MEASURING THE PH OF MILK AS IT TURNS SOUR1.0 ENGAGEIntroductionMilk contains a large number of a weak acid or a weak base in its salt. So, it behaves as abuffer solution. Fresh cow milk has a pH of between 6.7 and 6.5. Therefore, it is slightlyacidic. Values higher than 6.7 denote of mastitic milk while values lower than 6.5 denote thepresence of bacterial deterioration. As milk is a buffer solution, considerable aciddevelopment may occur before the pH changes. pH value lower than 6.5 therefore indicatesthat considerable acid development has taken place. This is normally due to the bacterialactivity. pH measurements are often used as acceptance tests for milk. pH is the abbreviationof the weight of hydrogen. This term was introduced in 1909 by the Danish biochemist S. P.L. SØrensen (1868-1939). The pH scale covers the active concentration of the H+ ions andOH- ions and therefore the pH value is defined as the negative common logarithm of theactive hydrogen ion concentration in an aqueous solution. The value of pH for neutral, acidityand alkalinity condition are 7, less than 7 and more than 7, respectively. Before this, litmus papers are widely used to test the acidity of a solution while pHpapers or pH meters are used to know the pH value of a solution. But nowadays, data loggersare more often used in experiments because the data collected by them are more accurate andthe experimental procedure become easier. However, the litmus papers and pH papers or pHmeters are still being used in certain experiments. Data loggers offer more flexibility and are available with a greater variety of inputtypes. Most data loggers collect data which may be directed transferred to a computer. Data isnormally collected in non volatile memory for later download to a computer. Data logger cancollect data independently of a computer. So, the computer does not need to be present duringthe data collection process. This makes them ideally suited for applications requiringportability. Besides, mistakes are not made in reading the results. Compared to human, data
loggers will not misread the data. Graphs and tables of results also can be producedautomatically by the data logging software. This advantage can save the time to draw thegraphs manually. However, data loggers also have disadvantages. The main disadvantage is the cost ofpurchasing the equipment. The price of the equipment is not too economical. If the datalogging equipment breaks down or malfunctions, some data would be lost or not recorded.The cost needed to repair the equipment is higher. So, the tendency of not being repaired isalso higher. Besides, by producing the graphs and tables automatically, the drawing skills ofthe user will become weaker. For this experiment, it looks at the changes in pH of milk as it goes sour. Milk iscontaminated by bacteria even before it leaves the udder, although at this point they areharmless and few in numbers. Processing and handling activities can introduce furthermicroorganisms. The two main groups of bacteria in milk are lactic acid bacteria andcoliforms. Lactic acid bacteria are the normal bacteria present in milk and dairy products.They are anaerobic and preferably live in a low pH environment. Coliforms are the mainreason for milk spoilage. One of the main ingredients of milk is lactose. This is the substance that the bacteriause to create lactic acid. The lactic acid bacteria live on the lactose, which they turn inglucose and then turn them into lactic acid:Lactose Glucose Lactic acid Measuring the milk acidity is an important test to determine the milk quality. Aciditymeasurements are also used to monitor processes such as cheese-making and yogurt-making.This experiment demonstrates the changes in the pH of milk over a several day period,depending on room temperature. This experiment is suitable for ages 13 and above. Theequipment used in this experiment to monitor the pH of the milk under the exposed conditionis data logger.Problem Statement
Ahmad bought milk from the nearby shop. He drank in a little amount and then left it on thetable. He forgot to store the milk into the refrigerator. The next day, drank the leftover milk.But, he found out that the taste was totally different than yesterday. The milk tasted sour. Hewonders what happened to the milk when it is left and exposed. 1. Why does the taste of the milk changes as it is exposed? 2. Is the sour milk acidic or basic? 3. If the milk is acidic or basic, what is the pH value?2.0 EMPOWERINGTo conduct the experiment, the following are the equipment and methodologies.Equipment required 1. Data logger connected to a PC This data logger by DrDAQ contain all these features: 4 digital inputs and outputs 3 sockets for external sensors High impedance input for pH or Redox measurements 100 kHz, 8–bit oscilloscope with a ±10 V range Signal generator with AWG for creating your own waveforms Captures fast signals USB connected and powered Use up to 20 USB DrDAQs on a single PC Data logger is an electronic device that records data over time and stored them. It isbased on a digital processor or computer. Data logger is used as specific devices that canmeasure a range of measurement applications to a very specific device for measuring in oneapplication type only. Data logger has the ability to automatically collect data on a widerange of time. Therefore, an accurate data of the environment conditions being monitored canbe obtained. To start using data logger, first the data logger is connected to a PC via USB interface.Accompanying data logger software is used to select logging parameters and activate the
