Home About us Contact
|
Home About us Contact | ||
|
|
||
Heat Inactivation (heat + inactivation)
Selected AbstractsPolyphenol Oxidase from Bean Sprouts (Glycine max L.)JOURNAL OF FOOD SCIENCE, Issue 1 2003T. Nagai ABSTRACT: Polyphenol oxidase (PPO) was purified and characterized from bean sprouts by ammonium sulfate precipitation, DEAE-Toyopearl 650M, CM-Toyopearl 650M, SuperQ-Toyopearl 650S and QAE-Toyopearl 550C column chromatographies. Substrate staining of the crude extract on electrophoresis showed the presence of 2 isozymic forms of this enzyme. The molecular weight of the purified enzyme was estimated to be about 54 kDa. The optimum pH was 9.0 and optimum temperature 40 °C. Heat inactivation occurred about 30 °C. PPO showed activity to catechol, pyrogallol and dopamine. These compounds such as ascorbic acid, L-cysteine, 2-mercaptoethanol, and glutathione used was the effective inhibitor. Enzyme activity was maintained for 7 d at 4 °C but suddenly decreased after 8 d. [source] Transformation of 2,4,6-trinitrotoluene in soil in the presence of the earthworm Eisenia andrei,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2000Agnès Y. Renoux Abstract The ability of the earthworm Eisenia andrei to metabolize 2,4,6-trinitrotoluene (TNT) was studied in experiments with TNT-spiked soils, dermal contact tests, and with an in vitro assay. Lethality of TNT in a forest sandy soil was first determined (14-d LC50 = 143 mg/kg). Then TNT at lethal and sublethal concentrations was applied to the same soil and was monitored along with its metabolites in extracts of soil and earthworm tissue for up to 14 d postapplication. High performance liquid chromatography-ultra violet analyses indicated that TNT was transformed in the presence of E. andrei by a reductive pathway to 2-amino-4,6-dinitrotoluene (2-ADNT), 4-amino-2,6-dinitrotoluene (4-ADNT), 2,4-diamino-6-nitrotoluene (2,4-DANT), and traces of 2,6-di-amino-4-nitrotoluene (2,6-DANT) in earthworm tissues. This transformation could be explained by either a metabolic mechanism within the earthworm or by the enhancement of an earthworm-associated microbial activity or both. The TNT concentrations decreased from the spiked soils. However, the monoamino-dinitrotoluene (2-ADNT and 4-ADNT) concentrations increased with exposure duration and were dependent on the initial TNT soil concentrations. This was also observed to a lesser extent in the TNT-spiked soils with no earthworms present. The biotransformation of TNT into 2-ADNT, 4-ADNT, and 2,4-DANT and the presence of these metabolites in E. andrei after dermal contact on TNT-spiked filter paper showed that dermal uptake can be a significant exposure route for TNT. In vitro experiments showed that earthworm homogenate could metabolize TNT and form 2-ADNT and 4-ADNT at room temperature and at 37°C. This effect was inhibited by heat inactivation prior to incubation or by incubation at 4°C, suggesting that the biotransformation of TNT in the presence of E. andrei may be enzymatic in nature. [source] ,- d -Mannopyranosyl-(1,2)-,- d -glucopyranosyl-(1,2)-glycerate in the thermophilic bacterium Petrotoga miotherma , structure, cellular content and functionFEBS JOURNAL, Issue 12 2007Carla D. Jorge The intracellular accumulation of low molecular mass organic compounds in response to stressful conditions was investigated in the thermophilic bacterium Petrotoga miotherma, a member of the order Thermotogales. This led to the discovery of a new solute, whose structure was established as ,- d -mannopyranosyl-(1,2)-,- d -glucopyranosyl-(1,2)-glycerate (MGG) by MMR spectroscopy and MS. Under optimum growth conditions (3% NaCl; 55 °C), MGG was the major solute [up to 0.6 µmol·(mg protein),1]; ,-glutamate and proline were also present but in minor amounts [below 0.08 µmol·(mg protein),1]. The level of MGG increased notably with the salinity of the growth medium up to the optimum NaCl concentration. At higher NaCl concentrations, however, the level of MGG decreased, whereas the levels of proline and ,-glutamate increased about five-fold and 10-fold, respectively. MGG plays a role during low-level osmotic adaptation of Petrotoga miotherma, whereas ,-glutamate and, to a lesser extent, proline are used for osmoprotection under salt stress. MGG is not part of the cell strategy for coping with heat or oxidative stress. Nevertheless, MGG was an efficient protector of pig heart malate dehydrogenase against heat inactivation and freeze-drying, although mannosylglycerate was better. This is the first report on the occurrence of MGG in living systems. [source] Some properties of polyphenol oxidase from lilyINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2008Ying Yang Summary A study of crude polyphenol oxidase (PPO) from