Bioactive Compounds in Foods

Chapter 3

Change in Radical-Scavenging Activity of Spices and Vegetables during Cooking 1

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Hitoshi Takamura , Tomoko Yamaguchi , Junji Terao , and Teruyoshi Matoba * Downloaded by UNIV OF PITTSBURGH on June 23, 2013 | http://pubs.acs.org Publication Date: July 8, 2002 | doi: 10.1021/bk-2002-0816.ch003

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Department of Food Science and Nutrition, Nara Women's University, Kitauoya-nishimachi, Nara 630-8506, Japan Department of Nutrition, School of Medicine, The University of Tokushima, Kuramoto-cho 3, Tokushima 770-8503, Japan 2

The change in radical-scavenging activity of vegetables and spices during cooking was analyzed by the l , l-diphenyl-2picrylhydrazyl-HPLC method. After boiling of vegetables, the radical-scavenging activity increased in burdock, green pepper, asparagus, eggplant, and carrot, while the activity in other vegetables decreased. In most cases, however, the total activity of cooked vegetable and cooking water was higher than that of fresh vegetables. Microwave heating increased the radical-scavenging activity in 9 of 14 vegetables. These results suggest that the intake of vegetables with cooking water or microwave-cooked vegetables can be recommended to use radical-scavenging components efficiently. In the process of curry cooking, the radical-scavenging activity of spices decreased, while that of vegetables increased. The radical-scavenging activity of curry also decreased after heating.

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© 2002 American Chemical Society

In Bioactive Compounds in Foods; Lee, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2002.

Downloaded by UNIV OF PITTSBURGH on June 23, 2013 | http://pubs.acs.org Publication Date: July 8, 2002 | doi: 10.1021/bk-2002-0816.ch003

35 Free radicals and active oxygen species are well known to induce many types of oxidative damage to biomolecules, which cause cancer, aging, and lifestyle related diseases (1). Dietary foods contain a wide variety of free radicalscavenging antioxidants, such asflavonoids,vitamin C, and so on (2). These compounds are abundantly present in vegetables, fruits, spices, and other plant origin foods. Epidemiological studies have shown that higher intake of fresh vegetables, fruits, tea, and wine is associated with lower risk of cancer and lifestyle related diseases (3,4). Hence, there is currently much interest in natural antioxidants and their role in human health and nutrition. However, we usually eat foods after cooking. In this work, we demonstrated the changes in radicalscavenging activity of vegetables and spices during cooking.

Materials and Methods

Preparation of Fresh and Cooked Vegetable Extracts Fourteen vegetables were obtained from local markets in Nara, Japan. The edible portions of fresh vegetables (10-20 g) were cut into small pieces and homogenized with 30 mL of water for 20-30 s, using a homogenizer. The resulting homogenate was centrifuged at 27,000*g for 20 min at 4°C, and the supernatant was filtered through a 0.45-|im filter. After appropriate dilution, the aqueous extract was used for the measurement of radical-scavenging activity. For the measurement of ascorbic acid content, 5% metaphosphoric acid with or without 1% stannous chloride was used instead of water. For boiling of vegetables, the edible portions offreshvegetables (80-150 g) were cut into small pieces. Cut vegetable was heated in 500 ml of boiling water for 5 min. Then, the extract of cooked vegetable was prepared as described above. The cooking water was also used for the measurement of radicalscavenging activity and ascorbic acid content after concentration. For microwave heating, cut vegetable was placed on a ceramic plate, covered with a plastic cap, and heated in a microwave oven (500 W) for 5 min. Then, the extract of cooked vegetable was prepared as described above.

Curry Preparation Curry is one of the most popular spicy dishes in Japan and other Asian countries which uses both vegetables and spices. Vegetables and meat were



36 cooked in water, and kept separately. Spice mixture was heated with butter and wheat flour to prepare curry paste. Then, cooked vegetables and meat and curry paste were combined and heated to prepare curry. Spice mixture used for curry cooking contained 9 flavoring spices; coriander (27%), cumin (8%), cardamon (5%), allspice (4%), cinnamon (4%), fenugreek (4%), clove (2%), fennel (2%), and mace (2%), 3 hot-tasting spices; ginger (4%), red pepper (4%), and white pepper (4%), and 1 coloring spice; turmeric (30%). This is a Japanese recipe for a popular curry powder with medium hot taste (J). One serving (260 g) of curry was prepared from 30 g carrot, 40 g onion, 60 g potato, 50 g beef, 2.5 g spice mixture, 12.5 g butter, and 10 g wheat flour. The curry preparation at each step was first extracted with 80% ethanol, and then with water. Extraction was carried out under the same procedure for fresh vegetables as described above. Both 80% ethanol and water extracts were used for the determination of radical-scavenging activity.

