Yam Exam Questions

Question 1

Give two factors related to ambient environment

Answer 1

Temperature, oxygen level, and light

Question 2

What are the three major factors that affect the shelf life of packaged food?

Answer 2

Food, Package, environment

Question 3

Which has more influence on the shelf life of packaged food: internal or external environment?

Answer 3

Internal environment because it is directly in contact with food

External environment is still important because it effects internal environment

Question 4

What is needed to select quality factors

Answer 4

Must be
measurable, reproducible, relevant

Question 5

Sensory measurements pros and cons

Answer 5

Pro: Directly related to consumer and measures more personal attributes

Cons: labor intensive and takes more time

Question 6

Instrument measurements pros and cons

Answer 6

Pro: More precision and more objective
Con: not as close to consumer and equipment can be expensive

Question 7

Can you compare rate constants between different orders

Answer 7

With just rate constants: No because the equation is different, and the unit of the rate constant is different

With additional information: yes

Question 8

What is the definition of Aw

Answer 8

Water in food available for reactions
ALSO Vapor pressure of water in food/ separate vapor pressure of water in air at the same temperature

Question 9

What is relative humidity

Answer 9

RH = Pa/PS x 100%

Question 10

Water activity and RH migration question

Answer 10

Given Aw and RH, determine movement of water

Question 11

What is 1 atm

Answer 11

14.7 psi
1.033 kgf/cm^2
760 mmHg

Question 12

Difference between partial pressure and total pressure

Answer 12

Total pressure: Sum of partial pressures of oxygen, nitrogen and CO2 and other gasses in environment

Partial Pressure: Pressure individual gas in environment

Question 13

3 steps of permeation through plastic film

Answer 13

Absorption
Activated diffusion (diffusion in solid phase)
Desorption

Question 14

Difference between HDPE and LDPE

Answer 14

LDPE: more side branches so molecule cannot be as closely packed
HDPE: more linear and more closely packed

Question 15

Crystallinity in polymer

Answer 15

More crystallinity increases mechanical strength and makes product more opaque

More ordered than amorphous

Some light is deflected

Question 16

Excel and graphing lines

Answer 16

Excel wants to minimize sum of squared error

Question 17

Why is there a negative sign in Ficks Law of diffusion

Answer 17

It tells you that diffusion occurs in a direction of decreasing concentration (high to low)

Question 18

How to derive permeation equation

Answer 18

Adsorption and desorption depends on Henry’s law

Diffusion depends on Fick’s Law

Use mass balance equation to derive permeation equation

Question 19

Is a permeable package a good barrier?

Answer 19

No, a permeable package is not a good barrier

Question 20

Reaction control and permeation control

Answer 20

Oxygen needs to go through package (permeation)

Reacts with food product once inside package

Food product does not automatically go bad once oxygen interacts with food

Shelf life depends on permeation of oxygen into the package and reaction of oxygen with food

Question 21

Rate determining step

Answer 21

Slowest step of the reaction (permeation)

Better barrier is more resistant and thus shelf life is longer

Question 22

Steady State vs Unsteady State

Answer 22

Unsteady state: Delta p changes with time
Bit more complicated

Steady state: Delta p is constant

Question 23

Overall change in area and thickness question

Answer 23

Understand how to account for overall change when thickness and area is changed