38 results on '"Karen M. Schaich"'
Search Results
2. Toxicity of Lipid Oxidation Products Consumed in the Diet
- Author
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Karen M. Schaich
- Subjects
Chromatography ,Lipid oxidation ,Chemistry ,Toxicity ,Metabolism ,Absorption (electromagnetic radiation) ,Digestion - Published
- 2020
3. System feasibility: Designing a chlorine dioxide self-generating package label to improve fresh produce safety part II: Solution casting approach
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Carol Saade, Bassam A. Annous, Anthony J. Gualtieri, Karen M. Schaich, LinShu Liu, and Kit L. Yam
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0404 agricultural biotechnology ,04 agricultural and veterinary sciences ,General Chemistry ,040401 food science ,Industrial and Manufacturing Engineering ,Food Science - Published
- 2018
4. Effects of CD36 Genotype on Oral Perception of Oleic Acid Supplemented Safflower Oil Emulsions in Two Ethnic Groups: A Preliminary Study
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Beverly J. Tepper, Karen M. Schaich, Katelyn Scoular, Iole Tomassini Barbarossa, Brenda Burgess, Michael Driver, Kathleen L. Keller, and Melania Melis
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0301 basic medicine ,chemistry.chemical_classification ,Taste ,030109 nutrition & dietetics ,food.ingredient ,biology ,Food additive ,CD36 ,Fatty acid ,030209 endocrinology & metabolism ,03 medical and health sciences ,Oleic acid ,chemistry.chemical_compound ,0302 clinical medicine ,food ,chemistry ,Emulsion ,Genotype ,Genetic variation ,biology.protein ,Food science ,Food Science - Abstract
Previous studies demonstrate humans can detect fatty acids via specialized sensors on the tongue, such as the CD36 receptor. Genetic variation at the common single nucleotide polymorphism rs1761667 of CD36 has been shown to differentially impact the perception of fatty acids, but comparative data among different ethnic groups are lacking. In a small cohort of Caucasian and East Asian young adults, we investigated if: (1) participants could detect oleic acid (C18:1) added to safflower oil emulsions at a constant ratio of 3% (w/v); (2) supplementation of oleic acid to safflower oil emulsions enhanced perception of fattiness and creaminess; and (3) variation at rs1761667 influenced oleic acid detection and fat taste perception. In a 3-alternate forced choice test, 62% of participants detected 2.9 ± 0.7 mM oleic acid (or 0.08% w/v) in a 2.8% safflower oil emulsion. Supplementation of oleic acid did not enhance fattiness and creaminess perception for the cohort as a whole, though East Asians carrying the GG genotype perceived more overall fattiness and creaminess than their AA genotype counterparts (P < 0.001). No differences were observed for the Caucasians. These preliminary findings indicate that free oleic acid can be detected in an oil-in-water emulsion at concentrations found in commercial oils, but it does not increase fattiness or creaminess perception. Additionally, variation at rs1761667 may have ethnic-specific effects on fat taste perception.
- Published
- 2018
5. Red/Green Currant and Sea Buckthorn Berry Press Residues as Potential Sources of Antioxidants for Food Use
- Author
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Jukka-Pekka Suomela, Karen M. Schaich, Baoru Yang, Anna Puganen, and Heikki Kallio
- Subjects
Oxygen radical absorbance capacity ,DPPH ,Color ,phenolic compounds ,Northern finland ,Article ,Antioxidants ,TRAP ,chemistry.chemical_compound ,Ribes ,0404 agricultural biotechnology ,Phenols ,Hippophae ,Phenol ,Food science ,currants ,antioxidant activity/capacity ,Waste Products ,Plant Extracts ,Chemistry ,ta1182 ,04 agricultural and veterinary sciences ,General Chemistry ,press residue ,Buckthorn Berry ,040401 food science ,Antioxidant capacity ,Fruit ,sea buckthorn ,ORAC ,General Agricultural and Biological Sciences - Abstract
The potential for using extracts of press residues from black, green, red, and white currants and from sea buckthorn berries as sources of antioxidants for foods use was investigated. Press residues were extracted with ethanol in four consecutive extractions, and total Folin-Ciocalteu (F-C) reactive material and authentic phenolic compounds were determined. Radical quenching capability and mechanisms were determined from total peroxyl radical-trapping antioxidant capacity (TRAP) and oxygen radical absorbance capacity (ORAC) assays and from diphenylpicrylhydrazyl (DPPH) kinetics, respectively; specific activities were normalized to F-C reactive concentrations. Levels of total F-C reactive materials in press residue extracts were higher than in many fruits and showed significant radical quenching activity. Black currant had the highest authentic phenol content and ORAC, TRAP, and DPPH reactivity. Sea buckthorn grown in northern Finland showed extremely high total specific DPPH reactivity. These results suggest that berry press residues offer attractive value-added products that can provide antioxidants for use in stabilizing and fortifying foods.
- Published
- 2018
6. System feasibility: Designing a chlorine dioxide self-generating package label to improve fresh produce safety part I: Extrusion approach
- Author
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Bassam A. Annous, Karen M. Schaich, Carol Saade, Kit L. Yam, Anthony J. Gualtieri, and LinShu Liu
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0301 basic medicine ,chemistry.chemical_classification ,Chlorine dioxide ,Moisture ,030106 microbiology ,Sodium chlorite ,Ethylene-vinyl acetate ,04 agricultural and veterinary sciences ,General Chemistry ,Polymer ,Bacterial growth ,040401 food science ,Industrial and Manufacturing Engineering ,03 medical and health sciences ,chemistry.chemical_compound ,0404 agricultural biotechnology ,chemistry ,Organic chemistry ,Extrusion ,Citric acid ,Food Science ,Nuclear chemistry - Abstract
There is need for in-package anti-microbial technology to control microbial growth on packaged fresh food. This research evaluated the feasibility of delivering chlorine dioxide (ClO 2 ) via package labels made of synthetic polymers extruded with citric acid (CA) and sprayed with sodium chlorite. Heat pressing facilitated ClO 2 generation and moisture triggered ClO 2 release. Of three synthetic polymers tested, only ethylene vinyl acetate (EVA) label withstood extrusion and storage conditions without structural changes. EVA labels containing 15 or 7.5% CA generated 3.2–4.2 and 0.5–1.0 mg ClO 2 /L air, respectively. Total inactivation of Salmonella cells on TSA plates (2.13 log CFU/plate) was achieved following exposure to 15% CA labels for 2 h; 7.5% CA labels gave partial inactivation (1.03 log CFU/plate) following up to 6 h of exposure. Our findings demonstrate: 1) the practical feasibility of this synthetic package label design; 2) ClO 2 generation and release following activation; and 3) antimicrobial effectiveness against Salmonella growth. Industrial relevance Feasibility for synthesizing a package label to generate and deliver chlorine dioxide (ClO 2 ) as an effective antimicrobial inside individual food packages has been demonstrated. The approach extrudes polymers with citric acid, then sprays the surface with sodium chlorite. Heat pressing the label just before application initiates reaction between these two agents to generate ClO 2 . Release of ClO 2 is stimulated and maintained by moisture in the film and emanating from fresh foods.
