Food Chem II Exam III Material

What is the fundamental principle of Atomic Absorption Spectroscopy (AAS)?

The absorption of light by free atoms in the ground state.

How does Atomic Emission Spectroscopy (AES) differ from AAS in terms of energy state?

AES measures light emitted by excited atoms as they return to the ground state, whereas AAS measures light absorbed by ground-state atoms.

What is the primary function of a hollow cathode lamp in AAS?

It provides a specific radiation source that emits characteristic light for the element being analyzed.

What is the purpose of a nebulizer in an AAS instrument?

To convert a liquid sample into small droplets for subsequent atomization.

Name the two common fuel-oxidant mixtures used in Flame AAS.

Air-acetylene or nitrous oxide-acetylene.

What are the three stages of heating in Electrothermal (Graphite Furnace) AAS?

Solvent evaporation, sample ashing, and element vaporization/atomization.

Which element is uniquely analyzed using the Cold-Vapor technique?

Mercury (Hg), because it is liquid and volatile at room temperature.

What chemical reagent is typically used in Hydride Generation to produce volatile hydrides?

Sodium borohydride.

What is the main advantage of using a beam chopper in an AAS spectrometer?

It allows for the cancellation of background light emitted by the flame.

Why must the sample concentration be kept dilute in AAS?

To avoid exceeding the instrument's capacity.

What is the primary advantage of ICP-OES over standard Flame AAS?

ICP-OES can measure a large number of elements (up to 74) simultaneously.

Define plasma in the context of ICP spectroscopy.

An electrically conducting medium consisting of roughly equal numbers of positively and negatively charged particles, produced by ionizing gas at high temperatures.

What is the role of the argon plasma torch in ICP-AES?

It uses radio frequency power to create high temperatures that ionize gas and atomize the sample.

What is the typical sample preparation method for food samples in AAS?

Wet-ashing to bring the sample into solution.

What is the sensitivity range of AAS?

Parts per billion (ppb) levels.

What are two common detectors used in atomic spectroscopy?

Photomultiplier tubes and charge-coupled devices (CCD).

Why are there fewer absorption lines in AAS compared to emission lines in AES?

Because only specific wavelengths can excite ground-state atoms, whereas emission occurs from various lower energy levels.

What is the typical precision of measurements in Flame AAS?

Better than 1% relative standard deviation.

How does the cathode composition in a hollow cathode lamp relate to the analysis?

The cathode is made from the specific metal being analyzed to ensure the emission of characteristic radiation for that element.

What is the primary benefit of the Graphite Furnace (GFAAS) compared to Flame AAS?

Some models can measure up to 48 elements simultaneously.

What is the function of the monochromator in an AAS instrument?

To isolate the specific wavelength of light required for the analysis.

What state of matter is plasma considered to be?

A distinct state of matter, similar to solid, liquid, or gas, achieved by adding enough energy to a gas.

What is the difference between ICP-OES and ICP-MS?

ICP-OES measures optical emission spectra, while ICP-MS measures mass-to-charge ratios of ions.

Why is it important to minimize ions in Flame AAS?

Because ions absorb light at different wavelengths than atoms, which can interfere with the analysis.

What is the typical shape of an AAS calibration curve?

Often curved, but linear if the concentration range is carefully chosen.

Are lamps used in Atomic Emission Spectroscopy (AES)?

No, AES relies on high temperatures to excite atoms, which then emit light upon relaxation.

What are three common elements analyzed using Hydride Generation?

Arsenic (As), Lead (Pb), and Selenium (Se).

What are the six components of proximate analysis in food?

Moisture, crude protein, crude fat, ash, carbohydrates, and minor components like vitamins and pesticides.

What is defined as 'ash' in food analysis?

The inorganic residue remaining after the incineration of organic matter.

What is the primary difference between dry ashing and wet ashing?

Dry ashing is for proximate composition, while wet ashing is for the analysis of specific heavy metals.

What is the typical temperature range for dry ashing?

550 degrees Celsius.

Why must samples be cooled in a desiccator after dry ashing?

To prevent moisture absorption from the air before weighing.

Which minerals are commonly volatile during dry ashing?

Fe, Se, As, Cd, B, Pb, P, TE, Hg, Zn, Sn, Sb, and S.

Which crucible material is known for high chemical inertness and excellent heat conductivity but is very expensive?

Platinum.

What are the primary advantages of dry ashing?

It is safe, simple, and allows for multiple samples to be processed simultaneously.

What is the main safety risk associated with wet ashing procedures?

The formation of perchlorate crystals, which can explode.

What is the purpose of atomization in elemental analysis?

To convert elements in an ash solution into free, unbound atoms or ions.

What is the distinction between enrichment and fortification?

Enrichment is the act of replenishing nutrients that were previously present in a food.

What defines 'temporarily hard' water?

The presence of calcium or magnesium bicarbonates, which can be precipitated by heating.

What are the three categories of dietary minerals based on intake requirements?

Macro minerals, trace minerals, and ultra-trace minerals.

Which minerals are classified as toxic in the context of food analysis?

Lead, mercury, cadmium, and aluminum.

What is the primary source of calcium in a typical diet?

Dairy products, cereal, nuts, fish, eggs, and certain vegetables.

What is the primary source of magnesium in a typical diet?

Nuts, cereal, and legumes.

What is the maximum temperature capacity of a high-temperature muffle furnace?

1,200 degrees Celsius (1,473 Kelvin).

Why is wet ashing preferred for trace element analysis?

It is very sensitive, requires little time, and minimizes loss from volatilization.

What is the typical ash content of fresh foods?

It rarely exceeds 5%.

What is the primary disadvantage of using steel crucibles for ashing?

They may contaminate the samples.

What happens to minerals during the dry ashing process?

