微生物来源的唾液酸转移酶研究进展

唾液酸转移酶属糖基转移酶家族,以唾液酸胞苷单磷酸酯(CMP-Neu5Ac)为供体底物,催化唾液酸转移至糖蛋白与糖脂末端,是合成唾液酸化寡糖途径中所必需的酶类。微生物来源的唾液酸转移酶具有较广泛的底物特异性,且容易在常见的原核生物表达系统中过量表达,对酶学特性的研究及丰富唾液酸寡糖种类具有重要意义。本文综述了唾液酸转移酶的分类与微生物来源、晶体结构、催化反应机理、酶学性质、异源表达以及在唾液酸寡糖合成中的应用,并对唾液酸转移酶的未来发展方向进行了展望,以扩展这些酶在糖化学和糖生物学中的应用。     

唾液酸在婴幼儿配方奶粉中的应用进展

母乳中含有丰富的唾液酸成分,大多数唾液酸是以与低聚糖结合的形式存在。目前,已有报道称唾液酸可以促进婴儿的大脑和神经系统的发育,但唾液酸的代谢机制和生物功能并不十分清晰。更重要的问题是,唾液酸作为一个在母乳中的有效营养成分,将其添加到婴幼儿配方奶粉中会有哪些优势体现尚不明确。课题对唾液酸的基本特性、生物活性、检测方法以及应用现状做了全面的概述,并对唾液酸未来应用于婴幼儿配方奶粉的可行性提供了可靠依据。     

唾液酸及在母婴食品中的应用

唾液酸是一类含有9碳骨架的酸性单糖,通常位于非还原性寡聚糖的末端。母乳中含有丰富的唾液酸,对促进婴幼儿的大脑和认知发育、抗病毒等方面具有重要作用,目前工业上主要通过微生物发酵法制备唾液酸。本文从唾液酸的性质、分布、功能以及制备方法等方面分析其在婴幼儿食品中应用的原理、方法以及前景,为提高唾液酸在母婴食品中的应用提供理论支持。     

唾液酸的生理功能、应用及其生产方法

唾液酸广泛的分布于多种生物组织中,通常位于非还原性寡聚糖的末端。在各种生命活动调节过程中起着重要的作用。唾液酸在食品和医药等领域的应用潜力,决定了需要对其进行大规模生产的必要性。本文对唾液酸的生理功能、应用和生产方法进行了综述,并对其未来发展方向进行了展望。     

唾液酸的生物活性及其在乳品中分布

唾液酸广泛存在于多种生物组织中,是构成细胞表面复合糖质的重要组分。唾液酸参与细胞表面的多种生理功能,在各种生命活动中有着重要作用。唾液酸的食物来源主要是乳及乳品,尤其初乳中含量较高。就唾液酸的结构性质、生物学功能及其唾液酸在乳品中的分布等进行综述,并展望唾液酸的应用前景。     

燕窝中结合唾液酸调节5种益生菌生长以及孕妇肠道菌群组成的研究

膳食动物源黏蛋白存在结合态唾液酸聚糖，可能对人体营养健康产生影响。该文以一种富含唾液酸的黏蛋白—燕窝(edible bird’s nest, EBN)为研究对象，通过酸处理切除燕窝糖蛋白末端唾液酸(acidolysis bird’s nest, ABN),分别进行体外模拟消化，比较酸处理前后的燕窝及唾液酸单体在抗氧化活性方面的差异，以及对不同益生菌和孕妇粪菌在体外发酵的影响。结果表明，EBN比ABN和唾液酸具有更好的抗氧化活性。EBN以及唾液酸可不同程度改善乳杆菌和双歧杆菌菌株的生长，并增加短链脂肪酸的生成。同时，EBN可以显著促进阿克曼黏细菌的生长。在体外进行的健康女性和孕晚期孕妇粪菌发酵中，EBN在24 h内可显著增加乙酸、丙酸和丁酸的产量，其中丙酸的增加最为显著。同时，EBN还能够降低大肠杆菌-志贺氏菌属、肠杆菌属和克雷伯氏菌属等潜在致病菌的相对丰度，并增加潜在益生菌(如拟杆菌属、粪杆菌属和粪球菌属)的相对丰度。EBN在降低致病菌丰度和增加益生菌丰度具有比ABN更加显著的效果。因此，EBN中结合了唾液酸的完整性对其生物学功能起重要作用。     

