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Thermal and Alternative Food Processing Technologies
Dr. Sirichai Songsermpong
Dept. of Food Science and Technology
Kasetsart University
alternative technologies
Microwave and Radio Frequency
Ohmic and Inductive Heating
High Pressure Processing
Pulsed Electric Field
Irradiation
High Voltage Arc Discharge
Pulsed Light
Oscillating Magnetic Fields
Ultraviolet Light
Ultrasound
overview
review of thermal and alternative technologies
discussion of principles that apply to all of the technologies, focusing on reaction kinetics
research needs are identified
thermal processes
Commercial sterilization
batch retort
batch retort
batch retort
Advantages
Cost of equipment
Accept different container size, type and product flexibility
Equipment failures for one retort don’t stop entire production line
Disadvantages
High energy cost
High labor cost
continuous systems
continuous systems
hydrostatic retorts
hydrostatic retort
Cans enter the hydrostatic retort in a “stick”
hydrostatic retort
continuous retort
Advantages
Low labor (15-40% less labor) and energy (25-50% less steam) cost per unit produced
Disadvantages
Cost of equipments
Limited to metal containers of one size
Equipment failure stops the entire line
Can only process one type of food at a time
Reaction kinetics
Establishing the mechanisms of a reaction
Obtaining experimental rate data
Correlating data by equations(kinetic parameters)
Designing food processes (heat transfer, electric fields,…)
Reaction rate and rate constant
Reaction rate
Rate constant
dt
dCr
...),,(
),,(),,(
),,,,(
BA
BA
BA
CCetcPTkr
etcCCfetcPTkr
etcPTCCfr
r = k C (first-order kinetics)
log C/Co
Salmonella in ground beef at 57.2 °C
(Goodfellow and Brown, 1978)
Ckdt
dC
tDC
C 1log
0
tkC
C'log
0
D-value
Decimal reduction time
C
CDt 0log
DDt 1
10log
DDt 10
100log
Microwave, ohmic and inductive heating
The energy absorption from microwaves and electric currents can raise the temperature of the food high enough to inactivate microorganisms for pasteurization or sterilization.
A number of studies suggest that the thermal effect is the essential contributor to the destruction of microorganisms as well as the degradation of vitamins, etc
Reported non-thermal effects are likely to be due to the lack of precise measurements
Microwave, ohmic and inductive heating
Thermal D-values provide a sound basis for development of processes for the microwave energy and electrical resistance (ohmic and inductive) technologies
High pressure and electric field
The concept of D-value can describe the microbial population reduction at a constant pressure or constant electric field.
D(P), D(E)
assumptions
a) The basic model assumes a first-order relationship between microbial population and time
b) D-value describes the microbial population reduction at a constantand defined temperature, pressure and/or electric field.
Research needs
Non-linear models
There are considerable discussions about the appropriateness of using a first-order model to describe the reduction in microbial population for all preservation technologies
Non-linear models
Demonstration of how forcing a straight line through a concave semi-logarithmic survival
curve can result in an over or under estimate of an organism's resistance to a lethal agent
(Peleg, 1999)
Non-linear models
Alternative models are being developed to explain microbial inactivation kinetics when the linearity of the data is questionable (Peleg and Cole 1998; Anderson 1996).
If there is evidence of a non-linear model, different parameters need to be identified for prediction purposes.
Non-linear models
Listeria monocytogenes in chicken meat at 70 °C
(Murphy et al., 2000).Salmonella in egg yolk (Michalski et al., 1999).
nbtC
C
0
log
Peleg’s model (1998)
assumptions
a) The basic model assumes a first-order relationship between microbial population and time
b) D-value describes the microbial population reduction at a constanttemperature, pressure or electric field.
Constant pressure
High pressure processing (HPP), also described as high hydrostatic pressure (HHP), or ultra high pressure (UHP) processing, subjects liquid and solid foods to pressures between 100 and 800 MPa.
HPP acts instantaneously and uniformly throughout a mass of food independent of size, shape, and food composition. Thus, package size, shape, and composition are not factors in process determination
Constant temperature?
Cold point
Heat penetration study
Data Acquisition System
Thermocouple
Typical heat penetration result
0.0
50.0
100.0
150.0
200.0
250.0
300.0
0 20 40 60 80 100 120 140
Time (minutes)
Tem
pera
ture
(d
eg
F)
PRODUCT TEMPERATURE
MEDIUM TEMPERATURE
Heating and Cooling Profiles
processing time
direct steam injection
tubular heat exchanger
Triple tube
Double tube
Triple tube
Double tube
Indirect: plate heat exchanger
Example: pasteurization
Pathogens
30 min, 63 C
D = 2.5 min
Vitamins
30 min, 63 C
D’ = 120 min
tDC
C 1log
0
Example: pasteurization
Pathogens
71 C
D = 0.021 min
Same lethality
Vitamins
71 C
D’ = 250 min
HTST pasteurization systems
155 degrees F (69 degrees C) for 30 minutesEggnog
280 degrees F (138 degrees C) At least 2 secondsAll milk products
Ultra-Pasteurized (Extended Shelf Life)
180 degrees F (83 degrees C) for 15 secondsEggnog
175 degrees F (80 degrees C) for 25 secondsIce cream mix
175 degrees F (80 degrees C) for 25 secondsCream
161 degrees F (72 degrees C) for 15 secondsMilk
HTST- Pasteurization
155 degrees F (69 degrees C) for 30 minutesIce cream mix
150 degrees F (66 degrees C) for 30 minutesCream
145 degrees F (63 degrees C) for 30 minutesMilk
Batch Pasteurization
155 degrees F (69 degrees C) for 30 minutesEggnog
280 degrees F (138 degrees C) At least 2 secondsAll milk products
Ultra-Pasteurized (Extended Shelf Life)
180 degrees F (83 degrees C) for 15 secondsEggnog
175 degrees F (80 degrees C) for 25 secondsIce cream mix
175 degrees F (80 degrees C) for 25 secondsCream
161 degrees F (72 degrees C) for 15 secondsMilk
HTST- Pasteurization
155 degrees F (69 degrees C) for 30 minutesIce cream mix
150 degrees F (66 degrees C) for 30 minutesCream
145 degrees F (63 degrees C) for 30 minutesMilk
Batch Pasteurization
Batch and HTST times
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