Milk, a vital and widely consumed beverage, has undergone numerous technological advancements to extend its shelf life while preserving its nutritional value. One such innovation is Ultra High Temperature (UHT) treatment, a process that revolutionizes milk preservation. UHT milk undergoes a rigorous heating process that eliminates harmful microorganisms, ensuring a longer shelf life without the need for refrigeration.

The science behind UHT milk involves a delicate balance of temperature, time, and the understanding of microbial growth. This innovative technology has revolutionized the dairy industry, making it possible to transport and store milk for extended periods without compromising safety or taste.

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This post will explore the scientific aspects of UHT milk and how it differs from conventional pasteurization. We will discuss the key stages involved in UHT treatment, including the heating process and its effects on the nutritional composition of milk. Furthermore, we will examine the microbiological factors, including the elimination of harmful bacteria and the importance of aseptic packaging in preserving the milk’s sterility.

Let’s dive in.

WHAT IS ULTRA HIGH TEMPERATURE (UHT) MILK?

When you visit a supermarket, you may notice two different types of milk storage: refrigerated milk and milk displayed on a shelf at room temperature. The distinction between these two types lies in the treatment they have undergone. Refrigerated milk has typically undergone pasteurization, while the milk on the shelf has been treated with the ultra-high temperature (UHT) method.

Ultra-High Temperature (UHT) milk refers to a type of milk that has undergone an intense thermal treatment process to achieve an extended shelf life without the need for refrigeration. This preservation method involves subjecting the milk to extreme heat of 284°F (140°C) for 4 seconds. This rapid heating is crucial as it ensures the destruction of bacteria, yeast, and molds that may be present in the milk. By eliminating these microorganisms, UHT milk remains safe for consumption over an extended period, even without refrigeration. A properly packaged UHT milk should last 3 to 6 months or longer.

This is the reason why UHT milk can be safely displayed on the shelf at room temperature. Sure, pasteurized milk has also been heat-treated, but the temperature is relatively lower. The temperature for milk pasteurization is 162°F (72°C) for 15 seconds. This does not completely sterilize the milk. Hence, some microorganisms, although significantly reduced in number, may still be present. These remaining microorganisms can multiply and cause spoilage if the milk is not refrigerated.

The advantages of UHT milk are significant. It allows for the distribution and availability of milk in the regions where refrigeration may be limited or unreliable. UHT milk also provides convenience for consumers, as it can be stored at room temperature until opened. An opened UHT milk under refrigeration has a shelf life similar to that of fresh milk, 7 to 10 days.

HOW IT IS MADE

The process begins with the collection of fresh milk from dairy farms. Quality control measures are implemented to assess the milk’s composition, including fat content, protein content, and absence of any abnormalities or contaminants.

The collected milk undergoes pre-treatment to remove any impurities or particles. This involves processes such as clarification, centrifugation, or filtration to ensure a clean milk base for further processing.

The pre-treated milk is then subjected to ultra-high temperatures. In UHT treatment, the milk is heated rapidly at 284°F (140°C) for 4 seconds. This time and temperature combination varies, depending on the manufacturer and brand.

Following the heating process, the milk is rapidly cooled to bring it back to a safe temperature. This step is crucial to halt the heating process and prevent any further undesirable changes in the milk’s composition.

During UHT processing, the sugars in the milk, such as lactose, can undergo caramelization due to the intense heat. This process leads to the formation of new compounds and the development of characteristic flavors and colors associated with caramelization. However, caramelization can contribute to a burnt or slightly cooked flavor, altering the natural sweetness of the milk. The milk may also lose some of its original creaminess or richness, resulting in a slightly thinner consistency.

Once cooled, the UHT milk is filled into sterilized containers through a process known as aseptic packaging.

With aseptic packaging, the packaging materials undergo sterilization to eliminate any microorganisms on their surfaces.

The aseptic carton or Tetra Pak is the most prevalent type of packaging used for aseptic packaging of UHT milk. These cartons have several layers, including a layer of paperboard, an aluminum foil layer, and layers of plastic film. This mix of components creates a barrier against light, oxygen, and bacteria, assuring the milk’s long shelf life and safety.

UHT MILK NUTRITIONAL COMPOSITION

UHT milk retains many of the essential nutrients, including proteins and calcium, found in fresh milk. But here is the thing though.

Although protein is still present in UHT milk, the intense heat during the UHT process denatures the proteins in the milk. Denaturation refers to the structural changes in proteins due to heat exposure. This leads to a loss of their original shape and function. The high temperatures used in UHT treatment can cause denaturation of the milk proteins, altering their structure. Denatured proteins may have reduced bioavailability. So proteins in UHT milk may be less efficiently digested and absorbed by the body compared to those in raw milk.

Furthermore, the heat treatment involved in UHT processing can impact the solubility of specific minerals, such as calcium. While UHT milk provides a similar calcium content as other milk types, the high temperatures used in UHT treatment can cause calcium to become insoluble, leading to the formation of precipitates or clumps. For this reason, the body may encounter challenges in effectively absorbing and utilizing the calcium in UHT milk when compared to raw milk.

