双酶协同转化龙眼汁中蔗糖生成低聚果糖

目的 探究葡萄糖氧化酶协同果糖基转移酶转化龙眼汁中蔗糖生成低聚果糖、并减少龙眼汁葡萄糖含量的效果,实现减少龙眼汁中热量糖含量制备出低热量龙眼汁。方法 以天然龙眼汁为原料,通过控制不同的酶添加次序、酶添加量、龙眼汁体系pH和酶处理时间的单因素变量法,探究葡萄糖氧化酶协同果糖基转移酶转化龙眼汁中蔗糖生成低聚果糖的较优工艺条件;采用高效液相色谱法测定龙眼汁中游离糖组成及含量。结果 采用两种酶分段处理的方法,控制葡萄糖氧化酶添加量为60 U/g、反应温度为35℃、初始pH值6.0、饱和碳酸钙溶液添加量9.6%、通氧处理时间4 h,可有效消耗龙眼汁中原始葡萄糖和转化过程中产生的葡萄糖,使葡萄糖消耗率达到93.56%,并使龙眼汁中低聚果糖占比由果糖基转移酶单独处理时的31.72%提高到了58.08%。结论 采用葡萄糖氧化酶协同果糖基转移酶处理龙眼汁的方法,能有效降低龙眼汁中热量糖含量,制备出低热量龙眼汁。     

米曲霉GX0015β-果糖基转移酶分离纯化及酶学性质研究

β-果糖基转移酶是由蔗糖生产低聚果糖所必需的酶。从米曲霉GX0015菌株分离纯化β-果糖基转移酶,并对该酶酶学性质进行了研究。     

果糖基转移酶及低聚果糖生产研究进展

该文详细介绍果糖基转移酶来源、性质及果糖基转移酶与低聚果糖生产,并分析果糖基转移酶和低聚果糖生产中存在问题。     

编码米曲霉果糖基转移酶基因在大肠杆菌中的重组表达

为了大量获得果糖基转移酶,本文通过RT-PCR扩增获得米曲霉果糖基转移酶基因,连接到大肠杆菌pEASY-E1质粒上,并转化到大肠杆菌BL21-DE3菌株中成功表达,通过对重组菌诱导表达条件的优化,最终确定在诱导温度为25℃,诱导剂异丙基硫代半乳糖苷(IPTG)浓度为1.0μmol/mL的条件下,该重组酶可以顺利表达。利用重组质粒PEASY-S1上的6×组氨酸标签,用亲和层析的方法纯化能够得到较高纯度的果糖基转移酶。以蔗糖为底物,用该酶进行果糖基转化生产低聚果糖的实验结果表明:重组果糖基转移酶具有一定催化能力,其酶活力达到59.0 U/g,且在低温诱导时稳定表达,具备一定的潜在开发利用价值。本实验成功在大肠杆菌中重组表达出果糖基转移酶,并且能够短时间内、大量表达具有催化活性的果糖基转移酶,可望为果糖基转移酶的工业化提供理论基础。     

β-D呋喃果糖苷酶合成低聚果糖的工艺研究

以蔗糖为底物 ,采用来源于米曲霉中的 β -D -呋喃果糖苷酶 (EC3 2 1 2 6)合成低聚果糖 ,酶反应最佳条件为 :反应温度 35℃ ,酶反应体系的pH为 8 0～ 8 2 ,酶浓度 2 7IU/ g(蔗糖 ) ,酶反应时间为 8h。低聚果糖的最大转化率为 5 4% ,82 %的蔗糖被转化     

酶处理促进龙眼果汁中蔗糖的转化和低聚果糖的生成

为了降低龙眼果汁中的蔗糖含量和制备一种富含低聚果糖的龙眼果汁,本研究以龙眼果汁为原料,探讨底物浓度、底物pH、果糖基转移酶添加量、酶处理温度和时间等单因素对果汁中蔗糖的转化和生成低聚果糖的影响。采用液相色谱法(HPLC)分析酶转化前后果汁中蔗糖、果糖、葡萄糖、低聚果糖含量的变化。结果表明,底物浓度、pH、酶用量、温度和处理时间等因素对龙眼果汁蔗糖转化和低聚果糖的生成有显著影响(p0.05)。在底物浓度30 oBrix、pH 6.0、酶用量9 U/g、55℃下转化7 h的龙眼果汁,蔗糖含量从164.36 mg/m L减少至22.34 mg/m L,生成的低聚果糖含量为97.88 mg/mL,占果汁中总糖的38.21%。利用果糖基转移酶处理龙眼果汁,能有效降低果汁中的蔗糖含量,获得一种低热量且富含低聚果糖的功能性果汁。     

重组毕赤酵母产果糖基转移酶发酵条件的优化

果糖基转移酶(EC 2.4.1.9)是利用蔗糖为底物制备低聚果糖的关键酶。利用前期构建的产果糖基转移酶的重组毕赤酵母为出发菌株,对其进行发酵优化。最适发酵产酶条件为:装液量30 m L/250 m L、V(甘油)∶V(甲醇)=1∶20、初始pH为5.5、诱导温度为30℃、初始甲醇浓度为1.0%、后续甲醇浓度为1.5%、硫酸铵浓度10 g/L、诱导时间为120 h。在优化的发酵产酶条件下,重组果糖基转移酶酶活力达218.3 U/m L,较优化前提高了5倍。     

