Food Packaging Moisture Control Quiz

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Questions and Answers

What factors primarily affect the rate of moisture permeation through packaging films?

Nature of the film and its thickness (correct)

Food weight and area of film

Water vapor partial pressure inside the food

Temperature and film area (correct)

Which of the following conditions is assumed about the package head space?

It is unaffected by temperature variations

It is large and provides resistance to mass transfer

It is small and offers little resistance to mass transfer (correct)

It offers uniform moisture but has significant mass transfer resistance

In the context of food moisture sorption, which variables are included in the equation for moisture content?

Nature of the package and head space volume

Film area and outside temperature

Nature of the food and water vapor partial pressure (correct)

Thickness of the film and temperature

What assumption is made regarding the food moisture content when analyzed in relation to the packaging environment?

It remains in equilibrium with the package environment Signup and view all the answers

Which of the following factors does NOT directly influence the rate of moisture sorption in food?

Type of packaging material used Signup and view all the answers

How is the water vapor partial pressure inside a package (aW) calculated?

aW = pW / pWo Signup and view all the answers

Which assumption implies uniform moisture content in food at any given time?

The resistance to moisture diffusion in the food is negligible Signup and view all the answers

What parameters are stated as constant for evaluating the moisture balance in the food-package system?

Temperature and relative humidity Signup and view all the answers

What is the value of the moisture content that signifies the limit of the fruit bar's shelf life?

0.10 g water/g dry solids Signup and view all the answers

What slope represents the moisture content change in the isotherm for the fruit bar?

0.12 g water/g dry solids per unit aw Signup and view all the answers

What is the moisture content of the fruit bar at 20% relative humidity?

0.05 g water/g dry solids Signup and view all the answers

How many total grams of dry solids are in the four fruit bars?

500 g Signup and view all the answers

What is the correct relationship expressed in equation (6) regarding moisture content?

pW1 - pW2 = (pWo/b)(me - m) Signup and view all the answers

What does equation (8) express about the change in moisture over time?

dm/dt = PW A pWo (me - m) Signup and view all the answers

What is the temperature condition for storing the fruit bar?

25°C Signup and view all the answers

What is the surface area of the pouch required to package the four fruit bars?

0.15 m² Signup and view all the answers

What is the moisture content of the fruit bar that represents the limit of its shelf life?

0.10 g water/g dry solids Signup and view all the answers

At what temperature and relative humidity is the fruit bar expected to be stored in the mentioned region?

25°C and 20% RH Signup and view all the answers

What is the vapor pressure of pure water at 25°C in atm?

0.0313 atm Signup and view all the answers

What element of packaging is most important to prevent microbial growth in the fruit bar?

Low moisture content Signup and view all the answers

What is the significance of the P W value in the context of shelf life?

It indicates the rate of oxygen permeation. Signup and view all the answers

Which material has the lowest P W value that is analyzed for the packaging of the fruit bar?

LDPE Signup and view all the answers

Which polymer film has the highest P W value?

PVC Signup and view all the answers

What is the slope of the moisture isotherm curve relevant to the fruit bar?

0.12 g water/g dry solids per unit aw Signup and view all the answers

What factor does NOT influence the rate of oxygen permeation through the film?

Food water activity Signup and view all the answers

What is the function of the film area (A) in oxygen permeation?

To influence the speed of oxygen diffusion Signup and view all the answers

How much total weight does the pouch require to package four fruit bars of 125 g each?

500 g Signup and view all the answers

Which polymer film would be closest to providing a 12 month shelf life based on the P W values?

PET Signup and view all the answers

Which packaging material comes closest to providing a shelf life of 12 months based on the given P W values?

PET Signup and view all the answers

In the unsteady-state material balance, which assumption is made regarding the package headspace?

It has uniform concentration at all times. Signup and view all the answers

Which parameter affects the rate of oxidative reactions in food packaging?

All of the above Signup and view all the answers

Which of the following factors does not affect the rate of oxygen permeation through the packaging film?

Food weight Signup and view all the answers

What assumption is made regarding the package headspace?

It has a uniform concentration at any time. Signup and view all the answers

Which parameter is least likely to influence the rate of oxidative reactions in food?

Thickness of the package film Signup and view all the answers

In the unsteady-state material balance, what is assumed about the resistance to oxygen diffusion in the food?

It is negligible and uniform concentration is assumed. Signup and view all the answers

Which of the following factors does not influence the rate at which oxygen reacts with food?