In a 2013 study conducted in Korea, the effect of various heat treatments on the solubility of calcium in commercial milk products was investigated. The findings revealed that raw milk exhibited the highest calcium levels, measuring 450.2 mg/kg and 444.2 mg/kg after two rounds of ultrafiltration. In comparison, UHT milk only contained 370.3-380.2 mg/kg and 371.3 mg/kg of calcium after undergoing ultrafiltration.

However, it is important to note that UHT milk still contains significant amounts of calcium. To compensate for potential calcium loss, some UHT milk products may be fortified with additional calcium to ensure an adequate intake of this essential mineral.

MICROBIAL DESTRUCTION AND STERILITY

The key principle behind UHT milk is the concept of thermal processing. This relies on the understanding that microorganisms and enzymes are heat-sensitive. Raw milk may contain pathogenic bacteria such as Listeria, Campylobacteria, Salmonella, Brucella, Cryptosporidium, and E. coli. When milk is exposed to such high temperatures, the heat disrupts the structure of these microorganisms. This renders them inactive and incapable of causing spoilage. Additionally, UHT treatment also inactivates enzymes that can lead to undesirable changes in flavor, texture, and nutritional quality.

After undergoing the Ultra High Temperature treatment, milk has to be packaged in a way that maintains its sterility and prevents recontamination. This is achieved through a process called aseptic packaging.

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Aseptic packaging involves filling the UHT milk into pre-sterilized containers under hygienic conditions. These containers are designed to create a barrier against any microorganisms or external contaminants that could compromise the milk’s safety and quality. Aseptic packaging is crucial in preserving the long shelf life of UHT milk without the need for refrigeration.

The containers used for aseptic packaging are typically made of materials such as cartons, bottles, or pouches. These packaging materials undergo a sterilization process to eliminate any microorganisms present on their surfaces. The sterilization techniques can include heat treatment, chemical sterilization, or a combination of both.

The post The Science Behind Ultra High Temperature (UHT) Milk appeared first on The Food Untold.

Pasteurization is one of the most widely used forms of food preservation. Pasteurization involves treating food with mild heat to destroy all disease-causing microorganisms and spoilage enzymes. The process is named after the French scientist, Louis Pasteur.

It all started in the 1860s when Napoleon III, emperor of France, requested to determine the cause of souring and contamination of wine. Pasteur then demonstrated that microorganisms caused it. And it could be prevented by heating the wine at 120°F (50°C) to 140°F (60°C) for several minutes. This mild thermal process eventually became what we know today as pasteurization. Today, pasteurization applies to foods such as eggs, fruit juices, beers, and milk.

Generally, pasteurization involves heating packaged or non-packaged with mild heat of less than 212°F (100°C). However, pasteurization comes in several types today. And one of them is flash pasteurization, also called high-temperature short time (HTST) pasteurization. In the United states, HTST is the most common method used, especially for milk.

During flash pasteurization, the product is treated with mild of heat of 162°F (72°C) to 165°F (74°C) for 15 to 20 seconds and then followed by rapid cooling.

In flash pasteurization of milk, the product is heated with mild heat of 161°F (71.7 °C) for 15 seconds to destroy Coxiella burnetii. Coxiella burnetii is the most heat-resistant pathogen in raw milk. The process is a standard US protocol for flash pasteurization of milk, which was first introduced in 1933. Flash pasteurized milk may last 16 to 21 days.

In processing of fruit juices, the product may be heated rapidly for about 1 minute and then filled into containers. The containers are sealed airtight under cover steam to sterilize the seal and then cooled. This process may be used for apple juice, orange juice, grape juice, etc.

ADVANTAGES OF FLASH PASTEURIZATION

The common applications of flash pasteurization include milk, beer, and fruit juices. Because flash pasteurization involves mild heat, it holds several advantage over other forms of heat treatment:

• There is minimal change in flavor, color, and nutrients
• It economically saves time and space
• Heats product uniformly, reducing cooked taste to a minimum
• Beneficial enzyme inactivation is obtained

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OTHER TYPES OF PASTEURIZATION

Ultra high temperature (UHT)

Ultra high temperature (UHT) pasteurization involves heating, usually milk, in commercially sterile equipment and pouring it into hermetically sealed packaging under aseptic conditions. The process involves heat of 284°F (140°C) for 4 seconds. The product is “shelf stable,” which means it doesn’t need to be refrigerated until it’s opened. And it can last up to 6 months or even longer. This type of pasteurization is also called aseptic processing.

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Low temperature long time (LTLT) pasteurization

Low temperature long time (LTLT) pasteurization, as the name suggest, involves low temperature and long time for pasteurization. In this type, the product is heated at 145°F (63°C) for 20 to 30 minutes. LTLT does not alter the structure as well as the taste of the milk. But prolonged holding time may change the milk protein’s structure and the taste. This type of pasteurization is called batch pasteurization.

References:

M. Shafiur Rahman (2007). Handbook of Food Preservation (2nd edition). CRC Press.

P. Fellow (2000). Food Processing Technology (2nd edition). CRC Press.

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