They are converted into silicates, oxides, sulfates, phosphates, and chlorides.

What is the primary limitation of Pyrex Gooch crucibles?

They are limited to a maximum temperature of 500 degrees Celsius.

What is the main disadvantage of wet ashing regarding equipment and labor?

It requires trained operators, constant attention, and expensive equipment like hollow cathode lamps.

What is the primary source of phosphorus in a typical diet?

Dairy products, grains, meat, fish, poultry, eggs, and legumes.

What defines permanently hard water?

Water containing sulfates of calcium or magnesium that cannot be softened by heating.

What is the ion exchange method for softening water?

A process where sodium ions are exchanged for calcium ions.

How does hard water affect the cooking of legumes?

Minerals like calcium and magnesium can cause dried beans, peas, and lentils to harden, making them difficult to cook.

What is the difference between enrichment and fortification?

Enrichment replaces nutrients lost during milling, while fortification adds nutrients not previously found in the food or adds them in higher amounts.

What is the definition of a 'grain' in the context of water hardness?

0.064 grams of calcium carbonate (CaCO3).

What is the range for 'hard' water on the hardness scale?

11-20 grains per gallon.

What is the primary role of EDTA in mineral titration?

It binds 1:1 with minerals to form a complex, allowing for concentration measurement.

What is the required pH range for stable mineral-EDTA complexation?

pH 10 to 11.

What color change indicates the endpoint in an EDTA titration using EBT indicator?

From pink/red to blue.

What is a precipitation titration?

A titration method where at least one product of the reaction is an insoluble precipitate.

What is the Mohr titration used for?

Determining chloride content, such as salt in butter.

How does the Volhard Method determine chloride content?

By back-titrating silver nitrate after the precipitation of chloride.

What are the advantages of using Ion Selective Electrodes (ISE)?

They are relatively inexpensive, simple to use, and durable for both field and lab environments.

What is the lower detection limit for Ion Selective Electrodes?

They generally cannot measure below 2-3 ppm.

What equipment can often be used as a voltmeter for an Ion Selective Electrode?

A standard laboratory pH meter.

What is the principle behind colorimetric mineral analysis?

Reacting a mineral with a color-producing reagent and measuring absorbance at a specific wavelength.

Which reagent is used to detect phosphate in colorimetric analysis?

Molybdovanadate.

What is the purpose of ashing samples before mineral analysis?

To specifically separate minerals from the food matrix.

Why must the pH be at least 10 for calcium-EDTA complexation?

The complexation equilibrium is strongly pH dependent; below pH 10, the complexes are not stable.

What is the function of phosphorus when added as a food additive?

To improve water holding capacity.

What is the function of calcium when added as a food additive?

To assist in gelation.

What is an example of a common food fortification practice?

Adding iodine to salt.

What is the primary limitation of precipitation titrations?

They may lack a clear endpoint indicator or fail to yield a single product of definite composition.

What is the purpose of the ammonia buffer in EDTA titration?

To maintain the solution at approximately pH 10 to ensure stable complex formation.

What is dry matter?

The material remaining after moisture has been removed from a sample.

Why is water considered a dipolar molecule?

It possesses both positive and negative charges, allowing it to be attracted to other charged molecules.

What is the bond angle between the two hydrogens in a water molecule?

104.5 degrees.

What are the three forms of water found in food?

Free water, adsorbed water, and water of hydration.

How does the strength of a hydrogen bond compare to a covalent bond?

Hydrogen bonds have approximately 10% of the strength of a covalent bond.

How many calories are required to break hydrogen bonds when water turns to steam?

540 calories per gram.

What happens to the volume of water when it turns to ice?

It expands due to the formation of crystals.

What are Standards of Identity?

Regulatory specifications that define the composition and moisture limits for specific food products.

Why is moisture content important for food stability?

It affects shelf-life by influencing susceptibility to mold, bacteria, and chemical deterioration.

What is the primary economic reason for controlling moisture content in food products?

Water is cheap to add to product weight but expensive to transport.

What is the general rule for selecting a moisture analysis method?

Choose the fastest, simplest, and most convenient method that provides the desired range of accuracy.

What is a major risk when using high temperatures for moisture analysis?

Thermal decomposition of organic compounds, such as sugars.

What is the purpose of a desiccator in moisture analysis?

To cool samples in a moisture-free environment before weighing.

Why is a vacuum oven used for moisture analysis?

To allow for moisture removal at lower temperatures, preventing thermal decomposition of heat-sensitive foods.

At what temperature should foods rich in fructose be dried in a vacuum oven?

70 degrees Celsius or below.

What are the primary advantages of oven drying methods?

They are simple, relatively rapid, and allow for the analysis of a large number of samples simultaneously.

What are two potential sources of error in oven drying moisture analysis?

Loss of non-water volatile components and weight gain from lipid oxidation or nonenzymatic browning.

What is the primary difference between a forced-draft oven and a convection oven?

A forced-draft oven uses air circulation to maintain a more uniform temperature with less 'load effect'.

What is the function of water as a dispersing medium in food?

It stabilizes colloids through hydration and disperses proteins and starch.

What is the role of water in food chemical reactions?

It acts as a reactant in processes like hydrolysis and leavening.

What is the difference between a calorie (cal) and a dietary Calorie (Cal)?

One dietary Calorie is equal to 1000 calories.

What are two non-oven methods for moisture analysis?

Distillation and Karl Fischer titration.

Why is moisture content reported on a dry weight basis?

To provide a uniform standard for nutritional values regardless of moisture fluctuations.

What is the effect of moisture on food texture?

It is a critical quality factor that determines the physical characteristics and stability of the food product.

What is the boiling point of water at standard pressure?

100 degrees Celsius.