Détermination of Radical-scavenging Activity and Ascorbic Acid Content The radical-scavenging activity of ascorbic and dehydroascorbic acids, vegetables, and curry preparations was determined by l,l-diphenyl-2picrylhydrazyl (DPPH)-HPLC method according to Yamaguchi et al (6). Briefly, 1 mL of 0.5 mM DPPH in ethanol was mixed with 0.8 mL of 100 mM Tris-HCl buffer (pH 7.4) and 0.2 mL of sample extract. The mixture was shaken vigorously and left to stand for 20 min at room temperature in the dark. Then, the reaction mixture was injected into HPLC with a 20-μ1 loop. HPLC analysis was performed using a TSKgel Octyl-80Ts column (4.6x150 mm, Tosoh, Tokyo, Japan) at room temperature with a mobile phase of methanol/water (70:30, v/v), and at a flow rate of 1 mL/min. DPPH was detected at 517 nm. Trolox was used as the standard to evaluate radicalscavenging activity. The ascorbic acid content was determined by HPLC according to Kishida et al (7). Then, the radical-scavenging activity due to ascorbic acid was calculated.

Results and Discussion Radical-scavenging Activity of Ascorbic and Dehydroascorbic Acids The radical-scavenging activity of ascorbic and dehydroascorbic acids was determined by the DPPH-HPLC method (Table I). Dehydroascorbic acid (50 μΜ) had no ability to scavenge DPPH radical, while the activity of 50 μΜ


37 ascorbic acid was approximately 60 μΜ Trolox equivalent. Electron spin resonance measurement also showed that dehydroascorbic acid has no scavenging activity on hydroxyl radical (data not shown). The combined effects of ascorbic acid and dehydroascorbic acid on DPPH radical-scavenging activity were also measured (Table I). There was no positive or negative synergism between the radical-scavenging activity of ascorbic and dehydroascorbic acids.


Change in Radical-scavenging Activity of Vegetables During Boiling Figure 1 shows the radical-scavenging activity of fresh vegetables, boiled vegetables, and cooking water. In burdock, green pepper, asparagus, eggplant, and carrot, the radical-scavenging activity of cooked tissue was higher than that of fresh tissue, though the ascorbic acid content decreased. This increase may be due to the thermal destruction of vegetable cell walls and subcellular compartments, the decrease of oxidative loss of active compounds by inactivation of oxidase, and/or the activation of inactive compounds by heating. In broccoli, pumpkin, and cabbage, the radical-scavenging activity in the tissue decreased after boiling. However, part of the activity was found in cooking water, and the total activity of cooked tissue and cooking water increased. Hence, in order to intake the radical-scavenging components efficiently, intake of cooking water together with cooked vegetable can be recommended, such as vegetable soup and stew. In Chinese cabbage, onion, kidney beans, Japanese radish, tomato, and spinach, the total radical-scavenging activity of cooked tissue and cooking water decreased after boiling. The active components in these vegetables may be unstable against heat.

Effect of Sodium Chloride on the Radical-scavenging Activity of Boiled Vegetable Table II shows the radical-scavenging activity of boiled spinach with or without sodium chloride. As the content of added sodium chloride increased, the radical-scavenging activity was retained more in the tissue, while the total activity did not change. Therefore, the addition of sodium chloride to the cooking water can be recommended to intake the radical-scavenging components efficiently, since it inhibits the release of the active components from the tissue to the cooking water.


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Table I. Radical-scavenging Activity of Ascorbic and Dehydroascorbic Acids Radical-scavenging Activity Concentrations (μΜ) (μΜ Trolox equivalent) Ascorbic Acid Dehydroascorbic Acid ND 0 50 56.9±1.9 50 0 59.5±0.4 50 25 59.2±1.5 50 50 50 75 59.9±2.6 61.0±2.1 50 100 59.9±1.3 50 200 50 60.0±1.9 250 58.8±0.8 50 500


a

b

*ND,not detected. b

The values are the means±SD of 3 determinations.

Table II. Effect of Sodium Chloride on Radical-scavenging Activity of Boiled Spinach Concen tration

0 1 2

Radical-scavenging Activity Total Activity Cooked Cooking Water Tissue 73.6 (20) 284.4 (76) 92.0 (25) 217.2 (58) 154.1 (41) 156.7 (42) b

c

(μτηοΐ Trolox equivalent/100 g) Ascorbic Acid Cooking Cooked Water Tissue 6.3(7) 9.1 (10) 6.6(7) 1-3 (1) 8.2 (9) 20.9(23) 3

Calculatedfromascorbic acid content. b

The values are the means of 3 determinations.

