Yongjun Qiu

Expression and characterization of a novel cold-adapted chitosanase suitable for chitooligosaccharides controllable preparation

Chitooligosaccharide is widely used as a functional food additive and a valuable pharmacological agent. The transformation of chitinous biomass into valuable bioactive chitooligosaccharides is one of the most exciting applications of chitosanase. A novel glycoside hydrolase (GH) family 46 chitosanase (GsCsn46A) from rhizobacterium Gynuella sunshinyii was cloned and heterologously expressed in Escherichia coli. GsCsn46A showed maximal activity at pH 5.5 and 30 °C. GsCsn46A featured remarkable cold-adapted property, which controllably hydrolyzed chitosan to three types of chitooligosaccharides at the mild reaction condition (reaction condition: pH 5.5 at 30 °C; method for stopping the reaction: 50 °C for 30 min). The yields of three types of chitooligosaccharides products (degree of polymerization (DP): 2-7, 2-5 and 2-3) were 70.9%, 87.1% and 94.6% respectively. This novel cold-adapted chitosanase provides a cleaner production process for the controllable preparation of chitooligosaccharides with the specific DP.

Kinetics and equilibria of the chromatographic separation of maltose and trehalose

Trehalose, a nonreducing disaccharide, has been extensively applied to food, cosmetics, and pharmaceutical goods. The resultant solution of trehalose prepared by enzymatic methods includes high amounts of maltose. However, it is quite difficult to separate maltose and trehalose on an industrial scale because of their similar properties. In this paper, a high-performance resin was selected as a stationary phase to separate trehalose and maltose, and the resolution of these sugars was 0.59. The potential of a cation exchange resin was investigated as the stationary phase in separating trehalose and maltose using deionized water as the mobile phase. Based on the equilibrium dispersive model, the axial dispersion coefficients and overall mass transfer coefficients of maltose and trehalose were determined by moment analysis at two different temperatures, 50 and 70°C. Other parameters, including the column void and the adsorption isotherms, were also determined and applied to simulate the elution curves of trehalose and maltose. The simulated results matched the experimental data, validating the parameters. The optimized parameters are critical to the chromatographic separation of trehalose and maltose on an industrial scale.

Recovery of beta-Amylase by Hybrid UF Membranes from the Soy Whey Wastewater

Large-scale manufacturing of soybean proteins results in huge volume of “wastewater” which contains substantial amount of β-amylase, and the recovery of β-amylase has potential high value. In order to evaluate the feasibility and effect of novel hybrid Ultrafiltration (UF) method against the normal method, the pretreated effluent was concentrated by a low molecular weight cut off (MWCO) 3 kDa UF membrane firstly, terminated at Volume Concentration Ratio (VCR) of ca.7. To this UF retentate was then precipitated by adding 1.2M (NH4)2SO4 to remove other proteins. The supernatant obtained following centrifugation was purified through a further higher 30 kDa MWCO UF membrane, which ended at VCR of ca.10. The prepared was purified 4.8 fold, with an enzyme activity concentration ratio of 61, and is associated with 74% combined recovery for the enzyme activity, giving a final specific activity of 14 U/mg (674 U/mL), of which enzyme activity is fully enough for the industrial applications. Preliminary data of this research indicate that this could be an effective method for treating kinds of related protein wastewaters.

Increasing thermal stability of glutamate decarboxylase from Escherichia. coli by site-directed saturation mutagenesis and its application in GABA production

Gamma-amino butyric acid (GABA) is an important bio-product used in pharmaceuticals, functional foods, and a precursor of the biodegradable plastic polyamide 4 (Nylon 4). Glutamate decarboxylase B (GadB) from Escherichia. coli is a highly active biocatalyst that can convert l-glutamate to GABA. However, its practical application is limited by the poor thermostability and only active under acidic conditions of GadB. In this study, we performed site-directed saturation mutagenesis of the N-terminal residues of GadB from Escherichia coli to improve its thermostability. A triple mutant (M6, Gln5Ile/Val6Asp/Thr7Gln) showed higher thermostability, with a 5.6 times (560%) increase in half-life value at 45 °C, 8.7 °C rise in melting temperature (Tm) and a 14.3 °C rise in the temperature at which 50% of the initial activity remained after 15 min incubation (T1550), compared to wild-type enzyme. Protein 3D structure analysis showed that the induced new hydrogen bonds in the same polypeptide chain or between polypeptide chains in E. coli GadB homo-hexamer may be responsible for the improved thermostability. Increased thermostability contributed to increased GABA conversion ability. After 12 h conversion of 3 mol/L l-glutamate, GABA produced and mole conversion rate catalyzed by M6 whole cells was 297 g/L and 95%, respectively, while those by wild-type GAD was 273.5 g/L and 86.2%, respectively.

Physicochemical Characteristics of Edible Bird’s Nest Proteins and Their Cooking Processing Properties

Abstract Edible bird’s nest (EBN) has a high nutritional and medicinal value. In this study, physicochemical and processing properties of EBN proteins were investigated for better application of EBN. EBN proteins were extracted by combination of several methods. Electrophoresis showed that EBN contained proteins with molecular weight of 128, 106, 80, 55, 43, and 34 kDa. The denaturation temperature of EBN proteins was 62.5°C and heating promoted hydrophobicity as well as dramatically affecting the gel microstructure of EBN proteins. EBN proteins also showed excellent emulsifying activity and stability while their foaming properties were not good enough.

Cronobacter spp., foodborne pathogens threatening neonates and infants

Cronobacter spp. (formerly Enterobacter sakazakii) are special foodborne pathogens. Cronobacter infection can cause necrotizing enterocolitis, sepsis and meningitis in all age groups, especially neonates and infants, with a high fatality of up to 80%, although the infection is rare. Outbreaks of Cronobacter infection are epidemiologically proven to be associated with contaminated powdered infant formula (PIF). Cronobacter spp. can resist dry environments and survive for a long period in food with low water activity. Therefore, Cronobacter spp. have become serious pathogens of neonates and infants, as well as in the dairy industry. In this review, we present the taxonomy, pathogenesis, resistance, detection and control of Cronobacter spp.

Interactions of γ-aminobutyric acid and whey proteins/caseins during fortified milk production

The potential interactions between milk proteins (whey proteins and caseins) and γ-aminobutyric acid (GABA), alone and in combination, and the physiochemical properties of GABA-fortified milk were investigated in the present study. After mixing 0.05–1.0% (w/w, based on the solution) GABA with 0.6% (w/v) whey proteins and with 2.6% (w/v) caseins, sequential preheating (60 °C), homogenization (20 MPa), and pasteurization (72 °C for 15 s and 138 °C for 2 s) processes were used to simulate practical processing conditions for GABA-fortified milk production. GABA mainly cross-linked β-lactoglobulin (but had no remarkable cross-linking effect on caseins), adducted with α-lactalbumin and αs1-casein fractions (not excluding other fractions in whey proteins/caseins) via the amide linkage under the sequential processing conditions, which was confirmed by electrophoresis, mass spectroscopy, and amino acid composition analysis. Characterization of the physiochemical properties (protein solubility, relative surface hydrophobicity, ζ-potential, particle size, and fluorescence intensity) of the GABA-fortified protein solutions substantiated the presence of the cross-links and adduction reactions. In addition, GABA tended to form its dimer, trimer (line-like structure) and 3–8 membered ring structure oligomers. The interaction between GABA and whey proteins/caseins provides insight into the evaluation of the food quality and chemical safety (due to protein/GABA derivatives) of GABA-fortified milk.