Phenolics are broadly distributed in the plant kingdom and are the most abundant secondary metabolites of plants. Plant polyphenols have drawn increasing attention due to their potent antioxidant properties and their marked effects in the prevention of various oxidative stress associated diseases such as cancer. In the last few years, the identification and development of phenolic compounds or extracts from different plants has become a major area of health- and medical-related research. This review provides an updated and comprehensive overview on phenolic extraction, purification, analysis and quantification as well as their antioxidant properties. Furthermore, the anticancer effects of phenolics in-vitro and in-vivo animal models are viewed, including recent human intervention studies. Finally, possible mechanisms of action involving antioxidant and pro-oxidant activity as well as interference with cellular functions are discussed.

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Plant phenolics: extraction, analysis and their antioxidant and anticancer properties.

Non-structural phenolic compounds perform a variety of functions in plants, including acting as antioxidants. We describe a microplate-adapted colorimetric total phenolics assay that utilizes Folin-Ciocalteu (F-C) reagent. The F-C assay relies on the transfer of electrons in alkaline medium from phenolic compounds to phosphomolybdic/phosphotungstic acid complexes, which are determined spectroscopically at 765 nm. Although the electron transfer reaction is not specific for phenolic compounds, the extraction procedure eliminates approximately 85% of ascorbic acid and other potentially interfering compounds. This assay is performed in microcentrifuge tubes and assessed in a 96-well plate reader. At least 64 samples can be processed in 1 d.

Estimation of total phenolic content and other oxidation substrates in plant tissues using Folin-Ciocalteu reagent.

Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects – A review

Polyphenols are the biggest group of phytochemicals, and many of them have been found in plant-based foods. Polyphenol-rich diets have been linked to many health benefits. This paper is intended to review the chemistry and biochemistry of polyphenols as related to classification, extraction, separation and analytical methods, their occurrence and biosynthesis in plants, and the biological activities and implications in human health. The discussions are focused on important and most recent advances in the above aspects, and challenges are identified for future research.

Chemistry and Biochemistry of Dietary Polyphenols

α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging method offers the first approach for evaluating the antioxidant potential of a compound, an extract or other biological sources. This is the simplest method, wherein the prospective compound or extract is mixed with DPPH solution and absorbance is recorded after a defined period. However, with the advancement and sophistication in instrumental techniques, the method has undergone various modifications to suit the requirements, even though the basic approach remains same in all of them. This article presents a critical review on various developments to the DPPH method.

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Genesis and development of DPPH method of antioxidant assay

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.

https://faculty.missouri.edu/~glaserr/3700s14/Antioxidant-Capacity_jf0502698.pdf

Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements

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.

Extraction of lipids from extruded corn‐soy blends1

Lipid Antioxidants: More than Just Lipid Radical Quenchers

Lipid autoxidation poses a significant problem for stabilizing sensory quality,
 nutritional value, and chemical safety of lipid containing foods. Peroxide value and
 volatile carbonyls are the most measured markers to assess oxidation, but products such
 as epoxides and alcohols are now being identified and quantified in foods. The
 mechanisms and conditions under which other products form are poorly understood,
 particularly how lipid structure and oxidation conditions affect reaction pathways,
 products, and rates. This research paper aims to show how number of double bonds affects
 oxidation product formation, how oxidation temperature affects reaction rates and
 product formation and decomposition, and how open or closed packaging systems affect
 reaction rates.Methyl oleate and methyl linoleate were autoxidized neat and incubated at
 25, 40, or 60Â Â°C for various incubation periods. Class assays for quantification of
 oxidation products included the following: conjugated dienes by UV absorbance at 233 nm;
 peroxide value by reaction with TPP; epoxide value by reaction with
 diethydithiocarbamate; soluble carbonyls by reaction with 2,4-dinitrophenylhydrazine.
 Direct separation of oxidation products was performed using NP-HPLC with detection and
 quantitation by UV and Corona Charged Aerosol (CAD) detection. Alternate
 autoxidation products competed with the formation of hydroperoxides in both autoxidizing
 oleate and linoleate.Â Epoxides were found to be the dominant product in oleate
 autoxidized at 25 C, reaching a maximum value of 69.2 mmol/mol lipid, while peroxide
 value reached a maximum of 23.71 mmol/mol lipid. Epoxides were also found to be a major
 product in linoleate autoxidation reaching a maximum value of 357.5 mmol/mol lipid at 25
 C, while peroxide value reached a maximum of 357.1 mmol/mol lipid. For both oxidized
 oleate and linoleate, rate of epoxide formation competed with that of hydroperoxides,
 demonstrating that alternate reactions are active and important in directing the
 reaction rates and product distributions of autoxidizing lipids.

Karen M. Schaich

Papers

Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements

Extraction of lipids from extruded corn‐soy blends1

Lipid Antioxidants: More than Just Lipid Radical Quenchers

Epoxides are major products in oxidation of methyl oleate and linoleate and their triacylglycerols