Film area Signup and view all the answers

What does the term 'equilibrium with the package environment' refer to in the context of food packaging?

Oxygen concentration inside the food mirrors that in the package. Signup and view all the answers

Which combination of parameters is critical for determining the oxygen permeation rate?

Nature of the film and film area Signup and view all the answers

According to the assumptions made, what condition must remain constant for accurate analysis?

Temperature and food moisture content Signup and view all the answers

What is the critical value of oxygen concentration in peanut butter that must not be exceeded to avoid oxidative rancidity?

100 ppm Signup and view all the answers

Which equation relates to the steady-state condition for oxygen concentration in the jar?

$PO A pO1 = QOs W$ Signup and view all the answers

What is the surface area of the jar containing peanut butter?

500 cm² Signup and view all the answers

What is the oxygen permeability of HDPE at 30°C?

$10.6 \times 10^{-11}$ mL O$_2$.cm/cm².sec.cm Hg Signup and view all the answers

What assumption is made about the closure of the jar?

It is considered impermeable. Signup and view all the answers

What is the thickness of the jar material used for the peanut butter container?

0.05 cm Signup and view all the answers

What is the density of oxygen at 30°C?

1.43 x 10^-3 g/mL Signup and view all the answers

What happens to the headspace oxygen concentration when the jar is sealed?

It remains at 0% O$_2$. Signup and view all the answers

Study Notes

Food Packaging

Food packaging systems involve moisture and oxygen transfer, impacting food quality and safety.
Moisture permeates through packaging films, diffuses through air spaces, and sorbs/desorbs within the food.
Permeation rate depends on film properties (e.g., permeability), thickness, area, pressure difference, and temperature.
Food moisture sorption depends on food type, weight, water vapor pressure inside the package, and temperature.

Material Balance

Package headspace is small, offering minimal resistance to mass transfer.
Resistance to moisture/oxygen diffusion within the food is negligible.
Food moisture content equilibrates with package environment and simple relationships with water vapor partial pressure (Pw2).
Environmental temperature and relative humidity are constant.
Input + Generation = Output + Accumulation (general material balance equation)
A key equation for moisture transport is: dm Ws = Pw A (pw1-pw2)/X (moisture transport equation)

Moisture Isotherm

The linear isotherm describes the relationship between moisture content and water activity (aw) of food.
The equation for linear isotherm is: m = b aw + c.
Constants (b and c) depend on the specific food and temperature.
Pure water vapor pressure at temperature (pwo) is used in calculations.

Oxygen-Sensitive Foods

Oxygen permeates through packaging film, diffuses through air spaces, and reacts with food within.
The rate of oxygen permeation depends on film properties, thickness, area, pressure difference (external vs internal), and temperature.
Oxidation reactions depend on food type, weight, oxygen partial pressure (inside package), temperature, and water activity (aw).
A critical equation for oxygen transport is: dVou/dt= Po A (p01-p02)- dVor/dt.

Unsteady-State Material Balance

The permeation rate is described by equations, assuming steady-state mass transport across the film.
The package headspace offers little resistance to oxygen transfer.
There's negligible oxygen diffusion resistance in the food.
An equation to illustrate is: dVou/dt = Po A (p01-p02)- rro W/X

Simplified Steady-State Model (Oxygen)

Oxygen reacts with food immediately after entering the package.
Food-package systems quickly reach a steady state.
A critical value Qos (cm³/g) determines when the food becomes unacceptable.
An equation for shelf life is: ts = Qos W X / (Po A p01).

Moisture-Sensitive Food (Fruit Bar)

Intermediate moisture fruit bars become unacceptable with excessive or insufficient moisture.
Shelf life is limited by the water activity.
Specific fruit bar data (e.g., initial moisture content, moisture isotherm, packaging characteristics) are used to calculate the shelf life.

Oxygen-Sensitive Food (Peanut Butter)

Peanut butter is sensitive to oxygen, leading to oxidative rancidity.
Maximum acceptable oxygen absorption is 100 ppm.
The thickness of the container will be a factor in shelf-life calculations.
Jar surface area, material permeability, and other parameters influence shelf life calculations.

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Description

Test your knowledge on the factors affecting moisture permeation in packaging films, the assumptions related to food moisture content, and the calculation of water vapor partial pressure within packaging. This quiz covers essential concepts related to moisture balance in food-package systems.