Degradation of N‐(1‐Deoxy‐d‐xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐xylulos‐1‐yl)proline using thermal treatment

The formation and degradation of N‐(1‐Deoxy‐d ‐xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d ‐xylulos‐1‐yl)proline, derived from the secondary amine Maillard reaction in xylose‐amino acid model solutions, were detailed in this study. The identification and quantitative analysis of N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline were carried out using high‐performance anion‐exchange chromatography and high‐performance liquid chromatography. The formation of intermediate and advanced products derived from N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline was also tested using an UV‐Vis spectrophotometer to gain a better comparing of the degradation process of the two important Maillard reaction products using thermal treatment. Results showed that the degradation of N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine was more significant than N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline. Moreover, xylose was tested in the degradation products of both N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)glycine and N‐(1‐Deoxy‐d‐ xylulos‐1‐yl)proline, which indicated that the degradation of N‐substituted 1‐amino‐1‐deoxyketoses was a reversible reaction to form reducing sugar.     

Catalytic efficiency of immobilized glucose isomerase in isomerization of glucose to fructose

Glucose isomerase (GI) from Streptomycesrubiginosus was immobilized covalently onto Eupergit C 250 L made by copolymerization of N,N-methylene-bis-methacrylamide, glycidyl methacrylate, allyl glycidyl ether and methacrylamide. The catalytic efficiency of immobilized GI in isomerization of glucose to fructose was found as three fold higher than that of free GI. The residual activity of immobilized GI after 18 reuses in a batch type stirred reactor was about 85% of its initial activity. The thermal stability of immobilized GI was almost same with that of the free GI at 60 °C for 18 h preincubation time. The residual activities of immobilized GI when stored at 5 °C and 25 °C for four weeks were 72% and 69% of the initial activity, respectively. However, free GI retained 88% and 78% of its initial activity at 5 °C and 25 °C upon four weeks storage, respectively. Thus, the use of Eupergit C 250 L immobilized GI instead of free GI is suggested in enzymatic isomerization of glucose to fructose.     

d‐Mannose: Properties,Production, and Applications: An Overview

d ‐Mannose is a C‐2 epimer of d ‐glucose, which is a natural monosaccharide. It can be obtained from both plants and microorganisms. Chemical synthesis and biotransformation of d ‐mannose from d ‐fructose or d ‐glucose by using d ‐mannose isomerases, d ‐lyxose isomerases, and cellobiose 2‐epimerase were intensively studied. d ‐Mannose is an important component of polysaccharides and glycoproteins. It has been widely used in the food, pharmaceutical, and poultry industries, acting as the source of dietary supplements, starting material for the synthesis of drugs and blocking colonization in animal feeds. d ‐Mannose is a glyconutrient with high research value in basic science because of its structure and function. This article presents a review of current studies on sources, characteristics, production, and application of d ‐mannose.     

固定化葡萄糖异构酶活化条件对其酶活的影响

固定化葡萄糖异构酶在使用前需先进行活化,从而使酶发挥其最佳催化功效。本文从糖液浓度、温度、pH、活化时间和金属离子五个方面研究了活化条件对GENSWEETTMIGI-SA固定化葡萄糖异构酶酶活的影响。该酶的最适活化条件为:葡萄糖液浓度60%、温度55℃、pH7.5、时间4h。经此条件活化之后,其酶活达815U/g,与常规活化条件相比,酶活提高了40%以上。固定化葡萄糖异构酶活化时不宜加入Mg2+、Co2+、Mn2+和Zn2+。     

Partial characterization of β‐ d‐xylosidase from wheat malts

Arabinoxylans (AXs) from wheat malts potentially affect beer quality and production. β‐ d ‐Xylosidase is a key enzyme that degrades the main chains of AXs to produce xylose. This study performed a partial characterization of β‐ d ‐xylosidase from wheat malts. The optimal temperature was 70 °C and the enzyme exhibited excellent thermostability, that is, residual activities were 92.6% at 60 °C for 1 h. The enzyme was stable over a pH range of 3.0–6.0 and showed optimum activity at pH 3.5 and 4.5. Kinetic parameters K_m and V_max of wheat malt β‐ d ‐xylosidase against p‐nitrophenyl‐xyloside were 1.74 mmol L⁻¹ and 0.76 m m min⁻¹, respectively. The enzyme activity was severely inhibited by Cu²⁺, moderately inhibited by Mn²⁺, Mg²⁺, Al³⁺, Ca²⁺, Ba²⁺ and Na⁺ and mildly inhibited by Fe³⁺ and Fe²⁺. The partial enzymatic characterization achieved in this study can be used as a theoretical basis for purifying β‐ d ‐xylosidase from wheat malts. Copyright © 2015 The Institute of Brewing & Distilling     

