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Heat- and light-treatment change the visible fluorescence of Akoya cultured pearls
Abstract
We exposed Akoya cultured pearls separately to heat (60–120 °C) and artificial light to investigate changes to fluorescence in the visible range and yellowing. We found that for both heat-treated and light-treated pearls, the fluorescence peak shifted from 480 to 430 nm with an increase in fluorescence intensity. This change in intensity was more prominent in heat-treated pearls, with the initial speed of increase rising with treatment temperature; treatment at 100 °C caused the greatest increase in fluorescence intensity. However, aminoguanidine suppressed the heat-induced change in the fluorescence of an ethylenediaminetetraacetic acid–soluble nacreous layer matrix. These results suggest that the heated-induced changes in the fluorescence of Akoya cultured pearls were caused largely by a buildup of fluorescent advanced glycation end products through the Maillard reaction. Although heat treatment led to a large increase in fluorescence intensity of the peak at approximately 430 nm in a deoxygenized environment, hardly any change in fluorescence intensity was observed after light treatment in this environment. Moreover, a new shoulder peak appeared at about 460 nm after light treatment. These results suggest that the Maillard reaction was not a major factor in the light-induced changes in the fluorescence of Akoya cultured pearls.
The durability of Akoya pearls is closely related to the mechanical strength of the nacre. Therefore, obtaining information about the mechanical strength of the nacre is very important in the quality control of pearls. The nacre of Akoya pearls is composed of aragonite contained within an organic matrix. The presence of the organic matrix provides mechanical strength and fracture toughness much higher than that of monolithic aragonite. In this study, we investigated the hardness and delamination strength of Akoya cultured pearls classified into four levels by “Gray Value (GV)”, a score given by a non-destructive inspection method based on UV fluorescence intensity that provides an indication of the condition of the nacre’s organic components. Pearl hardness decreased significantly with decreasing GV. Furthermore, delamination strength of the pearl surface layer was very low when the GV was very low. These results suggest that the GV indirectly represents the mechanical strength of the nacre and could be used as a non-destructive quality-control method to maintain the quality of pearls used as jewelry.
The colour of cultured pears of P. fucata can be changed by gamma-ray irradiation, which has been applied to pearl processing. The effect of gamma-ray irradiation on the colour and fluorescence of pearls was investigated experimentally. The experimental results show that a colour change of pearls to bluish-grey is mainly responsible for a decrease in the reflection factor of the nuclei. Furthermore, a significant change in the fluorescence spectra has been observed for pearls and nuclei. These changes are considered to be caused by the degradation of conchiolin contained in the nacre. Fluorescence from pearls is not affected by the nuclei, but the colour of pears is affected. Thus, the fluorescence method is suitable for investigating the effect of gamma-ray irradiation on the nacre.
To investigate the contribution of glycation and oxidation reactions to the modification of insoluble collagen in aging and diabetes, Maillard reaction products were measured in skin collagen from 39 type 1 diabetic patients and 52 nondiabetic control subjects. Compounds studied included fructoselysine (FL), the initial glycation product, and the glycoxidation products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine, formed during later Maillard reactions. Collagen-linked fluorescence was also studied. In nondiabetic subjects, glycation of collagen (FL content) increased only 33% between 20 and 85 yr of age. In contrast, CML, pentosidine and fluorescence increased five-fold, correlating strongly with age. In diabetic patients, collagen FL was increased threefold compared with nondiabetic subjects, correlating strongly with glycated hemoglobin but not with age. Collagen CML, pentosidine and fluorescence were increased up to twofold in diabetic compared with control patients: this could be explained by the increase in glycation alone, without invoking increased oxidative stress. There were strong correlations among CML, pentosidine and fluorescence in both groups, providing evidence for age-dependent chemical modification of collagen via the Maillard reaction, and acceleration of this process in diabetes. These results support the description of diabetes as a disease characterized by accelerated chemical aging of long-lived tissue proteins.
