Metabolic engineering pathways for rare sugars biosynthesis,physiological functionalities,and applications—a review

ABSTRACT

Biomolecules like rare sugars and their derivatives are referred to as monosaccharides particularly uncommon in nature. Remarkably, many of them have various known physiological functions and biotechnological applications in cosmetics, nutrition, and pharmaceutical industries. Also, they can be exploited as starting materials for synthesizing fascinating natural bioproducts with significant biological activities. Regrettably, most of the rare sugars are quite expensive, and their synthetic chemical routes are both limited and economically unfeasible due to expensive raw materials. On the other hand, their production by enzymatic means often suffers from low space-time yields and high catalyst costs due to hasty enzyme denaturation/degradation. In this context, biosynthesis of rare sugars with industrial importance is receiving renowned scientific attention, across the globe. Moreover, the utilization of renewable resources as energy sources via microbial fermentation or microbial metabolic engineering has appeared a new tool. This article presents a comprehensive review of physiological functions and biotechnological applications of rare ketohexoses and aldohexoses, including D-psicose, D-tagatose, L-tagatose, D-sorbose, L-fructose, D-allose, L-glucose, D-gulose, L-talose, L-galactose, and L-fucose. Novel in-vivo recombination pathways based on aldolase and phosphatase for the biosynthesis of rare sugars, particularly D-psicose and D-sorbose using robust microbial strains are also deliberated.     

稀有糖的研究进展

自然界中含量极少的稀有糖在膳食、保健、医药等领域发挥着重要的生理功能。本文简述了几种常见稀有糖的抗癌、清除自由基、神经保护等生物活性,并主要列举了3 种成熟的稀有糖合成策略,包括关环转换合成法、两步合成法、Izumoring 合成法。同时,对稀有糖的研究与应用前景加以展望。     

Effects of different processes on the carbohydrates of lima bean

Changes which occurred in the concentrations of free sugars, high-molecular weight carbohydrates (water-soluble carbohydrates, starch, hemicellulose, cellulose), and lignin in 3 differently processed varieties of lima bean have been studied. Samples were boiled, autoclaved or soaked in water and germinated for 3 days. Available carbohydrates (starch + sugars) which initially ranged from 53.3 to 54.8 g/100 g dry matter in the raw varieties, decreased very drastically with germination whilst raffinose disappeared and stachyose + verbascose were reduced to trace levels. Cooking as well as autoclaving brought about slight decrease in glucose, fructose and sucrose levels and increased oligosaccharide content of all the varieties. Changes in the content of the structural carbohydrates of all processed varieties were small. Cooking and germination, however effected some reductions in total unavailable carbohydrate content. The effect of these processes on improving the nutritional value of lima beans was discussed.     

Green and Effective Ammonium Carbonate-assisted Process for Drying Hemicellulose Obtained through Alkali Extraction of Bleached Bamboo Kraft Pulp

Hemicellulose has a wide range of applications,including that as an emulsifier for the food industry and raw material for the synthesis of bioethanol/biochemicals and biodegradable films.Hemicellulose is usually present as a spent liquor,such as the prehydrolysis liquor of the prehydrolysis kraft dissolving pulp production process and the alkali extraction liquor of the cold caustic extraction of pulp fibers.Due to its dilute nature,hemicellulose needs to be dried for practical utilization,and this is challenging.In this study,cellulose and hemicellulose in a bleached bamboo kraft pulp were separated using an alkali extraction process.Hemicellulose obtained from the extraction liquor was dried by an ammonium carbonate-assisted drying process.The effects of drying time and drying temperature were determined.Structure of the hemicellulose obtained by the ammonium carbonate-assisted drying process was similar to that of original hemicellulose,as revealed by detailed Fourier transform infrared and X-ray diffraction analyses.The novel drying method was more energy efficient and required a shorter drying time than the conventional freeze drying method,and the excellent solubility in alkaline solutions favored the chemical modification of hemicellulose.The dried hemicellulose can be used as a renewable raw material for the preparation of hydrogels and other substances such as bioethanol/biochemicals and biodegradable films.     

