Laboratory

Question 1

Why did the dye need to be filtered before measuring its absorbance?

Answer 1

Cornstarch particles would have accounted for scattering losses

Question 2

What is the consequence of scattering losses?

Answer 2

• Intensity of light leaving the sample: lower

- Decrease the percentage transmittance

Question 3

What is the consequence of a decrease in percentage transmittance?

Answer 3

• Related to absorbance in a logarithmic manner

- Absorbance increase

Question 4

What is the consequence of cornstarch particles in terms of absorbance?

Answer 4

Measured absorbance would have been higher than filtered

Question 5

Why is it important to determine the maximum absorbance of the dye?

Answer 5

• Beer’s Law is only valid through monochromatic radiation (cannot be used in practice, only in theory)
• Polychromatic radiation does not deviate from the law if the molar absorptivities are the same for all the wavelengths, which is at wavelength max
• Linear relationship holds

Question 6

What are the sources of error in the visible spectroscopy experiment?

Answer 6

• Beer’s Law only interprets the absorption of dilute samples (surpassed 0.01 –> deviations)

Question 7

What is precision?

Answer 7

Refers to the closeness of two or more measurements to each other (standard deviation)

Question 8

What is accuracy?

Answer 8

Refers to the closeness of a measured value to a standard or known value (experimental error)

Question 9

What is Beer’s Law?

Answer 9

• 𝐴 = 𝜀 ∙ 𝑏 ∙ 𝑐
• The absorbance (A) of a sample is the product of the molar absorptivity (𝜀), the path length (b), and the concentration (c).

Question 10

If the ____________ and _____________ are constant, the concentration of a sample can be determined through Beer’s Law

Answer 10

molar absorptivity

path length

Question 11

What is hydrogenation? Why is it used?

Answer 11

• Unsaturated oil converted to a saturated fat
• Hydrogenation processes change the physical characteristics of a food product, or to increase its shelf-life.
• Unsaturated fatty acids are more reactive to autoxidation deterioration processes, and have a shorter shelf-life than saturated lipids

Question 12

How can lipase enzymes be detrimental to the quality of an oil?

Answer 12

• The smoke point of an oil decreases due to lipolysis, characterized by the deterioration of the fatty acids, which produces smoke.
• The increase of free fatty acids in an oil also decreases its quality by creating undesirable tastes and color changes
• Also increases fat retention of the edibles cooked in the oil

Question 13

What is the method to determine the iodine value?

Answer 13

• Oil is dissolved in chloroform, and Wijs solution is added

- The sample is titrated with sodium thiosulfate

Question 14

What are the three chemical equations that illustrate what happens in Wijs method?

Answer 14

• –CH=CH– + 2ICl –ICH-ICH– + 2HCl
• ICl + KI KCl + I2
• 2Na2S2O3 + I2 2NaI + Na2S2O3

Question 15

What is the definition of the saponification value?

Answer 15

The number of milligrams of KOH required to saponify 1 gram of the fat

Question 16

What does the saponification value indicate?

Answer 16

The longer the carbon chains, the greater the molecular weight, utilizing a smaller amount of KOH. This leads to a smaller number of fatty acids liberated per gram of hydrolyzed lipid, and a smaller saponification number

Question 17

How is the saponification number related to the boiling point?

Answer 17

The lower the saponification number, the higher the boiling point

Question 18

What can pass through a dialysis bag?

Answer 18

Free amino acids and peptides with a molecular weight under 12 000 Daltons can pass through the semi-permeable membrane

Question 19

What was the intention of the hour-long dialysis process?

Answer 19

• The intention of the hour-long dialysis process was to allow the low- molecular weight products of trypsin hydrolysis to travel across the semi-permeable membrane
• The low-molecular weight products (in the dialysate solution) were analyzed spectroscopically with the ninhydrin reagent

Question 20

What is the reaction between the ninhydrin reactant and an amino acid? What does it form? What is the maximum absorbance

Answer 20

The amino acid is decarboxylated and deaminated, releasing ammonia, which reacts with ninhydrin and hydrindantin to form a violet-blue product that has a maximum absorbance at 570 nm

Question 21

What is the product formed from the ninhydrin reaction?

Answer 21

Ruhemann’s purple (blue-purple)

Question 22

What does the reaction between ninhydrin and an amino acid form?

