Octane-1,3-diol and its derivatives from pear fruits

 In extracts obtained by liquid-liquid extraction from seven pear (Pyrus communis L.) cultivars, octane-1,3-diol, 5(Z)octene-1,3-diol, methyl 3-hydroxyoctanoate, ethyl 3-hydroxyoctanoate and ethyl 5(Z)-3-hydroxyoctenoate were identified by capillary gas chromatography-mass spectrometry. Evaluation of the absolute configuration was achieved by multidimensional gas chromatography, using a polar achiral column (DB-Wax) and a chiral main column (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-β-cyclodextrin/OV 1701). Comparison of retention times of synthesized optically enriched reference compounds with those of isolated diols and hydroxy esters revealed (R)-configurations for the 3-hydroxy derivatives, exhibiting enantiomeric excesses greater than 99%. In addition, (2S, 4R)- and (2R, 4R)-2-methyl-4-pentyl-1,3-dioxane as well as (2S, 4R)- and (2R, 4R)-2-methyl-4-(2′(Z)-pentenyl)-1,3-dioxane, products formed by acetaldehyde and octane-1,3-diol or 5(Z)-octene-1,3-diol, respectively, were detected in pear fruits. Received: 13 February 1997     

Biochemical features and inhibitors of the 1-aminocyclopropane-1-carboxylic acid oxidase isolated from pear fruit

 1-Aminocyclopropane-1-carboxylic acid (ACC) oxidase, the enzyme that catalyzes the final step in ethylene biosynthesis, was recovered from pear (Pyrus communis L. cv. Blanquilla) fruit tissues with maximum activity at pH 6.5. The enzyme eluted as a single hydrophobic protein with an estimated molecular weight of 37.9 kDa in a three-step FPLC chromatographic procedure. The sensitivity of the pear ACC oxidase against a range of chemicals known by their inhibitory action on ethylene biosynthesis in vivo has been studied. Among them, and in contrast to a previous proposal, α-(p-chlorophenoxy)isobutyric acid, a substance possessing antiauxin properties, did not inhibit the in vitro enzyme activity. The significance of the results is discussed in terms of the nature and mechanism of the enzyme reaction. Received: 12 May 1999 / Revised version: 7 July 1999     

甘油与氯化钠模型热反应中生成3-氯-1,2-丙二醇的研究

以甘油、氯化钠、水为原料建立热反应模型,结合气相色谱-质谱法（gas chromatography-mass spectrometry,GC-MS）分析,对其生成的3-氯-1,2-丙二醇（3-MCPD）进行了研究。通过正交实验,考察了反应时间、温度和各原料用量对3-MCPD生成量的影响,同时研究了在热反应模型中分别加入不同种类单糖和氨基酸后3-MCPD生成量的变化规律,并对其反应机理进行了探讨。结果表明,反应时间2h、反应温度140℃、甘油用量0.05g（占原料总量0.31%）、NaCl用量1.0g（6.23%）、水用量15g（93.46%）,3-MCPD生成量最少;葡萄糖、果糖、木糖、甘露糖、半乳糖、缬氨酸、精氨酸、赖氨酸、丝氨酸、亮氨酸、苯丙氨酸、苏氨酸、组氨酸使3-MCPD的生成量减少;谷氨酸、蛋氨酸、丙氨酸、天冬氨酸、甘氨酸使3-MCPD的生成量增加;半胱氨酸、酪氨酸、脯氨酸、色氨酸对3-MCPD的生成无明显作用。      

Identification of key aroma compounds generated from cysteine and carbohydrates under roasting conditions

 Application of the aroma extract dilution analysis to volatile fractions obtained from dry-heated (180  °C for 6 min on silica) mixtures of cysteine and ribose (I), glucose (II) or rhamnose (III) revealed the following compounds with the highest flavour dilution factors: 2-furfurylthiol (FFT) and 2-acetyl-2-thiazoline in I; 2-acetyl-2-thiazoline, 2-propionyl-2-thiazoline and FFT in II; 5-methyl-2-furfurylthiol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 2-acetyl-2-thiazoline, 2-propionyl-2-thiazoline and (Z)-2-propenyl-3,5-dimethylpyrazine in III. A comparison of the data with results of previous studies, in which the same mixtures had been reacted under aqueous conditions (145  °C, 20 min) revealed that the dry-heating process favoured the formation of the roasty, popcorn-like smelling 2-acetyl- and 2-propionyl-2-thiazoline as well as the potato-chip-like 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine in all three reaction systems. 2-Ethenyl- and (Z)-2-propenyl-3,5-dimethylpyrazine, both having an intense roast potato smell were, however, selectively formed in the presence of ribose or rhamnose, respectively. Based on quantitative data, pathways generating the latter two pyrazines via their 1-desoxyosones as key intermediates are discussed. Received: 11 March 1998     

