氟化电热蒸发（ETV）－ICP－AES直接测定生物试样中不同挥发性元素的比较研究

本文以聚四氟乙烯（ＰＴＥＥ）悬浮体为氟化剂，对悬浮体制样ＥＴＶ－ＩＣＰ－ＡＥＳ直接测定生物试样中不同挥发性元素锡、铜和镉的蒸发行为，影响因素及分析性能进行了比较研究，得出了相应的规律性。在选定实验条件下，本法测定ＭＯ，Ｃｕ和Ｃｄ的检出限分别为０．４３、４．２和１４１ｎｇ／ｍＬ，ＲＳＤ分别为３．８％、４．２％和２．２％。提出的方法已应用于ＣＲＭ２８１生物标样分析，结果与参考值吻合。     

氟化电热蒸发（ETV）—ICP—AES直接测定生物试样中不同挥发性元素…

本文以聚四氟乙烯（ＰＴＥＥ）悬浮体为氟化剂，对悬浮体制样ＥＴＶ－ＩＣＰ－ＡＥＳ直接测定生物试样中不同挥发性元素钼、铜和镉的蒸发行为，影响因素及分析性能进行了比较研究，得出了相应的规律性。在选定实验条件下，本法测定Ｍｏ，Ｃｕ和Ｃｄ的检出限分别为０．４３、４．２和１４１ｎｇ／ｍＬ，ＲＳＤ分别为３．８％、４．２％和２．２％。提出的方法已应用于ＣＲＭ２８１生物标样分析，结果与参考值吻合。     

动力学—两次标准加入法同时测定钼和钨

本文提出了动力学－两次标准加入法双组份同时测定的新方法，讨论了测定的基本原理；用停流ＦＩＡ光度法研究了钼和钨共同催化的Ｈ２Ｏ２－Ｉ＾－动力学反应体系，并建立了钼和钨同时测定的条件，用本法测定了钢样和模拟样品中的钼、钨含量，结果满意，钼和钨的回收率分别为９７％－１０２．６％和９８．２％－１０３％；相对标准偏差分别为２．８％－３．２％和２．１％－３．５％。     

固定化乳杆菌细胞的离子交换吸附发酵生产乳酸

本文提出了固定化乳杆菌细胞的离子交换吸附发酵生产乳酸的新方法，该法以海藻酸钙凝胶为载体包埋固定化细胞用于生产乳酸，将离子交换树脂填充柱与发酵反应器相连接，用于从发酵液中及时地分离出产物乳酸。这种新方法成功地消除了产物乳酸对乳酸菌生长和产物形成的抑制作用。与常规的发酵法相比，利用离子交换树脂吸附发酵使糖转化率和乳酸生产速率分别由８６．２％和０．３２８ｇ／Ｌ·ｈ提高到９４．７％和０．４８２ｇ／Ｌ·ｈ。     

离子选择电极—流动注射分析法动力学测定葡萄糖存在下的果糖

本文将离子电极与流动注射分析相结合，利用３０℃下，在强碱性介质中，果糖和葡萄糖与２，４－二硝基酚钠反应速度明显差异，动力学测定了葡萄糖存在下果糖的含量。自制了２，４－二硝基酚电极作为动力学电位测定用的工作电极。本法测定果糖的范围为０．０２～１．００ｍｏｌ／Ｌ，其ＲＳＤ为４．０％～４．９％，ＲＥ为１．０～５．０％；当Ｃ葡／Ｃ果≤３倍时，葡萄糖的干扰不超过５％；本法也曾成功地用于果葡萄浆测定，其ＲＳＤ     

ICP-AES法同时测定化妆品中的Hg、As、Pb

采用高压溶样弹，将样品用硝酸－过氧化氢或高氯酸－过氧化氢溶解后，用ＩＣＰ－ＡＥＳ法对汞砷铅连续测定。方法的回收率分别为８６．０％、９６．２％、９９．８％，变异系数分别为３．１７％、２．５１％、２．０１％。与原子吸收法比较，无显著差异。应用于市售化妆品检测，结果满意。     

