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2) Food Chemistry I > Laboratory > Flashcards

Laboratory Flashcards

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1
Q

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

A

Cornstarch particles would have accounted for scattering losses

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2
Q

What is the consequence of scattering losses?

A
  • Intensity of light leaving the sample: lower

- Decrease the percentage transmittance

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3
Q

What is the consequence of a decrease in percentage transmittance?

A
  • Related to absorbance in a logarithmic manner

- Absorbance increase

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4
Q

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

A

Measured absorbance would have been higher than filtered

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5
Q

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

A
  • 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
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6
Q

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

A
  • Beer’s Law only interprets the absorption of dilute samples (surpassed 0.01 –> deviations)
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7
Q

What is precision?

A

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

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8
Q

What is accuracy?

A

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

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9
Q

What is Beer’s Law?

A
  • 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).
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10
Q

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

A

molar absorptivity

path length

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11
Q

What is hydrogenation? Why is it used?

A
  • 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
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12
Q

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

A
  • 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
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13
Q

What is the method to determine the iodine value?

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

- The sample is titrated with sodium thiosulfate

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14
Q

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

A
  • –CH=CH– + 2ICl –ICH-ICH– + 2HCl
  • ICl + KI KCl + I2
  • 2Na2S2O3 + I2 2NaI + Na2S2O3
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15
Q

What is the definition of the saponification value?

A

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

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16
Q

What does the saponification value indicate?

A

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

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17
Q

How is the saponification number related to the boiling point?

A

The lower the saponification number, the higher the boiling point

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18
Q

What can pass through a dialysis bag?

A

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

19
Q

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

A
  • 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
20
Q

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

A

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

21
Q

What is the product formed from the ninhydrin reaction?

A

Ruhemann’s purple (blue-purple)

22
Q

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

A
  • Ammonia
  • Hydrindantin
  • Aldehyde
  • Carbon dioxide
23
Q

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

A
  • 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
24
Q

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

A
  • Adding a base (NaOH)

- Produces sodium caseinate, and increases the pH

25
Q

Why is sodium caseinate dispersable in water?

A

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.

26
Q

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

A
  • Casein: 83%

- Whey: 17%

27
Q

How were whey proteins separated from the milk solution?

A

Ammonium sulfate precipitation (salting-out procedure)

28
Q

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

A
  • Whey proteins do not aggregate through acidification

- Cannot be isolated by adjusting the pH

29
Q

How does salting-out whey proteins work?

A
  • 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
30
Q

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

A
  • Whey
  • Lactose
  • Protein
  • Milk salts
31
Q

How is a Schiff base produced in the Maillard reaction?

A

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

32
Q

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

A
  • Cyclizes to a glycosylamine
  • Undergoes the Amadori rearrangement
  • Results in the loss of water and the formation of a ketosamine
33
Q

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

A
  • Subjected to scission

- Produces reactive cyclic products (HMF, furfural)

34
Q

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

A

Polymerized into brown pigments (melanoidins)

35
Q

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

A
  • Dicarbonyl intermediates formed in the Maillard reaction react with free amino acids
  • Forms aldehydes, producing strong flavors
36
Q

Why can’t sucrose participate in the Maillard reaction?

A

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

37
Q

Does amylose or amylopectin form strong gels?

A
  • 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
38
Q

How were the composition of starch granules analyzed?

A

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

39
Q

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

A

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

40
Q

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

A

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

41
Q

What happens in gelatinization?

A

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.

42
Q

How does urea influence gelling?

A

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

43
Q

How does NaCl influence gelling?

A

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

44
Q

What is the equation for water activity?

A

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

2) Food Chemistry I (31 decks)

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