机械活化甘蔗渣制备羧甲基纤维素及性能表征

为进一步提高甘蔗渣的利用率,获得高取代度的羧甲基纤维素,该文采用自制搅拌磨对甘蔗渣进行机械活化预处理,以不同活化时间的甘蔗渣为原料,氯乙酸为醚化剂,氢氧化钠为催化剂制备羧甲基纤维素。以羧甲基纤维素的取代度为评价指标,分别探讨机械活化时间、固液比、氢氧化钠与氯乙酸摩尔比、反应时间、反应温度、水与底物比等因素对甘蔗渣羧甲基化反应的影响。并采用红外光谱（Fourier transform infrared spectroscopy,FTIR）、X-射线衍射（X-ray diffraction,XRD）、氢核磁共振谱（1HNMR spectroscopy,1HNMR）对甘蔗渣和羧甲基化产物表征。结果表明,机械活化对甘蔗渣羧甲基化反应具有明显的强化作用,经机械活化预处理后的甘蔗渣比原甘蔗渣更容易进行羧甲基化反应,取代度随着活化时间的延长先增大后减少。机械活化破坏了甘蔗渣中木素对纤维素的包裹作用,结晶结构受到破坏,降低纤维素的结晶度,醚化化试剂更容易渗透到甘蔗渣内部使纤维素发生羧甲基化反应,降低了对固液比、氢氧化钠/氯乙酸比、H2O/底物比、反应时间、反应温度的依赖性,提高了反应活性。在固液比为1∶18 g/mL,氢氧化钠/氯乙酸（摩尔比）为2∶1,H2O/底物比为1∶1 mL/g,75℃醚化2.0 h条件下,制得甘蔗渣羧甲基纤维素的取代度高达1.521,黏度为13 mPa·s。研究结果将为制备高取代度羧甲基纤维素提供依据和基础数据。     

Fresh cucumber flavor in refrigerated pickles: comparison of sensory and instrumental analysis

The ability of nonacidified, refrigerated pickled cucumbers to produce the fresh cucumber flavor impact compounds (E,Z)-2,6-nonadienal and (E)-2-nonenal declined during storage. Production of these compounds decreased as the pH of refrigerated cucumbers was reduced. Despite the fact that the concentrations of (E,Z)-2,6-nonadienal and (E)-2-nonenal generated were over 10(5)-fold greater than the threshold levels, it was possible for a sensory panel to consistently detect differences in the intensity of fresh cucumber flavor, provided the pH difference between samples was 1 unit or greater. The presence of spices did not interfere with the ability of panelists to detect differences in fresh flavor intensity. There was a linear correlation between sensory scores and the amount of (E,Z)-2,6-nonadienal produced by cucumbers equilibrated at different pH levels.     

Comparison of nosespace,headspace, and sensory intensity ratings for the evaluation of flavor absorption by fat

The goal of this study was to better understand the correspondence between sensory perception and in-nose compound concentration. Five aroma compounds at three different concentrations increasing by factors of 4 were added to four matrixes (water, skim milk, 2.7% fat milk, and 3.8% fat milk). These were evaluated by nosespace analysis with detection by proton transfer reaction mass spectrometry (PTR-MS), using five panelists. These same panelists evaluated the perceived intensity of each compound in the matrixes at the three concentrations. PTR-MS quantification found that the percent released from an aqueous solution swallowed immediately was between 0.1 and 0.6%, depending on the compound. The nosespace and sensory results showed the expected effect of fat on release, where lipophilic compounds showed reductions in release as fat content increases. The effect is less than that observed in headspace studies. A general correlation between nosespace concentration and sensory intensity ratings was found. However, examples of perceptual masking were found where higher fat milks showed reductions in aroma compound intensity ratings, even if the nosespace concentrations were the same.     

Relationship between MALDI-TOF analysis of beta-CN f193-209 concentration and sensory evaluation of bitterness intensity of aged cheddar cheese

An internal standard method was previously developed to measure the concentration of a synthetic bitter peptide, beta-CN f193-209, by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The objective of this study was to evaluate the relationship between beta-CN f193-209 concentration in an aqueous extract of aged Cheddar cheese and bitterness intensity of the cheese. Concentrations of beta-CN f193-209 in cheese extracts were determined by MALDI-TOF at 0, 120, 180, and 270 days. Trained panels evaluated the bitterness intensity of the cheeses at 180 and 270 days. Correlation coefficients between MALDI and sensory data at 180 and 270 days were 0.803 and 0.554, respectively. The decreased correlation may be due to the presence of other bitter peptides more responsible for bitterness at longer aging or the production of compounds that mask bitterness intensity.     

