2, 4, 5-TRIHYDROXYBUTYROPHENONE (2, 4, 5-THBP)a AS A SUBSTRATE FOR MUSHROOM TYROSINASEb

2, 4, 5-THBP (2, 4, 5-trihydroxybutyrophenone) is a substrate for mushroom tyrosinase with a K_m value of 1.00 mM. The final product(s) formed is red (λ._max 480–490 nm) and it is rather stable with time. An intermediate red product(s), having a maximum at λ 505–515 nm, was detected and the time course of its conversion to the final red product(s) was studied. The data suggest that the intermediate red product(s) is 2, 4, 5-THBP-quinone which is converted to colorless polymerized 2, 4, 5-THBP-OH, which is then oxidized to a red polymerized 2, 4, 5-THBP-quinone(s), which is the final red product(s).     

p-HYDROXYPHENYLACETIC ACID AND-3,4-DIHYDROXYPHENYLACETIC ACID AS SUBSTRATES FOR MUSHROOM TYROSINASE

The hydroxylation of p-hydroxyphenylacetic acid (PHPAC) and the oxidation of 3,4-dihydroxyphenylacetic acid (DOPAC) by mushroom tyrosinase are illustrated. DOPAC quinone (4-carboxy-methyl-o-benzoquinone (λ_max= 400±10 nm) is the initial pigmented product formed when DOPAC is oxidized by the enzyme. DOPAC quinone is very unstable, and, once formed, is converted rapidly to further oxidation product(s).
The relationships between the rate of p-dihydroxyphenylacetic acid hydroxylation and 3,4-dihydroxyphenylacetic acid oxidation as a function of various concentrations of each substrate and of mushroom tyrosinase, are described.
The effect of the addition of various chemicals that can potentially conjugate otherwise affect DOPAC quinone was studied The Km value of 3,4-dihydroxyphenylacetic acid for mushroom tyrosinase was estimated to be 4.0 mM.     

2,3,4-TRIHYDROXYACETOPHENONE (2,3,4-THAP) AS A SUBSTRATE FOR MUSHROOM TYROSINASE1

2,3,4-Trihydroxyacetophenone (2,3,4-THAP) can serve as a substrate for mushroom tyrosinase with a K_m value of 1.2 mM. The product(s) formed is yellow, characterized by a peak at 420–430 nm. A lag period in 2,3,4-THAP oxidation to the yellow product(s) in the presence of ascorbate indicates that the initial product(s) is an o-quinone of 2,3,4-THAP. An oxime, characterized by a broad peak at 510–650 nm, is the likely product formed between o-quinone of 2,3,4-THAP and NH₂OH. The ?_m of the o-quinone of 2,3,4-THAP was estimated to be 1.6 × 10⁴ M^?1 cm^?1 at 425 nm. During relatively long incubation periods, the peak of the yellow product(s) shifts from 420–425 nm to 430–440 nm; the solution remains yellow and transparent for at least a week and no precipitate is formed. The final yellow product(s) is probably a low molecular weight polymer of THAP-o-quinone (dimer, tetramer, etc).     

EFFECT OF KOJIC ACID ON THE OXIDATION OF TRIHYDROXYPHENOLS BY MUSHROOM TYROSINASE1

Kojic acid [5-hydroxy-2-(hydroxymethyl)-4-pyrone] inhibited effectively the rate of pigment formation during the oxidation of pyrogallol, 2, 3,4-THAP (2, 3,4-trihydroxyacetophenone) and 2, 4,5-THBP (2, 4,5-trihydroxybutyrophenone) by tyrosinase. On the other hand, kojic acid had a synergistic effect on the rate of methyl gallate and n-propyl gallate oxidation to pigmented product(s) (λ_max= 360 nm and λ_max= 380 nm, respectively). However, kojic acid inhibited effectively the rate of oxygen uptake when each of the above trihydroxyphenols was oxidized by tyrosinase. These results suggest that kojic acid inhibits tyrosinase per se (probably due to its ability to bind copper at the active site of the enzyme) and that it exerts only an apparent stimulatory effect during the formation of pigmented product (s) from methyl gallate and n-propyl gallate. Proof for the latter was obtained by a time-course experiment of kojic acid addition and examination of the spectra of pigmented product(s) formed in the absence versus presence of kojic acid, which suggested that the o-quinone of n-propyl gallate and the o-quinone of methyl gallate can each convert kojic acid to a yellow product(s) absorbing at the 360–380 nm region.     

