Papers by Karen M. Schaich
Oxidation of unsaturated lipids is the most active chemical reaction leading to deterioration of ... more Oxidation of unsaturated lipids is the most active chemical reaction leading to deterioration of food quality and shortening of shelf life. Lipid oxidation is known to be a free radical chain reaction driven by lipid peroxyl and alkoxyl radicals abstracting hydrogen atoms from neighboring molecules to form stable hydroperoxide intermediates and transfer a radical to a new molecule. In this process, products accumulate only after hydroperoxides decompose. However, this simplistic reaction fails to account for observed kinetics and compounds generated. Recently, a more complex reaction scheme for lipid oxidation was proposed which integrates traditional hydrogen abstraction with alternate reactions of peroxyl and alkoxyl radicals-internal rearrangement, double bond addition, scission, dismutation. The alternate reactions run simultaneously and in competition with hydrogen abstraction, and alter the overall picture of lipid oxidation under different conditions. This dissertation resear...
IUPAC Standards Online, Mar 13, 2016
The chemical diversity of natural antioxidants (AOXs) makes it difficult to separate, detect, and... more 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. Keywords: 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)/Trolox-equivalent antioxidant capacity (TEAC); antioxidant capacity/activity; cereals; cupric reducing antioxidant capacity (CUPRAC); 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH); ferric reducing antioxidant power (FRAP); fruits; hydrophilic/lipophilic antioxidants; IUPAC Analytical Chemistry Division; oxygen radical absorbance capacity (ORAC); original and modified reducing antioxidant capacity CUPRAC methods; total antioxidant capacity (TAC) assays; total peroxyl radical-trapping antioxidant parameter (TRAP); vegetables. CONTENTS 1. BACKGROUND 1.1 HAT-based assays 1.2 ET-based assays 2. DETERMINATION OF HYDROPHILIC AND LIPOPHILIC ANTIOXIDANT CAPACITY: COMMENTS AND RESULTS *Sponsoring body: IUPAC Analytical Chemistry Division: see more details on p. 991.
Elsevier eBooks, 2016
Abstract During nearly 20 years of the low-/no-fat era, lipid oxidation was essentially forgotten... more Abstract During nearly 20 years of the low-/no-fat era, lipid oxidation was essentially forgotten as a stability problem. Now, the era of healthy fats focuses on reformulating foods with highly unsaturated (polyunsaturated) fatty acids (PUFAs). PUFAs are essential – they cannot be synthesized by humans and they are required for many physiological processes – but also are extremely sensitive to oxidation and can very rapidly degrade food quality, function, and nutrition by production of off-flavors and odors, loss of essential fatty acids, and co-oxidation of proteins and vitamins. Thus, a need for accurate and sensitive tracking of lipid oxidation has once again moved to the forefront in food analyses and quality control. Old “rules” of how to measure lipid oxidation do not always provide accurate pictures of lipid oxidation. Most critically, they often underestimate total oxidation levels and misrepresent active pathways. This chapter argues for a new paradigm in analysis of lipid oxidation. The main focus is on analyses used or likely to be applied in the food industry. Highly specialized methods such as electron paramagnetic resonance, nuclear magnetic resonance, and mass spectrometry requiring expensive instrumentation are not included.
Proceedings of the Virtual 2021 AOCS Annual Meeting & Expo, May 3, 2021
Cereal chemistry, Nov 1, 2003
Cereal Chem. 80(6):791-798 Antibodies specific for wheat proteins were used to identify protein f... more Cereal Chem. 80(6):791-798 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 of gliadins extracted in 1M urea and in 70% ethanol revealed total loss of cysteine-containing α, β, γ-gliadins but no obvious effects on sulfur-poor ω-gliadins, suggesting gliadin modification involves replacing intramolecular disulfides with intermolecular disulfide cross-links. Identifying protein fractions modified during different extrusion conditions may provide new options for tailoring extrusion to achieve specific textural characteristics.
Journal of Food Lipids, May 5, 2007
ABSTRACT Extruded corn-soy products developed for the US AID Food for Peace program contain high ... more 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.
Springer eBooks, 1980
Autoxidation processes generally proceed via free radical chain processes involving both the auto... more Autoxidation processes generally proceed via free radical chain processes involving both the autoxidizing compound itself and also, potentially, any other components of the system. Thorough understanding of such processes thus requires kinetic and structural data about the free radical reaction steps and intermediates comprising variously the initiation, propagation, and termination phases.
Israel Journal of Chemistry, 1984
A comprehensive reaction schema for oxidative cytotoxicity is presented, integrating known chemic... more 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.
... MAT.; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; LIPIDS; OXIDATION; NUCLE... more ... MAT.; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY; LIPIDS; OXIDATION; NUCLEIC ACIDS; CELL MEMBRANES; DAMAGE; HYDROGEN PEROXIDE; HYDROXYL RADICALS; ION EXCHANGE CHROMATOGRAPHY; IRON COMPLEXES ...
Packaging Technology and Science, 2005
have collaborated to develop a concept of using smart blending to generate functional packaging f... more 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.
Acs Symposium Series, Mar 4, 2002
Acs Symposium Series, May 5, 1994
... 1Department of Food Science, Cook College, Rutgers, The State University of New Jersey, New B... more ... 1Department of Food Science, Cook College, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903 2Department of Food Science, University of Delaware, Newark, DE 19716 3Kalsec, Inc., PO Box 511, Kalamazoo, MI 49005 ...
Proceedings of the Virtual 2021 AOCS Annual Meeting & Expo, May 3, 2021
Journal of the American Oil Chemists' Society, Dec 4, 2014
Acs Symposium Series, Mar 4, 2002
De Gruyter eBooks, Dec 31, 1984
Springer eBooks, 1982
A Continuation Order Plan is available for this series. A continuation order will bring delivery ... more A Continuation Order Plan is available for this series. A continuation order will bring delivery of each new volume immediately upon publication. Volumes are billed only upon actual shipment. For further information please contact the publisher.
Elsevier eBooks, 1990
Publisher Summary 8-Hydroxyquinoline (8-HOQ) is a very efficient chelator with a high binding con... more Publisher Summary 8-Hydroxyquinoline (8-HOQ) is a very efficient chelator with a high binding constant for a broad range of metals. 8-HOQ has been commercially coated onto controlled-pore glass (CPG) beads; and in this form, it provides the best method for the removal of metals from all volumes and classes of reagents used in oxygen radical reactions. This chapter discusses CPG/8-HOQ method to prepare metal-free solutions for the studies of active oxygen species. CPG/8-HOQ can be used in either batch or column procedures. In the batch procedure, an amount of dry CPG/8-HOQ equivalent to about 5 times the estimated or known content of iron is weighed into the reagent solution to be demetaled and stirred or shaken for 30 minutes. The chelator is removed by centrifugation or by settling, and the reagent is decanted. The metal content is analyzed by atomic absorption (AA) spectrophotometry, and the chelation procedure is repeated if necessary. This method is simple but great care must be exercised to avoid contamination during recovery of the reagent. Column procedures offer fewer opportunities for recontaminating the reagent, but they may be less efficient than batch extractions if the elution rate from the column is too fast.
Journal of Functional Foods, Oct 1, 2015
Assays developed to measure radical scavenging ability of natural compounds have been used as a b... more 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 understand how natural antioxidants can be used most effectively in foods.
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Papers by Karen M. Schaich