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Food Physical Systems > Yam Exam > Flashcards

Yam Exam Flashcards

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Gourmet Food flashcards
1
Q

Air by concentration of components

A

21% Oxygen
78% Nitrogen
.04% CO2

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2
Q

Factors affecting shelf life of packaged food

A

Food, Environment, Package

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3
Q

Environmental factors for food

A

Temperature, Relative Humidity, Properties of food affected by environment

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4
Q

Relative humidity and water

A

Vapor pressure of water at certain temperature/saturated vapor pressure at same temperature x100%

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5
Q

Water Activity and moisture content

A

Moisture content involves all water molecules and water activity involves water free for reaction

Water on the surface pushes upward

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6
Q

Aw Equation

A

Aw = Pf/Ps
Pf: water vapor pressure exerted by food
Pa: water vapor pressure exerted by air

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7
Q

Relative Humidity

A

RH: Pa/Ps x 100%

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8
Q

movement of water from air into food

A

Compare RH and Aw to see if there is a gain or loss of moisture in food

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9
Q

Pressure in food

A

Convert percentage of air components in atm

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10
Q

Modified Atmosphere

A

Modified from the normal composition of air by lowering oxygen to a concentration that best suits food product

Elevate CO2 to extend shelf life and reduce respiration rate

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11
Q

Steady State vs Unsteady State

A

Steady: No change in time and used for produce
Unsteady: change in time and applied during a warming or cooling period

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12
Q

Mass Balance and energy process

A

Mass that enters system must leave the system

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13
Q

Package environments

A

Ambient: normal ranges for gas concentration and temperature
Physical: handling and shipping
Human: consumer interactions with packaging and sensory

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14
Q

Modified Atmospheric Packaging System

A

Match respiration of fresh produce and storage temperatures to create optimum gas composition

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15
Q

Sugar Caking Overview

A

Sugar cakes because of moisture and chemical composition of sugar effects absorption rate

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16
Q

Factors that Influence sugar caking

A

Relative Humidity
High levels of RH form liquid bridges between sugar granules

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17
Q

Factors influenced by sugar caking

A

Package
Sugar
Internal environment
external environment

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18
Q

Process of sugar caking

A

Moisture absorption

Liquid Bridge formation (rising RH): Result of thin liquid films due to capillary films

Binding and aggregation: more liquid is absorbed, more liquid bridges and more lumping

Recrystallization: moisture evaporates, and sugar crystallizes which enhances binding between sugar granules

Hardening: Liquid bridges solidify after moisture evaporates

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19
Q

Rate of food deterioration

A

F(Composition factors, environmental factors)

Composition: catalyst or inhibitor, pH and Aw, microbial population
Environmental: temperature, humidity, light, headspace composition

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20
Q

How do determine Quality factors

A

Measurable, reproducible, relevant

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21
Q

Sensory quality factors

A

Taste, aroma, texture
Data is closely related to consumer acceptance
Data often has high variability

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22
Q

Instrumental measurements

A

Microbial count, pH, Aw
Data should low variability
Good indicator of consumer acceptance

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23
Q

Instrumental measurements pro vs con

A

Pro: smaller data variation, continuous operation of instruments
Cons: not directly related to consumer acceptability

24
Q

Sensory measurements Pro vs Con

A

Pro: related to consumer acceptability
Con: labor intensive, large data variation

25
Q

Interpolation vs Extrapolation

A

Intra: predict values inside data points
Extra: predict values outside data points

26
Q

Kinetic Rate Equation

A

dc/dt = +/- kc^n
Rate depends on concentration and rate constant

27
Q

How to compare reactions of the same rate order

A

Compare rate constants

28
Q

Zero Order Kinetics

A

Plot Time vs A/Ao to yield a straight line

29
Q

First Order Reactions

A

Plot Ln A/Ao vs T to get a straight line

30
Q

Key Factors that you can measure for deterioration

A

Oxidation, spoilage, enzymatic reactions

31
Q

Shelf life

A

Span of time until consumer does not accept product
Graph quality factor vs time and measure the curve

32
Q

Arrhenius plot

A

Plot Ln k (y) vs 1/T (x)
K = Change in A/Ts

33
Q

Permeation through a plastic film

A

Depends on type of plastic, type of gas or vapor, gas concentration gradient and temperature

