A. TEKNOLOGI PENGOLAHAN SUSU BUBUKPrinsip pengolahan susu bubuk : penghilangan air dengan biaya sekecil mungkin, pada kondisi higienis dgn mempertahankan semaksimal mungkin sifat alami susu yg dikehendaki - warna, flavour, kelarutan, dan nilai nutrisi.

Whole (full cream) milk mengandung air 87% dan skim milk mengandung 91% air. Selama pengolahan susu bubuk air dihilangkan dgn mendidihkan susu pada tekanan rendah yg dikenal dgn proses evaporasi.

Hasil evaporasi adalah susu kental yg selanjutnya disem-protkan dalam bentuk tetesan kecil ke arah udara panas utk penghilangan air lebih lanjut shg menghasilkan bubuk.

Sekitar 13 kg whole milk powder (WMP) atau 9 kg skim milk powder (SMP) dapat diperoleh dari 100 L susu segar.

KOMPOSISI RATA-RATA SUSU BUBUK

PRODUKProteinLemakLaktosaAbuAirWhole milk26,026,738,06,02,3Skim milk36,00,751,08,13,0Butter milk34,55,048,08,03,0Cream11,072,014,02,40,6Whey12,90,367,08,53,5

Susu bubuk

Proses konvensional untuk produksi susu bubuk dimulai dgn penerimaan susu, pasteurisasi dan separasi menghasilkan susu skim dan krim menggunakan centrifugal cream separator.

Jika diproduksi Whole Milk Powder (WMP) sejumlah krim ditambahkan kembali kepada susu skim menghasilkan produk susu dengan kadar lemak sesuai standar tertentu (umumnya 26-30% lemak dalam bubuk).

Krim yg berlebih digunakan untuk membuat butterSEPARASI / STANDARIATION

Efek pemanasan:Perlindungan thd lemak dari enzim perusakTimbul cooked flavorKelarutan turun karena denaturasi proteinPEMANASAN PENDAHULUAN (PREHEATING)/ PASTEURISASI (lanjutan)Tujuan pemanasan:Inaktivasi semua mikroba patogen, menurunkan total bakteriInaktifasi enzym, terutama lipaseMengaktifkan gugus SH groups dlm -Lacto-globulin shg meningkatkan stabilitas bubuk thd oksidasi selama penyimpanan.

Suhu dan waktu pemanasan

Suhu antara 75-120oC dipertahankan pd waktu tertentu mulai dari beberapa detik sampai bbrp menit (contoh: pasteurisasi 720C, 15 detik).

Metode pemanasan "High-short" lebih disukai karena dapat mencapai efek yg dikehendaki dan pembentukan senyawa antioksidan lebih banyak

Kelarutan bubuk meningkat jika dilakukan metode high-short. Pemanasan dgn metode ini selama 15-30 detik pada 88-95C, bahkan sampai 1300C

PEMANASAN PENDAHULUAN (PREHEATING)/ PASTEURISASI

Waktu dan suhu pemanasan bergantung tipe produk dan penggunaannya. Produk whole milk powder pemanasan lbh tinggi utk meningkatkan kualitas mikrobilogis dan memper-panjang umur simpan tetapi mengurangi kelarutan.

Preheating dapat secara tidak langsung (melalui heat exchangers), atau langsung (melalui steam injection atau infusi ke dalam produk), atau campuran dari dua cara tersebut. Pemanasan tidak langsung umumnya menggunakan limbah panas dari bagian proses yang lain utk menghemat energi.PEMANASAN PENDAHULUAN (PREHEATING)/ PASTEURISASI (lanjutan)

Tahap ini dilakukan sebab lbh ekonomis karena jika pengeringan langsung:

kebutuhan steam lbh besar memerlukan space lbh besarwaktu pengeringan lebih panjangukuran partikel kecil shg loss lbh besarketahanan flavor lbh kecil sebab lbh mudah oksidasipenanganan lebih sulitEVAPORASI

Tujuan:Memekatkan susu, yang awalnya memiliki total padatan sekitar 9.0% (skim milk) dan 13% (whole milk), menjadi total padatan 33-35% (drum drying) atau 40-50% (spray drying)

Prosedur: Susu dididihkan di bawah kondisi vakum pada suhu 45-750C, umumnya di bawah 720C di dalam falling film yg terletak di dalam tabung vertikal dan air dikeluarkan sebagai uap EVAPORASI (lanjutan)

Uap yg dihasilkan dapat di compress secara mekanis atau pemanasan, selanjutnya dpt digunakan utk memanaskan susu pada effect dari evaporator yg berikutnya yg mungkin beroperasi pada tekanan dan suhu lebih rendah dibandingkan sebelumnya.

