Chapter 9 Flashcards
Green patches on potatoes indicate increased levels of solanine, which is a
glycoalkaloid poison that might pose a risk to human health. Solanine is an
example of a …… present in food.
a. Environmental contaminant b. Natural toxin c. Harmful additive
A
In solutions with high concentration of salt, bacteria lose water due
to high …… pressure in the solution. (one word, small letters)
Osmotic
What is the major means of food preservation
Thermal (heat) processing
What is the utility of heat processing
Heat can denature proteins , inactivate enzymes , and gelatinize
starches.
Heat kills microorganisms by denaturing their proteins and
inactivating their enzymes
3 basic levels of heat treatment
Sterilization (hospital) Commercial sterility (food) Pasteurization/blanching
definition of sterility
: No living forms are alive or biologically
No spores, no vegetative cells
When sterility is achieved
Sterility can only be considered achieved when all parts of a product
have been heated to 121 C (reached by using steam) and held at that
temperature for 15 min
Why sterilization is used only in labs and hospitals
Under these very harsh conditions, foods would effectively become
inedible and of very poor nutritional quality
Commercial sterility refers to
Canning processing
Definition of commercial sterility
Definition of commercial sterility: all pathogenic and toxin forming
vegetative organisms are killed and their spores are inactivated, to
the extent that they cannot reproduce.
Commercial sterility is a practical level of sterility that ensures safety
while maintaining the food’s quality attributes (flavor, color, texture,
nutritional value) to a reasonable extent and gives a shelf life of >2
years.
Who is more resistant to heat: spores or vegetative cells
Vegetative cells
For low acid foods, canning refers to
), canning processes specifically target
heat resistant spores of Clostridium botulinum
Where C.botulinum can grow and what dies it produce
C. botulinum is ubiquitous and capable of growing in the anaerobic
environment of canned food (hermetically sealed) and producing
botulinum toxin, a deadly neurotoxin that kills if ingested in
microgram quantities.
In high acid foods ( pH ≤ 4.6 ), spores of C. botulinum are incapable
of germinating (i.e., of being reactivated to the toxin producing
vegetative state).
What temperatures are required for low-acid foods to be commercial sterile
temperatures higher than the boiling
point of water are required to achieve commercial sterility (spores can
survive for > 5 hours at 100 C).
High temperatures required to inactivate spores are provided by
steam under pressure
What temperature can water vapour reach under pressure
10 psi = 116 C 15 psi = 121 C 20 psi = 127 C
Pasteurization: what temperature, target and the result of this treatment requires
Pasteurization is a less severe heat treatment, usually below the
boiling point of water
Pasteurization of milk targets vegetative cells of pathogenic
microorganisms such as Mycobacterium tuberculosis that are relatively
thermally resistant
Pasteurization results in a limited shelf life extension on its own as
some food spoilage organisms, particularly spores , survive the
process and are the source of new vegetative outgrowths.
Refrigeration is usually required to extend the benefits associated
with pasteurization.
What is blanching and when it is used
Blanching is a short heat process similar to pasteurization but its intent
is to denature (knock out) deleterious enzymes in fruits and
vegetables, such as:
polyphenol oxidase (enzyme responsible for enzymatic browning
lipoxygenases (produce off flavors by catalyzing lipid oxidation )
Blanching is commonly carried out prior to freezing, high pressure, or
other non thermal processes to minimize enzymatic deterioration
during processing and storage.
Thermal processing is a balance of ___
destruction of
microorganisms/enzymes and maintenance of product quality
attributes (flavor, nutritional value, color, texture, etc.).
Cardinal rule in thermal processing
Safety takes precedence over all else
Thermal processing is based on the following scientific approach:
understanding time/temperature combinations and their effects on
microorganisms of concern
understanding the heat penetration characteristics of a product
calculating appropriate thermal processes for the food product based on (1)
and (2)
validating the efficacy of thermal processes
What is done to check if the method kills C.botulinum
C. botulinum is too dangerous to use in step ( 4 ) so a less dangerous
but even more temperature resistant spore former is used instead,
such as:
Clostridium sporogenes PA 3679 (PA = putrefactive anaerobe), or
Bacillus stearothermophilus
Concept: If the spores of these organisms are adequately destroyed
by a thermal process, then we should also be safe from C. botulinum ,
which is thermally less resistant.