磷的光化学分析新方法研究

在０．２ｍｏｌ／ＬＨ２ＳＯ４－１０％乙醇介质中及紫外光照射条件下磷钼杂我酸光还原为磷钼蓝，据此建立了一个测定０．０５－２．０μｇ／ｍｌ的光化学分析新方法，并用于度样分析，探讨了光化学反应机理。     

反相键合相高效液相色谱法分离测定萘普生

建立了分离测定萘普生和溴代萘普生的反相键合相高效液相色谱法。采用ＯＤＳ柱，以添加５０ｍｍｏｌ／Ｌ乳酸并用高氯酸调节ｐＨ为２．５的８０％甲醇－水溶液作为流动相，以苯甲酸为内标物，测定了不对称合成工艺产物中萘普生和溴代萘普生的含量。方法的准确度分别为９９．８３％～１０２．０７％（萘普生）和９９．０％～１００．８３％（溴代萘普生），相对标准偏差分别小于２．５８％（萘普生）和３．６４％（溴代萘普生）。方法可用于工艺条件的选择和质量检测。     

反相键合相高效液相色谱法分离测定萘普生

 建立了分离测定萘普生和溴代萘普生的反相键合相高效液相色谱法。采用ＯＤＳ柱，以添加５０ｍｍｏｌ／Ｌ乳酸并用高氯酸调节ｐＨ为２．５的８０％甲醇－水溶液作为流动相，以苯甲酸为内标物，测定了不对称合成工艺产物中萘普生和溴代萘普生的含量。方法的准确度分别为９９．８３％～１０２．０７％（萘普生）和９９．０％～１００．８３％（溴代萘普生），相对标准偏差分别小于２．５８％（萘普生）和３．６４％（溴代萘普生）。方法可用于工艺条件的选择和质量检测。     

置换络合极谱双点滴定法

本文提出了络合极谱双点滴定中置换滴定法的测定方法和定量公式，研究了以ＥＤＴＡ为络合剂，在ＨＡｃ－ＮａＡｃ缓冲溶液中，以乳酸置换与Ｓｎ＾４＋络合的ＥＤＴＡ，以ＣｄＣｌ２标准溶液为滴定剂测定Ｓｎ。对于５×１０＾－５ｍｏｌ的Ｓｎ，回收率达９９．２％。应用该法于青铜样品中Ｓｎ的含量的测定，结果较为满意。     

利用高效液相色谱-串联质谱追踪酸奶发酵过程中的酪蛋白磷酸肽

酪蛋白磷酸肽(CPPs)是酪蛋白被磷酸化的片段,具有促进矿物元素吸收、抗氧化、预防龋齿等多种生物功能。该文利用高效液相色谱-串联质谱研究牛奶经嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus debrueckii subsp.bulgaricus)发酵后CPPs的释放规律。结果表明,在内源性蛋白酶的作用下牛奶含内源性CPPs,内源性CPPs主要来源于高丰度酪蛋白αs1-CN和β-CN。经乳酸菌发酵后,在乳酸菌蛋白酶的作用下更多酪蛋白的磷酸化位点暴露而产生大量CPPs,其中含SpSpSpEE特征结构的CPPs也在酸奶中检测到,CPPs的释放与酪蛋白结构密切相关。研究结果表明,牛奶经乳酸菌发酵后释放大量含特征结构SpSpSpEE的CPPs,可提高结合矿物元素的能力,从而增强其促进人体健康的生物功能。     

Enterococcus durans产胞外多糖EPS-Ⅰ的分离纯化和结构分析

乳酸菌(LAB)作为对人类健康有益的食品级微生物正日益受到国内外科研工作者的关注.乳酸菌所产胞外多糖(EPS)即是LAB在生长代谢过程中分泌到细胞壁外的粘液多糖或荚膜多糖.不同种类的LAB所产的胞外多糖也不同,其结构变化多样,生物活性与其空间结构、分子量、分支度和溶解度有密切关系^[1,2].近年来国外有报道分离得到具有抗肿瘤和抗炎活性的乳酸菌EPS-Ⅰ^[3,4],但是国内对乳酸菌所产胞外多糖的研究尚未见报道.本实验从鸡肠道中的一株乳酸菌Enterococcus durans的发酵液中分离纯化得到一种具有免疫活性的胞外多糖EPS-Ⅰ^[5,6],通过化学和光谱分析证明它是由葡萄糖和甘露糖组成的五糖重复单元聚合的多糖,同时得出EPS2的五糖重复单元结构.     

