凉粉草胶稀溶液的性质

研究了凉粉草胶多糖在20-40℃之间特性粘度对温度的敏感性，计算得其稀溶液的临界线团交叠值C^＊[η]平均为1．13，半稀释区斜率b为0．8～1．2，与其他多糖进行了比较。结果表明：凉粉草胶多糖的特性粘度在所测温度区域内的变化不敏感；凉粉草胶多糖在水溶液中，分子链构象可能为刚性杆状结构。     

凉粉草胶的稳剪切流变学性质

研究了凉粉草胶在不同质量浓度、温度、pH、盐的种类及盐浓度和不同蔗糖浓度下的流体行为以及固定剪切速率下的表观粘度随不同条件的变化情况。结果表明,凉粉草胶溶液在不同的条件下呈牛顿流体或假塑性流体行为,在剪切速率52.8s-1下,10 g/dL凉粉草胶溶液的表观粘度随胶质量分数(1~20 g/dL)的增加而递增,随温度(25~70℃)的升高而递减,随pH(5~12)的变化则不具有单调性,随NaCl(0~3.0 g/dL)的添加而递减,随CaCl2(0~3.0 g/dL)的添加则先减小后增大,随蔗糖(10~50 g/dL)的添加则递增。     

核磁共振波谱在木素结构研究中的最新应用

阐述了核磁共振氢谱、核磁共振碳谱、二维核磁及核磁共振磷谱在木素分离研究中的应用进展,并指出目前核磁共振波谱法在木素结构分析中存在的问题,同时,对其以后的应用发展进行了展望。     

The Cannizzaro‐like metabolites of secoiridoid glucosides in some olive cultivars

Oleuropein (the most abundant bitter principle) and its analogue ligstroside, both secoiridoid biophenols, were extracted from Hojiblanca black olives and analysed by preparative flash chromatography and HPLC. During olive growth, maturation and processing, these compounds undergo biological and technological degradation to various metabolites, by enzymatic degradation through esterases, phenoloxidases and β‐glucosidases. An enzymatic system with regiospecific Cannizzaro‐like activity could be responsible for two novel metabolites, isolated and characterised by ¹H‐ NMR, ¹²C NMR and FAB‐MS as hydroxycarboxylic and lactone derivatives of terpenoid origin from the precursor oleoside‐11‐methylester, formed from both secoiridoid biophenols. The occurrence of these two secoiridoid metabolites requires a thermodynamically controlled sequential process, via hydride rearrangements, through the complex metabolic pathway. The possible reaction sequence was interpreted by molecular calculations performed on competitive isomers. Copyright © 2004 Society of Chemical Industry     

Bitterness of cassava: Identification of a new apiosyl glucoside and other compounds that affect its bitter taste

Compounds extracted by methanol from cassava parenchyma and cortex have been separated on a preparative HPLC column and identified by ¹H and ¹³C NMR spectroscopy. A new compound isopropyl-β-D -apiofuranosyl-(1 → 6)-β-D -glucopyranoside (IAG, structure I ) has been found as well as small amounts of phenylalanine and tryptophan. The composition of another HPLC fraction has not been elucidated. The amounts of the identified compounds and of linamarin, lotaustralin, citrate, malate and the various sugars present in cassava have been determined by HPLC methods. The threshold levels of bitterness of aqueous solutions of linamarin, lotaustralin and IAG, have been determined and together with published data on L -phenylalanine and L -tryptophan have allowed our evaluation of their contributions to the bitterness of cassava. Linamarin is the sole contributor in the parenchyma but (with two cultivars out of six studied) IAG contributes more to the bitterness of the cortex than does linamarin. The perception of bitterness of linamarin solutions is confounded in the presence of neutral citrate and malate which have a sour taste. These modify the taste of cassava tubers. There are many compounds that contribute to the taste of cassava tubers, hence it is not surprising that the bitterness of cassava is not always correlated positively with the cyanide potential.     

A Review of Thermo‐Oxidative Degradation of Food Lipids Studied by 1H NMR Spectroscopy: Influence of Degradative Conditions and Food Lipid Nature