p-HYDROXYPHENYLPROPIONIC ACID (PHPPA) AND 3,4-DIHYDROXYPHENYLPROPIONIC ACID (3,4-DPPA) AS SUBSTRATES FOR MUSHROOM TYROSINASE

p-Hydroxyphenylpropionic acid (PHPPA) and 3,4- dihydroxyphenylpropionic acid (3,4-DPPA) serve as substrates for tyrosinase. The Km value of 3,4-DPPA for tyrosinase is 1.3 mM. The yellow o-quinone of 3,4-DPPA (4-carboxyethyl-o-benzoquinone) (λ_max= 400nm), is detected initially and it is then converted to a red product(s) (λ_max= 480±10 nm), the o-quinone of 6,7-dihydroxy 3-dihydrocumarin (dihydroesculetin). When the concentration of the latter is relatively high, it polymerizes to a final brown product(s), characterized by an ill-defined spectrum.
H₂O₂ shortens the lag period of PHPPA hydroxylation, hastens the conversion of the yellow o-quinone of 3,4-DPPA to the red o-quinone of dihydroesculetin, and prevents the polymerization of the latter to the final brown product(s).
The relatively unstable o-quinone of 3,4-DPPA interacts with amines such as hydroxylamine (NH₂OH), p-aminosalicylic acid (PASA) and p-aminobenzoic acid (PABA), forming relatively stable final product(s) characterized by different spectra from those formed in their absence.
Acetohydroxamic acid (AHA) and salicylhydroxamic acid (SHAM) each has an effect on the spectrum of product(s) obtained when 3,4-DPPA is oxidized by tyrosinase, indicating that these hydroxamic acids derivatives interact with the o-quinone of 3,4-DPPA. The spectrum of the final product(s) was also different when 3,4-DPPA was oxidized by tyrosinase in the presence of benzenesulfinic acid than in its absence, suggesting the formation of a stable phenylsulfonyl derivative.     

Assessment of Autoxidation in Freeze-Dried Meats by a Fluorescence Assay

A simple and sensitive fluorescence-measuring technique was developed to assess extent of lipid oxidation in freeze-dried meats. Solvent extracts of reconstituted stored samples were assayed by fluorimetry. Spectra of “oxidized” meats show maximum excitation and emission wavelengths of λex = 350 and λem = 440 nm, respectively. At λem of 440 nm, “unoxidized” meats show three peaks in excitation spectrum at λex₁= 308, λex₂= 318 (max.), and λex₃= 350 nm. However, at λex of 350 nm, these samples show a peak at λem = 476 nm. The intensity ratio of λex₃ or λem over λex₂ are useful as sensitive and reliable “internal standards” of lipid oxidation. Presence of 100 ppm TBHQ (monotertiary butylhydroquinone), absence of oxygen, and compression of meat before freeze-drying, which protect against oxidation also result in corresponding reductions of these ratios.     

The independent and combined impact of front-of-pack labelling and sensory quality on calorie estimations and portion selection of commercial food products

Front-of-Pack (FOP) health and nutrition labels are intended to help consumers make better food choices, but labels that infer a product is ‘healthier’ than it is have been linked to increased consumption. Three studies were set up to assess whether a product’s sensory characteristics counteract label-generated biases in calorie estimation and portion selection across two product categories: soymilk and instant noodles. Participants in Study 1 (n = 116, 21–50 years) evaluated a range of popular FOP labels. Relative to a control, participants were willing to pay more for products with added labels, and estimated “healthier choice” and “reduced sugar/MSG” versions to have fewer calories per portion. Participants also selected larger portions of the “healthier choice” products. Participants in Study 2 (n = 48, 21–50 years) evaluated 10 different soymilks and 10 instant noodles in the absence of any labelling information. Increased taste intensity was linked to higher estimated calorie content, increased liking and larger portion selection. Study 3 (n = 94, 21–50 years) combined these factors to test the impact of “healthier choice” and “reduced” sugar/MSG labeling applied to products varying in sensory intensity. Label-generated beliefs that a product was healthier and contained fewer calories persisted regardless of how the product tasted, while portion decisions were primarily guided by sensory intensity. Although FOP health and nutrient labels can bias consumer judgements, portion selection may be based more on the sensory experience of eating. Findings suggest modifying a product’s sensory intensity could be more influential at shaping portion decisions than labelled health messages.     

