Time-temperature Conditions Research Articles

Effect of time–temperature conditions and clarification on the total phenolics and antioxidant constituents of muscadine grape juice

Juices have lower quantities of total phenolics content (TPC), anthocyanins, and antioxidant compared to the whole fruit. Furthermore, only low levels of these compounds are extracted from fruit skins during the initial juice processing steps with the majority staying in the skins and seeds. Once the initial juicing starts, degradative reactions begin to convert endogenous polyphenols into new compounds. Even though temperature is the key factor which determines this degradation rate, there is limited information about the temperature at which it begins, and the effects of centrifuging particles before or after thermal processing. The objectives were, first to determine the effects of different time–temperature conditions on the TPC, and antioxidant activity; second, to assess both parameters when the juice was clarified before or after thermal processing. Processing conditions were: 50–80 °C, and 1–30 min as residence time. At temperatures greater than 60 °C, both parameters began to decrease. The optimum processing condition for greatest retention of both parameters was 60 °C and 30 min. TPC and antioxidant activity retention were significantly higher on the juice clarified after thermal processing, compared to the one clarified before. This information can help juice processors and equipment manufacturers to optimize their process and design.

Non-isothermal phenomena in Mo/Si diffusion couple: Reaction kinetics and structure formation

Macrokinetic features and mechanism of Mo-Si reaction in conditions of rapid heating on a single particle level (Mo/Si diffusion couple) were studied by high-speed scanning electrothermography. The experiments were conducted in the temperature-time conditions (T = 1000–1600°C, t = 0.01–3.0 s) comparable to those of combustion synthesis of molybdenum disilicide. The rates of chemical heat release (depending on the thickness of silicon layer, δSi) were measured and the processes of phase/structure formation were explored. Over a wide range of δSi, two-stage chemical heat release was associated with occurrence of solid-solid Mo(s) + Si(s) (for T TmpSi), where TmpSi stands for the melting point of Si. Proposed was a new mechanism for siliconization of Mo in non-isothermal conditions.

Low temperature degradation and reliability of one-piece ceramic oral implants with a porous surface

Low temperature degradation of zirconia (3Y-TZP) oral implants and its effect on fatigue reliability is poorly documented. ObjectiveThe aim of this investigation was to follow the aging process occurring at the surface of implants exhibiting a porous coating and to assess its influence on their mechanical (fatigue) properties. MethodsTetragonal to monoclinic transformation (t–m) was evaluated during accelerated aging tests up to 100h in autoclave (134°C, 2 bars) by X-ray diffraction (XRD) and focused ion beam (FIB). A series of implants were steam-aged for 20h before fatigue testing. Such temperature–time conditions would correspond roughly to 40 years in vivo. The aged specimens and a non-aged control group were step-stress fatigued until failure or survival. ResultsThe evolution of XRD surface monoclinic content was slow, i.e. 16% and 35% for 20 and 100h respectively. However, FIB revealed a significant transformation, initiated at the interface between the porous layer and the bulk, preferentially growing towards the bulk. FIB is therefore better indicated than XRD to follow aging in such implants. Higher average fatigue strength (aged 1235N versus non-aged 826N) and reliability levels were observed for the 20h aged group. SignificanceAfter aging for durations compatible with clinical use, 3Y-TZP with porous surface presented higher fatigue performance. This is in contrast to previous studies where loss of strength due to aging was often reported. Generalizations must therefore be avoided when considering aging of zirconia dental products and every new material/process combination should be tested before drawing conclusions.

Secondary microstructure and its effect on the functional properties of Mg–Mn–Zn–Ca–Fe–O ferrites

The paper examines the dependence of the secondary microstructure and electromagnetic parameters on the heat-treatment conditions of ferrite elements in the Mg–Mn–Zn–Ca–Fe–O system used in switching and logic elements. An optical microscope revealed dotted and netted secondary microstructures. The dotted structure is found in the samples sintered at 1603 K, quenched at 1273 K, and additionally annealed at 823 K. It is shown that annealing for up to 3 h increases the coercivity H, without degradation of the other parameters. This made it possible to increase the cyield of elements by a factor of 1.5 by increasing the Hc of rejected (because of low coercivity) elements. We developed a technique that provides equal temperature–time conditions for all annealed samples in a lot and allows controlling the yield of elements by periodically adjusting the annealing duration based on inspection of samples from inspection lots.