This review summarizes present‐day knowledge provided by proton nuclear magnetic resonance (¹H NMR) concerning food lipid thermo‐oxidative degradation. The food lipids considered include edible oils and fats of animal and vegetable origin. The thermo‐oxidation processes of food lipids of very different composition, occurring at low, intermediate, or high temperatures, with different food lipid surfaces exposed to oxygen, are reviewed. Mention is made of the influence of both food lipid nature and degradative conditions on the thermo‐oxidation process. Interest is focused not only on the evolution of the compounds that degrade, but also on the intermediate or primary oxidation compounds formed, as well as on the secondary ones, from both qualitative and quantitative points of view. Very valuable qualitative and quantitative information is provided by ¹H NMR, which can be useful for metabolomic and lipidomic studies. The chemical shift assignments of spectral signals of protons of primary (hydroperoxides and hydroxides associated with conjugated dienes) and secondary, or further (aldehydes, epoxides, among which 9,10‐epoxy‐12‐octadecenoate [leukotoxin] can be cited, alcohols, ketones) oxidation compounds is summarized. It is worth noting the ability of ¹H NMR to detect toxic oxygenated α,β‐unsaturated aldehydes, like 4‐hydroperoxy‐, 4,5‐epoxy‐, and 4‐hydroxy‐2‐alkenals, which can be generated in the degradation of food lipids having omega‐3 and omega‐6 polyunsaturated groups in both biological systems and foodstuffs. They are considered as genotoxic and cytotoxic, and are potential causative agents of cancer, atherosclerosis, and Parkinson's and Alzheimer's diseases.     

Structural characterization of barley β-glucan extracted using a novel fractionation technique

A barley β-glucan concentrate prepared according to a novel technology was further purified and subjected to detailed structural characterization by NMR spectroscopy. β-Glucan was hydrolysed with β-glucan-4-glucanohydrolase (lichenase). Fractions of hydrolysate were collected using an HPLC-fraction collector. Intact β-glucan and the major fractions collected were subjected to MALDI-TOF–MS and NMR analyses. The two major oligosaccharides produced by lichenase hydrolysis of purified barley β-glucan were identified as β-d-Glc p-(1 → 4)- β-d-Glc p-(1 → 3)-β-d-Glc p and β-d-Glc p-(1 → 4)-β-d-Glc p-(1 → 4)-β-d-Glc p-(1 → 3)-β-d-Glc p based on ¹³C and ¹H NMR data. Spectrums were similar to those documented for barley β-glucan in the literature.     

Thermal stability and long-chain fatty acid positional distribution on glycerol of argan oil

The primary aim of this study was to determine the oxidative stability of argan oils by using peroxides and conjugated diene hydroperoxides measurements as analytical indicators. Both food and cosmetic argan oils were investigated. Their oxidative stability was also determined by monitoring the relative changes of their fatty acid profiles by ¹H NMR. In addition, valuable information regarding minor components as well as the acyl positional distribution, were obtained for both grades by high field ¹H and ¹³C NMR, respectively. Given that the cosmetic and food grades have a similar profile and content of phenolic antioxidants, vitamers, and squalene, it appears that the ratio of fatty acid aliphatic to bisallylic CH₂ groups, much higher in argan oils than in other vegetable oils, is responsible for their higher thermal stability.     

Fractionation and characterization of ball‐milled and enzyme lignins from abaca fibre

An Erratum has been published for this article in Journal of the Science of Food and Agriculture 79(15) 1999, 2122. Ball‐milled and enzyme lignins were produced from abaca fibre via ball milling for 6 days followed by cellulase treatment for 3 days. The crude lignin preparations were fractionated into milled lignin (ML), enzyme lignin (EL), hemicellulose‐rich milled lignin (HRML), and lignin‐rich enzyme lignin (LREL) fractions using a two‐step precipitation method instead of a traditional ether precipitation procedure. The yield and chemical composition of the resulting lignin samples are reported. The ML and EL fractions contained low amounts of associated neutral sugars (2.0–3.3%) and uronic acids (1.4–1.5%), and showed relatively low average molecular weights (2500–2660), while the LREL and HRML fractions contained large amounts of bound polysaccharides (35.6–38.3%), and showed high molecular weights (8800–25000). The four lignin fractions are composed of a large proportion of syringyl units with fewer guaiacyl and p‐hydroxyphenyl units. The ML is mainly composed of β–O–4 ether bonds between the lignin structural units. The less common β–β, β–5 and 5–5′ carbon–carbon linkages are also present in the lignin molecules. It was found that uronic acids and 41–63% of p‐coumaric acids are esterified to lignin in the three lignin‐rich fractions of ML, EL and LREL. This level increased to over 90% in the hemicellulose‐rich fraction of HRML. For ferulic acids, 92–97% were found to be etherified to lignin in the three lignin‐rich fractions of ML, EL and LREL, while in the hemicellulose‐rich fraction of HRML this reduced to only 13%, suggesting that a majority of the ferulic acids are esterified to hemicelluloses or lignin in this fraction. © 1999 Society of Chemical Industry     

Enzymatic synthesis of primeverosides using transfer reaction by Trichoderma longibrachiatum xylanase