SYNERGISM EXERTED BY 4-TERT-BUTYLCATECHOL AND TERT-BUTYLCATECHOL QUINONE ON THE RATE OF DL-DOPA OXIDATION BY MUSHROOM TYROSINASE1

4-tert-butylcatechol (t-BC), at concentrations ranging from 0.033 to 16.6 mM, has a pronounced synergistic effect on the rate of DL-DOPA oxidation to material absorbing at 475 nm (dopachrome) by mushroom tyrosinase. This phenomenon was found to be due to the ability of t-BC-quinone (formed by the oxidation of t-BC by mushroom tyrosinase or by sodium periodate) to oxidize DL-DOPA nonenzymatically.     

FORMULATION OF SOY‐BASED RTE FOODS INFLUENCES RADIATION SENSITIVITY OF LISTERIA MONOCYTOGENES AND POSTIRRADIATION PRODUCT SENSORY PROPERTIES1

Ionizing radiation can eliminate pathogenic bacteria from ready‐to‐eat (RTE) food products. An outbreak strain of L. monocytogenes was irradiated after inoculation onto (1) three meatless, soy‐based frankfurter products (“Soyl”, “Soy2”, “Soy3”), (2) soy‐based tofu (“Tofu”) and (3) a beef frankfurter product (“Beef”). The D₁₀ was significantly influenced by the substrate: Beef (0.622kGy) = Tofu (0.622 kGy) < Soy2 (0.680 kGy) = Soy3 (0.695 kGy) <Soy1(0.761 kGy). The antioxidant strength of the products also varied significantly, but was not correlated with the D₁₀ values obtained. To determine the sensory impact of irradiation, the products were treated with 1.5 kGy or 3.2 kGy, doses equivalent to 1.9–2.4 or 4.2–5.1 log₁₀ reductions, respectively. These doses significantly decreased redness in Beef and Soy2, and significantly increased redness in Soy3. The maximum shear force of Beef and Soy1 was significantly decreased following irradiation. Product formulation was found to be key in determining the product response to irradiation.     

鸡蛋中超氧化物歧化酶的分离与提纯

鸡蛋中的超氧化物歧化酶（SOD）可以抑制氮蓝四唑（NBT）的光化还原,可以根据SOD对NBT光化还原的抑制作为酶活性的定量测定。鸡蛋中的SOD活性均可被H2O2抑制,表明鸡蛋中提纯的SOD为CuZn－SOD。蛋清、蛋黄的精提液、透析液、过柱液经聚丙烯酸胺凝胶电泳及NBT酶活性染色,在蓝色背景上有相似的但有区别的无色透明同工酶谱带。经光谱分析波长图谱显示,蛋清SOD最大吸收波长在可见光区为620nm处,紫外光区为274nm处,蛋黄SOD最大吸收波长在可见区为610nm处,紫外光区为280nm处。     

Chemical Characteristics and Composition of „Gaz”︁ Gum from Tamarix manifera

“Gaz” Gum is a natural plant exudate of “Tamarix manifera” and is used as a thickener in the production of a toffee-type confectionery in Iran. Paper chromatography of its acid hydrolysate revealed the presence of glucose (30%), fructose (10%), mannose, xylose and arabinose. Proximate analysis of the gum showed over 90% carbohydrate, 4% protein and 2% ash in dry matter. The dried whole gum was yellowish in color, produced a colloidal suspension in water and was hygroscopic, sweet taste and sticky when moistened. The alcohol precipitate fraction stained with ruthenium red and with both alcoholic and aqueous solutions of methylene blue.     

EFFECT OF KOJIC ACID ON THE HYDROXYLATION OF L-TYROSINE AND TYRAMINE BY MUSHROOM TYROSINASE1

Kojic acid inhibits effectively the rate of L-tyrosine and tyramine hydroxylation by mushroom tyrosinase. It also affects the spectrum of product (s) formed, this being due to the ability of dopaquinone and dopamine-o-quinone to oxidize kojic acid to a yellow product(s). Kojic acid prevents the conversion of these o-quinones to their corresponding melanins. An insoluble yellow product(s) is formed when tyramine, but not L-tyrosine, is incubated with tyrosinase for 20 h in the presence of excess kojic acid.     

