Re: [CH] Blue garlic
Michael Nestrud (mike@ataraxis.org)
Mon, 24 Nov 2008 16:23:17 -0500
Hello all,
This just came out - it is available online. Contact me off list for a pdf.
It basically states that allinase, an enzyme, breaks down allin to
form sulfur compounds (the thiosulfinates). Thiosulfinates react with
amino acids to form color compounds. I'd be wary of other theories -
it is nothing to do with bacteria!
if you're interested in preventing it, do something to the garlic to
destroy the enzymes, i.e. heat shock. Microwave could also work.
Identification of Candidate Amino Acids Involved in the Formation of
Blue Pigments in Crushed Garlic Cloves (Allium sativum L.)
Cho et al.(2008). Journal of Food Science.
ABSTRACT: The color-forming ability of amino acids with thiosulfinate
in crushed garlic was investigated. We developed reaction systems for
generating pure blue pigments using extracted thiosulfinate from
crushed garlic and onion and all 22 amino acids. Each amino acid was
reacted with thiosulfinate solution and was then incubated at 60 °C
for 3 h to generate pigments. Unknown blue pigments, responsible for
discoloration in crushed garlic cloves (Allium sativum L.), were
separated and tentatively characterized using high-performance liquid
chromatography (HPLC) and a diode array detector ranging between 200
and 700 nm. Blue pigment solutions exhibited 2 maximal absorbance
peaks at 440 nm and 580 nm, corresponding to yellow and blue,
respectively, with different retention times. Our findings indicated
that green discoloration is created by the combination of yellow and
blue pigments. Eight naturally occurring blue pigments were separated
from discolored garlic extracts using HPLC at 580 nm. This suggests
that garlic discoloration is not caused by only 1 blue pigment, as
reported earlier, but by as many as 8 pigments. Overall, free amino
acids that formed blue pigment when reacted with thiosulfinate were
glycine, arginine, lysine, serine, alanine, aspartic acid, asparagine,
glutamic acid, and tyrosine. Arginine, asparagine, and glutamine had
spectra that were more similar to naturally greened garlic extract.
On Sun, Nov 16, 2008 at 10:54 AM, Jonathan Smillie
<jonathan.smillie@gmail.com> wrote:
> Not as OT as you might think... I've been steeping a gallon jar full of
> Bolivian Rainbow chiles and whole garlic cloves in white vinegar for a week
> now, intending to use it as the basis of some hot sauce, but over the last
> couple of days I've noticed that some - not all- of the garlic has begun to
> turn a rather fetching shade of blue (more lavender, really).
>
> I recall reading somewhere earlier on the list that this had to do with
> iodine content (although I haven't put salt, iodized or otherwise, in this
> mix) - but the core question is, is the blue garlic still safe to eat, or is
> the discoloration indicative of bacteria or something else that would
> recommend discarding this batch?
>
--
Michael A. Nestrud
Cornell University Sensory Science PhD Candidate
Culinary Institute of America, AOS 2004
"All that you taste... all that you eat."