lily bulbs was carried out to provide information useful for guiding food processing operations. Optimum pH for the enzyme activity in the presence of catechol, were 4.0 and 7.0 at room temperature(approximately 20 °C) and the enzyme was stable in the pH range from 5.0 to 6.5 at 4 °C for 10 h. Its optimum temperature was 40 °C and the heat inactivation of the enzyme followed first-order kinetics. Lily PPO possessed a diphenolase activity toward catechol, catechin and gallic acid; catechin was the best substrate for the enzyme considering the Vmax/Km ratio. The most effective enzyme inhibitor was sodium sulphite, although ascorbic acid, l -cysteine and thiourea were also effective inhibitors at high concentration. But NaCl and citric acid were poor inhibitors of the enzyme. Data generated by this study might help to better prevent lily bulbs browning. [source] History of science , sporesJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2006Lewis B Perry Memorial Lecture 200 Abstract Bacterial endospores were first studied 130 years ago by Cohn in 1876 and independently by Koch in the same year. Although spore dormancy and resistance have been much studied since then, questions still remain concerning the basic mechanisms and the kinetics of heat inactivation in particular. Likewise, the extreme dormancy and longevity of spores was recognized early on and later greatly extended but still evade complete understanding. Evidence has accumulated for the involvement of specific spore components such as calcium, dipicolinic acid, small acid soluble proteins in the core and peptidoglycan in the cortex. Involvement of physical factors too, such as the relative dehydration of the core, maybe in a high-viscosity state or even in a glassy state, has added to appreciation of the multicomponent nature of dormancy and resistance. Spore-former morphology formed the basis for early classification systems of sporeformers from about 1880 and consolidated in the mid-1900s, well prior to the use of modern genetic procedures. With respect to sporulation, groundbreaking sequence studies in the 1950s provided the basis for later elucidation of the genetic control widely relevant to many cell differentiation mechanisms. With respect to the breaking of dormancy (activation and germination), the elucidation of mechanisms began in the 1940s following the observations of Hills at Porton who identified specific amino acid and riboside ,germinants', and laid the basis for the later genetic analyses, the identification of germinant receptor genes and the elucidation of key germination reactions. The nonexponential nature of germination kinetics has thwarted the development of practical Tyndallization-like processing. So inactivation by heat remains the premier method of spore control, the basis of a huge worldwide industry, and still relying on the basic kinetics of inactivation of Clostridium botulinum spores, and the reasoning regarding safety first evolved by Bigelow et al. in 1920 and Esty and Meyer in 1922. ,Newer' processes such as treatment with ionizing radiation (first proposed in 1905) and high hydrostatic pressure (first proposed in 1899) may be introduced if consumer resistance and some remaining technical barriers could be overcome. [source] Characterization of Honey AmylaseJOURNAL OF FOOD SCIENCE, Issue 1 2007Sibel Babacan ABSTRACT:, The major ,-amylase in honey was characterized. The optimum pH range and temperature were determined for the enzyme as 4.6 to 5.3 and 55 °C, respectively. The enzyme was stable at pH values from 7 to 8. The half-lives of the purified enzyme at different temperatures were determined. The activation energy for heat inactivation of honey amylase was 114.6 kJ/mol. The enzyme exhibited Michaelis,Menten kinetics with soluble starch and gave KM and Vmax values of 0.72 mg/mL and 0.018 units/mL, respectively. The enzyme was inhibited by CuCl (34.3%), MgCl2 (22.4%), and HgCl2 (13.4%), while CaCl2, MnCl2, and ZnSO4 did not have any effect. Starch had a protective effect on thermal stability of honey amylase. Therefore, it might be critical to process or control the amylase in honey before incorporation into starch-containing foods to aid in the preservation of starch functionality. One step could involve heat treating honey with other ingredients, especially those that dilute and acidify the honey environment. [source] Mathematical modelling of the heat inactivation of trypsin inhibitors in soymilk at 121,154,°CJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2002Kin-Chor Kwok Abstract Response surface methodology (RSM) was used to investigate the effects of processing temperature and time on the inactivation of trypsin inhibitors (TI) in soymilk. The factorial experimental