What is bactofugation?

Bactofugation is a process used to eliminate bacteria contained in milk using centrifugal force. It is a special form of separation of microorganisms, mainly spore formers (Bacilli/Clostridia) to enable milk to be sterilized at lower temperature-time combinations. In order to be more effective, hot milk is used because it shows lower resistance to the destruction of bacterial cells compared to the cold.

Bactofugation is used to improve the bacterial quality of raw milk and also used to enhance the quality of powders, consumption milk and cream. This mechanical process is mainly used in the production of cheese to eliminate anaerobic spores that can affect the flavor and destroy the texture of cheese due to uncontrolled gas formation.

Bacteria removing centrifuges or bactofuges support a wide variety of dairy processes. Applications range from single-stage bacterial clarification through the 2-stage process to the special bacterial clarification of drinking milk, and variable bacterial clarification of cheese milk, treatment of whey concentrate and pre-treatment of milk powder.

The objectives of bactofugation are as follows:
· To improve hygienic quality of milk
· To avoid heat resistant bacteria without resorting to excessive heating
· To ensure exceptionally high degree of bacteriological purity in milk.

Bactofugation uses a centrifugal force to remove bacteria and spores from milk as a simple and cost-effective complement to regular pasteurization. Bactofuge are special nozzle clarifying separator with high separation precision that can remove microorganisms from milk based on their density difference (skim milk – 1.036; bacteria – 1.07 – 1.13 g/cm3).

During the process, centrifugation force is gradually accelerated to achieve gentle treatment. The optimum bactofugation temperature at which the best results are achieved is 55-60 °C. In the bactofuge, the milk containing bacteria and spores is pushed outwards and collected outside the bactofuge. Bactofugation of milk can remove 80-90% bacteria and 90-95% of spores.

Bacterial clarification is recommended before processing into cheese, because this allows the addition of nitrate to prevent so-called blowing to be significantly reduced or even dispensed with.

There are two types of bactofuge:
· Two–phase bactofugation have two openings at the top of the drum, one for continuous drainage of bactofugated milk and one for the bactofuge (2–3 % of the total amount of milk).
· The one-phase Bactofuge has only one outlet at the top of the bowl for the bacteria-reduced milk. The bactofugate is collected in a sludgespace at the periphery of the bowl and discharged at preset intervals.
What is bactofugation?

Flash pasteurization

Pasteurization is a method used to increase the shelf life of many products from milk to canned vegetables. In flash pasteurization, liquid is brought to a higher temperature for a shorter amount of time (usually 15-30 seconds), then rapidly cooled before being filled into the aseptic packaging.

Flash pasteurization is performed to kill spoilage microorganisms prior to filling containers, in order to make the products safer and to extend their shelf life compared to the unpasteurized foodstuff.

This method heats the milk between 72°C to 74°C for 15 to 20 seconds with targets resistant pathogenic bacterial spores (Clostridium botulinum spores).

In wine industry, Flash pasteurization not only brings forth tannin and aromatic elements, it mitigates unwanted characteristics, such as pyrazines, the compound responsible for bell pepper and vegetal notes, commonly found in underripe grape.

Flash pasteurization is especially beneficial in maintaining color and flavor also nutritional compounding of liquid products better than other HTST methods.

This method used effectively for milk products, kegged beer, and juice/puree-based products.
Flash pasteurization

Thermization of milk

Thermization of milk is a ‘heat treatment not equivalent to pasteurization’. There is no legal definition nor criteria for thermization. The thermization process is a subpasteurization heat treatment of milk at 62–65 °C for 10–20 s, followed by refrigeration.

Thermization should be applied soon after milk treatment and it is only effective if thermized milk is kept cool (4 °C).

Thermization markedly reduces the number of spoilage bacteria with minimum collateral heat damage to milk components and it does not cause changes in flavor. It is used as a prepasteurization treatment of raw milk to safeguard milk quality during prolonged storage in insulated silos. The process is also used as a postpasteurization treatment of dairy products.