The fluorescence spectra of pearls and shells of Pteria penguin (mabe), Pinctada fucata (Japan's Akoya oyster) and Pinctada maxima (yellow lip oyster) have been measured in order to distinguish species of the mother oyster which produce that pearl. A distinction is possible for these pearls using differences in the fluorescence spectra. The spectral difference has been attributable to colouring matter or screloprotain in pearls and shells.
The nonenzymatic glycosylation reaction that is accelerated in diabetes is the first step of the Maillard or nonenzymatic browning reaction that occurs in stored food. The glucose-protein adduct rearranges and dehydrates to form brown and fluorescent pigments, which can act as crosslinks, resulting in decreased protein solubility and altered mechanical properties. Evidence suggesting that this process occurs in vivo has been found in lens crystallins. The observation that nonenzymatic glycosylation and insolubility increases in collagen with age and diabetes led us to investigate the possible browning of human collagen. Insoluble human dura mater collagen was digested with collagenase. Absorbance at 350 nm and fluorescence at 440 nm (excitation at 370 nm) of the solubilized material was measured. A linear increase in the amounts of yellow and fluorescent material was observed with age. Samples obtained at autopsy from three type I diabetics and a young type II diabetic showed increased fluorescence and had absorbance values that corresponded to the amount of chromophore found in nondiabetics twice their age (P less than 0.025). The collagen adducts from aged and diabetic individuals had absorption and fluorescence spectra identical to those of collagen samples that underwent nonenzymatic browning with glucose in vitro. The structure of these collagen adducts is unknown. However, their likely occurrence throughout the body could explain the correlation between arterial stiffening, decreased joint mobility, and the severity of microvascular complications in type I diabetics.
The non‐enzymatic modifications of proteins through Amadori and Maillard reactions play an important role in the loss of seed
viability during storage. In the present study, the contribution of sugar hydrolysis and lipid peroxidation to Amadori and
Maillard reactions, and to seed deterioration was investigated in mungbean (Vigna radiata Wilczek). The contents of glucose and lipid peroxidation products in seed axes increased significantly during storage. The
accumulation of Amadori products in seed axes was correlated to the lipid peroxidation, whereas the accumulation of Maillard
products was closely correlated to sugar hydrolysis. The rate of accumulation of Maillard products was not well correlated
to the content of Amadori products in both seed axes and protein/glucose model system, reflecting the complex nature of Amadori
and Maillard reactions. The content of Amadori products in seed axes increased during the early stages of seed ageing, whereas
the content of Maillard products increased steadily during the entire period of storage. The accumulation of Maillard products
in seed axes was associated with the decline of seed vigour. These data suggest that, during seed ageing, sugar hydrolysis
and lipid peroxidation are coupled with non‐enzymatic protein modification through Amadori and Maillard reactions.
In order to clarify the structure of yellow pigment of silk fibroin produced by ultraviolet irradiation, the author liberated three types of pigment from the yellow fibroin and obtained the following results by measuring ultraviolet, infrared, fluorescent spectra, etc.
(1) The pigment 1 was yellow colored oily substance with benzen ring and carbonyl radical in its side chain. But, hydroxyl radical, carboxyl radical and nitrogen atmos were not observed.
(2) The pigment 2 was of red crystal, which seemed to be the chain molecule of C=O and C=C radicals strongly conjugated.
(3) The pigment 3 was yellow colored oily substance, which seemed to be the chain molecule of C=O and C=C radicals conjugated.
(4) Ultraviolet spectra of the pigment of indoleacetic acid and indolepropionic acid produced by ultraviolet rays were closely similar to that of pigment 1.
Accordingly, the pigment 1 can be supposed to have produced by the photoxidative decomposition of indole compounds. But such assumption leaves room for further examination.
(5) Besides, other various types of pigment differing in molecural size and structure seemed to be on the peptide chains.
