二肽甜味剂结构的研究进展

以aspartame为代表的二肽甜味剂在甜味剂市场上占有重要的地位，研究二肽甜味剂的结构与甜味变化的关系有助于开发和评价新的二肽甜味剂。二肽甜味剂对N-端的结构有严格的要求，C-端却是经常可以变化的。为进一步揭示二肽甜味剂的结构，本论文分析了一系列aspartame的衍生物。研究表明，苯丙氨酸上的疏水基团X当改变其结构大小时，甜度的变化不大。而肽键对于维持甜味是必需的，用酯键取代肽键导致甜味消失，氨基上的氢键对于维持甜味来说也是必需的，当它被甲基取代时甜味也消失了。     

二肽甜味剂结构的研究进展

二肽甜味剂对N-端的结构有严格的要求，C-端却是经常可以变化的。为进一步揭示二肽甜味剂的结构，分析了一系列aspartame衍生物。研究表明，苯丙氨酸上的疏水基团X当改变其结构大小时，甜度的变化不大。而肽键对于维持甜味是必需的，用酯键取代肽键导致甜味消失，氨基上的氢键对于维持甜味来说也是必需的，当它被甲基取代时甜味也消失了。     

高甜度二肽甜味剂的合成与特性

以异香兰素为原料,经Wittig反应、常温常压催化氢化、二异丁基氢化铝还原制得中间体3-(3-羟基-4-甲氧基苯基)丙醛。S-叔丁基-L-半胱氨酸甲酯与N-叔丁氧羰基-L-天冬氨酸-4-叔丁酯经1-乙基-(3-二甲基氨基丙基)碳酰二亚胺盐酸盐以及1-羟基苯并三唑水合物缩合制得二肽化合物N-(N-叔丁氧羰基-4-叔丁酯-L-α-天冬氨酰)-S-叔丁基-L-半胱氨酸-1-甲酯,并在氯化氢-二氧六环溶液中脱保护制得二肽化合物N-(L-α-天冬氨酰)-S-叔丁基-L-半胱氨酸-1-甲酯;然后将中间体3-(3-羟基-4-甲氧基苯基)丙醛与N-(L-α-天冬氨酰)-S-叔丁基-L-半胱氨酸-1-甲酯通过亚胺化钯碳氢气常压催化氢化得到目标化合物N-[N-[3-(3-羟基-4-甲氧基苯基)丙基]-L-α-天冬氨酰基]-S-叔丁基-L-半胱氨酸-1-甲酯。经红外光谱、质谱以及核磁共振仪对产物进行结构鉴定,确定目标产物结构。     

甜味蛋白的研究进展

糖类物质的过量所摄入引起的系列疾病,如糖尿病、肥胖、高血脂症、龋齿等已成为较为严重的社会问题.不仅在发达国家发病率迅速增长,发展中国家也已经出现相似的状况.因此,低热量的甜味剂被接受,如糖精不给人体提供热量,也不被人体分解和吸收,上百年来一直被用作食品和饮料的甜味剂.但市售人造低热量甜味剂可能具有其本身的问题.甜味蛋白作为一种新的甜味剂有望成为新型甜味剂.到目前为止,已从植物中获得了八种天然的甜味蛋白或甜味诱导蛋白,开展了甜味蛋白和人的甜味感受器之关系研究,初步阐明了甜味蛋白的甜味机制,甜味蛋白将越来越受到重视并具有广阔的应用前景.     

淀粉衍生物在饮料中应用

<正>淀粉衍生物作为改善饮料感官性状的重要配料,已有悠久的历史。从传统的碳酸饮料、非碳酸饮料、固体饮料、含酒精饮料到现今的新型功能饮料,高果玉米糖浆(HFCS)和麦芽糊精一直是标准配料。 淀粉衍生物可为饮料提供甜味,增强风味,改善口感和提高稳定性;亦是一些营养剂和发酵萃取物原料,如可用以生产特殊的啤酒添加剂;葡萄糖焦糖色素还是可乐型饮料重要组分。为了满足消费者对健康食品的要求,一种新型甜味剂——结晶赤藓糖醇也已出现于饮料中,其不仅能满足感官需要,同时又能大幅降低产品的热值。 本文综述淀粉衍生物在饮料中主要功能,并介绍使用复配甜味剂一些新认识。     

