Plant Foods for Human Nutrition 42: 297-304, 1992. 9 1992 Kluwer Academic Publishers. Printed in the Netherlands. Microorganisms associated with natural fermentation of Prosopis africana seeds for the production of okpiye O.K. ACHI Department of Science Technology, Federal Polytechnic, P.M.B. 1037, Idah, Nigeria Received 30 March, 1991; accepted in revised form 25 June, 1991 Key words: Seed fermentation, condiment, Okpiye, microbial ecology, bacteria, Prosopis africana Abstract. Okpiye is a food condiment prepared by the fermentation of Prosopis africana seeds. The traditional process for the production and microbiological characteristics of the condi- ment were investigated. During laboratory fermentation that lasted 96 h, the mesquite seeds underwent a natural fermentation that was characterised by the growth of microorganisms to 106.108 cfu/g. Several species of bacteria especially B. subtilis, B. licheniformis, B. megaterium, Staphylococcus epidermidis and Micrococcus spp were found to be the most actively involved organisms. However, significant contributions to the microbial ecology were made by Enterobacter cloacae and Klebsiella pneumoniae. Lactobacillus spp were present in low numbers towards the end of the fermentation. The presence of Proteus and Pseudomonas spp in traditional fermented samples demonstrate the variability which may exist in the microflora of individual fermented samples. Variations in the important microbial groups show that Bacillus spp were the most prevalent species and occurred until the end of fermentation. Temperature, pH and titratable acidity varied with time and were influenced by the metabolic activities of the microorganisms. Introduction Fermented foods form an integral and significant part of the diet of many people in Nigeria. Plant sources, notably seed legume crops, are fermented and used as traditional condiments (Odunfa, 1985a). The more popular ones include dawadawa from African locust bean (Parkiafilicoidea) (Antai and Ibrahim, 1986; Ikenebomeh et al., 1986; Odunfa, 1981a), castor oil bean (Ricinus communis) (Odunfa, 1985b) and melon seed (Citrullus vulgaris) (Odunfa, 1981 b). Prosopis africana is one of the lesser-known legume seed crops used as food condiment in Nigeria. The fermented mesquite is popular in some parts of Nsukka and Idah where it is locally called Okpiye. It adds variety and pleasure to the otherwise monotonous traditional diet. It serves not only as