Effect adalah unit tunggal dalam evaporator yg ber-operasi pada tekanan dan suhu tertentu. Evaporator umumnya memiliki tiga sampai tujuh effects shg panas digunakan kembali beberapa kali.EVAPORASI (lanjutan)

Diagram of a falling film evaporator (Source: GEA Niro Inc.)

HOMOGENISASITujuan: mencegah pengelompokan lemak selama proses shg mencegah creamingMengurangi lemak bebas yang tdk memiliki protective membrane shg mudah menggumpal dan menyebabkan oksidasiTahap ini harus dilakukan utk proses drum drying krn hasil berupa lempengan shg harus homogenSpray drying tidak harus melewati homogenisasi krn hasil berupa partikel-partikel shg mudah bercampur Homogenisasi dilakukan pada tekanan 50-150 bar.

Dua metode pengeringan yg umum digunakan adalah drum drying dan spray drying. Drum drying lapisan tipis dari konsentrat susu didistribusikan pada permukaan panas, menyebabkan sejumlah besar air teruapkan dalam beberapa detik. Spray drying konsentrat susu dibuat menjadi droplet kecil dan dikenakan udara panas sehingga air teruapkan dari dropletPENGERINGAN (Drying)

Lapisan tipis konsentrat susu (30-35% bahan kering) didistribusikan pada pengering drum berputar. Di dalam drum tdp uap panas sampai suhu 1450C. Dalam waktu kurang dari 3 detik kadar air yang tersisa mencapai 4% dan susu yang kering dikerok (scraped) dari drum menggunakan pisau (blade). Serpihan bubuk (powder flakes) jatuh ke atas conveyor, dipecah oleh hammer mill, didinginkan, di ayak selanjutnya dikemas. PENGERINGAN - Drum drying

Karena pemanasan tidak langsung, perlu suhu sangat tinggi yg dpt berakibat pada:

penurunan kelarutan karena denaturasi protein,diskolorasi (pencoklatan) karena karamelisasi laktosa dan reaksi Maillard, perubahan rasa dan aroma

Proses drum drying menghasilkan partikel datar (flat atau flake-like)PENGERINGAN - Drum drying (lanjutan)

PENGERINGAN - Drum drying (lanjutan)Diagram roll dryerPartikel bubuk hasil drum dryer

Unit Operations. Spray drying consists of the following unit operations: Pre-concentration of liquid Atomization (creation of droplets) Drying in stream of hot, dry air Separation of powder from moist air Cooling Packaging of product

Relatively high temperatures are needed for spray drying operations. However, heat damage to products is generally only slight, because of an evaporative cooling effect during the critical drying period and because the subsequent time of exposure to high temperatures of the dry material may be very short. The typical surface temperature of a particle during the constant drying zone is 45-50 C. For this reason, it is possible to spray dry some bacterial suspensions without destruction of the organisms. The physical properties of the products are intimately associated with the powder structure which is generated during spray drying. It is possible to control many of the factors which influence powder structure in order to obtain the desired properties.

Typical Spray Drying Systems. The diagram shows a schematic representation of a typical spray drying system for milk powder. For spray drying, it is usual to pump a concentrate of the liquid product to the atomizing device where it is broken into small droplets. These droplets meet a stream of hot air and they loose their moisture very rapidly while still suspended in the drying air. The dry powder is separated from the moist air in cyclones by centrifugal action. The centrifugal action is caused by the great increase in air speed when the mixture of particles and air enters the cyclone system. The dense powder particles are forced toward the cyclone walls while the lighter, moist air is directed away through the exhaust pipes. The powder settles to the bottom of the cyclone where it is removed through a discharging device. Sometimes the air-conveying ducts for the dry powder are connected with cooling systems which admit cold air for transport of the product through conveying pipes. Cyclone dryers, such as shown here have been designed for large production schedules capable of drying ton-lots of powder per hour.