Sterility is achieved by holding a sample at ……
C for 15
minutes. (answer with a number)
121
In terms of cell number commercial sterility is
1 million ( 10 6 ) spores in a can, a thermal
process that results in the reduction of the spore population by 12
logarithmic cycles to 10 6 spores represents
Interpretation of 10 6 surviving spores:
Statistically, there is only one
living spore in 10 6 cans.
Microbial death is assumed to follow a ___
Logarithmic rate function
What is decimal reduction type
The decimal reduction time (D value) is the heating time at a given
temperature required to reduce the microbial population by one log
unit
How many Ds is required to go from 10^6 to 1
6d
How many Ds is required for commercial sterility
12 D
How to obtain D value
The D value is a characteristic of a particular organism and is
determined experimentally by performing a standard plate count on
samples that have been heated for different amounts of time
Death rate ___ with increasing temperature
Increases
What happens to the slope of the graph and D value with increasing temperature
Accordingly, at a higher
temperature , the slope of this
plot would be steeper and the
D value would be smaller
What is z-value and how to calculate it
The magnitude of the effect of a given increase in temperature
depends on the thermal resistance (z value) of the organism :
Value of z can be obtained by determining D values at several
temperatures and plotting log D vs. temperature
z = temperature increase corresponding to reduction of D by one
log cycle (i.e., by a factor of 10
z=(T2-T1)/(log d1-log d2)
For example, if z value of the organism = 18 C and D 100 = 20 min,
then D 118 = 2 min. Calculate the amount of time needed for commercial sterilization at 100,118,82
At 100 o C, a 12D process will take 12 20 min = 240 min.
At 118 o C, a 12D process will take 12 2 min = 24 min.
At 82 o C, a 12D process will take 12 200 min = 2400 min (40 h).
What combination of temperature/time is used in commercial sterilization
Many time/temperature combinations will have the same lethality
(i.e., be equally effective in killing).
In general, shorter heating times at higher temperatures are less
detrimental to quality attributes than longer heating times at lower
temperatures.
Example of heat treatment for sweetened condensed milk to make it bad product and good
330 min @ 100 C off flavored brown milk is produced (Maillard
reaction)
0.78 min @ 127 C white, high quality product is produced
Drawback of HTST
Drawback to high temperature/short time (HTST) processing
More precisely controlled ( expensive ) equipment is needed to attain
accurate temperature and contact time control .
… …
is the heating time at a given temperature required to
reduce the microbial population by one log unit
D-value
Two types of thermal processing:
(1) Conventional processing : package first, then process thermally
traditional canning
(2) Aseptic processing : process thermally first, then package (tetra
brick type ) suitable for HTST processes
What equipment is used for canning
The simplest equipment used for canning is a batch retort , which is a
large pressure cooker in which steam under pressure is the heat
transfer medium.
Thermal processing with this type of equipment is a batch process (as
opposed to a continuous process)
Cans are filled and sealed and then loaded into the retort.
What is the basic steps in retort processing
The retort is sealed and filled with steam at the pressure required to
reach the desired process temperature [psi = pounds per square inch],
The retort is held at the process temperature for the required amount
of time ( hold time
The steam is then turned off and the retort is flooded with cold water .
When cooled to room temperature , the retort is
What is a hydrostatic cooker and cooler
cooler is a modified U shaped
tube filled with water and
steam that processes filled
containers
At what temperature microorganisms start to die
depends on thermal resistance value (Z)
What is done to obtain To obtain a time/temperature plot showing how a product heats up in
a retort
thermocouples are inserted in the cans and hooked up to a
data logger.
What is a cold point
or slowest heating
zone ) in each can because in the can
why thermocouples are placed in cold points
each particle of food must reach the
selected temperature specified and be held for the requisite time to
attain commercial sterility
On what characteristic the position of the thermometer depends
The location of the cold point ” depends on the type of heat transfer
that is predominant in the food
In solid foods (e.g., canned meat): Heat is transferred (slowly) by
conduction , i.e., from molecule to molecule .
