Traditional Food PreservationPemmican and Vitamin C

Food Preservation

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Food Preservation

Ways to preserve food:

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Pemmican• Dried meat

- pounded into coarse powder

• Melted fat

• Dried berries

• Preservation method- prevents spoiling of berries- can eat berries all year long

• Preserves vitamins and mineralsExample: vitamin C (ascorbic acid)

Drying Berries

Vitamin C TitrationDetecting Vitamin C in fruit

Vitamin C titration

+

=

O OO O

O OHO OH

OH

OH

Vitamin C (ascorbic acid)

+ I2 + 2I- + 2H+

Iodine Dehydroascorbic acid

OH

OH

No colour change!Colour change!

Step 1: Gather supplies• Berries• Diluted tincture of iodine• 1% (w/v) starch solution• 2 cups• Fork• 2 eye droppers• 2 small clear cups or test tubes• Stir stick (e.g. straw or popsicle

stick)

Step 2:Mash berries• Add berries to cup

• Mash berries up with fork

Step 3: Mash berries (cont.)• Add an equivalent amount of water to the

cup and continue to mash

• Remove the pieces of skin and other large chunks

Step 4: Aliquot berry juice• Separate the berry juice into two containers

Step 5: Add starch solution• Add 10 drops of 1% starch solution per 0.5mL of berry juice and stir sample

• Be sure to stir starch solution before use

Step 6: Begin titration• Add one drop of the iodine solution to

the sample you added the starch to.• Stir solution if colour change

observed• If colour disappears continue to step

5

Step 7: Continue titration• Continue to add iodine one drop at a

time• Stir solution after each drop is added• The titration is done when the colour

change remains after stirring

Step 8: Determine approximate Vitamin C concentration

• Can you determine the concentration of Vitamin C in the berry juice?

Step 9: Repeat Steps 2-8• Repeat steps 2-8 using berries

preserved using a different method (fresh, frozen, boiled, dried, juice)

• Compare results between preservation methods

- which berries require more drops of iodine?

- what does this tell us about the different preservation methods?