多糖微观构象与抗肿瘤活性关系研究进展

多糖因其特殊的结构而具有丰富的生物活性功能,而其中抗肿瘤功能已成为多糖研究领域的热点之一。然而,由于多糖结构的复杂性及传统光谱研究手段的局限性,以致于到目前为止多糖的结构与活性间的构效关系尚未深入探讨。基于此,本文从多糖结构与抗肿瘤活性的角度,具体阐述多糖的结构(如主链结构、螺旋构象等)对抗肿瘤活性的影响,探讨运用计算机分子模拟研究多糖微观构象与抗肿瘤活性关系的可行性,为抗肿瘤活性多糖的目的性筛选、进行分子修饰提供参考,为多糖的深度利用提供理论基础和科学依据。     

合成二肽降血压活性研究

研究利用可见光分光光度法系统地对34种合成二肽的ACE抑制活性进行筛选,结果发现34种二肽中氨基酸序列为半胱氨酸-异亮氨酸(Cys-Ile,CI)和半胱氨酸-赖氨酸(Cys-Lys,CK)的二肽ACE抑制活性最高,其ACE抑制率分别达到67.52%和38.39%。其余二肽中有25种无明显ACE抑制活性,有7种呈一定程度ACE抑制活性。经测定CI和CK的IC50值分别为39.77μmol/L和211.53μmol/L。SHR大鼠降血压实验表明CI在体内的降压效果显著。以10 mg/kg剂量灌胃后2h大鼠舒张压下降34.36±5.19 mm Hg;当CI剂量达到100mg/kg时,给药后2h大鼠舒张压下降83.95±10.28 mm Hg,降压效果高于同浓度卡托普利。比较给药后2h和4h的降压效果,发现给药后2h的降压效果已经整体达到最大药效,而给药后4h降压效果与给药剂量呈较好的正相关性(R0.8)。体外ACE抑制率测定及SHR大鼠降血压实验表明合成二肽CI具有较高的ACE抑制活性和较好的体内降血压效果,提示CI可以作为降血压保健食品的添加成分,值得进一步研究。     

壳聚糖衍生物抗菌活性研究进展

壳聚糖具有降低血液中胆固醇、降低血压、抗感染、控制关节炎、抗癌等多种作用。作为天然的食品防腐剂,壳聚糖不仅对人体无害,还具有很多保健作用。普通分子量的壳聚糖水溶性很差,一般使用酸溶液来溶解。通过合成各种壳聚糖的衍生物不仅提高了壳聚糖的水溶性还增强了它们的抗菌活性,使壳聚糖作为一种天然优质食品防腐剂成为可能。     

谷氨酰胺及其二肽的营养生理研究进展

谷氨酰胺（Ｇｌｎ）因其对人和动物的重要生理作用而引起广泛关注,大量的证据表明谷氨酰胺是一种十分重要的具有特殊营养作用的条件必需氨基酸。但由于它的不稳定性及低溶解度,使其应用受到限制,谷氨酰胺二肽克服了它的缺点并可被分解为氨基酸而被利用,且无任何毒副作用和不良反应。综述了谷氨酰胺及其二肽的营养生理作用研究进展。     

Structure-taste relationship of some sweet-tasting dipeptide esters.

The sweetness of dipeptide esters, structurally related to L-aspartyl-L-phenylalanine methyl ester (Aspartame), depends among other things on molecular size. This paper describes a method for predicting whether a dipeptide ester is sweet or not with the aid of atomic models. The method is based on the determination of the size, length and shape of the side chain (R) of the amino-acid ester attached to L-aspartic acid. We measured the side chains of 28 dipeptide esters, 13 of which were synthesized and evaluated for sweetness in our laboratory. Data of the other esters were taken from the literature. Twentyone dipeptide esters were sweet; the size and length of the side chains could be correlated with the degree of sweetness. An ester is sweet provided the length of the side chain (R) is between 4.8 and 8.8 A, and its size greater than or equal to 29 A; as for shape of R in sweet esters, there were two maxima in space filling at about 2 and 4 A or about 3 and 5 A from the asymmetric carbon atom.     

