Pasteurized Milk and its Application

     Pasteurization, heat-treatment process that destroys pathogenic microorganisms in certain foods and beverages. It is named for the French scientist Louis Pasteur, who in the 1860s demonstrated that abnormal fermentation of wine and beer could be prevented by heating the beverages to about 57° C (135° F) for a few minutes. Pasteurization of milk, widely practiced in several countries. [1] The objectives of milk pasteurization are to ensure the safety of fluid milk by killing pathogens known to occur in milk and to prolong shelf life by destroying undesirable enzymes as well as reduce the number of viable spoilage microorganisms. Pasteurization is a mild type of heat treatment that causes only minor changes in milk flavor and nutritional quality. [2]

Milk pasteurization technique

Milk and milk products may be pasteurized by batch or continuous method. The batch method or low-temperature–long-time (LTLT) method uses a minimum temperature–time combination of 63  C for 30 min. The milk is stirred relatively vigorously to promote rapid heating and cooling and to minimize temperature differential among milk particles during pasteurization (all milk should be within 0.5 degree C during pasteurization to prevent cold spots within the pasteurizer or outlet valve).

The advantage of batch pasteurization is the simplicity of the method – heat–hold–cool – which can be done with only a double-jacketed tank, although a typical licensed batch pasteurizer is quite sophisticated. However, this is a slow and inefficient process. To increase efficiency and to reduce energy costs, most fluid milk plants use plate heat exchangers that continuously heat milk to a minimum of 72 C for at least 15 s.

The continuous method is referred to as high-temperature–short-time (HTST) method. Energy efficiency is improved in the HTST pasteurizer by using regeneration of heat. Warm pasteurized milk gives off heat across separating plates to the incoming cold, raw milk within the regeneration section of the pasteurizer. Regeneration efficiencies of 90% or above are typically obtained, making these systems much more energy efficient than the batch pasteurizer. [2]

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Process of milk pasteurization

Pasteurized milk processing varies from plant to plant and among countries. Several features help assure the safety of HTST pasteurization. A flow diversion valve (FDV), controlled by a temperature detector, automatically diverts milk back to the balance tank if the milk is not at the required temperature at the exit of (or at the entrance to) the holding tube. Furthermore, use of a positive displacement pump ensures that the pressure of the pasteurized milk is higher than that of the raw milk, thereby prevents the mixing of raw milk into the pasteurized milk stream within the regeneration section of the pasteurizer. Other pumps can also be used to generate the pressure differential, which should be monitored continuously. Additional safety features include an indicator thermometer, positively sloped holding tube, vacuum break, and placement of the balance tank below the inlet valve to the system. While the process described above, and illustrated in Figure 1, is typical for milk pasteurization. [2]

Effects of Pasteurization

Microbial

Pasteurization kills most of the microorganisms in milk but does not render milk sterile. Spores and thermoduric bacteria can be especially difficult to destroy by pasteurization. Thus, pasteurized milk must be kept under proper refrigeration (preferably below 4  C) throughout distribution and storage.

Nutritional

Pasteurization causes only minor nutritional losses in milk. It should  be noted that the extent of vitamin loss during pasteurization depends on several other factors, notably temperature–time combinations during pasteurization and oxygen concentration.

Enzymatic

Several indigenous milk enzymes are destroyed.

Packaging

The package protects milk from microbial contamination and the intentional or unintentional addition of foreign objects. Furthermore, it should block the passage of ultraviolet (UV) and visible light, which could lead to sunlight-oxidized off-flavors in the milk and to the loss of light-sensitive vitamins. Last, but not the least, the packaging provides an important opportunity for communicating with customers.