In fluids/liquid containing foods : Hotter liquid rises convection
currents : more rapid heat transfer but rate is strongly dependent on
viscosity
Difference between conduction and convection insertion points for themometer
Conduction (solid food): cold point = center of the can Convection (liquid food): cold point = center of the can one third up from the bottom
Example of food that as both convection and conduction
Canned pineapple
How the heat transfer can be changed during processing
e.g., in products containing starch, heating to the gelatinization
temperature increases the viscosity of the liquid ” phase, which slows
down the rate of heat transfer
How should we obtain the temperature at which we should do the processing of the food
standardized foods in standardized
containers (e.g., cans), extensive tabulated data is available and can
be used with confidence.
Milk is …… when it immediately comes out of a healthy cow’s udder.
(one word, small letters)
sterile
During wine making, sulfur dioxide is used as a …… agent.
one word, small letters
preservative
During pickling, salt pulls …… out of vegetables immersed in brine.
(one word, plural, small letters)
sugars
…… is used to remove the bitter flavor from green olives before pickling. a. Lye solution b. Brine c. Olive oil
A
…… molds are used to produce tempeh, a cooked,
mashed cake of soybean (one word, capital first letter)
Rhizopus
…… fermentation turns cocoa beans into chocolate. a. Lactic acid b. Acetic acid c. Yeast d. Molds
Acetic acid
What s aceptic processing
: The food is first thermally processed and then
filled into pre sterilized containers followed by sealing with a pre
sterilized closure in an aseptic environment (i.e., an atmosphere free
of microorganisms).
Now aceptic processing is used to ___
Produce commercially sterile products
aceptic processing is useful for
heat sensitive products
Another name of aseptic processing on heat sensitive products
high temperature/short time (HTST)
processing .
3 stages of aceptic processing evolution
1 ) Batch processing: Pasteurization at 62.5 C for 30 min , then
2 ) 1930 s: Development of continuous HTST pasteurization, e.g., at 71 C
for 15 seconds followed by rapid cooling to 2 C and then packaging.
(3) 1970s: Development of UHT (ultra high temperature) processing, at
>100 C for ~1 second , usually by direct steam injection , followed by
rapid cooling and aseptic packaging .
Most dairy processors in North America pasteurize milk by using ____
a plate
heat exchanger : very efficient heat transfer due to high surface area
UHT produces what product
UHT processing produces a commercially sterile product: no refrigeration is
required (until package is opened), e.g., milk or cream “portion packs” for
restaurants (where they can stay on counter/table).
Advantage of aseptic processes
( Continuous
( Allow for very high and efficient heat transfer rates
(3) Heat transfer is not constrained by the container (size,
E.g., A high quality institutional can of ketchup can be prepared
aseptically whereas quality is severely compromised by conventional
thermal processing.
What is tetra brick system
The tetra brick is a folded sterile package made on site from a single
roll of laminate (cardboard, aluminum foil and
Integrated process : package forming machines are part of the
production line.
What is the productivity rate of aseptic processes
20000 packages/hour
What is used for sterilization of sanitary packaging
UV
Hydrogen peroxide
Many other types of packages can also be formed on site, including
coffee creamers, pouches, plastic bottles, or form filled trays
HTST pasteurization of milk is done by holding milk at ……
C for 15
seconds and then cooling to 2 C. (answer with a number)
71
What dictates which type of processing is employed
Economics and product characteristics
Other types of “thermal” processes include:
Microwave heating Ohmic heating Pulsed electric fields
All thermal processes require
stringent evaluation and validation to
ensure commercial sterility or adequate pasteurization.
There is a substantial level of government regulatory oversight over
thermal processes because of the risk that improperly processed
products pose.
