Standar Nasional Indonesia menentukan Batas Maksimum Cemaran Mikroba pada susu pasteurisasi 1 x 106 dan untuk susu pasteurisasi <3 x 104. Untuk koliform pada susu segar 2 x 101 MPN/gram danuntuk koliform pada susu pasteurisasi <0,1 x 101 MPN/gram.

Fluid milk is an industry term for milk processed for beverage use.

Milk, as defined by the U.S. Code of Federal Regulations (CFR), 21 CFR 131.110, is: “the lacteal secretion, practically free from colostrum, obtained from the complete milking of one or more healthy cows. Milk that is in its final package form for beverage use shall have been pasteurized or ultrapasteurized, and shall contain not less than 8.25% solids and not less than 3.25% milk fat. Milk may have been adjusted by separating part of the milkfat therefrom, or by adding thereto cream, dry whole milk, skim milk, or nonfat dry milk. Milk may be homogenized.” Milk solids are the non-water components of milk – protein , lactose, and minerals. Sometimes the combination of protein, lactose and minerals is called the solids not fat content, and when the fat is included it is called total solids content.

Although the CFR states that milk is obtained from cows, the production of milk from other dairy animals in the U.S. (goats, sheep, and water buffalo) also is covered in the Grade A Pasteurized Milk Ordinance (PMO).

Standardization

The fat content of milk varies with species (cow, sheep, goat, water buffalo), animal breed, feed, stage of lactation, and other factors. In order to provide the consumer with a consistent product, most milk in the U.S. is standardized.

To achieve standardization, milk is processed through centrifugal separators to create a skim portion and a cream portion of the milk. Separation produces a skim portion that is less than 0.01% fat and a cream portion that is usually 40% fat, although the desired fat content of the cream portion can be controlled by changing settings on the separator. The cream portion is then added back to the skim portion to yield the desired fat content for the product. Common products are whole milk (3.25% fat), 2% and 1% fat milk, and skim milk (< 0.1% fat).

Pasteurization

The majority of U.S. fluid milk is pasteurized using a high temperature short time (HTST) continuous process of at least 161°F (71.6°C) for 15 seconds. These conditions provide fresh tasting milk that meets the requirements for consumer safety. Higher heat processes, such as ultrapasteurization or aseptic processing , are used to extend the shelf life of refrigerated products or allow for storage at room temperature, respectively, but may impart a cooked flavor to the milk.

Homogenization

The fat in milk is secreted by the cow in globules of non-uniform size, ranging from 0.20 to 2.0 µm. The non-uniform size of the globules causes them to float, or cream, to the top of the container. Milk that is not homogenized is sometimes referred to as “creamline” milk. Pasteurized milk does not necessarily need to be homogenized. However, homogenized milk should be pasteurized to inactivate native enzymes that deteriorate fat (lipases) and cause rancidity, which results in off-flavors and reduced shelf life in milk.

The purpose of homogenization is to reduce the milk fat globules size to less than 1.0 µm which allows them to stay evenly distributed in milk. Homogenization is a high pressure process that forces milk at a high velocity through a small orifice to break up the globules. The result of homogenization is the creation of many more fat globules of a smaller size. The native milk fat globules are covered in a protein membrane that stabilizes the fat phase in the aqueous (water) phase of milk. Although the milk fat globule membrane is disrupted during the homogenization process, it spontaneously migrates back to the fat globules after homogenization. The new globules created during homogenization are spontaneously coated by proteins in the skim phase from the original milk fat globules.

Cornell University

Pasteurisasi adalah perlakuan panas yang diberikan pada bahan baku dengan suhu di bawah titik didih. Teknik ini digunakan untuk mengawetkan bahan pangan yang tidak tahan suhu  tinggi, misalnya susu. Pasteurisasi tidak mematikan semua mikroorganisme, tetapi hanya yang bersifat patogen dan tidak membentuk spora. Oleh sebab itu, proses ini sering diikuti dengan teknik lain misalnya pendinginan atau pemberian gula dengan konsentrasi tinggi. Produk hasil pasteurisasi bila disimpan pada suhu kamar hanya bertahan 1 sampai 2 hari sedang jika disimpan pada suhu rendah dapat tahan 1 minggu.Pasteurisasi memiliki tujuan:

1. Untuk membunuh bakteri patogen, yaitu bakteri yang berbahaya karena dapat menimbulkan penyakit pada manusia. Bakteri pada susu yang bersifat patogen misalnya Mycobacterium tuberculosis dan Coxiella bunetti  dan mengurangi populasi bakteri.

2. Untuk memperpanjang daya simpan bahan atau produk

3. Dapat menimbulkan citarasa yang lebih baik pada produk 4. Pada susu proses ini dapat menginaktifkan enzim fosfatase dan katalase yaitu enzim yang membuat susu cepat

rusak.

