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Food Physical Systems > Yam Exam > Flashcards

Yam Exam Flashcards

(57 cards)

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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

Study These Flashcards
A

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

24
Q

Sensory measurements Pro vs Con

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A

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

25
Interpolation vs Extrapolation
Intra: predict values inside data points Extra: predict values outside data points
26
Kinetic Rate Equation
dc/dt = +/- kc^n Rate depends on concentration and rate constant
27
How to compare reactions of the same rate order
Compare rate constants
28
Zero Order Kinetics
Plot Time vs A/Ao to yield a straight line
29
First Order Reactions
Plot Ln A/Ao vs T to get a straight line
30
Key Factors that you can measure for deterioration
Oxidation, spoilage, enzymatic reactions
31
Shelf life
Span of time until consumer does not accept product Graph quality factor vs time and measure the curve
32
Arrhenius plot
Plot Ln k (y) vs 1/T (x) K = Change in A/Ts
33
Permeation through a plastic film
Depends on type of plastic, type of gas or vapor, gas concentration gradient and temperature Gas moves from high concentration to low concentration
34
3 steps of permeation through a plastic film
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
Physical state of polymer
Solid: crystalline or amorphous Liquid: melt Gas: doesn’t exist
36
Thermoplastic
Flexible linear chains Polymer chain can slide past one another Most water bottles and cling wrap
37
Thermoset
Rigid 3D network Crosslinks prevent polymer chains from sliding past one another Will not become melt plastic Epoxy resins and unsaturated polymers
38
Crystalline polymer
Molecules lineup PE has a high degree of crystallinity Do not allow polymers enough time so it is often opaque
39
Semi-crystalline polymer
Uses both crystalline and amorphous Degree of crystalline Highly crystallinity more opaque
40
Various forms of Polyethylene
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
High Barrier Polymers PVDC and EVOH Copolymers
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
Chain entanglement
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
Temp Time History
Lower temp, slower deterioration rate and better food quality Shorter storage time, better food quality
44
K value in Arrhenius Equation
Affected by temperature and activation energy More sensitive for lower Ea values
45
Accelerated Shelf Life Testing
Method used to estimate shelf life of a product in a shorter time by exposing it to elevated stress conditions.
46
Procedures for ASLT
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
PVC Film
Used to seal fresh meats and designed to cling to smooth surfaces
48
Polycarbonate
Clear and tough, good impact strength at low temperatures Used in reusable water bottles
49
Cellophane
Regenerated cellulose film Used for baked goods, candies, and tobacco products Dries out under low humidity
50
Polylactic Acid
Obtained by condensation of lactic acid
51
Physical properties and MW
As MW increases, strength increases, melt viscosity also increases chain entanglement is an important factor contributing to physical properties of polymers
52
Properties of Packaging Plastics
Mechanical strength Gas and water barrier Salability Printability Adhesive property Ease to process
53
Process of packaging polymers
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
Ficks Law of diffusion
Negative because molecules are moving from high concentration to low concentration Rate of diffusion = -D * Area * (concentration difference/distance)
55
Henrys Law of Solubility
Concentration of gas in polymer film = solubility * partial pressure governs adsorption and desorption
56
What does diffusion of molecules depend on for Hole theory?
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
Estimation for Permeation Controlled Shelf Life
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 (5 decks)

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