Chlorohydrins in protein hydrolysates.

Four samples of neutral fractions of protein hydrolysates were separated by gas chromatography and the individual components were identified from the mass spectra obtained. Some of the identified compounds were not previously reported as volatile components of foodstuffs. Three of these compounds namely 3-chloropropan-1-ol, 2,3-dichloropropan-1-ol, and 1,3-dichloropropan-2-ol, were toxic chlorohydrins. 1,3-Dichloropropan-2-ol was present in samples in concentrations 0.17 to 0.94 mg/kg. To check the possibilities of the formation of these chlorohydrins and to find their precursor, glycerol, and hydrochloric acid mixtures were heated under conditions of producing protein hydrolysates. All three chlorohydrins, formerly found in protein hydrolysates have been identified.

Nonenzymic browning. XV. Effect of unsaturation on browning reactions of oxidized lipids with protein.

The amount of pigments produced by interaction of oxidized lipids with albumin and the intensity of coloration increase with increasing degree of unsaturation of the lipid fraction.

Lipid oxidation. Part 3. Oxidation of egg phosphatidylethanolamine.

Phosphatidylamine isolated from egg yolk phospholipids was autoxidized at 60 degrees C. Oxidation products were separated by thin layer chromatography on silica gel and by column chromatography of DEAE-cellulose. The fractions were characterized by UV and IR spectra and by chemical analysis. Polyunsaturated fatty acids were destroyed during the oxidation, the content of primary amino groups decreased and imine derivatives appeared.

Lipid oxidation. Part. 1. Effect of free carboxyl group on the decomposition of lipid hydroperoxide.

Hydroperoxido butyl oleate was decomposed by heating in excess palmitic acid at 60-120 degrees C. The decomposition followed the kinetics of a first order reaction with formation of both monomeric and oligomeric secondary products. The proportions of oligomers slightly increased with increasing reaction temperature and decreased with increasing concentration of hydroperoxide. The activation energy was 70.4 kJ/mol +/- 4.7 kJ/mol. The decomposition of hydroperoxides proceeded partially by monomolecular cleavage, partially by formation of esters with palmitic acid.

Lipid oxidation. Part 2. Oxidation products of olive oil methyl esters.

Olive oil was converted into methyl esters which were autoxidized at 60 degrees C. The composition of oxidized products was determined by the comparison of infrared spectra and NMR spectra of the original and acetylated samples, the sample reduced with potassium iodide and the acetylated reduced sample. Oxidized products were separated by preparative thin layer chromatography on silica gel and characterized by selective detection and by infrared spectrometry of the fractions. The oxidation products consisted of hydroperoxido butyl oleate, substituted hydroperoxides, mono- and disubstituted monomeric derivatives and a small amount of oligomers.

Changes of sensory value by interaction of alkanals with amino acids and proteins.

Alkanals as carriers of rancid flavour of fat-containing foods were stored in mixtures with nonlipidic substances. The intensity of odour due to alkanals decreased with increasing time of storage, the changes being more pronounced in case of casein than in that of cellulose. Results of sensory tests did not depend on the molecular mass of aldehyde. The water content affected the sensory evaluation only slightly. The formation of aldolization products or polymers and of gluey flavour compounds modified the character of flavour and confused less experienced judges. Both the binding of alkanals and the aldolization reactions were enhanced by presence of primary amino groups.

[Development of fish flavor by reaction of autoxidized lipids with amino acids and proteins]. / Bildung von Fischaroma durch Reaktion autoxydierter Lipide mit Aminosäuren und Proteinen

The rancid fish-oil flavour of autoxidized tetraene, pentaene and hexaene fatty acid esters disappears during storage or heating with free amino acids or proteins. Simultaneously, a flavour of raw, roasted or fried fish develops. The development of this fish flavour is of particular intensity in mixtures containing lysine or some other amino acids. Blocking of the free amino groups in casein or albumin inhibits the development of a fish flavour in mixtures with oxidized lipids. If the mixtures are added with lysine, the fish flavour reappears. The development of a fish flavour is associated with browning reactions.

Nonenzymic browning. XIV. Reaction of phospholipids with 1,4-benzoquinone.

Phosphatidylethanolamine reacts with 1,4-benzoquinone with the formation of a red unstable intermediary product consisting of one phosphatidylethanolamine residue and one 1,4-benzoquinone residue. The secondary reaction products are purple, violet, and reddish brown. Consequently, the absorption maximum shifts from 430 nm to 490 nm during the reaction. Finally, brown macromolecular end-products are formed. Phospholipids derived from choline, such as phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, contribute only a little to the browning reactions, in comparison with phospholipids containing a primary amino-group (phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylserine). The browning of a natural mixture of egg phospholipids depends on the content of derivatives containing a primary amino-group.

Nonenzymic browning. XII. Maillard reactions in green coffee beans on storage.

During storage of green coffee beans at increased temperature and at constant humidity reducing sugars present in original beans react with free amino acids with formation of colourless unstable products. Additional reducing sugars and free amino acids are produced by hydrolysis of polysaccharides and proteins, respectively. The second stage of storage is characterized by only slight changes in the content of free amino acids and sugars but by intensive browning reactions. This latter stage was characterized by deterioration of sensory quality of coffee beverage, especially of its odour. Lysine combined in protein was involved in browning reactions via colourless intermediary products.

Nonenzymic browning XIII. Effect of an antioxidant on the discoloration of lipid-protein mixtures.

Higher concentrations of butylated hydroxyanisole inhibited the autoxidation of mixtures of unsaturated cod liver oil fatty acid esters with model proteins. The rate of discoloration was far less efficiently affected by the antioxidant because the antoixidant did not prevent the further transformation into brown pigments of colourless precursors, mainly carbonyl lipid oxidation products, already present in the lipid fraction before the addition of antioxidant. The antioxidant also did not influence the pigments already formed.

Nonenzymic browning. XI. Effect of free amino groups on browning reactions in lipid-protein mixtures.

The course of browning was more rapid in mixtures of polyunsaturated fatty acid esters with casein that in those of the same lipids with formaldehyde-treated casein or with an inert inorganic substrate (barium sulphate or sodium sulphate). On the contrary, the content of oxidation products (peroxides and aldehydes) was much higher in lipids mixed with formaldehydetreated casein or with inorganic substrates. The results obtained with albumin were similar. The ratio of red to yellow pigments was higher in mixtures with non-treated casein than in the other two investigated reaction mistures. Brown pigments contained only low per centages of nitrogen.

[Interaction between proteins and oxidized lipids]. / Wechselwirkung zwischen Proteinen und oxydierten Lipiden

Oxidized lipids react with proteins to form lipoproteid complexes in which the lipids are bound to the proteins in part by physical forces, in part by covalency. The free radicals resulting from the cleavage by hydroperoxides are the major precursors of the lipoproteid complexes. The interaction is associated with protein denaturation and oligomer formation. The lipids contained in the lipoproteid complexes are only in part extracted by chloroform-methanol; in part not until after acid or alkaline hydrolysis. The nutritive value of the protein moiety is diminished by the reaction of the hydroperoxides with methionine and cysteine and by the reaction of the peroxidic radicals and aldehydes with lysine and other basic amino acids. Secondary reactions of the lipoproteid complexes lead to brown coloured, only partly soluble compounds which often impair the organoleptic value. The rancidity products of the fats are neutralized by the reaction with proteins. The action of highly unsaturated oxidized lipids on proteins results in the development of a fishy aroma.