Metode Pasteurisasi yang umum digunakan adalah:

1. Pasteurisasi dengan suhu tinggi dan waktu singkat (High Temperature Short Time/HTST), yaitu proses pemanasan

susu selama 15 – 16 detik pada suhu 71,7 – 750C dengan alat Plate Heat Exchanger. 2. Pasteurisasi dengan suhu rendah dan waktu lama (Low Temperature Long Time/LTLT) yakni proses pemanasan

susu pada suhu 610C selama 30 menit.

3. Pasteurisasi dengan suhu sangat tinggi (Ultra High Temperature) yaitu memnaskan susu pada suhu 1310C selama 0,5 detik. Pemanasan dilakukan dengan tekanan tinggi untuk menghasilkan perputaran dan mencegah terjadinya pembakaran susu pada alat pemanas.

Processing of Dairy Products:

Raw milk is brought to the dairy plant, it is then graded, weighed, and sampled. The butterfat content determines the price paid the farmer.

Processing of raw milk starts with clarification or separation, using centrifuges. The clarification process removes impurities like blood cells from the milk that will be sold as whole milk (milk containing all of its butterfat). Separation process removes butterfat as well as impurities from milk. Skim milk is produced when all the butterfat is removed from the raw milk.

Dairy cows are milked 2 or 3 times a day. Most dairy farms use milking machines. The fresh milk is strained through cotton to remove foreign matters, it is then cooled in the milk house and then sold in bulk form to dairy plants. Milk is shipped by truck in 10-gallon cans or in refrigerated tank trucks.

Milk is then pasteurized to kill harmful bacteria. Milk with butterfat is then homogenized to prevent the butterfat from separating from the milk

Processed milk is then chilled in a cooler and then placed in sterile containers. Processed milk is then packed individually in containers, which are usually plastic bottles or paper cartons, are put

on moving racks and pass under machine that will automatically fills and seals them.

Homogenization - is the process of breaking up the fat into smaller sizes so that it no longer separates from the milk.

Pasteurization - is the process of heating liquid for the purpose of destroying viruses and harmful organism. It is different from sterilization because pasteurization only aims to reduce the number of bacteria so they are unlikely to cause disease. Sterilization is not common in food processing because it can affect the flavor.

components of milk: water 88%,fat 3,5%, protein 3,2%,lactose 4,6%,minerals 7%.

IntroductionWhile pasteurization conditions effectively eliminate potential pathogenic microorganisms, it is not sufficient to inactivate the thermoresistant spores in milk. The term sterilization refers to the complete elimination of all microorganisms. The food industry uses the more realistic term "commercial sterilization"; a product is not necessarily free of all microorganisms, but those that survive the sterilization process are unlikely to grow during storage and cause product spoilage.

In canning we need to ensure the "cold spot" has reached the desired temperature for the desired time. With most canned products, there is a low rate of heat penetration to the thermal centre. This leads to overprocessing of some portions, and damage to nutritional and sensory characteristics, especially near the walls of the container. This implies long processing times at lower temperatures.

Milk can be made commercially sterile by subjecting it to temperatures in excess of 100° C, and packaging it in air-tight containers. The milk may be packaged either before or after sterilization. The basis of UHT, or ultra-high temperature, is the sterilization of food before packaging, then filling into pre-sterilized containers in a sterile atmosphere. Milk that is processed in this way using temperatures exceeding 135° C, permits a decrease in the necessary holding time (to 2-5 s) enabling a continuous flow operation.

Some examples of food products processed with UHT are:

liquid products - milk, juices, cream, yoghurt, wine, salad dressings foods with discrete particles - baby foods; tomato products; fruits and vegetables juices; soups larger particles - stews

Advantages of UHT

High quality: The D and Z valves are higher for quality factors than microorganisms. The reduction in process time due to higher temperature (UHTST) and the minimal come-up and cool-down time leads to a higher quality product.

Long shelf life: Greater than 6 months, without refrigeration, can be expected.

Packaging size: Processing conditions are independent of container size, thus allowing for the filling of large containers for food-service or sale to food manufacturers (aseptic fruit purees in stainless steel totes).

Cheaper packaging: Both cost of package and storage and transportation costs; laminated packaging allows for use of extensive graphics

Difficulties with UHT

Sterility: Complexity of equipment and plant are needed to maintain sterile atmosphere between processing and packaging (packaging materials, pipework, tanks, pumps); higher skilled operators; sterility must be maintained through aseptic packaging

Particle Size: With larger particulates there is a danger of overcooking of surfaces and need to transport material - both limits particle size

Equipment: There is a lack of equipment for particulate sterilization, due especially to settling of solids and thus overprocessing

Keeping Quality: Heat stable lipases or proteases can lead to flavour deterioration, age gelation of the milk over time - nothing lasts forever! There is also a more pronounced cooked flavour to UHT milk.

