Materi kuliah tentang proses termal.

1. Thermal Processing
Introduction
• Foods are highly reactive systems:
Chemical/bio reactions=> post harvest and
processing
• The systematic study of reactions in foods=>
food chemistry and food biochemistry.
• the rate of reactions => food process engineer

2. Introduction
• Thermal processing involves heating food,
either in a sealed container or by passing it
through a heat exchanger, followed by
packaging.
• Important=>to ensure that the food is
adequately heat treated and to reduce post
processing contamination (ppc).
• Important=> be cooled quickly

3. Reasons for Heating Foods
• The two most important issues : food safety and
food quality.
– Inactivate pathogenic or spoilage microorganisms,
– inactivate enzymes to avoid the browning of fruit by
polyphenol oxidases and minimize flavour changes
resulting from lipase and proteolytic activity.
– induces physical changes and chemical reactions:
starch gelatinisation, protein denaturation or
browning, which in turn affect the sensory
characteristics, such as colour, flavour and texture,
either advantageously or adversely.

4. Food safety
• Variation heat resistance of pathogens:
– heat-labile, such as Campylobacter, Salmonella, Lysteria and of more
recent concern Escherichia coli 0157, which are inactivated by
pasteurisation,
– greater heat resistance is Bacillus cereus, may survive pasteurisation
and also grow at low temperatures.
– heat-resistant pathogenic bacterial spore is Clostridium botulinum.
• Spoilage bacteria : yeasts, moulds and gas-producing and souring
bacteria.
• the most heat-resistant being the spores of Bacillus
stearothermophilus.
• The heat resistance of any microorganism depends on pH, water
activity, chemical composition of foods.
• After processing, it is very important to avoid reinfection of the
product (ppc)

5. • Calculation of thermal processing for the
destruction of microorganisms
• Optimization of thermal processes with respect
to quality
• Optimization of processes with respect to cost
• Prediction of the shelf life of foods as a function
of storage conditions
• Calculation of refrigeration load in the storage of
respiring agricultural produce
• Development of time-temperature integrators.
the most important applications of reaction kinetics in
food engineering

6. Two groups Reactions in food
processing
• Desirable or induced reactions: The pyrolysis of
carbohydrates during coffee roasting, the
hydrolysis of collagen when meat is cooked and,
the hydrogenation of oils to produce solid fats,
etc
• Undesirable reactions: Maillard-type browning in
lemon juice, onset of rancidity as a result of lipid
oxidation in nuts and crackers and, spoilage
reactions induced by microorganisms, dsb

7. Reaction order
• n = reaction order
• k=rate constant
• C=concentration
• t=time
• n=0 => Zero order, not very common, non-
enzymatic browning, caramelization and lipid
oxidation
• n=1=> first order, many phenomena, thermal
destruction of microorganisms, non-enzymatic
browning.

8. Reaction Kinetics
• Microbial Inactivation
– three distinct periods: a heating period, holding
period and cooling period.
– all three periods may contribute to the reactions. The
holding period is the most significant.
• Heat Resistance at Constant Temperature
– When heat inactivation studies are carried out at
constant temperature, it is often observed that
microbial inactivation follows first order reaction
kinetics i.e. the rate of inactivation is directly
proportional to the population.

10. • Every microorganism has its own characteristic heat
resistance and the higher its D value, the greater is its
heat resistance.
• Heat resistance is also affected by a wide range of
other environmental factors, such as pH, water activity
and the presence of other solutes, such as sugars and
salts.
• Example: for an organism with a D70 value of 10 s,
heating for 10 s at 70 C will achieve a 90% reduction in
the population, 20 s heating will achieve 2D (99%), 30 s
will achieve 3D (99.9%) and 60 s will achieve 6D
(99.9999%) reduction.

11. contoh
• In the counter-current heat exchanger, milk is cooled from 73ºC to 38ºC at the rate
of 2500 kg/h, using water at 15ºC which leaves the heat exchanger at 40ºC. The
pipework 2.5 cm in diameter is constructed from stainless steel 3 mm thick; the
surface film heat transfer coefficients are 1200 W/m2Kon the milk side and 3000
W/m2Kon the water side of the pipe. Calculate the OHTC and the length of pipe
required.