Screening of Nepalese crude drugs traditionally used to treat hyperpigmentation: in vitro tyrosinase inhibition

South-East Asian population is daily exposed to strong sunlight. As a result, the majority of population will have darker, ethnic skin. Moreover, many people suffer from dark spots, hyperpigmentation, which is considered to be a skin disorder and causes psychological disturbance. To treat dark spots, most of the population will still rely on traditionally used crude drugs, knowledge about which is transferred from generation to generation. Fifty-two crude drugs were selected based on the survey performed among local healers and beauticians of different ethnic origin. These crude drugs were screened for mushroom tyrosinase inhibitory activity, as tyrosinase inhibitors are becoming increasingly important as cosmetic and medicinal products, primarily to control hyperpigmentation. Among the tested crude drugs, methanolic extracts of Glycyrrhiza glabra, Morus alba, Syzygium aromaticum, Citrus aurantifolia, Cypreae moneta, Punica granatum and Citrus aurantium, at the final concentration of 50 microg mL(-1), showed mushroom tyrosinase inhibitory activity of 78.9%, 71.0%, 69.4%, 59.0%, 56.0%, 53.4 and 51.9%, respectively, with 91.4% inhibitory activity of kojic acid taken as positive control. To our knowledge, this is the first report that extracts of Cypreae moneta shell and Syzygium aromaticum flowering bud have tyrosinase inhibitory activity. These potent extracts were further evaluated at different concentration. The final concentration of the extracts in reaction mixtures was 50, 25 and 5 microg mL(-1) for the initial concentration of 1000, 500 and 100 microg mL(-1), respectively. They showed concentration-dependent inhibition of mushroom tyrosinase. Those extracts expressing relatively weak tyrosinase inhibitory activity may act through different inhibition pathway which is not based on tyrosinase activity. Further evaluation of the most potent tyrosinase inhibitors in in vivo conditions would be recommended.     

KOJIC ACID CONVERSION TO A YELLOW PRODUCT(S) BY THE HEMOGLOBLIN/H2O2 SYSTEM1

Kojic acid (5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one; also named 5-hydroxy-2-(hydroxymethyl)-γ-pyrone) in the presence of hydrogen peroxide, but not in its absence, can be oxidized by hemoglobin (Hb) to a yellow product(s). The yellow product(s) formed is characterized by a peak at 370–380 nm and is fluorescent. The relationship between the rate of oxidation of kojic acid and various concentrations of hemoglobin and of H₂O₂ is described. The changes with time in the spectrum of product(s) obtained when kojic acid is acted upon by the Hb/H₂O₂ system and the relationship between the various concentrations of hemoglobin, of kojic acid and of H₂O₂ on the spectrum of the “final yellow product(s)” are shown.     

“轻食51号”蘑菇新菌种中型生产试验和生产试验

本文报道“轻食５１号”蘑菇新菌种的中型生产试验和生产试验的结果。１９８８～１９９１年，“轻食５１号”蘑菇新菌种在浙江和江苏省８个试验点扩大栽培的总面积达５１．１５万ｍ￣２，新鲜蘑菇的总产量达２６５６ｔ，平均单位面积产量５．１９ｋｇ／ｍ￣２。在相同的栽培技术条件下，“轻食５１号”新菌种的平均单产比对照菌种上海“８９０２”和“８９０６”增产１５．６％，比福建“闽一号”和浙江“１２－１”增产２２．７％。在一些高产菇房中，“轻食５１号”新菌种的平均单产可达８．９４～１３．６８ｋｇ／ｍ￣２。罐藏加工试验的结果表明，“轻食５１号”新菌种蘑菇的预煮得率为５８．４～７９．６％（对照菌种为５４．０～６８．１％），整菇罐头的比例为４４．５～８５．１％（对照菌种为３４．５～３０．１％），原料消耗为７４５～９７７ｋｇ／ｔ（对照菌种为８５４～１０５０ｋｇ／ｔ）。感官评价的结果表明，由“轻食５１号”新菌种生产的蘑菇罐头的感官质量优于大生产对照菌种。     