Nondairy food applications of whey and milk permeates: Direct and indirect uses

Permeates are generated in the dairy industry as byproducts from the production of high-protein products (e.g., whey or milk protein isolates and concentrates). Traditionally, permeate was disposed of as waste or used in animal feed, but with the recent move toward a “zero waste” economy, these streams are being recognized for their potential use as ingredients, or as raw materials for the production of value-added products. Permeates can be added directly into foods such as baked goods, meats, and soups, for use as sucrose or sodium replacers, or can be used in the production of prebiotic drinks or sports beverages. In-direct applications generally utilize the lactose present in permeate for the production of higher value lactose derivatives, such as lactic acid, or prebiotic carbohydrates such as lactulose. However, the impurities present, short shelf life, and difficulty handling these streams can present challenges for manufacturers and hinder the efficiency of downstream processes, especially compared to pure lactose solutions. In addition, the majority of these applications are still in the research stage and the economic feasibility of each application still needs to be investigated. This review will discuss the wide variety of nondairy, food-based applications of milk and whey permeates, with particular focus on the advantages and disadvantages associated with each application and the suitability of different permeate types (i.e., milk, acid, or sweet whey).     

Determination of reducing sugars in selected beverages by capillary electrophoresis

 A method for the analysis of reducing sugar enantiomers in beverages using capillary zone electrophoresis is presented. Based on previous results, a resolution of all aldo-hexoses, -pentoses, -tetroses and trioses is achieved. Additional separation of uronic acids, deoxy and amino sugars in different buffer systems is demonstrated. Derivatives of sugar enantiomers change their migration order if derivatized with the phenylethylamine enantiomer. Thus, the use of a chiral derivatizing agent leads to simpler peak validation and opens new opportunities for the development of new applications. Screening of pharmaceutical drugs or food for rare sugar enantiomers with a detection limit of 25 fmol (5 μM) is feasible. Adaptation of the general method to wine, juice and instant coffee is demonstrated. The aldose, uronic acid and deoxy aldose enantiomer composition of the presented beverages is obtained in a single run.     

碳水化合物在生物加工过程中的变化与调控

生物转化是碳水化合物资源高效利用的有效途径.利用转糖基酶和异构化酶将现有的丰富的单糖、寡糖、环糊精等转化为功能性稀有糖、寡糖,为食品、医药、新材料等行业提供新的原料,对于社会经济发展具有明显的推动作用.本文综述了转糖基酶、异构化酶的结构、定向进化、催化过程调控策略等方面的最新研究进展,并就该领域面临的科学问题和发展趋势进行了总结和展望,以期对相关领域研究者有所启发.     

Determination of reducing sugars in selected beverages by capillary electrophoresis

 A method for the analysis of reducing sugar enantiomers in beverages using capillary zone electrophoresis is presented. Based on previous results, a resolution of all aldo-hexoses, -pentoses, -tetroses and trioses is achieved. Additional separation of uronic acids, deoxy and amino sugars in different buffer systems is demonstrated. Derivatives of sugar enantiomers change their migration order if derivatized with the phenylethylamine enantiomer. Thus, the use of a chiral derivatizing agent leads to simpler peak validation and opens new opportunities for the development of new applications. Screening of pharmaceutical drugs or food for rare sugar enantiomers with a detection limit of 25 fmol (5 μM) is feasible. Adaptation of the general method to wine, juice and instant coffee is demonstrated. The aldose, uronic acid and deoxy aldose enantiomer composition of the presented beverages is obtained in a single run. Received: 20 April 1998 / Revised version: 15 June 1998     

利用可再生资源生产酒精的细菌、酵母中的代谢工程

木质纤维素是地球上最充分的可更新的有机资源。将木质纤维素中的纤维素 (含葡萄糖 )、半纤维素 (含六碳糖和五碳糖 )水解成乙醇正在被广泛地研究。本文从代谢工程的策略和角度对利用木质纤维素生产乙醇的细菌 ,酵母重组菌的研究进展及相关菌株载体的构建方法进行了综述     

Post-harvest changes in fermentable sugars in sweet Sorghum (Sorghum bicolor cv. Wray)

Changes in sucrose and reducing sugar content of Sorghum bicolor (cv. Wray) were followed for 72 h after harvest to gauge the stability of the sugars between harvesting and milling and to devise suitable sampling procedures for analysis. Within the first 48 h, sucrose decreased from 34 to 19% of the dry matter while production of monosaccharides increased correspondingly from 9 to 23% of the dry matter. Processing of sorghum stems within 24 h of harvest will retain maximum sucrose content. This is necessary for commercial sugar production or when a knowledge of sugar composition at harvest is required. Beyond 24 h, inversion to reducing sugars is significant and may render the crop more suitable for use as an industrial feedstock (e.g. for liquid fuel production).     

