> David:

> I never came across this connection between cold and Maillard molecules
> before. It's particularly relevant today because I also learned this
> afternoon that although the in-shell almonds I've been eating (from Jaffe
> Bros, CA, USA) are not subjected to any heat, they are frozen before being
> shipped to Jaffe. I'm not sure how much significance to attach to this, but
> in light of your comment, I'm a bit concerned. Do you know of any other
> negative effects of freezing?


Of course, the Maillard reactions at high temperature are not the same
as those at room temperature, so maybe our body can metabolize
perfectly the molecules that appear the latter (and maybe not; wild
fires are natural too, but we know the ill effects of cooking).

By "cold storage", I meant storage at temperatures like 1-3 degree C
(34-38 F). The chemical reactions slow down, but are not stopped
completely. Thus, the quantity of some chemical compounds may be
abnormally high after a few weeks/months.

About freezing: given the low water-content of almonds, I might tend
to think that the effects are negligible (and after all, plants may
freeze naturally during fresh nights too), but here is some general
information (especially for meat, fish, vegetables, fruits):


Long answer, for the French anonymous (al.) co-lurkers: see
"Introduction a la biochimie et a la technologie des aliments", by
J-C. Cheftel, H. Cheftel & P. Besancon, Technique et
documentation-Lavoisier 1977.

Very long answer, for the non French readers: learn French and see
above.

Short answer:
------------

Even at temperatures like -18 degree C (0 F), a few % of water still
remains unfrozen, and can participate in chemical reactions.

The freezing of water causes modifications of concentrations, pH and
osmotic pressure; aggregation of proteins (meat and fish's texture
thus become harder). For numerous reasons, the WHC (water holding
capacity) lowers.

Due to differences of concentrations between extracellular and
intracellular water, ice forms first in the extracellular area. Cells
dehydrate by osmosis and shrink. Too much shrinking, formation of ice
crystals and volume variation (ice is less dense than water; the
internal tensions can be as high as several bars) are the three major
reasons for cell membrane damage.

The consequences of cell rupture are: water exsudation during thawing
(hence various losses), and the fact that enzymes are put in contact
with their substrates (hence an enzymatic browning).

During storage, various chemical reactions occur, such as: enzymatic
browning, and oxydation of lipids, vitamin C, pigments, chlorophyll.


All those deteriorations are reduced if the food is frozen quickly,
and kept at very low temperature.


Best wishes,

Jean-Louis.