PHYSICOCHEMICAL AND STRUCTURAL CHARACTERISTICS OF SODIUM CASEINATE BIOPOLYMERS INDUCED BY MICROBIAL TRANSGLUTAMINASE

Some physicochemical properties and structural characteristics of microbial transglutaminase (MTGase)‐induced biopolymers of sodium caseinate (SC) were investigated. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis and size‐exclusion–high‐performance liquid chromatography analyses showed that all components of SC were easily polymerized or transformed by MTGase to form high‐molecular weight biopolymers, and the susceptibility order of individual components was κ‐Casein (C) > α‐C > β‐C. The emulsifying properties of biopolymers depended on the incubation time with MTGase. The emulsifying activity index of biopolymers persistently increased with the MTGase (0–12 h) incubation time. The emulsion stability also increased with the incubation time (< 4 h), then declined a little with longer incubation (4–12 h). The differential scanning calorimetry analysis showed that the thermal properties of the biopolymers obtained after a 12‐h incubation were different from that of native SC or biopolymers obtained after a shorter incubation time (< 4 h), suggesting that the former has higher thermal stability. In addition, the ultraviolet (UV) spectra showed that the UV absorbance (at 275 nm) of MTGase‐induced biopolymers of SC decreased with an increasing incubation time with MTGase, and the maximal emission wavelength (λ _max ) slightly shifted to the “blue side.” The fluorescence spectra showed that the λ _max was related with incubation time with MTGase, slightly shifting to the “blue side” after 4 h with no further changes; its relative fluorescence intensity also increased. These results suggest a relationship between the functionalities and structural characteristics of the MTGase‐induced biopolymers of SC.     

Studies on the inhibitory effect of Graptopetalum paraguayense E. Walther extracts on mushroom tyrosinase

This study was aimed to evaluate the kinetic properties and capacities of 95% ethanolic (GE95), 50% ethanolic (GE50) and water (GWE) extracts from Graptopetalum paraguayense for their potential to inhibit mushroom tyrosinase activity. The results showed that GE95, GE50 and GWE showed potent inhibitory effects on l-3,4-dihydroxyphenylalanine (l-Dopa) oxidation catalyzed by tyrosinase. It was found that the tyrosinase inhibitory activities of all the extracts increased with the increase of their concentrations. The inhibition kinetics, analyzed by Lineweaver–Burk plots, revealed that G. paraguayense extracts showed a mixed-type inhibition for mushroom tyrosinase when l-Dopa was used as substrate. A comparison of the IC₅₀ and K_i values showed that GE95 exhibited the most effective inhibition of tyrosinase among the extracts.     

慈姑直链淀粉的分离与分子结构

利用正丁醇法分离慈姑直链淀粉与支链淀粉,并对慈姑直链淀粉进行了深入研究。试验结果表明:慈姑直链淀粉与碘的络合物最大吸收波长为620.5nm,其蓝值为0.844,特性黏度[η]为127mL/g。测得慈姑直链淀粉的分子结构参数为:聚合度DP=640,黏均分子质量η=3.11×105。     

蓝宝石的紫外-可见光谱及其致色机理分析

蓝宝石的紫外-可见吸收光谱和能谱分析结果表明, 蓝宝石从粉红色→紫色→蓝色→绿色→黄绿色→黄色, 其Fe3 的浓度相对Fe2 -Ti4 离子对浓度由低至高变化; 浅蓝色到深蓝色蓝宝石中的Fe和Ti均有所增加; 褐色蓝宝石含有相对较多的Fe和Cr; Mn可能与蓝宝石的紫色有成因联系. 热处理蓝色蓝宝石和辐照黄色蓝宝石在450, 375, 387 nm处的吸收较未处理的弱, 辐照黄色蓝宝石在405 nm处有吸收带.     

Wheat bran globulins: Competitive inhibitors of mushroom tyrosinase

The inhibitory capacity of the globulin fraction of wheat bran against the diphenolase activity of mushroom tyrosinase, using l-tyrosine as substrate, was evaluated. Enzyme kinetics was monitored in the presence of globulin solutions by measuring the absorbance at 475nm. Lineweaver-Burk plots were drawn in order to determine V_max, K_m, and type of inhibition. Results showed that globulins from wheat bran competitively inhibited, the activity of mushroom tyrosinase with a K_I of 0.79%(w/v). The degree of inhibition was 24% at 2 mM of the substrate L-tyrosine.