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Heat Stability (heat + stability)
Selected AbstractsEffect of dewaxing pretreatment on composition and stability of rice bran oil: Potential antioxidant activity of wax fractionEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2006Samia Mezouari Abstract The effect of dewaxing pretreatment on rice bran oil composition and stability was investigated, as well as the possibility to use rice bran oil waxes as natural antioxidants at high temperatures. A correlation between wax content and dewaxing time was noticed. The pre-dewaxing process led to a loss of minor compounds, which negatively affected the oxidative stability index (OSI) of the dewaxed oil. The addition of rice bran oil waxes improved the oil stability index and heat stability of sunflower oil. An increase of 60% of the OSI and a significant decrease in polymer formation (59.2%) were observed. [source] Probing the role of oligomerization in the high thermal stability of Pyrococcus furiosus ornithine carbamoyltransferase by site-specific mutantsFEBS JOURNAL, Issue 14 2001Bernard Clantin The Pyrococcus furiosus ornithine carbamoyltransferase (OTCase) is extremely heat stable and maintains 50% of its catalytic activity after 60 min at 100 °C. The enzyme has an unusual quaternary structure when compared to anabolic OTCases from mesophilic organisms. It is built up of four trimers arranged in a tetrahedral manner, while other anabolic enzymes are single trimers. Residues Trp21, Glu25, Met29 and Trp33 are located in the main interfaces that occur between the catalytic trimers within the dodecamer. They participate in either hydrophobic clusters or ionic interactions. In order to elucidate the role played by the oligomerization in the enzyme stability at very high temperatures, we performed mutagenesis studies of these residues. All the variants show similar catalytic activities and kinetic properties when compared to the wild-type enzyme, allowing the interpretation of the mutations solely on heat stability and quaternary structure. The W21A variant has only a slight decrease in its stability, and is a dodecamer. The variants E25Q, M29A, W33A, W21A/W33A and E25Q/W33A show that altering more drastically the interfaces results in a proportional decrease in heat stability, correlated with a gradual dissociation of dodecamers into trimers. Finally, the E25Q/M29A/W33A variant shows a very large decrease in heat stability and is a trimer. These results suggest that extreme thermal stabilization of this OTCase is achieved in part through oligomerization. [source] TEXTURE STABILITY OF HYDROGEL COMPLEX CONTAINING CURDLAN GUM OVER MULTIPLE FREEZE,THAW CYCLESJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009PATRICK D. WILLIAMS ABSTRACT The texture stability of hydrogel complexes containing curdlan gum over multiple freeze,thaw cycles (FTCs) was investigated. The hydrogels formed by curdlan and xanthan gum, locust bean gum, carrageenan or guar gum at various combinations were stored at 4C for 24 h before subjected to five FTCs alternating between,16 (18 h) and 25C (6 h). Xanthan/curdlan hydrogels showed the highest freeze,thaw stability in terms of syneresis, heat stability and adhesiveness. The viscosity of xanthan/curdlan combination was the lowest among all samples studied yet the most stable over the five FTCs, whereas significant changes were observed with locust bean/curdlan hydrogels. The guar/curdlan combination before freeze,thaw treatments exhibited predominant elasticity; however, as the cycles progressed the elasticity decreased. The most stable gel strength was achieved when curdlan was combined with guar or xanthan at 2% (w/v) total concentration, while carrageenan/curdlan gels were the least stable. PRACTICAL APPLICATIONS Texture instability remains the most significant challenge for frozen food products, especially with inevitable post-production temperature fluctuations. Loss of moisture and changes in textural attributes often results in significant reduction of product quality. Precise control of hydrogel complexes that provide texture stabilization over multiple freeze,thaw cycles will enhance the quality of existing products while enabling the development of new ones. [source] Aflatoxin Inactivation Using Aqueous Extract of Ajowan (Trachyspermum ammi) SeedsJOURNAL OF FOOD SCIENCE, Issue 1 2005Shruti S. Hajare ABSTRACT: Aqueous extract of ajowan seeds was found to contain an aflatoxin inactivation factor (IF). Thin layer chromatography analysis of the toxins after treatment with IF showed relative reduction of aflatoxin G1 > G2 > B1 > B2. Quantification of toxin using a fluorotoxin meter as well as the Enzyme Linked Immuno s orb ent Assay (ELISA) confirmed these findings. An approximate 80% reduction in total aflatoxin