Research question: How does increasing the temperature of a kiwi (Actinidia deliciosa) affect the ascorbic acid concentration, measured by a titration against a Dichlorophenolindophenol (DCPIP) solution?
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Summary document of Chapter 5 Evolution and biodiversity IB Biology
Tema 3: Metabolismo
IB Biology Full Course Notes + Required Drawings Units 1 - 11 & Option D
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RESEARCH QUESTION
How does increasing the temperature of a kiwi (Actinidia deliciosa) affect the ascorbic acid
concentration, measured by a titration against a Dichlorophenolindophenol (DCPIP)
solution?
INTRODUCTION
Boiling fruits and vegetables has been a common culinary practice since the beginning of
civilization. This practice not only enhances flavour but also increases tenderness.
Additionally, boiling also kills off any microbes, making fruits and vegetables safer to eat.
Although I also often boil my fruits and vegetables as I enjoy the added flavours and softer
texture, I have heard that it decreases the nutrient content significantly and thus decided to
carry out an experiment to investigate this claim. I have been underweight for most of my
life as I have a fast metabolism and so the nutrient and calorie content of food is critical to
me in order to maintain a healthy weight. Consequently, I decided to investigate how much
the nutrient concentration, specifically Vitamin C (ascorbic acid), is affected by changing the
cooking temperature? I chose to investigate this in kiwis as they are known to be “super-
fruits” for their high concentration in nutrients. This led me to form the research question:
how does increasing the cooking temperature of a kiwi affect the Vitamin C concentration
measured by a titration against DCPIP solution?
“Vitamin C, also known as L-ascorbic acid, is a [hydrophilic] vitamin that is naturally present
in some foods, added to others, and available as a dietary supplement” (Vitamin C Fact) and
aids a number of vital biological processes. Its primary role is the synthesis of collagen fibres
which form multiple tissues in the body such as skin and blood vessel walls. Additionally,
Vitamin C strengthens the immune system. A lack of Vitamin C will lead to scurvy which is a
condition characterized by blood vessel fragility, impairment in growth, fatigue, and,
ultimately, death (Li and Schellhorn 2171).
Vitamin C production and synthesis can be affected by various factors such as temperature.
Temperature is a key factor that heavily influences the fluidity of the cell membrane. The
cell membrane is made up of a phospholipid bilayer and membrane proteins. The
phospholipids each have a hydrophilic hydrocarbon tail, as well as hydrophobic phosphate
heads. Cholesterol in the membrane also plays a role in membrane fluidity. However, as
temperature increases, the hydrocarbon tails become less rigid, which causes the
membrane to increase in fluidity. This allows substances to pass in and out of the
membrane without restriction. High temperatures also cause peripheral and integral
proteins to denature and eventually be destroyed.
In relation to Vitamin C, higher temperatures will cause the vitamin to leave the cell as the
cell membrane is no longer regulating the flow of substances. This decreases the Vitamin C
concentration in the cell. Hence, when boiling fruits or vegetables that contain ascorbic acid,
the vitamin will leach out into the water.
1
, The aim of this experiment will be to investigate how the cooking temperature of Actinidia
deliciosa affects Vitamin C concentration. I will be using a titration method by slowly adding
DCPIP solution through a burette into a solution of Vitamin C with an unknown
concentration (this solution will contain the ascorbic acid that leached out from the kiwi
during the boiling process). DCPIP decolorises when reacting with ascorbic acid and will
eventually turn a dark blue. However, in my experiment I measured the endpoint of the
titration as a purple solution (the neutralisation between ascorbic acid in the kiwi solution
and DCPIP). I chose to use DCPIP as it reacts with ascorbic acid at a 1:1 ratio, so it will be the
simplest chemical to give me the most accurate results.
NULL HYPOTHESIS & ALTERNATE HYPOTHESIS
H0: If the cooking temperature of a kiwi (Actinidia deliciosa) increases, then there will be no
statistically significant difference in the Vitamin C concentration.
H1: If the cooking temperature of a kiwi (Actinidia deliciosa) increases, then there will be
statistically significant difference in the Vitamin C concentration.
VARIABLES
Independent Variable:
My independent variable will be the temperature of the water bath that I heat the
Actinidia deliciosa in.
How it will be altered:
I will use a water bath to change the temperature and this will be monitored using a
thermometer. I will also put the lid on of the water bath to prevent any heat from
escaping.
Intervals:
65.00, 75.00 85.00, 95.00, 100.00 (±0.01°C)
I chose these intervals because they are common temperatures used in culinary practices.
Dependent Variable
My dependent variable will be the ascorbic acid concentration.
How it will be measured:
I will measure the Vitamin C concentration by using a titration with 1% DCPIP against the
water from the boiling tubes the Actinidia deliciosa were heated in. I will then calculate
the average DCPIP volume required for the solution the titration to reach its endpoint
(purple).
Units of measurement
3 3
cm (±0.05 cm )
2
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