Food analysis

Provide 3 reasons why the Dumas method, for protein content, is being used more and more versus the Kjeldahl method.

Speed: Dumas is faster (few minutes per sample). No hazardous chemicals: Kjeldahl uses concentrated sulfuric acid, while Dumas avoids corrosive reagents. Automation and throughput: Dumas is easily automated, making it suitable for high-throughput labs.

For which food component are the following tests used? Sudan 3, Iodine, Benedicts

Sudan 3: Fats/lipids, Iodine: starch, Benedicts: reducing sugars

Knowing the water and sugar content of foods and beverages is important. Name 3 methods to measure the sugar content in food and 2 to determine the water content.

Sugar - refractometry, density, titrations (Rebelein, Lany-Eynon), UV/VIS spectroscopy (anthrone method, phenol-sulfuric acid method), chromatography, enzymatic Water – Karl Fischer titration, thermogravimetric analysis, spectroscopic analysis, GC, density, refractometry

What are the 3 types of antigens targeted in immunoassays for detection of microorganisms?

Surface antigens: Found on the outer membrane or cell wall (e.g., lipopolysaccharides in Gram-negative bacteria). Intracellular antigens: Found inside the microorganism, often detected after lysis. Toxins or secreted antigens: Produced and released by microbes, such as exotoxins.

If you have a method that you want to use to measure the % fat in a product and it is not AOAC approved, how would you determine if it is accurate?

Take known fat percentages and run them with the method to perform a standard curve so that you can determine the linear range of your method and assure its accuracy.

Name 3 way to analyze secondary lipid oxidation compounds.

TBARS, VOC, HPLC, gas chromatography, sensory panel

In Proximate Analysis, the Kjeldahl method is used to determine nitrogen content. To calculate the "crude protein" content of most foods, the nitrogen value is multiplied by a standard conversion factor. Provide that standard factor and explain why it is used.

The factor is 6.25. It is used because most proteins are assumed to contain approximately 16% nitrogen (100 / 16 = 6.25).

Explain the principle of the Kjeldahl method and what component of food it estimates.

The Kjeldahl method determines total nitrogen content by digesting organic nitrogen into ammonium sulfate using sulfuric acid, followed by neutralization, distillation, and titration. The measured nitrogen is converted to crude protein using a conversion factor, typically 6.25, assuming proteins contain about 16% nitrogen.

Describe the phenol-sulfuric acid method for total carbohydrates.

The Phenol-Sulfuric Acid Method is a widely used colorimetric assay for determining total carbohydrates in a sample. Concentrated sulfuric acid hydrolyzes polysaccharides and oligosaccharides into monosaccharides. The monosaccharides then undergo dehydration, forming furfural (from pentoses) or hydroxymethylfurfural (from hexoses). These furfural derivatives react with phenol, producing an orange-yellow complex. The intensity of this color is proportional to the carbohydrate concentration in the sample.

A sample of oil has a Saponification Value of 190. Explain what this value measures and what the given value suggests about the average molecular weight of the fatty acids in the oil.

The Saponification Value measures the number of milligrams of Potassium Hydroxide (KOH) required to neutralize the fatty acids released from 1 gram of fat. A higher saponification value (like 190) indicates a lower average molecular weight (or shorter chain length) for the fatty acids in the fat.

For the following food components, which functional groups are measured by IR? triglycerides, proteins, sugars

Triglycerides: C=O (carbonyl), C–H (aliphatic) Proteins: Amide I and II bands (C=O stretch, N–H bend) Sugars: O–H stretch, C–O stretch

Name three detectors used in HPLC.

UV-Vis, Refractive Index Detector, Fluorescence Detector

Explain method validation in food analysis, including accuracy, precision, limit of detection (LOD), and robustness.

Validation confirms method reliability. Accuracy measures closeness to true value; precision reflects repeatability; LOD is the lowest detectable concentration; robustness assesses tolerance to small procedural changes.

Give 2 ways to calculate water activity.

Vapor pressure of the food/vapor pressure of H2O Moles H2O + moles of substrate/moles of H2O

List the colors of the electromagnetic spectrum in order of their appearance, from highest energy to lowest.

Violet, indigo, blue, green, yellow, orange, red

Name two gravimetric and two volumetric methods to measure milk fat.

Volumetric - Babcock and Gerber; Gravimetric - Mojonnier and Roese Gottlieb

Describe the steps of a standard moisture analysis using an oven-drying method.

Weigh a clean, dry crucible. Add a known mass of sample. Dry in an oven (usually 105°C) until constant weight. Cool in a desiccator. Reweigh; moisture (%) = [(initial weight – dry weight) / initial weight] × 100.

Which detection method can not be used with gradient elution in HPLC? a. RID b. DAD c. FLD

a. RID

Gel filtration separation of proteins is taking advantage of: A. protein charge, B. protein size, C. molecular affinity, or D. pH?

B. protein size

What type of chromatography is generally used to separate positively charged molecules: A. Anion exchange chromatography, B. Affinity Chromatography, C. Cation Exchange Chromatography, or D. Reverse-Phased Chromatography?

C. Cation Exchange Chromatography