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). 1
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 longterm 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. 2
Retort KINETIKA KEMATIAN MIKROBA Pemusnahan m.o oleh panas... > pada T konstan... > penurunan jumlah mikroba hidup mengikuti reaksi ordo I dn = kn dt dimana, N= jumlah mikroba hidup k = konstanta laju reaksi (konstanta laju pemusnahan m.o.) dn = kdt N t NdN = k dt N0 0 N N ln = kt N0 Ln N = ln N o -kt Ln N Kemiringan = -k t Microbial death, like microbial growth, is described by a logarithmic equation. 3
Ingat! Ln X = 2.303 log X ln N = kt N0 2.303 log N = kt N0 logn = logn0 k - 2.303 t Oleh para ahli teknologi pangan (termobakteriologi), persamaan tsb dinyatakan sebagai : log N = logn 0 t - D atau N t log = N D 0 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 KurvaKematianTermalpadaSuhuKonstant, T 1 T 1 10,000 1,000 D-value 100 D-value 10 4
Contoh 1 Anggap suatu makanan dalam kaleng. Jikajumlahmoawalsebesar10 6 mikrobapembusuka/kaleng. NilaiD padasuhu121,1 o C = 15 detik. Berapajumlahmosetelahpemanasanselama1 menitpada121,1 o C Berapajumlahmosetelahpemanasanselama2 menitpada121,1 o C Jawab: Ingat... > log N = logn 0 t - D Untukt = 1 menit: 60 detik 6 logn = log10-15 detik log N = 6 4 = 2 2 N = 10 = 100 Untuk t = 2 menit : 6 120 detik logn = log10-15 detik log N = 6 8 = -2-2 N = 10 = 0,01 Peluang kebusukan!! KurvaKematianTermalpadaSuhuT 1 dant 2 T 1 Bagaimana jika suhu pemanasanpadat 2 >T 1??? D 1 SemakintinggiT... > semakin kecil nilai D D=f(T) D 1 T 2 >T 1 5
Secara empiris: log D D 0 = 121,1- T Z D 121,1-T Z = D 0 10 Nilai Z adalah perubahan suhu ( T) yang diperlukan untuk mengubah nilai D sebesar 1 siklus log Nilai Z = 18 o F =? o C D danz... > perluselaludiketahuidua-duanya! Misal: MikrobaA mempunyaid A,250F = 0.5 menit MikrobaB mempunyaid B,250F = 1 menit D A >D B Z A = 10 o C; Z B = 20 o C D A =D B D A <D B Apa artinya? Suhu (C) D A (menit) D B (Menit) 80.1 5000 100 90.1 500 101.1 50 10 111.1 5 121.1 0.5 1 131.1 0.05 141.1 0.005 0.1 151.1 0.0005 161.1 0.00005 0.01 Nilai D (menit) 10000 1000 100 10 1 0.1 0.01 0.001 0.0001 B 0.00001 0 50 100 150 200 A Suhu ( o C) 6
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 7
Contoh soal: Suatu suspensi pangan mempunyai kandungan mikroba pembusuka danb. MikrobaA sebanyak3 x 10 5 danmikroba B sebanyak8 x 10 6. Padasuhu121.1 o C, nilaid untukmikroba A danmikrobab adalah1.5 dan0.8 menit. Jikasuspensitsb dipanaskanpadasuhukonstan121.1 o C, berapalama untuk memperolehpeluangkebusukansebesar10-3. 8
Jawab: log N = logn 0 - Peluangkebusukan10-3 ; artinyan = 10-3. UntukmikrobaA : 5 3x10 t = 1.5 log -3 10 t = 1.5(8.477) = 12.72 menit UntukmikrobaB : 6 8x10 t = 0.8 log -3 10 t = 0.8(9.903) = 7.92 menit t D t = No Dlog N Jadi, untuk mendapatkan peluang kebusukan sebesar 10-3, maka pemanasan 121.1 o C 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. 9
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. 10
Lethality of Thermal Processes 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. Letalitas / lethal rate (L) adalah ekuivalen menit pada suhu 250 F (121 C) dengan pemanasan 1 menit pada suhu tertentu. 10 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, danlethal rate) harus diketahui. Kemudian harus diperoleh data profil suhu pada kondisi proses. Letalitas proses dihitung dengan cara integrasilethal rate terhadap waktu, dalam persamaan dapat ditulis: atau 11
Example For the flash sterilization of milk, a thermal treatment of 2 seconds at 131 C is recommended. Calculate the F0 value 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 F0 value for this process. Z value = 18 F. 12
Temperature ( F) 300 250 200 150 100 50 0 0 20 40 60 80 100 120 Time (min) 0.8 lethal rate 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 120 time 13
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