牛初乳与牛乳中乳清蛋白质组成及功能的对比分析

乳清富含多种功能特性和生物活性的蛋白质,本研究利用SDS-PAGE电泳将牛初乳与牛乳中乳清蛋白质的组成部分进行分离鉴定,发现牛初乳与牛乳中乳清蛋白质的组成存在较大的差异,且在牛初乳乳清中鉴定出290种蛋白,牛乳乳清中鉴定出325种蛋白。由GO功能注释分析发现,在生物过程中,牛初乳乳清蛋白在细胞定位建立和细胞定位中的作用略高于牛乳乳清蛋白。在分子功能上酶抑制活性作用是牛初乳乳清蛋白和牛乳中乳清蛋白的主要分子功能。在细胞组成上牛初乳乳清蛋白参与较多的是细胞外部分和细胞外空隙,与牛乳乳清蛋白相比参与的细胞组成大体相同。通过KEGG代谢通路分析可知,牛初乳和牛乳乳清蛋白均参与过补体及凝血级联反应通路。对牛初乳乳清蛋白组成进行研究,不仅能够增加牛初乳的利用率,并且为日后以乳清蛋白作为原料生产乳制品提供理论依据。     

Delactosed permeate as a dairy processing co-product with major potential value: a review

Delactosed permeate (DLP) is the co-product generated during the separation of pre-crystallised lactose from milk and whey permeates. DLP production has grown with the increased production of high protein content ingredients such as whey protein concentrates and isolates. Although DLP is nutritionally rich, with approximately 0.5–1.5, 68–70, 9–10 and 8–9 g/100 g dry matter of protein, total sugars, total mineral and organic acids, respectively, it is still currently underutilised, mostly for animal feed or energy production. There are a number of novel, promising and sustainable DLP-derived food and non-food applications which are the subject of current research. Therefore, there exists the opportunity to exploit this dairy co-product in the development of new value-added ingredients. In this comprehensive review, DLP production, processing challenges and potential applications are discussed, along with identification and assessment of selected strategies for the valorisation of DLP.     

Leveraging endogenous barley enzymes to turn lactose-containing dairy by-products into fermentable adjuncts for Saccharomyces cerevisiae-based ethanol fermentations

Acid whey, a by-product of strained yogurt production, represents a disposal challenge for the dairy industry. Utilization schemes are currently limited; however, acid whey contains valuable components that could be used to create value-added products. One potential scheme would be the fermentation of acid whey into an alcoholic beverage. Sour beers are gaining popularity and acid whey, which is sour to begin with, could provide a new product opportunity. However, the main sugar of acid whey, lactose, cannot be fermented by the traditional brewer's yeast, Saccharomyces cerevisiae. It has been reported that barley contains enzymes capable of hydrolyzing lactose to glucose and galactose, which are fermentable by S. cerevisiae. We investigated whether a barley-based mash resulted in detectable hydrolysis of lactose into sugars fermentable by S. cerevisiae. We demonstrated the ability to hydrolyze lactose in acid whey using a barley-based mash, resulting in the average release of 3.70 g/L of glucose. Additionally, the subsequent liquid was fermented by S. cerevisiae to an average ethanol concentration of 3.23% alcohol by volume. This work demonstrates the ability to hydrolyze the lactose in acid whey using barley and the opportunity to use acid whey as a fermentable sugar source in beer production.     

Carbohydrate Composition of Winged Bean (Psophocarpus tetragonolobus)

The carbohydrate composition of winged bean has been studied. The seeds contain about 42.2% total carbohydrates of which starch alone accounts for 36.2%. The total monosaccharides constituted 2.7% and were identified as glucose (1.17%) and fructose (1.5%); oligosaccharides amounted to only 0.61% and were identified as sucrose, raffinose, stachyose, and verbascose, on a dry defatted basis. The cold water soluble gum of winged bean contains glucose and xylose as the major sugars together with a small amount of arabinose while hot water soluble gum was found to be a glucantype polymer. Hemicellulose A consisted of glucose, xylose, and arabinose (15.5:9:1) whereas hemicellulose B consisted exclusively of glucose indicating that it is also a glucan-type polymer.     

Changes in Starch and Other Carbohydrates in Baking Ipomoea batatas

“Sweet potato” (var. Jersey) and “Yam” (var. Garnet) are mealy (dry) and soggy (moist) varieties, respectively, of Ipomoea batatas Poir. (Convolvulaceae). The raw fleshy roots of both varieties have essentially similar quantities of all measured variables except for cellulose, hemicelluloses, and amylose. On baking, only the amounts of non-reducing sugars and possibly cellulose appear unchanged, while the reducing sugars increase markedly in both varieties, with those of the yam far exceeding those of the sweet potato. The yam's starch content (particularly the amylose fraction) falls faster and to a lower level; its water-soluble pectin content increases; and its hemicellulose content is particularly decreased. Scanning electron microscopy (SEM) showed that the cell walls of the raw fleshy roots of both varieties are coated with long parallel fibrils, 0.25–1.5 μm in diameter, which appear to be hemicellulosic.     

