UNIT 1 Flashcards by Nancy He

What is a food matrix

complex nonhomogenous mixtures of many chemical substances, natural & synthetic

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True/false: only processed foods are complex food matrices

False

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What are some naturally occurring chemicals in food?

water, carbs, AA, peptides, lipids, vitamins, flavors, inorganic components…

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Examples of synthetic substances in food:

functional additives, food coloring, flavorings

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food may be contaminated with undesirable chemical substances such as:

environmental contaminants
process induced contaminants
agrochemical residues
food contact material residues

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The component of interest to be analyzed is called the _____

analyte

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What is the ‘matrix effect’

combined effect of ALL components in the sample (other than analyte) on measurement of the analyte (interference)

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The sample is composed of the analyte contained in the ____

matrix

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How are molecules classified according to size?

small: low molecular wt (<900Da) - simple sugars, AA, FA

large: (100000s of Da)
Protein, complex carbs

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True/False: hydrophobicity is the same thing as lipophilicity

False:
often used interchangeably, but not exactly the same thing
(hydrophobic - doesn’t like water; lipophilic - likes fat)

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Example of compound that is hydrophobic but not lipophilic:

fluorocarbons

hydrophobic and lipophobic

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What does ‘polarity’ refer to?

solubility
polar: soluble in water, protic organic solvents (hydrophilic)

nonpolar: soluble in nonpolar organic solvent (hydrophobic)

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examples of polar compounds:

simple sugars, oligosaccharides, AA, small protein/peptide, B and C vitamins

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examples of nonpolar compounds:

fats, PL, sterols, A, D, E, K vitamins, carotenoids

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hydrophobicity of a compound can be expressed as a ______ coefficient

Octanol-Water partition coefficient

Kow

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When a chemical is hydrophobic, Kow will be (low/high)

high

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How do you calculate Kow?

ratio of concentration in octanol vs concentration in water

in separatory funnel

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What are the units of Kow? how is it usually expressed?

no unit

log Kow

A chemical with log Kow = 5.66 is (hydrophobic/hydrophilic)

hydrophobic

caffeine should have a (high/low) log Kow

low

How is the ‘solubility of a solute’ defined?

proportion of solute in designated solvent, when saturated (max amount that can be dissolved)

expressed in concentration, molality, mole fraction, etc

Classifications of compounds according to volatility:

nonvolatile: (low vapor pressure/high boil pt) - sucrose, NaCl

Volatile: (high vapor pressure, low boil pt) - essential oil, low mol. wt FA, flavor compounds…

Challenges of food analysis: (3)

complex matrices
varied compositions among samples
need to be fast (maintain sample integrity, respond quickly to clients)

some technologies that allow rapid analysis, without manipulation: (5)

X ray fluorescence
Infrared spectroscopy (FTIR, NIR)
Guided Microwave Spectrometry (GMS)
MRI
Direct Analysis in Real Time (DART) MS

Advantages of rapid analysis techniques:

``` no sample prep automated convenient rapid can be done in-process nondestructive safer, no hazardous chemicals efficient - less energy/manpower/chemicals ```

What technology can be used for in-process analysis, and is even starting to be adapted for smartphones?

Near Infrared Technology

What technology can be used for elemental analysis, and what are its advantages?

total reflection xray fluorescence little to no sample prep little sample needed (few ug/uL)

What can be analyzed with the portable handheld XRF scanner?

``` monitor preservative Ca coatings elemental nutrient verification animal feed assessment/risk analysis analyze salt/sodium compounds in salty snacks milk/dairy/powder analysis for Fe and Ca Salt analysis for Iodine ```

Current limitations of direct analysis:

low sensitivity and selectivity surface vs bulk composition not standardized or approved instrument cost

What is the definition of separation?

separating components of a mixture without modifying them substantially

Carl Wilhelm Scheele was the first to do what?

separate citric acid by crystallizing it from lemon juice

What is partial vs complete separation?

partial: isolate one component of interest, others remain mixed complete: isolate all different components

Separations can be done based on what physicochemical characteristics?

size/mass charge polarity volatility

Partitioning, also known as _____, describes what process?

distributing solute is distributed amount phases (reaching equilibrium); certain % in each phase

What is adsorption?

distribution processes occurring between solute and the SURFACE of the phase

What is absorption?

distribution processes occurring between solute and the BULK of the phase

What is equilibrium?

system reaching a state where the properties (activity, concentration, etc) remain unchanged *driving force for many separations

The 2 types of 'driving force' for separations:

1. equilibrium (system tries to attain equilibrium) | 2. nonequilibrium (kinetic): rate at which solutes migrate provides driving force

Differential centrifugation is what type of separation? (driving force)

kinetic | separation caused by particles moving at different rates due to various density/sizes

In differential centrifugation, the (more/less) dense particles will reach the bottom first

examples of equilibrium driven separation techniques:

``` partition chromatography Extraction distillation precipitation crystallization ```

examples of kinetic driven separation techniques:

``` dialysis electrophoresis exclusion chromatography centrifugation filtration sedimentation membrane methods ```

what are hybrid/hyphenated techniques?

combination of instrumental methods | GC-MS, LC-MS, SPE-HPLC, CE-FTIR...