UHT Methods

There are two principal methods of UHT treatment:

1. Direct Heating2. Indirect Heating

Direct heating systems

The product is heated by direct contact with steam of potable or culinary quality. The main advantage of direct heating is that the product is held at the elevated temperature for a shorter period of time. For a heat-sensitive product such as milk, this means less damage.

Indirect vs Direct Heating (17 KB)

There are two methods of direct heating (please see schematic diagrams of the equipment;

1. injection2. infusion

Injection: High pressure steam is injected into pre-heated liquid by a steam injector leading to a rapid rise in temperature. After holding, the product is flash-cooled in a vacuum to remove water equivalent to amount of condensed steam used. This

method allows fast heating and cooling, and volatile removal, but is only suitable for some products. It is energy intensive and because the product comes in contact with hot equipment, there is potential for flavour damage.

Infusion: The liquid product stream is pumped through a distributing nozzle into a chamber of high pressure steam. This system is characterized by a large steam volume and a small product volume, distributed in a large surface area of product. Product temperature is accurately controlled via pressure. Additional holding time may be accomplished through the use of plate or tubular heat exchangers, followed by flash cooling in vacuum chamber. This method has several advantages:

instantaneous heating and rapid cooling no localized overheating or burn-on suitable for low and higher viscosity products

Indirect heating systems

The heating medium and product are not in direct contact, but separated by equipment contact surfaces. Several types of heat exchangers are applicable:

plate tubular scraped surface

Plate Heat Exchangers: Similar to that used in HTST but operating pressures are limited by gaskets. Liquid velocities are low which could lead to uneven heating and burn-on. This method is economical in floor space, easily inspected, and allows for potential regeneration.

Tubular Heat Exchangers: There are several types:

shell and tube shell and coil double tube triple tube

All of these tubular heat exchangers have fewer seals involved than with plates. This allows for higher pressures, thus higher flow rates and higher temperatures. The heating is more uniform but difficult to inspect.

Scraped Surface Heat Exchangers: The product flows through a jacketed tube, which contains the heating medium, and is scraped from the sides with a rotating knife. This method is suitable for viscous products and particulates (< 1 cm) such as fruit sauces, and can be adjusted for different products by changing configuration of rotor. There is a problem with larger particulates; the long process time for particulates would mean long holding sections which are impractical. This may lead to damaged solids

and overprocessing of sauce.

Packaging for Aseptic Processing

The most important point to remember is that it must be sterile! All handling of product post-process must be within the sterile environment.

There are 5 basic types of aseptic packaging lines:

1. Fill and seal: preformed containers made of thermoformed plastic, glass or metal are sterilized, filled in aseptic environment, and sealed

2. Form, fill and seal: roll of material is sterilized, formed in sterile environment, filled, sealed e.g. tetrapak 3. Erect, fill and seal: using knocked-down blanks, erected, sterilized, filled, sealed. e.g. gable-top cartons, cambri-

bloc 4. Thermoform, fill, sealed roll stock sterilized, thermoformed, filled, sealed aseptically. e.g. creamers, plastic soup

cans 5. Blow mold, fill, seal:

There are several different package forms that are used in aseptic UHT processing:

cans paperboard/plastic/foil/plastic laminates

flexible pouches thermoformed plastic containers flow molded containers bag-in-box bulk totes

It is also worth mentioning that many products that are UHT heat treated are not aseptically packaged. This gives them the advantage of a longer shelf life at refrigeration temperatures compared to pasteurization, but it does not produce a shelf-stable product at ambient temperatures, due to the possibility of recontamination post-processing.

University of Guelph, Dairy Science and Technology

Milk is virtually sterile when it is synthesized in a healthy cow's udder (mammary gland). Cows, like humans, are natural reservoirs of bacteria. Many of these bacteria are not harmful to humans, but some may be harmful to humans even though the cows are not affected and appear healthy.

Milk may become contaminated with bacteria during or after milking. The mammary glands of cows (and humans) can become inflamed due to a bacterial infection called mastitis. During a mastitis infection, very high numbers of bacteria present can be in the udder and in the milk. Some disease causing organisms (pathogens) can be shed through cow feces and may contaminate the outside of the udder and teats, the farm environment (bedding, for example) and the milking equipment. Although optimal growth conditions for bacteria are different for different organisms, milk contains important nutritional components for mammal growth, and, therefore, it is also an ideal medium for the growth of many different bacteria. Temperature plays an important role in bacterial growth. Many bacteria prefer to grow at body temperature (86-98°F, 30-37°C), but will grow at lower temperatures (such as refrigerator temperature) at slower rates.