The purpose of this treatment is to protect against microorganisms that may grow during storage of raw milk, especially Gram-negative psychotropic bacteria.

Thermization allows the milk to be stored below 8 °C (46 °F) for three days, or stored at 0–1 °C (32–34 °F) for seven days. Later, the milk may be given stronger heat treatment to be preserved longer. Cooling thermized milk before reheating is necessary to delay/prevent the outgrowth of bacterial spores.
Thermization of milk

Milk pasteurization

In 1864, Louis Pasteur developed the pasteurization process while he was tasked with finding practical solutions for problems such as keeping harmful bacteria at bay in different foods. Pasteurization is a process in which certain foods (such as milk and fruit juice) are treated with mild heat, usually less than 100 °C, to eliminate pathogens and extend shelf life.

Primarily it is designed to remove pathogenic bacteria and vegetative organisms but not heat resistant spores which are not destroyed at the temperatures employed. Raw milk can carry dangerous bacteria such as Salmonella, E. coli, Listeria, Campylobacter, and others that cause foodborne illness, often called “food poisoning.”

Second, pasteurization is designed to reduce the enzymatic activity in the product. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time of food.

There are four methods of milk pasteurization
*High Temperature Short Time (HTST)
*Higher Heat Shorter Time
*Ultra-High Temperature (UHT)
*Ultra-Pasteurized

In most milk processing plants, chilled raw milk is heated by passing it between heated stainless-steel plates until it reaches 71.7°C for no less than 15 seconds. Once the milk has been heated, it is then cooled very quickly to less than 3°C. The equipment which is used to heat and cool the milk is called a ‘heat exchanger’.
Milk pasteurization

Bacterial contamination in milk

Milk is a suitable medium for contamination by microorganisms. Generally, milk and dairy products are rich in nutrients, delivering high quality proteins, micronutrients, vitamins and energy-containing fats. Milk, thus, provides an ideal environment for the growth of wide variety of food-borne microorganisms and zoonotic agents.

Pathogenic bacteria in milk have been a matter of public health concern since the early days of the dairy industry. Many diseases such as tuberculosis, brucellosis, diphtheria, scarlet fever, Q-fever, and gastroenteritis are transmissible via milk products.

Pathogenic bacteria are defined as those bacteria capable of causing disease, infection, or intoxication in a susceptible host. Staphylococcus aureus, Salmonella spp., Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter are the most frequent potential pathogens associated with milk or dairy products in industrialized countries and are the main microbiological hazards linked to raw milk and raw cheese.

Temperature has a key role in the spoilage of milk. If milk is produced in poor hygiene conditions then it contains increased numbers of psychrotrophic bacteria in the total microbial population and under low temperature contain proteinases and lipases of psychrotropic bacteria undergoes spoilage of milk product.

Generally, pathogenic microorganisms can contaminate raw milk in two ways.
*Endogenous contamination occurs when milk is contaminated by a direct transfer of pathogens from the blood (systemic infection) of an infected animal into the milk, or via an infection in the udder.
*Exogenous contamination, occurs where milk is contaminated during or after collection by animal feces, the exterior of the udder and teats, the skin, and other environmental sources.
Bacterial contamination in milk 

Aflatoxin M1

Aflatoxins are mycotoxins of major concern to the dairy industry. Several types of aflatoxin (14 or more) occur in nature, but four – aflatoxins B1, B2, G1 and G2 are particularly dangerous to humans and animals as they have been found in all major food crops; but most human exposure comes from contaminated nuts, grains and their derived products.

Aflatoxin M1 (AFM1) is a mycotoxin from Aspergillus flavus and A. parasiticus, classified as carcinogenic and hepatotoxic. Aflatoxin M1 is a hydroxylated metabolite of AFB1, that is excreted in milk in the mammary glands of both humans and lactating animals.