Distribution of aflatoxin M1 in cheese obtained from milk artificially contaminated

Small-scale manufacture of cheese using artificially AFM1 contaminated milk as raw material to study the distribution of such toxin both in whey and in cheese, was carried out. Whole milk with undetectable levels of AFM1 was used. The toxin was added in concentration that varied from 1.7 to 2.0 microg/l of milk. After the home-made production of cheese, the concentration of AFM1 was determined both in whey and in cheese, using the enzymatic immunoassay technique. The greatest proportion, 60%, was detected in whey while 40% AFM1 remained in cheese.     

水预水解提取半纤维素对碱法桉木浆H_2O_2漂白的影响

由水预水解提取半纤维素后的桉木片和原木片分别通过烧碱-蒽醌法和硫酸盐法蒸煮获得4组浆料,分析了浆料中铜、锰、铁含量,比较了不同条件H_2O_2漂白后的浆料白度及H_2O_2消耗.研究结果表明,水顶水解提取半纤维素的木片,其碱法浆在H_2O_2漂白中的可漂性明显提高,相同漂白条件下浆料白度提高了4-7个白度单位,漂至相同白度时H_2O_2的消耗量明显降低.木片的水预水解使其碱法浆中的Cu、Mn含量明显降低.对浆料进行漂前预处理使4种浆料样品中的金属元素含量处于相近水平,但相同条件下H_2O_2漂白后白度有明显差别.     

HPLC sugar profiles of Algerian honeys

Sugar profiles of fifty honey samples from different regions of Algeria are analysed by HPLC with pulsed amperometric detection. These samples consisted of 25 multifloral and 25 unifloral honeys. Eleven sugars (two monosaccharides, nine oligosaccharides) are quantified. The mean values of fructose and glucose are in the range 35.99–42.57% and 24.63–35.06%, respectively. These monosaccharides are the main sugars of all honey samples. The sucrose, maltose, isomaltose, turanose and erlose are present nearly in all the samples, while raffinose and melezitose are detected in few samples. Furthermore, trehalose is present only in two samples and none of the samples contain melibiose. Low amounts of melezitose, raffinose and erlose are present in the range of 0.03–2.14%, 0.03–0.35% and 0.01–2.35%, respectively. PCA (Principal Component Analysis) showed that the cumulative variance was approximately 40% and Apiaceae honeys are correctly classified using FDA (Factorial Discriminant Analysis).     

Protein profile of dairy products: Simultaneous quantification of twenty bovine milk proteins

While proteomic techniques allow the identification and relative quantification of thousands of proteins in a single run, methods for absolute quantification remain laborious. In this study, a newly developed multiple reaction monitoring (MRM) method using liquid chromatography mass spectrometry (LC-MS) that enables the simultaneous quantification of twenty key milk proteins is presented. The selected proteins comprise all individual caseins, the major whey proteins and most well-known milk fat globule membrane (MFGM) proteins. For validation, the twenty milk proteins in raw milk, raw cream, raw milk Emmental cheese and whey, were quantified as well as in eighteen commercial heat-treated dairy products. The method presented is ideally suited for various applications, for example, the comparison of the protein patterns in raw milk of cows at different stages of lactation or of different breeds.     

Utilization of Whey and Grape Must for Citric Acid Production by Two Yarrowia lipolytica Strains

In this study, utilization of whey and grape must were investigated for citric acid production using Yarrowia lipolytica NBRC 1658 and a domestic strain Y. lipolytica 57. In addition to its use as a sole nutrient source, whey was also fortified with glucose or fructose as well as other nutrients. The best results for citric acid production were obtained in the medium containing whey supplemented with fructose. Maximum citric acid concentrations in this medium were 49.23 and 32.65 g/L for the domestic and NBRC 1658 strains, respectively. In grape must, maximum citric acid concentrations obtained using domestic and NBRC 1658 strains were 32.09 and 10.39 g/L, respectively. Both of the natural nutrient sources were found to be promising for utilization in citric acid production process. A domestic Turkish yeast strain was confirmed to be superior for citric acid production for the first time. This can be targeted for enhancing citric acid production efficiencies from locally available substrates such as whey or grape must.