4 Measurement of Ph and Acidity

FST 202: Food Quality Control Laboratory Report Experiment 4 – MEASUREMENT OF PH AND ACIDITY IN FOOD

Name

: Nur Adha Bin Suhairom

Student ID

: 2010140857

Class

: AS116 5B1

Lecturer

: Madam Mardiana Ahmad Zabidi

EXPERIMENT 4 MEASUREMENT OF PH AND ACIDITY IN FOODS

INTRODUCTION The pH is a measure of the concentration of free hydrogen ions in a chemical or biological system. It's a very important concept in cell biochemistry. Titratable acid, on the other hand, is a simple measure of the related amount of acid in a juice. There is no direct relationship between titratable acidity and pH in apple juice, although generally the pH goes up as the acid goes down and vice-versa. The exact relationship differs from sample to sample and depends on concepts like 'buffering capacity' which will vary for a whole host of reasons. Nevertheless some general empirical relationships may be obtained. It must be stressed that they only refer to those fruits growing in those locations at that time. They cannot be held to be exact in other circumstances In general, titratable acid relates pretty well to the 'acid taste' of a juice. If it doubles, people will tend to perceive it as twice as acidic. The pH relates more to things like microbial stability and susceptibility to mould and bacterial spoilage. In particular, the antimicrobial effectiveness of sulphur dioxide is very pH dependent, and this is the reason that titratable acid is measured by titration and pH by a pH meter. A pH meter is tricky to set up and calibrate, and only really worthwhile if it's being used daily in a laboratory environment.

OBJECTIVE To determine the percentages of predominant acid of food sample.

MATERIAL Balance Conical flask Burette Pipette 0.1 N NaOH Phenolphthalein indicator

PROCEDURE 1. 2. 3. 4.

The pH of the sample was measured. 5 mL of the sample was placed in a conical flask. A few drops of phenolphthalein indicator were added. 0.1 N NaOH from the burette was slowly added (while swirling the flask) until a permanent but faint pink colour remains. (Placing a white sheet of paper under the flask aids in seeing the colour change). 5. The volume of base added was then used to calculate the titratable acidity of the sample. 6. The titratable acidity was frequently reported in grams per 100 mL or percent based on the predominant acid.

RESULT Table 4.1 Sample

% Predominant acid

pH

Apple juice

0.36 %

3.59

100 Plus

0.15 %

3.61

CALCULATION

DISCUSSION The pH of both apple juice and 100 Plus is slightly differs from each other which is 3.59 and 3.61 respectively. Both have an acidic pH as the basic properties of a soft drink are its acidity. With the exception of soda water, soft drinks are acidified by the addition of fruit juice or by the inclusion of an acid. Acids are used in soft drinks to fulfil two main functions that are to inhibit the growth of micro-organisms such as yeasts, moulds and bacteria and also to improve the taste profile of a drink by balancing the sweetness. From the formula of calculation for the percentage of predominant acid, it was found that apple juice has the highest percentage of predominant acid of 0.36 % while 100 Plus is 0.15 %. The predominant acid that has been added to both drinks are malic acid for apple juice and phosphoric acid for 100 Plus.

CONCLUSION The pH of apple juice is 3.59 and pH of 100 Plus is 3.61. The percentage of predominant acid of apple juice is 0.36 % and 0.15 % for 100 Plus. The predominant acid of apple juice and 100 plus is malic acid and phosphoric acid respectively.

QUESTIONS 1. From the experiment, which sample has the lowest pH? Apple juice has the lowest pH of 3.59.

2. From the experiment, which sample has the highest amount of acidity? Apple juice has the highest amount of acidity of 0.36 %.

3. Do you think tap water from different sources has the same pH? Why? Yes, because water out of the tap can have a lot of carbon dioxide in it which lowers the pH. The mineral salts content in the water also can affects the pH.

4. Name one product that is neutral (pH 7). Soybean milk which the pH may varies from 6.8 – 7.0.

REFERENCES 1. http://www.winemakingtalk.com/entries/how-to-measure-titratable-acidity.html 2. http://nh1.ccone.com/neutral-foods.html 3. http://www.britishsoftdrinks.com/default.aspx?page=409