PROSES THERMAL
The industrial application of food preservation by heat began with the work of the French inventor Nicolas Appert (1749–1841) who first demonstrated that long-term preservation of different kinds of foods can be achieved by heating the foods for a long time (many hours) in
hermetically closed containers.
The microbial origin of food spoilage and the relationship between
thermal destruction of microorganism and food preservation were
demonstrated only later by Louis Pasteur (French chemist and biologist,
1822–1895).
Depending on their intensity, thermal preservation processes are classified into two categories:
1) Pasteurization : heat processing at relatively mild temperature (say 70–
100°C). Pasteurization destroys vegetative cells of microorganisms but has almost no effect on spores.
2) Sterilization : heat processing at high temperature (above 100°C) with the objective of destroying all forms of microorganisms, including spores.
Sterilization alone provides long-term preservation of foods, on the condition that recontamination is prevented by proper packaging.
Pasteurization, on the other hand, provides only short-term stability or requires additional preserving factors (hurdles) such as refrigeration or low pH for long- term effectiveness.
Commercial Sterilization
• When foods are industrially canned, they are sterilized in a process called commercial sterilization.
• Commercial sterilization is carried out in a large retort which works the same way as an autoclave.
• Commercial sterilization is used to kill C. botulinum
• If C. botulinum is destroyed, any other significant
spoilage/pathogenic bacteria will be destroyed.
Retort
KINETIKA KEMATIAN MIKROBA
Pemusnahan m.o oleh panas
...> pada T konstan
...> penurunan jumlah mikroba hidup mengikuti reaksi ordo I
dt kN dN=
− dimana,
N= jumlah mikroba hidup
k = konstanta laju reaksi (konstanta laju pemusnahan m.o.)
N kt ln N
0
−
=
N kdt dN=−
dt N k
dN
N
N
t
0 =− 0
∫ ∫
Ln N = ln No- kt
t Ln N
Kemiringan
= - k
Microbial death, like microbial growth, is described by a logarithmic equation.
2.303t - k N log N
log = 0
N kt ln N
0
−
=
Ingat !
Ln X = 2.303 log X
N kt 2.303 log N
0
−
=
Oleh para ahli teknologi pangan (termobakteriologi), persamaan tsb dinyatakan sebagai :
D - t N0 log N log =
D = Decimal Reduction Time
= waktu yg diperlukan u/ mengurangi jml mo dengan faktor 1 desimal
= waktu yg diperlukan u/ mengurangi jml mo sebanyak 1 siklus log
= waktu yg diperlukan u/ mengurangi jml mo sebanyak 90% populasi atau
D t N0
log N −
=
D-value
D-value 10,000
1,000
100
10
Kurva Kematian Termal pada Suhu Konstant, T
1T1
Contoh 1
Anggap suatu makanan dalam kaleng.
Jika jumlah mo awal sebesar 106mikroba pembusuk A/kaleng.
Nilai D pada suhu 121,1oC = 15 detik.
Berapa jumlah mo setelah pemanasan selama 1 menit pada 121,1 oC Berapa jumlah mo setelah pemanasan selama 2 menit pada 121,1 oC
D - t N0 log N log ====
Jawab : Ingat...>
100 10 N==== 2 ====
2 4 6 N
log ==== −−−− ====
ik det 15
detik -60 10 log N
log ==== 6 Untuk t = 1 menit :
0,01 10
N==== -2====
- 2 8 6 N
log ==== −−−− ====
ik det 15
detik -120
10 log N
log ==== 6 Untuk t = 2 menit :
Peluang kebusukan!!
T1
Kurva Kematian Termal pada Suhu T
1dan T
2Bagaimana jika suhu pemanasan pada T2>T1???
T2>T1
D1
D1
Semakin tinggi T ...>
semakin kecil nilai D D=f(T)
Nilai Z adalah perubahan suhu (∆∆∆∆T) yang diperlukan untuk mengubah nilai D sebesar 1 siklus log
Nilai Z = 18oF = ? oC Secara empiris:
====
ZT - 121,1 0
10 D D
Z T - 1 , 121 D
log D
0
====
Suhu (oC)
0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000
0 50 100 150 200
Nilai D (menit)
B A
D dan Z ...> perlu selalu diketahui dua-duanya!
Misal:
Mikroba A mempunyai DA,250F= 0.5 menit Mikroba B mempunyai DB,250F= 1 menit ZA= 10oC; ZB= 20oC
Apa artinya?
