How can we prevent freshly squeezed orange juice from going bitter
when stored overnight in a refridgerator?

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Request for Question Clarification by redhoss-ga on 09 Aug 2004 06:05 PDT

What kind of a container are you keeping the juice in.

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Clarification of Question by davidhit-ga on 09 Aug 2004 13:48 PDT

I will answer your question at the end of this paragraph.
But you probably need to know how the juice is produced.
We use a commercial electric citrus juicer (with a central juice
head that turns around as you hold the orange down onto it).
This naturally takes some of the interior pulp from the orange skin, which
I am told contains an oil which turns bitter with storage (in 24 hours).
We must continue to use this juicer. So is there some product that neutralises
this acidic oil that we can add to extend service life?
We are keeping the juice in a plastic jug.
Thank you.

I have an orange tree, and routinely squeeze my orange juice using a
black and decker product, that seems identical to yours.  However, I
generally do not have the bitterness issues you're experiencing, even
after the juice has been stored for several days.

I usually store my orange juice in a glass container in the
refrigerator, closed and sealed tightly with saran wrap.  All fresh
juices can oxidize and this may be where you are picking up your
bitter flavor.

Alternatively, if your orange juice is comming in contact with a metal
container, this might also cause the bitter flavor as the acid tends
to leach out minerals from the metal container.

Because I generally don't like pulp in my orange juice, I use a coffee
filter to strain out the last bits of pulp.

I do not believe that it is the 'oil' in the juice that is causing the
bitter flavor, and neutralizing this would probably create some kind
of off flavor.
However, sodium benzoate is a common preservative that is used in
commercial orange juice. 
http://www.cargillfoods.com/pdfs/juice.pdfs/COJFM,Pres,LoPlp.pdf


chugs,

What kind of tree is it?
Valencia oranges keep well but Navel (which is what we have here in the
Australian Winter) don't, I am told.
We keep our juice in a sealed plastic container.
I have read elsewhere that squeezing an orange helps it keep because
of the bitter oils in the hull.
Sodium benzoate: is this one reason why commercial juice tastes so artificial?
If so, I don't think this is our answer.

I agree with dr_bob. I used to keep juice in a plastic container. I
have since switched to glass and any juice keeps much longer. I have
also read that some pretty nasty stuff leaches out of plastic that
might not be good for any of us.

I don't think this is right at all.
We've tried keeping the juice in glass (actual drinking glasses
covered with airtight plastic wrap; it makes no difference.
Please, let us not get off the track with discussions about the dangers
of certain materials (plastic, teflon, aluminium etc) and what might
leach out of them: as far as I can make out, none of such claims have
ever been proven to be more than marketing ploys for somebody's
competing product.
Is there anyone who can tell me SCIENTIFICALLY what process is occurring 
chemically and what may be done about it? I am certain it is a process
occurring in the juice - particularly of Navel oranges - not something
which is leaching into the juice.

"The juice of the navel orange is not desirable for processing or
freezing due to the bitterness caused by limonine."

http://sarasota.extension.ufl.edu/FCS/FlaFoodFare/OrangesN.htm

Note that the more common spelling is "limonene."

Indeed, I have a valencia type tree!  Grumble for you!

So, i decided to actually do real work here and look this up.  You can
verify all the facts by looking in any scientific journal. J. Agric.
Food Chem., 51 (13), 3709 -3714

This actually turned out to be kinda interesting!

The compound is called limonin, it is NOT limonene.  

Limonene is orange oil, a terpene. It is the common essence associated
with oranges. It does not turn bitter, or generally react(oxidize) to
form bitter products. In fact limonene oxide has a nice fruity flavor.

Bitterness is associated with conversion of Limonoate A-ring lactone,
to a bitter compound, limonin, under acidic conditions. It is a
component of your oranges, probably not the peel.

If there were a solution to this problem, someone would have come up
with it and sold a ton of navel orange juice. Most work is centered
around passing the juice through an ion exchange type resin--out of
the league of the average orange consumer. Sorry I can't give you a
better answer.

You could try freezing the juice(this would reduce the rate of
lactonization((reaction))).  Alternatively, addition of sodium
bicarbonate(baking soda) might also help reduce the acidity and
prevent the formation of the second lactone.  Just my guesses!

Bob

NOW THAT IS TRULY INTERESTING - thanks!
However, it now appears that there is no satisfactory answer to my question.
But I sure appreciate your efforts.
Genetically modified Navel oranges?
I don't have the skills to do this...
Dr David Hitchins

Hey, cool, I think i got an idea.... Gotta try this...

Agric. Food Chem., 52 (12), 3772 -3775, 2004.

Well, as it turns out Valencia oranges, specifically the seeds,
contain an enzyme, called limonin D-ring lactone hydrolase (LDLH). 
This converts limonin, back to the non bitter, limonoate a-ring
lactone.

Thus, grind up some valencia orange seeds and chuck them in, OR, i bet
if you just mixed in one valencia orange with your navel oranges,
you'll probably have juice that lasts a lot longer.

Bob.

As usual, Bob is right.

I am married to a chemist, but his knowledge is not contagious. ;-)

This article might be of interest:

http://www.sbir.dsu.edu/sbhti/home/proposal_preparation/sample_proposals/usda_sample2.htm

Wait!
The question remains now: what inhibits the reaction the produces the bitter
limonin when the juice is in the orange?
A Navel orange can sit there for a week and taste delicious when juiced but
if you keep the juice in an airtight container for a week, it would taste 
terrible. 
What catalyses the reaction?
David

What causes this reaction to occur?

Man, I wish I had this one figured out.

First, you're making an ester, specifically  a six membered lactone,
makes this a favorable process. However, you don't have an strong
acids around, and you're in water, which makes things a little slower.
 I myself have been asking "what keeps this reaction from NOT
occuring?"...  Thermodynamically, limonin is the favored compound.

My guess is, that the limonoate a ring lactone, is probably protected
from the acidic juice.  Likely in the 'pulp' sections.  When you break
up the juice sacks, it gets into the orange juice.

According to several papers, it only takes around 6 ppm of limonin to
ruin your juice..