不同加工工艺对燕窝产品唾液酸含量的影响

本文以毛燕为原料,研究浸泡、挑拣、高温灭菌等工艺流程处理后燕窝唾液酸含量的变化。采用LC-MS/MS检测分析燕窝中唾液酸种类,此外,测定了不同加工条件下燕窝产品唾液酸含量并分析加工条件对唾液酸含量的影响,进一步分析了唾液酸热稳定性。结果表明:燕窝中唾液酸仅由N-乙酰基神经氨酸(Neu5Ac)组成,经不同工艺条件处理后,Neu5Ac保留率均可高达95%以上,且Neu5Ac热稳定性好,不同情况下Neu5Ac含量无明显差异。说明燕窝经过上述加工处理后不会造成燕窝酸的大量流失,并且其受工艺条件变化影响小,燕窝加工产品可以很好地保存燕窝的营养价值,从而稳定发挥其营养功效,具有很高的消费价值。     

分光光度法检测燕窝及其制品中燕窝含量

本文利用乙酸提取燕窝中的唾液酸糖蛋白,并将其酸解为唾液酸,唾液酸与酸性茚三酮形成稳定的黄色物质,于470nm处测量吸光度。探讨了除去干扰的方法,选用纯正燕窝作为标准,可以求出样品中含纯正燕窝的百分含量。     

红肉中N-羟乙酰神经氨酸在人体中的代谢途径及危害

唾液酸(Sialic acid,Sia)是一类含有9个碳骨架的酸性糖类,在胚胎和中枢神经系统发育、细胞识别、黏附、分化、信号传导等多方面具有重要的生理意义。N-羟乙酰神经氨酸(N-glycolylneuraminic acid,Neu5Gc)是一种含有9个碳原子并具备吡喃糖结构的酸性氨基糖。Neu5Gc作为唾液酸中的一种比较特殊的存在,与人类癌症以及动脉粥样硬化、2型糖尿病等疾病的发生发展有着密切联系。该文主要阐述了Neu5Gc的基本结构以及在人体的来源、代谢、吸收和蓄积的过程,并介绍了红肉特异性致病理论及Neu5Gc的危害。     

废弃鸡蛋壳的化学组成及其中唾液酸的生物学功能

主要阐述了废弃鸡蛋壳的化学组成以及其中生物活性物质唾液酸的生物学功能问题.废弃蛋壳包括蛋壳、蛋壳膜和残留蛋清,含有唾液酸、糖醛酸以及氨基酸等成分.其中唾液酸是一类分布在复合糖类糖链末端的九碳糖,在各种生命活动中起着重要的作用,如体内润滑、维持正常神经活动、益智、抗菌、抗病毒、抗肿瘤等,旨在为废弃蛋壳中唾液酸的开发利用以及今后相应的科研工作提供理论依据.     

Sialic acid in plant tissues: A history of incorrect identification due to the use of non-specific colorimetric reactions

Finely ground seeds of wheat, sunflower, coffee and french bean were either hydrolysed in acid directly, or after extraction with ethanol and/or after treatment in alkali to hydrolyse any O-acetyl sialic acids present. The acid hydrolysates were fractionated by ion-exchange chromatography. Sialic acid was not detected in any of the materials examined but quinic acid was found in all of them. It is concluded that some previous reports of sialic acid in plant seeds and tissues may have been due to the presence of quinic acid and of other compounds, which show rather similar properties to sialic acid in chromatographic and colorimetric methods of analysis.     

A Sensitive and Selective Fluorimetric Method of Quick Determination of Sialic Acids in Egg Products by Lectin‐CdTe Quantum Dots as Nanoprobe

Sialic acids (SA) are widely found as components of oligosaccharide units in mucins, glycoproteins and other microbial polymers in nature food. The aim of this study is to create a new fluorimetric detection method applied for determinating SA in egg products by using a sensitive lectin‐CdTe quantum dots (QDs) nanoprobe. Water‐soluble and high luminescent CdTe QDs were conjugated with sambucus nigra bark lectin (SNA) as probe for SA detection. As a result of specific interaction between SA and SNA‐CdTe QDs, the conjugations finally lead to the change of a fluorescent signal. Under optimal conditions, fluorescence intensity increase linearly with the increase of the concentration of SA ranging from 12 to 680 ng/mL. The low detection limit is 0.67 ng/mL. This quick and selective analysis method for SA detection has been used in synthetic samples and egg products with recovery between 97.92% and 110.42%, which demonstrates the application of this assay is feasible and practical.     