Suhu (C) DA(menit) DB(Menit)
80.1 5000 100
90.1 500
121.1 0.5 1
131.1 0.05
141.1 0.005 0.1
151.1 0.0005
161.1 0.00005 0.01
111.1 5
101.1 50 10
DA=DB DA<DB DA>DB
KETAHANAN PANAS BAKTERI PEMBENTUK SPORA YANG DIGUNAKAN DALAM STERILISASI
JENIS M.O. NILAI D250
(menit)
NILAI Z ( ° C)
B.stearothermophillus 4,0 7,0
B.substilis 0,48-0,76 7,4-13,0
B.cereus 0,0065 9,7
B.megaliticum 0,04 8,8
C.perfringens 10,0
C.sporogenes 0,15 13,0
C.sporogenes (PA 3679) 0,48-1,4 10,6
C.botulinum 0,21 9,9
C.thermosaccharolyticum 3,0-4,0 8,9-12,2
A suspension of bacterial spores containing 160 000 spores per ml is heated at 110°C. The number of survivors is determined in samples withdrawn every 10 minutes. The results are:
Assuming ‘ first order ’ kinetics, calculate the decimal reduction time
Contoh soal:
Suatu suspensi pangan mempunyai kandungan mikroba
pembusuk A dan B. Mikroba A sebanyak 3 x 10
5dan mikroba
B sebanyak 8 x 10
6. Pada suhu 121.1
oC, nilai D untuk mikroba
A dan mikroba B adalah 1.5 dan 0.8 menit. Jika suspensi tsb
dipanaskan pada suhu konstan 121.1
oC, berapa lama untuk
memperoleh peluang kebusukan sebesar 10
-3.
Jawab :
Peluang kebusukan 10-3; artinya N = 10-3. Untuk mikroba A :
D - t N0 log N
log ====
=
N No
log D t
menit 12.72 (8.477)
1.5
t= =
10 10 x log 3 1.5
t -3
5
=
Untuk mikroba B :
menit 7.92 (9.903) 0.8
t = =
10 10 x log 8 0.8
t -3
6
=
Jadi, untuk
mendapatkan peluang kebusukan sebesar 10-3, maka pemanasan 121.1oC harus dilakukan selama 12.72 menit.
In a laboratory experiment it was found that heating a suspension of spores at
120°C for 100 seconds results in a 9-log killing of the spores. To achieve the
same reduction at 110°C, 27.5 minutes are needed. Calculate the decimal
reduction time at the two temperatures and the z value.
Lethality of Thermal Processes
From the foregoing discussion it can be concluded that the same ‘lethality’ , i.e. the same reduction in the number of microorganisms can be achieved under different time–temperature combinations.
In order to compare different processes as to their lethality, the concept of ‘F value’ is
defined. ‘F value’ is the duration (in minutes) required to achieve a given reduction ratio
in the number of microorganism at a given constant temperature.
Consider a thermal process during which the temperature T of the product varies according to a known time–temperature profile, T=f(t). A certain log reduction ratio log(N0/N) is achieved. We would like to calculate the duration in minutes (the F value) of an ‘equivalent’ process at a given constant temperature (reference
temperature R) that would result in the same reduction ratio. The calculation requires specification of the reference temperature R and knowledge of the z value of the microorganism considered.
Lethality of Thermal Processes
Letalitas / lethal rate (L) adalah ekuivalen menit pada suhu 250°F (121°C) dengan pemanasan 1 menit pada suhu tertentu.
Untuk evaluasi dan penetapan proses termal, maka harus diidentifikasi mikroorganisme atau enzim yang menjadi target. Kinetika destruksi mikroorganisme yang menjadi target (nilai D, nilai z, dan lethal rate) harus diketahui. Kemudian harus diperoleh data profil suhu pada kondisi proses. Letalitas proses dihitung dengan cara integrasi lethal rate terhadap waktu, dalam persamaan dapat ditulis:
atau
10
⁄∆
For the flash sterilization of milk, a thermal treatment of 2 seconds at 131°C is recommended. Calculate the F
0value of the process.
Example
The following data represent the temperature at the slowest heating point in a canned food processed at a retort temperature of 250 ◦F. Calculate the F
0value for this process.
Z value = 18 ◦F.
Example
0 50 100 150 200 250 300
0 20 40 60 80 100 120
Time (min) Temperature
(°F)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0 20 40 60 80 100 120
