Tag: #pasteurization

YOGURT- a fermented milk product

Yogurt is a basic fermented milk product that usually contains the basic bacterial starter cultures of Lactobacillus bulgaricus and Streptococcus thermophillus.
Although the composition of different types of yogurts changes but there is some fixed composition of fats present in them. It is important to note that all yogurts must contain at least 8.25% of solid which is not fat. The fat composition changes with the type of yogurt like full fat yogurt must contain not less than 3.25% of milk fat whereas low fat yogurt must not contain more than 2% milk fat. Also there is a category of non fat yogurt where the fat composition is even less than 0.5%.
The yogurt is basically a mixture of milk and cream which is then fermented by using a culture of Lactic acid producing bacteria. The types of milk which can be used are whole, reduced-fat, low-fat or non-fat depending on which the type of yogurt is decided. The lactic acid produced by the starter culture bacteria is basically responsible for lowering the pH of the yogurt making it acidic and tart. This finally causes the milk protein to thicken. These bacteria ferment the milk which results in the production of yogurt leads to partial digestion of the milk making it more easily digestible. In addition, these bacteria also act as a beneficial microorganisms for the human body as they act as oral-antibiotic therapy and helps in eliminating the pathogenic-bacteria from the gut and replenishing the non-pathogenic bacteria.


Ingredients of yogurt –
Milk
Cream
Sweeteners (e.g. sugar, honey, aspartame, etc)
Flavorings (e.g. vanilla, coffee, etc)
Other ingredients (e.g. fruits, preserves, stabilizers such as gelatin)

Types of yogurt –

  1. Set yogurt – This type of yogurt has a jelly-like structure and texture and is incubated and cooled in a final package.
  2. Stirred yogurt – This type is less firm than set yogurt. It is incubated in a tank and final coagulum is broken by stirring before cooling.
  3. Drinking yogurt – It also has coagulum broken before cooling though very little reformation of coagulum will occur.
  4. Frozen yogurt – This type of yogurt is incubated in the same way the stirred yogurt is incubated. It has an ice-cream like texture.
  5. Flavored yogurt – In this type of yogurt, flavors are added just before yogurt is poured into pots and the sugar content present in this type of yogurt is about 50%.

General processing of yogurt –

  1. Adjusting milk composition and blending all the ingredients
  2. Pasteurization of milk (at 85 degrees celcius for 85 minutes)
  3. Homogenization of milk (2000-2500psi)
  4. Cooling of milk to 42 degree celcius
  5. Inoculation with bacterial starter cultures into the cooled milk
  6. pH reduction by waiting for sometime
  7. Again cooling to 7 degree celcius
  8. Addition of fruits and flavors
  9. Packaging of prepared yogurt.

Health benefits of yogurt:
• Yogurt is comparably easier to digest than milk.
• It is rich in variety of vitamins.
• It is a rich source of protein.
• As it is source of protein, it may help in losing weight and gain muscles.
• It acts as a booster for immune system
• It is also important and useful for digestive system. It destroys the pathogenic microorganisms from the gut.
• It is good for bones especially for kids and elderly
• It may also be useful in lowering the blood pressure.

USE OF PHYSICAL METHODS IN MICROBIAL CONTROL

Although microorganisms are beneficial and necessary for human well being, microbial activities have undesirable consequences such as food spoilage and disease. To minimize there destructive effects, it is essential to kill a wide variety of microorganisms or inhibit their growth.

  1. Heat
    Heating is still one of the most popular ways to destroy microorganisms. Fire and boiling water have been used since the time of Greeks for sterilization and disinfection. Exposure to boiling water for 10 minutes is sufficient to kill or destroy vegetative cells and eukaryotic spores, but not enough to kill or destroy bacterial endospores, hence boiling does not sterilize but can be used for disinfection of drinking water and objects not harmed by water. This can be carried out within an autoclave. Hot and saturated steam enters a chamber and the desired temperature and pressure which is usually 121°C and 15 pounds is reached. At this temperature and pressure the steam destroy all vegetative cells and endospores. Moist heat is thought to kill so effectively by degrading nucleic acids and by denaturing enzymes and other essential proteins It may also disrupt cell membranes.
    Pasteurization is a process where many substances such as milk, are treated with controlled heating at temperatures well below boiling. There are two types of pasteurization- flash pasteurization or high temperature short term (HTST) pasteurization and the other method used is ultra high temperature (UHT) pasteurization.
    Dry heat sterilization can also be used on many objects in the absence of water. The items to be sterilized are placed in an oven at 160 to 170°C.
  2. Low temperatures
    Another convenient method to inhibit the growth and reproduction of microorganisms is to use lower temperatures like freezing or refrigeration. Mostly this method of control is used in food microbiology. Freezing items at -20°C or lower stops microbial growth because of the absence of liquid water and the ice crystal destruction of cell membranes at this temperature. This method is also used for long term storage of microbial samples in the laboratory in the form of glycerol stocks. This method of control at low temperatures slows microbial growth and reproduction but does not half it completely. Fortunately most pathogens are mesophilic and do not grow well at low temperatures around 4°C. Thus, refrigeration is a good technique only for short-term storage of food and other items.
  3. Filtration
    The filters simply remove the microbes instead of killing them. The material used mostly is glazed porcelain, asbestos or other similar materials. Membrane filters are also used and have replaced depth filters in recent times. These filters are used to remove most vegetative cells, but not viruses from solutions ranging in volume from 1 ml to many liters.
    The other way this method is used is in the laminar flow biological safety cabinet where the air is sterilized by filtration. These cabinets contain high efficiency particulate air(HEPA) filters.
  4. Radiation
    The radiations like ultraviolet and ionizing can be used for sterilizing objects. UV radiation is used as a sterilizing agent only in a few specific situations like UV lamps are placed on the ceilings of room for in biological safety cabinet to sterilize air and other exposed surfaces. Commercial UV units are available for water treatment. Pathogens and microorganisms are destroyed when a thin layer of water is passed under the lamps (water purifiers).
    Ionizing radiation penetrates deep into objects and is an excellent sterilizing agent. It destroys bacterial endospores and vegetative cells of both prokaryotic and eukaryotic origin but not against viruses. Gamma radiation from a Cobalt 60 source is used in the cold sterilization of antibiotics, hormones and plastic disposable supplies such as syringes and petri dishes.