Gas moves from high concentration to low concentration

34
Q

3 steps of permeation through a plastic film

A

Molecule near wall of film diffuse onto surface

Some are absorbed and some are desorbed

Molecules move through solid film by diffusion through a solid (activated diffusion)

Diffusion governed by Fick’s Law

Adsorption and desorption governed by Henry’s Law

35
Q

Physical state of polymer

A

Solid: crystalline or amorphous
Liquid: melt
Gas: doesn’t exist

36
Q

Thermoplastic

A

Flexible linear chains
Polymer chain can slide past one another
Most water bottles and cling wrap

37
Q

Thermoset

A

Rigid 3D network
Crosslinks prevent polymer chains from sliding past one another
Will not become melt plastic
Epoxy resins and unsaturated polymers

38
Q

Crystalline polymer

A

Molecules lineup
PE has a high degree of crystallinity
Do not allow polymers enough time so it is often opaque

39
Q

Semi-crystalline polymer

A

Uses both crystalline and amorphous
Degree of crystalline
Highly crystallinity more opaque

40
Q

Various forms of Polyethylene

A

HDPE: High density PE with higher crystallinity, stiffer and a better gas barrier

LDPE: Lower density PE, clearer, better impact resistance and good heat seal properties

LLDPE: Linear Low density PE, density like LDPE with greater reduced branching, good clarity, heat sensitivity and strength

41
Q

High Barrier Polymers PVDC and EVOH Copolymers

A

Both copolymers are high O2 barrier plastics

EVOH has the advantage of being a better O2 carrier than PVDC while EVOH is more expensive and its O2 barrier decreases as relative humidity increases

PVDC has advantages of being less expensive and its O2 barrier is not affected by relative humidity.

However PVDC is considered environmentally unfriendly because it generates corrosive HCL and toxic dioxins during processing and incineration

42
Q

Chain entanglement

A

Long chains can become entangled with one another

Motion of entangled polymer chains resembles the wriggling movement of long worms

Chain entanglement is responsible for for holding polymer chains together, as it is hard to unravel long entangled chains

43
Q

Temp Time History

A

Lower temp, slower deterioration rate and better food quality
Shorter storage time, better food quality

44
Q

K value in Arrhenius Equation

A

Affected by temperature and activation energy

More sensitive for lower Ea values

45
Q

Accelerated Shelf Life Testing

A

Method used to estimate shelf life of a product in a shorter time by exposing it to elevated stress conditions.

46
Q

Procedures for ASLT

A

Conduct experiments to obtain [A] versus t for at least three temperatures

Estimate shelf life at each temperature

Use Arrhenius Plot to estimate shelf life at lower temperature

47
Q

PVC Film

A

Used to seal fresh meats and designed to cling to smooth surfaces

48
Q

Polycarbonate

A

Clear and tough, good impact strength at low temperatures

Used in reusable water bottles

49
Q

Cellophane

A

Regenerated cellulose film
Used for baked goods, candies, and tobacco products
Dries out under low humidity

50
Q

Polylactic Acid

A

Obtained by condensation of lactic acid

51
Q

Physical properties and MW

A

As MW increases, strength increases, melt viscosity also increases

chain entanglement is an important factor contributing to physical properties of polymers

52
Q

Properties of Packaging Plastics

A

Mechanical strength
Gas and water barrier
Salability
Printability
Adhesive property
Ease to process

53
Q

Process of packaging polymers

A

Extrusion of plastic film: supply mechanical energy and push resin toward die to melt with shear action. Resin cools once it exists heating system

Coextrusion

Extrusion coating

Adhesive Laminating

Extrusion Laminating

54
Q

Ficks Law of diffusion

A

Negative because molecules are moving from high concentration to low concentration

Rate of diffusion = -D * Area * (concentration difference/distance)

55
Q

Henrys Law of Solubility

A

Concentration of gas in polymer film = solubility * partial pressure

governs adsorption and desorption

56
Q

What does diffusion of molecules depend on for Hole theory?

A

Availability of sufficiently large holes (function of free volume, density and degree of packing of polymer chains)

Ease of hole formation (function of segmental chain mobility)

57
Q

Estimation for Permeation Controlled Shelf Life

A

Ts = Tolerance limit of O2/OTR through package

OTR = Q = PA/L * delta p

For O2, may need to find weight and then use Ideal Gas Law to convert to volume

Food Physical Systems (4 decks)

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