Various factors such as heat and sunlight cause the quality of akoya pearls to deteriorate. We examined the influence of heat and sunlight treatments on the nacreous shell matrix proteins (NSMPs) of akoya pearl by detecting changes in the reflectance (i.e. the ratio of reflectance at a wavelength of 254 nm and 282 nm) and fluorescence peak intensity (fluorescence intensity at 340 nm). Heat treatment at 100°C for up to 768 h caused a small decrease in reflectance value and a large decrease in fluorescence peak intensity, whereas sunlight at 250 W/m 2 for up to 768 h caused large decreases in both reflectance value and fluorescence peak intensity. Quantitative analysis of amino acid composition revealed that the only aromatic amino acid that decreased in content with heat treatment was tyrosine (by 18 %). Sunlight treatment decreased the tryptophan content by 78 % and tyrosine by 33 %. These results implied that the degeneration mechanisms of NSMPs by heat and sunlight treatments were different. By assessing these different changes in reflectance value and fluorescence peak intensity it may be possible to judge the two types of quality deterioration without the need to destroy the pearl.
The sugar compositions of yellow and white pearles were compared, since it being concluded in the previous paper that the pigments resulting from the interaction of conchiolin-like substances and some sugar derivatives are responsible for the yellow color of pearl. The pigments extracted from the decalcified nacres of pearls with In Hcl-methanol and the residual conchiolin were hydrolysed with 4Nh2 S04 in a boiling water bath separately. Each of the resulting hydrolyzates was fractionated into neutral and basic fractions using ion exchange resins. After trimethylsilylation, both fractions were subjected into GLC for sugar analysis. Xylose, fucose, mannose, galactose, and glucose were found in the neutral fraction of the yellow pearl pigments. On the basis of their peak areas, the relative amounts of xylose and mannose were found to be larger than those of fucose, galactose, and glucose. Sugars of the same sort as those in the yellow pearl were also found in the neutral fraction of the white pearl pigments. Fucose was present in relatively larger amounts than were the other sugars. The basic fraction of the yellow pearl pigments contained the amino sugars, galactosamine and glucosamine, while white pearl contained only glucosamine. © 1977, The Japanese Society of Fisheries Science. All rights reserved.
メイラード反応は食品の加工, 貯蔵時の化学的成分変化の中で最も重要な反応の一つである。この反応は非酵素的に進行し, 土壌中や生体内においても進行する。メイラード反応は酸化的反応と非酸化的反応に類別できる。酸化的反応において, グルコースの自動酸化や酸化的糖化反応 (glycoxidation) によって後期段階反応生成物 (AGE) が生成する。その反応過程に活性酸素が生成する。非酸化的反応においては3-デオキシグルコソン (3DG) のようなデオキシオソンが生成し, AGEの生成へと反応は進行する。一方, AGEの一種でもあるメラノイジンはヒドロキシルラジカル, 過酸化水素, スーパーオキシドのような活性酸素を強力に消去する。この消去活性はメラノイジンの抗酸化性や脱変異原性発現機構の一つとして説明できうる。
Wool may be excited by both mid-and near-u.v. radiation, emitting fluorescence. The extent of visible fluorescence depends on the origin of the wool and the degree of weathering, (the tips of the fibres being more fluorescent than the roots) and chemical modification. In particular oxidative treatments such as chlorination of shrink-resist procedures or peroxide bleaching processes increase the intensity of visible fluorescence but decrease the intensity of u.v. fluorescence (emission maximum at about 350 nm). It is proposed that the presence of these fluorescent chromophores in the fibre relates to the susceptibility of wool to yellow on exposure to light.
Aminoguanidine (AG) is a prototype therapeutic agent for the prevention of formation of advanced glycation endproducts. It reacts rapidly with alpha,beta-dicarbonyl compounds such as methylglyoxal, glyoxal, and 3-deoxyglucosone to prevent the formation of advanced glycation endproducts (AGEs). The adducts formed are substituted 3-amino-1,2,4-triazine derivatives. Inhibition of disease mechanisms, particularly vascular complications in experimental diabetes, by AG has provided evidence that accumulation of AGEs is a risk factor for disease progression. AG has other pharmacological activities, inhibition of nitric oxide synthase and semicarbazide-sensitive amine oxidase (SSAO), at pharmacological concentrations achieved in vivo for which controls are required in anti-glycation studies. AG is a highly reactive nucleophilic reagent that reacts with many biological molecules (pyridoxal phosphate, pyruvate, glucose, malondialdehyde, and others). Use of high concentrations of AG in vitro brings these reactions and related effects into play. It is unadvisable to use concentrations of AG in excess of 500 microM if selective prevention of AGE formation is desired. The peak plasma concentration of AG in clinical therapy was ca. 50 microM. Clinical trial of AG to prevent progression of diabetic nephropathy was terminated early due to safety concerns and apparent lack of efficacy. Pharmacological scavenging of alpha-oxoaldehydes or stimulation of host alpha-oxoaldehyde detoxification remains a worthy therapeutic strategy to prevent diabetic complications and other AGE-related disorders.
