Total Phenolic Content and Antioxidant Activity of Cereals - American

Chapter 13

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on November 3, 2015 | http://pubs.acs.org Publication Date: September 19, 2008 | doi: 10.1021/bk-2008-0993.ch013

Total Phenolic Content and Antioxidant Activity of Cereals 1

Ting Sun and Chi-Tang Ho

2

1

Department of Food Science, Louisiana State University, Baton Rouge, LA 70803 Department of Food Science, Rutgers, The State University of New Jersey, New Brunswick, NJ 08903

2

Cereals are good sources of various antioxidants that can prevent cardiovascular diseases and certain types of cancer. For barley, buckwheat, corn, millet, oat, rice, rye, sorghum and wheat, the total phenolics content of the selected cereals have been summarized in the literature. Based on the available data of 2,2 '-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2'-diphenyl-l-picrylhydrazyl (DPPH) free radical scavenging activity in the literature, the antioxidant activity of sorghum (not including white sorghum) is higher than the other cereals, rye has the lowest antioxidant activity, and the other cereals are in the medium antioxidant activity group. The total phenolics content and antioxidant activity of cereals are significantly correlated.

Cereals are important staple foods. According to the annual global production of major cereal grains in 2005, the mostly consumed cereals with production amount from high to low was corn, wheat, rice, barley, sorghum, millet, oat, rye and buckwheat. Corn, wheat and rice accounted for 87% of all grain production (1). Cereal grains supply most of their food energy as starch. Whole grains are good sources of dietary fiber and essential fatty acids. Cereals also contain phenolic acids, flavonoids, vitamins and minerals. Contribution of © 2008 American Chemical Society In Functional Food and Health; Shibamoto, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

143

144


the identified antioxidants in grains to health benefit has not been fully explored (2). The major health benefits of cereals include antibacterial, antiviral, anti inflammatory, and antiallergic effect. Cereals can also slow digestibility, lower cholesterol, prevent cardiovascular disease and reduce colon cancer (3,4). It is generally suggested that the health benefit of grains are mainly due to their antioxidants. The objective of this review is to summarize and compare the total phenolics content and antioxidant activity of the commonly consumed cereals.

Phenolic Acids of Cereals Ferulic acid is the most abundant phenolic acid in cereals. Wheat contains 0.8-2 g/kg dry weight of ferulic acid, which is 90% of total phenols present. The other major phenolic acids in cereals are caffeic acid, vanillic acid, /?-coumaric acid, />hydroxybenzoic acid, protocatechuic acid, sinapic acid and syringic acid (5). The total amount of phenolic acid in cereals is as high as 500 mg/kg of groat (5). Phenolic acids exist mainly as benzoic and cinnamic acid derivatives in cereals. Cereal grains contain several parts: hull, bran, endosperm and germ. The distribution of phenolic acids in cereal groat is not even, generally, the outer layer, such as bran, contains higher amounts of phenolic acids than the center of grain. It is found that p-coumaric acid in barley increases greatly from the center to the outer layer of grain. Free and soluble conjugated phenolic acids in cereal flour are very low and their total amount ranges between 2.3 (wheat) and 16.5 (corn) ^ig/kg (6). No single method can extract all the cereal antioxidants. Methanol, ethanol, and acetone are commonly used to extract free phenolic acid in cereals, and small amounts of HC1 or acetic acid can be added to release the soluble conjugated phenolic acids. Bound phenolic acids are not available for extraction by these solvents. Most phenolic acids in cereals exist as insoluble bound forms associated with cell wall polysaccharides. To hydrolyze the bound phenolic acids from cell walls, alkali hydrolysis and enzyme hydrolysis are used. There is an increase of phenolic acid content by 14.2 mg ferulic acid equivalents/g crude extract after hydrolysis of whole wheat (7). Phenolic acids are the common antioxidants in cereals and have been thought to contribute significantly to the total antioxidant properties of cereals.

Total Phenolic Content of Cereals The total phenolics content of cereals is often determined using FolinCiocalteu reagent, which includes phenolic acids, flavonoids, ascorbic acid, among others. In most studies, cereal groat is extracted with methanol or acetone without complete hydrolysis of the bound phenolics, which are the data reported in Table I. Data from the literature were used to calculate the same unit

In Functional Food and Health; Shibamoto, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.


145 of \xmoVg dry weight. The total phenolics content is reported using different standards, such as gallic acid, ferulic acid or catechin equivalents. Based on the data in Table I, relative total phenolics content index (%) is developed to facilitate the comparison of the total phenolics content of cereals expressed as different standards. For the data expressed as each standard, the highest value of cereal was considered as 100%, and the values of the other cereals are expressed as a percentage of it. Then, for each cereal, the mean value of the percentage for different standards is calculated as this cereal's relative total phenolics content index (%). Grain color of sorghum includes red, black, brown and white, and the data of each color of sorghum are reported individually. As shown in Figure 1, the rank of the relative total phenolics content index of cereal groat from high to low is: brown sorghum, red sorghum, black sorghum, wheat, barley, oat, buckwheat, rice, corn, millet, white sorghum, and rye. The high total phenolics content group includes brown, red and black sorghum. The low total phenolics content group includes rye and white sorghum, and the other cereals belong to the medium total phenolics content group.

