LAPORAN PENELITIAN HIBAH PENELITIAN STRATEGIS NASIONAL TAHUN ANGGARAN 2009
IDENTIFIKASI PERUBAHAN KUALITAS PASTEURISASI SUSU SAPI SEGAR MENGGUNAKAN TEKNOLOGI PULSED ELECTRIC FIELD (PEF)
LA CHOVIYA HAWA, STP. MP RATNA IKA PUTRI, ST. MT Dr. Ir. BAMBANG SUSILO, Msc.Agr
Dibiayai Oleh Direktorat Jenderal Pendidikan Tinggi, Departemen Pendidikan Nasional, Sesuai Dengan Surat Perjanjian Pelaksanaan Hibah Penelitian Strategis Nasional, Nomor : 0174.0/023-04.2/XV/2009, tanggal 31 Desember 2008 dan berdasarkan SK Rektor Nomor: 160/SK/2009, tanggal 7 Mei 2009.
UNIVERSITAS BRAWIJAYA NOVEMBER 2009
RINGKASAN
Di Indonesia, proses pasteurisasi susu segar yang umum digunakan adalah pasteurisasi termal, yaitu proses pengolahan susu dengan menggunakan pemanasan antara 60°C-100°C. Selama periode pengolahan pangan termal, energi dalam jumlah besar ditransferkan ke makanan. Energi ini dapat menyebabkan reaksi yang tidak diinginkan, seperti adanya kehilangan vitamin,nutrisi esensial perubahan warna, rasa dan bau. Salah satu pilihan teknologi pengawetan susu segar yang ditawarkan adalah pengolahan pangan dengan metoda non termal yang menggunakan kejutan listrik tegangan tinggi (Pulse Electric Field atau PEF), yaitu sistem pengolahan bahan pangan yang didasarkan pada aplikasi denyut pendek pada tegangan tinggi (antara 20 – 80 kV/cm) ke bahan makanan yang ditempatkan diantara dua elektroda pada suhu kamar atau di bawahnya selama beberapa detik. Metode ini sangat efektif karena dapat menginaktifkan mikroorganisme sampai 99% tanpa merubah warna, rasa dan bau dan kandungan gizi dalam waktu yang sangat singkat. Tujuan dari penelitian ini adalah merancang bangun unit pasteurisasi susu berbasis teknologi pulse electric field (PEF) dengan penggunaan variasi tegangan, jumlah pulsa perdetik dan waktu kejutan serta menganalisa perubahan nilai mutu fisik susu segar dengan parameter kadar air, viskositas, warna, berat jenis, titik didih dan titik beku, perubahan mutu kimiawi dengan parameter tingkat keasaman, pH dan total padatan terlarut, perubahan nilai gizi dengan parameter protein, lemak, karbohidrat, abu dan vitamin C dan total mikroba, total koliform, dan total staphylococcus aurues. Berdasarkan hasil pengujian mikrokontroler, rangkaian mikrokontroler dan perangkat lunaknya telah bekerja dengan baik. Mikrokontroler telah dapat menghasilkan sinyal pulsa dengan duty cycle 0,5 dengan frekuensi 20KHz. Duty cycle 0,5 menunjukkan waktu pulsa on (Ton) sama dengan pulsa off (Toff). Pada waktu pulsa on tegangan keluaran mikrokontroler sebesar 4,2 V, sedangkan frekuensi kerja mikrokontroler disesuaikan dengan kinerja HV trafo yang hanya dapat bekerja pada frekuensi 22KHz. Lamanya pulsa yang diberikan tergantung pengaturan waktu yang disetting melalui keypad. Berdasarkan pengujian mikrokontroler telah dapat mengatur lamanya waktu pengolahan yang diseting melalui keypad. Berdasarkan pengujian rangkaian driver untuk HV trafo, rangkaian ini juga telah bekerja dengan baik. Rangkaian driver ini terdiri dari dua bagian yaitu