Sterilization is a convenient method for preserving food products A. True B. False
False
…… steam is used to reach temperatures above the boiling pion of
water during commercial sterilization (one word, capital first letter)
Pressurized
During pasteurization, temperatures …… boiling point of water are used a. Below b. Equal to c. Greater than
Below
How cold processing helps in preserving food
Cold processing reduces the chemical reaction rate in food
Chilling does not kill most microbes or denature enzymes
It just slows the deterioration of food
Rate of spoilage increases when food is brought back to room temperature
Refrigeration : advantages
, the gentlest way to store food, causes few flavor or
texture changes
The more ___ food is chilled, the better the quality and nutritive value
rapidly
Variables to control during refrigeration
temperature, air circulation, humidity, and gas
atmospheres
Ideally refrigeration occurs ___
right after harvest or slaughter
Refrigerators are designed to maintain temperatures below
4 C
40 F)
What is the coldest section in the fridge
Because cold air sinks , lower sections of a home refrigerator are
colder than top sections
How air circulation helps to preserve food in the fridge
Air circulation helps move heat away from food
What is important in the fridge in regards to humidity
Circulating air must be at the right humidity level to maintain
freshness
If too low , moisture will be pulled from food causing foods to dry out
Humidity is best controlled with proper packaging
What is respiration in food
Animal and plant tissue absorb and give off gas, a process called
respiration
How can you extend shelf life of the product influencing respiration
Changing the gas content can halt respiration and extend a food s
shelf life
Replacing oxygen with carbon dioxide prevents the chemical reactions that
cause food spoilage
Refrigeration can also cause undesirable changes in food , such as
bananas turning black bread staling faster tomatoes becoming mushy foods absorbing flavor and odors from other foods stored in the same refrigerator
Food processors reduce the temperatures of some foods to
extend their shelf life
allow for proper aging of cheese, beef, and wines
make products like bread and roasted meats firmer prior to slicing
Ethylene is produced during refrigerated storage of bananas. To avoid premature spoilage, the gas is removed by proper …… a. Refrigeration b. Air circulation c. Humidification
B
Why freezing technology is important for industry
Freezing has allowed products to be stored and presented in ready
to eat form (e.g., Pizza)
What invention assisted in convenience of frozen foods
Microwaves
Dissolved solutes results in
Freezing point depression
What is eutectic point
when residual water and all solutes co crystallize
the eutectic point for most foods lies
Below -50C
Commercial frozen products are held at
-18C (0F), where most (99%) is the crystalline form
Why commercial products are kept at -18C
C provides a balance between product quality and energy costs
Is there any chemical reactions happening when food is frozen
Yes, Therefore frozen foods continue to deteriorate albeit much more
slowly
Some changes which can take place in foods during freezing or when
frozen
Solubility reduction e.g., Crystallization of lactose in ice cream sandy
grainy texture
Protein denaturation due to salting out loss of water holding capacity
in meat, fish
Changes in pH due to concentration of inorganic and organic acids can cause protein denaturation/coagulation Destruction of sensitive emulsions Loss of gas solubility beer, soft drinks
…… is the temperature at which a particular mixture freezes. a. Freezing point b. Eutectic point c. Cold point
B
Why water freezing is unusual
Water is unusual in that it expands rather than contracts upon
freezing will burst pipes, bottles
This behavior is due to hydrogen bonding between H 2 O molecules
Ice crystal role of freezing
Formation of large ice crystals within cells can disrupt and cause
damage at the cellular level
Basic rule: slow freezing produces large ice crystals damages
tissues, f ast freezing produces smaller ice crystals less damage
Crystal size dependent upon freezing rate
What factors can influence the rate of freezing
The thicker the package , the longer it takes to freeze to the center
The colder the temperature , the faster the food freezes
As airflow increases , the rate of freezing increases
Other factors related to freezing rate
Temperature differential Surface area/product shape Air velocity Heat transfer characteristics Composition (product specific heat)
What is cryogenic freezing
It is therefore best to use a large temperature differential to drive the
freezing process whenever possible i.e., cryogenic freezing liquid
nitrogen (- 198 C)
Very costly
The base cost is considered to be about___
10 of the product
Freezer temperature usually fluctuate
from -22 to -12 C
What is sublimination of water
the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage.
