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Journal ArticleDOI

Mechanisms of heat damage in proteins. 2. Chemical changes in pure proteins.

01 Mar 1970-British Journal of Nutrition (Br J Nutr)-Vol. 24, Iss: 1, pp 313-329
TL;DR: The degree of correlation of lysine binding in different proteins with ammonia liberation and amide changes has led us to suggest that the main reaction of e-amino lYSine groups is with amide groups of asparagine and glutamine, which is considered to be partially responsible for the lysines binding in heated proteins.
Abstract: 1 Bovine plasma albumin (BPA) containing approximately 14% moisture, when heated for 27 h at 115° suffered an appreciable loss of cystine and a small loss of lysine; at 145° all the amino acids except glutamic acid and those with paraffin side-chains, showed considerable losses Isoleucine also showed some loss through racemization to alloisoleucine2 BPA heated at 115° evolved H2S; at 145° other sulphur compounds were released as well, all coming from the breakdown of cystine Possible mechanisms for this are discussed3 Ammonia was also liberated from BPA heated at 115° The degree of correlation of lysine binding in different proteins with ammonia liberation and amide changes has led us to suggest that the main reaction of e-amino lysine groups is with amide groups of asparagine and glutamine Reaction of e-amino groups with carboxylic groups is thought to be less important4 Model experiments have shown that a reaction between amide groups and the e-amino group of lysine in proteins can occur at practical drying temperatures5 Reactions of the e-amino group of lysine with destruction products of cystine is also considered to be partially responsible for the lysine binding in heated proteins

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the major functional properties of food proteins, e.g., solubility, binding properties, surfactant properties, viscogenic texturizing characteristics, etc.
Abstract: Proteins for foods, in addition to providing nutrition, should also possess specific functional properties that facilitate processing and serve as the basis of product performance. Functional properties of proteins for foods connote the physicochemical properties which govern the behavior of protein in foods. This general article collates the published information concerning the major functional properties of food proteins, e.g., solubility, binding properties, surfactant properties, viscogenic texturizing characteristics, etc. The effects of extraction and processing on functional properties and possible correlations between structure and function are discussed, in relation to practical performance in food systems. Modification of proteins to improve functional characteristics is briefly mentioned.

1,223 citations

Journal ArticleDOI
TL;DR: The experimental data obtained suggest that enzymes are extremely thermostable in anhydrous organic solvents due to their conformational rigidity in the dehydrated state and their resistance to nearly all the covalent reactions causing irreversible thermoinactivation of enzymes in aqueous solution.
Abstract: Three unrelated enzymes (ribonuclease, chymotrypsin, and lysozyme) display markedly enhanced thermostability in anhydrous organic solvents compared to that in aqueous solution. At 110-145 degrees C in nonaqueous media all three enzymes inactivate due to heat-induced protein aggregation, as determined by gel filtration chromatography. Using bovine pancreatic ribonuclease A as a model, it has been established that enzymes are much more thermostable in hydrophobic solvents (shown to be essentially inert with respect to their interaction with the protein) than in hydrophilic ones (shown to strip water from the enzyme). The heat-induced aggregates of ribonuclease were characterized as both physically associated and chemically crosslinked protein agglomerates, with the latter being in part due to transamidation and intermolecular disulfide interchange reactions. The thermal denaturation of ribonuclease in neat organic solvents has been examined by means of differential scanning calorimetry. In hydrophobic solvents, the enzyme exhibits greatly enhanced thermal denaturation temperatures (T(m) values as high as 124 degrees C) compared to aqueous solution. The thermostability of ribonuclease towards heat-induced denaturation and aggregation decreases as the water content of the protein powder increases. The experimental data obtained suggest that enzymes are extremely thermostable in anhydrous organic solvents due to their conformational rigidity in the dehydrated state and their resistance to nearly all the covalent reactions causing irreversible thermoinactivation of enzymes in aqueous solution.

211 citations

Book ChapterDOI
01 Jan 1985
TL;DR: In this paper, the authors summarise the vast literature on the composition of green coffee beans paying particular attention to those components which are peculiar to coffee, focusing on compositional factors that might be determinants of acceptability, and situations where the data are incomplete or contradictory.
Abstract: This chapter summarises the vast literature on the composition* of green coffee beans paying particular attention to those components which are peculiar to coffee. The corresponding data are given for roasted beans and where possible for soluble powders. Attention is focused on compositional factors that might be determinants of acceptability, and situations where the data are incomplete or contradictory with the intention of provoking thought, comment and further investigation.