Spray Dryerdiagram of a typical spray drying operation utilizing a centrifugal atomizer and a cyclone separator

Pre-Concentration of Liquid Feed. For operation of a spray dryer it is usual practice to pre-concentrate the liquid as much as possible. There are several reasons for this :

Economy of operation (evaporation is less expensive) Increased capacity (amount of water evaporation is constant) Increase of particle size (each droplet contains more solids) Increase of particle density (reduction of vacuole size) More efficient powder separation (related to increased density) Improved dispersibility of product (reduction in surface area)

First, it must be recognized that water removal in a vacuum evaporator and in a spray dryer are two very different processes. Evaporation under vacuum is a process which takes place at a much lower temperature than spraydrying. Generally, the temperature of the first stage is only 65 C and subsequent stages even less. For this reason, vacuum evaporation in multiple stages permits the use of low-cost energy and regeneration of the energy contained in the vapor removed from the product. In principle, very little heat energy is used or lost during vacuum evaporation.In contrast, spray drying takes place at atmospheric pressure; therefore, the drying air needs to be heated to high temperatures, generally around 150-175 C. This requires high-cost fuel in the form of gas or oil. Besides, there is almost no opportunity to regenerate the energy from the vapor phase. Thus, for efficient industrial spray drying operation, it is usual to combine the two processes.

Next, it must be recognized that the performance of a spray dryer is rated according to the maximum amount of water which can be removed per hour by that system. For example, a spray dryer rated at 1000 kg/hr water evaporation will produce only 111 kg/hr of bone-dry powder from a liquid of 10% total solids. If that liquid is concentrated to 45% total solids, the powder production increases to 818 kg/hr of bone-dry powder.

Finally, the powder structure and, therefore, the physical properties of a powder is very dependent upon the total solids concentration of the liquid which is being dried. If the droplets are maintained at a constant size, then, the amount of solids will affect both the size and the density of the dry particles. The structure of a spray-dried particle is a hollow sphere, with the solids being a shell which surrounds a central vacuole. As the total solids of the feed increases, the shell becomes thicker and, as a consequence, the particle does not shrink as much during drying. Similarly, as the air-filled vacuole decreases in size, the particle density increases.

The increase in particle density has a pronounced influence on the efficiency of powder separation/collection by the cyclones, because these operate on the principle of a difference in the buoyant density difference between air and particles. It is well-known in the spray-drying industry that drying a liquid of low solids content is the cause of very fine particles which are difficult to collect. This results in product losses as well as environmental pollution when they are discharged into the atmosphere.

Konsentrat susu disemprotkan ke atas menara pengering menggunakan spray nozzle atomizer ber-tekanan tinggi atau rotary atomizer tower menghasilkan droplet (tetesan) kecil dgn diameter 50-80 m (tahap atomization)

Tahap atomization dilakukan dlm chamber pengering besar yang dialiri udara panas bersuhu 150-300C

Konsentrat dipanaskan sebelum atomization utk menurunkan viskositasPENGERINGAN - Spray drying

Droplet yg terbentuk selama atomization memper-tahankan bentuk selama proses pengeringan shg partikel bubuk hasil spray-drying berbentuk spherical.

Udara yg terperangkap dlm partikel menghasilkan densitas yg rendah.

Air dlm droplet yg sangat kecil akan teruapkan dengan cepatPENGERINGAN - Spray drying (lanjutan)

Suhu maksimum partikel selama pengeringan sekitar 65-75C.

Air diuapkan dalam drying chamber, menghasilkan bubuk halus dgn kadar air 6% dan ukuran diameter partikel rata-rata < 0.1 mm.

Pengeringan akhir atau "sekunder" dilakukan dlm fluid bed yang mengalirkan udara panas melalui lapisan bubuk yang dialirkan utk menghilangkan air shg produk memiliki kadar air 2-4%.

Selanjutnya bubuk dipisahkan dr udara pengeringan dgn bantuan cyclone dan didinginkan dgn udara dinginPENGERINGAN - Spray drying (lanjutan)

Limitations on Pre-Concentration. The limit on the extent of pre-concentration of the feed is dictated by the viscosity of the liquid, which must not be so high, that the product cannot be pumped or atomized. For milk powder manufacture, it is common to pre-concentrate the milk (9% total solids in skim milk; 13% total solids in whole milk) to 45% in an evaporator. For many protein isolates, such a high concentration cannot be used, because most protein solutions are very viscous. In this case, spray drying must be done with a concentrate of about 25% total solids concentration. This practice, however, causes the powder particles to have a lower density. Therefore, these products are typically very light and fluffy and the unit cost of operation increases dramatically.

