Introduction
In this assignment Titratable acidity (TA) and pH are methods used to measure levels of acidity. In this experiment pH testing and Titratable Acidity measurements were carried out on fresh milk and buttermilk. The purpose of this assignment was to determine the acidity levels in fresh milk and buttermilk and then by using a pH meter to determine the pH of both fresh milk and buttermilk.
The aims for this research project was to understand how data is collected using a pH meter and carrying out a Titratable Acidity test on samples of fresh milk and buttermilk and comparing them to a set of standard values, by doing so this allowed for a better understanding of the experiment and what was hoped to be achieved.
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The TA test of milk has two kinds, these include natural acidity and developed acidity. Natural Acidity is due to the citrated and phosphates present in the milk. Developed acidity is due to the lactic acid produced by bacteria on the lactose in the milk. By titrating the milk with the phenolphthalein, the acidity of the milk can be determined. Titratable acidity measured the total acidity in a sample in this case milk in both free hydrogen ions and as hydrogen ions still bound to acids (Murano, 2003).
Buttermilk and Milk differ as products. By breaking down both samples some of the differences included, calories, fat content and calcium. For consumer who are lactose intolerant they are still able to drink buttermilk as it has a lower lactose content than regular milk.
Milk is a which liquid that is rich in fat and protein coming from the mammary glands in a female cow to produce milk for her calf. Milk is a complex biological fluid, the major constituent is water but according to species milk contains varying quantities of lipids, proteins and CHO which are synthesized within the mammary gland (Class Notes, 2020). The composition of milk contains around 87% water, 3.5% proteins (casein and whey) 3.6% fat. 4.9% carbohydrate (Lactose) while also containing some vitamins, minerals, and enzymes such as Lipases, Proteases and peroxidase. Buttermilk is a sour liquid which is left after butter has been churned and is commonly used in baking. The composition of buttermilk is around 90% water, 5% lactose, 3% casein protein and around 2% butterfat.
Discussion
This experiment was conducted to gather results for Titratable Acidity and pH and to compare the values against the samples of fresh milk and buttermilk to analyse any differences there may have been. From conducting these tests it was discovered that not only did fresh milk have a higher pH of 6.67 in comparison to buttermilk that had a pH of 4.36 this meant that the sample of fresh milk is more of an alkaline than buttermilk. This may have been because of the bacteria in buttermilk produces lactic acid the pH level is reduced and casein which is the primary protein solidifies. When the pH decreased the buttermilk then thickens (Panoff, 2019). This is because of a lower pH in the buttermilk more acidic. Due to buttermilk being more acidic this allowed for the sample to have a longer shelf-life. Opened buttermilk can last up to 14days in the correct storage condition whereas, milk can only last up to 7days once opened.
As the titratable acidity experiment was conducted on a sample of milk and buttermilk this allowed for the progress of fermentation to be monitored. This is the breakdown of carbohydrates into sugar and acids and is essential for fermented milk quality.
In comparison to Murano’s findings it was discovered that the pH of fresh milk was between 6.5 and 6.7 while having a Titratable Acidity of around 0.14-0.18. in comparison to results gathered from conducting this experiment the value found for pH of fresh milk was 6.67 and the Titratable Acidity was an average of 0.156%. These values for fresh milk proved to be like Murano’s findings. This would indicate that the experiment was carried out correctly.
As the milk gets older the lactic acid bacteria converts lactose into lactic acid and this increases the acidity. Titratable Acidity is useful for monitoring small changes in acidity than pH and because of this it is very commonly used within the dairy industry. This experiment determines the percentage of acidity of milk and buttermilk and the acidity is expressed as the percentage of lactic acid.
By adding the Rosailine Solution this reduced the standard colour at the end point of the titration. The colour of the end point had a pink tinge and the aim of this was to get the same reaction into the sample dish. By using 1.44ml of Phenolphalein Solution this resulted in the same pick tinge to appear after stirring into the milk sample. Phenolphalien Solution is a colourless acidic solution and when the pH becomes greater than 8 this allows for the sample to turn pink.
Sodium hydroxide helped to neutralise 0.01g of lactic acid, because of this it allowed the calculation for the Titrate Acidity to be expressed as lactic acid percentage by volume.
In milk the lipid content is mainly composed of fat, known as butterfat containing small amounts of phospholipids, sterols, carotenoids and vitamins D and A. Milk is a solution consisting of proteins, lactose, minerals and some vitamins that carry fat globules and colloidally dispersed casein micelles consisting of protein. If casein is precipitated at pH 4.6 the resultant residue is known as whey or serum (Coultate, 1996).
The importance for testing the pH level in milk is to check for impurities or spoilage in the milk. pH measurements allow for an understanding for what might be causing compositional changes. Fresh milk usually has a pH of 6.7. when the value decreases below this is indicates spoilage in the sample by bacteria. Bacteria from lactobacillaceae is lactic acid bacteria and is often responsible for a breakdown of the lactose in the milk to form lactic acid. When the milk reaches an acidic pH curdling begins and the taste and smell is often described as sour. When the pH is higher than 6.7 this usually indicated an infection. If infected the cow’s immune system releases histamine to fight the infection.
By using phenolphthalein this helped to determine the endpoint of the pH. When using the Rosaniline Acetate Solution this placed a pink tinge on the milk to help. By using Sodium Hydroxide (NaOH) to the milk until an endpoint is established. This endpoint was indicated by colour change at the pH, when using the Phenolphthalein solution, a colour change happens at around a pH of 8.1.
When a TA test was conducted this was to determine if the milk sample had such a high acidity to keep its quality and heat stability. There are two types of acidity in milk these include natural acidity and developed acidity. Natural acidity happens when phosphates and citrates is present in the milk as well as dissolved CO2 during the process of milking. Developed acidity occurs when lactic acid is produced by bacteria in the lactose in the milk sample.
To ensure accuracy while conducting these experiments it is important that all machinery is calibrated to get the most accurate results possible. By doing this it minimises the chance of inaccurate results and by calibrating machinery it quantifies and controls any human errors that may occur and allows for the accuracy to be at an acceptable level. Human error could also occur during Titratable Acidity testing because if the air bubbles are still present or the meniscus is not on the line then this might also allow the risk of error leading to inaccurate results.
Conclusions
To conclude this experiment and research project was successful. However, research could be carried out to try a new method of completing this experiment. Alternative equipment for this experiment may have included that instead of using a pH meter that litmus paper may be a cheaper alternative. By using litmus paper, it allows the experiment to be completed faster as the calibration of the pH meter could be avoided. Instead of carrying out the Titratable Acidity by hand an automatic machine may be an alternative as it may reduce the chances of human error, however, this equipment may be expensive.
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