Approximately 0.3% to 6.2% of the ingested AFB1 is converted to the monohydroxy derivative aflatoxin M1 in the liver of lactating animals, by the action of cytochrome P 450, and is secreted in the urine and milk of the cow. Aflatoxin M1 excreted in milk, depending on factors such as the genetics of the animals, seasonal variation, the milking process and the environmental conditions.

Even though it is less toxic than AFB1, AFM1 has hepatotoxic and carcinogenic effects, and is relatively stable during milk pasteurization, storage, and processing.

Milk that is sold commercially is checked for aflatoxin M1. When aflatoxin M1 is found at concentrations of 0.5 parts per billion (ppb) or greater, the milk is discarded because it cannot be used for products that go into the human food supply.

Studies have shown that the presence of AFM1 in milk and milk products is a health issue because in many countries, every age group regularly consumed these products in their daily diet. It has been verified that they can initiate and advance liver, lung, and colon cancer.

It may contaminate other dairy products, such as cheese, yoghurt, and may generate health concerns for consumers.
Aflatoxin M1

Lactose intolerance

The most common types of food sensitivities include lactose intolerance and celiac disease.

A common intolerance, lactose is a principle carbohydrate found in milk and other dairy products. Deficient enzyme lactase in the lower intestine or other intestinal injury interferes with lactose absorption and produces unpleasant symptoms.

When a person with lactose intolerance consumes milk or other dairy products, some or all of the lactose they contain remains undigested, retains fluid and ferments in the colon, resulting in abdominal cramps, bloating, diarrhea and gas.

Symptoms usually begin between thirty minutes and two hours after consumptions of dairy foods.

Lactose intolerance in varying forms of severity may affect all segments of the population. It can occur up to 90 percent of some ethic groups, such as Greeks, Arabs, Jews, black Americans, Japanese, Thai, Formosans, and Filipinos.

Anthropological study has demonstrated that lactose intolerance is most common in regions of the world where adults do not drink milk.
Lactose intolerance

Food contamination of Listeria monocytogenes

Although Listeria monocytogenes was recognized as a cause of human disease for more than 75 years it was not until the 1980s that food foodborne association was realized and accepted.

Listeria monocytogenes is a gram-positive, facultative anaerobic, non-sporeforming rod, which expresses a typical tumbling motility at 20-25 ° C, but not at 35 ° C. The organism is psychotropic and grows over a temperature range of 0°  to 45 ° C, with an optimum around 37 ° C.

Listeria can survive acid, nitrite and salt and can thrive even in the refrigerator. It is well established that any fresh food product of animal or plant origin may harbor varying numbers of Listeria monocytogenes.

In general, the organism has been found in raw milk; soft cheese, fresh and frozen meat, poultry and seafood products; and on fruits and vegetable products.

Its prevalence in milk and dairy products has received much attention because of early outbreaks. Dairy cow that appear healthy can serve as reservoirs for Listeria monocytogenes and secret the organism in milk. Once obtained from the cow, milk may further contaminated through inadvertent contact with feces and silage, both of which often contain Listeria and are normally present in the diary farm environment.

Raw vegetables also have been implicated as sources in multiple listeriosis outbreaks. Vegetables may become increasingly important in human listeriosis transmission since current trend in food consummation patterns reflect increasing consumption of raw and ready-to-eat vegetable.
Food contamination of Listeria monocytogenes

Cow’s milk allergy in infant

Cow’s milk hypersensitivity involves to milk protein by the infants immune system. It is a complex disorder, in which most major cowls milk protein have been implicated in allergic response, including both casein and whey proteins.

Beta-lactoglobulin is the most highly allergenic component of cow’s milk. This sensitivity may be worsened by secondary disaccharide intolerance, resulting in severe diarrhea. Infants typically exhibit vomiting and failure to thrive.

Hippocrates (460-370 BC) was among the first to report the adverse effects of cow’s milk, including hives and gastrointestinal disorders.