logger. The logger is then connected to a sensor. After the desired monitoring period, the dataconnected to the computer and will read out the data and display the measurement in a graph. Diagram 1: Data logger Diagram 2: data logger compartments 2. pH sensor Diagram 3: pH sensor The pH sensor is used to measure the pH of milk in this experiment. The advantages of using pH sensor compared to a traditional pH meter are this sensor provides automatic data collection, graphing, and data analysis when connected to the data logger. This sensor can measured pH from range 0 to 14. 3. Bottle of milk
Methodologies 1. The milk from bottle is pour into a glass. 2. The milk is then allow to reach the room temperature without cooking and re- pasteurising it. 3. The pH probe is plug into the data logger socket. 4. The pH probe is inserted into the milk. 5. Run the software. 6. All data are recorded and displayed in graph form. Diagram 4: data logger connected to PC Diagram 5: pH probe inserted into milk
Result Graph 1Discussion The experiment is to investigate and measure the pH of milk as it goes sour. The pHprobe will measured the pH of the milk and send the data to data logger to be processed bythe software. The data obtained is then plotted in graph 1. The graph 1 shows that the pH ofthe milk will decrease as days passed by. The decreasing in the pH of the milk indicating thatthe milk becomes acidic. As the milk turns sour, the pH decreasing. We can also see from thegraph that as the time of milk exposed to the environment increasing, its pH value decreased. From the graph 1, the reduction in pH can be seen shortly after starting theexperiment. However, the changes are little. This depends on the freshness of the milk thatwe used. If the milk is no longer fresh, we may see rapid decreasing in the pH value becausethere is bacteria content inside the milk. Therefore, when exposed to air, these bacteria willstart to grow rapidly contributing to the sourness of the milk. After few days, we can see thatthe pH starting to decrease to a lower value. Bacteria and other organism is the main contribution to the changes in pH of the milk.Milk contains lactose, but at the same time milk also contained bacteria. Some bacteria work
efficiently in warm conditions and causes milk become sour. Eventhough pasteurized milkundergo series of steps, bacteria are not completely killed in this process. Therefore, the leftbacteria will gradually reproduce and turns the milk into sour. The main reason why milkturns sour is because the lactose in the milk is converted to lactic acid. As the acid levelincreases, the pH levels drops. If milk is exposed, the bacteria in the milk will start to produceand forms gases and chemicals which change its smell, taste, texture. Over the entire experiment, the reduction in pH is not constant. From the graph, wecan see that the gradient significantly increases half way through for fresh pasteurized milk.As the time increases or from first day to fourth day, we can see that the pH is reduced.Reduction in pH means that the milk has increases in its acidity.As milk begins to sour, its pH levels fall sharply. This makes milk even more acidic. Thesugars in milk are converted into acids by certain bacteria named Lactobacilli, therebyreducing its pH. Completely sour milk has a pH of about 4.4. Knowing the pH of milk mayalso help to cut down intake of high acidic foods and to keep acid-base related disorders. The extent of change in pH can be calculated by subtracts the pH value of milk in firstday with the value pH value of milk in fourth day. From the graph, the pH of milk in first dayis 6.75. In contrast, the pH of milk in fourth day is 4.8. So, the change in pH is 𝑇𝑒 𝑒𝑥𝑡𝑒𝑛𝑡 𝑜𝑓 𝑐𝑎𝑛𝑔𝑒 𝑖𝑛 𝑝𝐻 = 6.75 − 4.8 = 1.95 UHT stands for “Ultra High Temperature” processing, which is just another way ofheating milk in order to kill the bacterial spores. In the UHT process, the milk is heated at thetemperature of 135°C for one to two seconds. This extreme heat is said to kill off any sporesin the milk. UHT milk tastes different than its pasteurized milk. It tastes like it comes from abox. Since a single microbial cell of an organism capable of growth in UHT milk maycause spoilage in a container when the product may be stores for six months or more atambient temperatures, the methods used for detecting contamination must be very sensitive.This sensitivity is usually achieved by doing pre incubation. So, we can say that if weincubate UHT milk in a closed arrangement over the same time period, this will providesvery high bactericide effect and decreased the contamination risk down to zero. The obtained
result of this incubation can be considered as very stable because there are no bacteria and thetaste of the milk will remain the same. Microorganisms are everywhere. They can be found in the air, in water, in soil, onanimals and even on humans. Some are beneficial and others can cause spoilage. A smallnumber are pathogenic and can cause disease, which is food borne disease. Food borne illnessor food borne disease is any illness result from the consumption of contaminated food. Threetypes of microorganisms can contaminate food and cause foods borne illness are bacteria,viruses and parasites. The most common symptoms of food borne illness are diarrhea,vomiting, fever, sore throat with fever and jaundice. Our stomach is an acidic place. Once we start eating, acid is secreted into the stomachto start the digestion process. The secretion then mix with the food in the stomach. Theresulting mixture can have a pH of very acidic condition. The acid content in the food that wehave eaten have the ability to impact the digestive process. When too many foods that arehigh in acid content are consumed, they may trigger miserable symptoms which include sourtummy, acid reflux and an uncomfortable bloated state.1.3.1 ENHANCE 1.3.1 CheeseFigure 1 (a): Curd Cheese Figure 1 (b): Curd Cheese