Identification of the key odorants in raw French beans and changes during cooking

 By application of aroma extract dilution analysis (AEDA) to an extract prepared from raw French beans, 25 odour-active compounds with flavour dilution (FD) factors in the range 4–2048 were detected and subsequently identified. Among them, (Z)-3-hexenal (green, leaf-like), 1-octene-3-one (mushroom-like), 3-isobutyl-2-methoxypyrazine (earthy, beany) and (E,Z)-2,6-nonadienal (cucumber-like) showed the highest FD factors. In an extract prepared from the same amount of cooked beans, 3-isobutyl-2-methoxypyrazine was identified as the most potent odorant, followed by 1,5-(Z)-octadiene-3-one (geranium-like), 3-isopropyl-2-methoxypyrazine (earthy, beany), 3-(methylthio)propanal (methional; cooked potato), 4,5-epoxy-(E)-2-decenal (metallic) and an unknown compound (FD 256) with a smell of geranium leaves. A decrease in (Z)-3-hexenal and 1-pentene-3-one (etheral, pungent) and an increase in methional during cooking were shown to be mainly responsible for the flavour changes induced by cooking the beans. Received: 22 January 1998 / Revised version: 16 March 1998     

Identification of the key odorants in raw French beans and changes during cooking

 By application of aroma extract dilution analysis (AEDA) to an extract prepared from raw French beans, 25 odour-active compounds with flavour dilution (FD) factors in the range 4–2048 were detected and subsequently identified. Among them, (Z)-3-hexenal (green, leaf-like), 1-octene-3-one (mushroom-like), 3-isobutyl-2-methoxypyrazine (earthy, beany) and (E,Z)-2,6-nonadienal (cucumber-like) showed the highest FD factors. In an extract prepared from the same amount of cooked beans, 3-isobutyl-2-methoxypyrazine was identified as the most potent odorant, followed by 1,5-(Z)-octadiene-3-one (geranium-like), 3-isopropyl-2-methoxypyrazine (earthy, beany), 3-(methylthio)propanal (methional; cooked potato), 4,5-epoxy-(E)-2-decenal (metallic) and an unknown compound (FD 256) with a smell of geranium leaves. A decrease in (Z)-3-hexenal and 1-pentene-3-one (etheral, pungent) and an increase in methional during cooking were shown to be mainly responsible for the flavour changes induced by cooking the beans. Received: 22 January 1998 / Revised version: 16 March 1998     

Isolation and characterization of mutatoxanthin-epimers from red paprika (Capsicum annuum)

 (3S,5R,8R,3′R)- and (3S,5R,8S,3′R)-mutatoxanthin were isolated from red spice paprika (Capsicum annuum) and characterized by their UV-VIS, CD, ¹H-NMR, ¹³C-NMR and mass spectra. Received: 22 November 1999 / Revised version: 11 February 2000     

On the reaction of glyoxal with proteins

 The reaction of arginine and arginine derivatives with glyoxal under mild conditions revealed the formation of a previously unknown amino acid, designated as “Glarg”. ¹H-, ¹⁵N- and ¹³C-NMR analysis of the new compound elucidated its structure to be 1-(4-amino-4-carboxybutyl)-2-imino-5-oxo-imidazolidine. Experiments with solutions containing N ^α -acetylarginine and glyoxal showed that “Glarg” is formed quickly under physiological conditions, but is labile at higher temperatures as well as at low pH values. After incubation of β-casein with glyoxal, the formation of protein-bound “Glarg” in enzymatic hydrolysates via amino acid analysis could be demonstrated. Due to the fast reaction of glyoxal with arginine residues, under physiological conditions, proteins may act as scavengers for glyoxal. Received: 8 November 1996 / Revised version: 10 January 1997     

Studies on melanoidin-type colorants generated from the Maillard reaction of protein-bound lysine and furan-2-carboxaldehyde – chemical characterisation of a red coloured domaine