Determination of sialic acids in infant formula by chromatographic methods: a comparison of high-performance anion-exchange chromatography with pulsed amperometric detection and ultra-high-performance liquid chromatography methods

Sialic acid determination in an infant formula presents many challenges, including efficient sialic acid release from glycoconjugates, effective sample preparation, and rugged chromatography. This work compares 2 chromatographic assays developed for determination of sialic acids in infant formula. Prior to chromatography, both assays release sialic acids by acid hydrolysis and treat the hydrolysate with a subsequent anion-exchange sample preparation. Both high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and fluorescence ultra-high-performance liquid chromatography (UHPLC) sample analysis methods were evaluated to compare assay performance and convenience. Calibration ranges were chosen to encompass the expected amounts of 2 sialic acids in infant formula: N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc). Response was linear by either method with coefficients of determination of 1.00 by HPAEC-PAD between 5.0 and 100pmol of Neu5Ac and between 0.34 and 6.8 pmol of Neu5Gc and >0.99 by UHPLC between 5.0 and 260 pmol of Neu5Ac and between 0.20 and 9.8 pmol of Neu5Gc. Both methods had sufficient sensitivity to determine these sialic acids in infant formula. Three infant formulas were analyzed to evaluate accuracy and precision of the assays. The HPAEC-PAD assay was found to be faster overall and the UHPLC assay was more sensitive. Reaction efficiency, and therefore sensitivity, was dependent on the sample matrix. This work illustrates sample-specific complexity that must be considered in choosing an assay.     

Bovine milk glycome

Bovine milk oligosaccharides have several potentially important biological activities including the prevention of pathogen binding to the intestinal epithelial and as nutrients for beneficial bacteria. It has been suggested that milk oligosaccharides are an important source of complex carbohydrates as supplements for the food and the pharmaceutical industries. However, only a small number of structures of bovine milk oligosaccharides (bMO) are known. There have been no systematic studies on bMO. High-performance mass spectrometry and separation methods are used to evaluate bMO, and nearly 40 oligosaccharides are present in bovine milk. Bovine milk oligosaccharides are composed of shorter oligomeric chains than are those in human milk. They are significantly more anionic with nearly 70%, measured abundances, being sialylated. Additionally, bMO are built not only on the lactose core (as are nearly all human milk oligosaccharides), but also on lactose amines. Sialic acid residues include both N-acetyl and N-glycolylneuraminic acid, although the former is significantly more abundant.     

离子交换法提取发酵液中唾液酸

研究了离子交换树脂从发酵液中提取唾液酸的方法,包括树脂的筛选、吸附条件和洗脱条件的确定,唾液酸纯度达到97.4%.     

母乳中的多不饱和脂肪酸

母乳含有丰富的多不饱和脂肪酸,为婴儿的生长发育所必需,尤其是促进婴儿中枢神经系统的发育,因此母亲膳食多摄取多不饱和脂肪酸,提高母乳中的营养成分,以及在婴儿奶粉中强化多不饱和脂肪酸都是十分重要的。     

食品中D-氨基酸的形成机制及生理功能研究进展

自然界构成蛋白质的20种氨基酸中，除甘氨酸外，其他19种氨基酸均具有两个互为镜像的立体异构体（D型和L型）。传统观点认为L-氨基酸是参与生命活动的主体，而D-氨基酸在生物体内的存在及生理活性未被重视。随着氨基酸手性分析技术的发展，从包括人类在内的哺乳动物、植物、微生物等有机体中发现大量D-氨基酸及含有D-氨基酸的生物活性肽。D-氨基酸具备独特的生理活性，主要表现在神经信号传导、激素调节、抗菌、免疫调节等方面。日常膳食是人体D-氨基酸的主要来源，其为人类日均提供约100 mg D-氨基酸。食品中的D-氨基酸主要在发酵、高温及一定的p H值等加工条件下产生，少量来自食品原料本身。目前市场上已开始出现以D-氨基酸为主要成分的新兴功能性食品，其蕴含的巨大潜力仍有待深入挖掘，并有望成为未来新型功能性食品的重要原料。     

支链氨基酸生物合成及其代谢工程育种研究进展

支链氨基酸(亮氨酸、异亮氨酸和缬氨酸)主要由细菌、真菌和植物合成,是人体必需氨基酸。因其特殊的结构和功能,在人类生命代谢中占有特别重要的地位,支链氨基酸在医药、食品及饲料领域中有着广泛的用途。目前支链氨基酸主要采用发酵法生产,生产菌种主要为Corynebacterium glutamicum(包括黄色短杆菌Brevibacterium flavum)。作者主要分析了Corynebacterium glutamicum中支链氨基酸生物合成途径及其代谢调控,并对支链氨基酸代谢工程育种情况进行了综述。     

支链氨基酸生物合成及其代谢工程育种研究进展

支链氨基酸(亮氨酸、异亮氨酸和缬氨酸)主要由细菌、真菌和植物合成,是人体必需氨基酸。因其特殊的结构和功能,在人类生命代谢中占有特别重要的地位,所以支链氨基酸在医药、食品及饲料领域中有着广泛的用途。目前支链氨基酸主要采用发酵法生产,生产菌种主要为Corynebacterium glutamicum(包括黄色短杆菌Brevibacterium flavum)。作者主要分析了Corynebacterium glutamicum中支链氨基酸生物合成途径及其代谢调控,并对支链氨基酸代谢工程育种情况进行了综述。