14. Contoh

16. Process lethality
• There are two types of bacterial populations of concern in
canned food Sterilization : to reduce the population of
organisms of public health significance and to avoid economic
losses from spoilage-causing bacteria of much greater heat
resistance in low acid food
• The organism : Clostridium botulinum (a safe level of survival
probability 10–12, or one survivor in 1012 cans processed/12 D
concept for botulinum cook.
• the highest D121 value known for this organism in foods is 0.21
min, the minimum lethality value for a botulinum cook is F =
0.21×12 = 2.52 min
• Most food companies accept a spoilage probability of 10–5
from mesophilic spore Clostridium sporogenes
• Max D121 value 1 min; F = 1.00 × 5 = 5.00 min
• thermophilic spoilage is a concern, the target value for the
final number of survivors is usually taken as 10–2,

17. Lethality Values (Fo) for Commercial Sterilization
of Selected Canned Food Products

18. Kinetika kematian mikroorganisme
• Waktu pemanasan bergantung kepada jumlah
mikroba awal dan mikroba akhir yang
diinginkan
• t= D log(No/N)
• Dengan acuan suhu standar 121oC
• Fo= D121 Log (No/N)
• Fo = t.10(T-121)/z
• Untuk suhu tidak konstan, Fo=∫ t.10(T-121)/z

19. Contoh
• Suatu proses pemanasan makanan catan suhu di pusat
panasnya (thermal center) adalah sbb:
Waktu
(menit)
Suhu oC Waktu Suhu
0 80 (26,7) 40 225 (107,2)
15 165 (73,9) 50 230,5
(110,3)
25 201 (93,9) 64 235 (112,8)
30 212,5 (100,3)
• Jika nila Fo untuk Cl. Botulinum 2,45 menit dan z:18oF,
apakah proses tersebut diatas telah memenuhi?

20. • Hitung nilai 10(T-250)/z pada berbagai waktu
• Menit ke 0; 10(T-250)/z = 10(80-250)/18 = 3,6x10-10
• Waktu Suhu 10(T-250)/z luasan
0 80 3,6 x 10-10
15 165 1,9 x 10-5 15x...
25 201 0,00189 10 x ...
30 212,5 0,00825 5 x 00,00507
40 225 0,0408 10 x 0,0245
50 230,5 0,0825 10 x 0,06165
64 235 0,1465 14 x 0,1145

21. Aseptic Processing
• Material condition : pumpable
• Process : a continous process involving separate
sterilization of a pumpable food, containers, and
closures followed by the cooling of the food and
filling and sealing in containers under a sterile
environment
• Products : mostly acid food
• Size of package : ranged from consumer-size
retail packs of a few grams (60–180 g) to bulk
storage containers up to more than about 4–6 m3

22. • The aseptic packaging system achieves this room-
temperature shelf stability by filling a sterilized
package with a sterile food product within the
confines of a hygienic environment.
• This remarkable packaging system allows :
– perishable products could be distributed and stored
without refrigeration for periods up to six months or more
– No preservatives and/or refrigeration to achieve a long
shelf life.
• Other advantages :
– Lightweight container,
– space-efficient block shape,
– easy-open, easy-pour, and reclosable features
– no exposed sharp edges,
– easy to crush

23. Comparation
aseptic process traditional canning hot-fill canning
•Product is sterilized outside the
package using an ultra-high
temperature process that rapidly
heats, then cools, the product
before filling.
•The processing equipment
allows the time (generally 3 to
15 seconds) and temperature
(195° to 285° F) to be tailored to
place the least amount of
thermal stress on the product,
while ensuring safety.
•This flash-heating-and-cooling
aseptic process substantially
reduces the energy use and
nutrient loss associated with
conventional sterilization.
requires products
to be heated in the
container for 20 to
50 minutes.
Hot-fill canning
uses the heat
of the product
to sterilize both
the product and
the package, a
process which
takes 1-3
minutes for
heating and
another 7-15
minutes for
cooling

24. Isn’t the aseptic package an example of
excessive packaging?
• the aseptic package is an excellent example of
minimal packaging.
• Comparation by weight
– An aseptic package is typically 95 percent
beverage to 5 percent packaging.
– PET bottles are 95 percent product to 5 percent
packaging;
– steel cans are 89 percent product to 11 percent
packaging; and
– glass bottles are 65 percent product to 35 percent
packaging.