Separate and Concentrate Lactic Acid Using Combination of Nanofiltration and Reverse Osmosis Membranes

The processes of lactic acid production include two key stages, which are (a) fermentation and (b) product recovery. In this study, free cell of Bifidobacterium longum was used to produce lactic acid from cheese whey. The produced lactic acid was then separated and purified from the fermentation broth using combination of nanofiltration and reverse osmosis membranes. Nanofiltration membrane with a molecular weight cutoff of 100–400 Da was used to separate lactic acid from lactose and cells in the cheese whey fermentation broth in the first step. The obtained permeate from the above nanofiltration is mainly composed of lactic acid and water, which was then concentrated with a reverse osmosis membrane in the second step. Among the tested nanofiltration membranes, HL membrane from GE Osmonics has the highest lactose retention (97 ± 1%). In the reverse osmosis process, the ADF membrane could retain 100% of lactic acid to obtain permeate with water only. The effect of membrane and pressure on permeate flux and retention of lactose/lactic acid was also reported in this paper.     

牙菌斑有机酸的气相色谱-质谱分析

采用ＧＣ／ＭＳ联用技术分析了正常人牙菌斑内有机酸成分。发现了１４种有机酸,其中有８种直链饱和脂肪酸、４种直链非饱和脂肪酸、２种芳香酸。含量最多的是Ｃ１６∶０,Ｃ１８∶０,Ｃ１８∶１３种脂肪酸。其中苯乙酸、苯丙酸及十五碳酸等３种成分是第１次在牙菌斑中检测出。     

Enhanced <Emphasis Type="SmallCaps">l</Emphasis><Emphasis Type="Italic">-</Emphasis>(+)-Lactic Acid Production by an Adapted Strain of <Emphasis Type="Italic">Rhizopus oryzae</Emphasis> using Corncob Hydrolysate

Corncob is an economic feedstock and more than 20 million tons of corncobs are produced annually in China. Abundant xylose can be potentially converted from the large amount of hemicellulosic materials in corncobs, which makes the crop residue an attractive alternative substrate for a value-added production of a variety of bioproducts. Lactic acid can be used as a precursor for poly-lactic acid production. Although current industrial lactic acid is produced by lactic acid bacteria using enriched medium, production by Rhizopus oryzae is preferred due to its exclusive formation of the l-isomer and a simple nutrition requirement by the fungus. Production of l-(+)-lactic acid by R. oryzae using xylose has been reported; however, its yield and conversion rate are poor compared with that of using glucose. In this study, we report an adapted R. oryzae strain HZS6 that significantly improved efficiency of substrate utilization and enhanced production of l-(+)-lactic acid from corncob hydrolysate. It increased l-(+)-lactic acid final concentration, yield, and volumetric productivity more than twofold compared with its parental strain. The optimized growth and fermentation conditions for Strain HZS6 were defined.     

Determination of organic acid impurities in lactic acid obtained by fermentation of sugarcane juice

Lactic acid produced by fermentation process mostly contains a number of aliphatic carboxylic acids as impurities. In this work, carboxylic acid impurities in lactic acid samples from a number of sources were determined at ppm levels. A simple HPLC method was developed that utilized a new generation polar embedded reverse phase, 20mM phosphate buffer at pH 2.20 (±0.05) and UV detection at 210 nm. The method enabled quantitative analysis of the above acids in lactic acid matrix. The experimental conditions for column temperature, mobile phase pH and flow rate were optimized. A detailed validation of the method was performed for linearity, precision, accuracy, selectivity, limit of detection (LOD), limit of quantitation (LOQ), ruggedness and repeatability and reproducibility (R&R).     

