Formation Of Fluorescent Substances Research Articles

Formation of fluorescent substances and correlation with process flavor changes of dehydrated Maillard reaction intermediates of peanut protein hydrolysates

Maillard reaction intermediates (MRIs) derived from peanut protein hydrolysates (PPH) and xylose (Xyl) were prepared using the water bath combined with spray drying and vacuum drying. The monitoring of free amino content, browning precursors, and taste characteristics was carried out throughout the thermal treatment at low temperature, where the Maillard reaction process was slowed down, and the formation and degradation of MRIs were dynamically balanced at low conversion rates. The reaction between amino compounds and the reducing sugars contributed to the increased taste characteristics during the early phase of Maillard reaction. Fluorescence intensity was reduced after reaching its maximum value and browning intensity was significantly increased during vacuum drying, which confirmed that the Maillard reaction entered into an advanced stage. Vacuum drying also led to a significant increase in the total amount of volatile compounds in the subsequent thermal processing reaction (from 212.93 ng/g to 564.91 ng/g), which demonstrated that the higher fluorescence intensities resulted in the more accumulation of MRIs and better capabilities of flavor formation.

Modification of Low Density Lipoprotein Subfractions Separated from Rabbit Hypercholesterolemic Serum.

Low density lipoprotein (LDL) subfractions, LDL-1, LDL-2, and LDL-3, separated from rabbit hypercholesterolemic serum and normal LDL from normal rabbit serum were modified by exposure to air in the absence or presence of Cu2+ at 37°C. When these LDLs were incubated in the presence of Cu2+, the lipid peroxide level and the mobility in agarose gel electrophoresis were increased in the following order: LDL-1>LDL-2>LDL-3>normal LDL. In the absence of Cu2+, the increases were also remarkable for LDL-1, less for LDL-2, but nonexistent for LDL-3 and normal LDL. Incubation in the presence of Cu2+ brought about the degradation of apo B-100 and the formation of fluorescent substances in these samples, but such did not occur in the absence of Cu2+. LDL samples modified in the presence of Cu2+ were taken up by rat peritoneal macrophages to the following extents: LDL-1>LDL-2>LDL-3>normal LDL. This tendency was supported by fluorescence microscopic observation using 1, 1′-dioctadecyl 3, 3, 3′, 3′-tetra-methylindocarbocyanine perchloride-labeled samples, and by the contents of total cholesterol in macrophages. These results indicate that LDL-1, which was identified as the main component of intermediate density lipoprotein, is more susceptible to lipid peroxidation-mediated modification and is more atherogenic than other subfractions of LDL.

Fatty acid hydroperoxide lyase in germinating soybean seedlings

A fatty acid hydroperoxide lyase from soybean seeds (Glycine max var. Williams) has been partially purified by differential centrifugation, ion-exchange chromatography, and gel filtration. The enzyme preparation, which is free of cis-3:trans-2-enal isomerase, has an optimum pH in the range 6-7. The lyase cleaves the 13-hydroperoxides of linoleic and linolenic acids to form the volatile aldehydes hexanal and cis-3-hexenal, respectively. In both case the omega-oxo carboxylic acid 12-oxo-cis-9-dodecenoic acid is also formed. The enzyme does not act on 9-hydroperoxides of these acids. The activity of hydroperoxide lyase was followed for 6 days of germination and found to increase constantly. Lipoxygenase activity (L-2 + L-3) also increased, as did the level of fluorescence in the phospholipids extracted. These facts suggest that lipoxygenase and hydroperoxide lyase may be involved in the formation of fluorescent substances.

Time dependent changes occurring in rat liver microsomes upon lipid peroxidation.

Steady-state fluorescence anisotropy of diphenylhexatriene and n-(9-anthroyloxy)stearic acids (n = 2,12) in rat liver microsomes showed a marked increase in the early stages of enzymatically or non-enzymatically induced lipid peroxidation. The changes in fluorescence anisotropy occurred in parallel with the formation of thiobarbituric acid-reactive substances (TBA-RS). Parallel to these changes, the fluorescence emitted from peroxidized microsomes increased markedly in the early stages of lipid peroxidation. In contrast to the changes in the fluorescence anisotropy and in the formation of TBA-RS, the fluorescence showed a continuing increase over the three hr period of lipid peroxidation. Glucose-6-phosphatase was inactivated in the early stages of lipid peroxidation, whereas NADH-cytochrome b5 reductase underwent a slow deactivation over three hr. The apparently slow deactivation of the peripheral protein may be explained by the formation of fluorescent substances.

Formation of fluorescent substances in reaction of aliphatic aldehydes and methylamine

AbstractTreatment of monofunctional aliphatic aldehydes (alkanals, 2‐alkenals and 2,4‐alkadienals) with methylamine at pH 7 produced fluorescence with excitation maxima at 340–360 nm and emission maxima at 410–470 nm. The reaction of 1‐butanal and methylamine gave 2‐ethyl‐2‐hexenal (ii), an aldol condensation product of 1‐butanal, and 3,5‐diethyl‐2‐propyl‐1‐methylpyridinium salt (i). The fluorescence was formed by the reaction of 1‐butanal and/or ii with methylamine in the presence of molecular oxygen. Fluorescent products I, II and III formed by the reaction were partially purified. Fluorescence characteristics of I, II and III were close to those of the fluorophores derived from the reaction of oxidized fatty acids and primary amines, with respect to maximum wavelengths in excitation and emission, and the resistance to sodium borohydride reduction.

Formation of fluorescent substances in the reaction of the hydroperoxide isomers of methyl linoleate and amylamine.

The formation of fluorescent substances through the reaction of degradation products of four geometrical isomers of methyl linoleate hydroperoxides with amylamine was studied. The 9-and 13-positional monohydroperoxide isomers having the cis-trans and trans-trans configurations were separated from autoxidized methyl linoleate by high performance liquid chromatography (HPLC) and their abilities to form fluorescent substances with amylamine in the presence of heme were compared. These four isomers produced the same fluorescent substances exhibiting excitation and emission maxima at 350 and 420 nm, respectively, and also showed the same abilities for fluorescence formation and the same elution profiles of fluorescent substances (FS-1 and FS-II) on HPLC. This study proved that all four geometrical isomers were involved in the production of fluorescent substances upon reaction with amino compounds.

The formation of fluorescent substances by lipidperoxides. I (author's transl)

The formation of fluorescent substances by lipidperoxides. I (author's transl)