PHYTOCHEMICAL, ANTIOXIDANT AND ANTIMICROBIAL STUDIES OF MUCUNA PRURIENS

                                          Abstract

This study evaluated the phytochemical, antioxidant and antimicrobial activities of Mucuna pruriens seeds. Extractions were carried out with ethanol, methanol, and petroleum ether, water Acetone. The preliminary phytochemical study of the extracts of seed of Mucuna pruriens revealed the presence of alkaloids, Hydrogen cyanide, saponin, flavonoids, phenols, and tannins. The highest level of phytochemical screening was observed in the hydrogen cyanide which was signified with +++ (highly present) while the antioxidant screening revealed the high presence of nitric oxide radical scavenging and protein signified with +++ (Highly present). The extracts were tested against Staphylococcus aureus, Bacillus subtilis and Escherichia coli using agar well diffusion method. The petroleum ether, methanol, ethanol, water and acetone extracts of Mucuna pruriens seed possess various degrees of significant inhibitory effect against the tested organism. The highest antibacterial effect was observed in the ethanol extract against Staphylococcus aureus, (13mm inhibition zone) while the lowest inhibition zone of antibacterial effect was observed in the water extract against Staphylococcus aureus (7mm inhibition zone). Also the highest antifungal effect was observed in methanol extract against Aspergillus niger (13mm inhibition zone), Ethanol against Saccharomyces cerevisiae and Mucor (12mm inhibition zone) while the lowest antifungal effect was observed in the water extract against Aspergillus niger and Aspergillus flavus (1mm inhibition zone). Broth dilution method was used to estimate Minimum inhibition concentration (MIC) against the selected pathogens. The results shows that the methanol extract of Mucuna pruriens seed has antifungal effect while the ethanol extract has antibacterial effect and may be used in treatment of some diseases. The results of the study suggest that adequate fermentation process should be carried out in the preparation of Mucuna pruriens seeds because of the high level of hydrogen cyanide.

TABLE OF CONTENTS

S/N                  Title                                                          Pages 

Title page                                                                                            i

Dedication                                                                                          ii

Certification                                                                                       iii

Acknowledgements                                                                            iv

Table of contents                                                                                v

List of table’s                                                                                      vii

List of Figures                                                                                     viii

Abstract                                                                                              ix

CHAPTER ONE

1.0                   Introduction                                                                                        1

1.1                   Aim and Objective of the Study                                                         4

CHAPTER TWO

2.1                  Literature Review                                                                               5

2.2                   Origins and Early Uses                                                                       6

2.3                  Taxonomy and Characteristics of Mucuna pruriens                          13

2.3.1               Classification                                                                                      13

2.3.2               Species Description                                                                            15

2.4                  Current Uses of Mucuna pruriens                                                      16

2.4.1                Antimicrobial Activity                                                                       16

2.4.2               Nutraceutical Versatility                                                                    16

2.4.3               Antioxidant property                                                                          18

2.4.4               Antivenin property                                                                              18

2.4.5                Fertility-enhancing property                                                               19

2.4.6                Growth-promoting property                                                               20

2.3.7                Hypoglycemic property                                                                      20

2.4.8                Anthelmintic property                                                                        20

2.4.9                Mucuna pruriens as a Food and Feed Source                                    21

2.5                   Nutritional Value                                                                                23

2.5.1                Protein Concentration                                                                         23

2.5.2                Other Nutrients                                                                                   25

2.8                   Comparison to Other Legumes                                                           25

2.9                   Antinutritional and Toxic Properties                                                  27

2.9.1                Tannins                                                                                               28

2.9.2                Proanthocyanidins                                                                              29

2.9.3                Hydrolyzable tannins                                                                          30

2.9.4                L-Dopa                                                                                                31

CHAPTER THREE

3.0                   Materials and Methods                                                                       33

3.1                   Materials                                                                                             33