외부 운반 학교급식의 미생물학적 품질 평가

The purpose of this study was to provide a basic resource for establishment of hygienic management stand- ards for meal delivery from the central kitchen to schools. Flow diagrams for delivery of food were analyzed, and time-temperature conditions of the food and environment were measured. Four different foods samples in- cluding Mexican salad, radish salad, stir-fried pork and vegetables, and stir-fried chicken and vegetables were collected after production and before service. Microbiological analysis was performed for aerobic plate counts (APC), Enterobacteriaceae, coliforms, E. coli, Salmonella spp., S. aureus, B. cereus, C. perfringens, and L. monocytogenes. After completion of production of cooked foods 2∼3 hours were taken for the cooked foods to reach the temperature danger zone. Food temperatures at the meal service did not meet the recommended temperatures (10/57 o C) for conventional school food service systems. The highest APC counts were observed in radish salad (5.70 log CFU/g), followed by Mexican salad (5.18 log CFU/g). Enterobacteriaceae and coli- form counts were within acceptable levels of those recommended by the UK Public Health Laboratory Service. No E. coli or pathogens were found. These results provide useful information for determination of microbiological hazards in school food service systems, and suggest that time-temperature control during deliv- ery is necessary for the safety of cooked foods.

Modeling of flow and BOD fate in horizontal subsurface flow constructed wetlands

A numerical modeling effort of flow and Biochemical Oxygen Demand (BOD) fate in horizontal subsurface flow (HSF) constructed wetlands (CWs), under Mediterranean conditions, is presented. The Visual MODFLOW family computer code, based on the finite difference method, was used for the numerical simulation of flow in five pilot-scale HSF CW units containing various vegetation and porous material types, and operating under various temperature and hydraulic residence time (HRT) conditions. BOD fate and transport was simulated using the MT3DMS computer code. Experimental data from these CW units were used in estimating the BOD removal coefficient, required in the above modeling effort. Values of this removal coefficient were found to depend on temperature and HRT. Relations are presented for the prediction of this coefficient. The model was calibrated and verified using the measured BOD concentrations, and was used in test runs comparing performance under various vegetation, porous media size, temperature and HRT conditions. Model performance was found acceptable, indicating its usefulness in the simulation of BOD fate in CWs and in the design of these facilities.

Temperature and time behavior of the parameters of the domain structure of triglycine sulfate crystals near the phase transition

This paper reports on the results of the investigation into the temperature and time behavior of the parameters of the domain structure in nominally pure and doped (α-alanine, chromium, phosphorus) triglycine sulfate crystals, which has been revealed by piezoresponse force microscopy during observation of the domain structure. The relaxation time dependences on the total perimeter of the domain walls, the velocity of lateral domain-wall motion, and the coefficient of static unipolarity have been obtained using computer image processing of the domain structure of the crystals under investigation. The temperature dependences of these parameters near the Curie temperature have been found. A comparison with the data available in the literature has been made, as well as with the results of our measurements of the permittivity for the same samples and under the same temperature-time conditions.

Morphology and chemical composition of Cu/Sn/Cu and Cu(5 at-%Ni)/Sn/Cu(5at-%Ni) interconnections

In the present paper, scanning and transmission electron microscopies aswell as energy dispersive X-ray spectroscopy investigations were performedto describe the morphology and chemical composition of the intermetallic phasesgrowing in Cu/Sn/Cu and Cu(Ni)/Sn/Cu(Ni) interconnectionsduring the diffusion soldering process. The obtained results revealed thateven a small amount of Ni addition (5 at-%) to the Cu substratetotally changes the morphology and the rate of formation of the intermetallicphase layers in the solder/substrate reaction zone of the interconnectionsprepared at the same time and joining temperature conditions. The presentedstudies are promising in terms of the shortening of the soldering time inthe electronic industry.