Antioxidant Activity of Cereals More than 15 methods are available for determination of antioxidant activity of foods (8). However, there are no officially standardized methods established yet for analyzing the antioxidant activity of foods. Hydrogen atom transfer (HAT) reactions include oxygen radical absorbance capacity (ORAC), total radical-trapping antioxidant parameter (TRAP), and inhibition of autoxidation of induced low-density lipoprotein (LDL). In most HAT-based methods, antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. Electron transfer-based methods include 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), 2'-diphenyl-l-picrylhydrazyl (DPPH) and cupric reducing antioxidant capacity (CUPRAC) methods. These methods measure the ability to reduce an antioxidant by the color change of the oxidant. However, there is no simple universal method by which antioxidant activity can be measured accurately and quantitatively (8). Therefore, data generated with several methods are used in this article. To facilitate the comparison, data from different methods are standardized (see below for more detailed information). As little research about antioxidant activity of millet is found, the data of antioxidant activity of millet is not reported in this review. In most research on antioxidant activity of cereals, antioxidants are extracted with methanol, ethanol or acetone, without hydrolysis to release the conjugated phenolic acid; the bound phenolic acids were not extracted by these solvents. Thus the obtained antioxidant activity of cereals is smaller compared to sample with bound phenolics hydrolyzed during extraction. The antioxidant activity data of eight


146


Table I. Total Phenolic Content (umol/g dry weight) of Some Cereal Groats Extracted Without Hydrolyzing the Insoluble Bound Phenolic Acids. Catechin equivalent 4.3 * 13.1 (9)

Barley Buckwheat Corn Millet Oat

Rice Rye Sorghum

Gallic acid equivalent

( 9 )

11.2 2.1

(14) (9)

2.9

(19)

Black Brown Red

129.1

(14)

White

4.6

(14)

Wheat

17.9 1.6

(H) (12)

1.6 1.0 1.5 10.1

05) (16) (17) (18)

39.2 40.6 117.6 15.3 32.7 32.3 6.5 5.9 3.0 4.6 1.2

(20) (21) (20) (21) (21) (21) (20) (21) (22) (23) (19)

Ferulic acid equivalent 10.2 (10) 2.9

(13)

6.7

(10)

12.0 10.6

(24) (25)

^References are given in parentheses.

cereals are collectedfromthe references, ABTS and DPPH methods are the two most commonly used methods to analyze the antioxidant activity of cereals. Similar to the total phenolic content index, the data in Table II are expressed as a percentage of the highest value of a cereal (100%) determined by each method and the mean value of the percentages from different methods is calculated as this cereal's relative antioxidant activity index (%). As shown in Figure 2, the antioxidant activity of cereals can be divided into high, medium and low groups. The high group includes brown, black and red sorghum. Rye has low antioxidant activity, and the other cereals are among the medium antioxidant activity group. With the increase of total phenolics content, antioxidant activity of cereal groat was also increased. Total phenolics content and antioxidant activity of cereal groat is significantly correlated (n = 11, R = 0.84, p < 0.01). Red, brown and black sorghum have both high total phenolics content and antioxidant activity, rye has both the lowest total phenolics content and antioxidant activity, and the other cereals belong to the group with medium total phenolics content and antioxidant activity.



147

Figure 1. Relative total phenolics content index of cereal groat extracted without hydrolyzing the insoluble bound phenolic acids.

Figure 2. Relative antioxidant activity index of cereal groats extracted without hydrolyzing the insoluble bound phenolic acids.


148


Table II. Antioxidant Activity of Some Cereals (pinol Trolox equivalent/g dry weight) Extracted without Hydrolyzing the Insoluble Bound Phenolic Acids Determined with ABTS and DPPH Methods. ABTS 10.1 (9)*

Barley

Buckwheat Corn Oat

Rice Rye Sorghum

Black

Brown

Red

White

Wheat

11.3 14.6 23.2 18.9 48.1 29.4 2.8 4.3 22.2 4.2 57.1 110.2 44.1 226.0 32.2 55.1 53.2 112.3 56.0 6.2 10.3 39.1 9.5 1.7 2.4 0.4

(2) (70) (9) (28) (30) (9) (32) (10) (30) (9) (20) (21) (33) (20) (21) (32) (20) (21) (33) (20) (21) (33) (30) (23) (32) (24)

DPPH 1.1 (26)

53.2 21.2

(27) (29)

0.9 27.0

(31) (29)

13.4

(29)

41.2 50.1

(20) (21)

202.3 15.2

(20) (21)

28.1 40.3

(20) (21)

6.0 5.1

(20) (21)

29.6 7.4

(29) (25)

*References are given in parentheses.


149


More work on total phenolics content and antioxidant activity of cereals is needed. It is necessary to extract cereals with hydrolysis of the bound phenolics before determining their total phenolics content and antioxidant activity, as this will more accurately reflect the real antioxidant activity of cereals in the human body after digestion. It is also important to determine antioxidant activity of cereals using other methods in addition to ABTS and DPPH method to reflect the antioxidant activity of different polarities of antioxidants in cereals.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

12. 13. 14. 15. 16. 17. 18. 19.

