PHYTOCHEMICAL COMPOSITION, ANTIOXIDANT AND ANTIMICROBIAL PROPERTIES OF FOUR NIGERIAN SPICES

 

ABSTACT

This study evaluated phytochemical composition, antioxidant and antimicrobial properties of four Nigerian spices, namely Ocimum viride (leaves),  Monodora myristica (seeds), Monodora tenuifolia (seeds) and Tetrepleura tetrapetra (fruits). The spices were screened for phytochemical [alkaloid, saponin, oxalate, phytate, total phenol (TP), condensed tannin (CT), total flavonoid (TF) and total anthocyanin (TA)] contents and antioxidant activities in five
different extracting solvents [distilled water, 95 % methanol, acetone / hexane (1 : 1, v/v), hexane / methanol / acetone (2 : 1 : 1, v/v/v) and acetone / water / acetic acid (70 : 29.5 : 0.5, v/v/v)] using standard methods. Antioxidant capacities of the extracts to scavenge 1,1- diphenyl-2-picrylhydrazyl (DPPH) radical, reduce iron (iii) chloride (FeCl3), suppress linoleic acid ( LA) peroxidation in ferric thiocyanate (FTC) oxidizing systems and inhibit formation of thiobarbituric acid reactive substances (TBARS) in refrigerated (4OC, 14 days) spice-treated (0, 0.6. 1.2 and 2.0%, w/w basis) beef and pork patties were investigated. Aqueous extracts (10% w/w) of beef, rice and vegetables were treated with the spices (0, 2.5 and 7.5%, w/v), inoculated with the pathogens Escherichia coli, Salmonella typhii and Staphylococcus aureus (5logCFU/ml), and periodically analysed, by enumerating surviving populations after 24h intervals, during 10 days of storage (4OC) to determine antimicrobial activities of the spices. Phytochemical contents differed significantly (p < 0.05) among the spices and  among solvent extracts of the same spice.

The highest phytochemical content was total Phenol which ranged from 2.13 garlic acid equivalent per100 g (GAE / 100 g) in M. myristica to 13.93 GAE / 100 g in T. tetrapetra while total anthocyanin content was the lowest and ranged from 0.00 GAE / 100g in M. tenuifolia to 0.06 GAE / 100g in M. myristica. The extracts of spices exhibited high degree of antioxidant and antimicrobial activities. The spices suppressed lipid peroxidation in cooked ground beef (from 2.58 to 0.76 mean thiobarbituric acid value) and pork patties (from 4.33 to 1.03 thiobarbituric acid value) in  dose-dependent order during 14
days of storage. Spice extracts reduced Fe3+ to Fe2+, scavenged DPPH radical (78 – 93%) and inhibited LA peroxidation (46 – 95%) in dose-dependent order. Methanol (95 %) extracts of M.

myristica, M. tenuifolia and O. viride, and water extract of T. tetrapetra exhibited the highest (1.6 nm) reducing power while the acetone/water/acetic acid extracts exhibited the highest (93%) scavenging capacity of DPPH radical. Water extracts of O. viride and T. tetrapetra, methanol extract of M. tenuifolia and acetone/water/acetic acid extract of M. myristica had the highest inhibition of LA peroxidation. The four spices exhibited dose-dependent bactericidal
effects against E. coli (from 42.25 to 0.00 x 106 CFU / ml), S. typhii (from 47.1 to 3.7 x 106 CFU / ml) and S. aureus subsp.aureus (from 48.95 to 0.00 x 106 CFU / ml). During storage, antimicrobial effects of the spices were more pronounced in food extracts than in nutrient broth and in rice and vegetable extracts than in beef extracts. Of the four pathogens, E. coli was most susceptible to these spices, followed by S. aureus subsp. aureus. Tetrapleura tetrapetra was the most potent of these spices against the pathogens, followed by O. viride. The antioxidant and antimicrobial properties exhibited by these spices increased with spice concentrations and occurred in the following decreasing order: T. tetrapetra > O. viride > M. myristica > M. tenuifolia.