调亏灌溉对番茄品质与风味组分的影响

为优化番茄调亏灌溉条件,设计了轻度、中度和重度调亏灌溉处理(浇水量分别是正常灌水的75%、50%和25%),研究不同调亏灌溉处理对番茄果实的含水量、可溶性固形物、可滴定酸、糖酸比和Vc等营养成分和风味组分的变化。结果表明,果实含水量随着调亏灌溉程度的加深而降低,重度和中度处理轻度处理对照;可溶性固形物为重度和中度处理轻度处理对照。可滴定酸是中度调亏灌溉时含量明显高于重度调亏灌溉和对照;糖酸比在重度调亏灌溉时最高,明显高于对照,但与中度和轻度调亏灌溉间差异不显著;Vc含量以重度调亏灌溉的最高。对芳香组分的测定发现,调亏灌溉程度对风味组分也有很大影响。其中,中度调亏灌溉检测出的特征效应化合物最多,正常灌水条件下最少。     

Headspace GC and sensory analysis characterization of the influence of different milk additives on the flavor release of coffee beverages

Previous investigations of coffee flavor have been confined to the analysis of the aroma substances. These investigations showed that about 30 volatile compounds were substantially responsible for the coffee flavor. The aim of this study was to investigate the influence of different milk additives and one coffee whitener on the release of flavor impact compounds from coffee beverages. For the investigation of these effects an external static headspace technique was developed. With this technique the most potent odorants of the coffee beverage were determined. Analyses were performed by gas chromatography/olfactometry, flame ionization detection, and mass spectrometric detection. In addition, sensory studies of the odor profiles were performed. Milk and vegetable products as additives for coffee beverages affected the release of aroma substances in the brew through their lipid, protein, and carbohydrate components. All beverages with an additive showed reduced, but typical, odor profiles for each additive.     

Characterization of espresso coffee aroma by static headspace GC-MS and sensory flavor profile.

The aromas of three espresso coffee (EC) samples from different botanical varieties and types of roast (Arabica coffee, Robusta natural blend, and Robusta Torrefacto blend (special roast by adding sugar)) were studied by static headspace GC-MS and sensory flavor profile analysis. Seventy-seven compounds were identified in all of the EC samples. Among them, 13 key odorants have been quantified and correlated with their flavor notes by applying multivariate statistical methods. Some correlations have been found in the EC samples: some aldehydes with fruity flavors, diones with buttery flavors, and pyrazines with earthy/musty, roasty/burnt, and woody/papery flavors. By applying principal component analysis (PCA), Arabica and Robusta samples were separated successfully by principal component 1 (60.7% of variance), and Torrefacto and Natural Robusta EC samples were separated by principal component 2 (28.1% of total variance). With PCA, the aroma characterization of each EC sample could be observed. A very simple discriminant function using some key odorants was obtained by discriminant analysis, allowing the classification of each EC sample into its respective group with a success rate of 100%.     

Dispersion and zeta potential of pure clays as related to net particle charge under varying pH, electrolyte concentration and cation type

The effect of changing pH and electrolyte concentration on the dispersion and zeta potential of Na-and Ca-forms of kaolinite, illite and smectite was investigated in relation to changes in their net negative charge. The percentage of dispersible Na-clay and the percentage increase in net negative charge was positively correlated with pH, but the slopes varied from clay to clay. In general, the net negative charge was the primary factor in clay dispersion, and the pH affected clay dispersion by changing the net charge on clay particles. Na-smectite had larger net charge at all pHs than Na-illite and Na-kaolinite, and it always had larger flocculation values. The role of electrolyte concentration could be due to its effect both on flocculation and variable charge component of the clay minerals. The zeta potential at different pHs also reflected the same trend of clay dispersion with net particle charge. In Ca-clays the trends were similar to Na-clays up to pH 7.0. In more alkaline solution CaCO₃ formation led to charge reduction on clay particles, resulting in flocculation and reduction of zeta potential. At similar pHs the electrophoretic mobilities of all the clays showed constant potential behaviour. However, the zeta potentials of Ca-clays were always smaller than those of sodic clays because the clays were more aggregated. Net particle charge was the most important factor in controlling clay dispersion for the whole range of pH and ionic strength and for all types of cations.     