Figure 1 (c): Curd CheeseMany of the cheese are produced in food industry. Cheese can be produced by using milk andsoy milk. How curd or cheese can be produced by own at home or in kitchen? A very simple cheese can make by anyone with nothing but milk, vinegar or lemonjuice, a piece of cloth, and a few utensils that everyone has around the house. A wide varietyof milks commercially purchased pasteurized homogenized cow’s milk, raw’s cow milk,goat’s milk, sheep or soy milk can be used to make cheese, each with unique flavour. Thebest cheese is from unpasteurized milk but should be cured for 2-4 months if there is anydoubt about pathogens in the milk. If used pasteurized milk, need to add little calciumchloride to firm up the curd because the heat makes the calcium unavailable. Basically, when acid (either produced by bacteria or added to the mix) and/ or rennetact on milk to cause the milk fat and protein to separate from the liquid, leaving a substancethat we call cheese. Most milk simply curdled by a combination of heat and added acid, suchas vinegar or lemon juice. Once the cheese has curdled the following is being made. A soft,fresh cheese might be drained at this point and can be eaten immediately. If want hard cheese,might be heated further to remove moisture, pressed into mold, and then aged to develop acharacteristic intense flavour. Besides the milk, acidifiers are needed to convert milk sugar to lactic acid and “ripen”milk. An acidifier can be something as simple as lemon juice or bacterial special startercultures purchased from cheese-making suppliers. Bacteria are added to acidify the milk, so
that the rennet will work, and to aid in the curing. Some recipes add chemicals acid to acidifythe milk. Make cheese is one way to keep milk and its nutritional value around for a relativelylong time. Milk would sour quickly without refrigeration, so cheese from the milk made itpossible to make use the milk’s nutritional value over a longer period. 1.3.2 Yogurt Yogurt is one of the Malaysian’s choices. Yogurts come from milk that may helpprevent from Osteoporosis. How yogurt can be made from milk? Milk is fermented with the help of lactose-loving bacteria to make yogurt. Thelactose-loving bacteria consume lactose (the sugar in the milk) and produce lactic acid aswaste product. This lactic acid is responsible for both the tart flavor and the thickening byacting on the casein protein in the milk. The yogurt-like products each varies by thickness and acidity by used differentcompositions of lactic-acid bacteria. For example, yogurt in the Unites States is made withlactobacillus bulgaricus and streptococcus thermophilus. The milk needs to be fairly warmbetween 105 and 115 degrees in order to the organisms in this culture to function. 1.3.3 Further StudiesFor enhance phase, there are four further studies that can be done. The four further studies are 1. Repeating the experiment using unpasteurized and Ultra Heat treated milk, 2. Keeping the container of milk at different temperature whether in fridge or an incubator, 3. Using different milk source such as goat’s milk, cow’s milk and soy milk in experiment, and 4. Using different milk product such as Dutch Lady, Marigold, Everyday, Nestle and Farmhouse Milk (F&N). The experiment can be done by using the unpasteurized milk and Ultra Heat Treated(UHT) milk to study the pH of milk when leaved for a few days. The different between
unpasteurized milk and UHT milk results in difference pH after leave for a few days. Thedifference is due to the presence of bacteria in unpasteurized milk and UHT milk. The unpasteurized milk is raw milk that can harbor dangerous microorganisms thatcan affect serious health risks. The unpasteurized milk can have dangerous bacteria such asSalmonella, E.coli and Listeria that responsible for causing numerous food borne illnesses.These bacteria can cause vomiting, diarrhea, abdominal pain, fever, headache and body ache. Usually, people are more likely to consume or drink Ultra Heat Treated Milk (UHTMilk) or ultra-pasteurization. This is because UHT milk undergoes sterilization by heatingmilk for an extremely short period, around 1-2 seconds at temperature exceeding 135 degreeCelsius (temperature required to kill spores in the milk). UHT milk have typical shelf of 6month to 9 month, until opened. Second, the pH of milk can be measured also when milk is placed whether in fridge orin incubator. In this experiment, we are study whether the temperature affect the pH value ofmilk. We can compare the pH value between milk in fridge that has low temperature andincubator that has high temperature. The next further studies are using different milk source from goat, cow and soy.From this experiment, we can identify which milk that has higher acidity after leave for a fewdays. Milk that has higher acidity means that have more bacteria presence that producestoxicity within a few days. In addition, we can also replaced by using different milk brandlike Dutch Lady, Marigold, Nestle, Everyday and Farmhouse Milk (F&N). Then, we canknow which milk brand has higher acidity.
