2–4 mg protein for assay.

• Absorbance could be contributed from bile pigments if present.

• High concentration of ammonium salts interfere with the reaction.

• Color varies with different proteins; gelatin gives a pinkish-purple color.

• Opalescence could occur in the final solution if high levels of lipid or carbohydrate are present.

What are the advantages of the Lowry method?

• Very sensitive

• Less affected by turbidity of the sample.

• More specific than most other methods.

• Relatively simple; can be done in 1–1.5 h.