Temperature fluctuations will cause
Temperature fluctuations cause changes in the ratio of water : ice
which results in sublimation of water from smaller ice crystals to
larger ones over time can cause damage
Freezer temperature cycles
Freezer temperature cycles take place approximately every 2 hours ,
typically ~4,000 cycles/year hence temperature is not static nor is
ice : water ratio
These temperature cycles contribute significantly to quality
deterioration
When most of deterioration happens with freezed food
Most quality deterioration takes place during thawing
Ice concentrated components (salting out) start to react and
microorganisms start to grow
Microwave thawing has improved this situation dramatically
shortens thawing time reduces microbial outgrowth
……. is a short heat process similar to pasteurization but its intent is to denature
deleterious enzymes in fruits and vegetables (one word, capital first letter)
Blanching
Food is first thermally processed and then filled into pre sterilized containers followed by sealing a. Aseptic processing b. UHT c. HTST
A
Subjecting milk to temperatures >100
C for ~1 second using direct
steam injection is …… (Three letters acronym, all capital)
UHT
Apple juice freezes at 0 C A. True B. False
False
I don t buy frozen food products on sale. Their quality is inferior to those which are not. a. True b. False
False
What is home freezing
food is frozen by exposure to still air , which means it is not moving
What is commercial freezing (3 ways)
contact with cold air, either still or moving indirect contact with a cooling medium immersion into a cooling medium
Still air (sharp) commercial freezing is alike to
Slow/common method in freezer at home
At what temperature sharp freezing happens
Basically an insulated room maintained at 23 to 30 C with some air
circulation
To what products sharp freezing is applied
Generally used for storage of products previously frozen by other
means or used to freeze “rate insensitive” products , meaning to those to which the size of ice crystals is not important e.g., Ice cubes
Blast freezing is performed using
Use of high velocity air to speed the freezing rate using high speed
fans
Sharp vs Blast freezing
30 lb can of egg yolk freezes in 72 hrs in sharp freezer vs. 12 18 hrs
in a blast freezer both are batch operations
Apart from sharp and blast freezers , what other freezer is used for batch operations
Plate freezers, which use
indirect contact to speed up the freezing (heat transfer) process. Freezers something flat
What is a tunnel freezer, for what product it is used
3 ) Tunnel freezer Product placed on trays or mesh belt and run counter current to high velocity cold air continuous process Typical product is "individually quick frozen" (IQF) shrimp Freezing is very rapid/efficient
Tunnel freezer: problem
Problem is maintaining control over product dehydration ( freezer burn ) due to ice sublimation Moisture loss is controlled by spraying a water mist on product to coat it with a thin layer of ice so this moisture sublimes rather than losing water from within the product
What is freezer burn and when it can happen
Freezer burn is caused by ice sublimating or evaporating from a
frozen food product
Damaged packages and air pockets allow moisture to escape
Food cannot regain lost moisture, which causes damage to the surface of the
food
What is done to avoid freezer burn
To reduce freezer burn, freeze food quickly and avoid thawing and
refreezing
Indirect contact plate freezer is used for, and how the freezing is performed
Commonly used for flat packed products , e.g., fish, fruits and
vegetables, hamburger patties
Refrigerated plates press package between them using pressure to
give good contact and efficient conduction
Freezing food in an insulated room maintained at 23 to 30 C with some air circulation is a. Blast freezing b. Sharp freezing
B
Scraped surface heat exchanger: what work principals are used for what product are freezed with it
Scraped surface heat exchanger
Use ethylene glycol in the exterior jacket as a coolant
Commonly used to freeze pre concentrated products i.e., Orange
juice concentrate obtained from an evaporator
High surface area, forced convection, excellent heat transfer
characteristics and continuous
Immersion freezing: for what products and what is used for it
) Immersion freezing
Packaged product immersed in refrigerated medium such as
ethylene glycol ( 67 C), sugar or salt solution resulting in good
contact, good heat transfer, excellent for irregular shaped products
Typical product shrink wrapped, turkey/chicken
Refrigerated brine is used where
used in fishing industry on board boats to freeze
fish
cryogenic freezing lies between ___ and ___ freezing
A technology that lies between static and immersion freezing
Common cryogenics and their boiling temperature
liquid nitrogen (- 196 C) and liquid CO2 ( -79 C)
Explain cryogenic freezing with nitrogen
Liquid N 2 provides great cooling force Δ T)
Latent heat of evaporation from the change of state from a liquid to
gas (phase transition) 196 to 195 C ) is 200 kj/kg
An additional 186 kj/kg is absorbed in going from 195 C to 18 C
How much heat per kg of product is removed with liquid nitrogen going from liquid to vapour
386 kilojoules of heat/kg of product
What is done to N2 to obtain efficient cooling
sprayed onto the product on a
continuous wire mesh belt
Liquid nitrogen requires no primary refrigerant compared to
Ammonia or freon
How liquid nitrogen is obtained
By direct gas compression
Advantages and disadvantages of liquid nitogen
Non toxic, non ozone deteriorating, displaces air and produces a
very superior frozen product but very expensive
How freezing with carbon dioxide occurs
Dry ice (solid) can be mixed with product directly cools product as it
sublimes
High pressure liquid CO 2 turns to dry ice when sprayed due to reduction
in pressure
Dry ice “snow” then sublimes to gaseous CO 2 to cool product
What is better to use CO2 or nitrogen for freezing?