25. What products are available in aseptic
packages
• In USA : milks, juices, tomatoes, soups, broths,
tofu, soy beverages, wines, whipping cream,
teas.
• In UE : pasteurized milk and yogurt drinks to fruit-
based desserts and sauces.
• The bulk storage : need refrigeration.
• Bulk storage : tomato paste storage and shipment
(190 L drums), banana puree, rail car and truck
containers) and 378,000 L tanks for storage of soy
sauce and other liquids.

26. Assembled aseptic processing system

27. Aseptic packaging material
• Packaging material: high-quality
paperboard, polyethylene, and
aluminum.
• Paper (70 percent) provides stiffness,
strength and the efficient brick shape to
the package.
• Polyethylene (24 percent) on the
innermost layer forms the seals that
make the package liquid-tight. A
protective coating on the exterior keeps
the package dry.
• Aluminum (6 percent) forms a barrier
against light and oxygen. This ultra-thin
layer of foil eliminates the need for
refrigeration and prevents spoilage
without using preservatives.
• The aseptic package contains a total of
six layers in this order: polyethylene,
paper, polyethylene, aluminum foil,
polyethylene, and polyethylene.

28. Thermal proccesing of product
• The thermal sterilitization depend on: (1)
nature of the food (e.g., pH and water
activity); (2) storage conditions following the
thermal process (refrigerated versus room
temperature); (3) heat resistance of the
microorganisms or spores; (4) heat transfer to
the food; and (5) the initial load of
microorganisms.

29. Approximations of heat processes for destruction of C.
botulinum and commercial
sterility

30. Predicting process temperature
T = process temperature (°C) measured at the end of
the hold tube,
TR = reference temperature (°C),
Z = temperature (°C) change necessary for the D-value
to change by a factor of 10 or for 1-log or 90%
reduction,
t = hold time (minutes or seconds) calculated from flow
rate and tube diameter, and
F = sterilizing value needed to achieve commercial
sterility for the product

31. • rapid heat transfer rate in heating and cooling :
minimizes undesirable changes in the taste and
nutritional quality of the resulting product.
• Continuous process: produces uniform product
quality that does not depend on the size of a
container,
• This attribute is especially important for products
containing heat-sensitive ingredients and highly
viscous products with poor heat transfer
properties

32. Sterilization of packaging material
• 3% of total m.o on surface material are spores
• Plastic film and paperboard laminated on reels: assumed 1000
m.o/m2 and 30 spores
• Cup : 3000
• Method of sterilization :
– Irradiation
• UV
• IR
• Gamma
– Heat
• Steam
• Hot Air
– Chemical treatment
• Hydrogen peroxide
• Peracetic acid
• Ethylene oxide

33. Irradiation
• Reqirement for packaging materials:
– smooth surface
– Free from dust
– Irradiation resistance
• UV : 200-315 nm, most effective of microbial
destruction 250-280 nm
• IR : max temp 140oC
• Gamma rays from Co 60 or Cesium 139, dose of 20
kGy can sterilize 105 spores of B. stearothermophillus

34. Heat
• Steam :
– most reliable sterilant
– Need high pressure
– Need to remove air
– Condensation of steam
• Hot Air :
– High temperature can be reached at atmospheric
pressure
– Need more time to sterilize

35. Chemical treatment
• Hydrogen peroxide : 20% concentration at 80oC for
15 s
• Concentration in food not more than 100 ppb
– Dipping
– Spraying
– Rinsing
• Paracetic acid:
– Effective against aerob and anaerob m.o
– 1% solution, eliminate 107-108 for 5 min 20oC
• Ethylen oxide
– Toxic gas that can penetrate porous material

36. Indicator
Sterilization medium Indicator organism
Steam B. stearothemophillus
Dry heat B. polymyxa
H2O2 and heat B. stearothemophillus
H2O2 and UV B. Subtilis
Ethylene oxide C. sporogenes
Gamma irradiation B. pumilus

37. Filling and Packaging
• The sterilization to the films is done by the
soak in H2O2 liquor and dried by the aseptic
air, and with the shining of UV lights.
• The aseptic environment is made by the
H2O2 atomizer and the UV lights.
• The machine can be linked with the UHT
sterilizing machine, and CIP system to make
up a automatic production line for
commercial required aseptic liquid
products.
• The filling environment is sterilized by heat
or chemicals. After sterilization, the
environment
• is maintained sterile using filtered air or
inert gas (Clark 2004). The filters
• must be sterilized and validated to assure
that there is no recontamination of the
sterile
• environment.