Sequential analysis of malic acid and both enantiomers of lactic acid in wine using a high-performance liquid chromatographic column-switching procedure.

A liquid chromatographic column-switching method for the sequential determination of malic acid and both enantiomers of lactic acid in wine is described. The procedure involves the heart cutting of lactic acid enantiomers from a reversed-phase high-performance liquid chromatography chromatogram, retaining them, and back-flushing them through a chiral ligand-exchange column in which they are separated. The method is used to determine the concentration of lactic acid enantiomers in commercial wines. The results are in satisfactory agreement with those of other methods. The malic acid contents of various wines are also determined. The total analysis time for one experiment is approximately 10 min.     

The Influence of Propolis on Dental Plaque Reduction and the Correlation between Dental Plaque and Severity of COVID-19 Complications—A Literature Review

Current studies suggest that cariogenic bacteria in dental plaque influence the severity of COVID-19 complications since the oral cavity is a reservoir for respiratory pathogens potentially responsible for the development of hospital-acquired pneumonia. This article focuses on the association between dental plaque and COVID-19 concerning the influence of altered oral biofilm on the risk of increased severity of SARS-CoV-2 infection. Moreover, it concentrates on the usefulness of propolis, with its apitherapeutic antibacterial properties, for treating oral bacterial infections co-occurring with SARS-CoV-2 infection. A review of the literature on PubMed, Cochrane Library and Medline between 2000 and 2021 revealed 56 published articles indicating that a link between dental plaque and COVID-19 complications was probable. Furthermore, they indicated that propolis may minimize COVID-19 severity by reducing dental plaque accumulation. The possibility that improved oral health could reduce the risk of COVID-19 complications should be of interest to scientists.     

Stimulation of Nisin production from whey by a mixed culture of Lactococcus lactis and Saccharomyces cerevisiae

The production of nisin, a natural food preservative, by Lactococcus lactis subsp. lactis (ATCC 11454) is associated with the simultaneous formation of lactic acid during fermentation in a whey-based medium. As a result of the low concentration and high separation cost of lactic acid, recovering lactic acid as a product may not be economical, but its removal from the fermentation broth is important because the accumulation of lactic acid inhibits nisin biosynthesis. In this study, lactic acid removal was accomplished by biological means. A mixed culture of L. lactis and Saccharomyces cerevisiae was established in order to stimulate the production of nisin via the in situ consumption of lactic acid by the yeast strain, which is capable of utilizing lactic acid as carbon source. The S. cerevisiae in the mixed culture did not compete with the nisin-producing bacteria because the yeast does not utilize lactose, the major carbohydrate in whey for bacterial growth and nisin production. The results showed that lactic acid produced by the bacteria was almost totally utilized by the yeast and the pH of the mixed culture could be maintained at around 6.0. Nisin production by the mixed culture system reached 150.3 mg/L, which was 0.85 times higher than that by a pure culture of L. lactis.     

Poly(l‐lactic acid)‐modified silica stationary phase for reversed‐phase and hydrophilic interaction liquid chromatography

Poly(l ‐lactic acid) is a linear aliphatic thermoplastic polyester that can be produced from renewable resources. A poly(l ‐lactic acid)‐modified silica stationary phase was newly prepared by amide bond reaction between amino groups on aminopropyl silica and carboxylic acid groups at the end of the poly(l ‐lactic acid) chain. The poly(l ‐lactic acid)‐silica column was characterized in reversed‐phase liquid chromatography and hydrophilic interaction liquid chromatography with the use of different mobile phase compositions. The poly(l ‐lactic acid)‐silica column was found to work in both modes, and the retention of test compounds depending on acetonitrile content exhibited “U‐shaped” curves, which was an indicator of reversed‐phase liquid chromatography/hydrophilic interaction liquid chromatography mixed‐mode retention behavior. In addition, carbonyl groups included into the poly(l ‐lactic acid) backbone work as an electron‐accepting group toward a polycyclic aromatic hydrocarbon and provide π–π interactions.