3.1.2                Sample collection                                                                               33

3.2                   Methods                                      33

3.2.1                Sample Preparation                                                                            33

3.2.2               Solvent extraction of the sample                                                        33

3.3                  Phytochemical Analysis of Mucuna Pruriens Powder                        34

3.3.1                Determination of Hydrogen cyanide                                                  34

3.3.2                Determination of Phenol                                                                    34

3.3.3                Determination of Tannin                                                                    34

3.3.4                Determination of Alkaloid                                                                 35

3.3.5                Determination of Saponin                                                                  36

3.3.6                Determination of Flavonoid                                                               37

3.4                   Detertmination of Antioxidant Properties of Mucuna pruriens           37

3.4.1                Protein Determination                                                                        37

3.4.2                Nitric oxide radical scavenging activity                                             38

3.4.3                Iron chelating activity                                                                        39

3.5                   Antimicrobial Determination of Mucuna pruriens                            39

3.5.1                Antibacterial activity of Mucuna pruriens                                         39

3.5.2                Antifungal activity of Mucuna pruriens                                             40

3.5.3                Minimum inhibitory concentration                                                    40

3.6                   Statistical analysis                                    40                            

CHAPTER FOUR

4.1                   Results                                                                                41

CHAPTER FIVE                   

5.1                   Discussion                                                                                           48

5.2                   Conclusion                                                                                          50

5.3                  Recommendation                                                                               50

5.4                  Suggestion for future study.                                                               51

References                                                                             Appendix

List of Tables

Tables           Title                                                                  Pages

    1                  Scientific and common names of Mucuna pruriens       14

    2                  Ethnobotany: worldwide uses or functions of Mucuna pruriens        17

    3                  Mineral concentration of different cultivars of Mucuna (mg/100g DM)            26

    4                  Phytochemical Properties of Mucuna Pruriens    42

   5                Antioxidant Properties of Mucuna Pruriens       43

    6                   Showing the minimum inhibitory concentration (MIC) of Bacterial Isolates.    46

 7                  Showing the minimum inhibitory concentration (MIC) of fungal isolates.                 47

List of figures

Figures        Title                                                                        pages

  1                    Antibacterial activity of various extract of  Mucuna pruriens seeds on selected organisms.                   44

2                    Antifungal activity of various extract of Mucuna pruriens seeds on selected organisms.                                                  45

                                                            CHAPTER ONE

1.0       INTRODUCTION

Mucuna pruriens is an annual climbing legume indigenous to tropical regions with numerous uses as a food, feed, and nutraceutical. Like many other legumes, however, it has molecular components that can adversely affect its nutritional value, but the ability of these molecules to inhibit enzymes, to selectively bind and enter the circulatory system may be useful in pharmacology. Therefore, nutritionists and medical researchers have contrasting views about the toxicity of the genus.

According to Szabo and Tebbett (2002) the major drawback of Mucuna, which has compromised its usefulness as a food source for either humans or livestock, is associated with its chemical concentration. Mucuna contains novel alkaloids, saponins, and sterols (Manyam et al., 2004) and a high concentration of L-Dopa. In addition, serotonin and a number of indolic alkaloids structurally related to serotonin have been reported in various parts of the Mucuna plant, several of which have hallucinogenic properties of considerable strength (Szabo and Tebbett, 2002). It would, however, be unlikely for these low-level alkaloids to have any effect on human and animal consumers because their absorption across the gastrointestinal tract is negligible (Szabo, 2003).

According to Taylor (2004) beans of Mucuna are not only high in protein, but also in non-structural carbohydrates, lipids, and minerals. In South and Mid America, Mucuna beans have been roasted and ground to make a coffee substitute and the bean is also cooked and eaten as a vegetable. Mucuna is also one of the most remarkable green manures as it can add up to 30 ton/ha of organic matter to soils (Pretty et al., 1998).

The crop has a long history of use in Indian medicine and traditional medical practice in several countries where it is used to treat a wide variety of ailments including 12 Parkinson’s disease (Manyam and Sanchez-Ramos, 1999; Nagashayana et al., 2001). However, many of such uses are based on anecdotal healing properties that require verification and scientific validation.