content over the controls was observed. This observed phenomenon of reduction in total toxin was referred to as toxin inactivation. Temperature was found to influence the rate of toxin inactivation. At 45 °C, it was found to be rapid during the initial 5 h and slowed later. The IF was found to retain considerable activity even after boiling and autoclaving, indicating partial heat stability. The activity was lost below pH 4.0. Above pH 4.0, it increased gradually, reaching the maximum at pH 10.0. IF was found to be stable to gamma irradiation. Toxin decontamination in spiked corn samples could be achieved using IF. This study emphasizes the potential of ajowan IF in aflatoxin removal from contaminated food commodities. However, the biological toxicity, if any, of the IF inactivated aflatoxins needs to be confirmed, and the work in this direction is in progress. [source] Thermal Inactivation Kinetics of Peroxidase and Lipoxygenase from Broccoli, Green Asparagus and CarrotsJOURNAL OF FOOD SCIENCE, Issue 1 2002E.F. Morales-Blancas ABSTRACT: Thewermal inactivation curves for peroxidase (POD) and lipoxygenase (LOX) in broccoli (florets), green asparagus (tip and stem), and carrots (cortex and core) extracts were determined in the range of 70 to 95 °C for 0 to 600 s. The capillary tube method was used to obtain quasi-isothermal conditions. The kinetics of both enzymes showed a biphasic first-order model, while at 70 °C, LOX in asparagus showed a monophasic first-order behavior. LOX activity was not detected for carrots. Kinetic parameters, k and Ea, were determined for heat-labile and heatresistant isoenzyme fractions. Additionally, initial and residual activities for both enzymes within tissue sections showed a different distribution and heat stability. [source] PVC nanocomposites,Nanoclay chemistry and performance,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2008Daphne Benderly Nanoclay applications in poly(vinyl chloride) (PVC) have been limited, as the organic modifier of conventional nanoclays can promote PVC degradation. Novel nanoclays designed for enhanced PVC compatibility were compounded with PVC. Hectorite and bentonite clays were studied as nanoclay fillers. Two incorporation methods were evaluated to determine the effect on nanoclay dispersion and composite performance. A two-stage method, in which the nanoclay was predispersed in plasticizer, resulted in good nanoclay dispersion at both the micrometer and nanometer scales. The nanocomposites were characterized by using a wide range of analytical tools. They exhibited significantly improved heat stability, an increase of up to 200% in storage modulus, and a decrease of up to 77% in oxygen permeation, as compared to unfilled PVC. Bentonite nanoclays provided a greater increase in barrier and mechanical properties. No change was seen in the PVC glass transition temperature. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers [source] Peroxide crosslinking of rigid poly(vinyl chloride)JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2008Anoma Gunewardena Peroxide crosslinking of unplasticized poly(vinyl chloride) with trimethylolpropane trimethacrylate was investigated. Formulations used in this work contained a nontoxic lead-free stabilizer and showed good color and heat stability. The samples were examined by differential scanning calorimetry, and their tensile properties were measured at room temperature and at 130°C. Gel content or tetrahydrofuran-insoluble material was measured as an indication of crosslinking. It was shown that premature crosslinking could be avoided during processing and that 190°C was the optimum processing temperature for maximum gel content. The residual unsaturation was monitored by using FTIR spectroscopy. J. VINYL ADDIT. TECHNOL., 2008. © 2008 Society of Plastics Engineers [source] Optimizing performance of benzoate and phthalate blends for vinyl applicationsJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2005William D. Arendt To achieve required performance, blends of plasticizers are commonly used in flexible vinyl applications. Typically, when fast fusion is required, high solvating phthalates have been utilized in plasticizer blends. Benzoate esters are high solvators and can also be used in these blends. However, even though benzoate plasticizers offer additional performance benefits that can complement general-purpose phthalate performance, most of the literature does not include the use of benzoate plasticizers in blends with phthalates. The purpose of this article is to demonstrate the performance benefits of blending benzoate and phthalate plasticizers. The approach selected to accomplish this task was to develop performance data by utilizing a mixture design approach with DOE (design of experiments) software. A resilient flooring plastisol formulation was selected as the model. The following properties were obtained: degassing, low and high shear viscosity, viscosity stability of the plastisol, gel and fusion characteristics, tensile strength vs. temperature, vinyl heat stability, stain resistance, volatility, and UV stability. The data indicate how to utilize the advantage of benzoates as "process aids" to speed production rates and improve product quality. J. VINYL. ADDIT. TECHNOL. 