On an equivalent weight basis, CO 2 can absorb 2x as much energy as
liquid nitrogen , making up for the temperature differential 79 vs 196
C)
Hence CO 2 freezing can be competitive in certain applications
What are new technologies in freezing
There is a slow migration to more advanced super freezer ” freezing
and storage systems operating at ~ 60 C
This brings us to eutectic temperatures and result in very high quality
maintenance
This can be beneficial for high value products like tuna
Why refrigeration and freezing can be inconvenient
A crucial process from the standpoint of convenience but involves an
ongoing cost can thus become very expensive especially if the
product does not turn over rapidly in the market
What is an indicator of perishability
Water activity
Categories of processed foods preserved by reduced water activity
are
dehydrated concentrated intermediate moisture
Orginally drying was based on ___ energy
Solar
Disadvantages of solar drying
Simple drying is limited to reducing moisture content to 15
Uncontrolled susceptible to weather patterns
Susceptible to contamination (microbes, insect and
Solar drying advantages
Simple Low tech Low cost Still used extensively today coffee, cocoa, apricots
More controlled drying is known as
Food dehydration
Well designed dehydration processes can readily reach moisture
contents of
1-5%
Advantage of food dehydration
Biggest benefit is that all dried products can be preserved for an
extended period of time
Other benefit is reduction in weight (but not always a reduction in
bulk or volume)-> lower transportation cost
The challenge associated with dehydration technology
reconstitution to produce a product somewhat similar to the starting
material
If successful one has convenience just add water instant mashed
potatoes, instantized milk, instant pudding …
…… % is the lowest moisture content that can be achieved by
traditional methods of food dehydration (answer with a number)
15
Principles of drying
Depends on the relationship between heat and mass transfer
Heat (energy) must be transferred into the product to convert the
moisture into water vapor and the vapor (mass) has to be moved
out of the product
Maximizing heat/mass transfer is the key to efficient dehydration
technology
What should be done with surface area for better evaporation
Maximizing surface area provides for maximal heat and mass
transfer
There is an exponential relationship between surface area and
particle size
More surface area better heat/mass transfer
What is a product profile parameter in drying
Product profile minimize the distance heat has to travel in and moisture to travel out Equivalent volume packages differing surface areas
What is relative humidity
The amount of moisture that air can hold at a particular
temperature
How to take moisture out of the product
Temperature differential between the heating medium and the
product (driving force for heat transfer)
Relative humidity of the air used for drying (related to temperature)
a food product will either lose or gain moisture as a function of the relative humidity of its environment (usually air)
The amount of water that warmer air can hold is ___
Higher
What does it mean saturated air
RH is 100%
If air having a starting RH of 0% is used to dry a product at 20 or 30
C, what temperature will be more efficient at taking the moisture
the air at 30 C will be much more efficient for drying as it
capable of picking up and holding much more water before it
becomes saturated
When the product will not gain or lose moisture
The only time no loss or gain of moisture will occur is when the relative
humidity of the air and food product are identical
Or
Aw* 100 = RH
Sharp freezing is a continuous process. A. True B. False
B
The freezing agent is …… in a tunnel freezer. a. High velocity cold air b. Ethylene glycol c. Sugar solution spra y
A
Food is immersed in liquid CO 2 to be frozen. A. True B. False
B
The total amount of energy that is absorbed by liquid nitrogen per kg of food is
…… kilojoules during cryogenic freezing when the product reaches 18 C. (answer
with a number)
386