- Published
- 2017
7. Thinking outside the classical chain reaction box of lipid oxidation: Evidence for alternate pathways and the importance of epoxides
- Author
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Brandon A. Bogusz, Jia Xie, and Karen M. Schaich
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0301 basic medicine ,03 medical and health sciences ,030109 nutrition & dietetics ,0404 agricultural biotechnology ,Lipid oxidation ,Control and Systems Engineering ,Chemistry ,Organic chemistry ,04 agricultural and veterinary sciences ,040401 food science ,Chain reaction ,General Biochemistry, Genetics and Molecular Biology ,Food Science - Published
- 2017
8. Hurdles and pitfalls in measuring antioxidant efficacy: A critical evaluation of ABTS, DPPH, and ORAC assays
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Xin Tian, Karen M. Schaich, and Jia Xie
- Subjects
Nutrition and Dietetics ,Antioxidant ,ABTS ,Antioxidant efficacy assays ,ABTS•+ – 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) assay ,Chemistry ,DPPH ,Radical quenching kinetics ,Nutrition. Foods and food supply ,medicine.medical_treatment ,ORAC Assays ,Medicine (miscellaneous) ,chemistry.chemical_compound ,Limitations ,ORAC – Oxygen Radical Absorbance Capacity assay ,medicine ,Organic chemistry ,TEAC – Trolox equivalent antioxidant capacity assay ,TX341-641 ,Biochemical engineering ,Food Science - Abstract
Assays developed to measure radical scavenging ability of natural compounds have been used as a basis for ranking and recommending best foods for consumption. However, assays often were adapted for screening assays with inadequate consideration of reaction chemistry, particularly kinetics. Recent research results raise serious questions about the chemistry, execution, and application of these assays. This paper critically evaluates conceptual and technical issues that limit use and compromise validity of three commonly-used assays – TEAC/ABTS•+, DPPH, and ORAC. Recommendations are made for discontinuing use of ABTS•+ and DPPH radicals for measuring radical quenching, redirecting them instead to distinguishing electron transfer reaction mechanisms. Conditions required for accurate results in ORAC are reviewed, and recommendations are made for redirecting this assay to distinguishing compounds that quench radicals by hydrogen atom transfer. The mechanistic information so gained can be then applied to understanding how natural antioxidants can be used most effectively in foods.
- Published
- 2015
9. Re-evaluation of the 2,2-Diphenyl-1-picrylhydrazyl Free Radical (DPPH) Assay for Antioxidant Activity
- Author
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Jia Xie and Karen M. Schaich
- Subjects
Steric effects ,Reaction mechanism ,Antioxidant ,DPPH ,medicine.medical_treatment ,Biphenyl Compounds ,General Chemistry ,Redox ,Antioxidants ,Chemistry Techniques, Analytical ,Adduct ,Absorbance ,Kinetics ,chemistry.chemical_compound ,Picrates ,chemistry ,medicine ,Organic chemistry ,General Agricultural and Biological Sciences ,Oxidation-Reduction ,Stoichiometry ,Nuclear chemistry - Abstract
Kinetics and stoichiometry of reactions between the 2,2-diphenyl-1-picrylhydrazyl (DPPH) stable radical and 25 antioxidant compounds with different structure, molecular weight, number of -OH groups, and redox potential were investigated by recording the loss of DPPH(•) absorbance at 515 nm continuously for 10 min. A series of antioxidant concentrations was tested to determine linear response ranges and reaction saturation points. The primary feature distinguishing antioxidant activity--rate of initial reaction (30 s)--was controlled by whether the dominant antioxidant mechanism was electron (very fast) or hydrogen atom (slow) transfer and by impairment of steric accessibility to the DPPH radical site by bulky ring adducts and multiple phenolic rings. Results raise serious questions regarding application of the DPPH assay for ranking antioxidants and natural extracts and suggest possible redirection of this assay to distinguish active reaction mechanisms by comparing reactions rates and patterns in different solvents and in 50% water/methanol mixtures at different pH values.
- Published
- 2014
10. Methods of measurement and evaluation of natural antioxidant capacity/activity (IUPAC Technical Report)
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Shela Gorinstein, Karen M. Schaich, Kubilay Güçlü, Mustafa Özyürek, Reşat Apak, and Volker Böhm
- Subjects
Task group ,Quantification methods ,Antioxidant ,Chemistry ,General Chemical Engineering ,medicine.medical_treatment ,Chemical nomenclature ,General Chemistry ,Food labeling ,Antioxidant capacity ,Biochemistry ,Chemical diversity ,medicine ,Biochemical engineering ,Beneficial effects - Abstract
The chemical diversity of natural antioxidants (AOXs) makes it difficult to separate, detect, and quantify individual antioxidants from a complex food/biological matrix. Moreover, the total antioxidant power is often more meaningful to evaluate health beneficial effects because of the cooperative action of individual antioxidant species. Currently, there is no single antioxidant assay for food labeling because of the lack of standard quantification methods. Antioxidant assays may be broadly classified as the electron transfer (ET)- and hydrogen atom transfer (HAT)-based assays. The results obtained are hardly comparable because of the different mechanisms, redox potentials, pH and solvent dependencies, etc. of various assays. This project will aid the identification and quantification of properties and mutual effects of antioxidants, bring a more rational basis to the classification of antioxidant assays with their constraints and challenges, and make the results more comparable and understandable. In this regard, the task group members convey their own experiences in various methods of antioxidants measurement.
