Phenolic Compounds in Foods and Natural Health Products

Chapter 10

Downloaded by NORTH CAROLINA STATE UNIV on May 4, 2015 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0909.ch010

Radical Scavenging Properties of Cold-Pressed Edible Seed Oils John W. Parry, Kequan Zhou, and Liangli (Lucy) Yu Department of Nutrition and Food Science, 0112 Skinner Building, University of Maryland, College Park, MD 20742

Cold-pressed cranberry, black raspberry, black caraway, carrot, and hemp seed oils were evaluated for their free radical scavenging capacities against ABTS , DPPH and oxygen radical (ORAC), as well as total phenolic contents (TPC). All tested cold-pressed seed oils directly reacted with and quenched DPPH in the reaction mixture. The cold-pressed black caraway seed and cranberry seed oils at concentrations of 5.3 and 22.6 mg oil equivalent/mL exhibited stronger DPPH radical scavenging activities than that of 50 mM α-tocopherol. The DPPH scavenging capacity was both time and dose dependent for all tested seed oils. Significant ABTS scavenging activities were detected in the cold-pressed seed oils in a range of 9-31μ m o l eTE/goil. The greatest ORAC value of 220 μmole TE/g oil was detected in black caraway seed oil, and was followed by that of 160 and 28 μmole TE/g oil for carrot and hemp seed oils, respectively. In addition, the total phenolic contents were 0.1, 0.43, 1.6 and 3.5 mg gallic acid equivalent per gram of oil for the cold-pressed black raspberry, hemp, cranberry and black caraway seed oils, respectively. These results suggest that the cold-pressed edible seed oils may serve as dietary sources for natural antioxidants. •+

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© 2005 American

Chemical Societv

In Phenolic Compounds in Foods and Natural Health Products; Shahidi, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.

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108 It is well recognized that dietary factors may influence human health and life quality. More consumers are interested in disease prevention and health promotion by dietary improvements. Recently, cold-pressed seed oils, including black caraway, carrot, hemp, cranberry and black raspberry seed oils, have become commercially available. The cold-pressing procedure involves neither heat nor chemicals, and is becoming a more interesting substitute for conventional practices because of consumers' desire for natural and safe food products. Cold-pressed seed oils may retain more natural beneficial components of the seeds such as natural antioxidants. Antioxidants are well recognized for their potential in health promotion and prevention of aging-associated diseases, such as cancer and heart disease (1,2). Several chemical mechanisms have been proposed to explain the beneficial effects of antioxidants. These mechanisms included directly reacting with and quenching free radicals, forming chelating complexes with transition metals, reducing peroxides, and stimulating antioxidative defense enzymes. Novel dietary sources of natural antioxidants are desired for health benefits. Several cold-pressed seed oils have been investigated for their fatty acid composition and oxidative stability, as well as other physical properties (3). Cold-pressed cranberry and hemp seed oils contain about 20% alinolenic acid, and may serve as dietary sources for ω-3 fatty acids. Cold-pressed carrot seed oil was high in oleic acid content (80%) and low in total saturated fatty acids. These results showed the potential health benefits from consuming cold-pressed edible seed oils. In addition, the cold-pressed seed oils exhibited excellent oxidative stability compared to commercial soybean and corn oils, suggesting the possible presence of natural antioxidants in the cold-pressed seed oils (3). Therefore, the present study was conducted to evaluate the radical scavenging properties of cold-pressed carrot, hemp, black caraway, cranberry, and black raspberry seed oils.

Materials and Methods Materials. Cold-pressed, 'extra virgin,' unrefined black caraway, carrot, hemp, cranberry and black raspberry seeds oils were provided by Badger Oil Company (Spooner, WI). Fluorescein (FL), 2,2'-bipyridyl and 2,2-diphenyl-l-


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picryhydrazyl radical (DPPH*), 2,2'-bipyridyl, and 6-hydroxy-2,5,7,8tetramethylchroman-2-carboxylic acid (Trolox) were purchased from SigmaAldrich (St. Louis, MO), while 2,2-azobis (2-amino-propane) dihydrochloride (AAPH) was obtained from Wako Chemicals USA (Richmond, VA), βcyclodextrin (RMCD) was purchased from Cyclolab R & D Ltd. (Budapest, Hungary). A total antioxidant status kit was purchased from Randox Laboratories Ltd. (San Francisco, CA). All other chemicals and solvents were of the highest commercial grade and used without further purification.

Preparation of antioxidant extract A measured amount of cold-pressed seed oil was extracted with methanol at ambient temperature. The methanol extract was flushed with nitrogen, and kept in the dark until further analysis. In order to prepare dimethyl sulfoxide DMSO) solution, methanol was removed under vacuum from a known volume of the methanol extract, and the residue was completely dissolved in DMSO. The resulting DMSO solution was also kept in the dark after nitrogen flushing until further analysis.

Radical DPPH scavenging activity Radical DPPH* scavenging capacity of the antioxidant extract was estimated according to the previously reported procedure (/). Freshly made DPPH* solution was added to antioxidant extracts with known concentrations and mixed to start the radical-antioxidant reaction. The initial concentration was 100 μΜ for DPPH*, and the total volume was 2000 μΐ, for each reaction mixture. The absorbance at 517 nm was determined against a blank of pure methanol at 0, 0.5, 1, 2, 5, 10, 20, 40 and 80 minute of reaction and used to estimate the remaining radical levels according to the standard curve. The dose and time dependencies of carrot oil extract and DPPH* reactions were demonstrated by plotting the percent of DPPH* remaining against time for each level of the carrot seed oil extract tested. Tests were done in triplicate for each antioxidant.

Radical cation ABTS" scavenging activity Radical scavenging capacity of each antioxidant extract was evaluated against ABTS* generated by the enzymatic method using a commercial kit from Randox Laboratories Ltd. (San Francisco, CA) (2,4). The absorbance at 734 nm was measured at 1 min of the antioxidant-radical reaction, and used to calculate +


110 the trolox equivalent using a standard curve prepared with trolox. The tests were conducted in triplicate for each extract.


ORAC assay The ORAC assay was performed usingfluorescein(FL) as the fluorescent probe following a previously described protocol (5). The DMSO stock solution was diluted with the 7% RMCD in acetone/water (1:1, v/v) to obtain the assay sample. The final assay mixture contained 0.067 μΜ of FL, 60 mM of AAPH, 300 μL of the assay sample or 7% RMCD containing DMSO for a reagent blank. The total volume was 3000 μΐ. for each reaction mixture. Thefluorescenceof each assay mixture was determined and recorded once per minute using a Turner Quantech™ Fluorometer (Dubuque, IA). Trolox was used to prepare the standard curve to calculate the trolox equivalent of the cold-pressed seed oil.

Total phenolic contents The total phenolic content of each oil extract was determined using FolinCiocalteu reagent (/). The reaction mixture contained 100 μL· of the oil extract in DMSO, 500 μΐ. of the Folin-Ciocalteu reagent, and 1.5 mL of 20% sodium carbonate. The final volume was made up to 10 mL with pure water. After two hours of reaction at ambient temperature, absorbance at 765 nm was measured and used to calculate the phenolic contents using a standard curve prepared with gallic acid. Triplicate reactions were performed.

Statistic analysis Data were reported as mean ± standard deviation (SD). Analysis of variance and least significant difference tests were conducted to identify differences among means. Statistical significance was declared at p

Phenolic Compounds in Foods and Natural Health Products

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