Shelf Life

One of the objectives of pasteurization is to increase the shelf life of milk by reducing spoilage organisms and inactivating several milk enzymes.  [2]

Milk cream

Cream is a dairy product composed of the higher-fat layer skimmed from the top of milk before homogenization. In un-homogenized milk, the fat, which is less dense, eventually rises to the top. In the industrial production of cream, this process is accelerated by using centrifuges called "separators". Cream skimmed from milk may be called "sweet cream".  Cream produced by cattle (particularly Jersey cattle) grazing on natural pasture often contains some natural carotenoid pigments derived from the plants they eat; this gives it a slightly yellow tone, hence the name of the yellowish-white color: cream. This is also the origin of butter's yellow color. Cream from goat's milk, water buffalo milk, or from cows fed indoors on grain or grain-based pellets, is white. Cream is used as an ingredient in many foods, including ice cream, many sauces, soups, stews, puddings, and some custard bases, and is also used for cakes. [3]

Processing of milk cream

Cream may have thickening agents and stabilizers added. Thickeners include sodium alginate, carrageenan, gelatine, sodium bicarbonate, tetrasodium pyrophosphate, and alginic acid. [3] A flow sheet of milk processing cream is given below…

Figure 2: Milk cream processing [4]

Butter

Butter, a yellow-to-white solid emulsion of fat globules, water, and inorganic salts produced by churning the cream from cows’ milk. [5] Although butter is also made from the milk of other mammals like sheep, goats, and buffalo.

Many different types of butter are available, including salted, unsalted, grass-fed, and clarified butter — each of which varies based on their respective ingredients and production method. [6]

Butter is a high-energy food, containing approximately 715 calories per 100 grams. It has a high content of butterfat, or milk fat (at least 80 percent), but is low in protein. Butter has substantial amounts of vitamin A and minor amounts of calcium, phosphorus, and vitamin D. The colour of butter is caused by carotene and other fat-soluble pigments in the fat. [5] 

Butter making process

Milk & cream

Collected from cows. Butter can also be produced from the milk of buffalo, camel, goat, ewe, and mares. Cream is separated from the milk. The cream can be either supplied by a fluid milk dairy or separated from whole milk by the butter manufacturer. The cream should be sweet (pH greater than 6.6), not rancid, not oxidized, and free from off flavors. The cream is pasteurized at a temperature of 95°C or more to destroy enzymes and micro-organisms.

Figure 3: Butter making process [7]

Ripening

Sometimes, cultures are added to ferment milk sugars to lactic acid and desirable flavor and aroma characteristics for cultured butter. This is more common in European butters.

Aging

Cream is held at cool temperatures to crystallize the butterfat globules, ensuring proper churning and texture of the butter. In the aging tank, the cream is subjected to a program of controlled cooling designed to give the fat the required crystalline structure. As a rule, aging takes 12 - 15 hours. From the aging tank, the cream is pumped to the churn or continuous buttermaker via a plate heat exchanger which brings it to the requisite temperature.

Churning

Cream is agitated, and eventually butter granules form, grow larger, and coalesce. In the end, there are two phases left: a semisolid mass of butter, and the liquid left over, which is the buttermilk.

Draining & washing

Thus the cream is split into two fractions: butter grains and buttermilk. In traditional churning, the machine stops when the grains have reached a certain size, whereupon the buttermilk is drained off. With the continuous buttermaker the draining of the buttermilk is also continuous.

After draining, the butter is worked to a continuous fat phase containing a finely dispersed water phase. It used to be common practice to wash the butter after churning to remove any residual buttermilk and milk solids but this is rarely done today. This washing process would ensure that all the butter milk is washed out of the butter. Otherwise the butter would not keep and go rancid.

Salting & working

Salt is used to improve the flavor and the shelf-life, as it acts as a preservative. Further, the butter is worked to improve its consistency.

Packing & storage

The butter is finally patted into shape and then wrapped in waxed paper and then stored in a cool place. As it cools, the butterfat crystallizes and the butter becomes firm. Whipped butter, made by whipping air or nitrogen gas into soft butter , is intended to spread more easily at refrigeration temperatures. [7]

Cheese

Cheese is a dairy product, derived from milk and produced in wide ranges of flavors, textures and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During production, the milk is usually acidified and the enzymes of rennet (or bacterial enzymes with similar activity) are added to cause the milk proteins (casein) to coagulate. [8] Cheese is a great source of calcium, fat, and protein. It also contains high amounts of vitamins A and B-12, along with zinc, phosphorus, and riboflavin. Cheese made from the milk of 100 percent grass-fed animals is the highest in nutrients and also contains omega-3 fatty acids and vitamin K-2. [9]

Cheese processing

Making cheese is both an art and a science. Cheesemakers rely as much on measurements of pH levels and inoculations of specific molds as they do their own senses of sight, touch, and smell.

