Spoilage potential of psychrotrophic bacteria isolated from raw milk and the thermo-stability of their enzymes

The storage and transportation of raw milk at low temperatures promote the growth of psychrotrophic bacteria and the production of thermo-stable enzymes, which pose great threats to the quality and shelf-life of dairy products. Though many studies have been carried out on the spoilage potential of psychrotrophic bacteria and the thermo-stabUities of the enzymes they produce, further detailed studies are needed to devise an effective strategy to avoid dairy spoilage. The purpose of this study was to explore the spoilage potential of psychrotrophic bacteria from Chinese raw milk samples at both room temperature （28 ℃） and refrigerated temperature （7 ℃）. Species of Yersinia, Pseudomonas, Serratia, and Chryseobacterium showed high proteolytic activity. The highest proteolytic activity was shown by Yersinia intermedia followed by Pseudomonas fluorescens （d）. Lipolytic activity was high in isolates of Acinetobacter, and the highest in Acinetobacter guillouiae. Certain isolates showed positive ^-galactosidase and phospholipase activity. Strains belonging to the same species sometimes showed markedly different phenotypic characteristics. Proteases and lipases produced by psychrotrophic bacteria retained activity after heat treatment at 70, 80, or 90 ℃, and proteases appeared to be more heat-stable than lipases. For these reasons, thermo-stable spoilage enzymes produced by a high number of psychrotrophic bacterial isolates from raw milk are of major concern to the dairy industry. The results of this study provide valuable data about the spoilage potential of bacterial strains in raw milk and the thermal resistance of the enzymes they produce.

Purification and characterization of manganese peroxidases from native and mutant Trametes versicolor IBL-04

Extracellular manganese peroxidases （MnPs） produced by native and mutant strains of Trametes versicolor IBL‐04 （EB‐60, EMS‐90） were purified by ammonium sulphate precipitation and dialysis, followed by ion‐exchange and gel‐permeation chromatography. The purified enzymes elucidated a single band in the 43‐kDa region on sodium dodecyl sulphate‐polyacrylamide gel electrophoresis. The optimum pH and temperature of the purified enzymes were found to be 5.0 and 40 °C, respec‐tively. Mutant strain MnPs exhibited a broader active pH range and higher thermal stability than native MnP. Purified MnPs from selected mutants showed almost identical properties to native MnP in electrophoresis, steady‐state kinetics, and metal ion and endocrine‐disrupting compound （EDC） degradation efficiency. Although the fastest reaction rates occurred with Mn2＋, MnPs displayed the highest affinity for ABTS, methoxyhydroquinone, 4‐aminophenol and reactive dyes. MnP activity was significantly enhanced by Mn2＋and Cu2＋, and inhibited in the presence of Zn2＋, Fe2＋, ethylene‐diaminetetraacetic acid and cysteine to various extents, with Hg2＋ as the most potent inhibitory agent. MnPs from all sources efficiently catalyzed the degradation of the EDCs, nonylphenol and triclosan, removing over 80%after 3 h of treatment, which was further increased up to 90%in the presence of MnP‐mediator system. The properties of T. versicolor MnPs, such as high pH and ther‐mal stability, as well as unique Michaelis‐Menten kinetic parameters and high EDC elimination effi‐ciency, render them promising candidates for industrial exploitation.

Synthesis and Crystal Structure of a Novel Ca(Ⅱ) Coordination Polymer Containing Dipyridine Dicarboxylic Ligand

The novel alkaline metal complex Ca（BPDCH）2 （1, BPDCH2 = 2,2＇-bipyri- dine-5,5＇-dicarboxylic acid） has been synthesized by the hydrothermal reaction of Ca（NO3）2·4H2O with 2,2＇-bipyridine-5,5＇-dicarboxylic acid. The molecular and crystal structures of complex 1 have firstly been characterized by FTIR, elemental analysis, and X-ray single-crystal diffraction. The 3D MOF structure of complex 1 was interpreted by the versatile binding modes-the intermolecular hydrogen bonds and π-π stacking interactions of 2,2＇-bipyridine-5,5＇-dicarboxylic acid ligand. The analysis results show complex 1 belongs to a coordination polymer with 3D MOF structure. The results of thermogravimetric analysis and solubility demonstrate complex 1 is a thermostable compound and does not dissolve in water and traditional organic solvents.

Evaluation of Efficacy of Stabilizers on the Thermostability of Live Attenuated Thermo-adapted Peste des petits ruminants Vaccines

In this study, thermo-adapted （Ta） PPR vaccines were assessed for their stability at 25, 37, 40, 42 and 45℃ in lyophilized form using two extrinsic stabilizers {lactalbumin hydrolysate-sucrose （LS） and stabilizer E} and in reconstituted form with the diluents （1 mol/L MgSO4 or 0.85% NaC1）. The lyophilized vaccines showed an expiry period of 24-26 days at 25℃, 7-8 days at 37℃ and 3-4 days at 40℃. LS stabilizer was superior at 42℃ with a shelf-life of 44 h, whereas in stabilizer E, a 40 h shelf-life with a comparable half-life was observed. At 45 ℃, the half-life in stabilizer E was better than LS and lasted for 1 day. Furthermore, the reconstituted vaccine maintained the titre for 48 h both at 4℃ and 25℃ and for 24-30 h at 37℃. As both the stabilizers performed equally well with regard to shelf-life and half-life, the present study suggests LS as stabilizer as a choice for lyophilization with 0.85% NaCldiluent, because it has better performance at higher temperature. These Ta vaccines can be used as alternatives to existing vaccines for the control of the disease in tropical countries as they are effective in avoiding vaccination failure due to the breakdown in cold-chain maintenance, as this vaccine is considerably more stable at ambient temperatures.

Thermal Studies of Commercial Low Calorie Sweeteners

This paper presents the thermal analysis of artificial sweeteners, and natural sugar substitutes. Thermal analysis was done on commercial compositions of sweeteners using simultaneous DSC/TGA (SDT). Heat flow, and mass vs. temperature and time thermograms, along with DSC peak enthalpies and transition temperatures are reported. A number of the sweeteners were found to undergo transitions and reactions before or at 190°C (375°F, normal baking temperatures) and all dextrose containing sweeteners show an endothermic peak around 80°C due to the liberation of bound water molecules. The major components of sweeteners studied were found to be generally thermostable at or below 100°C.

Synthesis and characterization of biodegradable thermoplastic elastomers derived from N.N-bis （2-carboxyethyl）-pyromellitimide, poly（butylene succinate） and polyethylene glycol

Abstract Biodegradable poly（ether-imide-ester） elasto- mers were synthesized from succinic acid, 1,4-butanediol, polyethylene glycol 1000 and N＇,N-bis（2-carboxyethyl）- pyromellitimide which was derived from pyromellitic dianhydride and glycine. The chemical structures, crystal- linities, thermal stabilities, mechanical properties, hydro- philicities and biodegradabilities of these elastomers were investigated. The hard segments of the linear aliphatic poly （ether-ester） exhibited monoclinic chain packing. Increas- ing the amount of aromatic bisimide moieties in the poly （ether-ester） reduced the crystallinity of the material and improved the thermal stability and tensile strength of the elastomers. In addition, introducing a suitable amount of aromatic bisimide moieties into the poly（ether-ester） backbones endowed the elastomers with improved biode- gradability but too many aromatic bisimide groups reduced the biodegradability of the elastomers.