Atomization. The size and uniformity of droplets are determined by the atomization. Karel (1975) has described this operation as the most important feature of a spray dryer. Two different principles are illustrated in the following diagrams.Centrifugal Atomizer. This is a spinning disk assembly with radial or curved vanes which rotates at high velocities (2000-20,000 rpm). The feed is delivered near the center and spreads between the two plates and is accelerated to high linear velocities before it is thrown off the disk in the form of thin sheets, ligaments or elongated ellipsoids. However, the subdivided liquid immediately attains a spherical shape under the influence of surface tension. The atomizing effect is dependent upon centrifugal force but also must depend upon the frictional influence of the external air. Centrifugal atomizers have the great advantage of less tendency to become clogged. For this reason, they are preferred for spray drying of non-homogeneous foods.

Centrifugal Atomizer for Cyclone Spray Dryers.A. Top view. B. Side view.High Pressure Spray Jets. High pressure jets are alternative atomizing systems in which a fluid acquires a high-velocity tangential motion while being forced through the nozzle orifice. The fluid emerges with a swirling motion in a cone shaped sheet, which breaks up into droplets.

Faktor yg Menentukan Sifat Susu Bubuk Spray DryingKondisi preheating dan derajat pengentalan yg me- nentukan TS setelah penguapanDesain pengering (metode atomizing)Temperatur operasi (inlet & outlet temperature)Umumnya spray drying tdk menyebabkan denaturasi protein Penurunan kelarutan disebabkan oleh stabilitas komplek kasein-fosfatPENGERINGAN - Spray drying (lanjutan)

Susu bubuk perlu dilindungi dari kelembapan, oksigen, cahaya, dan panas untuk menjaga mutu dan umur simpan

Susu bubuk mudah menyerap uap air dari udara menyebabkan turunnya mutu dan penggumpalan

Kandungan lemak dalam WMP dapat bereaksi dgn oksigen di udara menyebabkan off-flavours, terutama pada penyimpanan suhu tinggi (> 30C)

Susu bubuk dikemas dalam kantong plasti multi-layer atau kaleng. PENGEMASAN DAN PENYIMPANAN

WMP sering dikemas dengan aliran gas Nitrogen utk melindungi produk dari oksidasi dan mempertahankan flavour dan umur simpan.

Pemilihan kemasan harus melindungi produk dari kelembapan, oksigen dan cahaya. Umumnya berupa kantong yg tdd beberapa lapis utk menyediakan kekuatan dan perlindungan.

Transportasi susu bubuk harus menghindari paparan sinar matahari langsung.

Beberapa jam transportasi pada suhu tinggi (> 40C) dapat mengurangi mutu yg dipertahankan selama bbrp minggu penyimpanan dlm kondisi yg baik.PENGEMASAN DAN PENYIMPANAN

B. TAHAP PENGOLAHAN SUSU BUBUK FORMULASusu Bubuk FormulaMerupakan susu bubuk rekonstitusi dari susu skim yang ditambah lemak susu atau lemak nabatiFormula lebih mudah ditentukan tergantung tujuan atau permintaan pasarSumber lemak dapat berasal dari minyak nabatiPengkayaan zat gizi lebih mudah dilakukanProses lebih sederhana, tidak menggunakan unit evaporasi

Proses pembuatan tdd 3 (tiga) tahap: Pembuatan susu bubuk inti Formulasi dan pencampuran Pengepakan / pengalenganTAHAP PENGOLAHAN SUSU BUBUK FORMULA

TAHAP PENGOLAHAN SUSU BUBUK FORMULA (lanjutan)Pembuatan susu bubuk intiTerdiri dari beberapa tahap sbb:a. Pencampuran: minyak, bubuk skim, lesithin (stabilizer), airb. Penyaringanc. Pemanasan d. Homogenisasie. Spray dryingf. Pengepakan

2. Komposisi Formula- Komposisi formula disesuaikan tujuan atau permintaan pasar - Komponen utama dalam formulasi:* Susu bubuk inti* Susu skim untuk mencapai jumlah protein yg diinginkan* Gula, vitamin, mineral- Komponen lain: zat anti kempal, antioksidan, dllTAHAP PENGOLAHAN SUSU BUBUK FORMULA (lanjutan)

Susu Bubuk Instan Susu bubuk yg mudah larut jika diberi air dingin.Merupakan partikel yang besar dan bersifat porous