The area of dairy microbiology is large and diverse. The bacteria present in dairy products may cause disease or spoilage. Some bacteria may be specifically added to milk for fermentation to produce products like yogurt and cheese. A detailed discussion of fermentation bacteria is outside the scope of this web site, although these organisms are discussed briefly in the section on yogurt production and cheese production. This section of the web site is dedicated to the discussion of pathogens because of their importance in human health.

Human illness from milkborne pathogens is usually associated with consumption of raw milk or products made from raw milk such as fresh cheeses. In the past 20 years, foodborne illnesses from dairy product consumption have been predominantly associated with Salmonella enterica, Listeria monocytogenes, Campylobacter jejuni, and Escherichia coli O157:H7. These organisms have been isolated from bulk tank samples at rates ranging from 0.87% of samples taken for E. coli O157:H7 analysis in Ontario, Canada to 10% for E. coli O157:H7 in Wisconsin (Jayarao et al., 2001 and 2006; McManus and Lanier, 1987; Padhye and Doyle, 1991; Steele et al., 1997; Van Kessel et al., 2004). Because there is a risk of pathogen contamination in milk produced from healthy cows under sanitary milk conditions, pasteurization of milk prior to consumption will destroy pathogens and provide protection for illness associated with consumption of dangerous microbes. Occasionally, human illness has been linked to pasteurized milk products but these cases usually have been a result of contamination of the product after pasteurization or improper pasteurization.

The Purpose of Pasteurization

1. To increase milk safety for the consumer by destroying disease causing microorganisms (pathogens) that may be present in milk.

2. To increase keeping the quality of milk products by destroying spoilage microorganisms and enzymes that contribute to the reduced quality and shelf life of milk.

Pasteurization Conditions

Minimum pasteurization requirements for milk products are shown in Table 1 below, and are based on regulations outlined in the Grade A Pasteurized Milk Ordinance (PMO). These conditions were determined to be the minimum processing conditions needed to kill Coxiella burnetii, the organism that causes Q fever in humans, which is the most heat resistant pathogen currently recognized in milk. Milk can be pasteurized using processing times and temperatures greater than the required minimums.

Pasteurization can be done as a batch or a continuous process. A vat pasteurizer consists of a temperature-controlled, closed vat. The milk is pumped into the vat, the milk is heated to the appropriate temperature and held at that temperature for the appropriate time and then cooled. The cooled milk is then pumped out of the vat to the rest of the processing line, for example to the bottling station or cheese vat. Batch pasteurization is still used in some smaller processing plants. The most common process used for fluid milk is the continuous process. The milk is pumped from the raw milk silo to a holding tank

that feeds into the continous pasteurization system. The milk continuously flows from the tank through a series of thin plates that heat up the milk to the appropriate temperature. The milk flow system is set up to make sure that the milk stays at the pasteurization temperature for the appropriate time before it flows through the cooling area of the pasteurizer. The cooled milk then flows to the rest of the processing line, for example to the bottling station. There are several options for temperatures and times available for continuous processing of refrigerated fluid milk. Although processing conditions are defined for temperatures above 200°F, they are rarely used because they can impart an undesirable cooked flavor to milk.

Table 1. Pasteurization conditions used for milk products.

Pasteurization Type Typical Product Typical Storage Temperature Holding Time

Batch, vat Milk Refrigerated 145°F (62.8°C) 30 min

"

Viscous products, or products with more than 10% fat or added sweetener

" 150°F (65.6°C) 30 min

"Egg nog, frozen dessert mixes

" 155°F (68.3°C) 30 min

Continuous, high temperature short time (HTST)

Milk " 161°F (71.7°C) 15 sec

"

Viscous products, or products with more than 10% fat or added sweetener

" 166°F (74.4°C) 15 sec

"Egg nog, frozen dessert mixes

" 175°F (79.4°C) 25 sec

" " " 180°F (82.2°C) 15 sec

Continuous, higher heat shorter time (HHST)

Milk " 191°F (88.3°C) 1 sec

" " " 194°F (90°C) 0.5 sec

" " " 201°F (93.8°C) 0.1 sec

" " " 204°F (96.2°C) 0.05 sec

" " " 212°F (100°C) 0.01 sec

Continuous, Ultrapasteurization

Milk and cream Refrigerated, extended

storage 280°F (137.8°C) 2 sec

Aseptic, ultra high temperature (UHT)

Milk Room temperature 275-302°F (135-

150°C) 4-15 sec

Sterilization Canned products " 240°F (115.6°C) 20 min

University of Cornell.The sterilization of Milk,Th. E. Galesloot,Dr. Ir