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