应用膜技术制备高纯度低聚果糖

研究了低聚果糖纳滤条件(操作压差、料液浓度、温度、循环流量、pH)对渗透通量和各糖组分截留率的影响,其最佳纳滤条件为:操作压差1.1MPa,料液浓度10%,温度40℃,循环流量为6L/min,pH6.0。应用纳滤提纯低聚果糖,其纯度达到85.05%。然而该纳滤膜对蔗糖具有较高的截留率,从而限制了低聚果糖纯度的提高空间。为了进一步提高低聚果糖纯度,研究尝试了将膜分离和酶反应耦联的技术,利用其边反应边分离的特性,滤除单糖,转化普通级低聚果糖中的蔗糖,最终获得高纯度低聚果糖,其纯度达到95.79%。      

应用膜技术制备高纯度低聚果糖

研究了低聚果糖纳滤条件(操作压差、料液浓度、温度、循环流量、pH)对渗透通量和各糖组分截留率的影响,其最佳纳滤条件为:操作压差1.1MPa,料液浓度10%,温度40℃,循环流量为6L/min,pH6.0。应用纳滤提纯低聚果糖,其纯度达到85.05%。然而该纳滤膜对蔗糖具有较高的截留率,从而限制了低聚果糖纯度的提高空间。为了进一步提高低聚果糖纯度,研究尝试了将膜分离和酶反应耦联的技术,利用其边反应边分离的特性,滤除单糖,转化普通级低聚果糖中的蔗糖,最终获得高纯度低聚果糖,其纯度达到95.79%。     

利用重组葡萄糖脱氢酶提高低聚果糖纯度

用IPTG（诱导基因工程菌）M15／pQE31-gdh表达葡萄糖脱氢酶，纯化，该重组葡萄糖脱氢酶用于高纯度低聚果糖生产研究。以含量为51．11％（低聚果糖／总糖）低聚果糖的产品为底物，葡萄糖脱氢酶（5U／g总糖）作用2h，将低聚果糖含量提高到61，37％，消除了48，81％的葡萄糖。以30％（w／v）蔗糖为底物，利用有果糖基转移酶活性的米曲霉GX0015（15U／g总糖）作用6h后，加入葡萄糖脱氢酶（5U／g总糖）协同作用4h，得到成分为：低聚果糖含量76．87％、葡萄糖11．05％、蔗糖含量5.21％的产品。由果糖基转移酶和葡萄糖脱氢酶组成的系统能够有效降低葡萄糖含量，提高低聚果糖含量。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

An internet compendium of analytical methods and spectroscopic information for monomers and additives used in food packaging plastics

An internet website (http://cpf.jrc.it/smt/) has been produced as a means of dissemination of methods of analysis and supporting spectroscopic information on monomers and additives used for food contact materials (principally packaging). The site which is aimed primarily at assisting food control laboratories in the European Union contains analytical information on monomers, starting substances and additives used in the manufacture of plastics materials. A searchable index is provided giving PM and CAS numbers for each of 255 substances. For each substance a data sheet gives regulatory information, chemical structures, physico-chemical information and background information on the use of the substance in particular plastics, and the food packaging applications. For monomers and starting substances (155 compounds) the infra-red and mass spectra are provided, and for additives (100 compounds); additionally proton NMR are available for about 50% of the entries. Where analytical methods have been developed for determining these substances as residual amounts in plastics or as trace amounts in food simulants these methods are also on the website. All information is provided in portable document file (PDF) format which means that high quality copies can be readily printed, using freely available Adobe Acrobat Reader software. The website will in future be maintained and up-dated by the European Commission's Joint Research Centre (JRC) as new substances are authorized for use by the European Commission (DG-ENTR formerly DGIII). Where analytical laboratories (food control or other) require reference substances these can be obtained free-ofcharge from a reference collection housed at the JRC and maintained in conjunction with this website compendium.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Chlorohydrins of bisphenol A diglycidyl ether (BADGE) and of bisphenol F diglycidyl ether (BFDGE) in canned foods and ready-to-drink coffees from the Japanese market

BADGE.2HCl and BFDGE.2HCl were determined in 28 samples of ready-to-drink canned coffee and 18 samples of canned vegetables (10 corn, 5 tomatoes and 3 others), all from the Japanese market. HPLC was used as the principal analytical method and GCMS for confirmation of relevant LC fractions. BADGE.2HCl was found to be present in one canned coffee and five samples of corn, BFDGE.2HCl in four samples of canned tomatoes and in one canned corn. No sample was found which exceeded the 1mg/kg limit of the EU for the BADGE chlorohydrins. However the highest concentration was found for the sum of BFDGE.2HCl and BFDGE.HCl.H₂O at a level of 1.5mg/kg. A Beilstein test confirmed that all cans containing foods contaminated with BADGE.2HCl or BFDGE.2HCl had at lest one part coated with a PVC organosol.     

European priorities for research to support legislation in the area of food contact materials and articles

A strong science base is required to underpin the planning and decision-making process involved in determining future European community legislation on materials and articles in contact with food. Significant progress has been made in the past 5 years in European funded work in this area, with many developments contributing to a much better understanding of the migration process, and better and simpler approaches to food control. In this paper this progress is reviewed against previously identified work-areas (identified in 1994) and conclusions are reached about future requirements for R&D to support legislation on food contact materials and articles over the next 5 or so years.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

Announcing a new international peer-reviewed journal:Food Science and Human Wellness now accepting manuscript submission in English

<正>We are pleased to announce the launch of a new international peer-reviewed journal-Food Science and Human Wellness,ISSN 2213-4530,which is an open access journal,produced and hosted by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.Food Science and Human Wellness is an international peer-reviewed English journal that provides a forum for the dissemination of the