Glucose molecules may enter into a Maillard reaction with reactive amino groups present in wool, transforming these groups to their N-glycoside derivatives. No changes to the physical or mechanical properties of wool fibres following glucose treatment have been observed. However, an increase in the pick-up of reactive and acid dyes was recorded after wool was pretreated with an aqueous glucose solution.
Part 1 of this review discussed the effects of light on wool keratin and the factors that affect the rate of photoyellowing. Part 2 describes the various photochemical mechanisms that have been proposed to account for photoyellowing of wool by sunlight, and focuses in particular on their strengths and weaknesses. The mechanisms involved in the rapid photoyellowing of wool treated with a fluorescent whitening agent are described in some detail since this remains a serious commercial problem. Existing methods for reducing the rate of wool photoyellowing are reviewed, together with a discussion of the remaining scientific and technical challenges to achieve bright, white wool fabrics and garments of high photostability.
The chemical reactions that may lead to the loss of seed viability were investigated both during the accelerated aging and natural aging of soybeans (Glycine max Merrill cv. Chippewa 64). Under conditions of accelerated aging (36°C and 75% RH), fluorescence of soluble proteins accumulated, which was closely correlated with the loss of seed germinability and vigor. We were able to show this correlation by using partially purified proteins for the assay. Fluorescence also increased in seeds under good storage conditions (5°C for up to 21 years), although there was a less significant correlation between seed viability and the accumulation of fluorescent products during the time of natural aging. The rise in protein fluorescence is interpreted as an increase of Maillard products. The carbonyl content of soluble proteins (a measure of the oxidative damage) did not change significantly during either accelerated aging or natural aging: however the elimination of carbonyls during germination seemed to be hindered in seeds that had poor germination. The Maillard reaction may be a consequence of the formation of reducing sugars through a gradual hydrolysis of oligosaccharides during aging. Preliminary evidence from the natural aging study showed that, when seeds were in the glassy state, the sugar hydrolysis was inhibited. These results suggest that the Maillard reaction and oxidative reaction may play an important role in seed deterioration.
The yellowing of wool exposed to sunlight is a serious commercial shortcoming compared to cotton and synthetic fibres, particularly when photostable brilliant whites and bright pastel shades are required. Part 1 of this review discusses the effects of light on wool keratin and the factors that affect the rate of photoyellowing, including oxidative bleaching, fluorescent whitening and the presence of moisture. The effect of variation of the wavelength of light, particularly attenuation of the ultraviolet wavelengths in sunlight by window glass that can result in photobleaching of wool is described. The experimental techniques that have been used to study the complex photochemistry involved in yellowing, and to identify the nature of the yellow chromophores formed, are also discussed. Part 2 of the review will focus on the photochemical mechanisms involved, and discusses potential ways for improving wool's photostability.
Spectrofluorimetric analysis of proteinaceous binding media is particularly promising because proteins employed in paintings
are often fluorescent and media from different sources have significantly different fluorescence spectral profiles. Protein-based
binding media derived from eggs, milk and animal tissue have been used for painting and for conservation, but their analysis
using non-destructive techniques is complicated by interferences with pigments, their degradation and their low concentration.
Changes in the fluorescence excitation emission spectra of films of binding media following artificial ageing to an equivalent
of 50 and 100 years of museum lighting include the reduction of bands ascribed to tyrosine, tryptophan and Maillard reaction
products and an increase in fluorescent photodegradation. Fluorescence of naturally aged paint is dependent on the nature
of the pigment present and, with egg-based media, in comparison with un-pigmented films, emissions ascribed to amino acids
are more pronounced.
