Cooking Tomato Juice: Investigating Vitamin C Concentration

[PhiPhenomenon]

Hey,

If you haven't guessed from the title this is kind of a weird question.

I'm a science student at UBC and for a lab today we had to analyze vitamin C contents in a substance of our choice. Long story short, I decided to look at how temperature effects Vitamin C concentration in tomato juice.

Anyway, I'm posting this because something weird happened when the juice got up to 85 degrees Celsius, it started to cool down despite the fact that heat was still being added to the system. It was in a glass beaker with a tinfoil top (to prevent evaporation) and a small hole just big enough to fit a thermometer through. The tomato juice continued to cool down to ~80 degrees Celsius before heating up again.

Can anybody explain why this might happen? My thoughts are that at around 85 degrees molecules begin to decompose and that makes the heat constant shoot up dramatically but I have no idea.

 

[Borek]

What was the heating method? Have you seen it once, or have you repeated the experiment?

 

[PhiPhenomenon]

What was the heating method? Have you seen it once, or have you repeated the experiment?

I only did it once. It was ~250 mL heated over a hot plate.

 

[technician]

You must repeat the experiment and get reproducible results to be sure it is a real effect.
Was the mixture stirred?

 

[PhiPhenomenon]

You must repeat the experiment and get reproducible results to be sure it is a real effect.
Was the mixture stirred?

It was not.

 

[256bits]

You don't mention from where you obtained your tomato juice - ie from a can or freshly prepared by yourself from the tomato fruit. Canned juice is homogenized where the solid particles are processed mechanically to be smaller and remain thus in suspension. I am not sure if this beginning characteristic would have an affect upon your experiment, but the canned juice would have broken cells whereas the fresh would not.

At the end of your experiment, when the 'juice cooled' was it still appear as a colloidal suspension or did the liquid and solid separate after a length of time? Was the viscosity higher or lower after the heating?

Tomato juice contains pectin and pectin methyl esterase, both of which may have had an affect upon the heated tomato juice. Pectin methyl esterase is deactivated with heat so if you used fresh that could be a factor. Canned juice should have had the enzyme already de-activated.

These are not answers for your experiment - rather the chemistry of cooking plays an valuable part in how your final "dish" will turn out, and what you were doing is cooking tomato juice.

 

[PhiPhenomenon]

You don't mention from where you obtained your tomato juice - ie from a can or freshly prepared by yourself from the tomato fruit. Canned juice is homogenized where the solid particles are processed mechanically to be smaller and remain thus in suspension. I am not sure if this beginning characteristic would have an affect upon your experiment, but the canned juice would have broken cells whereas the fresh would not.

At the end of your experiment, when the 'juice cooled' was it still appear as a colloidal suspension or did the liquid and solid separate after a length of time? Was the viscosity higher or lower after the heating?

Tomato juice contains pectin and pectin methyl esterase, both of which may have had an affect upon the heated tomato juice. Pectin methyl esterase is deactivated with heat so if you used fresh that could be a factor. Canned juice should have had the enzyme already de-activated.

These are not answers for your experiment - rather the chemistry of cooking plays an valuable part in how your final "dish" will turn out, and what you were doing is cooking tomato juice.

Interesting.

The juice was canned. The viscosity reduced significantly but the juice still seemed homogeneous with no real suspension even after cooling down to 20 degrees Celsius.

I should also point out that seeing tomato juice cool after reaching a certain point while cooking wasn't the experiment. It was just something weird that happened while I was cooking tomato juice to analyze the effects heat had on Vitamin C concentration.