Conventional food preservation methods by adjustment of water activity (aw) have adverse effects on the flavor of the finished product. Recent research showed that a mild reduction of a, (i.e. to 0.90 -0.95) together with other factors will produce microbiologically stable products. The purpose of this work was to determine the kinetics of brown color development in model systems adjusted to the range of a, 0.90 -0.95. From results obtained one can see the strong influence of temperature and pH and the lack of influence of aw in the rate of brown color development.
A compound with properties identical with the glucose-containing dolichyl diphosphate oligosaccharide present in animal tissues was detected in alfalfa roots incubated with [14C]glucose. The products of mild acid hydrolysis behaved the same on paper chromatography, on treatment with specific glucosidases and on N-deacetylation.
A lipid-bound oligosaccharide was isolated from pea (Pisum sativum) cotyledons incubated with I'4Clmannose. The oligosaccharide moiety appeared to be identical with the one obtained from rat liver, known to contain three glucoses, nine mannoses, and two N-acetylglucosamines, and to be involved in protein glycosylation.Enzymes obtained from soya (Glcine mar) roots and developing pea cotyledons were found to catalyze the transfer of oligosaccharide from the lipid intermediate to endogenous protein. The enzymes require Mn2' and detergent for activity. Evidence is presented indicating that the lipid-bound oligosaccharide with three glucoses is transferred faster than that with less. Some of the peripheral mannoses could be removed without affecting the rate of transfer.The protein-bound oligosaccharide, formed by incubation of whole cotyledons or by transfer with the enzyme preparation, could be released by protease and endo--N-acetylglucosinidase treatment, as expected for an asparagine-bound high mannose oligosaccharide.
The effect of different polyols (glycerol, propylene glycol, sorbitol, 1,3-butylene glycol, polyethylene glycol200, and polyethylene glycol 400) and various alkali metal chlorides (KCl, NaCl, LiCl, and CsCl) on the kinetics of nonenzymatic browning in glucose-lysine solutions, of high water activity (a,,,) was studied. No particular inhibitory or promoting effect on browning of glucose-lysine solutions, when adjusting a, with the various polyols, was found. The alkali metal chlorides had a significant influence on the rate of browning and the relative effect of cations (Li > Na > K,Cs) paralleled the hydrated ionic radii in solutions.
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