Cow’s milk allergy develops in 2.2 to 2.8% of infants, of whom 85% outgrow the reactivity by their third birthday. Children who develop sensitivity after age 3 less likely to outgrow the problem.

In addition to gastrointestinal symptoms, dermatologic, respiratory, and possibly systemic reactions, such as anaphylactic shock, may occur in milk allergy.
Cow’s milk allergy in infant

Milk rancidity

A rancid flavor to milk can have a serious impact on consumers.

Milk with rancid flavor is soapy or bitter. This characteristic odor of rancid milk is derived from the unpleasant volatile fatty acids that formed as the result of lipid hydrolysis. It caused by the chemical cleavage of short chain fatty acids from triglycerides.

Lipase activity that forms free fatty acids from milk fat continues to occurs until milk is pasteurized.

Intact protein membranes normally encapsulate milk fat molecules and protect the fat from enzyme activity. Short chain fatty acids – butyric, caproic, caprylic, lauric and capric acids in the sn1 and sn3 positions of the triacyl-glycerols are particular susceptible to hydrolysis by lipase.

Rancidity is produced by hydrolysis of the fatty acid from the glycerol backbone of the triglyceride.

Triglycerides are structurally similar in all edible fats and oils. Triglycerides of milk fat are unique because they contain a group of fatty acids that are small enough when free to be volatile and odorous.
Milk rancidity

Salmonella in milk

Compared with other pathogens on the family Enterobacteriaceae, the reservoirs of Salmonella encompass a greater variety of warm and cold-blooded animal.

Salmonella species may be found in milk, and have been implicated in milkborne disease.

All Salmonella so far can be killed by properly applied pasteurization. Many other heat treatments that are common in the production of milk products, are believed to be able to kill Salmonella.

Heat treatment of milk should be complemented by good hygiene and correct operating –practices at all stages between producer and consumer.

The second highest risk milk product after raw milk is cheese. Many S. enterica strains are capable for surviving in cheese even ones with a relatively low pH such as Cheddar.

Outbreaks of milk borne infection including Salmonella associated with contaminated to inadequately heat-treated milks products have been reported in North America.

In 1985 according to the Journal of the American Medical Association, sixteen thousand confirmed illnesses of salmonella infection which traced to 2 percent milk from a single dairy plant in Chicago Illinois.

An outbreak of salmonellosis reported in Canada and the US in 1993 affected three infants following the consumption of powdered infant formula milk contaminated with S. Tennessee.

Salmonella in milk

Bacterial contamination in milk

Milk drawn from healthy cows under hygienic milking conditions is relatively clean and free from bacteria.

However many factors increase bacterial count substantially such as atmosphere, dirty and poor health udder, unclean utensils or unhealthy cows.

Nevertheless, contamination from soil, faces or bedding is also a potential source of food poisoning bacteria.

In order to reduce or eliminate contamination by spoilage and pathogenic organisms from farm to the dairy plant, the cow’s teat and surrounding udder area and all utensils and equipment used during milking and processing should be properly cleaned and sanitized.

Milk residue left on equipment contact surfaces support the growth of a variety of bacteria such as Micrococcus, Streptococcus and Bacillus spp.

Having limited bacterial contamination during milking, it is essential that contamination from equipment situated between the cow and the refrigerated storage tank is kept to a minimum.

Cooling the milk also one of the measures to reduce the bacterial contamination. Bacteria grow and multiply rapidly in warm milk. Cool milk to 16 C within 20 minutes and to 4 C within 90 minutes after it is drawn from the cow will preventing bacterial growth in milk.

A variety of sources of contamination also exist in the processing plant. Personnel and air probably contribute little to the contamination of pasteurized milks.

One of the worst bacterial contamination involved Snow Brand Milk Products Company in Japan, which infected more than thirteen thousand people and led to closure of thirty factories across the nation.

Bacterial contamination in milk