Plant Pathogen Eradication During Composting: A Literature Review

The process of composting, when managed in such a way that adequate temperature conditions are achieved, can lead to significant reductions in the levels of many plant and human pathogens. When adequate pathogen reduction is achieved, it is possible to create a beneficial and safe product from waste materials that would otherwise be disposed of in a landfill or incinerator. Time and temperature conditions necessary for the eradication of various types of plant pathogens during composting were evaluated via a literature review. Varying time-temperature conditions have been suggested in the literature and by compost standards organizations in Europe to treat plant pathogens in compost. Literature data suggested conditions for the eradication of phytopathogens were compared with the time-temperatures specified by the Canadian Council of Ministers of the Environment (CCME) and US Environmental Protection Agency (USEPA) for human pathogens. Most bacterial plant pathogens and nematodes, and many fungi and fungus-like organisms (including the Oomycetes and Plasmodiophoromycetes) are likely to be eradicated if compost operations adhere to the human pathogen time-temperature guidelines set out by the CCME and USEPA. Other fungi and fungus-like phytopathogens, and a number of viruses are more heat resistant. Results in the literature have been inconsistent for some hardier species, with some studies showing eradication during composting and others finding that these same species were still viable in finished products. In general, most researchers agree that commercial-scale composting, if monitored and controlled properly, will likely eliminate most phytopathogens, with the exception of a few hardy viruses and fungi/fungus-like organisms such as tobacco mosaic virus, Fusarium oxysporum, and Plasmodiophora brassicae. The higher temperatures and longer exposure times suggested in European guidelines and standards are likely to be effective against a broader range of phytopathogens than the CCME and USEPA requirements. Phytopathogen inactivation in composting trials at different experimental scales was considered. Bench-scale time-temperature studies using pathogen suspensions or cultures on media often did not reliably predict what would happen in full-scale composting systems. If particular pathogens are of concern in a region, either pilot or full-scale studies should be done to evaluate their fate within the composting process used locally, or a more consistently predictive bench scale procedure should be developed.

Thermal properties of new varieties of yam starches

AbstractStarches isolated from yam varieties of Dioscorea alata and Dioscorea cayenensis‐rotundata species were prepared at different time–temperature conditions and characterised by DSC, amperometric iodine titration, light microscopy and rheology and compared to native and chemical modified tapioca starches. The observation by light microscopy showed different morphologies of the granules when heated above 100°C and the tendency for disintegration decreased in the order native tapioca starch > yam starch > modified tapioca starch. Differences between yam and tapioca starches were also revealed by DSC. Yam starch enthalpy is higher than tapioca starch, but the peak temperature is low. However, the significant differences between yam and the other tested starches were found in terms of their rheological behaviour. The viscosity of yam starch was very stable at high temperatures on the viscograph. With this property, yam starch can be used as thickening and gelling agent in food.

Modeling germination of fungal spores at constant and fluctuating temperature conditions

The germination of Penicillium expansum and Aspergillus niger spores was monitored microscopically on malt extract agar at isothermal conditions ranging from 0 to 33°C and 5 to 41.5°C, respectively. The obtained germination data, expressed as percentage of germination (% P) versus time, were fitted to the modified Gompertz equation for the estimation of the germination kinetic parameters (lag time, λ(g), and germination rate, μ(g)), which were further modeled as a function of temperature via the use of Cardinal Models with Inflection (CMI). The effect of temperature on these parameters was similar with that previously reported for mycelium growth kinetics of the tested isolates. The germination of spores was also studied at various dynamic time-temperature conditions including single or sequential temperature shifts. The germination of spores at fluctuating temperatures was predicted using the modified Gompertz equation in conjunction with the CMI models for λ(g) and μ(g) and based on the assumptions that i) a temperature shift does not result in any additional λ(g) and, thus, the total lag can be calculated by adding relative parts of the lag time, and ii) after a temperature shift the germination rate μ(g) adapts instantaneously to the new temperature. The comparison between predicted and observed data showed that the germination of spores is strongly affected by the extent of the temperature shift, the percentage of germinated spores at the time of the shift and the fungal species. Apart from the scientific interest in understanding the dynamics of spores' germination, the models developed in this study can be used as tools in effective quality management systems for fungi control in foods.

Regularities of the filling of Mg3Si2O5(OH)4 hydrosilicate nanotubes with solutions of sodium hydroxide and sodium chloride

The filling of nanotubes of the synthetic magnesium hydrosilicate Mg3Si2O5(OH)4 with a chrysotile structure by solutions of sodium hydroxide and sodium chloride has been investigated under different temperature-time conditions.

Antimicrobial Activity of Peptide P34 During Thermal Processing

In the present work, the influence of pH and sodium chloride concentration on thermal stability of antimicrobial peptide P34 was evaluated under different time–temperature conditions by a 22 factorial design experiment. At sterilization conditions (121 °C for 20 min), maximum retention (36%) was obtained at pH between 5.5 and 8.5 and sodium chloride concentration between 0.4 and 0.75 mol/l. For boiling conditions (100 °C for 20 min), antimicrobial activity was about 100% combining pH between 6.0 and 8.0 and salt concentration in the range of 0.65 to 1 mol/l. At low temperature pasteurization conditions (30 min at 65 °C), antimicrobial activity was not affected within the pH range from 5.0 to 8.0. For the three time–temperature conditions tested, the antimicrobial activity was minimal at more acidic or alkaline pH. Sodium chloride concentration of 0.65 mol/l increased thermostability of the peptide P34. Combination of sodium chloride and slight alkaline pH may increase the stability of peptide P34, which is essential to the proper utilization of bacteriocins in food industry.