- Published
- 2013
11. Target release rate of antioxidants to extend induction period of lipid oxidation
- Author
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Donghwa Chung, Kit L. Yam, Xi Chen, Xuntao Zhu, and Karen M. Schaich
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Antioxidant ,medicine.medical_treatment ,Induction period ,Linoleic acid ,Shelf life ,Controlled release ,chemistry.chemical_compound ,Biochemistry ,chemistry ,Lipid oxidation ,medicine ,Tocopherol ,Food science ,Incubation ,Food Science - Abstract
Evidence from literature has shown that compared with instant addition, slow release of antioxidants has some advantages to inhibit lipid oxidation and extend shelf life of food products. In this paper, the hypothesis that there is a range of release rates of antioxidants which could provide the maximum extension of induction period for lipid oxidation was tested in a model system using a syringe pump to deliver tocopherol into linoleic acid. Conjugated dienes, the first products appearing in lipid oxidation, were measured to determine the length of induction period for onset of lipid oxidation during incubation at 30 and 40 °C. Maximum inhibition of oxidation occurred at the release rates of 3.3 × 10− 4 and 7.7 × 10− 4 g/day at 30 and 40 °C, respectively, supporting the hypothesis. Based on the results, a term “target release rate” was defined and its application in controlled release packaging was discussed.
- Published
- 2012
12. Antioxidant Effects of Sesamol Released from Polymeric Films on Lipid Oxidation in Linoleic Acid and Oat Cereal
- Author
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Kit L. Yam, Karen M. Schaich, Xuntao Zhu, and Xi Chen
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Antioxidant ,Materials science ,Mechanical Engineering ,medicine.medical_treatment ,Induction period ,Linoleic acid ,General Chemistry ,Hexanal ,chemistry.chemical_compound ,chemistry ,Lipid oxidation ,medicine ,Butylated hydroxytoluene ,Organic chemistry ,General Materials Science ,High-density polyethylene ,Food science ,Sesamol - Abstract
The antioxidant effects of sesamol films were evaluated using a food simulant (linoleic acid) and a real food (oat cereal). Sesamol was melt blended with high density polyethylene, linear low density polyethylene and ethylene-vinyl acetate resins using co-extrusion to produce sesamol films of multilayer structure; for comparison, films containing butylated hydroxytoluene (BHT) or no additive (as control) were also produced. At least 60% of the initial amount of sesamol remained in the films after extrusion. The release of sesamol from the sesamol films was about six times faster at 30°C than at 10°C. The antioxidant effectiveness of sesamol and BHT was evaluated on the basis of induction period of lipid oxidation, conjugated dienes (for linoleic acid), hexanal (for oat breakfast) and sensory evaluation. Compared with the control film, the sesamol films extended the induction period of linoleic acid by five and eight times at 40°C and 23°C, respectively. After 12 month storage at 23°C, hexanal formation was 59% less in cereal packaged with sesamol films than that packaged with control film. Rancid odours were detected in cereal packaged with control films, but not with sesamol or BHT films. The incorporation of sesamol had only slight effects on tensile properties and transparency. Copyright © 2012 John Wiley & Sons, Ltd.
- Published
- 2012
13. Thinking outside the classical chain reaction box of lipid oxidation
- Author
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Karen M. Schaich
- Subjects
chemistry.chemical_classification ,Basic knowledge ,chemistry ,Lipid oxidation ,Control and Systems Engineering ,Nanotechnology ,Biochemical engineering ,Chain reaction ,General Biochemistry, Genetics and Molecular Biology ,Food Science ,Polyunsaturated fatty acid - Abstract
For the past few decades, research on lipid oxidation mechanisms has been rather stagnant due to a pervasive attitude that reactions of lipid oxidation were well understood, so only tailoring applications of basic knowledge to stabilize individual systems was needed. This simplistic approach worked during the low fat/no fat era because there was little lipid substrate to oxidize. However, with current reformulation of foods with polyunsaturated fatty acids for health, preventing oxidation of these essential fatty acids presents major challenges that cannot always be solved with traditional thinking. Because critical gaps in our understanding prevent moving forward with improved processing, formulations, and packaging to provide high-PUFA lipid foods that remain shelf-stable beyond a few months, details about oxidation mechanisms that were previously considered irrelevant have now become critically important. Considered here are alternate reaction pathways that compete with classical hydrogen abstraction and must be integrated into the overall free radical chain to more accurately account for kinetics and products of lipid oxidation.
- Published
- 2012
14. Gelatin–pectin composite films from polyion-complex hydrogels
- Author
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Stefano Farris, Peter H. Cooke, Karen M. Schaich, Luciano Piergiovanni, LinShu Liu, and Kit L. Yam
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chemistry.chemical_classification ,food.ingredient ,Pectin ,Chemistry ,General Chemical Engineering ,macromolecular substances ,General Chemistry ,Polymer ,Gelatin ,chemistry.chemical_compound ,food ,Chemical engineering ,Ultimate tensile strength ,Polymer chemistry ,Self-healing hydrogels ,medicine ,Thermal stability ,Glutaraldehyde ,Swelling ,medicine.symptom ,Food Science - Abstract
Preparation and properties of composite films from gelatin and low-methoxyl pectin from simultaneous reversible and permanent polyion-complex hydrogels are presented. Ionic interactions between positively charged gelatin and negatively charged pectin produce reversible physical hydrogels with homogeneous molecular arrangement that improve both mechanical and water resistance but do not alter thermal stability relative to single polymer gels. Subsequent addition of 0.3 weight percent (wt.%) glutaraldehyde crosslinks gelatin heterogeneously, due to the presence of domains with non-uniform crosslinking, as revealed by the structural analysis. Resulting interspersed permanent chemical hydrogel showed a decreased swelling attitude by nearly 10 fold relative to films from gelatin alone and further improved mechanical performance (tensile strength and elongation at break). Results demonstrate that simultaneously exploiting the specific reactivity provided by the functional groups of both biopolymers can be used to create unique new structures with improved properties and offer potential for tailoring these to a wide range of targeted applications.