 The identification of a coloured substructure of melanoidin-type colorants is reported in the present paper. Brown-orange melanoidins with mass >10000 daltons were isolated from a thermally treated aqueous solution of casein and furan-2-carboxaldehyde using ultracentrifugation. After complete enzymatic digestion of the protein skeleton, two intense red coloured compounds were detected in the melanoidin hydrolysate by HPLC. These compounds were identified as the previously unknown chromophoric amino acid (S)-2-amino-6-{4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl) methylidene]-2,3-dihydro-3-oxo-1H-pyrrol-1-yl}hexanoic acid and its 2-[(Z)-(2-furyl)methylidene] isomer, by using several NMR techniques, by MS, UV, and IR spectroscopy. The identification of these novel compounds verifies the idea that melanoidin-type colorants can be generated by a cross-linking reaction between a low molecular weight chromophore and a non-coloured high molecular weight biopolymer. Received: 19 August 1997 / Revised version: 24 October 1997     

Studies on melanoidin-type colorants generated from the Maillard reaction of protein-bound lysine and furan-2-carboxaldehyde – chemical characterisation of a red coloured domaine

 The identification of a coloured substructure of melanoidin-type colorants is reported in the present paper. Brown-orange melanoidins with mass >10000 daltons were isolated from a thermally treated aqueous solution of casein and furan-2-carboxaldehyde using ultracentrifugation. After complete enzymatic digestion of the protein skeleton, two intense red coloured compounds were detected in the melanoidin hydrolysate by HPLC. These compounds were identified as the previously unknown chromophoric amino acid (S)-2-amino-6-{4-[(E)-1-formyl-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl) methylidene]-2,3-dihydro-3-oxo-1H-pyrrol-1-yl}hexanoic acid and its 2-[(Z)-(2-furyl)methylidene] isomer, by using several NMR techniques, by MS, UV, and IR spectroscopy. The identification of these novel compounds verifies the idea that melanoidin-type colorants can be generated by a cross-linking reaction between a low molecular weight chromophore and a non-coloured high molecular weight biopolymer. Received: 19 August 1997 / Revised version: 24 October 1997     

Growth inhibitory effects of anthranilic acid and its derivatives against Legionella pneumophila

Legionella pneumophila is the principal etiologic agent of Legionnaires' disease. We found that the growth of L. pneumophila was markedly inhibited by its own cell lysate and the inhibitory effect was abolished by heat-treatment of the lysate. The genomic library of L. pneumophila was constructed in Escherichia coli and screened to determine the gene involved in the growth inhibition. A clone harboring the gene encoding anthranilate synthase (TrpE), which is involved in tryptophan biosynthesis, exhibited an inhibitory effect on the growth of L. pneumophila. Anthranilic acid exogenously added also exhibited antibacterial activity against L. pneumophila. A series of single-gene-knockout mutants of L. pneumophila lacking tryptophan synthesis genes were constructed and assessed for their susceptibility to anthranilic acid. Although the growth of mutants deficient in anthranilate phosphoribosyltransferase (TrpD) and N-(5'-phosphoribosyl)anthranilate isomerase (TrpF) was not affected by exogenous anthranilic acid, the indole-3-glycerophosphate synthase (TrpC) deficient mutant exhibited an increased susceptibility compared with the parent strain. These observations strongly indicate that 1-(2-carboxyphenylamino)-1'-deoxyribulose-5'-phosphate (CPADR-5'-P), which is an intermediate of tryptophan synthesis from anthranilic acid, is responsible for the growth inhibition of L. pneumophila.     

黄花倒水莲多糖的纯化、表征与体外抗氧化活性研究

提取纯化黄花倒水莲多糖(polysaccharide of Polygala fallax Hemsl.,PFP),对其结构进行表征,并测定其体外抗氧化活性。采用水提醇沉法提取PFP,运用Sevag法除蛋白、活性炭脱色以及G-75葡聚糖凝胶柱层析对其进行纯化分离获得不同的多糖组分。分别用红外光谱(infrared spectrum,IR)、凝胶渗透色谱(gel permeation chromatography,GPC)与1-苯基-3-甲基-5-吡唑啉酮(1-phenyl-3-methyl-5-pyrazalone,PMP)柱前衍生高效液相色谱(high performance liquid chromatography,HPLC)法对PFP组分进行表征分析。最后测定PFP组分对DPPH自由基、羟基自由基、超氧阴离子自由基和ABTS+自由基的清除率来评价其体外抗氧化活性。经分离纯化得到两种PFP组分(PFP1与PFP2)。其中PFP1的分子量为20 794 Da,多分散指数为1.32,红外光谱中呈现多糖的典型特征吸收峰,PFP1是由甘露糖、半乳糖醛酸、鼠李糖、葡萄糖、半乳糖、阿拉伯糖与一种未知单糖组成的一种杂多糖,且摩尔比为0.09∶1∶0.48∶0.64∶0.71∶0.35。PFP1对4种自由基均有清除能力,且在一定浓度范围内呈正相关。因此PFP在体外具有抗氧化活性,为今后进行更深入的研究与开发利用提供依据。     