Adsorption of mercury(II), methyl mercury(II) and phenyl mercury(II) on chitosan cross-linked with a barbital derivative

The sorption behavior of glutaraldehyde cross-linked chitosan (G-Chitosan) and barbital-glutaraldehyde cross-linked chitosan (BG-Chitosan) was investigated for the sorption of Hg(II), CH3Hg(II) and C6H5Hg(II). The pHZpc values were found to be 7.5 and 7.9 for G-Chitosan and BG-Chitosan respectively. Batch experiments were conducted to study the effect of adsorption under different pH (1–10), temperature (30–70°C) and contact time (20–180min) conditions. The optimum pH was found to be 4.5 and 6–8 for Hg(II), CH3Hg(II) and C6H5Hg(II) respectively in case of G-Chitosan while in case of BG-Chitosan it was >8 for CH3Hg(II) and 7 for Hg(II) and C6H5Hg(II). Adsorption was found to be endothermic in the case of Hg(II) and exothermic for CH3Hg(II) and C6H5Hg(II). FT-IR analysis showed the possibility of metal binding to amino groups and free aldehyde groups of G-Chitosan and amide N and O of BG-Chitosan.

Effect of deproteination and deacetylation conditions on viscosity of chitin and chitosan extracted from Crangon crangon shrimp waste

Deproteination of decalcified chitin from Crangon crangon shells and deacetylation to chitosan was investigated to find out optimum conditions for a high viscosity chitosan. Deproteination was carried out with an optimum shrimp shell:alkali (s:a) ratio of 1:4 from 30 °C to 65 °C and at each temperature, incubation times were varied from 2 to 5 h for maximal efficiency. Viscosity of the chemically extracted chitin samples at different temperature–time conditions ranged from 195 to 391 mPa s. A two-way ANOVA with Bonferroni post test was performed on experimental data. Chitin extracted at various temperatures and incubation times was deacetylated with 50% (w/w) NaOH at increasing reaction times. The highest chitosan viscosity of 1976 mPa s was observed in a sample deproteinated for 5 h at 55 °C and deacetylated for 1 h at 105 °C and 2 bar N 2 pressure. One-way ANOVA test for chitosan viscosity measurements indicated a significant P value of <0.05. Viscosity was not dependent on acetic acid release during deacetylation. A central composite design (CCD)–response surface analysis (RSA) was carried out and the resulting optimised model solutions confirmed the results. Highly viscous chitin and chitosan compared to commercially available products could be prepared within a short time by selecting suitable process conditions.

Phase separation and crystallization in glasses of the lithium silicate system xLi2O · (100 − x)SiO2 (x = 23.4, 26.0, 33.5)

The phase separation in ultimately homogenized glasses of the lithium silicate system xLi2O · (100 − x)SiO2 (where x = 23.4, 26.0, and 33.5 mol % Li2O) has been investigated. The glasses of these compositions have been homogenized using the previously established special temperature-time conditions, which provide the maximum dehydration and the removal of bubbles from the glass melt. The parameters of nucleation and growth of phase_separated inhomogeneities and homogeneous crystal nucleation have been determined. The absolute values of the stationary nucleation rates I st of lithium disilicate crystals in the 23.4Li2O · 76.6SiO2 and 26Li2O · 74SiO2 glasses with the compositions lying in the metastable phase separation region have been compared with the corresponding rates I st for the glass of the stoichiometric lithium disilicate composition. It has been established that the crystal growth rate have a tendency toward a monotonic increase with an increase in the temperature, whereas the dependences of the crystal growth rate on the time of low-temperature heat treatment exhibit an oscillatory behavior with a monotonic decrease in the absolute value of oscillations. The character of crystallization in glasses with the compositions lying in the phase separation region of the Li2O-SiO2 system is compared with that in the glass of the stoichiometric lithium disilicate composition. The inference has been made that the phase separation weakly affects the nucleation parameters of lithium disilicate and has a strong effect on the crystal growth.

Mathematical modeling of off-flavor development during beef storage

Beef quality characteristics can be measured by several physicochemical methods, but consumers usually evaluate beef quality by color or off-flavor. Thus, the detection of off-flavor can be an ultimate quality factor determining consumer purchases. Sensory off-flavor development (OFD) times, in this study, were statistically determined by logistic regression on the sensorial binomial responses for the presence and absence of off-flavor. Furthermore, a kinetic model was created to predict OFD time during beef storage and it was evaluated by comparing sensory and predicted OFD times under dynamic time–temperature conditions. The model was based on the OFD time corresponding to the reciprocal of the reaction constant (1 / k). The temperature dependence of the OFD times could be expressed by an Arrhenius relationship. The model for OFD time was proven to be effective at predicting OFD time for several cuts of beef. Consequently, by using this new model, the OFD time of beef can be predicted from its time–temperature history during storage.