What is moisture sorption isotherm
Change in weight (water activity) in relation
to RH at a specific
temperature
How we construct moisture sorption isotherm
Set up a series of hermetically
sealed chambers containing
different saturated salt
solutions
After 3 days, measure the change in weight as a function of RH
The product should be weighted before and after the experiment
Plot the change in weight of the product against the relative
humidity associated with its corresponding RH chamber
What salts should be chosen for moisture sorption isotherm
Pick salts which cover a range of RH values ( 10% -100%
Moisture sorption is affected by ___
Temperature
The moisture sorption isotherm is a graph that plot the moisture content in a
food product as a function of RH at a specific …… (one word, small letters)
temperature
What The Moisture Sorption Isotherm Tells You
1 ) shows the expected moisture sorption behavior of a food product
as a function of environmental RH at one temperature
2 ) can indicate the effect of temperature on the moisture sorption
isotherm
3 ) allows one to determine the expected Aw of a product at a
specific temperature and RH which is the point where no absorption or
release of moisture occurs
Aw important in predicting product stability
4 ) allows one to predict the final moisture content one can expect to
achieve if exposed to a specific temperature and relative humidity
combination
Thus it is important knowledge for predicting drying behavior
Can predict expected final moisture content for RH/temperature
combinations for a food product
5 ) also indicative of the packaging requirements for a food product
relative to the H 2 O vapor transfer rates of packaging materials
Factors affecting the drying process
-
RH of air and aw of the product
1 ) reducing pressure ––(e.g., Under vacuum) reduces the
temperature difference required in any drying process as the boiling
point of water is reduced
2 ) latent heat (enthalpy) of evaporation cooling effect due to the
phase change from liquid to gas (minimize product damage)
3 ) makeup/structure of the product food products are usually not
homogeneous cellular structure, fat (insulator)
For every___ rise in temperature, air holds twice as much
moisture in vapor form
15 C (27 F)
Faster frying means what for quality of the product
Faster drying means less change in food quality
What will happen to the product if the drying is too rapid
If drying is too rapid, a dry skin forms and traps moisture inside, called
case hardening
Increasing surface area means what when drying
increases exposure to oxygen
Oxygen exposure causes formation of ___
Oxygen exposure causes formation of tannic acid ( browning ) in foods high
in polyphenols such as apples, grapes, and tea
Is dehydration is enough to stop oxidation?
Dehydration temperatures are not high enough to denature enzymes
so many foods are pretreated to inactive enzymes
What heat process methods can control enzymatic activity
Pasteurization is used with animal based products like milk and eggs
Blanching in boiling water is used with vegetables
-sodium bisulfite
Describe treatment of products with sulfite
Sulfiting involves soaking food in a sodium bisulfite and water
solution for 10 to 30 minutes before drying
Problems with sulfiting
extends drying time
may cause breathing difficulties for people allergic to sodium bisulfite
-destroys thiamine
What is sulfuring
Sulfuring involves exposing fruits to fumes from burning sulfur for up to 4 hours Food is placed on stacked trays in a covered area where sulfur dioxide (SO 2 ) can circulate may be dipped in sulfur dioxide
Disadvantage if sulfuring
A disadvantage is that some people are allergic to sulfur dioxide
-destroys thiamine
Advantage of sulfuring
shortened drying time, inhibited mold growth due to sulfur dioxide fumes,
and the ability of sulfur dioxide odors to repel insects
Advantages of sulfuring and sulfiting are
few or no effects on heat sensitive nutrients, food color, and texture
From a moisture sorption isotherm, one can tell the time needed for the
dehydration process to reach a specific moisture content.
