Full Length Research Paper

Isolation and identification of the genera Acetobacter and Gluconobacter in coconut toddy (mnazi)

T. T. Kadere¹*, T. Miyamoto², R. K. Oniang`o¹, P. M. Kutima¹ and S. M. Njoroge¹

¹Department of Food Science and Technology, Jomo Kenyatta University of Agriculture and Technology (JKUAT), P.O. Box 62000, Nairobi.

²Animal Food Functions Laboratory, Faculty of Agriculture, Okayama University, Japan

*Corresponding author. E-mail: tunjekadere@yahoo.com. Tel: 254-722-285937 or 254-67-52558.

Accepted 4 July, 2008

This study investigated the occurrence and identified the dominant spoilage genera of acetic acid bacteria in coconut wine (mnazi), by plating the dilution series previously pre-enriched in a basal medium onto GYP agar, followed by physiological and biochemical tests. Both Acetobacter and Gluconobacter strains were Gram variable, oxidase negative and catalase positive. All Acetobacter strains over-oxidized ethanol to acetic acid and finally to CO₂ and H₂O, while Gluconobacter were unable to oxidize acetic acid to CO₂ and H₂O. Acetobacter and Gluconobacter alike showed positive growth at 25, 30 and 40°C and also at pH 7.0 and 4.5, while there was no growth at 45°C, pH 2.5 and 8.5. Acetobacter strains oxidized both lactate and acetate while Gluconobacter oxidized lactate only. Both genera were unable to liquefy gelatin. Acetobacter showed negative growth at 15°C and also in peptone medium, while Gluconobacter showed positive growth both in peptone medium and at 15°C. Both genera were able to ferment arabinose, xylose, ribose, glucose, galactose, mannose and melibiose and unable to ferment amylagdine, cellibiose, esculine, lactose, maltose, mannitol, melezitose, Na-gluconate, raffinose, rhamnose and salicine. The Acetobacter and Gluconobacter strains isolated in this study were found to be responsible for the spoilage of mnazi.

Key words: Mnazi, palm wine, acetic acid bacteria, Acetobacter, Gluconobacter.