Sheet resistance and surface topology time dynamics of intrinsic oxide film on InSe crystals

It has been shown that a result of InSe crystal oxidation is formation of an intrinsic oxide film that has not insulating but conductive properties. This conductive film forms a potential barrier with the semiconductor substrate. Sheet resistance measurements of the InSe oxide film in dependence on the oxidation time under various temperature conditions were carried out. The resistance was also tested for oxide films obtained for two mutually orthogonal crystal faces: perpendicular and parallel to the с axis. It has been established that the film sheet resistance is substantially changed only for 5 min of the oxidation time, and further oxidation does not affect its value that is about 100-150 Ohm/square. Surface topology of InSe intrinsic oxide was studied using the atomic-force microscopy method. It was found that this surface becomes nanostructured and contains nanoneedles oriented perpendicularly to the plane of sample surface. Dynamics of surface topology changes in dependence on temperature-time conditions of the oxidation process has been ascertained. It manifests itself in a change of lateral and vertical dimensions of nanoneedles as well as their density.

Can qualitatively similar temperature-histories be obtained in different pilot HP units?

Abstract An experimental protocol to harmonize the pressure and temperature-histories of model samples treated in different individual high pressure pilot units was developed. This protocol was based on the endpoint strategy. Step zero of this protocol consisted of an exploratory measurement of the pressure, temperature-history of the pressure transmitting medium in the different chambers without the use of a container. In steps one and two of the protocol, the temperature of a sample was measured, which was placed in a container. Two types of samples were considered, a pure water sample allowing free convection (step 1) and a viscous water-based system (using a water soluble thickener) preventing free convection in the sample container (step 2). The high pressure units differed primarily in pressure build-up and pressure release times. The suggested endpoint strategy enabled the minimization of differences in temperature-histories during the pressure holding phase. Pressure, temperature-histories measured in the different high pressure units and information on the inactivation kinetics of α-amylase based systems were used to compare the process impact of different pressure, temperature-histories on the enzyme inactivation. The differences in temperature-histories significantly influenced the degree of enzyme inactivation; in particular the temperature-histories during the pressure build-up phase substantially contributed to differences in residual enzyme activity. Industrial relevance Both in laboratory scale studies (e.g. microorganism and enzyme inactivation) as well as in the industrial implementation, different high pressure units are being used. Different layouts (e.g. vessel volume, sensor locations etc.) are observed leading to a.o. differences in pressure build-up and release and consequently in dynamic temperature pressure time conditions in different vessels and at different locations of one single vessel. Specific attention should be given to this issue, both in conducting kinetic studies as well as in scale-up from lab-scale processes to industrial scale processes. This manuscript shows that if the same process is implemented in different units, differences in pressure temperature time conditions are observed resulting in differences in impact (shown by enzyme inactivation). These differences can be minimized using an end point strategy, i.e. when implementing protocols based on a specified endpoint condition at the start of the holding phase.

Mechanical properties of thermally-treated and recycled glass fibres

This paper investigates the effects of temperature, heating time and atmosphere on the tensile modulus and strength of thermally-treated E-glass fibres. The heating conditions that were investigated are identical to those used in thermal recycling of waste polymer matrix composite materials, and therefore this study determines the effects of the recycling process conditions on the properties of reclaimed fibreglass. The loss in fibre strength is dependent on the temperature and time of the thermal process, and large strength loss occurs under the heating conditions used for high temperature incineration of polymer composites. A phenomenological model is presented for the residual fibre strength for the temperatures and heating time of the thermal recycling process. The reduction in fibre strength is dependent on the thermal recycling atmosphere under low temperature or short heating time conditions, but at high temperatures the strength loss is the same, regardless of furnace atmosphere (ambient air, dry air or inert gas). Quantitative fractographic analysis of the fibres shows that fracture for all heat treatments is caused by surface flaws. The strength loss is most probably due to structural relaxation during thermal annealing and a secondary effect of adsorbed surface water attacking the glass by thermally-activated stress-corrosion. It is shown that large reductions in fibre strength due to thermal recycling are not recovered during composite manufacture, therefore resulting in composite materials with significantly lower strength. The reduced strength of the composite matches the reduced fibre strength following thermal recycling.