UHT Milk Spoilage and the Influence of Fat Content

l.Introduction

Over 6 billion people worldwide consume milk and milk products. Dairy manufacturers do their best to extend the shelf life of milk as well as to maintain its quality and flavor. To obtain that, dairy industry commonly applies ultra-high-temperature processing, which seems to be the most effective way to meet these goals. Nevertheless, this method does not prevent milk from spoilage, but only postpones this process. One of the factors that can determine the rate of UHT milk spoilage is fat content. According to research, the process of breaking down fats in UHT milk contributes to milk acidity¹. Moreover, the process of UHT milk spoilage also involves a process called creaming which can be directly observed as a thin and viscous layer of fat on the milk surface. Therefore, this paper aims to explore the changes in the pH of milk and the process of creaming that taken together represent the dependent variable, that is UHT milk spoilage. Most importantly, the connection between fat content and the dependent variable will be investigated. The research suggests² that the rate of UHT milk spoilage increases with the amount of fat present in the milk, and this investigation will assess the validity of this statement. I chose this topic since my diet, which corresponds to my blood group, is based mainly on milk, and I would like to find out more about the main component of the meals I consume. Moreover, I want to know how fast UHT milk with different fat contents goes sour. There are many variations of this product that differ from each other only by fat content and I have never come across a clear and explicit answer relating to its impact on milk quality over time. The importance of this subject is significant because UHT milk consumption constantly increases, reaching the threshold of 119 million tons in 20 1 9³ and constitutes a strong fundament of people’s diet. My research extends the knowledge about the process of UHT milk spoilage and its link with fat content as well as gives food for thought when it comes to the UHT milk preservation methods, shelf life, and the impact of other ingredients on the process of spoilage.

Research question: How different amounts of fat (0.0%, 0.5%, 2.0%, 3.2% and 3.8%) in ultra-high processed milk (UHT) influence the rate of its spoilage?

2.Investigation

2.1: Hypothesis

Hi: The rate of UHT milk spoilage increases as the fat content increases.

Hq: The fat content has no effect on the rate of UHT milk spoilage rate.

2.2: Background information

The process of UHT milk spoilage is a very broad concept but in general, it refers to any unwanted change or a decline in the quality of milk caused by various factors, such as the presence of microorganisms. Referring to the research question, it turned out that a certain genus- Pseudomonas- is especially important when looking for the answer to my research question. The study on a similar subject concluded that Pseudomonas in raw milk produce proteinases and lipases that later break down proteins and lipids respectively. Furthermore, these enzymes are heat-resistant, so they survive UHT treatment and retain their activity after this process in UHT milk⁴. Additionally, the by-product of proteolysis and lipolysis is the just mentioned milk acidity, which results in a pH decrease. When it comes to creaming, it is one of the three processes, apart from age gelation and sedimentation, which together result in the formation of a dense layer that reduces milk fluidity⁵. However, age gelation and sedimentation create an appreciable protein-rich layer, whereas creaming can be described as a process of forming a relatively thin layer of excess fat that accumulates on the top of the protein-rich structure created by the above processes and depends on the temperature, size of fat globules, and the fat content⁶. Then, the lipid molecules are especially valuable to degradative actions which reduce the shelf life and spoil UHT milk.

2.3: Variables

Independent variable: The percentage of fat in UHT milk.

Dependent variable: The rate of UHT milk spoilage determined by pH value and the intensity of the creaming process.

Controlled variables:

1. The volume of milk in each container was kept at 100 cm3 and the milk was fit for consumption at the beginning of the experiment and the expiry dates of milk were very similar.
2. The samples were kept at the average temperature of 21.8 degrees Celsius.
3. The same brand of milk was used in each sample.
4. The measurements were taken at the same time of the day (8pm) using the same equipment.
5. The samples were kept in the same light conditions at all times.
6. The milk in each sample had the same amount of lactose in it (10 grams per sample).
7. All samples had coverings, so no other elements from the air had access to the samples.
8. The number of stirs when adding lactose to UHT milk was the same (10 stirs in the anti-clockwise direction).