There are six important steps in cheese making: acidification, coagulation, separating curds and whey, salting, shaping, and ripening.

Acidification

The first step to making cheese is acidification. During this stage, a starter culture is added to milk that will change lactose (milk sugar) into lactic acid. This changes the acidity level of the milk and begins the process of turning milk from a liquid into a solid.

Coagulation

Coagulation is the process of transforming the liquid into a semisolid. When making cheese, an enzyme called rennet is added either as a liquid or paste to further encourage the milk to solidify.

Curds and Whey

As the milk solidifies, it forms curd and whey. The curds are the solid part and whey is the liquid. In this step, the curds are cut using a knife or a tool that resembles a rake. Cutting the curds further encourages them to expel whey. Generally, the smaller the curds are cut, the harder the resulting cheese will be. Soft cheeses like Camembert or Brie are hardly cut at all. Harder cheeses like cheddar and Gruyere are cut into a very fine texture. For these harder cheeses, the curds are further manipulated by cheddaring and/or cooking. Cooking the curd changes its texture, making it tender rather than crumbly. When this process is complete, the whey is drained away, leaving the curd alone to become cheese.

Salting

Salt is added for flavor. It also acts as a preservative so the cheese does not spoil during the long months or years it spends aging and it helps to form a natural rind on the cheese.

There are several ways to use salt. Salt can be added directly into the curd as the cheese is being made. The outside of the wheel of cheese can be rubbed with salt or with a damp cloth that has been soaked in brine (heavily salted water). The cheese can also be bathed directly in a vat of brine, as it is for mozzarella.

Shaping

In this stage, each type of cheese takes its familiar form as a solid block or wheel. The cheese is put into a basket or a mold to form it into a specific shape. At the same time, the cheese is also pressed with weights or a machine to expel any remaining liquid.

Ripening

Referred to as affinage, this process ages cheese until it reaches optimal ripeness. During this time, the temperature and humidity of the cave or room where the cheese ages are closely monitored.

An experienced affineur knows how to properly treat each cheese so it develops the desired flavor and texture. For some cheeses, ambient molds in the air give the cheese a distinct flavor. For others, mold is introduced by spraying it on the cheese (Brie) or injecting it into the cheese (blue cheese). Some cheeses must be turned, some must be brushed with oil, and some must be washed with brine or alcohol. The amount of time a cheese is left to ripen depends on the type of cheese and the cheesemaker's desired outcome. It may take several months to quite a few years for a cheese to age, but once finished, it is ready to be packaged. [11]

Figure 4: Cheese making process [10]

Risks

Ø Some people are sensitive to cheese. Cheese contains lactose, a sugar that can’t be digested by lactose intolerant people because their bodies lack the enzyme that breaks it down. In these cases, too much lactose can lead to digestive problems including gas and bloating.

Ø People can also be allergic to casein, one of the main proteins found in milk, in which case a low-lactose cheese wouldn’t help.

Ø Cheese is also a calorie-dense food. Depending on the variety of cheese you eat, you’re getting about 100 calories per ounce.

Ø It’s also usually loaded with sodium, which makes it easy to overeat and can be an issue for people with high blood pressure.

Ø Cheese is also high in fat, and some experts, though not all, still advise limiting your intake of saturated fat.