不同施氮水平对红花大金元烟叶香味物质和感官评吸质量的影响

【目的】 氮素施用水平主导着烟叶的氮素代谢,影响烟叶中有机酸、酚类、石油醚提取物、木质素等香味物质的含量,进而影响烟叶的感官评吸质量。探索不同氮素施用量对红花大金元 (简称红大) 烟叶香味物质和感官评吸质量的影响,以期为烤烟栽培中氮素的科学施用提供理论依据。 【方法】 2013 年在云南玉溪和大理烟区以烤烟红大为供试材料进行田间试验。设置施氮水平 0、45、90 和 135 kg/hm2 (分别以 N₀、N₁、N₂ 和 N₃ 表示),分析了烤烟香味物质和感官评吸质量指标。 【结果】 烟叶中挥发酸含量随施氮量的增加而显著提高,大理试验以 N₃ 处理含量最高,达到 0.13%;烟叶中高级脂肪酸总量和多元有机酸均以 N₂ 处理最高,玉溪分别为 19.71 和 82.65 mg/g,大理分别为 20.67 和 94.12 mg/g。烟叶中多酚含量在N₂ 水平最高,至 N₃ 时出现下降。烟叶石油醚提取物含量随施氮水平的提高而显著增加,玉溪和大理试验点 N₃ 处理含量分别为 6.25% 和 6.05%。烟叶木质素含量以 N₂ 处理最低,玉溪和大理试验点含量分别为 5.19% 和 5.42%。红大烟叶感官评吸总分均以N₂ 处理最高,玉溪和大理试验点的评分分别为 77.4 和 78.1。 【结论】 氮素施用水平中等时 (90 kg/hm2),烟叶挥发酸和石油醚提取物含量适中,高级脂肪酸和多元有机酸含量较高,酚类物质积累较多,木质素含量较低,烟叶各香味物质含量协调性较好,感官评吸时烟叶香气质、香气量、余味、杂气、劲头和评吸总分较高,烟叶品质优良。      

Identification and sensory evaluation of volatile compounds in oxidized porcine liver

Headspace solid phase microextraction (HS-SPME) was used to isolate the off-flavor volatile compounds, which are formed during the oxidation of porcine liver induced by iron. Poly(dimethylsiloxane)/divinylbenzene fiber was used in the HS-SPME. Changes in the volatile compounds of oxidized porcine liver and unsaturated fatty acids induced by iron were examined. Results showed that 1-octen-3-one (metallic), hexanol (weak metallic), 1-octen-3-ol (mushroomlike), (E)-2-nonenal (cardboardlike), and (E,E)-2,4-decadienal (fatty, oily) were the main contributors to the overall off-flavor of porcine liver. The results of the sensory evaluation revealed that oxidized arachidonic acid has a major impact on metallic and liverlike off-flavor and that when liverlike off-flavor is perceived, metallic is also included. Oxidized linolenic acid was the most important contributor to the objectionable fishy off-flavor. Oxidized porcine liver exhibited distinct metallic, liverlike, and weak fishy background notes. Liverlike flavor had a high correlation coefficient with odor characteristics such as metallic (0.839) and fishy (0.777). In this study, it was clearly observed that the stronger the metallic and fishy off-flavor the higher the perception of liverlike off-flavor.     

Spectrophotometric determination of cyclamate in soft drinks and desserts: complementary collaborative study

Fifteen official food control laboratories participated in a collaborative study of a spectrophotometric method to determine cyclamate in a soft drink and a dessert at concentrations of 90-311 mg/L and 202-526 mg/kg, respectively, with blind duplicates and a blank. Average recovery from the soft drink was 97.5%, and from the dessert, 98.6%. Reproducibility relative standard deviations were 4.7-6.5% and 6.9-8.5%, respectively. The outlier percentage was 5.5%. This study complements an earlier work by leading Nordic food laboratories and was designed according to the latest recommendations. The results of this study were compared with those of the earlier collaborative study and with general collaborative results obtained by AOAC.     

Liquid chromatographic determination of saccharin in beverages and desserts: complementary collaborative study

A complementary collaborative study was conducted on a liquid chromatographic method for determination of saccharin in accordance with the latest international recommendations. One industrial and 6 official food control laboratories analyzed 3 samples of a juice, a soft drink, and a dessert at concentration levels of 26-90 mg/L, 33-73 mg/L, and 56-147 mg/kg, respectively. Blind duplicates and a blank were supplied for each type of material at each concentration level. The beverage was chromatographed directly and the dessert was extracted with ethanol before chromatography. Average recoveries were 95-107%. The reproducibility relative standard deviations were 6.4-7.3% for the juice, 9.2-20.6% for the soft drink, and 13.4-16.2% for the dessert. The outlier percentage was 14.3%. The results were compared with those of an earlier collaborative study by Nordic laboratories and with general collaborative results obtained by AOAC.     