Prinsip pengolahan ACRSAglomerasi : menyebabkan terjadinya aglomerasi susu bubuk dengan mencampurkan airRe-dries : setelah pencampuran dengan air, dikering-kan kembali shg terbentuk partikel yg besar dan porousCools : pendinginan Sizes : penyeragaman ukuranC. PENGOLAHAN SUSU BUBUK INSTAN

AglomerasiSusu bubuk dari loading hopper dimasukkan dalam aglomerating tube (AT)Uap dimasukkan AT dgn kecepatan tinggi shg membasahi partikel susu bubuk dan menggabungkannya menyebab-kan terbentuknya kluster (kesatuan partikel yg volumenya lbh besar = 0,1-0,3 mm) dlm btk tak beraturan (aglomerat)Bubuk aglomerat terdispersi dlm air lbh cepat dan tidak mudah berhamburan shg lbh mudah ditangani.Kluster yg lebih besar dipisahkan dari aliran udara ke dalam wet collector. Selama pembasahan laktosa akan mengkristal sebagian oleh krn itu susu bubuk instan lebih tidak higroskopisTAHAP PENGOLAHAN SUSU BUBUK INSTAN (lanjutan)

PROSES INSTANISASI DAN AGLOMERASI PARTIKELA is a representation of regular powder. B represents aggregates from drying a rewetted powder

As the development went on, the concentration was carried out in forced recirculation evaporators. In this evaporator the milk streams upwards through a number of tubes or plates. On the outside the heating medium, usually steam, is applied. The heating surface is thus increased in this system, but the evaporation surface is still limited, as the tubes and plates remain filled with product, which therefore becomes superheated in relation to the existing boiling temperature. Not until the product leaves the top of the tubes, are the vapours released and the product temperature decreases. For the separation of liquid and vapours, centrifugal separators were preferred. In order to obtain the desired degree of evaporation the product was recycled in the system. The concentration was thus controlled by the amount of concentrate discharged from the plant. Fig. 1 shows a diagram of a forced recirculation evaporator.

Falling Film Evaporators

In order to make the evaporator work as an integral unit the following auxiliary equipment is needed:Separators Product distribution system Preheaters Pasteurization/holding equipment Low thermophilic heating/pasteurizing equipment Condensation and vacuum equipment Cooling towers High-concentrators Flash coolers Sealing water equipment Instrumentation and automation

EVAPORATION OF LIQUID The liquid to be evaporated is evenly distributed on the inner surface of a tube (see page 39). The liquid will flow downwards forming a thin film, from which the boiling/evaporation will take place because of the heat applied by the steam. See Fig. 3. The steam will condense and flow downwards on the outer surface of the tube. A number of tubes are built together side by side. At each end the tubes are fixed to tube plates, and finally the tube bundle is enclosed by a jacket, see Fig. 3a. The steam is introduced through the jacket. The space between the tubes is thus forming the heating section. The inner side of the tubes is called the boiling section.

EVAPORATION OF LIQUID Together they form the so-called calandria. The concentrated liquid and the vapour leave the calandria at the bottom part, from where the main proportion of the concentrated liquid is discharged. The remaining part enters the subsequent separator tangentially together with the vapour. The separated concentrate is discharged (usually by means of the same pump as for the major part of the concentrate from the calandria), and the vapour leaves the separator from the top. The heating steam, which condenses on the outer surface of the tubes, is collected as condensate at the bottom part of the heating section, from where it is discharged by means of a pump.

Fig. 3 Evaporation in a falling film evaporator tubeFig. 3a Evaporator calandria

In order to understand the heat and mass transfer, the basis for the evaporation, it is necessary to define various specific quantities. From a given quantity of feed (A) part of the solvent is evaporated (B) leaving the concentrate or the evaporated product (C). And thusA = B + C(1)

See Fig. 4, showing specific quantities and the corresponding heat flow diagram. The evaporation ratio (e) is a measure for the evaporation intensity and can be defined either as the ratio between the amount of feed and concentrate or the ratio between the solids percentage in the concentrate and in the feed.e =A/C = C-Concentrate/C-Feed(2)

The principle of all spray dryers is to transform the concentrate into many small droplets which are then exposed to a fast current of hot air. Because of the very large surface area of the droplets (11 of concentrate will be atomized to 1.5 x 1010 particles of 50 with a total surface of 120 m2) the water evaporates almost instantaneously and the droplets are transformed into powder particles.