Ø Finally, cheese contains no fiber, and excessive intake of pasteurized dairy may cause constipation. [9 ]

Egg powder

Powdered eggs are fully dehydrated eggs. They are made using spray drying in the same way that powdered milk is made. The major advantages of powdered eggs over fresh eggs are the reduced weight per volume of whole egg equivalent and the shelf life. Other advantages include smaller usage of storage space, and lack of need for refrigeration. Powdered eggs can be used without rehydration when baking, and can be rehydrated to make dishes such as scrambled eggs and omelettes. The process of drying eggs so as to make powdered eggs oxidizes the cholesterol, which has been shown to be helpful at reducing aortic atherosclerosis in animal trials. [12]

Egg powder processing is need to

Ø Longer shelf life

Ø Ease in shipping and transportation

Ø Changing dietary habits from carbohydrate-based food to protein-rich food

Ø Increasing demand with flourishing bakery industry and food industry altogether. [13]

Egg powder processing

Figure 5: Egg powder processing [13]

v Eggs are broken and the outer shell is removed

v Egg yolk and albumen are separated. This step is omitted in case of whole egg powder

v The mixture or each component is filtered and stored in storage tanks at 4 degree C

v It is pasteurized in the tubular heater at about 65 degree C for 8-10 minutes

v It is dried in spay drier which yields egg powder

v Finally, the powder is packed per the end use. [13]

Food sector in Bangladesh

Bangladesh has a rapidly growing consumer market and due to a large population base, the demand for food products is always on the rise. The market and the product range have evolved significantly over the last decade and many companies have entered the food business which was otherwise not into this level of diversification in the past.

Golden Harvest sees a lot of potential in the growth of the food market. The rational consumer is inclined toward having a good product at the right price. [14] The food processing industry in Bangladesh represents one of the major potential sectors within the industrial segments in terms of contribution to value addition and employment. The sector accounts for over 22% of all manufacturing production and employs about 20% of labor forces. All food processing enterprises account for 2% of the national GDP. The food processing sector includes processing of cereals, pulses & oilseeds, bakery and confectionary, fruits and vegetables, dairy, carbonated beverages and non‐carbonated fruit juices, drinks, other beverage and various other food items. [15]

The major food processing sub-sectors in Bangladesh include dairy, edible oil, sugar, rice, wheat, fruit and vegetable, tea, poultry/beef, pulses and spices and fish processing industries.

Name of some food industries are given below…….

ü PRAN Foods Ltd.

ü ACI Foods Ltd.

ü IFAD Multi Products Ltd.

ü Fu-Wang Foods Ltd.

ü Ispahani Foods Ltd.

ü Bombay Sweets & Co. Ltd.

ü Square Food & Beverage Ltd. (SFBL)

ü Akij Food and Beverage Ltd. (AFBL). Etc [16]

References

1. Pasteurization, heating process written by The Editors of Encyclopaedia Britannica

2. Liquid Milk Products: Pasteurized Milk, Lisbeth Meunier-Goddik, Oregon State University, Corvallis, OR, USA; S Sandra, GPI Inc., Newmarket, ON, Canada.

3.https://en.wikipedia.org/wiki/Cream#:~:text=Cream%20is%20a%20dairy%20product,using%20centrifuges%20called%20%22separators%22.

4. Calibration of Infrared Milk Analyzers: Modified Milk Versus Producer Milk, K.E. Kaylegian, G.E. Houghton, J.M. Lynch, David M Barbano.

5. https://www.britannica.com/topic/butter

6. https://www.healthline.com/nutrition/is-butter-bad-for-you#what-it-is

7. http://www.webexhibits.org/butter/process-steps.html

8. https://en.wikipedia.org/wiki/Cheese

9. https://www.healthline.com/health/is-cheese-bad-for-you

10.https://www.researchgate.net/figure/Flowchart-of-the-cheese-making-process_fig1_263514709

11.https://www.thespruceeats.com/important-steps-in-cheesemaking-591566#:~:text=There%20are%20six%20important%20steps,to%20make%20cheese%20at%20home.

12. https://en.wikipedia.org/wiki/Powdered_eggs

13. https://www.foodbuddies.in/egg-powder-processing/

14. https://www.thedailystar.net/food-industry-in-bangladesh-6622

15. Developing 08 countries D‐8, 3rd D‐8 Ministerial Meeting on Industry, 7th Meeting of the Working Group on Industrial Cooperation, 08‐10 October 2012, MoI, GoB

16.https://www.businesshaunt.com/top-10-food-and-beverage-companies-in-bangladesh/