206 citations

Journal ArticleDOI
TL;DR: In this article, the authors compared solvent-extracted chicken muscle, bovine plasma albumin (BPA) and other proteins, all severely heated in the absence of carbohydrates so as to cause a large decrease in their fluorodinitrobenzene (FDNB)-reactive lysine contents.
Abstract: 1. Studies have been made with solvent-extracted chicken muscle, bovine plasma albumin (BPA) and other proteins, all severely heated in the absence of carbohydrates so as to cause a large decrease in their fluorodinitrobenzene (FDNB)-reactive lysine contents.2. ɛ-N-(β-L-aspartyl)-L-lysine and ɛ-N-(γ-L-glutamyl)-L-lysine isopeptides were determined after enzymic digestion of heated chicken muscle, and their content was found to increase as the material was subjected to more heat treatment. Heated chicken muscle was not found to contain lanthionine. Heated BPA, on the other hand, was found to contain lanthionine but not the isopeptides. Both lanthionine and isopeptide cross-linkages were detected in most of the other heated proteins. There was some difficulty in quantifying the amounts of isopeptides formed on heat treatment, because the enzymic digestion procedure used in their isolation appeared to be incomplete. Neither lysinoalanine nor ornithinoalanine was detected in any of the test materials.3. The severely heated chicken muscle was fed to rats, and ileal and faecal digestibilities were studied. Protein digestibility was found to be greatly reduced after heat treatment, although the isopeptides themselves appeared to be at least as digestible as the total N component, total lysine, or FDNB-reactive lysine. However, the reduction in ileal N digestibility only partly accounted for the much larger reduction in nutritive value, as measured by net protein ratio ((weight loss of N-free animals + weight gain of test animals) ÷ weight of crude protein (N × 6.25) consumed by test animals). Possible reasons for this are discussed.

196 citations

Book ChapterDOI
TL;DR: This chapter discusses and attempts to organize and correlate the different types of carbonyl–amine reactions found in proteins with their organic chemistry, and focuses on the carbonies–-amine reaction in biological processes, naturally occurring deteriorative reactions, and their commercial applications.
Abstract: Publisher Summary Reaction of a carbonyl group with an amino group is the key reaction in many enzymic and other biological processes, such as vision. This chapter discusses and attempts to organize and correlate the different types of carbonyl–amine reactions found in proteins with their organic chemistry. The chapter focuses on the carbonyl–-amine reaction in biological processes, naturally occurring deteriorative reactions, and their commercial applications. The most characteristic chemical property of amines is their ability to act as nucleophiles because they possess a lone pair of electrons on the nitrogen atom, while, the reactivity of the carbonyl bond is primarily because of the difference in electronegativity between carbon and oxygen, which leads to a significant contribution of the dipolar resonance form, oxygen being negative and carbon being positive. The rate of the carbonyl–amine reaction usually shows acharacteristic pH dependence that results in a bell-shaped curve. Formaldehyde reacts not only with primary amino groups in proteins, but also with sulfhydryl groups. Carbonyl–amine reactions play important roles in catalytic reactions in enzymes, cross-linking in structural proteins like collagen and elastin and the visual process.

146 citations

References
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Journal ArticleDOI
TL;DR: It is recommended that the proteases described in this paper shall be considered identical until evidence to the contrary is adduced, and that they be called leaf proteases, adding where necessary the name of the plant.
Abstract: No evidence has been found to show that the protease is a mixture ofenzymes or that the protease of one plant is distinguishable from another. It has been customary to name a protease after the generic name of the plant in which it is found. This custom, both here and in future work, implies an indefinite extension in the number of proteases. It is therefore recommended that the proteases described in this paper shall be considered identical until evidence to the contrary is adduced, and that they be called leaf proteases, adding where necessary the name of the plant.

314 citations

Journal ArticleDOI
24 May 1968-Science
TL;DR: The authors showed that epsilon-(gamma-glutamyl)lysine cross-links form in human fibrin during polymerization catalyzed by factor XIII, and showed that the cross-link formation was not observed in non-cross-linked fibrins with ethylenediaminetetraacetic acid.
Abstract: (epsilon)-((gamma)-Glutamyl)lysine has been isolated from enzymatic hydrolyzates of cross-linked human fibrin. This compound was not detected in "non-cross-linked" fibrin prepared with ethylenediaminetetraacetic acid, which inhibits factor XIII; intermediate amounts were observed when the fibrin was prepared with glycine ethyl ester, which inhibits factor XIII competitively. These and ancillary experiments furnish conclusive evidence that epsilon-(gamma-glutamyl)lysine cross-links form in human fibrin during polymerization catalyzed by factor XIII.

297 citations

Journal ArticleDOI
TL;DR: Transient free-radicals are produced in peroxidizing lipid-protein reaction systems and the pattern of damage to proteins, induced by these radicals, is similar to that observed in the case of radiation damage.

211 citations