Essential oils composition of Ocimum basilicum L. and Ocimum gratissimum L. from Kenya and their inhibitory effects on growth and fumonisin production by Fusarium verticillioides

Abstract

This work investigated the constituents and the efficacy against Fusarium verticillioides infection and fumonisin production of essential oils of Ocimum basilicum L. and Ocimum gratissimum L. from different locations in Kenya.

The oil of leaves and flowering tops of O. basilicum from Sagana contained mainly linalool (95%). The flowering tops and leaves from Yatta contained mainly camphor (32.6 and 31.0%, respectively) and linalool (28.2 and 29.3, respectively). Eugenol was the main constituent in the oil of O. gratissimum leaves from both Sagana (95.5%) and Yatta (70.1%). The oil of the flowering tops had significantly less eugenol. The main component of the oil of flowering tops from Yatta was Z-β-ocimene (34.1%). Oil from both species had some antifungal activity. The oils of O. basilicum and O. gratissimum from different locations showed chemical variation, antifungal activity, free radical scavenging capacity and antimycotoxicogenic property. These properties are attributed to the phenolic compound eugenol.

Industrial relevance

This manuscript gives the chemical composition and some biological effects of essential oil of two Ocimum species in Kenya namely Ocimum basilicum L. and Ocimum gratissimum L. The work reveals that there are chemovarieties of these plants in different locations in the country. Of significance is the presence of very high amounts of linalool in one chemovariety of O. basilicum while geranial and neral are major in another. The third variety contains almost equal amounts of camphor and linalool. The first two containing high quantities of linalool, geranial and neral could be cultivated after agronomic studies to provide essential oils useful in perfumery, soap or food industry while that containing camphor and linalool may find use in medicine.

Proper seed selection and good agricultural practice for O. gratissimum containing high amount of eugenol could serve as good substitute for cloves which grows best only in a few islands in East Africa. Clove oil due to its high eugenol content has many biological activities including those demonstrated in the present work, and many applications in medicine and commercial world.

There is need for more research on these plants especially on cultivation and commercial exploitation of the herbs.

Introduction

Fungi of the genus Fusarium are widely found in plant debris and crop plants worldwide (Marasas, Kriek, Fincham, & Van Rensburg, 1984). Several species from this genus are economically relevant because, apart from their ability to infect and cause tissue destruction on important crops such as corn, wheat and other small grains on the field, they produce mycotoxins on the crops in the field and in storage grains. Fumonisins are mycotoxins produced mainly by the fungi Fusarium verticillioides and Fusarium proliferatum. Fumonisin B1 (FB1) is generally the most abundant member of the family of mycotoxins and is known to cause animal diseases including equine leucoencephalomalacia, porcine pulmonary edema and alter some diet and inmunobiological parameters in mice and rats (Theumer, Lopez, Masih, Chulze, & Rubinstein, 2002). Additionally, fumonisins are potent liver toxins in most animal species and are suspected human carcinogens (Nelson, Desjardins, & Plattner, 1993).

Aromatic plants are used in folk medicine as antimicrobial agent and their essential oils have been known to have antibacterial and antifungal proprieties (Pinto, Ribeiro Salgueiro, Cavaleiro, Palmeira, & Gonçalves, 2007). Ocimum basilicum L. and Ocimum gratissimum L. (Ocimum suave Willd., Ocimum tomentosum Oliv.) (Lamiaceae family) are grown in Africa. The last, is very common in disturbed areas such as secondary bushland, forest margins, grasslands and riverine sites. In dry areas it is always on higher hills (Agnew & Agnew, 1994). Both plants are used widely in East Africa, with O. basilicum root decoction being drunk by pregnant women for stomach pains and as an enema in constipation. Vapour from boiling leaves is inhaled for treatment of nasal and bronchial catarrh and the leaves are put in the house to drive away mosquitos (Kokwaro, 1980). In Asia, the leaves are considered stomachic, carminative and sudorific. Seeds have a slight laxative effect (Van Duong, 1993). O. gratissimum leaves are used for abdominal pains, sore eyes, ear troubles, coughs and blocked noses. An infusion of the leaves is used as a disinfectant and as an insecticide (Kokwaro, 1980). In Asia, it is used as a stomachic, diaphoretic and febrifuge (Van Duong, 1993).

Several strategies are used at controlling fungal growth and the mycotoxin synthesis in stored grains by chemical treatments with ammonia, acids and bases or with food preservatives by physical methods and by biological methods. These methods require sophisticated equipment and expensive chemicals or reagents. Therefore, it is important to find a practical, cost effective and non-toxic method to prevent fungal deterioration of stored grains (Reddy, Reddy, & Muralidharan, 2009). In recent years, particular interest has been focused on the potential application of plant essential oils (EOs) to prevent fungal growth and mycotoxins yield in the cereals and grain-based food. Some essential oils are classified as Food Additives by the FDA. A wide variety of EOs and many of their majority compounds, mainly mono and sesquiterpenes have been shown to have antifungal and antimycotoxins activities. Generally, the EOs possessing the strongest antifungal activities against food borne pathogens contain a high percentage of phenolic compounds such as carvacrol, eugenol, isoeugenol and thymol (Lambert, Skandamis, Coote, & Nychas, 2001).

In this study, we report for the first time, the chemical composition, antifungal, antiradical and antimycotoxigenic activities of the essential oils of O. bassilicum and O. gratissimum from different locations in Kenya.