- Published
- 2011
15. Development of polyion-complex hydrogels as an alternative approach for the production of bio-based polymers for food packaging applications: a review
- Author
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Kit L. Yam, LinShu Liu, Stefano Farris, Karen M. Schaich, and Luciano Piergiovanni
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chemistry.chemical_classification ,food.ingredient ,business.industry ,Bio based ,Food technology ,Nanotechnology ,Polymer ,Gelatin ,Food packaging ,food ,chemistry ,Self-healing hydrogels ,business ,Food Science ,Biotechnology - Abstract
Development of packaging materials from renewable resources has for a long time been desirable for sustainability reasons, but with recent explosion in prices of petroleum products, this now becomes also more economically viable. This paper shows how fundamental chemistry underlying three forms of hydrogels—physical hydrogels, chemical hydrogels, and interpenetrating polymer networks (IPN)—can be integrated to produce a new family of food packaging materials from biopolymers, illustrated here using gelatin and low-methoxyl pectin as examples. Application of this technique to create hydrogels from bio-based materials offers the potential for developing novel, biodegradable packaging applications, particularly for foods, that meet the ever-increasing demands for natural and environmentally compatible materials.
- Published
- 2009
16. EXTRACTION OF LIPIDS FROM EXTRUDED CORN-SOY BLENDS1
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Karen M. Schaich and E. D. Strange
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chemistry.chemical_classification ,Chloroform ,Chromatography ,Starch ,Butanol ,Extraction (chemistry) ,Fatty acid ,General Chemistry ,Peroxide ,chemistry.chemical_compound ,chemistry ,Lipid oxidation ,lipids (amino acids, peptides, and proteins) ,Acid hydrolysis ,Food Science - Abstract
Extruded corn-soy products developed for the US AID Food for Peace program contain high levels of lipids (about 12%) and vitamins and minerals, including oxidation-sensitive vitamins A and C and iron. Because lipid stability is probably the most important factor in maintaining long-term storage stability of these products, being able to analyze lipid content and oxidation is critical. In cereals, substantial amounts of lipid are bound to starch, making cereal lipids notoriously difficult to extract. Conventional methods such as acid hydrolysis, hot water-saturated butanol, and exhaustive soxlet extractions result in damage to the lipids and thus give inaccurate measures of lipid stability. A new method of extracting lipids from cereal-based products without damage is proposed using pretreatment with α-amylase to digest the starch and release bound lipids. One gram of the product is slurried with 25 mg α-amylase in water and incubated for 16 h. Lipids are then extracted from this mixture with 2:1 (v/v) dichloromethane or chloroform:methanol. This procedure was quantitative, extracting 98.7% of the lipid, and it gave an extract suitable for analysis of fatty acid contents and lipid oxidation products, e.g. peroxide values, and carbonyl contents.
- Published
- 2007
17. Inhibitory effects of cranberry polyphenols on formation and acidogenicity ofStreptococcus mutansbiofilms
- Author
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Stacy Gregoire, Karen M. Schaich, Simone Duarte, Ajay P. Singh, William H. Bowen, Nicholi Vorsa, and Hyun Koo
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Flavonols ,Microbiology ,Anthocyanins ,Streptococcus mutans ,chemistry.chemical_compound ,Glucosyltransferases ,Phenols ,Genetics ,Humans ,Proanthocyanidins ,Molecular Biology ,Flavonoids ,chemistry.chemical_classification ,biology ,Plant Extracts ,Biofilm ,Polyphenols ,food and beverages ,Glycoside ,Hydrogen-Ion Concentration ,biology.organism_classification ,Vaccinium macrocarpon ,Proanthocyanidin ,chemistry ,Polyphenol ,Biofilms ,Quercetin ,Glycolysis - Abstract
Cranberry fruit is a rich source of polyphenols, and has shown biological activities against Streptococcus mutans. In the present study, we examined the influence of extracts of flavonols (FLAV), anthocyanins (A) and proanthocyanidins (PAC) from cranberry on virulence factors involved in Streptococcus mutans biofilm development and acidogenicity. PAC and FLAV, alone or in combination, inhibited the surface-adsorbed glucosyltransferases and F-ATPases activities, and the acid production by S. mutans cells. Furthermore, biofilm development and acidogenicity were significantly affected by topical applications of PAC and FLAV (P
- Published
- 2006
18. Advancing controlled release packaging through smart blending
- Author
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Amanda LaCoste, D. A. Zumbrunnen, Karen M. Schaich, and Kit L. Yam
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Food packaging ,Engineering ,business.industry ,Mechanical Engineering ,technology, industry, and agriculture ,General Materials Science ,Nanotechnology ,General Chemistry ,business ,Controlled release ,humanities ,Manufacturing engineering - Abstract
Researchers from Rutgers University and Clemson University have collaborated to develop a concept of using smart blending to generate functional packaging films for the controlled release of active compounds such as antimicrobials, antioxidants and flavour compounds to extend the shelf-life of food. In this paper, literature results are reviewed to justify the significance of controlled release packaging (CRP) and the research gaps for further development are identified. A major research gap is the lack of packaging materials that can provide the release of active compounds at rates suitable for a wide range of food packaging applications. Smart blending is a promising technology for bridging this research gap. To fully realize the potentials of smart blending, a systematic approach for developing CRP using smart blending is also presented. Copyright © 2005 John Wiley & Sons, Ltd.
- Published
- 2005
19. Immunochemical and Electrophoretic Analysis of the Modification of Wheat Proteins in Extruded Flour Products
- Author
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Karen M. Schaich, Yan Jiang, J.H. Skerritt, and Michael A. K. Partridge
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biology ,Molecular mass ,Globulin ,Chemistry ,Organic Chemistry ,Wheat flour ,food and beverages ,Glutenin ,Biochemistry ,Immunochemistry ,biology.protein ,Extrusion ,Gliadin ,Polyacrylamide gel electrophoresis ,Food Science - Abstract
Antibodies specific for wheat proteins were used to identify protein fractions modified during extrusion of Hard Red Spring wheat flour (14% protein) under four different combinations of extrusion conditions (18 and 24% feed moisture and 145 and 175°C die temperature). Antibody binding was assessed on immunoblots of proteins extracted from flour and extrudates separated by SDS-PAGE. Antibodies to high molecular weight glutenin subunits (HMW-GS) and to B-group low molecular weight glutenin subunits (LMW-GS) recognized intact subunits from both flour and extrudates. Antibodies to C-group LMW-GS had diminished binding to extruded proteins. Glutenin-specific antibodies also recognized protein in the extrudates migrating as a smear at molecular weights higher than intact subunits, indicating cross-linked proteins. Antibodies recognized albumins or globulins in flour but not in extrudates, evidence that these fractions undergo significant modification during extrusion. Acid-PAGE and antibody reaction o...