Enzymatic synthesis of two phenyl xylopyranosyl glucopyranosides, through transfer reaction by Trichoderma longibrachiatum endoxylanase, was achieved in the presence of n-hexane used as solvent, phenyl glucoside (10 mM) as acceptor and xylan (2 g/l) as donor. Kinetic study showed that only one compound, identified by ¹H and ¹³C NMR and heteronuclear 2D (¹H–¹³C) chemical shift correlation as phenyl primeveroside (phenyl 6-O-β-xylopyranosyl-1-β-d-glucopyranoside), was synthesized when the reaction time was beyond 1 h. Benzyl and hexyl primeverosides were obtained under the same conditions. When several phenyl glucoside concentrations, from 5 to 50 mM, were used with 2 g/l of xylan, a phenyl primeveroside isomer, identified as phenyl 4-O-β-xylopyranosyl-β-d-glucopyranoside, accumulated in the medium whereas the production of phenyl primeveroside decreased. Only phenyl primeveroside was produced when several xylan concentrations from 2 to 10 g/l were used with 10 mM of phenyl glucoside and its concentration in the reaction mixture increased with the increase of xylan concentration.     

Oxidation of corn oil at room temperature: Primary and secondary oxidation products and determination of their concentration in the oil liquid matrix from H nuclear magnetic resonance data

The oil liquid matrix of several corn oil samples that have been stored at room temperature in closed receptacles for different periods of time is studied by means of ¹H nuclear magnetic resonance (¹H NMR), in order to further knowledge about this type of edible oil oxidation. As expected, the degradation of linoleic acyl groups predominates. In samples at early oxidation stages the presence of hydroperoxides and of (Z,E) conjugated-dienic systems is demonstrated, the concentration of the first group being higher than that of the second. In addition to these compounds, the presence of hydroxy derivatives supporting (Z,E) conjugated-dienic systems, as well as of hydroperoxy derivatives supporting (E,E) conjugated-dienic systems, in samples at intermediate and advanced oxidation stages, is also shown. Corn oil samples at advanced stages of oxidation also contain aldehydes, among which there are alkanals, (E)-2-alkenals, (E,E)-2,4-alkadienals, 4-hydroxy-(E)-2-alkenals, 4-hydroperoxy-(E)-2-alkenals and 4,5-epoxy-(E)-2-alkenals. The concentrations of the different kinds of intermediate compounds above mentioned as well as of the different kinds of aldehydes present in the oil liquid matrix were determined. These latter compounds can be either free or joined to truncated structures of triglycerides. In addition, a principal component analysis between storage conditions and oxidation level of the samples was carried out.     

Phytochemical profile of Rosmarinus officinalis and Salvia officinalis extracts and correlation to their antioxidant and anti-proliferative activity

The goal of this study was to monitor the anti-proliferative activity of Rosmarinus officinalis and Salvia officinalis extracts against cancer cells and to correlate this activity with their phytochemical profiles using liquid chromatography/diode array detection/electrospray ion trap tandem mass spectrometry (LC/DAD/ESI-MSⁿ). For the quantitative estimation of triterpenic acids in the crude extracts an NMR based methodology was used and compared with the HPLC measurements, both applied for the first time, for the case of betulinic acid. Both extracts exerted cytotoxic activity through dose-dependent impairment of viability and mitochondrial activity of rat insulinoma m5F (RINm5F) cells. Decrease of RINm5F viability was mediated by nitric oxide (NO)-induced apoptosis. Importantly, these extracts potentiated NO and TNF-α release from macrophages therefore enhancing their cytocidal action. The rosemary extract developed more pronounced antioxidant, cytotoxic and immunomodifying activities, probably due to the presence of betulinic acid and a higher concentration of carnosic acid in its phytochemical profile.     

Isolation and evaluation of the antioxidant activity of phenolic constituents of the Garcinia brasiliensis epicarp

A new glycosylated biflavonone, morelloflavone-4′″-O-β-d-glycosyl, and the known compounds 1,3,6,7-tetrahydroxyxanthone, morelloflavone (fukugetin) and morelloflavone-7″-O-β-d-glycosyl (fukugeside) were isolated from the epicarp of Garcinia brasiliensis collected in Brazil. The structures of these compounds were established using ¹H and ¹³C NMR, COSY, gHMQC and gHMBC spectroscopy. The compounds exhibited antioxidant activity. The greatest potency was displayed by morelloflavone (2), with IC₅₀ = 49.5 mM against DPPH and absorbance of 0.583 at 400 μg/mL for the reduction of Fe³⁺. The weakest potency was displayed by 1,3,6,7-tetrahydroxyxanthone (1), with IC₅₀ = 148 mM against DPPH and absorbance of 0.194 at 400 μg/mL for the reduction of Fe³⁺.