rangkaian pemisah antara HV trafo dengan mikrokontroler yang terdiri dari transistor daya C2211, trafo OT dan transistor daya C5802 dan rangkaian masukan HV trafo yang berfungsi untuk pengaturan besar tegangan tinggi yang dihasilkan HV trafo. Pengaturan tegangan tinggi yang dihasilkan dapat dilakukan pada saklar pemilih. Pada penelitian ini tegangan tinggi dapat diatur mulai 20 kV, 40 kV, 60 kV dan 80 kV. Bentuk gelombang yang dihasilkan rangkaian pembangkit pulsa tegangan tinggi berbentuk pulsa kotak. Efisiensi maksimum pulsa kotak tergantung pada rise time pulsa yang pendek. Rangkaian pembangkit pulsa tegangan tinggi pada penelitian ini menghasilkan bentuk gelombang pulsa kotak dengan frekuensi 22KHz. Sehingga periode untuk setiap pulsa yang dihasilkan sebesar 0,45 µs. Jumlah pulsa yang dihasilkan
rangkaian pembangkit pulsa ini dalam satu detik sebesar 1/ 0,45 µs = 22000 pulsa. Rangkaian pembangkit pulsa yang dihasilkan dapat mengatur waktu pengolahan. Dengan waktu pengolahan selama 10 detik, maka jumlah pulsa yang diberikan ke chamber sebesar 220.000 pulsa. Semakin lama waktu pengolahan maka jumlah pulsa yang dikirim ke chamber juga akan semakin besar. Hasil analisa menunjukkan bahwa, sifat fisik susu hasil pasteurisasi tidak berubah secara signifikan yang meliputi berat jenis, viskositas, kadar air, titik didih, titik beku, angka kejernihan, warna merah dan kuning. Berat jenis memiliki kisaran antara 1.0198 – 1.026 gr/cm3. Viskositas berkisar antara 0.9444 – 0.9581 cp. Kadar air berkisar antara 89.48 – 90.2%. Titik didih dan titik beku berkisar antara 94 – 95% dan -4 hingga -5°C. Angka kejernihan antara 67.7 – 69.2, angka merah 9.8 – 12.8 dan angka kuning 10.4 – 15.90. Hasil analisa kimia menunjukkan bahwa susu hasil pasteurisasi tidak berubah secara signifikan yang meliputi pH, total asam dan total padatan terlarut. pH berkisar antara 6.57 – 6.73, total asam 0.04% dan total padatan terlarut 11.25%. Kandungan gizi susu hasil pasteurisasi yang diamati tidak berubah secara signifikan yang meliputi karbohidrat, protein, lemak, abu dan vitamin C. Karbohidrat berkisar antara 2.14 – 3.97%, protein berkisar antara 2.49 – 2.81%, lemak berkisar antara 3 – 4.29%, abu berkisar antara 0.54 – 0.85% dan vitamin C berkisar antara 0.41 – 0.44%. Teknologi pulsed electric field mampu menurunkan jumlah total mikroba, total koliform, dan total staphylococcus aureus. Semakin besar tegangan dan semakin panjang waktu perlakuan, maka mikroba yang terbunuh semakin banyak. Perlakuan terbaik diperoleh pada tegangan 100 kV selama 30 detik, dengan total mikroba akhir sebesar 9.7x103 cfu/ml atau (dari mikroba awal sebesar 2.9x105 cfu/ml) dan tingkat keefektifan pembunuhan mikroba sebesar 96.65%. Total koliform akhir sebesar 300 cfu/ml (dari koliform awal sebesar 1.3x103 cfu/ml) dan tingkat keefektifan pembunuhan koliform sebesar 76.92%. Total staphylococcus aureus akhir sebesar 160 cfu/ml (dari jumlah awal sebesar 1.6x103 cfu/ml) dan tingkat keefektifan pembunuhan staphylococcus aureus sebesar 90%.