True/false
False
Food processors consider these factors when determining the best
dehydration method
the type of food what quality is desired how much consumers are willing to pay whether food is whole, divided, pureed, or liquid
Describe tray drying
Food is held on trays with holes in an enclosed cabinet for up to 20
hours
Air is blown over the food or rises up through the trays
Moisture filled air is vented out of the system
This method is used in small scale operations for fruit and vegetables
Describe belt drying: what moisture content it can reach, what product is the best for it
This method continuously feeds food into a tunnel dehydrator on
moving belts
Food can reach moisture levels of 5 % to 7 % in as little as one hour
Using a belt trough dryer causes food to tumble for even drying
Grains, peas, and beans work best in this dryer
Describe drum drying
Rotating heated drums pick up food and dry it as the drums rotate
The drying time needed determines the size of the drum and the speed of
rotation
The method is best with heat resistant foods that are brittle when dry,
such as
mashed potatoes, mashed sweet potatoes, and tomato pastes
Spray drying : technology and best food for it
Very small drops of the food are sprayed into the top of a heated
chamber or tower and dehydrate as they fall
The method is used with heat sensitive products like milk, eggs, protein
powders, flavorings, and instant coffee
Spray drying is the ___ of all methods
This is the fastest drying method
Food can dehydrate in seconds
Describe the technology of vacuum drying
Heated trays or shelves called platens transfer heat in a vacuum
chamber
Lowering the atmospheric pressure lowers the boiling point, minimizing heat
damage
Vacuum drying is used for ___, produces the highest ___ and is ___ (cost)
produces the highest quality is expensive is used for fruit juices
Another name for freeze-drying is
lypholization , or dehydrofreezing
Methodology for freeze-drying and advantage among other methods
Food is frozen , then placed in a vacuum chamber and heated
Food temperatures and atmospheric pressure are lowered until water
sublimates
The process maintains better flavor and color than other drying methods
The best method to produce powdered milk is A. Drum drying B. Spray drying C. Tray drying D. Belt drying
B
What is food concentrates and food concentration
Food concentration is removing a portion of the water from a food
product
Concentrates are foods that are reduced in volume by having part of
their water removed, such as
fruit juice concentrate, maple syrup, condensed milk, and condensed soups
Food concentration can be the first step of ___
Dehydration
Benefits if concentrates are ___
lower shipping costs because of less volume and weight, extended shelf
life , and better handling ease prior to dehydration
Problems with concentrates
cooked flavors , color changes , gritty textures , and denatured proteins
what foods require extra preservation on top of concentrating
Low acid to destroy pathogens
What is the open kettle concentration method: for what it is used, what are the problems
is the oldest way to remove water requires frequent stirring can result in flavor and color changes with high heat and long cooking times is the method used to make some jams, jellies, and condensed soups
The technology in heat evaporation method and advantages comparing to open kettle
enters and leaves an evaporator in a continuous process
is exposed to high temperatures for short periods
has a fresher flavor than with the open kettle method because heat
damage is limited
What is vacuum evaporation method
a vacuum is added to the evaporator and food moves through a series of
chambers, each with lower atmospheric pressure
What is filtration method of concentrating
smaller particles pass through filters, isolating and concentrating the original
food source
What are intermediate moisture foods
have a moisture content of 20 % to 50 with enough dissolved solutes to
prevent the growth of microbes
are nutrient and calorie dense because they are concentrated
Not dried, but not concentrated foods
Conditions for intermediate-moisture foods storage and what might be added to it
may or may not need refrigeration may need preservatives or antioxidants added to prevent enzymatic activity
Reduction of water activity is not the only mechanism that
explains the preservative effect of concentration.
A.
True
B.
False
True
A container that is made of cardboard, aluminum foil and plastic and that is formed
on site is …… (two words space in between, all small letters)
Tetra brick
The decrease of the freezing point of a solvent on addition of a non volatile solute is …… a. Eutectic point b. Freezing point depression c. Freezing point d. Cold point
B
Fast freezing produces …… ice crystals a. Smaller b. Larger
A
Production represents …… % of the total cost of frozen products.
(answer with a
10
According to the U.S. National Institute of Standards and Technology, liquids of gases that
have boiling points below 180 C are referred to as …… liquids (one word, small letters)
Cryogenic
A thicker package will take …… to freeze. a. Shorter time b. Longer time c. Doesn’t matter
B
……
C is the accepted temperature financially and
commercially to store frozen products. (answer with a number)
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