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Questions and Answers

Which volatile nitrogen compound is produced by bacterial action in fish and meat?

  • Cadaverine
  • Ammonia
  • TMA (correct)
  • Urea

An increase in TBV-N or TMA levels indicates an improvement in the freshness of food products.

False (B)

What is the process through which cadaverine is formed?

Descarboxylation of lysine

The primary nitrogen fraction produced during the degradation of proteins is called ___-N.

<p>TBV</p> Signup and view all the answers

Match the following nitrogen compounds with their formation sources:

<p>TMA = Bacterial action Ammonia = Deamination of amino acids DMA = Autolytic enzymes during freezing Cadaverine = Descarboxylation of lysine</p> Signup and view all the answers

What does an increase in TBV-N or TMA levels signify in food chemistry?

<p>Higher degradation (B)</p> Signup and view all the answers

The Kjeldahl method is primarily used for measuring non-protein nitrogen content in food.

<p>False (B)</p> Signup and view all the answers

___ is produced during the deamination of amino acids and nucleotide cataboites.

<p>Ammonia</p> Signup and view all the answers

What is required for the cadaverine test to occur?

<p>Heating with Ninhydrine (B)</p> Signup and view all the answers

The Kjeldahl method can be used to determine total nitrogen content, including both proteic and non-proteic nitrogen.

<p>True (A)</p> Signup and view all the answers

What is the value of the molar mass of NH3 used in calculations?

<p>17.0304 g/mol</p> Signup and view all the answers

The percentage of protein can be calculated using the formula % Protein = % Nitrogen x ______.

<p>CONSTANT</p> Signup and view all the answers

Match the following nitrogen fractions with their definitions:

<p>Proteic Nitrogen = Nitrogen found in proteins Non-proteic Nitrogen = Nitrogen not associated with proteins Total Nitrogen = Sum of proteic and non-proteic nitrogen Ammonia = A product of nitrogen breakdown</p> Signup and view all the answers

Which of the following indicates the output of the cadaverine test?

<p>Color change observed (D)</p> Signup and view all the answers

The titration step using H2SO4 in the nitrogen analysis determines the amount of H3BO3 used.

<p>False (B)</p> Signup and view all the answers

What is the purpose of boiling the sample in the Kjeldahl method?

<p>To convert nitrogen to ammonium</p> Signup and view all the answers

What is the conversion factor for calculating protein content from nitrogen in milk and derivatives?

<p>6.38 (D)</p> Signup and view all the answers

The Kjeldahl method only measures protein nitrogen and ignores free amino acids.

<p>False (B)</p> Signup and view all the answers

What is the primary purpose of the Kjeldahl method?

<p>To determine the nitrogen content in various samples.</p> Signup and view all the answers

The nitrogen content is expressed as a percentage and can be calculated by the formula: % Nitrogen = n(NH3) = n(N) = n(HCl) = VHCl x 10-3 MHCl where [HCl] = ______ moL/L.

<p>0.1</p> Signup and view all the answers

Match the following sources with their nitrogen content:

<p>Milk and derivatives = 6.38 Corn = 6.25 Rice = 5.95 Wheat = 5.70 Pea flour = 5.40</p> Signup and view all the answers

During the Kjeldahl digestion process, which catalyst is commonly used?

<p>Se (D)</p> Signup and view all the answers

The foaming properties of proteins are determined through calculations involving nitrogen content.

<p>False (B)</p> Signup and view all the answers

What is added to the sample after the initial digestion with H2SO4 for neutralization?

<p>NaOH</p> Signup and view all the answers

After distillation, ammonia (NH3) is recovered with ______ acid for titration.

<p>boric</p> Signup and view all the answers

What is a limitation of the Kjeldahl method?

<p>It determines total nitrogen including non-protein compounds. (B)</p> Signup and view all the answers

Flashcards

Cadaverine test

A test used to determine the presence of amines, specifically cadaverine, in a sample.

Total Nitrogen (N)

The sum of proteic nitrogen and non-proteic nitrogen (NPN).

Kjeldahl method

A method to determine the total nitrogen content in a sample.

Proteic Nitrogen

Nitrogen present in proteins in a sample.

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Non-proteic Nitrogen (NPN)

Nitrogen found in organic compounds excluding proteins.

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Protein composition

The percentage of protein in a sample related to the total organic nitrogen.

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TVB-N

Total Volatile Basic Nitrogen; a measure of nitrogen in a sample in the form of volatile amines.

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% protein calculation

Calculation of protein percentage from the percentage of Nitrogen content using a constant dependant on amino acid composition.

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TBV-N (Total Volatile Basic Nitrogen)

A measurement of the total amount of volatile nitrogen compounds, which are formed during protein degradation in foods like fish and meat.