Chemoreception of sweet-tasting dipeptide esters: A third binding site

The question whether dipeptide esters with the general formula COO^?.C.CNH⁺₃.CO.NH.CR.CO.OCH₃ are sweet or not cannot be explained solely by the presence of two binding sites (NH⁺₃ and COO^?) acting together as the so-called AH-B system.On the basis of data collected at this laboratory and elsewhere, a third binding site is postulated, located at the centre of the bulky R constituent. The position of this third site is compared with those proposed for the sweet nitroaniline series by Kier (1972) and for sugars by Shallenberger & Lindley (1977).     

Expression of the sweet-tasting protein brazzein in Lactobacillus spp.

As sucrose has been implicated in healthrelated problems such as obesity and diabetes, awareness of a safe natural non-sugar sweetener has increased. Brazzein is the intensely sweet-tasting plant protein which consists of 54 amino acids. In this study, brazzein was expressed in Lactobacillus spp., probiotics, which are widely used in food industry. Three Lactobacillus spp. (Lb. paracasei KLB58, Lb. plantarum KLB213, and Lb. reuteri KCTC3594) were electrotransformed with pMSP3545::Braht which contains brazzein gene along with nisin-controlled expression (NICE) system. Brazzein expression in Lactobacillus spp. was confirmed by Western blot analysis. Overall, higher expression rate was obtained with nisin concentration of 25–40 ng/mL.     

染料木素抗肿瘤衍生物的研究进展

染料木素具有雌激素样作用,具备抗肿瘤、防止骨质疏松、抗氧化、降血脂、抗动脉粥样硬化等多种生物活性,近年来已逐渐成为国内外学者研究的热点。本文着重对染料木素抗肿瘤衍生物的研究进展进行了综述,以促进其研究和应用,并为进行抗肿瘤前药分子设计提供依据。     

活性包装释放控制的研究进展

活性包装是以包装材料为传送载体,释放抗菌剂、抗氧化剂等保鲜剂以达到维持或改善食品品质,延长食品的货架期的包装技术。本文从释放动力学过程展开探讨,分类介绍了释放控制的四种方式:树脂基体组成、多层复合、纳米材料复合及微囊化,最后从活性包装保鲜效果评价进行释放与保鲜的关联,并提出了展望。      

壳聚糖衍生物的抗氧化性能研究进展

官能团的存在对于物质的性质和功能有着重要的影响。经醚化、酯化、酰化等改性后,壳聚糖衍生物的抗氧化能力发生改变。综述国内外壳聚糖衍生物抗氧化性能的重要研究进展。     

Residue mutations in the sweetness loops for the sweet-tasting protein brazzein

To identify critical residues, important for sweetness, of the sweet protein brazzein, 11 mutants of the residues in three loops of brazzein were constructed by site-directed mutagenesis. We found that mutations of Glu41 to Ala, Lys, or Arg at position 41 in loop 40–43 made the molecules significantly sweeter than brazzein, while mutations at two distant residues (changing Arg43 to Lys or Glu) decreased sweetness. A similar pattern occurred at loop 30–33, where mutation of the His31 to Arg significantly increased sweetness, while mutations at positions 30 or 33 in the immediate vicinity of this region significantly decreased sweetness. In addition, a Gln17 residue in the loop 9–19 was necessary for structural integrity. From these results, we suggest that the loops containing His31 and Glu41 are critical regions of the molecule for eliciting sweetness, and the charge and/or structure of the side chain of these residues play an important role in the multi-point interactions between brazzein and the sweet-taste receptor.     

生物活性肽制备的研究进展

现代生物代谢研究发现 :人类摄取的蛋白质经过消化道的多种酶水解后 ,不象以前认为的那样仅以氨基酸的形式吸收 ,更多的是以低肽的形式直接吸收 ,而且二肽和三肽的吸收速度比同一组成的氨基酸快。其中某些低肽不仅能提供人体生长发育所需的营养物质 ,且同时具有重要的生理功能 ,如促进矿物质吸收肽、防治肝性脑病肽 ,易消化吸收肽、抗菌肽、吗啡片肽、类吗啡拮抗肽、血管紧张素转换酶抑制肽、抑制胆固醇作用肽、机体防御功能肽等[1] 。上述功能是原蛋白质或组成氨基酸所不具备的独特的生理机能 ,且许多活性肽的组成氨基酸并不一定是必需氨基…