Effect of d‐Psicose Used as Sucrose Replacer on the Characteristics of Meringue

Excessive intake of sugar‐rich foods leads to metabolic syndrome. d ‐Psicose (Psi) not commonly found in nature, is noncalorie sweetener with a suppressive effect on the blood glucose level. Thus, Psi has the potential to be utilized as a sucrose (Suc) replacer in sugar‐rich foods, including meringue‐based confectionery (MBC). In this study, we investigated the effect of Psi on the physical and chemical properties of meringue. Meringue was made by whipping egg white and Suc (at a weight ratio of 1:1) and baking at 93 °C for 2 h. Thirty percent of the total weight of Suc was replaced with d ‐ketohexoses such as Psi, d ‐fructose, d ‐tagatose, and d ‐sorbose. The meringues containing d ‐ketohexoses had higher specific volume than the meringue not containing d ‐ketohexoses (Ct‐meringue). Baking of meringue caused differences between Psi and the other d ‐ketohexose meringues. Meringue containing Psi (P30‐meringue) had the highest breaking stress (7.00 × 10⁵ N/m²) and breaking strain (4.40%), resulting in the crunchiest texture. In addition, P30‐meringue also had the highest antioxidant activity (491.84 μM TE/mg‐meringue determined by ABTS method) and was the brownest due to a Maillard reaction occurring during baking. The replacement of Suc with Psi improved the characteristics of baked meringue. Thus, Psi was found to be useful in modifying the physical and chemical properties of MBC.     

Sorption of ethyl acetate and d‐limonene in poly(lactide) polymers

Poly(lactide) (PLA) polymers have garnered increased attention in the last few years as food packaging materials because they are environmentally friendly polymers. As the production of PLA increases and price per pound drops, PLA is becoming a growing alternative as a green food packaging material. In this research, the organic vapor barrier properties of commercially available PLA polymers were studied. Gravimetric sorption tests in PLA films were carried out, and the diffusion (D), solubility (S) and permeability (P) coefficients for ethyl acetate and d‐limonene in PLA were determined. For ethyl acetate, values of P = 1.22 × 10^?17 kg m m^?2 s^?1 Pa^?1, D = 2.63 × 10^?15 m² s^?1, and S = 4.62 × 10^?3 kg m^?3 Pa^?1) at 45 °C and a partial pressure of 12 654 Pa were obtained. For d‐limonene, no trace was detected after 21 days of testing at 45 °C and 258 Pa, which indicates a permeability coefficient lower than 9.96 × 10^?21 kg m m^?2 s^?1 Pa^?1. Poly(lactide) polymers demonstrated good aroma barrier to ethyl acetate and d‐limonene, and will most likely be good aroma barriers. PLA is not likely to promote flavor loss by either permeation or scalping. Copyright © 2005 Society of Chemical Industry     

Glycyrrhetic Acid 3‐O‐Mono‐β‐d‐glucuronide (GAMG): An Innovative High‐Potency Sweetener with Improved Biological Activities

Glycyrrhetic acid 3‐O‐mono‐β‐d ‐glucuronide (GAMG) is an important derivative of glycyrrhizin (GL) and has attracted considerable attention, especially in the food and pharmaceutical industries, due to its natural high sweetness and strong biological activities. The biotransformation process is becoming an efficient route for GAMG production with the advantages of mild reaction conditions, environmentally friendly process, and high production efficiency. Recent studies showed that several β‐glucuronidases (β‐GUS) are key GAMG‐producing enzymes, displaying a high potential to convert GL directly into the more valuable GAMG and providing new insights into the generation of high‐value compounds. This review provides details of the structural properties, health benefits, and potential applications of GAMG. The progress in the development of the biotransformation processes and fermentation strategies to improve the yield of GAMG is also discussed. This work further summarizes recent advances in the enzymatic synthesis of GAMG using β‐GUS with emphasis on the physicochemical and biological properties, molecular modifications, and enzymatic strategies to improve β‐GUS biocatalytic efficiencies. This information contributes to a better framework to explore production and application of bioactive GAMG.     

Acidothermus cellulolyticus 11B葡萄糖异构酶基因的克隆、表达及酶活性研究

葡萄糖异构酶是生物法转化葡萄糖为果糖制备果葡糖浆的关键酶。本文克隆到一种葡萄糖异构酶基因xyl,来源于嗜酸耐热型微生物Acidothermus cellulolyticus 11B(ATCC43068)。以pET-22b(+)为载体质粒,E.coliBL21(DE3)为宿主细胞,构建了基因重组菌,IPTG可诱导目的重组葡萄糖异构酶过量表达;经亲和层析纯化的重组蛋白样品进行SDS-PAGE分析,在约43kDa处出现显著的特征蛋白条带;活性检测结果表明该重组葡萄糖异构酶具有较高的果糖转化活性。