Which O.J. Should You Buy?
How orange juice processing
affects the rate of vitamin C loss.
Background Information
• Vitamin C is an organic molecule known as
ascorbic acid.
• Ascorbic acid reacts chemically with
indophenol, an indigo indicator, resulting in
the bleaching of the dark color.
• Relative concentration of ascorbic acid is
determined by counting the number of
drops of solution required for bleaching.
More breakdown…
• Ascorbic acid breaks down in the process of
oxygen in an oxidation reaction.
• Enzymes present in citrus fruits increase the
rate of oxidation.
• During juice processing, loss of A.A.
potency due to enzymes is minimal because:
– A deaeration step minimizes amount of oxygen.
– High pasteurization temperatures readily
destroy the enzyme’s oxidative properties.
Just a little more…
• In flash pasteurization, juices are
heated briefly and then rapidly cooled.
• Vitamin C is a sensitive molecule that
is altered in the presence of heat.
• Tin competes with ascorbic acid for
oxygen and tin is preferentially
oxidized.
Initial Scientific Model
of Vitamin C Depletion
[Vitamin C]
time
oxygen
[Vitamin C]
decrease
Ascorbic acid breaks down over time when
exposed to oxygen..
Assumptions
• Initial differences in ascorbic acid concentration in
juice did not affect the rate of breakdown.
• Storing juice in plastic containers would remove the
container variable on rate of ascorbic acid depletion.
• Flash pasteurized juices are exposed to less heat than
juices which experience standard pasteurization.
• All juices tested did not have fructose added:
– Ascorbic acid reacts with carbonyl group of fructose to
decrease ascorbic acid concentration.
Methods
• I acquired four different types of Orange Juice:
– Pasteurized Juice stored in a tin Container
» Western Family Orange Juice
– Pasteurized Juice never stored in tin
» Western Family Orange Juice
– Flash Pasteurized
» Odwalla Orange Juice
– Fresh Squeezed (non-pasteurized)
» California Navel Oranges
Then…
• I collected juice from
6 California Navel
oranges and stored it
in a plastic juice
bottle.
• I stored some orange
juice from a tin can in
a plastic juice bottle –
the remaining juice
was left in the tin
container for
additional testing.
Finally…
• I used a 60 mg/L solution
of indophenol.
• Set up two equal vials of
water and indicator (10
ml).
• Titrated O.J. to solutions
using an eye-dropper until
colors were the same.
• Recorded the number of
drops.
Results
Number of Drops of
Indophenol
Relative Ascorbic Acid Concentrations in a Variety
of Orange Juices
20
WF (tin)
Odwalla
WF Plastic
Tin
Fresh
15
10
5
0
0
2
4
Time (days)
6
8
Ascorbic Acid Loss…
Approximate indicator drop increase per day
• Fresh Squeezed Juice
• W.F. (tin)
• W.F. (packaged in tin
but stored in plastic)
• Odwalla
• W.F. (plastic)
• 0 drops/day
• 0.14 drops/day
• 0.29 drops/day
• 0.43 drops/day
• 0.71 drops/day
Connections…
• Claim 1: Juice exposed to tin will lose
ascorbic acid at a slower rate
than juice not exposed to tin.
• Support: According to the data table, all
pasteurized juice that had been
exposed to tin lost ascorbic acid
at a slower rate. Of the juice
originally packaged in tin, the juice
stored in tin lost ascorbic acid more
slowly.
• Refute: Fresh juice did not loose ascorbic
acid, and therefore was better at
retaining ascorbic acid than juice
exposed to tin.
Connections Continued…
• Claim 2: Juices exposed to higher
temperatures will loose ascorbic
acid more gradually than juices
exposed to less heat due to the
inactivation of enzymes that
degrade ascorbic acid.
• Refute: When comparing juices never
stored in tin, ascorbic acid loss was
inversely proportional to heat time
exposure: the greater the heat, the
more rapid the loss.
Revised Model
enzymes
oxygen
[Vitamin C]
time
heat
oxygen
tin
Oxidation of
Vitamin C
Decreased
[Vitamin C]
Oxidation of
Tin
So that got me wondering…
What would happen if
the juice containers
were not capped, but
rather exposed to the
oxygen of the
refrigerator?
What would happen if
fructose was added to
the fresh squeezed
juice?