Hay-like off-flavour of dry parsley

 The flavour of parsley was found to change during drying and storage. Quantification of 27 potent odorants, selected by dilution experiments and calculation of odour activity values, indicated that 3-methyl-2,4-nonanedione was mainly responsible for the hay-like off-flavour. Two furanoid fatty acids, known to be precursors of 3-methyl-2,4-nonanedione, were detected in dry parsley. The decrease in the intensities of the parsley-like, metallic and green notes in the odour profile during storage of dry parsley was due to losses of p-mentha-1,3,8-triene, myrcene and (Z)-6-decenal. Sulphurous cabbage-like and malty notes were caused by dimethyl sulphide, methylpropanal as well as 2- and 3-methylbutanal. The effect of the water activity (at a _w levels of 0.15, 0.25, 0.35) on the changes in the concentrations of all these compounds during storage of dry parsley was investigated. Received: 24 July 1997     

Determination of Bisphenol A diglycidyl ether (BADGE) and its hydrolysis products in canned oily foods from the Austrian market

 Bisphenol A diglycidyl ether (BADGE) is determined in canned oily foods from Austria using a new simplified HPLC method. Samples are extracted with pentane, back extracted with methanol, and finally dissolved in the mobile phase (cyclohexane/tert–butyl methyl ether). Separation is performed on a normal-phase HPLC column using fluorescence detection. Verification of the BADGE-containing peak is carried out by using off-line GC-MS. Additionally, the synthesis and determination of BADGE hydrolysis products, Bisphenol A bis(2,3-dihydroxypropyl) ether (BADGE.2H₂O) and Bisphenol A glycidyl (2,3-dihydroxypropyl) ether (BADGE.H₂O) are presented. From 67 analyzed cans, containing various fatty meat or fish products, 16% were above the maximum quantity of 1 mg/kg tolerated by the European Community, 45% were in the range between 0.1–1 mg/kg, 24% between 0.02 and 0.1 mg/kg, and in 15% the BADGE concentrations were below the detection limit of 0.02 mg/kg. The hydrolysis product BADGE.H₂O was not detected in any sample, whereas BADGE.2H₂O was found in some samples up to a concentration of 0.5 mg/kg. Received: 11 May 1998 / Revised version: 1 July 1998     

Bioactivity of Ocimum gratissimum L. oil and two of its constituents against five insect pests attacking stored food products

The fumigant and repellent effects of Ocimum gratissimum L. oil and its constituents, β-(Z)-ocimene and eugenol, were evaluated against adults of Sitophilus oryzae (L.), Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Callosobruchus chinensis (L.). The fumigant toxicities of the oil and two of its constituents were assessed at four rates (0, 1, 5 and10 μL/L air) in space fumigation, whereas repellence of the oil and eugenol in acetone was evaluated in choice bioassays at five rates (0, 1.0, 2.0, 3.0 and 4.0 μL oil/2 g grain). Results showed that fumigant toxicity and repellence of the oil and its constituents were significantly (P<0.0001) influenced by concentration and time after treatment. At 1 μL/L air, the oil caused 98%, 99% and 100% mortality of R. dominica, O. surinamensis and C. chinensis, respectively, 24 h after treatment, whereas eugenol achieved 79%, 61% and 100% kill of the same insects. β-(Z)-ocimene produced a weaker toxicity with 8%, 11% and 59% mortality of R. dominica, O. surinamensis and C. chinensis, respectively. Except for T. castaneum which was more tolerant, LC₅₀ values for tested insects ranged from 0.20 to 14, 0.01 to 17 and 0.80 to 23 μL/L air 24 h after treatment for O. gratissimum oil, eugenol and β-(Z)-ocimene, respectively. All test insects had percentage repellence (PR) values which ranged from 37.5% to 100% and 45% to 100% for the oil and eugenol, respectively. However, C. chinensis showed a dose-dependent decrease in PR values in the eugenol bioassay with a corresponding dose-dependent mortality on treated grains. Ocimum gratissimum oil and its constituents are potential alternatives to synthetic fumigants in the treatment of durable agricultural products. Successful adoption of plant oils in the protection of food commodities promises an eco-friendly option compatible with international biosafety regulations.     