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TMA (Trimethylamine)

A volatile nitrogen compound that develops as proteins break down during food spoilage. Recognized by a fishy smell.

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TBV-N increase/TMA increase

Higher levels of TBV-N or TMA indicate a greater degree of food spoilage or deterioration.

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Cadaverine Formation

Cadaverine, a foul-smelling volatile amine, is created by the microbial breakdown of the amino acid lysine.

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Volatile Nitrogen Compounds

Nitrogen compounds that readily evaporate at room temperature and are often associated with the odor and spoilage of foods.

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Protein Degradation

The breakdown of proteins into smaller components, like amino acids and volatile compounds, in food due to microbes, enzymes, or other factors.

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Microbial Action

The actions of bacteria, yeasts, molds, or other microorganisms on food components, often leading to spoilage.

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Descarboxylation Reaction

A chemical reaction where a carboxyl group is removed from a molecule, often creating volatile amines during bacterial breakdown.

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Nitrogen Content (% N)

Percentage of nitrogen in a sample, used to estimate protein content.

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Protein Estimation Method

A method to determine the protein content in a food sample, using the Kjeldahl method.

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Digestion step (Kjeldahl)

The process of converting organic nitrogen to ammonia using strong acid and catalyst.

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Distillation step (Kjeldahl)

Separating the ammonia (NH3) generated during digestion from the acidic solution.

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Titration using HCl

Measuring the amount of ammonia collected by neutralizing it with a known acid concentration (HCl).

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Conversion factor (protein)

A factor used to convert the percentage of nitrogen in a sample to the percentage of protein (e.g., milk).

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Protein (% Protein)

Expresses the amount of protein present in a food sample.

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Sample + H2SO4 + Catalyst (Se)

Ingredients for initial digestion in the Kjeldahl method.

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Foaming properties of proteins

The ability of protein solutions to form and maintain a foam.

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Study Notes

Food Chemistry Practical Classes

  • TP1: Protein Alteration Study

    • A: Determining total basic volatile nitrogen (TBV-N)
    • B: Cadaverine test
    • Freshness/degradation in protein products (fish, meat) is linked to TBV-N and TMA content. Higher levels indicate more advanced deterioration. TBV-N comprises TMA (bacterial), DMA (autolytic), ammonia, and other volatile nitrogen compounds.

  • TP2: Total Nitrogen Determination (Kjeldahl Method)

    • Measures total nitrogen, not just protein nitrogen.
    • Different protein sources have different nitrogen conversion constants.
      • Milk/derivatives: 6.38
      • Corn: 6.25
      • Rice: 5.95
      • Wheat: 5.70
      • Pea flour: 5.40
    • The method determines total nitrogen (proteins, free amino acids, biogenic amines, purines, amides, and alkaloids) which is used to estimate protein content.

  • TP3: Foaming Properties of Proteins

    • Examines foaming capacity (how much foam is produced).
    • Foaming stability (how long the foam lasts) depends on pH, protein concentration, temperature, agitation, and the matrix.
    • Food applications include soufflés, meringues, ice cream, cakes, and beer foam.
    • Foaming involves a gas dispersing in a liquid or semi-solid, with proteins at the gas/liquid interface.

  • TP4: Fruit-Based Product Analysis (Refractometry)

    • Analyses fruit products (e.g., quince jam) and determines saccharide content using refractometry.
    • Refractive index is a function of temperature, wavelength, concentration, and chemical nature.
    • Brix scale measures the percentage of sucrose in a solution (w/w).

  • TP5: Red Beet Jelly Making

    • Demonstrates pectin's role in jelly making.
    • Jelly formation depends on sugar concentration and pectin amount.
    • Different treatments (control, low sugar, high sugar, low pectin) are used to observe consistency variation

Additional Notes

  • TBV-N Formation:

    • Bacteria and autolytic enzymes create volatile compounds (TMA and DMA), ammonia from amino acid deamination, and other volatile nitrogen compounds.

  • Cadaverine Formation:

    • Microbial de-carboxylation of lysine produces cadaverine (an amine).

  • Moisture Determination:

    • The moisture percentage is calculated from the initial and final weights of the sample after drying.

  • Refractometry Procedure:

    • A sample is placed on a refractometer prism, and the refractive index is read directly from the instrument scale.

  • Data Analysis:

    • Data collected from experiments should be analyzed to draw conclusions and correlations based on factors such as pH, concentration, and time.

  • Calculations: Various calculations are performed to analyze protein content, nitrogen content, and dissolved solids in each experiment. Formulas relating volume, concentration, and time are important to understand.

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