- Published
- 2003
20. Extrusion Chemistry of Wheat Flour Proteins: I. Free Radical Formation
- Author
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Karen M. Schaich and C. A. Rebello
- Subjects
chemistry.chemical_classification ,Chemistry ,Radical ,Organic Chemistry ,Intermolecular force ,Wheat flour ,Mineralogy ,Peptide ,Photochemistry ,law.invention ,Plant protein ,law ,Electron paramagnetic resonance ,Free Radical Formation ,Bond cleavage ,Food Science - Abstract
Electron paramagnetic resonance (EPR) spectroscopy was used to study free radical production in hard red wheat flours extruded according to a two-level fractional factorial experimental design (11 and 14% protein content, 160 and 185°C, 16 and 20% moisture, 300 and 500 rpm screw speed, and mass flow rate of 225 and 400 g/min). All spectra showed dominant broad singlets (g = 2.0053–2.0059) from nitrogen-centered radicals originating from heat-induced peptide scission and reactions of lipid radicals with side-chain amino groups. At 77 K, sulfur-oxyl or peroxyl radicals (g = 2.008–2.018), thiyl radicals (g = 2.025), and disulfide radical species (g = 2.032–2.035 and 2.05–2.06), resulting from intra- and intermolecular electron migration and shear-induced scission of disulfides, sometimes were present. The strongest EPR signals occurred under conditions of maximum free radical production and minimum opportunity for radical recombination: high protein flour (14%), high die temperature (180°C), and low...
- Published
- 1999
21. Genotoxic Effects of Airborne Agents
- Author
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Raymond R. Tice, Daniel L. Costa, Karen M. Schaich, Raymond R. Tice, Daniel L. Costa, and Karen M. Schaich
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- Genetic toxicology--Congresses, Mutagenicity testing--Congresses, Carcinogenicity testing--Congresses
- Abstract
For at least 40 years there has been a great interest in the problems created by infectious airborne agents and other toxic sub stances transported through the air. During the Second World War, this problem grew out of the very high incidence of upper respira tory infections appearing in new military recruits who were brought together in very large, open quarters. As a result, very interest ing methods were developed to measure these airborne agents, espe cially bacteria, and some important methods were refined for their control. These methods primarily concentrated on ultraviolet radia tion, propylene glycol and other means to reduce the dust in an en vironment. Because of the specialized circumstances at that time the whole consideration of airborne particles became prominent. Now, with the new strides in the recognition of mutagenic and carcinogenic effects attributed to exposure to airborne chemicals from today's technology, the problem has again become quite promi nent. The development of experimental chambers has made it possible to conduct studies under carefully controlled conditions.
- Published
- 2012
22. Effects of molecular structure on kinetics and dynamics of the trolox equivalent antioxidant capacity assay with ABTS(+•)
- Author
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Xin Tian and Karen M. Schaich
- Subjects
ABTS ,Quenching (fluorescence) ,Molecular Structure ,Kinetics ,Trolox equivalent antioxidant capacity ,General Chemistry ,Photochemistry ,Medicinal chemistry ,Redox ,Antioxidants ,Chemical kinetics ,chemistry.chemical_compound ,chemistry ,Phenol ,Phenols ,Benzothiazoles ,Chromans ,Sulfonic Acids ,General Agricultural and Biological Sciences ,Oxidation-Reduction - Abstract
Reaction kinetics in the Trolox equivalent antioxidant capacity (TEAC) assay between ABTS(+•) [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical] and compounds with different structure, molecular weight, number of OH groups, and redox potential were investigated by recording loss of ABTS(+•) absorbance (734 nm) continuously over time. Curves showed six distinguishable kinetic patterns, including both immediate and extended reaction components. Radical quenching rates in the immediate component most relevant to reactions in foods and tissues depended on phenol structure and steric accessibility to the hindered radical, while reaction stoichiometry correlated with the number of phenol groups (0.81) but not redox potential. Current assay procedures measure antioxidant capacity under conditions not relevant to actual applications and do not determine radical quenching rates. Results raise serious questions regarding the ability of reactions with the hindered ABTS(+•) to rank actual radical quenching by compounds with different structures and invalidate reporting antioxidant activity as Trolox equivalents.
- Published
- 2013
23. List of Contributors
- Author
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Michel Aliani, Peter Eck, N. A. Michael Eskin, H. Douglas Goff, Juan He, Arthur R. Hill, Chi-Tang Ho, Ernst Hoehn, Prashanti Kethireddipalli, Herman Lutterodt, Yoshinori Mine, Michael C. Qian, Christiane Queiroz, Karen M. Schaich, Fereidoon Shahidi, Margaret Slavin, Graham G. Stewart, Vera Lúcia Valente Mesquita, Pedro Vazquez-Landaverde, Monica Whent, Liangli Yu, Hua Zhang, Ying Zhong, and Kequan Zhou
- Published
- 2013
24. Lipid Oxidation
- Author
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N.A. Michael Eskin, Ying Zhong, Fereidoon Shahidi, and Karen M. Schaich
- Subjects
Lipid oxidation ,Chemistry ,Organic chemistry - Published
- 2013
25. Rapid method for preparation of pure veratryl alcohol for the assay of lignin peroxidase
- Author
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Kanyawim Kirtikara, Chaim Frenkel, Karen M. Schaich, and Julie M. Fagan
- Subjects
Microbiology (medical) ,chemistry.chemical_classification ,Chromatography ,biology ,Veratraldehyde ,Substrate (chemistry) ,Lignin peroxidase ,biology.organism_classification ,Microbiology ,Sodium borohydride ,chemistry.chemical_compound ,Enzyme ,chemistry ,biology.protein ,Organic chemistry ,Lignin ,Phanerochaete ,Molecular Biology ,Peroxidase - Abstract
We present a simple method for the rapid preparation of veratryl alcohol by reducing commercially available veratraldehyde with sodium borohydride resulting in high-purity veratryl alcohol. The lag period in the activity of lignin peroxidase from Phanerochaete chrysosporium that is associated with use of commercial preparations of the substrate is eliminated with the use of pure veratryl alcohol. The compound affords also estimation of low enzymatic activity.