Answer 22

• Ammonia
• Hydrindantin
• Aldehyde
• Carbon dioxide

Question 23

Why do proteins precipitate at the isoelectric point? What is it?

Answer 23

• pH at which the compound has a net charge of 0
• The solubility is lowest at this point
• Proteins are stabilized in part by electrostatic repulsion, which are impaired at the isoelectric point due to the lack of an overall charge, promoting aggregation

Question 24

How can casein be re-dispersed in a water solution?

Answer 24

• Adding a base (NaOH)

- Produces sodium caseinate, and increases the pH

Question 25

Why is sodium caseinate dispersable in water?

Answer 25

As a salt, the polarity of water molecules can dissolve the ionically bonded sodium caseinate to form a sol, which is a solid dispersed in a liquid.

Question 26

What is the theoretical percentage of whey and casein protein in skim milk?

Answer 26

- Casein: 83% | - Whey: 17%

Question 27

How were whey proteins separated from the milk solution?

Answer 27

Ammonium sulfate precipitation (salting-out procedure)

Question 28

Why did we salt-out whey proteins instead of adjusting the pH?

Answer 28

- Whey proteins do not aggregate through acidification | - Cannot be isolated by adjusting the pH

Question 29

How does salting-out whey proteins work?

Answer 29

- Whey is sensitive to high salt concentrations - Ammonium sulfate (extremely soluble) compete with whey to bind water - If the concentration is high enough, whey will no longer be able to bind to water --> precipitation

Question 30

After casein is precipitated from milk, what does the remaining solution contain?

Answer 30

- Whey - Lactose - Protein - Milk salts

Question 31

How is a Schiff base produced in the Maillard reaction?

Answer 31

Carbonyl group of a reducing sugar reacts with a primary amine to form a Schiff base

Question 32

What happens to the Schiff base in the Maillard reaction? What does it produce?

Answer 32

- Cyclizes to a glycosylamine - Undergoes the Amadori rearrangement - Results in the loss of water and the formation of a ketosamine

Question 33

What is the end-product of the Maillard reaction subjected to? What does it produce?

Answer 33

- Subjected to scission | - Produces reactive cyclic products (HMF, furfural)

Question 34

What do the reactive cyclic products of the Maillard reaction form?

Answer 34

Polymerized into brown pigments (melanoidins)

Question 35

What happens in the Strecker degradation?What does it produce?

Answer 35

- Dicarbonyl intermediates formed in the Maillard reaction react with free amino acids - Forms aldehydes, producing strong flavors

Question 36

Why can't sucrose participate in the Maillard reaction?

Answer 36

Since both of its anomeric carbons are involved in the O-glycosidic bond, inhibiting the opening of the ring structure, which hinders its reaction with the primary amine

Question 37

Does amylose or amylopectin form strong gels?

Answer 37

- High-amylose starches produce extensive hydrogen-bonding networks, allowing them to form strong gels. - High-amylopectin starches produce viscous products, as the branching of the molecules increases the molecular weight, and, thus, viscosity

Question 38

How were the composition of starch granules analyzed?

Answer 38

Through a staining procedure with a solution composed of potassium iodide and iodine, which were dissolved in water to form a triiodide ion

Question 39

What happens to the triiodide ion in amylose? What color does it form?

Answer 39

Penetrates the hydrophobic interior of the amylose helix and produces a blue color

Question 40

What happens to the triiodide ion in amylopectin? What color does it form?

Answer 40

Ions cannot form long-chains in the branched structure of amylopectin, the amylopectin-iodide complex forms a reddish-purple color

Question 41

What happens in gelatinization?

Answer 41

The chemical disruption due to heat causes amylose molecules to escape the starch granules, and amylopectin to bind to water through hydrogen bonds, which increases the thickness and viscosity due to a decreased availability of water.

Question 42

How does urea influence gelling?

Answer 42

Significantly increases the swelling of the cornstarch, contributing to the firmness of the gel by breaking hydrogen bonds to increase the space in the granule, which allowed for more water to penetrate

Question 43

How does NaCl influence gelling?

Answer 43

Decreased the swelling, and firmness, of both the cornstarch and gelatin gels as sodium chloride competes for binding with water, which reduces its contribution to gel formation

Question 44

What is the equation for water activity?

Answer 44

Aw = P/Po (T) = ERH/100