11:150,154, 2005. © 2005 Society of Plastics Engineers [source] l -leucine aminopeptidase production by filamentous Aspergillus fungiLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2005K.M. Nampoothiri Abstract Aims:, To screen various filamentous fungi belonging to Aspergillus spp. producing leucine and methionine aminopeptidases. Methods and Results:, Twenty-eight Aspergillus strains representing 14 species within the genus were screened for l -leucine aminopeptidase (LAP) production in two media in shake flask fermentation. Two Aspergillus sojae (NRRL 1988 and NRRL 6271) and one Aspergillus oryzae (NRRL 6270) strains were selected as the best producers for further studies. The peak LAP activities were 2·61, 2·59 and 1·30 IU ml,1 for the three fungi on days 2, 5 and 4 respectively. In addition to LAP, l -methionine aminopeptidase (MAP) activity was also detected. Apart from submerged fermentation, the highest LAP yields by solid-state fermentation were 11·39, 17·40 and 13·02 IU g,1 dry matter for the above fungi. The temperature and pH optimum of the enzyme was found to be in the range of 65,75°C at pH 8·0,9·0 for all three fungi. Metal ions, Co2+ and Fe2+ in 2 mmol l,1 concentration apparently enhanced the relative enzyme activity and heat stability. Conclusions:, Two A. sojae (NRRL 1988 and NRRL 6271) and one A. oryzae (NRRL 6270) strains were found to be the best producers of LAP and MAP. The preliminary characterization studies revealed that the enzyme is considerably thermostable and belongs to the class metalloenzymes. Significance and Impact of the Study:, A good number of aspergilli were screened and the ability of the fungal aminopeptidase to release a particular N-terminal amino acid along with its high thermal stability, makes them interesting for controlling the degree of hydrolysis and flavour development for a wide range of substrate. [source] Properties of wheat bran polyphenol oxidaseMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 1 2004dem Soysal Abstract Polyphenol oxidase (PPO) obtained from wheat bran catalyzed the oxidation of 4-methyl catechol. Phenolic compounds found naturally in crude extract played role as an endogeneous substrate and activity of crude extract needed correction. Activity versus enzyme concentration gave a linear plot at high substrate concentration whereas a nonlinear plot was obtained at low substrate concentration which proved the presence of endogeneous substrate. Adsorption on celite and extraction with polyvinylpyrrolidone (PVPP) caused the removal of phenols. Adsorption of PPO on celite yielded a 4-fold increase in specific activity whereas extraction with PVPP yielded a 2.5-fold increase in specific activity compared to the crude extract. The kinetics of PPO catalyzed oxidation obeyed Michaelis-Menten model; Km and Vmax values were found as 218 mM and 99 ,M/min, respectively. The enzyme was inhibited by ethyl alcohol, dithiothreitol (DTT) and isoproterenol and exhibited heat stability up to a temperature of 90°C. The optimum pH of the enzyme was found to be 5.0. [source] Modification of functional properties of egg-white proteinsMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 6 2003Lydia Campbell Abstract Egg-white proteins are extensively utilised as food ingredients due to their unique functional properties. Several attempts have been made in order to improve the functional properties of egg-white proteins and to identify the optimal formulations for unique food products. Experimental data proves that controlled denaturation of egg-white proteins can have a beneficial impact on various functional applications in the food industry such as emulsifying ability, heat stability, gelation. This review describes the effect of heat-induced denaturation on protein structure and functionality. Studies on the impact of Maillard reaction, which aim to elucidate the structure-function relationship of egg-white proteins, are presented. A novel approach which could be the basis for the development of new methods aiming to improve the functional properties of egg-white proteins is also discussed. [source] In situ reinforcement of poly(butylene terephthalate) and butyl rubber by liquid crystalline polymerPOLYMER COMPOSITES, Issue 5 2009S. Kumar Ternary in situ butyl rubber (IIR)/poly(butylene terephthalate) (PBT) and