2.4: Preliminary experiment

A preliminary experiment was carried out over the course of 8 days to ensure that the differences in pH are significant between the UHT milk with different fat content to assess how much sugar should be added to the milk to make its spoilage neither too slow, nor too fast. The procedure was the same as in section 3.3, however, it was simplistic. Fewer types of milk were used and the measurements were not as accurate as in this research because the purpose of the preliminary experiment was to understand the whole phenomenon, check the effectiveness, and to note down important observations rather than taking accurate measures and making calculations. It has allowed me to make several amendments such as adding lactose, not saccharose, to the milk, equaling the level of this sugar in milk, or extending the duration of the experiment. The pre­experiment has also helped me to come up with the method of measuring the milk creaming process. This information allowed me to decide that my experiment should be 10 days long, and that each of the 25 samples should have 100 cm3 of volume and should contain 10 grams of lactose.

3. Procedure

3.1: Equipment

1. 25, 250 cm3 containers.
2. Plastic pipette-to make small corrections in measuring out the UHT milk.
3. 500 cm3 of UHT milk of each type: 0.0% of fat, 0.5% of fat, 2.0% of fat, 3.2% of fat and 3.8% of fat content.
4. 129 grams of lactose-to even out the percentage of this sugar in UHT milk.
5. Scales (± 0.01g) -to weight the lactose needed.
6. Spatula-to transfer the lactose to the milk.
7. 25 coverings-to provide stable and persistent environment in the containers.
8. pH meter (± 0.01 pH).
9. Sifter-to separate the milk in the „liquid state” (particles’ size less than 1 mm) from the gunky and rancid milk at the end of the experiment.
10. 100 cm3 cylinder (± 0.5cm3) -to measure out the volume of UHT milk at the beginning of the experiment and to assess the spoilage of milk (creaming) after the experiment.

3.2: Methodology

1. Prepare the 250cm3 container and weight the lactose needed using scales (± 0.01g).
2. Using spatula, place the calculated amount of lactose into the container to even the amount of this sugar in UHT milk to 10 grams.
3. Add 100 cm3 of milk using a cylinder (±0.5cm3) and stir it 10 times in an anti-clockwise direction.
4. Measure the pH of the UHT milk using a pH meter (±0.01 pH). Note observations if necessary.
5. Cover the container.
6. Take pH measurements daily at the same time of the day for 10 days.
7. After the last measurement, transfer the UHT milk from the container to the 100 cm3 cylinder using a sifter.
8. Measure the volume of UHT milk in the 100 cm3 cylinder (± 0.5cm3).
9. Repeat steps 1-8 four times. It gives 5 repetitions for each fat content and 25 repetitions in total.

3.3: Justification

Five pH measurements of each type of UHT milk were carried out to improve the reliability of the experiment. Five types of UHT milk were chosen to make the supposed trend more distinctive. The same brand of UHT milk was used in all samples to avoid unwanted differences due to variations in its composition and the coverings were used to provide a stable environment. When it comes to equaling the level of lactose, it was done to even out the pace of spoilage in all samples and to eliminate any unwanted changes in the spoilage process that would not be caused by the difference in fat content. The constant number of stirs and the same direction of stirring helped to ensure that lactose is equally dissolved in each sample of UHT milk. Furthermore, the samples were kept at a room temperature and half-light conditions to accelerate the process of spoilage and at the same time not increasing it too much. The dependent variable was chosen because of a variety of signs that indicate the UHT milk spoilage process. I chose to investigate pH values and the process of creaming since it makes my research more objective; it is a combination of qualitative and quantitative data. Furthermore, there is not much research on creaming and I believe that my experiment will increase the knowledge about this process.

3.4: Risk assessment

Safety Issues: Do not drink the milk at any stage of the experiment.

Ethical Issues: There were no ethical issues to be taken into account.

Environmental Issues: There were no environmental issues to be taken into account.

4. Raw data

Because of certain irregularities (caused probably by the previous contamination of milk), the data from 3.2% fat content UHT milk was withdrawn from the analysis. As a result, data from 4 types of milk is presented in the tables below.

Table 1: A table showing how the pH of UHT skim milk (0.0% fat content) varies over the course of 10 days at an average temperature of 21.8 degrees Celsius.

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Table 2: A table showing how the pH of 0.5% fat content milk varies over the course of 10 days at an average temperature of 21.8 degrees Celsius.

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Table 3: A table showing how the pH of 2.0% fat content milk varies over the course of 10 days at an average temperature of 21.8 degrees Celsius.

Abbildung in dieser Leseprobe nicht enthalten

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¹ Bellow, F., Yagoub, S. and El-Zubeir, I., 2008.

² Muir, D., 2011.

³ Global UHT Milk Market Analysis Forecast, 2019.

⁴ Erkmen, O. and Bozoglu, T., 2016.

⁵ Anema, S., 2018.

⁶ Karlsson, M. et al., 2019.