SUMMARY Thermal pasteurization is the most common pasteurization used for milk in Indonesia. It is typically in the temperature between 60oC to 100oC. During this thermal process, a large amount of energy is applied to the product. This process will likely affect undesired reaction, such as vitamin and essential nutrition loss, change of color, taste and aroma. An alternative preservation technology is proposed for substituting the thermal process. It is the pulse electric field (PEF), i.e. a food process technology that applies short-pulse high-voltage to the milk. This voltage is located between to electrodes in the room temperature in a few second. This method is very effective since it is able to inactivate the microorganism up to 99% without changing its color, taste, aroma and nutrition. The objective of this research is to design PEF based milk pasteurization system using variety of voltage, pulse count and time. The products of these various treatments then were analyzed for its physical properties, i.e. water content, viscosity, color, density, melting and boiling point and its chemical properties, i.e. pH, total suspended solid, nutrition (protein, fat, carbohydrate, ash and vitamin C) as well as its microbial count, i.e. total of microbe, colliform and Staphylococcus aureus. According to the microcontroller test result, this device is able to work well. The microcontroller is able to generate pulse signal with duty cycle of 0.5 with frequency of 20 KHz. This duty cycle showed that the time for on-pulse (Ton) was equal to off-pulse (Toff). At the time of Ton, the generated voltage was 4.2 V with its frequency was 22KHz. The duration of applied pulse was set in keypad. According to the test, this microcontroller is able to set the desired time using its keypad. This device also showed that in the test of driver circuit for HV transformator it was able to work well. This circuit consists of two main parts, i.e. circuit for splitting HV transformator and microcontroller that consists of power transistor C2211, OT transformator and power transistor C5802 and HV transformator input circuit that is used for adjusting the voltage level generated by the HV transformator. This voltage adjustment could be done to the adjustment buttons. In this experiment, a various voltages being used were 20kV, 40kV, 60kV and 80kV. The wave generated by the pulse generator is in the form of squared shape. The maximum efficiency was depending on the short pulse rise time. The high voltage pulse generation circuit that was used in this experiment generated squared-shape pulse with frequency of 22 KHz. The period of each generated pulse was 0.45 µs. The numbers of generated pulse of each second were 22000 pulses. This pulse generating circuit was able to adjust the treatment time. The results of the experiments show that there was no significant change of the physical properties of the pasteurized milk. It had 1.0198−1.026 g/cm3 of density and 0.9444−0.9581 cp of viscosity, 89.48%−90.2% of water content. Its boiling point and melting point were in the range of 94oC−95oC and -4oC − -5oC respectively. Its turbidity level was 67.7−69.2, red level 9.8−12.8 and yellow level 10.4−15.90.
The chemical analysis shows that there was no significant change on its chemical properties such as pH (6.57−6.73), total acid (0.04%) and total suspended solid (11.25%). As well, this result shows that no significant change occurred on its nutrition contents, i.e. carbohydrate (2.14%−3.97%), protein (2.49%−2.81%), fat (3%−4.29%), ash (0.54%−0.85%) and vitamin C (0.41%−0.44%). The PEF technology shows its ability to degrade the number of total microbe, total colliform, and total staphylococcus aureus. The bigger the voltage the bigger the microbial degradation of the microbe. The bigger microbe degradation was also showed for the longer voltage applied. The best treatment was demonstrated by the 100kV voltage for 30 second with total final microbe was 9.7x103cfu/ml (the initial count was 2.9x105cfu/ml) and its affectivity on degrading microbe was 96.65%. Its final total colliform was 300cfu/ml (its initial count was 1.6x103cfu/ml) and its affectivity on degrading colliform was 76.92%. The final total staphylococcus aureus was 160 cfu/ml (its initial count was 1.6x103cfu/ml) and its affectivity on degrading staphylococcus aureus was 90%.
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