 

CHAPTER ONE

 INTRODUCTION

In Nigeria, a high proportion of the rural and urban population resort to natural food ingredients, particularly because of their availability. Spices are a large group of such natural ingredients, and include dried seeds, fruits, roots, rhizomes, barks, leaves, flowers and any other vegetative substances used in a very small quantity as food additives to colour, flavour or preserve food (Birt, 2006). Spices are fragrant, aromatic and pleasant. The bulk of the spices consist of carbohydrates such as cellulose, starch, pentosans and mucilage, and some amount of protein and minerals (Ogutimein et al., 1989). Only very small  fractions of dry matter of the spices such as the phytochemicals are responsible for the flavouring, colourng, preservative and health-promoting characteristics (Cowan, 1999).

These phytochemicals are plant metabolites (Sofowurra, 1993) which act as natural defense systems for host plants, and also provide characteristic colour, aroma and flavour in specific plant parts. They are a group of non-nutrient compounds that are biologically active when consumed by human. Many phytochemicals are health-promoting and are of many diseasepreventive (Rowland, 1999; Birt, 2006). Both epidemiological and clinical studies have
proven that phytochemicals present in cereals, fruits and vegetables are mainly responsible for reduced incidence of chronic and degenerative diseases among populations whose diets are high in these foods (Shahidi, 1996). As a result there has been an increased search for phytochemical constituents that possess antioxidant and antimicrobial potency in recent time (Jayaprakasha and Jaganmohan, 2000, Birt, 2006). Typical phytochemicals with antioxidant
and antimicrobial activities include polyphenols, phenolic acids and their derivatives, flavonoids, phospholipids, ascorbic acid, carotenoids and sterols. A number of exotic spices of international recognition with known phytochemical constituents have been proven to be good natural antioxidants (Dorko, 1994; Abd El-Alim et al., 1999; Seifried et al,, 2007), antimicrobial (Mitscher et al., 1972; Billing and Sherman, 1998) and health-promoting agents (Chan et al., 1995, Arai et al., 2000; Zhou et al. 2003).

Some of such internationally recognized spices include chili pepper, garlic, onion, anise, cinnamon, ginger, curry, rosemary and nutmeg (Dorko, 1994; Arai et al., 2000; Birt, 2006). However, there is paucity of information on the phytochemical compositions, antioxidant and antimicrobial properties of many Nigerian spices which have been in use for centuries as flavouring ingredients in many traditional dishes. Prominent Nigerian spices, including Tetrapleura tetrapetra (Schum & Thonn), Monodora myristica (Gaertn), Monodora tenuifolia (Benth) and Ocimum viride (Willd) need to be evaluated for these important properties for broader application in food processing and preservation. The parts of these plants used as spices are fruits of Tetrapleura tetrapetra, seeds of Monodora myristica and Monodora tenuifolia, and leaves of Ocimum viride. The vernacular names of these spices in Igbo, Nigeria are Ehuru for Monodora myristica, Ehu for Monodora tenuifolia, Hiohio for Tetrapleura tetrapetra and Nchu-anwu or Ahunji for Ocimum viride. The study is therefore designed to evaluate phytochemical compositions, antioxidant and antimicrobial properties of solvent extracts of Tetrapleura tetrapetra (fruits), Monodora myristica (seeds), Monodora tenuifolia (seeds) and Ocimum viride (leaves).

 

PHYTOCHEMICAL COMPOSITION, ANTIOXIDANT AND ANTIMICROBIAL PROPERTIES OF FOUR NIGERIAN SPICES

 

1.2 Statement of the problem

Information abound in literature on the phytochemical composition, antioxidant and antimicrobial properties of many exotic spices and this promote their use internationally as natural preservatives and as components of functional foods to promote health. Such information is dearth on most indigenous Nigerian spices and this limits their use internationally as preservatives and functional ingredients. It is therefore necessary to evaluate phytochemical compositions, antioxidant and antimicrobial properties of some popular Nigerian spices, namely Tetrapleura tetrapetra, Monodora myristica (Ehuru), Monodora tenuifolia (Ehu) and Ocimum viride (Nchu-anwu) to diversify their use as natural preservatives and as culinary spices that contain active ingredients that promote health and reduce the risk of disease.

 

PHYTOCHEMICAL COMPOSITION, ANTIOXIDANT AND ANTIMICROBIAL PROPERTIES OF FOUR NIGERIAN SPICES

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