°The values in parentheses are the percentages to the activities offreshvegetables.


39 Burdock/Fresh Boiled Water


Broeeoli/Fresh Boiled Water Green pepper/Fresh Boiled Water Asparagus/Fresh Boiled Water Spinach/Fresh Boiled Water Eggplant/Fresh Boiled Water Japanese radish/Fresh Boiled Water Pumpkin/Fresh Boiled Water Cabbage/Fresh Boiled Water Kidney beans/Fresh Boiled Water, Tomato/Fresh Boiled Water Chinese cabbage/Fresh Boiled Water Onion/Fresh Boiled Water Carrot/Fresh Boiled Water! 0

• Ascorbic acid • Components other than ascorbic acid 250

500

750

1000

1250

Radical-scavenging activity (μηιοί Trolox equivalent/100g) Figure 1. Change in radical-scavenging activity of vegetables during boiling.


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Change in Radical-scavenging Activity of Vegetables During Microwave Heating Figure 2 shows the radical-scavenging activity of fresh and microwaveheated vegetables. In 9 of 14 vegetables, especially in burdock and eggplant, the radical-scavenging activity increased by microwave heating. The activities of microwave-heated vegetables were higher than those of boiled vegetables, since there was no release of active components to boiling water during microwave heating. Hence, microwave heating can be recommended to intake the radicalscavenging components efficiently. In onion, Japanese radish, spinach, kidney beans, and pumpkin, the radical-scavenging activity decreased after microwave heating. However, microwave heating is effective in the cooking of spinach, since the loss of the activity was minimized by microwave heating.

Change in Radical-scavenging Activity of Vegetables and Spices During Curry Cooking The changes of the radical-scavenging activity during curry cooking are shown in Figure 3. The activity of fresh vegetables and meat was 75 μηιοί Trolox equivalent per one serving. The activity increased to 205 μηιοί after heating. On the contrary, the activity of spice mixture decreased from 318 to 162 μτηοΐ during preparation of curry paste. This decrease may be due to decomposition or evaporation of active compounds, since spices were heated with butter at high temperature. In spite of the loss by heating, however, spices still contained high activity. The activity of curry was 312 μηιοί Trolox equivalent per one serving, which is 20% Iowa* than the total activity (367 μηιοί) of cooked vegetables and meat and curry paste. Hence, heating of curry for a long time cannot be recommended to keep radical-scavenging activity. However, spicy dishes such as curry are useful to intake radical-scavenging components contained in spices as well as vegetables.

References 1.

Halliwell, B.; Gutteridge, J. M . C.; Cross, C. E. J. Lab Clin. Med. 1970, 119, 598-620. 2. Shahidi, F; Naczk, M . Food Phenolics, Sources, Chemistry, Effects, Applications; Technomic Publishing Co. Inc.: Lancaster, PA, 1995; pp 75107.


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Burdock/Fresh Heated Broccoli/Fresh Heated


Green pepper/Fresh Heated Asparagus/Fresh Heated Spinach/Fresh Heated Eggplant/Fresh Heated j j Japanese radish/Fresh; Heated Pumpkin/Fresh Heated Cabbage/Fresh Heated Kidney beans/Fresh Heated Tomato/Fresh Heated Chinese cabbage/Fresh Heated Onion/Fresh Heated Carrot/Fresh 1 Heated J

H Ascorbic acid • Components other than ascorbic acid 500

1000

1500

2000

2500

Radical-scavenging activity (μηιοί Trolox equivalent/100g) Figure 2. Change in radical-scavenging activity of vegetables during microwave heating.



Figure 3. Change in radical-scavenging activity of vegetables and spices during curry cooking.

0 100 200 300 400 Radical-scavenging Activity (μηαοί Trolox equivalent/serving)

Curry/After Heating

Curry/Before Heating

Curry Paste/After Heating

Spiee Mixture/Before Heating

Vegetable and Meat/After Heating

Vegetable and Meat/Before Heating


43 Ames, Β. Ν.; Shigenaga, M . K.; Hagen, T. M . Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 7915-7922. 4. Willett, W. C. Science, 1994, 264, 532-537. 5. Hamada, T. Jpn. Food Sci., 1970, 12, 51-56. 6. Yamaguchi, T.; Takamura, H.; Matoba, T.; Terao, J. Biosci. Biotechnol. Biochem. 1998, 62, 1201-1204. 7. Kishida, E.; Nishimoto, Y.; Kojo, S. Anal. Chem. 1992, 64, 1505-1507.


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Bioactive Compounds in Foods

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