liquid crystalline polymer (LCP) blends were prepared by compression molding. The LCP used was a versatile Vectra A950, and the matrix material was IIR/PBT 50/50 by weight. Morphological, thermal, and mechanical properties of blends were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), differential scanning calorimetry, and thermogravimetric analysis (TGA). Microscopy study (SEM) showed that formation of fibers is increasing with the increasing amount of LCP A950. Microscopic examination of the fractured surface confirmed the presence of a polymer coating on LCP fibrils. This can be attributed to some interactions including both chemical and physical one. The increased compatibility in polymer blends, consisting of IIR/PBT, by the presence of LCP A950 may be explained by the adsorption phenomena of the polymer chains onto the LCP fibrils. SEM and AFM images provided the evidence of the interaction between IIR/PBT and the LCP. Dynamic mechanical analyses (DMA) and TGA measurements showed that the composites possessed a remarkably higher modulus and heat stability than the unfilled system. Storage modulus for the ternary blend containing 50 wt% of LCP exhibits about 94% increment compared with binary blend of IIR/PBT. From the above results, it is suggested that the LCP A950 can act as reinforcement agent in the blends. Moreover, the fine dispersion of LCP was observed with no extensional forces applied during mixing, indicating the importance of interfacial adhesion for the fibril formation. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Production of biopharmaceuticals and vaccines in plants via the chloroplast genomeBIOTECHNOLOGY JOURNAL, Issue 10 2006Henry Daniell Dr.Article first published online: 27 SEP 200 Abstract Transgenic plants offer many advantages, including low cost of production (by elimination of fermenters), storage and transportation; heat stability; and absence of human pathogens. When therapeutic proteins are orally delivered, plant cells protect antigens in the stomach through bioencapsulation and eliminate the need for expensive purification and sterile injections, in addition to development of both systemic and mucosal immunity. Chloroplast genetic engineering offers several advantages, including high levels of transgene expression, transgene containment via maternal inheritance and multi-gene expression in a single transformation event. Hyper-expression of vaccine antigens against cholera, tetanus, anthrax, plague or canine parvovirus (4,31% of total soluble protein, tsp) in transgenic chloroplasts (leaves) or non-green plastids (carrots, tomato), as well as the availability of antibiotic-free selectable markers or the ability to excise selectable marker genes, facilitate oral delivery. Hyper-expression of several therapeutic proteins, including human serum albumin (11.1% tsp), somatotropin (7% tsp), interferon-gamma (6% tsp), anti-microbial peptide (21.5% tsp), facilitates efficient and economic purification. Also, the presence of chaperones and enzymes in chloroplasts facilitate assembly of complex multi-subunit proteins and correct folding of human blood proteins with proper disulfide bonds. Functionality of chloroplast-derived vaccine antigens and therapeutic proteins has been demonstrated by several assays, including the macrophage lysis assay, GM1-ganglioside binding assay, protection of HeLa cells or human lung carcinoma cells against encephalomyocarditis virus, systemic immune response, protection against pathogen challenge, and growth or inhibition of cell cultures. Thus, transgenic chloroplasts are ideal bioreactors for production of functional human and animal therapeutic proteins in an environmentally friendly manner. [source] Trypsin Inhibition Activity of Heat-Denatured Ovomucoid: A Kinetic StudyBIOTECHNOLOGY PROGRESS, Issue 1 2004Iesel Van der Plancken A kinetic study was conducted on the effect of heating in the temperature range of 75,110 °C on the trypsin inhibition activity of ovomucoid. Heat treatment of isolated ovomucoid resulted in a time-dependent decrease in trypsin inhibition activity that could accurately be described by a first-order kinetic model. The magnitude and the temperature dependence of the rate constants was affected by the pH during heat treatment. The heat stability of ovomucoid was the lowest at pH 7.6. Heat treatments intended to decrease the trypsin inhibition activity should therefore be carried out as soon as possible after laying, because the ovomucoid was inactivated faster at the pH of fresh egg white (pH 7.6). The presence of the other egg white constituents decreased the heat stability of ovomucoid compared to that of the model system of ovomucoid in buffer, presumably by the formation of ovomucoid-lysozyme complexes in the former. [source] | ||||||||||||||||