Influence of flavor solvent on flavor release and perception in sugar-free chewing gum

The influence of flavor solvent [triacetin (TA), propylene glycol (PG), medium chained triglycerides (MCT), or no flavor solvent (NFS)] on the flavor release profile, the textural properties, and the sensory perception of a sugar-free chewing gum was investigated. Time course analysis of the exhaled breath and saliva during chewing gum mastication indicated that flavor solvent addition or type did not influence the aroma release profile; however, the sorbitol release rate was statistically lower for the TA formulated sample in comparison to those with PG, MCT, or NFS. Sensory time-intensity analysis also indicated that the TA formulated sample was statistically lower in perceived sweetness intensity, in comparison with the other chewing gum samples, and also had lower cinnamon-like aroma intensity, presumably due to an interaction between sweetness intensity on aroma perception. Measurement of the chewing gum macroscopic texture by compression analysis during consumption was not correlated to the unique flavor release properties of the TA-chewing gum. However, a relationship between gum base plasticity and retention of sugar alcohol during mastication was proposed to explain the different flavor properties of the TA sample.     

水热条件和土壤类型对纤维素分解菌的影响

试验选择中国东部3个气候带上的主要农田土壤:寒温带黑龙江海伦的黏化湿润均腐土(黑土)、暖温带河南封丘的淡色潮润雏形土(潮土)和中亚热带江西鹰潭的黏化湿润富铁土(红壤),在海伦、封丘和鹰潭3个生态试验站建立土壤置换试验,研究玉米不同生育期水热条件和土壤类型对好氧性纤维素分解菌数量的影响。结果表明,暖温带气候条件下土壤好氧性纤维素分解菌数量高于中温带和中亚热带气候条件;土壤类型显著影响了土壤好氧性纤维素分解菌数量,变化顺序为黑土>潮土>红壤;在玉米不同生育期土壤纤维素分解菌数量的顺序均为抽雄期>收获后>种植前;施用化肥提高了土壤中好氧性纤维素分解菌的数量。相关分析显示土壤好氧性纤维素分解菌数量与土壤有机质、全氮、全磷、全钾、含水量和pH值呈显著正相关,土壤温度和含水量是影响土壤好氧性纤维素分解菌数量的重要环境因子。通径分析结果表明,土壤养分是决定土壤好氧性纤维素分解菌数量的主要因子,水热条件对其直接作用并不明显,但水热、施肥、土壤类型对纤维素分解菌数量有显著的交互作用。     

Correlation of malt quality parameters and beer flavor stability: multivariate analysis

Malt is known to have an impact on beer flavor stability mainly due to the presence of antioxidants. In this study, five barley varieties were malted at industrial and micro scale, and quality parameters of the resulting malts were measured (diastatic power, friability, beta-glucan content, antiradical power, reducing power, lipoxygenase activity, and nonenal potential) and correlated with the sensory data obtained for the corresponding fresh and forced aged beers. A statistical strategy using multiple linear regressions was applied to explore relationships between the malt chemical parameters and beer sensory data, showing antiradical power as the major contribution of malt to beer flavor stability. Additionally, the measured antiradical power, which is well correlated with the polyphenolic content, was found to be very similar for malt and barley, emphasizing the key role of barley endogenous polyphenols.     

Effect of type of oil and addition of delta-tocopherol on model flavor compound stability during storage

The objective of this study was to investigate approaches to protect selected flavor compounds from deterioration when stored in an oil matrix. An aroma compound model mixture was prepared in a medium-chain triglyceride (MCT) or sunflower oil (SfO) matrix and stored under either an ambient air or argon atmosphere containing, respectively, ca. 20 and <0.5% residual oxygen as controls or containing a natural antioxidant, delta-tocopherol (0.01%). Samples were analyzed by static headspace GC/FID to determine the stability over time of the compounds in mixture. It was found that the type of oil had the greatest effect (P < 0.01) on overall compound stability. A low-oxygen atmosphere also had a significant (P < 0.05) protective effect on the aroma compounds in both oils. The addition of delta-tocopherol generally offered little additional protection. No significant relationship could be determined between the oxidation of the lipid matrix and the loss of oxidation-sensitive thiol compounds.