- Published
- 1995
26. L
- Author
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Steve Werblow, Micha Noah, Ralph A. Simmons, George W. Arndt, William E. Franklin, Terrie K. Boguski, Paul Fry, Thomas Eie, Karen M. Schaich, Robert R. Luise, and Diana Twede
- Published
- 2010
27. Bioavailability and tissues distribution of cranberry flavonol glycosides in mice
- Author
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Elena Shabrova, Ajay P. Singh, Hong Jin, Nicholi Vorsa, Karen M. Schaich, and Loredana Quadro
- Subjects
chemistry.chemical_classification ,chemistry ,Genetics ,Glycoside ,Distribution (pharmacology) ,Food science ,Molecular Biology ,Biochemistry ,Biotechnology ,Bioavailability - Published
- 2007
28. Standardized methods for the determination of antioxidant capacity and phenolics in foods and dietary supplements
- Author
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Ronald L. Prior, Xianli Wu, and Karen M. Schaich
- Subjects
Antioxidant ,Oxygen radical absorbance capacity ,Photochemistry ,medicine.medical_treatment ,Dietary supplement ,Trolox equivalent antioxidant capacity ,Antioxidants ,Nutraceutical ,Phenols ,International congress ,medicine ,Food science ,Chromans ,Fluorescent Dyes ,Molybdenum ,Chemistry ,Reproducibility of Results ,General Chemistry ,Tungsten Compounds ,Food Analysis ,Antioxidant capacity ,Dietary Supplements ,Luminescent Measurements ,General Agricultural and Biological Sciences ,Reactive Oxygen Species ,Oxidation-Reduction - Abstract
Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.
- Published
- 2005
29. Factors affecting DNA damage caused by lipid hydroperoxides and aldehydes
- Author
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Karen M. Schaich and Ming-Hua Yang
- Subjects
Lipid Peroxides ,Double bond ,DNA damage ,Linoleic acid ,Radical ,Iron ,DNA, Single-Stranded ,Photochemistry ,Biochemistry ,Antioxidants ,Lipid peroxidation ,chemistry.chemical_compound ,Structure-Activity Relationship ,Physiology (medical) ,Cations ,Inositol ,chemistry.chemical_classification ,Electrophoresis, Agar Gel ,Aldehydes ,Spectrophotometry, Atomic ,Free Radical Scavengers ,Pentetic Acid ,Kinetics ,chemistry ,Linoleic Acids ,Agarose gel electrophoresis ,Solvents ,Lipid Peroxidation ,DNA ,DNA Damage ,Plasmids - Abstract
Single (SSB) and double strand breaks (DSB) in supercoiled plasmid DNA pBR322 reacted with linoleic acid hydroperoxides (LOOH) were followed by agarose gel electrophoresis to obtain definitive information about factors affecting LOOH interaction with DNA. In water, LOOH induced extensive DSB, which were metal mediated and increased with incubation time. Adventitious metal bound to DNA was sufficient to decompose LOOH to reactive radicals, activity that was not readily inhibited by chelators DTPA and desferrioxamine. Added Fe 2+ and Fe 3+ increased SSB and DSB, although the effects of Fe 2+ were more extensive. Above 100 μM both valences inhibited DNA damage. Strand breakage by LOOH proceeded via lipid alkoxyl and peroxyl radicals. Aldehydic lipid peroxidation products induced strand breaks via oxidation of double bonds, not by reactions of the carbonyl groups. Lipophilic antioxidants BHA, BHT, and a-tocopherol were about 20 times more effective than hydrophilic free radical scavengers sodium benzoate, inositol, DMSO, and mannitol in preventing LOOH-induced strand breaks, supporting lipid phase localization of the damage.
- Published
- 1996
30. Rancidity in foods (3rd edn)
- Author
-
Karen M. Schaich
- Subjects
Chemistry ,Food Science ,Biotechnology - Published
- 1995
31. Cytotoxicity from Coupled Redox Cycling of Autoxidizing Xenobiotics and Metals: A Selective Critical Review and Commentary on Work-in-Progress
- Author
-
Karen M. Schaich and Donald C. Borg
- Subjects
Lipid peroxidation ,chemistry.chemical_compound ,Membrane ,chemistry ,Autoxidation ,Lipid oxidation ,Superoxide ,Radical ,Organic chemistry ,General Chemistry ,Oxidative phosphorylation ,Photochemistry ,Hydrogen peroxide - Abstract
A comprehensive reaction schema for oxidative cytotoxicity is presented, integrating known chemical mechanisms of oxygen radical reactions and observed pathophysiology. The key features of the schema are the coupling of (1) redox cycling of autoxidizable substrates to form the equilibrium pair of superoxide anion (O−2)/and its conjugate acid, perhydroxyl radical (HO2); (2) hydrogen peroxide (H2O2) generation via O−2 dismutation; (3) catalytic redox cycling of metals reducing H2O2 to reactive hydroxyl radicals (OH); (4) direct reaction of OH with target molecules, including critical cell macromolecules and polyunsaturated lipids in membranes; (5) transfer of oxidative potential from initial to distant sites via H2O2 and O−2/HO2 diffusion, lipid free radical chain peroxidations in membranes, and migration of non-radical lipid oxidation products; and (6) cytotoxic damage at those distant sites mediated by reaction of lipid radical species and other lipid oxidation products with critical target molecules (proteins, DNA, etc.). Although there is a broad consensus of agreement within the cognizant research community concerning many aspects of this schema, there exists considerable controversy and/or misconception about several important issues. In this paper critical analyses of four presently controversial points are put forth. (1) The question of metal-dependency of Fenton generation of OH is considered first and data are presented to show that previous observations of apparent H2O2 decomposition by various semiquinone radicals most likely resulted from trace metal contamination. (2) The strong electrophile from H2O2 reduction has sometimes been ascribed to a non-free “crypto-hydroxyl” radical because of failure of traditional scavengers to inhibit its reactions in the expected ways or it has been ascribed to iron-oxy complexes based on similar “atypical” scavenger patterns plus requirements for preformed ferric iron. The behavior of these species in multiphasic, inhomogeneous systems, which is alleged to be inconsistent with that characteristic of OH, is reconciled with the competitive kinetics expected of OH in three situations: (a) compartmentalization at the cellular level (i.e., in vesicles or their membranes) which prevents access of scavengers to the sites of OH generation, (b) site-specificity at the molecular level (OH reaction occurring within a few Angstroms of specific metal-binding sites on macromolecules or in/on membranes), and (c) reactivity of secondary radicals formed by the “scavenging” of OH. (3) The significance of lipids in propagating oxidative damage from the initiation sites of lipid peroxidation to distant sensitive target molecules (proteins and nucleic acids) is discussed, along with the capability of O−2 and H2O2 to serve similar roles in propagating damage from the sites of autoxidation. (4) Finally, some common misinterpretations regarding “scavengers” and inhibitors of oxygen radical reactions from both chemical and metabolic/physiological standpoints are considered in the context of medical implications and applications.