During storage of foods and biological systems, fluorescent products are developed through the Maillard reaction, along with the brown pigments. Fluorescent products have been proposed as early indicators of this reaction. The aim of present work was to compare the kinetics of fluorescence and pigment development in order to define adequate early markers. Model glucose–aminoacid systems were prepared in several salts and buffers and stored at 55 °C. Pigment and florescence development was evaluated as a function of time. The results showed that, under unfavourable conditions for the reaction (low pH, presence of retardant salts), fluorescence was detected after important colour changes had occurred. However, under favourable conditions for the reaction (neutral pH, accelerating salts) fluorescent products could be considered as adequate markers because they sensitively reflected early steps of the reaction. Compositional factors and/or environmental conditions are the key factors for defining the performance of fluorescence as an adequate early marker.
Maillard reaction products (MRPs) were prepared by heating 2% porcine plasma protein (PPP) and reducing sugars (glucose, fructose and galactose) at the levels of 1% or 2% at 100 °C up to 5 h without pH control. Browning and intermediate products, as monitored by absorbance at 420 nm and absorbance at 294 nm, increased as heating time increased (P < 0.05). However, fluorescence (Ex 347 and Em 415 nm) sharply increased within 1 h and subsequently decreased when heating time increased (P < 0.05). Increase in browning and formation of intermediate products was observed with a concomitant decrease in free amino groups. Among sugars and concentrations used, galactose at 2% rendered the highest browning and intermediate products. MRPs derived from galactose, especially at a level of 2% possessed greater reducing power and DPPH radical-scavenging activity than those prepared from fructose and glucose. MRPs derived from fructose or galactose at the level of 2% showed the increase in reducing power and DPPH radical-scavenging activity in a concentration-dependent manner. In general, antioxidative activity of PPP–sugar MRPs was coincidental with the browning development and the formation of intermediate products.
The Maillard reaction is a complex and poorly understood series of reactions between reducing sugars and the primary amino groups of proteins. The resulting advanced glycation end-products (AGEs) and active oxygen species are thought to contribute to the development of diabetic complications and aging. This review describes the basic chemistry of the Maillard reaction.
Fluorescence spectra of pearls of Pinctada fucata (Japan's Akoya oyster) and Pinctada maxima (white lip oyster) have been measured in order to distinguish species of the mother oyster which produce that pearl. A distinction is possible for these pearls using the difference in the fluorescence spectra under N_2 laser excitation.
Color of cultured pearls of P. fucata (Akoya oyster) can be changed by light irradiation, which has been applied to pearl processing. The effects of light irradiation on fluorescence and optical reflectance of pearls have been investigated experimentally. Changes in the fluorescence and reflectance spectra have been observed. These changes depend on the wavelength of light and are considered to be due to degradation of conchiolin (a kind of scleroprotein) and discolouration of pigments contained in the nacre (the surface layer around the core of a pearl).
Making Mother of Pearl
Nacre is an iridescent layer of calcium carbonate lining the inside of shells of marine mollusks and is commonly known as “mother of pearl.” It is composed of layers of uniformly oriented crystals of aragonite (a metastable form of calcium carbonate) separated by layers of organic matrix. How the ordered structure of aragonite layers is achieved has been unclear. Suzuki et al. (p. 1388 , published online 13 August 2009; see the Perspective by Kröger ) identified two acidic matrix proteins (Pif 97 and Pif 80) that regulate nacre formation in the Japanese pearl oyster. The proteins appear to form a complex in which Pif 80 binds to aragonite and Pif 97 binds to other macromolecules in the organic matrix.
Age-associated increases in collagen cross-linking and accumulation of advanced glycosylation products are both accelerated
by diabetes, suggesting that glucose-derived cross-link formation may contribute to the development of chronic diabetic complications
as well as certain physical changes of aging. Aminoguanidine, a nucleophilic hydrazine compound, prevented both the formation
of fluorescent advanced nonenzymatic glycosylation products and the formation of glucose-derived collagen cross-links in vitro.