Residues of DDT and HCH in wheat samples collected from different states of India and their dietary exposure: A multicentre study

Under a multicentre study conducted by the Indian Council of Medical Research, 1712 samples of wheat grain/flour were collected from urban and rural areas in 11 states representing different geographical regions of India. These samples were analysed for residues of DDT (2,2-bis (p-chlorophenyl)-1,1,1-trichloro ethane) and different isomers of HCH (1,2,3,4,5,6-hexachloro cyclohexane, a mixture of isomers) by gas-liquid chromatography. Residues of DDT were detected in 59.4% of 1080 samples of wheat grain and in 78.2% of 632 samples of wheat flour. Different isomers of HCH were present in about 45-80% of the samples of wheat grain/flour. Medians of DDT and total HCH, respectively, for pooled samples of wheat grain were 0.013 and 0.035 mg kg^-1, while those for wheat flour were 0.01 and 0.02 mg kg^-1. Estimated daily intakes of DDT and different isomers of HCH through the consumption of wheat contaminated at their median and 90th percentiles constituted a small proportion of their acceptable daily intakes. Amongst the pesticide residues analysed, statutory maximum residue limits have been fixed only for γ-HCH in wheat in India, as 0.1 mg kg^-1 in wheat grain and zero in wheat flour. Residue levels of γ-HCH exceeded these maximum residue limits in five of 1080 samples of wheat grain and in 340 of 632 samples of wheat flour. The failure to meet the requirement of the γ-HCH maximum residue limit in large number of wheat flour samples was attributed to the fixation of practically unachievable zero limit. Comparing the previous studies and the present one, the levels of residues of DDT and HCH in wheat were significantly decreased.     

Preparation and characterization of molecular weight standards of low polydispersity from oat and barley (1→3)(1→4)-β- -glucan

Purified (1→3)(1→4)-β- -glucans (β-glucans) from oat and barley with broad molecular weight (MW) distribution were separated into seven fractions using gradient precipitation with ammonium sulfate (NH₄)₂SO₄. The MW of each fraction decreased consecutively with the concentration of (NH₄)₂SO₄ at which it was precipitated. The MW distribution of each fraction was much narrower compared to the parent sample and is comparable to commercially available pullulan MW standards. To determine whether the fractionation process was separating sub-fractions of different structure, the original β-glucan sample and each fraction were hydrolyzed by a (1→3)(1→4)-D-β-glucan-4-glucanohydrolase (lichenase, E.C.3.2.1.73) and the liberated oligosaccharides were analyzed by high performance anion exchange chromatography. The analysis revealed no differences in oligosaccharide pattern (DP 2–9) derived from each fraction and the parent sample. In particular, the tri/tetra oligosaccharide ratio remained constant for all fractions, indicating no fractionation based on structural features had taken place. The effect of starting β-glucan concentration on the fractionation process was studied. The results showed that it was possible to achieve good separation at overlapping parameter c[η] lower than 3.5. Further increase in starting β-glucan concentration hindered clear separation of the fractions. Temperature also affected the fractionation efficiency. The higher the temperature, the lower the amount of (NH₄)₂SO₄ that was necessary to precipitate the samples of same MW. A Mark Houwink relationship was derived from the measured MW and intrinsic viscosity for fractions from oat and barley, respectively.     

Optimised methodology for carboxymethylation of (1→3)‐β‐d‐glucan from Yeast (Saccharomyces cerevisiae) and promotion of mechanical activation

With a view to utilise yeast (1→3)‐β‐d ‐glucan as biological response modifiers with better water solubility, carboxymethylation was carried out by a two‐step alkalisation and etherification with monochloroacetic acid. Four technological parameters of carboxymethylation were investigated by orthogonal experiments for obtaining the maximum degree of substitution (DS), apparent viscosity (η) and solubility of carboxymethyl derivatives. In view of the orthogonal analysis, the optimal technological parameters were reaction temperature 50 °C, total reaction time 5 h, 3 mL of 50% sodium hydroxide as the second alkali dosage and 15 mL of 4 m chloroacetic acid. In addition, it was found that ball milling pretreatment for original (1→3)‐β‐d ‐glucan can be an advantage for carboxymethylation. By contrast, DS, η and solubility of carboxymethyl product increased 24%, 6% and 22%, respectively, suggesting the effect of ball milling pretreatment could not be neglected on improvement of DS, η and solubility for carboxymethyl products.