- Published
- 1984
32. Interaction of peroxidizing methyl linoleate with some proteins and amino acids
- Author
-
Marcus Karel, Ram B. Roy, and Karen M. Schaich
- Subjects
chemistry.chemical_classification ,Chemical Phenomena ,Free Radicals ,Chemistry ,Proteins ,Methyl linoleate ,General Chemistry ,Peroxides ,Amino acid ,Radiation Effects ,Egg White ,Linoleic Acids ,Biochemistry ,Muramidase ,Amino Acids ,Cobalt Radioisotopes ,General Agricultural and Biological Sciences ,Oxidation-Reduction - Published
- 1975
33. An electrochemical study of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and its oxidation products
- Author
-
Clovis A. Linkous, Karen M. Schaich, Donald C. Borg, and A. Forman
- Subjects
MPTP ,Inorganic chemistry ,Biophysics ,Electrolyte ,Oxidative phosphorylation ,Electrochemistry ,Medicinal chemistry ,Redox ,Ion ,chemistry.chemical_compound ,chemistry ,Neurotoxin ,Pyridinium ,Physical and Theoretical Chemistry - Abstract
Cyclic voltammetric and chronoamperometric experiments were performed on the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and its oxidative metabolites, 1-methyl-4-phenyl-2,3-dihydropyridinium ion (MPDP+) and 1-methyl-4-phenylpyridinium ion (MPP+). In neutral phosphate buffer electrolyte, MPTP underwent a 2-electron, 1-proton electrooxidation to MPDP+ according to an ECE mechanism where U2o < U1o. Further oxidation could be achieved in alkaline solution. MPDP+ could be reduced to the radical state (Uo ⩽ −0.560 V versus SHE) followed by dimerization and other side reactions. It was also shown that MPDP+ gradually disproportionates to produce MPTP and MPP+. With an Uo = −1.067±0.010 V, MPP+ underwent a 1-electron reduction, followed by dimerization. The redox potentials of MPP+ and possibly even MPDP+ were beyond the limits of known physiological reducing potentials; therefore, the primary cytotoxic action of MPP+ does not proceed via redox cycling of its reduction radical, as do other pyridinium-based toxins such as methyl viologen.
- Published
- 1988
34. Prooxidant action of desferrioxamine: Fenton-like production of hydroxyl radicals by reduced ferrioxamine
- Author
-
Karen M. Schaich and Donald C. Borg
- Subjects
Paraquat ,Antioxidant ,Free Radicals ,Hydroxyl Radical ,Reducing agent ,Iron ,medicine.medical_treatment ,Radical ,Electron Spin Resonance Spectroscopy ,Hydrogen Peroxide ,Deferoxamine ,Ferric Compounds ,Biochemistry ,Redox ,Combinatorial chemistry ,chemistry.chemical_compound ,chemistry ,Oxidizing agent ,Hydroxides ,medicine ,Hydroxyl radical ,Hydrogen peroxide ,Oxidation-Reduction - Abstract
It is common practice in biochemical research to assume that iron bound to desferrioxamine (DFO) to form ferrioxamine (FOA) has been rendered inactive to subsequent redox chemistry within the range of physiological redox potentials, both in vitro and in vivo. However, plants and microorganisms can make iron metabolically available from ferrioxamine and closely related trihydroxamate siderophores, and at neutral pH, cyclic voltammetry of FOA demonstrates a reversible one-electron reduction at about -0.42 to -0.45 V (vs. normal hydrogen electrode), which is within the range of a number of reducing enzymes. We present evidence for the Fenton-like ability of FOA reduced by paraquat cation radicals to consume H2O2 and produce hydroxyl radicals (OH.) in the process. Similar reactions may explain previously reported potentiation of the oxidizing toxicity of paraquat in rats by high doses of DFO, as well as several other examples of prooxidant actions of DFO in vivo. We present the hypothesis that biphasic antioxidant/prooxidant behavior of DFO as a function of dose may be common with iron-catalyzed oxidizing reactions when mobile strong reducing agents are present. Hence, the real possibility of amplifying oxidizing damage must be considered when planning treatment with DFO, and failure of DFO to inhibit a particular response to oxidizing stress or its enhancement by DFO cannot, by itself, be considered sufficient evidence to rule out an iron-dependent process.