design consisted of four levels of temperature and six levels of time in a temperature range of 121,154,°C and a time interval of 10,90,s. A quadratic polynomial equation, relating log(% TI retained) as a function of heating time and temperature, was satisfactorily fitted to the experimental data by least squares regression with r2 (correlationcoefficient),=,0.959. Within the range of heating times investigated, TI in soymilk was satisfactorily destroyed to 10% retained at 143 and 154,°C with 62 and 29,s heating time respectively. © 2002 Society of Chemical Industry [source] Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and the mesophilic alga Chlorella sorokinianaPLANT CELL & ENVIRONMENT, Issue 7 2006VITTORIA DI MARTINO RIGANO ABSTRACT Temperature responses of nitrate reductase (NR) were studied in the psychrophilic unicellular alga, Koliella antarctica, and in the mesophilic species, Chlorella sorokiniana. Enzymes from both species were purified to near homogeneity by Blue Sepharose (Pharmacia, Uppsala, Sweden) affinity chromatography and high-resolution anion-exchange chromatography (MonoQ; Pharmacia; Uppsala, Sweden). Both enzymes have a subunit molecular mass of 100 kDa, and K. antarctica NR has a native molecular mass of 367 kDa. NR from K. antarctica used both NADPH and NADH, whereas NR from C. sorokiniana used NADH only. Both NRs used reduced methyl viologen (MVH) or benzyl viologen (BVH). In crude extracts, maximal NADH and MVH-dependent activities of cryophilic NR were found at 15 and 35 °C, respectively, and retained 77 and 62% of maximal activity, respectively, at 10 °C. Maximal NADH and MVH-dependent activities of mesophilic NR, however, were found at 25 and 45 °C, respectively, with only 33 and 23% of maximal activities being retained at 10 °C. In presence of 2 µm flavin adenine dinucleotide (FAD), activities of cryophilic NADH:NR and mesophilic NADH:NR were stable up to 25 and 35 °C, respectively. Arrhenius plots constructed with cryophilic and mesophilic MVH:NR rate constants, in both presence or absence of FAD, showed break points at 15 and 25 °C, respectively. Essentially, similar results were obtained for purified enzymes and for activities measured in crude extracts. Factors by which the rate increases by raising temperature 10 °C (Q10) and apparent activation energy (Ea) values for NADH and MVH activities measured in enzyme preparations without added FAD differed slightly from those measured with FAD. Overall thermal features of the NADH and MVH activities of the cryophilic NR, including optimal temperatures, heat inactivation (with/without added FAD) and break-point temperature in Arrhenius plots, are all shifted by about 10 °C towards lower temperatures than those of the mesophilic enzyme. Transfer of electrons from NADH to nitrate occurs via all three redox centres within NR molecule, whereas transfer from MVH requires Mo-pterin prosthetic group only; therefore, our results strongly suggest that structural modification(s) for cold adaptation affect thermodynamic properties of each of the functional domains within NR holoenzyme in equal measure. [source] Immune complex-stimulated production of interleukin-12 in peripheral blood mononuclear cells is regulated by the complement systemCLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 3 2004A. TEJDE SUMMARY Immune complexes (IC) can induce cytokine production in vitro. While immune aggregates (IA) consisting of heat-aggregated gamma globulin (HAGG) as model IC increased interleukin (IL)-10 levels in cell cultures with native human serum, IL-12p40/p70 production was inhibited. Three series of experiments suggested that the effects of IA on IL-12 production depended on a functionally intact complement system: (1) heat-inactivation of serum inverted the inhibitory effect of IA on IL-12p40/p70 production; (2) IA-induced IL-12p40 production in a C4 deficient serum was lowered by addition of C4; and (3) addition of the peptide compstatin, which blocks C3 activation, mimicked the effects of heat inactivation on IL-12p40 levels. Neutralization of IL-12 resulted in modestly increased IL-10 levels, while neutralization of IL-10 had no effects on IL-12p40 production. IA-induced production of IL-10 was partially blocked by anti-Fc,,RII antibodies, whereas Fc,,R or CR blockade had no effect on IL-12p40 production. IC and local or systemic complement activation characterize rheumatoid arthritis, systemic lupus erythematosus and many malignancies. Different and complement-dependent effects on the production of IL-10 and IL-12 can be of importance in these diseases, where control of the complement system might be a way to direct IC-induced cytokine production in either a type 1 or type 2 direction. [source] | |||||||||||||