Beans: A Source of Natural Antioxidants - American Chemical Society

Chapter 8

Beans: A Source of Natural Antioxidants Terrence Madhujith and Fereidoon Shahidi

Downloaded by UNIV OF ARIZONA on May 21, 2013 | http://pubs.acs.org Publication Date: July 21, 2005 | doi: 10.1021/bk-2005-0909.ch008

Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland A1B 3X9, Canada

Antioxidant efficacy of beans with different colors were studied. Beans are well recognized for their macronutrients, but little is known about their bioactive components. Beans supply many bioactives, once classified as antinutrients, in minor amounts, but these may contribute to beneficial metabolic and physiological effects. Pulses, including beans, are known to possess hypoglycemic, hypocholesterolemic, antimutagenic and anticarcinogenic as well as other therapeutic effects. Antioxidants in beans might also contribute to their cardiovascular and anticarcinogenic effects. Antioxidant potential, including inhibition of human LDL oxidation, as well as prevention of DNA double strand breakage of different beans is described in this contribution.

Introduction Foods that contain physiologically active ingredients with health benefits above their basic nutrition are known as functional foods (/). Beans (Phaseolus vulgaris L.), staple foods in Mexico, Central and South America as well as some African countries, are a good source of protein, vitamins, minerals (2) and polyphenols compounds (J) which have been shown to be responsible for a myriad of health benefits. In view of the presence of a number of phytochemicals, beans are receiving increasing attention as a functional food. Once known as the poor man's meat, beans are now presented as staple

© 2005 American Chemical Society

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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foods for vegetarians and most health organizations encourage their frequent consumption (4). Intake of beans has been linked to reduce risk of diabetes and obesity (5). Beans, among other pulses, are known as one of the foods with low glycémie index (glycémie index [GI] refers to the blood glucose raising potential of carbohydrate foods after consumption) (6). The protein, fiber, starch, vitamins, minerals and other components of beans contribute to the cardiovascular disease (7). Pulses, including beans, contain a wide range of nutrients and non-nutritive bioactives such as protease inhibitors, saponins, lectins, galactosides and phytates that may be protective against cancer when consumed in sufficient quantities (8). Table I lists the bioactive compounds present in pulses.

Table I. Bioactive Compounds in Pulses and Their Health Effects Compound Protease inhibitors Phytic acid Phytoestrogen Lignans Saponins Phytic acid Lectins Amylase inhibitors Tannins Saponins Phytosterols Phytic acid Isoflavones

Health Effect

Anticarcinogenic

Glucose lowering effect

Hypolipaemic effect

From Ref. 37 and 38.

Yokota et al (9) reported that oral administration of fermented bean crude residues repressed experimentally induced inflammation in rats, de Meja et al. (10) indicated that methanolic extracts of beans inhibited mutagenicity in Salmonella typhimurium. Beans contain significant quantities of polyphenols compounds such as flavonoids, phenolic acids and lignans, but are typically low in ascorbic acid, β-carotene, and α-tocopherol (//). Bean seed coat contains a number of anthocyanin pigments that exhibit antioxidative activity. Tsuda et al. (12) indicated that anthocyanin pigments (eyanidin-3-0-P-D-glucoside,



85 pelargonidin 3-0-P-D-glucoside and delphinidin 3-OP-D-glucoside) isolated from seed coat s of Phaseolus vulgaris had marked antioxidant activity in liposomal and rat liver microsomal systems, an inhibitory effect on malonaldehyde levels by UV radiation and radical scavenging effect against hydroxyl and superoxide anion radicals. Anthocyanins and anthocyanidins, which are metabolic products of flavanones (75), constitute a major portion of antioxidants in beans (14). Most of the naturally occurring anthocyanins and anthocyanidins carry hydroxyl groups at the Opposition. Anthocyanins such as cyanidin and delphinidin, found in beans, contain a hydroxyl group at C-3" position while pelargonidin does not (15). Figure 1 depicts the structures of anthocyanin pigments identified in seed coats of beans. Tsuda et al. (14) investigated the antioxidant activity of cyanidin 3-glucoside in linoleic acid, liposome, rabbit erythrocyte membrane ghost and rat liver microsomal systems. Their results in an in-vitro system suggested that these pigments play a role in the prevention of lipid oxidation. The pigments pelargonidin 3-O-P-glucoside and delphinidin-3-0-P-glucoside isolated from red and black beans do not possess any antioxidative activity at pH 7.0 while cyanidin-3-0-p-glucoside exhibits antioxidative activity, but all three pigments have strong activity under acidic conditions (16). This suggests that antioxidative activity is related to the stability of the flavylium cation (16), which is generally quite stable under acidic conditions (17). Cyanidin may be produced from cyanidin glucosides by hydrolysis with β-glucosidase of intestinal bacteria after ingestion, indicating that cyanidin rather than cyanidin-3-glucoside may act as an antioxidant in living systems (16). In addition to anthocyanins, beans contain procyanidins and phenolic acids. Drumm et al. (18) identified ferulic, /?-coumaric, sinapic and cinnamic acids (Figure 1) in four varieties of beans (navy, dark red kidney, pimanto and black turtle soup). Depending on the cultivar, beans contain a variety of flavonoids/anthocyanins and may have different coat colors. Four colors are most common; red, brown, black and white (15). The antioxidative activity of extracts of pea beans has been evaluated by different authors (10J2J4J6J921). Tsuda et al. (12) evaluated the antioxidative activity of a number of common beans using linoleic acid autoxidation system (Table II). The effect of crude extracts of hulls of navy bean on the oxidative stability of edible oils was reported by Onyeneho and Hettiarachchy (22) who suggested that extracts of navy bean hulls can be used commercially to inhibit oxidation of vegetable oils. Although beans are cultivated throughout the world and consumed in both eastern and western dishes, little attention has been paid to their antioxidant and antigenotoxic potentials. Thus, in this study we examined the antioxidant potential of several bean extracts.