Aminoguanidine administration to rats was equally effective in preventing diabetes-induced formation of fluorescent advanced
nonenzymatic glycosylation products and cross-linking of arterial wall connective tissue protein in vivo. The identification
of aminoguanidine as an inhibitor of advanced nonenzymatic glycosylation product formation now makes possible precise experimental
definition of the pathogenetic significance of this process and suggests a potential clinical role for aminoguanidine in the
future treatment of chronic diabetic complications.
Vesperlysines A and B, 6-hydroxy-1,4-di{6-(L-norleucyl)}-1H-pyrrolo[3,2-b]pyridinium and its 5-methyl derivative, respectively, and Vesperlysine C, 5-hydroxy-methyl-1,6-di{6-(L-norleucyl)}-1H-pyrrolo[3,4-b] pyridinium, are isolated as major fluorescent advanced glycation end products (AGEs) from hydrochloric acid hydrolysis of AGE-BSA, bovine serum albumin (BSA) modified by the Maillard reaction with glucose. These fluorophores are glycation products and not artifacts of hydrolysis, since they are also detected in the reaction mixture of lysine and glucose prior to hydrolysis. Vesperlysines are crosslinked products from two lysine side-chains in proteins and are considered to be generated from lysines and the oxidative degradation of glucose, because the six carbon skeleton of glucose in its original form was not incorporated into each structure. These compounds are most likely glycoxidation products like pentosidine. This reasoning is supported by the formation of the same compounds in the Maillard reactions in which ascorbic acid or other sugars with shorter carbon chains are used.
We have isolated a new matrix protein family (N16) which is specific to the nacreous layer of the Japanese pearl oyster, Pinctada fucata, and have cloned and characterized the cDNAs coding for the components. Analysis of the deduced amino acid sequence revealed that N16 showed no definitive homology with other proteins. The in vitro studies of the crystallization clarified that N16 induced aragonite crystals when fixed on the substrate but inhibited crystal formation without it. The aragonite crystals showed platy morphology different from those formed inorganically, and long intervals of incubation resulted in crystalline layers highly similar to the nacreous layer.
Calcified shell layer is composed of two polymorphs of CaCO(3), aragonite or calcite, and an organic matrix. The organic matrix consists of EDTA-soluble and insoluble fractions. These fractions are thought to regulate the formation of the elaborate shell structure. After decalcification of powdered pearl with 0.3 M EDTA, an EDTA-insoluble fraction was extracted with 0.3 M EDTA/8 M urea. This extraction step enabled us to purify a new class of EDTA-insoluble protein, Pearlin, almost homogeneously. Pearlin has a molecular weight of about 15 kDa and contains a sulfated mucopolysaccharide. We cloned the complementary DNA coding for Pearlin and deduced its complete amino acid sequence. Sequence analysis reveals that Pearlin is composed of 129 amino acids with a high proportion of Gly (10.8%), Tyr (10.0%), Cys (8.5%), Asn (7.7%), Asp (7.7%), and Arg (7.7%). Northern blot analysis showed that Pearlin messenger RNA was expressed specifically in mantle epithelium. From the sequencing data, Pearlin was shown to be quite different from the fibrous protein rich in Ala and Gly. The function of this protein in biomineralization is discussed.
Shinju no Kagaku—Shinju no Dekiru Shikumi to Miwakekata
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The influence emission spectra of egg-, casein-and collagen-based painting media
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A consider of silk yellowing
- Hirao
Hirao C (1977) A consider of silk yellowing. J Seric Sci Jpn 46:361–362 (in Japanese)
Initiation of mineralization in bivalve molluscs
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Studies on antioxidant activity of amino-car-bonyl reaction products part II. Influence of reaction-condition of tryptophan and glucose on antioxidant activity of the resulting browning-solution
- Tomita
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Homotsu-Shinju no Zaishitsu-Chosa Hokoku
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Shinju-Soshiki no Itamidoai Kara mita Kako-Shoriho no Hyoka
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Shosoin-Homotsu (Raden, Kaigara) Zaishitsu-Chosa Hokoku
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Creatine interference in the protein modification as AGE formation
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