- Published
- 1986
35. Cytotoxic reactions of free radical species of oxygen
- Author
-
John J. Elmore, Karen M. Schaich, Donald C. Borg, and J. A. Bell
- Subjects
Free Radicals ,Cell Survival ,Radical ,Ascorbic Acid ,In Vitro Techniques ,Photochemistry ,Biochemistry ,Redox ,Catalysis ,chemistry.chemical_compound ,Oxygen Consumption ,Superoxides ,Physical and Theoretical Chemistry ,Hydrogen peroxide ,chemistry.chemical_classification ,Reactive oxygen species ,Autoxidation ,Chemistry ,Superoxide ,Singlet oxygen ,Quinones ,General Medicine ,Hydrogen Peroxide ,Lipid Metabolism ,Peroxides ,Oxygen ,Cell killing ,Oxidation-Reduction - Abstract
— We report on autooxidation reactions related to selective cell killing in vivo and present oxygen uptake and EPR data on the molecular nature of these changes, with a note on a reaction used to test for singlet oxygen. Selective obliteration by 6-hydroxydopamine, 6-aminodopamine and their congeners of beta-adrenergic cell receptors and of adrenergic and dopaminergic neurons in vivo and in vitro have been reported recently. These effects devolve from autoxidation of the compounds in situ after appropriate biological concentration, but it is unclear whether cytotoxicity is mediated by the reactive oxygen species themselves or by nucleophilic reactions of the product quinones. Because of the possibility of harnessing these reactions for a generalized “chemical surgery” if the former mechanism is operative, and because many other oxidative damage reactions involving unsaturated lipids of biomembranes seem to share similar autoxidative initiating and chain-carrying steps, we have studied the autoxidation of ascorbate and other reductants catalyzed by polyhydroxy quinols related to 6-hydroxydopamine. We find that superoxide anion mediation may or may not be important, depending on redox potentials and reaction kinetics of particular compounds. To the extent that the cellular toxicity of these compounds is oxidative in nature, it is facilitated by—and may depend upon—hydroxyl radical production due to Fenton-type reactions. Likely Fenton reactants in vivo are hydrogen peroxide produced from the quinol-catalyzed autoxidations and non-heme iron reduced cyclically by superoxide anions from the same autoxidations. Studies using flow systems adapted for EPR at 35 GHz have provided support for some of the reaction mechanisms proposed. In nonaqueous solvents eerie oxidation produced transient free radicals from hydrophobic diphenyl and isobenzo furans, which are often cited as “specific” probes for singlet oxygen detection in biochemistry.
- Published
- 1978
36. AUTOXIDATIVE CYTOTOXICITY: IS THERE METAL-INDEPENDENT FORMATION OF HYDROXYL RADICALS? ARE THERE 'CRYPTO-HYDROXYL' RADICALS?
- Author
-
Donald C. Borg, Karen M. Schaich, and Arthur Forman
- Published
- 1984
37. Free radical reactions of peroxidizing lipids with amino acids and proteins: an ESR study
- Author
-
Marcus Karel and Karen M. Schaich
- Subjects
Free Radicals ,Stereochemistry ,Protein Conformation ,Radical ,Lysine ,Cystine ,Molecular Conformation ,Photochemistry ,Biochemistry ,chemistry.chemical_compound ,Amino Acids ,Histidine ,chemistry.chemical_classification ,Binding Sites ,Organic Chemistry ,Tryptophan ,Electron Spin Resonance Spectroscopy ,Proteins ,Cell Biology ,Glutathione ,Amino acid ,Peroxides ,chemistry ,Linoleic Acids ,Oxidation-Reduction ,Cysteine ,Protein Binding - Abstract
Free radical transfer from oxidizing methyl linoleate to amino acids and proteins was studied in dry model systems incubated for periods up to 20 days. Electron spin resonance was used to study free radical production. Free radicals were detectable in the amino acids lysine, arginine, histidine, tryptophan, and cysteine. Reduced glutathione and, to a limited extent, cystine also gave free radical signals. Free radicals produced in proteins primarily showed central singlet lines, attributable to carbon-centered radicals, with g= 2.004+/- 0.001. Sulfhydryl proteins also exhibited downfield shoulders at g approximately equal to 2.015 and 2.023 that were essentially identical to peaks observed in cysteine and reduced gluathione. The field positions of sulfur resonace in cysteine and proteins suggested a sulfur-oxygen complex rather than thiyl radicals.
- Published
- 1976
38. Failure of desferrioxamine to modify the toxicity of paraquat in rats
- Author
-
Merrill R. Osheroff, Donald C. Borg, Karen M. Schaich, and Robert T. Drew
- Subjects
Male ,Paraquat ,medicine.medical_specialty ,Pulmonary toxicity ,medicine.medical_treatment ,Iron ,Intraperitoneal injection ,Deferoxamine ,Biochemistry ,Toxicology ,chemistry.chemical_compound ,Fibrosis ,Internal medicine ,Edema ,medicine ,Hydroxides ,Animals ,Respiratory system ,Lung ,Chelating Agents ,Hydroxyl Radical ,Rats, Inbred Strains ,Hydrogen Peroxide ,medicine.disease ,Rats ,Endocrinology ,chemistry ,Toxicity ,Histopathology ,medicine.symptom - Abstract
The feasibility of using desferrioxamine (DF), an iron chelator, as a therapeutic agent against paraquat (PQ/sup + +/) toxicity in male Sprague-Dawley rats was explored, based on the rationale of limiting toxic hydroxyl radical production from hydrogen peroxide by removing redox-active iron. Body weights, mortality, and lung histopathology were followed for periods up to 14 days after intraperitoneal injection of PQ/sup + +/ (20 or 25 mg/kg body weight) with or without concurrent daily subcutaneous injections of DF (300 mg/day). Animals receiving PQ/sup + +/ showed the expected typical patterns of mortality and of lung histopathology, namely: marked edema, subpleural hemorrhage, acute inflammation, perivascular mononuclear cell infiltrates, sloughing of alveolar and bronchiolar lining cells, and diffuse interstitial fibrosis. Desferrioxamine alone was non-toxic. Surprisingly, results when both PQ/sup + +/ and DF were administered indicated a failure of DF to ameliorate toxic effects of PQ/sup + +/ in the lung, and even suggested an accentuation of PQ/sup + +/-induced damage by DF. Mortality data showed that PQ/sup + +//DF animals died in greater numbers (20 mg PQ/sup + +//kg) or died earlier (25 mg PQ/sup + +//kg) than animals receiving DF alone. Qualitative histopathology in PQ/sup + +//DF animals was comparablemore » to PQ/sup + +/ animals in early stages, but damage was more severe in both incidence and severity of lesions in PQ/sup + +//DF animals, particularly at the 25 mg PQ/sup + +//kg dose level. After 14 days, surviving animals receiving PQ/sup + +/ alone showed almost complete resolution of previous inflammation and other acute effects, whereas in the only surviving PQ/sup + +//DF animal initial fibrosis had persisted and become more generalized. 51 references, 6 figures, 2 tables.« less
- Published
- 1985
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