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.0

H

H

Cyanidin 3-0-p-D-glucoside Peiargonidin 3-0-p-D-gIucoside Delphinidin 3-0-p-D-glucoside

Ri ~ OH, R = H R, = H, R = H Rï = O H , R = OH 2

2


Ç 2°

2

COOH

Ri = R = H R,==H,R jOH i ~ H, R - O C H 3 Ri - R - O C H 2

2

R

2

2

3

p-coumaric acid caffeicacid ferulic acid sinapic acid

Figure 1. Structures of anthocyanins and phenolic acids in bean seed coats.

Table II. Antioxidative Activity of Edible Beans Common Name

Species

Antioxidative Activity ++ + + + + 1

Kidney bean P. vulgaris L. cv. Honkintoki Kidney bean P. vulgaris L. cv. Ohtebo Scarlet runner bean P. coccineus L. Hyacinth bean Lablab purpureus L. Sweet Winged bean Psophocarpus tetragonolobus L. Horse gram Macrotyloma uniflorus (Lam.) Antioxidative activity in a linoieic acid autoxidation system using the thiocyanate method. Adapted from Ref. 12.


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Evaluation of Antioxidant Activity of Bean Extracts Beans with different coat colors (red, brown, black and white) were obtained from a local grocery store in Singapore and evaluated for their total phenolic content and Trolox equivalent antioxidant capacity. Phenolic compounds present in defatted bean samples were extracted with 80% acetone under reflux conditions. The resulting slurries were centrifuged and the supernatants collected. The residue was re-extracted with 80% acetone and the supernatants combined and desolventized in vacuo. The resulting concentrated solutions were lyophilized and used in the experiments. The total phenolic content was determined, essentially according to an improved version of the procedure explained by Singleton and Rossi (23), and expressed as catechin equivalents. The method explained by van den Berg (24) was used to determine the Trolox equivalent antioxidant capacity (TEAC) of the extracts. Among primary catalysts that initiate in-vivo and in-vitro oxidation, transition metal ions and complexes containing metals have been identified. Transition metal ions, such as iron and copper participate in direct and indirect initiation of lipid oxidation (25). Therefore, metal chelation can be regarded as one of the important characteristics of certain antioxidants. In our study, the metal chelation efficacy of the bean extracts was determined using the method explained by Terasawa et al. (26).

Total Phenolic Content Preliminary studies in this work and literature data indicated the presence of catechin and catechin-related compounds in beans. Therefore, the total phenolic contents were expressed as catechin equivalents. In all four bean types, hulls contained a higher amount of total phenolics when compared to those of their whole seed counterparts. Thus, the phenolic compounds are mainly concentrated in the seed coats. Total phenolic content of extracts of black bean hulls (LHE) was highest while that of white hull extract (WHE) was the lowest with the following trend: black > brown > red > white (See Table III). This trend is different from that observed for the whole bean extracts, possibly due to the proportional difference in the hull content in different beans. As white bean


88 extracts did not contain a considerable amount of total phenolics, they were not studied any further.

1

Table III. Total Phenolic Content (TPC) of Bean Extracts Sample

TPC, mg Catechin Equivalents Per Gram Extract 93.6±2.1 Red whole bean extract (RWE) 91.4±1.6 Brown whole bean extract (BWE) 44.0±2.5 Black whole bean extract (LWE) Whole white bean extract (WWE) 4.9±0.8 223.5±1.9 Red hull extract (RHE) 253.2±2.3 Brown hull extract (BHE) 270.0±1.6 Black hull extract (LHE) White hull extract (WHE) 6.7±0.9 Results reported are mean values of three determinations ± standard deviation. Means in each column sharing the same superscript are not significantly (p>0.05) different from one another. c

C

b


a

d

e

f

a

Trolox Equivalent Antioxidant Capacity TEAC value of a compound represents the concentration of a Trolox solution that has the same antioxidant capacity of a known or unknown compound or a mixture of compounds. Therefore, TEAC value can be used to rank the efficacy of an unknown compound or known antioxidants. Whole seed extracts were used at the same concentration while the hull extracts were diluted to a final concentration of 0.05 mg/mL. Figure 2 shows the TEAC values of whole seed and hull extracts of beans. Whole bean extracts showed low TEAC values ranging from 4.64 to 8.84 (whole bean extracts are 4.64 to 8.84 times as effective as Trolox) whereas TEAC values of hull extracts varied from 40.74 to 46.68. In both cases, the red bean extract showed the highest TEAC value followed by extracts of brown and black beans. In both whole bean and hull extracts, at the same concentration, TEAC values were in the order of red > brown > black. TEAC values of red and brown bean hulls were about 5.5 times higher than those of their corresponding whole seed extracts while black hulls were about 9 times more effective than black whole seed extracts.



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Figure 2. Trolox equivalent antioxidant activity of whole seed and hull extracts of beans. Abbreviations as given in Table III

Metal Chelation Capacity 2+

The chelation of Fe by 50 ppm catechin equivalents of phenolics in RWE and BWE was moderate and at 58 and 56%, respectively. This is slightly lower than that for catechin (60%); meanwhile chelation capacity of LWE was significantly (p

Beans: A Source of Natural Antioxidants - American Chemical Society

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