LETCURER: ASSOC PROF DR SOPIA MD YASSIN<br />Class: 4 Science 1<br />Time: 7.40 a.m. – 9.00 a.m.<br />Theme: Physiology of Living Things<br />Learning Area: Development of Technology in Food Processing<br />Learning outcome: Relate food processing methods with factors causing food spoilage.<br />
PhaseContentLearning and Teaching ActivitiesNotesEngageRefer to Appendix ATeacher gets students ideas on the causes of food spoilage.Students share their prior knowledge on this issue.What happen to the milk if it is left for 1 day? Why?EmpowerRefer to Appendix BPlanning and Doing Experiment – observation of the change in pH when the milk is left for 1 day. Students get the result and analyze the data.Students relate the reduction of pH with bacterial fermentation that causes milk spoilage.Teacher explains to students how bacterial fermentation reduces the pH of milk and causing milk spoilage.Observation.Equipment required:Data logger connected to a PCOne pH probe A bottle of milkAnalyzing the data.A few question related to the reduction on pH of milk.Discussion.EnhanceRefer to Appendix CTeacher gives an example about milk spoilage and asks students to give their opinion related to this issue. School Milk Programme.
SCIENTIFIC CONCEPT<br />Milk is contaminated by bacteria even before it leaves the udder, although at this point they are harmless and few in numbers. <br />The two main groups of bacteria in milk are Lactic acids and coliforms. Lactic acid is the normal bacteria present in milk and dairy products. Coliforms are the main reason for milk spoilage. <br />ENGAGE<br />Appendix A <br /> <br /> Before After 1 day<br />Procedures<br />Equipment required<br />Data logger connected to a PC<br />One pH probe <br />A bottle of milk<br />Experiment set up<br />
The milk is allowed to reach room temperature without cooking and re-pasteurising it.
The pH probe is plug into the data logger socket and the probe is inserted into the container of milk.
Carrying out the experiment<br />Data logger is started recording the data and displaying the graph. The experiment is kept in a stable environment as the extremes in room temperature may give false readings.<br />EMPOWER<br />Appendix B<br />Result<br />Time (hour)pH15.44225.44235.44245.38055.36065.34075.29985.27895.258105.237115.230125.197135.186145.174155.158165.149175.142185.133195.121205.117215.112225.096235.074245.063<br />Graph<br />Discussion<br />Q1. Did you see a reduction in pH shortly after starting the experiment?A1.This partly depends upon the freshness of the milk but there should be little change at this stage.<br />Q2. What causes the change in pH as the milk turns sour?A2.The lactose in the milk is converted to lactic acid. As the acid level increases the pH level drops.<br />Q3. Is the reduction in pH constant over the entire experiment?A3. No. We can see from our graph the gradient significantly increases half way through for fresh pasteurised milk.<br />Q4. Calculate the extent of change in pH obtained during the experiment.A4. This will partly depend upon the students results. For our graph the milk went through a change in pH of 1.95 (6.75 - 4.8).<br />Q5. What do you think will be the result of incubating UHT milk over the same time period?A5. This question is there to make the students think of the different ways, and reasons for processing milk. I expect the results to be very stable over the same time period. <br />ENHANCE<br />School Milk Program has to be postponed for a time being because the food poisoning case among students due to milk spoilage. What are the factors causing the milk spoilage and how to overcome the problems?<br />UNIQUE FEATURES<br />Low cost because we only use a bottle of milk.<br />Easy to perform because this experiment only contain one variable which is pH.<br />By using data logger, we do not need a constant observation. The experiment can be left and after 24 hours, we can obtain the result.<br />The result can be analyze and interpreted easily. <br />The graph can be plotted easily.<br />REFERENCE<br />Measuring the pH of Milk. Retrieved on 31st August 2010 from http://www.picotech.com/experiments/ph_of_milk/ph_of-milk.html<br />