Conclusions The pH of the milk from 6.75 in the first day reduced to 4.8 in the fourth day. Thismeans that the acidity of the milk increases from the first day to the fourth day. The milk hasa high acidity in the fourth day because of the presence of the bacteria that convert the sugarsin the milk into acid. The benefits use of data logger are the low-cost and used as educational data loggerthroughout the world. The most important of data logger use in educations is it motivatestudents in learning process. In future,data logger can be used in school in Malaysia and alsoeducational institutions. The properties of data logger that can increase the student’s interestand motivate student as well help student in learning process. The usage of data logger canalso make students more familiar with technology instrument or computer. Not only that, the data obtain both during and after experiment are viewable in bothspreadsheet and graphical format. The data that viewable make students more easily toanalyse the data. The pH measuring kit, allows to accurately measure and record the acidityand alkalinity of solution. So, the data logger can be used for schools and educationalinstitutions in Malaysia. Furthermore, many applications of data logger ranging from industrial operations tobiological processes requires accurate measurement and analysis of pH is needed. Some ofthe applications include biochemistry, agronomy, food science, chemical research andengineering, and environmental research and pollution control. These applications demands alow cost portable devices and also a low power.
ReferencesRalph Early (1998). The Technology of Dairy Products. Thomson Science. London, UK.K. Kaan Tekinsen, Mehmet Elmali & Zeynep Ulukanli (2007). Microbiological Quality of UHT Milk Consumed in Turkey. Internet Journal of Food Safety. Vol. 7 (45-48). Retrieved from http://www.internetjfs.org/articles/ijfsv9-9.pdfAngela M. Fraser (2006). Microbial Hazards. Retrieved November 23, 2012 from http://www.foodsafetysite.com/resources/pdfs/EnglishServSafe/ENGSection2.pdfErich K. Springer (2006). pH Measurement Guide. Retrieved November 23, 2012 from http://www.hamiltoncompany.com/downloads/E_610277_04%20with%20Pathfinde r.pdfFrank O’Mahony (1988). Milk Chemistry. Retrieved November 23, 2012 from http://www.ilri.org/InfoServ/Webpub/fulldocs/ilca_manual4/Milkchemistry.htmGrace Yim & Clive Glover (2003). Food Microbiology: The Basic and The details of Cheese Production. Retrieved November 23, 2012 from http://www.scq.ubc.ca/food- microbiology-the-basics-and-the-details-of-cheese-production/Omega Engineering (2012). Introduction to Data Loggers. Retrieved November 25, 2012 from http://www.omega.com/prodinfo/dataloggers.htmlAnonymous (2009). Coagulation of Milk. Retrieved on November 28, 2012 from http://chestofbooks.com/food/science/Experimental-Cookery/Coagulation-Of- Milk.html#.ULYVepNzPZsAnonymous (2012). The Danger of Raw Milk: Unpasteurized Milk Can Pose A Serious Health Risk. Retrieved on November 28, 2012 from http://www.fda.gov/Food/ResourcesForYou/consumers/ucm079516.htmAnonymous (2012). Curd. Retrieved on November 28, 2012 from http://en.wikipedia.org/wiki/Curd
Dunlap, W. (2009). Acid-Coagulated Soft Cheeses In Your Own Kitchen. Retrieved on November 29, 2012 from http://slumberland.org/sca/articles/easy_cheesemaking.pdfFazila Binti Aziz (2009). Data Logger Using Pic. Retrieved on November 29, 2012 from http://eprints2.utem.edu.my/4698/1/Fazila_Aziz-24_pages.pdfFankhouser, D. B. (2003). Beginning Cheese Making. Retrieved on November 29, 2012 from http://biology.clc.uc.edu/fankhauser/cheese/cheese_course/cheese_course.htmMagee, E. (2012). The Benefits Of Yogurts. Retrieved on November 29, 2012 from http://www.webmd.com/diet/features/benefits-of-yogurtSchmidling, J. (2012). Cheese Making. Retrieved on November 28, 2012 from http://schmidling.com/making.htmV. Ramya and B. Palaniappan (2012). Embedded Ph Acquisition and Logging. Advanced Computing: An International Journal (ACIJ), Vol.3, No.1. Retrieved on November 27, 2012 from http://airccse.org/journal/acij/papers/0112acij04.pdfWatson, J. (2012). Dairy Science Information. Retrieved on November 28, 2012 from http://www.dairyconsultant.co.uk/si-section13.phpWeaver, S. (2003). Cheese Making Basics. Retrieved on November 29, 2012 from http://www.hobbyfarms.com/food-and-kitchen/cheese-making-14872.aspx