IB Biology SL IA: Investigating the effect of different temperature intervals on the pH of milk (UHT Milk) and rate of spoilage.
I got a high 6 in Biology SL (just a few points off a 7), and this IA played a major component in my grades.
Investigate the effect of different temperatures (10 ˚C,20 ˚C, 30 ˚C, 40 ˚C,50 ˚C,60˚C)
on the pH of Devondale Full cream Milk (UHT Milk) and rate of spoilage
Background:
Spoilage refers to the deteriorating of food that leaves it unsuitable for human
consumption. Microbial spoilage is one the most common forms of spoilage, in this
case, milk is spoiled by lactic acid bacteria in milk. Lactose is feasted upon by bacteria
like Streptococci to convert into glucose and galactose, producing lactic acid as a by-
product (Rupp,2016). As lactic acid continues to build up, pH of milk increases till
Streptococci can no longer grow, another Lactobacilli steps up and the process
continues gain till the bacteria can no longer multiply in these acidic conditions that
causes milk to sour (Rupp,2016)
In my investigation, I will use 6 temperature intervals each with 6 test tubes to
investigate the effect of temperature on the rate of spoilage of milk. I will first measure
the initial pH to find the change in pH, through that determine the rate of spoilage. pH is
relevant as an indicator of spoilage, measuring the the acidity after the reaction. When
presented the right conditions, bacteria can produce more enzymes. Enzymes are
globular protein which acts as catalysts to biological reactions like digestion of lactose
necessary to keep the organism alive. At cold temperatures, bacteria don’t get enough
thermal energy to activate enzyme-catalysed reaction. As the temperature increases,
there’s more kinetic energy, increases the speed of enzyme and substrate. More
frequent collisions between the two, resulting in higher rate of reaction till optimum
temperature. During this process, the enzyme and substrate bind forming an enzyme-
substrate complex – which is converted into a product and released. These conditions
allow bacteria to breakdown food and gain energy to continue to grow. At an optimal
temperature, the rate of enzyme activity will be the highest – this temperature vary from
enzyme to enzyme.
Personal Engagement:
My interest in milk comes in the fact that it plays a big part in my daily diet, even from
my early childhood. In the recent years, there has been great surge in demand for milk
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, in Vietnamese households, this prompted an influx in foreign milk imports to sate the
demands not fulfilled by the domestic production of raw milk. UHT (Ultra-Heat-Treated)
Milk in particular, has been particularly favorable by being able to withstand the hot
tropical climate. The pasteurizing process heats the milk at a higher temperature, above
135 °C– for 2 to 5 seconds (Uoguelph.ca, 2019), this in turn, kills the spores in milk to
allow it to be stored at room temperature for a long time.
Microorganisms often find their way through hair, udder and teats of cows, some
containing harmful pathogens to human consumption. Illnesses born from contaminated
milk has been a concern for decades, bacterial infections like Brucella
melitensis( Beach,2019) occur from consumption of unpasteurized milk can cause
anorexia, malaise and fatigue. It is thanks to modern quality control that this has
become less of a concern, yet these risks still continue with people consuming milk left
outside for a long time. Understanding these risks will prevent people from contracting
dangerous illnesses and store milk safely as well as prevent economic losses from
micro bacterial contamination.
Hypothesis
Changing the temperatures (10 ˚C,20 ˚C, 30 ˚C, 40 ˚C,50 ˚C,60˚C) will have an effect
on the pH of milk. The lower the temperature milk is left at, the lower the pH change of
milk and rate of spoilage.
Variables
Independent: change in temperature of milk (˚C)
Dependent: change in pH of milk (10 ˚C,20 ˚C, 30 ˚C, 40 ˚C,50 ˚C,60˚C), layer of
curdling in milk
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