Wikipedia, Cereal, http://en.wikipedia.org/wiki/Cereal. Madhujith, T.; Izydorczyk, M . ; Shahidi, F. J. Agric. Food Chem. 2006, 54, 3283-3289. Hill, M . J.; Path, F. R. Nutri. Res. 1998, 18, 653-659. Zielinski, H. Polish Journal of Food and Nutrition Sciences 2002, 11, 3-9. Andlauer, W.; Furst, P. Cereal Foods World 1998, 43, 356-360. Sosulski, F.; Krygier, K.; Hogge, L. J. Agric. Food Chem. 1982, 30, 337340. Liyanapathirana, C.; Shahidi, F. Biofactors 2004, 21, 325-328. Huang, D. J.; Ou, B. X.; Prior, R. L. J. Agric. Food Chem. 2005, 53, 18411856. Zielinski, H.; Kozlowska, H. J. Agric. Food Chem. 2000, 48, 2008-2016. Zdunczyk, Z.; Flis, M.; Zielinski, H.; Wroblewska, M . ; Antoszkiewicz, Z.; Juskiewicz, J. J. Agric. Food Chem. 2006, 54, 4168-4175. Quettier-Deleu, C.; Gressier, B.; Vasseur, J.; Dine, T.; Brunet, C.; Luyckx, M.; Cazin, M . ; Cazin, J. C.; Bailleul, F.; Trotin, F. J. Ethnopharmacol. 2000, 72, 35-42. Dewanto, V.; Wu, X. Z.; Liu, R. H. J. Agric. Food Chem. 2002, 50, 49594964. Camire, M . E.; Dougherty, M. P.; Briggs, J. L. Cereal Chem. 2005, 82, 666670. Towo, E. E.; Svanberg, U.; Ndossi, G. D. J Sci. Food Agric. 2003, 83, 980986. Emmons, C. L.; Peterson, D. M . Cereal Chem. 1999, 76, 902-906. Emmons, C. L.; Peterson, D. M.; Paul, G. L. J. Agric. Food Chem. 1999, 47, 4894-4898. Peterson, D. M.; Emmons, C. L.; Hibbs, A. H. J. Cereal Sci. 2001, 33, 97103. Goffman, F. D.; Bergman, C. J. J. Sci. Food Agric. 2004, 84, 1235-1240. Kahkonen, M . P.; Hopia, A. I.; Vuorela, H. J.; Rauha, J. P.; Pihlaja, K.; Kujala, T. S.; Heinonen, M. J. Agric. Food Chem. 1999, 47, 3954-3962.



150 20. Awika, J. M.; Rooney, L. W.; Wu, X. L.; Prior, R. L.; Cisneros-Zevallos, L. J. Agric. Food Chem. 2003, 51, 6657-6662. 21. Dykes, L.; Rooney, L. W.; Waniska, R. D.; Rooney, W. L. J. Agric. Food Chem. 2005, 53, 6813-6818. 22. Kamath, V. G.; Chandrashekar, A.; Rajini, P. S. Journal of Cereal Science 2004, 40, 283-288. 23. Yu, L.; Haley, S.; Perret, J.; Harris, M.; Wilson, J.; Qian, M. J. Agric. Food Chem. 2002, 50, 1619-1624. 24. Liyana-Pathirana, C. M.; Shahidi, F. J. Sci. Food Agric. 2006, 86, 477-485. 25. Mpofu, A.; Sapirstein, H. D.; Beta, T. J. Agric. Food Chem. 2006, 54, 1265-1270. 26. Bonoli, M.; Verardo, V.; Marconi, E.; Caboni, M. F. J. Agric. Food Chem. 2004, 52, 5195-5200. 27. Przybylski, R.; Lee, Y. C.; Eskin, N . A. M. J. Am. Oil Chem. Soc. 1998, 75, 1595-1601. 28. Wettasinghe, M.; Boiling, B.; Plhak, L.; Parkin, K. J. Food Sci. 2002, 67, 2583-2588. 29. Miller, H. E.; Rigelhof, F.; Marquart, L.; Prakash, A.; Kanter, M . J. Am. Coll. Nutr. 2000, 19, 312S-319S. 30. Nagah, A. M.; Seal, C. J. J. Sci. Food Agric. 2005, 85, 1177-1185. 31. Sun, T.; Xu, Z.; Godber, J. S.; Prinyawiwatkul, W. Cereal Chem. 2006. 83, 451-454. 32. Yu, L.; Perret, J.; Davy, B.; Wilson, J.; Melby, C. L. J. Food Sci. 2002, 67, 2600-2603. 33. Dicko, M . H.; Gruppen, H.; Traore, A. S.; Van Berkel, W. J. H.; Voragen, A. G. J. J. Agric. Food Chem. 2005, 53, 2581-2588.


Total Phenolic Content and Antioxidant Activity of Cereals - American

Recommend Documents