The genus Mucuna, belonging to the Fabaceae family, sub family Papilionaceae, includes approximately 150 species of annual and perennial legumes. Among the various under-utilized wild legumes, the velvet bean Mucuna pruriens is widespread in tropical and sub-tropical regions of the world. It is considered a viable source of dietary proteins (Janardhanan et al., 2003; Pugalenthi et al., 2005) due to its high protein concentration (23–35%) in addition its digestibility, which is comparable to that of other pulses such as soybean, rice bean, and lima bean (Gurumoorthi et al., 2003). It is therefore regarded a good source of food.

The dozen or so cultivated Mucuna spp. found in the tropics probably result from fragmentation deriving from the Asian cultigen, and there are numerous crosses and hybrids (Bailey and Bailey, 1976). The main differences among cultivated species are in the characteristics of the pubescence on the pod, the seed color, and the number of days to harvest of the pod. “Cowitch” and “cowhage” are the common English names of Mucuna types with abundant, long stinging hairs on the pod. Human contact results in an intensely itchy dermatitis, caused by mucunain (Infante et al., 1990). The nonstinging types, known as “velvet bean” have appressed, silky hairs. The plant Mucuna pruriens, widely known as “velvet bean,” is a vigorous annual climbing legume originally from southern China and eastern India, where it was at one time widely cultivated as a green vegetable crop (Duke, 1991). It is one of the most popular green crops currently known in the tropics; velvet beans have great potential as both food and feed as suggested by experiences worldwide. The velvet bean has been traditionally used as a food source by certain ethnic groups in a number of countries. It is cultivated in Asia, America, Africa, and the Pacific Islands, where its pods are used as a vegetable for human consumption, and its young leaves are used as animal fodder.

The plant has long, slender branches; alternate, lanceolate leaves; and white flowers with a bluish-purple, butterfly shaped corolla. The pods or legumes are hairy, thick, and leathery; averaging 4 inches long; are shaped like violin sound holes; and contain four to six seeds. They are of a rich dark brown color, and thickly covered with stiff hairs. In India, the mature seeds of Mucuna bean are traditionally consumed by a South Indian hill tribe, the Kanikkars, after repeated boiling to remove anti-nutritional factors. Most Mucuna spp. exhibit reasonable tolerance to a number of abiotic stresses, including drought, low soil fertility, and high soil acidity, although they are sensitive to frost and grow poorly in cold, wet soils (Duke, 1991). The genus thrives best under warm, moist conditions, below 1500 m above sea level, and in areas with plentiful rainfall. Like most legumes, the velvet bean has the potential to fix atmospheric nitrogen via a symbiotic relationship with soil microorganisms.

Mucuna spp. have been reported to contain the toxic compounds L-dopa and hallucinogenic tryptamines, and anti-nutritional factors such as phenols and tannins (Awang et al., 1997). Due to the high concentrations of L-dopa (4–7%), velvet bean is a commercial source of this substance, used in the treatment of Parkinson's disease. The toxicity of unprocessed velvet bean may explain why the plant exhibits low susceptibility to insect pests (Duke, 1991). Velvet bean is well known for its nematicidic effects; it also reportedly possesses notable allelopathic activity, which may function to suppress competing plants (Gliessman et al., 1991). Despite its toxic properties, various species of Mucuna are grown as a minor food crop. Raw velvet bean seeds contain approximately 27% protein and are rich in minerals (Duke, 1991). During the 18 and 19 centuries, Mucuna was grown widely as a green vegetable in the foothills and lower hills of the eastern Himalayas and in Mauritius. Both the green pods and the mature beans were boiled and eaten. In Guatemala and Mexico, M. pruriens has for at least several decades been roasted and ground to make a coffee substitute; the seeds are widely known in the region as “Nescafé,” in recognition of this use.

1.1       AIMS AND OBJECTIVES OF THE STUDY

This review focuses on the following aspects of Mucuna pruriens: taxonomy and physical characteristics, nutritional value, antinutritional and toxic properties, methods for detoxifying the bean and their impact on its nutritional value.

Specific Objectives include;

1.     to identify the phytochemical compounds of Mucuna pruriens

2.      to identify the antioxidant components of Mucuna pruriens

3.     to determine the antimicrobial activity of Mucuna pruriens extract on some bacteria and  fungi

4.      to determine the minimum inhibitory concentration (MIC) of the Mucuna pruriens seed extracts.

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